Bjørn Jamtveit

• Kristina G. Dunkel, Sascha Zertani, Vladimir Roddatis & Bjørn Jamtveit (2026). Zoned feldspar records hydration-dehydration cycles in lower-crustal shear zones. Contributions to Mineralogy and Petrology. ISSN 0010-7999. 181(5). doi: 10.1007/s00410-026-02317-w. Full text in Research Archive Show summary

  Metamorphic reactions provide crucial insights into the conditions that rocks experienced and significantly influence their rheological behaviour. However, some reactions are challenging to identify in the rock record. This study focuses on zonation and microstructures in plagioclase as indicators of metamorphic history, employing a case study from Lofoten, northern Norway, where various types of plagioclase microstructures are preserved together. We use a combination of electron microscopy techniques (electron backscatter diffraction, transmission electron microscopy, and electron microprobe analyses) complemented with local equilibrium thermodynamic modelling to examine the relationships between composition, microstructures, and underlying metamorphic processes, and put that in context with previous observations of metamorphically zoned plagioclase, often referred to as “complex feldspar”. Needle-shaped Ca-richer zones in plagioclase represent pseudomorphs after zoisite/clinozoisite, indicative of plagioclase breakdown following fluid infiltration at high pressure and subsequent reversal of the reaction. Polygonal plagioclase with complex zonations also originates from the hydration/dehydration cycle but has additionally undergone deformation during hydration. Minor changes in pressure and temperature at upper amphibolite-facies conditions can significantly affect the stability and microstructures of plagioclase and thereby the rheological behaviour of the lower crust.

• Sascha Zertani, Luca Menegon, Martin J. Whitehouse, Heejin Jeon & Bjørn Jamtveit (2024). Dating fossil lower-crustal earthquakes by in-situ apatite U-Pb geochronology. Earth and Planetary Science Letters. ISSN 0012-821X. 630. doi: 10.1016/j.epsl.2024.118621. Full text in Research Archive Show summary

  Determining the precise age of fossil earthquakes is essential for understanding the tectonic setting in which they occurred. Pseudotachylytes are quenched frictional melts that occur along coseismic fractures and represent evidence of fossil earthquakes in the rock record. Here, we present the first in-situ apatite U-Pb ages for three samples from Lofoten in the northern Norwegian Caledonides, that occur within and adjacent to lower-crustal pseudotachylytes: a pristine pseudotachylyte, a mylonitized pseudotachylyte, and a mylonite that contains pseudotachylyte transposed into the shear plane. The apatite U-Pb ages are combined with cathodoluminescence and electron backscatter diffraction analysis to provide microstructural constraints on the interpretation of ages. Apatite shows evidence of either fragmentation and annealing, or dislocation creep in response to coseismic rupture. The results suggest that the short-lived thermal pulse generated by the earthquake is sufficient to reset the apatite U-Pb system. The age of 426 ± 19 Ma is interpreted to date lower-crustal seismicity during the early Caledonian orogeny. Later fluid-rock interaction along the same structures led to partial resetting of the apatite U-Pb systematics, indicating that seismic brittle failure of the lower continental crust occurs at the incipient stages of continental collision, and that the resulting structures are preferential pathways for later fluid flow in the otherwise impermeable anhydrous lower crust.

• Marija Plahter Rosenqvist, John M. Millett, Sverre Planke, Rakul Maria Ingunardóttir Johannesen, Simon R. Passey & Erik V. Sørensen [Show all 8 contributors for this article] (2024). The architecture of basalt reservoirs in the North Atlantic Igneous Province with implications for basalt carbon sequestration. Geological Society Special Publication. ISSN 0305-8719. 547(1), p. 389–413. doi: 10.1144/SP547-2023-96. Full text in Research Archive Show summary

  Offshore CO2 sequestration in basaltic formations of the North Atlantic Igneous Province may allow permanent storage of large volumes of CO2 through rapid carbonate mineralization. Characterizing the internal architecture of such reservoirs is key to assessing the storage potential. In this study, six photogrammetry models and three boreholes on the Faroe Islands have been used to characterize the internal lava sequence architectures as a direct analogue to potential offshore North Atlantic Igneous Province storage sites. The studied formations are dominated by c. 5 to 50 m thick simple and compound lava flows, with drill core observations documenting a transition from pāhoehoe moving towards ‘a’ā lava flow types interbedded with thin (<5 m thick) volcaniclastic rock units. The identification of flow margin breccias is potentially important as these units form excellent reservoirs in several other localities globally. Stacked, thick simple flows may present sealing units associated with dense flow interiors. Connected porous and permeable lava flow crusts present potential reservoirs; however, the degree of secondary mineralization and alteration can alter initially good reservoir units to impermeable barriers for fluid flow. Large-scale reservoir volumes may be present mainly within both vesicular, fractured pāhoehoe and brecciated flow margins of transitional simple lava flows.

• Sascha Zertani, Luca Menegon, Giorgio Pennacchioni, Iris Buisman, Fernando Corfu & Bjørn Jamtveit (2023). Protracted localization of metamorphism and deformation in a heterogeneous lower-crustal shear zone. Journal of Structural Geology. ISSN 0191-8141. 176. doi: 10.1016/j.jsg.2023.104960. Full text in Research Archive Show summary

  Deformation of the continental crust is influenced by the pre-existing structural framework, fluid availability, strain rate, and pressure-temperature conditions. We investigate the evolution of a large (hundreds-of-meters wide) heterogeneous shear zone and associated brittle and ductile deformation structures (Lofoten, Norway) using structural analysis, mineral-chemical and microstructural observations, and U-Pb dating. The shear zone developed through a sequence of metamorphic stages: (1) migmatization and granulite-facies metamorphism, (2) eclogite-facies metamorphism, and (3) amphibolite-facies metamorphism. Stage (1) was related to magmatic activity at lower-crustal conditions prior to 1.7 Ga. Stage (2) likely occurred during the early phases of the collision between Baltica and Laurentia (Caledonian collision). Stage (3) was related to shortening during the main phase of the Caledonian collision (∼430–400 Ma) and was accompanied by hydration of the shear zone. We demonstrate how mechanical heterogeneities influence the deformation style from the centimeter to meter scale. Zones with a pre-existing fabric deformed by ductile shearing and folding, whereas homogeneous, dry rocks fractured. Fractures provided precursors for small-scale shear zones. These contrasting deformation styles occurred repeatedly. Consequently, pre-existing structures define the deformation style and serve as conduits for the channelization of fluids over extended periods of time.

• Marija Plahter Rosenqvist, Max William John Meakins, Sverre Planke, John M. Millett, Hans Jørgen Kjøll & Martin J. Voigt [Show all 7 contributors for this article] (2023). Reservoir properties and reactivity of the Faroe Islands Basalt Group: Investigating the potential for CO<inf>2</inf> storage in the North Atlantic Igneous Province. International Journal of Greenhouse Gas Control. ISSN 1750-5836. 123. doi: 10.1016/j.ijggc.2023.103838. Full text in Research Archive Show summary

  Offshore injection of CO2 into volcanic sequences of the North Atlantic Igneous Province may present a large-scale, permanent storage option through carbonate mineralization. To investigate this potential, onshore studies of reservoir properties and reactivity of the subaerially erupted Faroe Islands Basalt Group have been conducted. Outcrop and borehole samples reveal that the lava flow crusts commonly contain vesicles that have been filled with secondary minerals due to hydrothermal fluid circulation, however, unmineralized and highly porous layers do occur. Bulk density measurements, micro-computed tomography (µ-CT) image analysis, and microscope studies of samples from onshore boreholes give present-day porosities ranging from 0.5% to 36.2% in the volcanic sequences. The unmineralized brecciated lava flow crusts contain the largest estimated porosity and simulated absolute permeability (reaching up to 10−12 m2). µ-CT studies of the mineralized, brecciated flow crusts indicate initial porosities reaching up to 45%, before clogging. Kinetic experiments of rock dissolution show that the reactivity of the basalt and volcaniclastic sediments depends on the alteration state with more altered basalt being less reactive. However, the presence of reactive, high porosity, and high permeability flow crusts prior to clogging indicate the existence of promising and very large CO2 reservoirs in less altered offshore sequences.

• Evangelos Moulas, Boris Kaus & Bjørn Jamtveit (2022). Dynamic pressure variations in the lower crust caused by localized fluid-induced weakening. Communications Earth & Environment. 3. doi: 10.1038/s43247-022-00478-7. Full text in Research Archive Show summary

  Abstract Metamorphism of dry, lower crust within orogens is often localized in shear zones composed of mechanically weaker rocks 1–4 . Several field-based studies suggest shear zone development is preceded by brittle faults which provide the fluid pathways required for metamorphism and weakening 4–12 . However, a unifying model which couples long-term geological deformation to fluid migration and metamorphic reactions does not exist. Here, we present a visco-elasto-plastic model where the most pertinent features observed in transformed lower crust emerge from basic mechanical principles during the deformation of a coherent rock volume with associated fluid introduction. These include a strikingly dynamic and heterogeneous pressure distribution in the reacting and deforming rock volumes. Lower crustal pressure variations may reach 1 GPa at the same depth. This will have first order effects on the pattern of fluid migration in the lower crust, and may explain the apparent discrepancies between the relevant tectonic settings and petrologically-inferred burial depths.

• John Mark Aiken, Robert A. Sohn, Francois Renard, Juerg Matter, Peter Kelemen & Bjørn Jamtveit (2022). Gas Migration Episodes Observed During Peridotite Alteration in the Samail Ophiolite, Oman. Geophysical Research Letters. ISSN 0094-8276. 49(21). doi: 10.1029/2022GL100395. Full text in Research Archive Show summary

  Serpentinization and carbonation of mantle rocks (peridotite alteration) are fundamentally important processes for a spectrum of geoscience topics, including arc volcanism, earthquake processes, chemosynthetic biological communities, and carbon sequestration. Data from a hydrophone array deployed in the Multi-Borehole Observatory (MBO) of the Oman Drilling Project demonstrates that free gas generated by peridotite alteration and/or microbial activity migrates through the formation in discrete bursts of activity. We detected several, minutes-long, swarms of gas discharge into Hole BA1B of the MBO over the course of a 9 month observation interval. The episodic nature of the migration events indicates that free gas accumulates in the permeable flow network, is pressurized, and discharges rapidly into the borehole when a critical pressure, likely associated with a capillary barrier at a flow constriction, is reached. Our observations reveal a dynamic mode of fluid migration during serpentinization, and highlight the important role that free gas can play in modulating pore pressure, fluid flow, and alteration kinetics during peridotite weathering.

• Marthe Grønlie Guren, Henrik Andersen Sveinsson, Anders Hafreager, Bjørn Jamtveit, Anders Malthe-Sørenssen & Francois Renard (2021). Molecular dynamics study of confined water in the periclase-brucite system under conditions of reaction-induced fracturing. Geochimica et Cosmochimica Acta. ISSN 0016-7037. 294, p. 13–27. doi: 10.1016/j.gca.2020.11.016. Full text in Research Archive Show summary

  The volume-increase associated with hydration reactions in rocks may lead to reaction-induced fracturing, but requires a stable water film to be present at reactive grain boundaries even when subject to compressive stress. Hydration of periclase to brucite is associated with a solid volume increase of ca. 110%. Recent experiments on the periclase-brucite system observed that when the effective mean stress exceeds 30 MPa, the reaction rate slows down dramatically. We hypothesize that for the brucite forming reaction to progress, the fluid film between grains must remain stable. If the applied pressure becomes larger than the hydration force, the fluid film will collapse and be squeezed out of the grain contacts. To quantify this effect, we study the behavior of a water film confined between periclase or brucite surfaces subject to compressive stress, by performing molecular dynamics simulations. The simulations are carried out using the ClayFF force field and the single point charge (SPC) water model in the molecular dynamics simulations program LAMMPS. The setup consists of two interfaces of either periclase or brucite surrounded by water. Our simulations show that when the pressure reaches a few tens of MPa, the water film collapses and reduces the water film to one or two water layers, while the self-diffusion coefficient of water molecules by a factor of eight. A water film thickness below two water layers is thinner than the size of the hydration shell around Mg2+-ions, which will limit ion-transport. The observed collapse of the water film to a single layer at a normal pressure of 25–30 MPa might explain the observed slow-down of reaction-induced fracturing in the periclase-brucite system.

• Arianne Juliette Petley-Ragan, Oliver Plümper, Benoit Ildefonse & Bjørn Jamtveit (2021). Nanoscale earthquake records preserved in plagioclase microfractures from the lower continental crust. Solid Earth (SE). ISSN 1869-9510. 12(4), p. 959–969. doi: 10.5194/se-12-959-2021. Full text in Research Archive Show summary

  Seismic faulting causes wall rock damage, which is driven by both mechanical and thermal stress. In the lower crust, co-seismic damage increases wall rock permeability, permits fluid infiltration and triggers metamorphic reactions that transform rock rheology. Wall rock microstructures reveal high-stress conditions near earthquake faults; however, there is limited documentation on the effects of a thermal pulse coupled with fluid infiltration. Here, we present a transmission electron microscopy study of co-seismic microfractures in plagioclase feldspar from lower crustal granulites from the Bergen Arcs, Western Norway. Focused ion beam foils are collected 1.25 mm and 1.8 cm from a 1.3 mm thick eclogite facies pseudotachylyte vein. Dislocation-free plagioclase and K-feldspar aggregates in the microfractures record a history of fluid introduction and recovery from a short-lived high-stress state caused by slip along the nearby fault. The feldspar aggregates retain the crystallographic orientation of their host and are elongated subparallel to the pseudotachylyte. We propose that plagioclase partially amorphized along the microfractures at peak stress conditions followed by repolymerization to form dislocation-free grain aggregates. Repolymerization and recrystallization were enhanced by the infiltration of fluids that transported Ca and K into the microfractures. Subsequent cooling led to exsolution of intermediate plagioclase compositions and the formation of the Bøggild–Huttenlocher intergrowth in the grains from the fracture closest to the pseudotachylyte. Our findings provide unequivocal evidence that the introduction of fluids in the microfractures occurred within the timescale of the thermal perturbation, prompting rapid annealing of damaged wall rock soon after earthquake rupture.

• Xin Zhong, Arianne Juliette Petley-Ragan, Sarah Incel, Marcin Dabrowski, Niels Højmark Andersen & Bjørn Jamtveit (2021). Lower crustal earthquake associated with highly pressurized frictional melts. Nature Geoscience. ISSN 1752-0894. 14(7), p. 519–525. doi: 10.1038/s41561-021-00760-x. Full text in Research Archive Show summary

  Abstract Earthquakes at lower crustal depths are common during continental collision. However, the coseismic weakening mechanisms required to propagate an earthquake at high pressures are poorly understood. Transient high-pressure fluids or melts have been proposed as a viable mechanism, but verifying this requires direct in situ measurement of fluid or melt overpressure along fault planes that have hosted dynamic ruptures. Here, we report direct measurement of highly overpressurized frictional melts along a seismic fault surface. Using Raman spectroscopy, we identified high-pressure quartz inclusions sealed in dendritic garnets that grew from frictional melts formed by lower crustal earthquakes in the Bergen Arcs, Western Norway. Melt pressure was estimated to be 1.8–2.3 GPa on the basis of an elastic model for the quartz-in-garnet system. This is ~0.5 GPa higher than the pressure recorded by the surrounding pseudotachylyte matrix and wall rocks. The recorded melt pressure could not arise solely from the volume expansion of melting, and we propose that it was generated when melt pressure approached the maximum principal stress in a system subject to high differential stress. The associated palaeostress field demonstrates that a strong lower crust accommodated up to 1 GPa differential stress during the compressive stage of the Caledonian orogeny.

• Bjørn Jamtveit, Kristina G Dunkel, Arianne Juliette Petley-Ragan, Håkon Olaf Austrheim, Fernando Corfu & Daniel Walter Schmid (2021). Rapid fluid-driven transformation of lower continental crust associated with thrust-induced shear heating. Lithos. ISSN 0024-4937. 396-397. doi: 10.1016/j.lithos.2021.106216. Full text in Research Archive
• Joanna Dziadkowiec, Matea Ban, Shaghayegh Javadi, Bjørn Jamtveit & Anja Røyne (2021). Ca2+ ions decrease adhesion between two (104) calcite surfaces as probed by Atomic Force Microscopy. ACS Earth and Space Chemistry. 5(10), p. 2827–2838. doi: 10.1021/acsearthspacechem.1c00220. Full text in Research Archive Show summary

  Solution composition-sensitive disjoining pressure acting between the mineral surfaces in fluid-filled granular rocks and materials controls their cohesion, facilitates the transport of dissolved species, and may sustain volume-expanding reactions leading to fracturing or pore sealing. Although calcite is one of the most abundant minerals in the Earth’s crust, there is still no complete understanding of how the most common inorganic ions affect the disjoining pressure (and thus the attractive or repulsive forces) operating between calcite surfaces. In this atomic force microscopy study, we measured adhesion acting between two cleaved (104) calcite surfaces in solutions containing low and high concentrations of Ca2+ ions. We detected only low adhesion between calcite surfaces, which was weakly modulated by the varying Ca2+ concentration. Our results show that the more hydrated calcium ions decrease the adhesion between calcite surfaces with respect to monovalent Na+ at a given ionic strength, and thus Ca2+ can sustain relatively thick water films between contacting calcite grains even at high overburden pressures. These findings suggest a possible loss of cohesion and continued progress of reaction-induced fracturing for weakly charged minerals in the presence of strongly hydrated ionic species.

• Kristina G Dunkel, Luiz F.G. Morales & Bjørn Jamtveit (2021). Pristine microstructures in pseudotachylytes formed in dry lower crust, Lofoten, Norway. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. ISSN 1364-503X. 379(2193). doi: 10.1098/rsta.2019.0423. Full text in Research Archive Show summary

  Feldspar-rich pseudotachylytes from the island of Moskenesøya, Lofoten, formed in dry granulites under lower crustal conditions during the Caledonian orogeny. The central parts of the pseudotachylytes, where the cooling rates were slowest, are characterized by microlites and spherulites of plagioclase and K-feldspar. K-feldspar surrounding plagioclase is consistent with crystallization from a melt during cooling instead of devitrification as the origin of the spherulites. Very thin (a few micrometres wide) injection veins, which experienced very rapid quenching, contain amorphous or cryptocrystalline material. The preservation of this material and of the fine-grained microstructures shows that, under fluid-absent conditions, recrystallization and reactions are slow and the original microstructures of the pseudotachylytes can be preserved. This article is part of a discussion meeting issue ‘Understanding earthquakes using the geological record’.

• Claire Olga Maryse Aupart, Luiz F.G. Morales, Marguerite Godard & Bjørn Jamtveit (2021). Seismic faults triggered early stage serpentinization of peridotites from the Samail Ophiolite, Oman. Earth and Planetary Science Letters. ISSN 0012-821X. 574. doi: 10.1016/j.epsl.2021.117137. Full text in Research Archive Show summary

  Serpentinization of mantle peridotites has first order effects on the rheology and tectonic behavior of the oceanic lithosphere, on the global water cycle, and on the biosphere at mid-oceanic ridges. Investigating serpentinization of abyssal peridotites is limited by the scarce occurrences of peridotites at or close to the ocean floor at slow and ultra-slow ridge environments where peridotite is exposed by long-lived detachments. The processes controlling hydration of the upper mantle below a thick magmatic crust at fast spreading ridges are poorly constrained. Here we present results based on samples from cores drilled in peridotites from the Samail ophiolite obtained during the Oman Drilling Project. We describe an early generation of highly localized brittle faults ubiquitous through all the peridotite cores and investigate their relation to the main serpentinization event represented by mesh-textured serpentinites. We combine microstructural observations with mineral and bulk chemical analyses as well as oxygen isotope microanalyses obtained by secondary ion mass spectrometry (SIMS). Asymmetric wall rock damage, weakening of crystal preferred orientation (CPO) in small fault clasts, and intense fragmentation within the fault zones even in association with very small displacements suggest that the early stage faults represent seismic events and predate mesh formation. Hydration and mesh texture formation follows in the wake of this faulting. Serpentinization is associated with moderate enrichment of fluid mobile elements including B, Li, Rb and U, indicative of fluid rock interaction characterized by relatively low fluid/rock ratios. This is consistent with a scenario where serpentinization took place below a thick magmatic crust following an earthquake-induced permeability increase. The oxygen isotope compositions of mesh serpentine are consistent with off-axis serpentinization at temperatures in the range 200-250 °C

• Xin Zhong, Marcin Dabrowski & Bjørn Jamtveit (2021). Analytical solution for residual stress and strain preserved in anisotropic inclusion entrapped in an isotropic host. Solid Earth (SE). ISSN 1869-9510. 12(4), p. 817–833. doi: 10.5194/se-12-817-2021. Full text in Research Archive Show summary

  Raman elastic thermobarometry has recently been applied in many petrological studies to recover the pressure and temperature (P–T) conditions of mineral inclusion entrapment. Existing modelling methods in petrology either adopt an assumption of a spherical, isotropic inclusion embedded in an isotropic, infinite host or use numerical techniques such as the finite-element method to simulate the residual stress and strain state preserved in the non-spherical anisotropic inclusions. Here, we use the Eshelby solution to develop an analytical framework for calculating the residual stress and strain state of an elastically anisotropic, ellipsoidal inclusion in an infinite, isotropic host. The analytical solution is applicable to any class of inclusion symmetry and an arbitrary inclusion aspect ratio. Explicit expressions are derived for some symmetry classes, including tetragonal, hexagonal, and trigonal. The effect of changing the aspect ratio on residual stress is investigated, including quartz, zircon, rutile, apatite, and diamond inclusions in garnet host. Quartz is demonstrated to be the least affected, while rutile is the most affected. For prolate quartz inclusion (c axis longer than a axis), the effect of varying the aspect ratio on Raman shift is demonstrated to be insignificant. When c/a=5 , only ca. 0.3 cm−1 wavenumber variation is induced as compared to the spherical inclusion shape. For oblate quartz inclusions, the effect is more significant, when c/a=0.5, ca. 0.8 cm−1 wavenumber variation for the 464 cm−1 band is induced compared to the reference spherical inclusion case. We also show that it is possible to fit an effective ellipsoid to obtain a proxy for the averaged residual stress or strain within a faceted inclusion. The difference between the volumetrically averaged stress of a faceted inclusion and the analytically calculated stress from the best-fitted effective ellipsoid is calculated to obtain the root-mean-square deviation (RMSD) for quartz, zircon, rutile, apatite, and diamond inclusions in garnet host. Based on the results of 500 randomly generated (a wide range of aspect ratio and random crystallographic orientation) faceted inclusions, we show that the volumetrically averaged stress serves as an excellent stress measure and the associated RMSD is less than 2 %, except for diamond, which has a systematically higher RMSD (ca. 8 %). This expands the applicability of the analytical solution for any arbitrary inclusion shape in practical Raman measurements.

• Sarah Incel, Jörg Renner & Bjørn Jamtveit (2020). Evolution of Brittle Structures in Plagioclase-Rich Rocks at High-Pressure and High-Temperature Conditions - Linking Laboratory Results to Field Observations. Geochemistry Geophysics Geosystems. 21(8). doi: 10.1029/2020GC009028. Full text in Research Archive Show summary

  Plagioclase‐rich granulites exposed on the Lofoten archipelago, Northern Norway, display strain localization in pseudotachylytes as well as ductile shear zones that formed under similar high‐pressure and high‐temperature conditions. Pseudotachylytes or pseudotachylyte networks reveal no or very little hydration, whereas ductile shear zones reveal significant hydration. We combine these observations from the field with experimental results to characterize the structural evolution of brittle faults in plagioclase‐rich rocks at conditions of the lower continental crust. We performed a series of deformation experiments on intact granulite samples prepared from a natural granulite sample at 2.5 GPa confining pressure, a strain rate of 5 × 10−5 s−1, and temperatures of 700°C and 900°C to total strains of ~7–8% and ~33–36%. Samples were either deformed “as‐is” or with ~1 wt.% H2O added. Striking similarities between the experimental and natural microstructures suggest that the transformation of precursory brittle structures into ductile shear zones at eclogite‐facies conditions is most effective in samples deformed with added water triggering reaction and subsequent plastic deformation of the products along the faults and in the adjacent wall‐rock.

• Kristina G Dunkel, Xin Zhong, Paal Ferdinand Arnestad, Lars Vesterager Valen & Bjørn Jamtveit (2020). High transient stress in the lower crust: Evidence from dry pseudotachylytes in granulites, Lofoten Archipelago, northern Norway. Geology. ISSN 0091-7613. 49(2), p. 135–139. doi: 10.1130/G48002.1. Full text in Research Archive Show summary

  Seismic activity below the standard seismogenic zone is difficult to investigate because the geological records of such earthquakes, pseudotachylytes, are typically reacted and/or deformed. Here, we describe unusually pristine pseudotachylytes in lower-crustal granulites from the Lofoten Archipelago, northern Norway. The pseudotachylytes have essentially the same mineralogical composition as their host (mainly plagioclase, alkali feldspar, orthopyroxene) and contain microstructures indicative of rapid cooling, i.e., feldspar microlites and spherulites and “cauliflower” garnets. Mylonites are absent, both in the wall rocks and among the pseudotachylyte clasts. The absence of features recording precursory ductile deformation rules out several commonly invoked mechanisms for triggering earthquakes in the lower crust, including thermal runaway, plastic instabilities, and downward propagation of seismic slip from the brittle to the ductile part of a fault. The anhydrous mineralogy of host and pseudotachylytes excludes dehydration-induced embrittlement. In the absence of such weakening mechanisms, stress levels in the lower crust must have been transiently high.

• Xin Zhong, Niels Højmark Andersen, Marcin Dabrowski & Bjørn Jamtveit (2019). Zircon and quartz inclusions in garnet used for complementary Raman thermobarometry: application to the Holsnøy eclogite, Bergen Arcs, Western Norway. Contributions to Mineralogy and Petrology. ISSN 0010-7999. 174. doi: 10.1007/s00410-019-1584-4. Full text in Research Archive Show summary

  Mineral inclusions are common and have been widely used to investigate complex geological history. When a rock undergoes cooling and decompression after the entrapment of an inclusion into a host mineral, residual pressure may develop within the inclusion because of the differences in thermal expansivity and compressibility between the inclusion and host. By combining laser Raman spectroscopy and experimental data relating hydrostatic pressure and Raman shift, it is possible to estimate the entrapment pressure–temperature (P–T) conditions using an isotropic elastic model. In this study, we report Raman spectroscopic data on both zircon and quartz inclusions in garnet host from the Holsnøy eclogite, Bergen Arcs, Norway. Averaged residual pressures based on different Raman peaks for zircon and quartz inclusions are obtained to be ca. 0.6 GPa and ca. 0.65 GPa respectively. Using the equation of state for zircon and quartz, the entrapment P–T conditions are constrained to be 1.7–1.9 GPa, 680–760 °C, consistent with previous estimates based on phase equilibria. Heating/cooling experiments are performed on an entrapped zircon inclusion. A clear trend is found between the residual zircon inclusion pressure and the externally controlled temperature. We show that the residual zircon inclusion pressure sealed in garnet host is very sensitive to the entrapment temperature, and can be used as a Raman thermometer. The effects of laser heating and the thermo-elastic anisotropy of zircon inclusion are quantified and discussed.

• Arianne Juliette Petley-Ragan, Yehuda Ben-Zion, Håkon Olaf Austrheim, Benoit Ildefonse, Francois Renard & Bjørn Jamtveit (2019). Dynamic earthquake rupture in the lower crust. Science Advances. 5(7). doi: 10.1126/sciadv.aaw0913. Full text in Research Archive Show summary

  Earthquakes in the continental crust commonly occur in the upper 15 to 20 km. Recent studies demonstrate that earthquakes also occur in the lower crust of collision zones and play a key role in metamorphic processes that modify its physical properties. However, details of the failure process and sequence of events that lead to seismic slip in the lower crust remain uncertain. Here, we present observations of a fault zone from the Bergen Arcs, western Norway, which constrain the deformation processes of lower crustal earthquakes. We show that seismic slip and associated melting are preceded by fracturing, asymmetric fragmentation, and comminution of the wall rock caused by a dynamically propagating rupture. The succession of deformation processes reported here emphasize brittle failure mechanisms in a portion of the crust that until recently was assumed to be characterized by ductile deformation.

• Sarah Incel, Loic Labrousse, Nadège Hilairet, Timm John, Julien Gasc & Feng Shi [Show all 11 contributors for this article] (2019). Reaction -induced embrittlementog the lower continental crust. Geology. ISSN 0091-7613. 47(3), p. 235–238. doi: 10.1130/G45527.1. Full text in Research Archive Show summary

  Field observations and geophysical data reveal a causal link between brittle seismic failure and eclogitization of the lower continental crust. We present results from experimental deformation of plagioclase-rich samples at eclogite-facies conditions and quantify the link between rock rheology and the kinetics of the eclogitization reactions. The deformation was ductile both in the absence of reaction and when the progress of eclogitization was fast compared to the imposed strain rate. However, when the reaction rate was relatively slow, the breakdown of plagioclase into nanocrystalline reaction products induced a weakening that triggered seismic failure. Fluid-induced plagioclase breakdown under eclogite- facies conditions is an exothermic reaction accompanied by a negative change in solid volume. This is similar to other mineral transformations that are known to trigger transformational faulting. We demonstrate that mineral reactions lead to brittle deformation in situations where reaction rates are slow compared to the deformation rate. This reaction-induced instability may provide a generic mechanism for embrittlement at depths beyond the normal seismogenic zone.

• Bjørn Jamtveit, Arianne Juliette Petley-Ragan, Sarah Incel, Kristina G Dunkel, Claire Olga Maryse Aupart & Håkon Olaf Austrheim [Show all 9 contributors for this article] (2019). The effects of earthquakes and fluids on the metamorphism of the lower continental crust. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 124(8), p. 7725–7755. doi: 10.1029/2018JB016461. Full text in Research Archive Show summary

  Rock rheology and density have first‐order effects on the lithosphere's response to plate tectonic forces at plate boundaries. Changes in these rock properties are controlled by metamorphic transformation processes that are critically dependent on the presence of fluids. At the onset of a continental collision, the lower crust is in most cases dry and strong. However, if exposed to internally produced or externally supplied fluids, the thickened crust will react and be converted into a mechanically weaker lithology by fluid‐driven metamorphic reactions. Fluid introduction is often associated with deep crustal earthquakes. Microstructural evidence, suggest that in strong highly stressed rocks, seismic slip may be initiated by brittle deformation and that wall‐rock damage caused by dynamic ruptures plays a very important role in allowing fluids to enter into contact with dry and highly reactive lower crustal rocks. The resulting metamorphism produces weaker rocks which subsequently deform by viscous creep. Volumes of weak rocks contained in a highly stressed environment of strong rocks may experience significant excursions toward higher pressure without any associated burial. Slow and highly localized creep processes in a velocity strengthening regime may produce mylonitic shear zones along faults initially characterized by earthquake‐generated frictional melting and wall rock damage. However, stress pulses from earthquakes in the shallower brittle regime may kick start new episodes of seismic slip at velocity weakening conditions. These processes indicate that the evolution of the lower crust during continental collisions is controlled by the transient interplay between brittle deformation, fluid‐rock interactions, and creep flow.

• Xiaojiao Zheng, Benoit Cordonnier, Jessica Ann McBeck, Elodie Boller, Bjørn Jamtveit & Wenlu Zhu [Show all 7 contributors for this article] (2019). Mixed‐mode strain localization generated by hydration reaction at crustal conditions. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 124(5), p. 4507–4522. doi: 10.1029/2018JB017008. Full text in Research Archive Show summary

  Hydration reactions influence rock density and rheology. For example, volume increases produced in hydration reactions may generate sufficient tensile and shear stress to fracture both the rock undergoing the reaction and the surrounding host rock. We performed in situ dynamic X‐ray synchrotron microtomography experiments to investigate reaction‐induced fracturing. Two experiments on hydration of periclase were performed at 180 or 190 °C, under a confinement of 10 or 80 MPa, a pore fluid pressure of 5 or 75 MPa, and with or without differential stress. The sample assembly consists of a periclase cylinder inserted into a central hole within a serpentinite cylinder. The reaction from periclase to brucite results in a large volume increase (110%), pushing the periclase/brucite against the serpentinite and ultimately breaking it. Using time‐resolved three‐dimensional imaging, we quantify the spatial and temporal distribution of the reaction‐induced fractures. We perform digital volume correlation analysis to obtain the incremental strain tensors throughout the hydration and fracturing process. We use numerical models to assess the distribution of stress within the serpentinite. The digital volume correlation results show mixed‐mode strain localization. The von Mises strain, indicative of shear, increases by a larger percentage than the contractive or dilatative strain components as the reaction‐induced fractures grow. The distribution of von Mises strain follows a power law relationship in the cumulative frequency‐magnitude domain, indicative of long‐range elastic stress interactions during fracturing. This experimental finding sheds insights on the mechanisms of microseismicity measured in areas undergoing active serpentinization.

• Kristina G Dunkel, Bjørn Jamtveit & Håkon Olaf Austrheim (2019). Ophicarbonates of the Feragen Ultramafic Body, central Norway. Norwegian Journal of Geology. ISSN 2387-5844. 99(3), p. 1–18. doi: 10.17850/njg99-3-3. Full text in Research Archive Show summary

  The carbonation of ultramafic rocks is a common alteration process in ophiolites and can occur in various settings. We provide the first detailed description of the carbonated peridotites (ophicarbonates) of the Feragen Ultramafic Body, central Norway, which have unusually variable compositions and microstructures. Lithologies range from pervasively carbonated serpentinites through carbonated serpentinite breccias to carbonated ultramafic conglomerates. Carbonate phases are Ca-carbonate, magnesite and dolomite. Some breccias are also cemented by coarsegrained brucite. This variability records strong variations in fluid chemistry and/or pressure and temperature conditions, both spatially and temporally. By analysing these altered ultramafic rocks using field relationships, optical microscopy, electron microprobe analysis and oxygen and carbon isotope compositions, we elucidate the history of the Feragen Ultramafic Body in more detail and emphasise the importance of deformation for the extent and type of alteration.

• Sarah Incel, Alexandre Schubnel, Jörg Renner, Timm John, Loic Labrousse & Nadège Hilairet [Show all 10 contributors for this article] (2019). Experimental evidence for wall-rock pulverization during dynamic rupture at ultra-high pressure conditions. Earth and Planetary Science Letters. ISSN 0012-821X. 528, p. 1–10. doi: 10.1016/j.epsl.2019.115832. Full text in Research Archive Show summary

  The mechanisms triggering intermediate and deep earthquakes have puzzled geologists for several decades. There is still no consensus concerning whether such earthquakes are triggered by brittle or ductile mechanisms. We performed a deformation experiment on a synthetic lawsonite-bearing blueschist at a confining pressure of 3 GPa and temperatures from 583 to 1,073 K. After deformation, the recovered sample reveals conjugated shear fractures. Garnet crystals are dissected and displaced along these narrow faults and reveal micro- and nanostructures that resemble natural pulverization structures as well as partial amorphization. Formation of such structures at low confining pressures is known to require high tensile stresses and strain rates and is explained by the propagation of a dynamic shear rupture. The absence of shearing in the pulverized wall rock is taken as evidence that these structures pre-date the subsequent heat-producing frictional slip. In analogy to observations at low pressure we infer that the garnet structures in our experiment result from rapid propagation of a shear fracture even at the high pressure exerted on the sample and thus suggest that brittle deformation is possible at lower crustal to upper mantle depths.

• Xin Zhong, Marcin Dabrowski & Bjørn Jamtveit (2019). Analytical solution for the stress field in elastic half-space with a spherical pressurized cavity or inclusion containing eigenstrain. Geophysical Journal International. ISSN 0956-540X. 216(2), p. 1100–1115. doi: 10.1093/gji/ggy447. Full text in Research Archive Show summary

  We present an analytical solution based on the series expansion of Papkovich-Boussinesq's displacement potentials to derive the elastic solution of a spherical inclusion containing an eigenstrain or pressurized cavity in an elastic half-space. The inclusion–host interface can be treated as perfectly bonded or allowing different amount of interface sliding as a function of shear stress. The analytical solution allows systematic investigation on some key parameters that control the elastic stress field, such as inclusion depth, elastic moduli and the amount of interface sliding. The model is applied to study the distributions of stresses and displacements within and around the inclusion. Stress trajectories and slip lines are computed around a pressurized cavity based on the analytical solution to study potential fracture modes and patterns. The amount of inclusion pressure relaxation due to the free surface is also systematically investigated as a function of inclusion depth and shear modulus ratio between the host and inclusion. A MATLAB code is provided that allows one to directly apply the analytical solution to natural systems given any elastic parameters. The code is benchmarked with Mindlin's solution for loaded homogeneous inclusion in proximity to a free surface and 3-D finite element simulations for heterogeneous inclusion. This model may contribute to the study of the mechanical properties of natural systems at various scales, from km size magma chamber to mm-μm size mineral inclusions sealed in thin section.

• Claire Olga Maryse Aupart, Kristina G Dunkel, Luiza Angheluta, Håkon Olaf Austrheim, Beniot Ildefonse & Anders Malthe-Sørenssen [Show all 7 contributors for this article] (2018). Olivine Grain Size Distributions in Faults and Shear Zones: Evidence for Nonsteady State Deformation. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 123(9), p. 7421–7443. doi: 10.1029/2018JB015836. Full text in Research Archive Show summary

  The grain size distribution of deformed rocks may provide valuable information about their deformation history and the associated mechanisms. Here we present a unique set of olivine grain size distributions from ultramafic rocks deformed under a wide range of stress and strain rate conditions. Both experimentally deformed and naturally deformed samples are included. We observe a surprisingly uniform behavior, and most samples show power law grain size distributions. Convincing lognormal distributions across all scales were only observed for samples experimentally deformed at high temperature (1200 °C) and for some mantle‐deformed natural samples. Single power law distributions were observed for natural samples deformed by brittle mechanisms and by samples deformed experimentally in the regime of low‐temperature plasticity. Most natural samples show a crossover in power law scaling behavior near the median grain size from a steep slope for the larger grain fraction to a more gentle slope for the smaller grains. The small grain fraction shows a good data collapse when normalized to the crossover length scale. The associated power law slope indicates a common grain size controlling process. We propose a model that explains how such a scaling behavior may arise in the dislocation creep regime from the competition between the rate involved in the dislocation dynamics and the imposed strain rate. The common departure from lognormal distributions suggests that naturally deformed samples often have a deformation history that is far from a steady state scenario and probably reflects deformation under highly variable stress and strain rates. ©2018. American Geophysical Union. All Rights Reserved.

• Adriane Clerc, Francois Renard, Håkon Olaf Austrheim & Bjørn Jamtveit (2018). Spatial and size distributions of garnets grown in a pseudotachylyte generated during a lower crust earthquake. Tectonophysics. ISSN 0040-1951. 733, p. 159–170. doi: 10.1016/j.tecto.2018.02.014. Full text in Research Archive Show summary

  In the Bergen Arc, western Norway, rocks exhumed from the lower crust record earthquakes that formed during the Caledonian collision. These earthquakes occurred at about 30–50 km depth under granulite or amphibolite facies metamorphic conditions. Coseismic frictional heating produced pseudotachylytes in this area. We describe pseudotachylytes using field data to infer earthquake magnitude (M ≥ ~6.6), low dynamic friction during rupture propagation (μd < 0.1) and laboratory analyses to infer fast crystallization of microlites in the pseudotachylyte, within seconds of the earthquake arrest. High resolution 3D X-ray microtomography imaging reveals the microstructure of a pseudotachylyte sample, including numerous garnets and their corona of plagioclase that we infer have crystallized in the pseudotachylyte. These garnets 1) have dendritic shapes and are surrounded by plagioclase coronae almost fully depleted in iron, 2) have a log-normal volume distribution, 3) increase in volume with increasing distance away from the pseudotachylyte-host rock boundary, and 4) decrease in number with increasing distance away from the pseudotachylyte -host rock boundary. These characteristics indicate fast mineral growth, likely within seconds. We propose that these new quantitative criteria may assist in the unambiguous identification of pseudotachylytes in the field.

• Arianne Juliette Petley-Ragan, Kristina G Dunkel, Håkon Olaf Austrheim, Benoit Ildefonse & Bjørn Jamtveit (2018). Microstructural Records of Earthquakes in the Lower Crust and Associated Fluid-Driven Metamorphism in Plagioclase-Rich Granulites. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 123(5), p. 3729–3746. doi: 10.1029/2017JB015348. Full text in Research Archive Show summary

  Coseismic damage associated with earthquakes in the lower continental crust is accompanied by postseismic annealing and fluid‐mediated metamorphism that influence the physical and chemical development of the continental crust on regional scales. A transition from brittle deformation to crystal‐plastic recrystallization is a recurring characteristic of rocks affected by lower crustal earthquakes and is observed in plagioclase adjacent to pseudotachylytes in granulite facies anorthosites from the Bergen Arcs, western Norway. The microstructural and petrological records of this transition were investigated using electron microscopy, electron microprobe analysis, and electron backscatter diffraction analysis. Microfractures associated with mechanical twins are abundant within plagioclase and contain fine‐grained aggregates that formed by fragmentation with minor shear deformation. The presence of feather features, which are described for the first time in feldspar, suggests that fractures propagate at near the shear wave velocity into the wall rock of earthquake slip planes. Grain size insensitive recrystallization took place within the time frame of pseudotachylyte formation, forming high‐angle grain boundaries required for shear zone initiation. Fluid infiltration synfracture to postfracture facilitated the epitactic replacement of plagioclase by alkali feldspar and the nucleation of clinozoisite, kyanite, and quartz. The grain size reduction and crystallization associated with the microfractures create rheologically weak areas that have the potential to localize strain within the plagioclase‐rich lower crust. ©2018. American Geophysical Union. All Rights Reserved.

• Bjørn Jamtveit, Yehuda Ben-Zion, Francois Renard & Håkon Olaf Austrheim (2018). Earthquake-induced transformation of the lower crust. Nature. ISSN 0028-0836. 556(7702), p. 487–491. doi: 10.1038/s41586-018-0045-y. Full text in Research Archive Show summary

  The structural and metamorphic evolution of the lower crust has direct effects on the lithospheric response to plate tectonic processes involved in orogeny, including subsidence of sedimentary basins, stability of deep mountain roots and extension of high-topography regions. Recent research shows that before orogeny most of the lower crust is dry, impermeable and mechanically strong1. During an orogenic event, the evolution of the lower crust is controlled by infiltration of fluids along localized shear or fracture zones. In the Bergen Arcs of Western Norway, shear zones initiate as faults generated by lower-crustal earthquakes. Seismic slip in the dry lower crust requires stresses at a level that can only be sustained over short timescales or local weakening mechanisms. However, normal earthquake activity in the seismogenic zone produces stress pulses that drive aftershocks in the lower crust2. Here we show that the volume of lower crust affected by such aftershocks is substantial and that fluid-driven associated metamorphic and structural transformations of the lower crust follow these earthquakes. This provides a ‘top-down’ effect on crustal geodynamics and connects processes operating at very different timescales.

• Xiaojiao Zheng, Benoit Cordonnier, Wenlu Zhu, Francois Renard & Bjørn Jamtveit (2018). Effects of Confinement on Reaction-Induced Fracturing During Hydration of Periclase. Geochemistry Geophysics Geosystems. 19(8), p. 2661–2672. doi: 10.1029/2017GC007322. Full text in Research Archive Show summary

  Hydration of a nominally dry rock can cause expansion of the solid volume, resulting in reaction‐induced fracturing and an associated increase in the porosity and permeability of the rock. We study the effect of confinement on the coupling between stress generation, reaction‐induced fracturing, and porosity evolution during the hydration of periclase (MgO) into brucite (Mg(OH)2). Samples of a microporous MgO ceramic were hydrated at 170–210 °C, 5–80 MPa confining pressure, 6–95 MPa differential stress, and 5–75 MPa pore fluid pressure in a purpose‐designed triaxial load cell. Hydration‐induced changes were recorded in situ by X‐ray microtomographic imaging at 5‐min intervals. Below 30 MPa effective mean stress, the fraction of periclase replaced by brucite is a sigmoidal function of time. After a slow start, the replacement rate picks up with concomitant intense fracturing. The porosity increase resulting from the reaction‐induced fractures is transient (pulse‐like). Following the porosity pulse the rate of replacement declines until the replacement is almost complete. Above 30 MPa, the reaction rate is slow, porosity decreases monotonically without any observable fracturing during the time of the experiment. At these stress conditions, the lack of fracturing cannot be limited by the thermodynamic affinity of the reaction. A possible interpretation is that the stress generated by the reaction may overcome the disjoining pressure at the grain‐grain interface, expelling the water film trapped there and thereby dramatically reducing the reaction rate.

• Bjørn Jamtveit, Evangelos Moulas, Torgeir Bjørge Andersen, Håkon Olaf Austrheim, Fernando Corfu & Arianne Juliette Petley-Ragan [Show all 7 contributors for this article] (2018). High Pressure Metamorphism Caused by Fluid Induced Weakening of Deep ontinental Crust. Scientific Reports. 8. doi: 10.1038/s41598-018-35200-1. Full text in Research Archive Show summary

  Studies of mineral equilibria in metamorphic rocks have given valuable insights into the tectonic processes operating at convergent plate margins during an orogeny. Geodynamic models simulating orogenesis and crustal thickening have been constrained by temperature and pressure estimates inferred from the mineral assemblages of the various lithologies involved along with age constrains from increasingly precise geochronological techniques. During such studies it is assumed that the pressure experienced by a given rock is uniquely related to its depth of burial. This assumption has been challenged by recent studies of high pressure (HP) and ultrahigh pressure (UHP) rocks. Here, we describe an example of Caledonian HP metamorphism from the Bergen Arcs in western Norway, and show that the associated formation of Caledonian eclogites at the expense of Proterozoic granulites was related to local pressure perturbations rather than burial, and that the HP metamorphism resulted from fluid-induced weakening of an initially dry and highly stressed lower crust when thrust upon the hyperextended margin of the Baltic shield.

• Håkon Olaf Austrheim, Kristina G Dunkel, Oliver Plümper, Benoit Ildefonse, Yang Liu & Bjørn Jamtveit (2017). Fragmentation of wall rock garnets during deep crustal earthquakes. Science Advances. 3(2). doi: 10.1126/sciadv.1602067. Full text in Research Archive Show summary

  Fractures and faults riddle the Earth’s crust on all scales, and the deformation associated with them is presumed to have had significant effects on its petrological and structural evolution. However, despite the abundance of directly observable earthquake activity, unequivocal evidence for seismic slip rates along ancient faults is rare and usually related to frictional melting and the formation of pseudotachylites. We report novel microstructures from garnet crystals in the immediate vicinity of seismic slip planes that transected lower crustal granulites during intermediate-depth earthquakes in the Bergen Arcs area, western Norway, some 420 million years ago. Seismic loading caused massive dislocation formations and fragmentation of wall rock garnets. Microfracturing and the injection of sulfide melts occurred during an early stage of loading. Subsequent dilation caused pervasive transport of fluids into the garnets along a network of microfractures, dislocations, and subgrain and grain boundaries, leading to the growth of abundant mineral inclusions inside the fragmented garnets. Recrystallization by grain boundary migration closed most of the pores and fractures generated by the seismic event. This wall rock alteration represents the initial stages of an earthquake-triggered metamorphic transformation process that ultimately led to reworking of the lower crust on a regional scale.

• Kristina G Dunkel, Håkon Olav Austrheim, Francois Renard, Benoit Cordonnier & Bjørn Jamtveit (2017). Localized slip controlled by dehydration embrittlement of partly serpentinized dunites, Leka Ophiolite Complex, Norway. Earth and Planetary Science Letters. ISSN 0012-821X. 463, p. 277–285. doi: 10.1016/j.epsl.2017.01.047. Full text in Research Archive Show summary

  Dehydration of partly or completely serpentinized ultramafic rocks can increase the pore fluid pressure and induce brittle failure, a process referred to as dehydration embrittlement. However the extents of strain localization and unstable frictional sliding during deserpentinization are still under debate. In the layered ultramafic sections of the Leka Ophiolite Complex in the Central Norwegian Caledonides, prograde metamorphism of serpentinite veins led to local fluid production and to the growth of Mg-rich and coarse-grained olivine with abundant magnetite inclusions and δ18O values ‰ below the host rock. Embrittlement associated with the dehydration caused faulting along highly localized (<10 μm-wide) slip planes near the centers of the original serpentinite veins and pulverization of wall rock olivine. These features along with an earthquake-like size distribution of fault offsets suggest unstable frictional sliding rather than slower creep. Structural heterogeneities in the form of serpentinite veins clearly have first-order controls on strain localization and frictional sliding during dehydration. As most of the oceanic lithosphere is incompletely serpentinized, heterogeneities represented by a non-uniform distribution of serpentinite are common and may increase the likelihood that dehydration embrittlement triggers earthquakes.

• Andrew Putnis, Bjørn Jamtveit & Håkon Olaf Austrheim (2017). Metamorphic processes and seismicity: The Bergen Arcs as a natural laboratory. Journal of Petrology. ISSN 0022-3530. 58(10), p. 1871–1898. doi: 10.1093/petrology/egx076. Full text in Research Archive
• Oliver Plümper, Alexandru Botan, Catharina Los, Yang Liu, Anders Malthe-Sørenssen & Bjørn Jamtveit (2017). Fluid-driven metamorphism of the continental crust governed by nanoscale fluid flow. Nature Geoscience. ISSN 1752-0894. 10(9), p. 685–690. doi: 10.1038/ngeo3009. Full text in Research Archive Show summary

  The transport of fluids through the Earth’s crust controls the redistribution of elements to form mineral and hydrocarbon deposits, the release and sequestration of greenhouse gases, and facilitates metamorphic reactions that influence lithospheric rheology. In permeable systems with a well-connected porosity, fluid transport is largely driven by fluid pressure gradients. In less permeable rocks, deformation may induce permeability by creating interconnected heterogeneities, but without these perturbations, mass transport is limited along grain boundaries or relies on transformation processes that self-generate transient fluid pathways. The latter can facilitate large-scale fluid and mass transport in nominally impermeable rocks without large-scale fluid transport pathways. Here, we show that pervasive, fluid-driven metamorphism of crustal igneous rocks is directly coupled to the production of nanoscale porosity. Using multi-dimensional nano-imaging and molecular dynamics simulations, we demonstrate that in feldspar, the most abundant mineral family in the Earth’s crust, electrokinetic transport through reaction-induced nanopores (<100 nm) can potentially be significant. This suggests that metamorphic fluid flow and fluid-mediated mineral transformation reactions can be considerably influenced by nanofluidic transport phenomena.

• Kristina G Dunkel, Håkon Olaf Austrheim, Benoit Ildefonse & Bjørn Jamtveit (2017). Transfer of olivine crystallographic orientation through a cycle of serpentinisation and dehydration. Contributions to Mineralogy and Petrology. ISSN 0010-7999. 172(8). doi: 10.1007/s00410-017-1378-5. Full text in Research Archive Show summary

  Our ability to decipher the mechanisms behind metamorphic transformation processes depends in a major way on the extent to which crystallographic and microstructural information is transferred from one stage to another. Within the Leka Ophiolite Complex in the Central Norwegian Caledonides, prograde olivine veins that formed by dehydration of serpentinite veins in dunites exhibit a characteristic distribution of microstructures: The outer part of the veins comprises coarse-grained olivine that forms an unusual, brick-like microstructure. The inner part of the veins, surrounding a central fault, is composed of fine-grained olivine. Where the fault movement included a dilational component, optically clear, equant olivine occurs in the centre. Electron backscatter diffraction mapping reveals that the vein olivine has inherited its crystallographic preferred orientation (CPO) from the olivine in the porphyroclastic host rock; however, misorientation is weaker and associated to different rotation axes. We propose that prograde olivine grew epitaxially on relics of mantle olivine and thereby acquired its CPO. Growth towards pre-existing microfractures along which serpentinisation had occurred led to straight grain boundaries and a brick-like microstructure in the veins. When dehydration embrittlement induced slip, a strong strain localisation on discrete fault planes prevented distortion of the CPO due to cataclastic deformation; grain size reduction did not significantly modify the olivine CPO. This illustrates how a CPO can be preserved though an entire metamorphic cycle, including hydration, dehydration, and deformation processes, and that the CPO and the microstructures (e.g. grain shape) of one phase do not necessarily record the same event. © 2017 Springer Verlag

• Ole Ivar Ulven, Andreas Beinlich, Jörn-Erik Hövelmann, Håkon Olav Austrheim & Bjørn Jamtveit (2017). Subarctic physicochemical weathering of serpentinized peridotite. Earth and Planetary Science Letters. ISSN 0012-821X. 468, p. 11–26. doi: 10.1016/j.epsl.2017.03.030. Full text in Research Archive Show summary

  Frost weathering is effective in arctic and subarctic climate zones where chemical reactions are limited by the reduced availability of liquid water and the prevailing low temperature. However, small scale mineral dissolution reactions are nevertheless important for the generation of porosity by allowing infiltration of surface water with subsequent fracturing due to growth of ice and carbonate minerals. Here we combine textural and mineralogical observations in natural samples of partly serpentinized ultramafic rocks with a discrete element model describing the fracture mechanics of a solid when subject to pressure from the growth of ice and carbonate minerals in surface-near fractures. The mechanical model is coupled with a reaction–diffusion model that describes an initial stage of brucite dissolution as observed during weathering of serpentinized harzburgites and dunites from the Feragen Ultramafic Body (FUB), SE-Norway. Olivine and serpentine are effectively inert at relevant conditions and time scales, whereas brucite dissolution produces well-defined cm to dm thick weathering rinds with elevated porosity that allows influx of water. Brucite dissolution also increases the water saturation state with respect to hydrous Mg carbonate minerals, which are commonly found as infill in fractures in the fresh rock. This suggests that fracture propagation is at least partly driven by carbonate precipitation. Dissolution of secondary carbonate minerals during favorable climatic conditions provides open space available for ice crystallization that drives fracturing during winter. Our model reproduces the observed cm-scale meandering fractures that propagate into the fresh part of the rock, as well as dm-scale fractures that initiate the breakup of larger domains. Rock disintegration increases the reactive surface area and hence the rate of chemical weathering, enhances transport of dissolved and particulate matter in the weathering fluid, and facilitates CO2 uptake by carbonate precipitation. Our observations have implications for element cycling and CO2 sequestration in natural gravel and mine tailings.

• Christopher Hawkins, Luiza Angheluta, Marcin Krotkiewski & Bjørn Jamtveit (2016). Reynolds-number dependence of the longitudinal dispersion in turbulent pipe flow. Physical Review E (PRE). ISSN 2470-0045. 93(4). doi: 10.1103/PhysRevE.93.043119. Full text in Research Archive
• Dániel Keszthelyi, Dag Kristian Dysthe & Bjørn Jamtveit (2016). First principles model of carbonate compaction creep. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 121(5), p. 3348–3365. doi: 10.1002/2015JB012481. Full text in Research Archive Show summary

  Rocks under compressional stress conditions are subject to long‐term creep deformation. From first principles we develop a simple micromechanical model of creep in rocks under compressional stress that combines microscopic fracturing and pressure solution. This model was then upscaled by a statistical mechanical approach to predict strain rate at core and reservoir scale. The model uses no fitting parameter and has few input parameters: effective stress, temperature, water saturation porosity, and material parameters. Material parameters are porosity, pore size distribution, Young's modulus, interfacial energy of wet calcite, the dissolution, and precipitation rates of calcite, and the diffusion rate of calcium carbonate, all of which are independently measurable without performing any type of deformation or creep test. Existing long‐term creep experiments were used to test the model which successfully predicts the magnitude of the resulting strain rate under very different effective stress, temperature, and water saturation conditions. The model was used to predict the observed compaction of a producing chalk reservoir.

• Dániel Keszthelyi, Dag Kristian Dysthe & Bjørn Jamtveit (2016). Compaction of North-Sea Chalk by Pore-Failure and Pressure Solution in a Producing Reservoir. Frontiers in Physics. doi: 10.3389/fphy.2016.00004. Full text in Research Archive
• Bjørn Jamtveit, Håkon Olav Austrheim & Andrew Putnis (2016). Disequilibrium metamorphism of stressed lithosphere. Earth-Science Reviews. ISSN 0012-8252. 154, p. 1–13. doi: 10.1016/j.earscirev.2015.12.002. Full text in Research Archive Show summary

  Most changes in mineralogy, density, and rheology of the Earth's lithosphere take place by metamorphism, whereby rocks evolve through interactions between minerals and fluids. These changes are coupled with geodynamic processes and have first order effects on the global geochemical cycles of a large number of elements. In the presence of fluids, metamorphic reactions are fast compared to tectonically induced changes in pressure and temperature. Hence, rocks evolve through near-equilibrium states during fluid-producing metamorphism. However, much of the Earth's lower crust, and a significant fraction of the upper mantle do not contain free fluids. These parts of the lithosphere exist in a metastable state and are mechanically strong. When subject to changing temperature and pressure conditions at plate boundaries or elsewhere, these rocks do not react until exposed to externally derived fluids. Metamorphism of such rocks consumes fluids, and takes place far from equilibrium through a complex coupling between fluid migration, chemical reactions, and deformation processes. This disequilibrium metamorphism is characterized by fast reaction rates, dissipation of large amounts of energy as heat and work, and the generation of a range of emergent pore structures and fracture patterns that often control transport properties and thus further reaction progress. Fluid-consuming metamorphism leads to mechanical weakening due to grain size reduction, the formation of sheet silicates, and local heat production. Strain localization in the lower crust and upper mantle is therefore likely to be controlled by the availability of fluids. Fault-controlled migration of meteoric fluids from the brittle crust to the underlying ductile region in areas of compressive stress may provide a spatial and temporal link between localized strain and seismic activity in the upper crust and shear zone controlled deformation below. In a similar way, channelized fluid migration from areas undergoing prograde metamorphism in the lower plate of a subduction zone, may control the distribution of retrograde metamorphism and strain localization in the lower parts of the upper plate.

• Trond Helge Torsvik, Hans E. Foss Amundsen, Reidar G Trønnes, Pavel Doubrovine, Carmen Gaina & Nick J. Kusznir [Show all 12 contributors for this article] (2015). Continental crust beneath southeast Iceland. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 112(15), p. E1818–E1827. doi: 10.1073/pnas.1423099112. Full text in Research Archive Show summary

  The magmatic activity (0–16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Iceland—and especially the Öræfajökull volcano—is characterized by a unique enriched-mantle component (EM2-like) with elevated 87Sr/86Sr and 207Pb/204Pb. Here, we demonstrate through modeling of Sr–Nd–Pb abundances and isotope ratios that the primitive Öræfajökull melts could have assimilated 2–6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of ∼350-km-long and 70-km-wide extension of the Jan Mayen Microcontinent (JMM). The extended JMM was marginal to East Greenland but detached in the Early Eocene (between 52 and 47 Mya); by the Oligocene (27 Mya), all parts of the JMM permanently became part of the Eurasian plate following a westward ridge jump in the direction of the Iceland plume.

• Anja Røyne & Bjørn Jamtveit (2015). Pore-scale controls on reaction-driven fracturing. Reviews in Mineralogy and Geochemistry, Mineralogical Society of America. ISSN 1529-6466. 80(1), p. 25–44. doi: 10.2138/rmg.2015.80.02. Full text in Research Archive
• Ole Ivar Ulven, Bjørn Jamtveit & Anders Malthe-Sørenssen (2014). Reaction-driven fracturing of porous rock. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 119(10), p. 7473–7486. doi: 10.1002/2014JB011102. Full text in Research Archive
• Bjørn Jamtveit, Marcin Krotkiewski, Maya Kobchenko, Francois Marie Paul L Renard & Luiza Angheluta (2014). Pore-space distribution and transport properties of an andesitic intrusion. Earth and Planetary Science Letters. ISSN 0012-821X. 400, p. 123–129. doi: 10.1016/j.epsl.2014.05.042. Full text in Research Archive
• Christopher Hawkins, Luiza Angheluta & Bjørn Jamtveit (2014). Hydrodynamic shadowing effect during precipitation of dendrites in channel flow. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. ISSN 1539-3755. 89(2). doi: 10.1103/PhysRevE.89.022402. Full text in Research Archive Show summary

  A supersaturated fluid flowing over a reactive, rough surface leads to complex precipitation patterns. We study the growth and interaction between discrete precipitates along a reactive wall in a nonlaminar channel flow. We show that the competition between advective transport, diffusion, and mixing strongly influences the downstream precipitates morphology and the typical correlation length between different precipitates. © 2014 American Physical Society

• Maya Kobchenko, Andreas Hafver, Espen Jettestuen, Francois Marie Paul L Renard, Olivier Galland & Bjørn Jamtveit [Show all 8 contributors for this article] (2014). Evolution of a fracture network in an elastic medium with internal fluid generation and expulsion. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. ISSN 1539-3755. 90(5). doi: 10.1103/PhysRevE.90.052801. Full text in Research Archive
• D.B. Meier, E. Gunnlaugsson, I. Gunnarsson, Bjørn Jamtveit, C.L. Peacock & L.G. Benning (2014). Microstructural and chemical variation in silica-rich precipitates at the Hellisheioi geothermal power plant. Mineralogical magazine. ISSN 0026-461X. 78(6), p. 1381–1389. doi: 10.1180/minmag.2014.078.6.04. Full text in Research Archive
• Hamed Panahi, Paul Meakin, Francois Marie Paul L Renard, Maya Kobchenko, Julien Scheibert & Adriano Mazzini [Show all 9 contributors for this article] (2013). A 4D Synchrotron X-Ray-Tomography Study of the Formation of Hydrocarbon-Migration Pathways in Heated Organic-Rich Shale. SPE Journal. ISSN 1086-055X. 18(2), p. 366–377. doi: 10.2118/162939-PA. Full text in Research Archive
• Trond Helge Torsvik, Hans Amundsen, Ebbe Hvidegård Hartz, Fernando Corfu, Nick Kusznir & Carmen Gaina [Show all 10 contributors for this article] (2013). A Precambrian microcontinent in the Indian Ocean. Nature Geoscience. ISSN 1752-0894. 6(3), p. 223–227. doi: 10.1038/ngeo1736. Full text in Research Archive Show summary

  The Laccadive–Chagos Ridge and Southern Mascarene Plateau in the north-central and western Indian Ocean, respectively, are thought to be volcanic chains formed above the Réunion mantle plume1 over the past 65.5 million years2,3. Here we use U–Pb dating to analyse the ages of zircon xenocrysts found within young lavas on the island of Mauritius, part of the Southern Mascarene Plateau. We find that the zircons are either Palaeoproterozoic (more than 1,971 million years old) or Neoproterozoic (between 660 and 840 million years old). We propose that the zircons were assimilated from ancient fragments of continental lithosphere beneath Mauritius, and were brought to the surface by plume-related lavas. We use gravity data inversion to map crustal thickness and find that Mauritius forms part of a contiguous block of anomalously thick crust that extends in an arc northwards to the Seychelles. Using plate tectonic reconstructions, we show that Mauritius and the adjacent Mascarene Plateau may overlie a Precambrian microcontinent that we call Mauritia. On the basis of reinterpretation of marine geophysical data4, we propose that Mauritia was separated from Madagascar and fragmented into a ribbon-like configuration by a series of mid-ocean ridge jumps during the opening of the Mascarene ocean basin between 83.5 and 61 million years ago. We suggest that the plume-related magmatic deposits have since covered Mauritia and potentially other continental fragments.

• Christopher Hawkins, Luiza Angheluta, Øyvind Hammer & Bjørn Jamtveit (2013). Precipitation dendrites in channel flow. Europhysics letters. ISSN 0295-5075. 102(5). doi: 10.1209/0295-5075/102/54001. Full text in Research Archive
• Maya Kobchenko, Andreas Hafver, Espen Jettestuen, Olivier Galland, Francois Marie Paul L Renard & Paul Meakin [Show all 8 contributors for this article] (2013). Drainage fracture networks in elastic solids with internal fluid generation. Europhysics letters. ISSN 0295-5075. 102(6). doi: 10.1209/0295-5075/102/66002. Full text in Research Archive
• Andreas Beinlich, Oliver Plümper, Jörn-Erik Hövelmann, Håkon Olav Austrheim & Bjørn Jamtveit (2012). Massive serpentinite carbonation at Linnajavri, N-Norway. Terra Nova. ISSN 0954-4879. 24(6), p. 446–455. doi: 10.1111/j.1365-3121.2012.01083.x. Full text in Research Archive
• Bjørn Jamtveit & Øyvind Hammer (2012). Sculpting of rocks by reactive fluids. Geochemical Perspectives. ISSN 2223-7755. 1, p. 341–481. doi: 10.7185/geochempersp.1.3. Full text in Research Archive
• Oliver Plümper, Anja Røyne, Anna Magraso & Bjørn Jamtveit (2012). The interface-scale mechanism of reaction-induced fracturing during serpentinization. Geology. ISSN 0091-7613. 40(12), p. 1103–1106. doi: 10.1130/G33390.1. Full text in Research Archive
• Simon Daniel De Villiers, Anders Nermoen, Bjørn Jamtveit, Joachim Mathiesen, Paul Meakin & Stephanie Werner (2012). Formation of Martian araneiforms by gas-driven erosion of granular material. Geophysical Research Letters. ISSN 0094-8276. 39(13). doi: 10.1029/2012GL052226. Full text in Research Archive
• Oliver Plümper, Anja Røyne, Anna Magraso & Bjørn Jamtveit (2012). The interface-scale mechanism of reaction-induced fracturing during upper mantle serpentinization. Geology. ISSN 0091-7613. 40(12), p. 1103–1106. doi: 10.1130/G33390.1. Full text in Research Archive
• Jan O. Haerter, Bjørn Jamtveit & Joachim Mathiesen (2012). Communication Dynamics in Finite Capacity Social Networks. Physical Review Letters. ISSN 0031-9007. 109(16). doi: 10.1103/PhysRevLett.109.168701. Full text in Research Archive
• Jörn-Erik Hövelmann, Håkon Olav Austrheim & Bjørn Jamtveit (2012). Microstructure and porosity evolution during experimental carbonation of a natural peridotite. Chemical Geology. ISSN 0009-2541. 334, p. 254–265. doi: 10.1016/j.chemgeo.2012.10.025. Full text in Research Archive
• Elisabeth Gundersen, Eirik Grude Flekkøy, Knut Bjørlykke, Jens Feder & Bjørn Jamtveit (2011). Fracture spacing during hydro-fracturing of cap-rocks. Geofluids. ISSN 1468-8115. 11(3), p. 280–293. doi: 10.1111/j.1468-8123.2011.00338.x. Full text in Research Archive
• Bjørn Jamtveit, Maya Kobchenko, Håkon Olav Austrheim, Anders Malthe-Sørenssen, Anja Røyne & Henrik Svensen (2011). Porosity evolution and crystallization-driven fragmentation during weathering of andesite. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 116. doi: 10.1029/2011JB008649. Full text in Research Archive
• Anja Røyne, Paul Meakin, Anders Malthe-Sørenssen, Bjørn Jamtveit & Dag Kristian Dysthe (2011). Crack propagation driven by crystal growth. Europhysics letters. ISSN 0295-5075. 96(2). doi: 10.1209/0295-5075/96/24003. Full text in Research Archive
• Christophe Raufaste, Bjørn Jamtveit, Timm John, Paul Meakin & Dag Kristian Dysthe (2011). The mechanism of porosity formation during solvent-mediated phase transformations. Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences. ISSN 1364-5021. 467(2129), p. 1408–1426. doi: 10.1098/rspa.2010.0469. Full text in Research Archive
• Maya Kobchenko, Hamed Panahi, Francois Marie Paul L Renard, Dag Kristian Dysthe, Anders Malthe-Sørenssen & Adriano Mazzini [Show all 9 contributors for this article] (2011). 4D imaging of fracturing in organic-rich shales during heating. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 116(12). doi: 10.1029/2011JB008565. Full text in Research Archive
• Øyvind Hammer, Stein-Erik Lauritzen & Bjørn Jamtveit (2011). Stability of dissolution flutes under turbulent flow. Journal of Cave and Karst Science. ISSN 1090-6924. 73(3), p. 181–186. doi: 10.4311/2011JCKS0200. Full text in Research Archive
• P. Japsen, Dag Kristian Dysthe, Ebbe Hvidegård Hartz, SLS Stipp, Viktoriya M. Yarushina & Bjørn Jamtveit (2011). A compaction front in North Sea chalk. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 116. doi: 10.1029/2011JB008564. Full text in Research Archive
• Øyvind Hammer, Dag Kristian Dysthe & Bjørn Jamtveit (2010). Travertine terracing: patterns and mechanisms. Geological Society Special Publication. ISSN 0305-8719. 336, p. 345–355. doi: 10.1144/SP336.18. Full text in Research Archive
• Paul Meakin & Bjørn Jamtveit (2010). Geological pattern formation by growth and dissolution in aqueous systems. Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences. ISSN 1364-5021. 466(2115), p. 659–694. doi: 10.1098/rspa.2009.0189. Full text in Research Archive
• Jan Kihle, D.E. Harlov, Ø. Frigaard & Bjørn Jamtveit (2010). Epitaxial quartz inclusions in corundum from a sapphirine-garnet boudin, Bamble Sector, SE Norway: SiO2-Al2O3 miscibility at high P-T dry granulite facies conditions. Journal of Metamorphic Geology. ISSN 0263-4929. 28(7), p. 769–784. doi: 10.1111/j.1525-1314.2010.00891.x. Full text in Research Archive
• Henrik Svensen & Bjørn Jamtveit (2010). Metamorphic Fluids and Global Environmental Changes. Elements. ISSN 1811-5209. 6(3), p. 179–182. doi: 10.2113/gselements.6.3.179. Full text in Research Archive
• Bjørn Jamtveit (2010). Metamorphism: From Patterns to Processes. Elements. ISSN 1811-5209. 6(3), p. 149–152. doi: 10.2113/gselements.6.3.149. Full text in Research Archive
• Bjørn Jamtveit & Håkon Olav Austrheim (2010). Metamorphism: The Role of Fluids. Elements. ISSN 1811-5209. 6(3), p. 153–158. doi: 10.2113/gselements.6.3.153. Full text in Research Archive

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• Joanna Dziadkowiec, Shaghayegh Javadi, Matea Ban, Bjørn Jamtveit & Anja Røyne (2022). Ion-dependent adhesion between calcite surfaces. Full text in Research Archive
• Joanna Dziadkowiec, Matea Ban, Shaghayegh Javadi, Bjørn Jamtveit & Anja Røyne (2021). Ion-specific adhesion between brittle calcite surfaces. Full text in Research Archive
• Xin Zhong, Marcin Dabrowski, Roger Powell & Bjørn Jamtveit (2020). “EosFit-Pinc: A simple GUI for host-inclusion elastic thermobarometry” by Angel et al. (2017)—Discussion. American Mineralogist. ISSN 0003-004X. 105, p. 1585–1586. doi: 10.2138/am-2020-7267. Full text in Research Archive
• Claire Olga Maryse Aupart, Marguerite Godard, Luiz F.G. Morales & Bjørn Jamtveit (2020). Early faulting and cataclasis in the Samail peridotites. Full text in Research Archive
• Marthe Grønlie Guren, Xiaojiao Zheng, Bjørn Jamtveit, Anders Hafreager, Henrik Andersen Sveinsson & Anders Malthe-Sørenssen [Show all 7 contributors for this article] (2019). Molecular dynamics simulations of the hydration force and transport properties of a water film during reaction-induced fracturing. Full text in Research Archive
• Claire Olga Maryse Aupart, Vera Schlindwein, Yehuda Ben-Zion, Francois Marie Paul L Renard & Bjørn Jamtveit (2019). Fracture network and serpentinization at oceanic spreading ridges: in-situ observations and comparison with a fossilized system. Full text in Research Archive
• Oliver Plümper, Alexandru Botan, Catharina Los, Yang Liu, Anders Malthe-Sørenssen & Bjørn Jamtveit (2019). Erratum to: Fluid-driven metamorphism of the continental crust governed by nanoscale fluid flow (Nature Geoscience, (2017), 10, 9, (685-690), 10.1038/ngeo3009). Nature Geoscience. ISSN 1752-0894. 12(1), p. 80–80. doi: 10.1038/s41561-018-0276-4. Full text in Research Archive
• Sarah Incel, Loic Labrousse, Nadege Hilaret, Timm John, Julien Gase & Wang Yanbin [Show all 11 contributors for this article] (2018). Reaction-induced faulting in granulite: New insights for the generation of intermediate-depth earthquakes in lower continental crust. Full text in Research Archive Show summary

  Pseudotachylite-networks in granulites on Holsnøy in the Bergen Arcs, SW Norway, and seismic tomography of the Tibetan plateau reveal that earthquakes were triggered even at the high temperature/ high pressure condi- tions of the lower continental crust. Both, field and geophysical observations, demonstrate a strong link between the nucleation of intermediate-depth earthquakes and areas of partial eclogitization within nominally anhydrous granulitic lower crust. This study presents four deformation experiments performed on granulite samples from Holsnøy. To accelerate reaction kinetics, which is very slow in dry rocks, we applied confining pressures of 2.5-3 GPa and temperatures in the range 995-1225 K, significantly higher than the expected eclogitization conditions of the Bergen Arcs (pressure= 1.5-2 GPa, temperature= 923-973 K). Based on the mechanical data, micro- and nanos- tructural observations, and recorded acoustic emissions, we were able to correlate the degree of eclogitization to the rheological behavior of the samples. Depending on the net eclogitization rate relative to the deformation rate (5 ×10−5s−1) the sample either behaved strong and ductile if no reaction occurred, mainly brittle when the rate of eclogitization was slow, or mostly weak ductile when the rate of eclogitization was fast. Our experimental re- sults emphasize that shear localization due to grain size reduction triggered by the breakdown of plagioclase under eclogite-facies conditions lead to brittle failure accompanied by acoustic emissions. These and other experiments on a variety of lithologies suggest that there could be one common mechanism that triggers intermediate and deep earthquakes.

• Sarah Incel, Loic Labrousse, Nadège Hilairet, Timm John, Julien Gasc & Feng Shi [Show all 11 contributors for this article] (2018). Reaction-induced faulting in granulite causes earthquakes in the lower continental crust. Full text in Research Archive Show summary

  Pseudotachylite-networks in granulites on Holsnøy in the Bergen Arcs, SW Norway, and seismic tomography of the Tibetan plateau reveal that earthquakes were triggered even at the high temperature/ high pressure conditions of the lower continental crust. Both, field and geophysical observations, demonstrate a strong link between the nucleation of intermediate-depth earthquakes and areas of partial eclogitization within nominally anhydrous granulitic lower crust. This study presents four deformation experiments performed on granulite samples from Holsnøy. To accelerate reaction kinetics, which is very slow in dry rocks, we applied confining pressures of 2.5-3 GPa and temperatures in the range 995-1225 K, significantly higher than the expected eclogitization conditions of the Bergen Arcs (pressure= 1.5-2 GPa, temperature= 923-973 K). Based on the mechanical data, micro- and nanostructural observations, and recorded acoustic emissions, we were able to correlate the degree of eclogitization to the rheological behavior of the samples. Depending on the net eclogitization rate relative to the deformation rate (5∙10-5 s-1) the sample either behaved strong and ductile if no reaction occurred, mainly brittle when the rate of eclogitization was slow, or mostly weak ductile when the rate of eclogitization was fast. Our experimental results emphasize that shear localization due to grain size reduction triggered by the breakdown of plagioclase under eclogite-facies conditions lead to brittle failure accompanied by acoustic emissions. These and other experiments on a variety of lithologies suggest that there could be one common mechanism that triggers intermediate and deep earthquakes.

• Ole Ivar Ulven, Håkon Olaf Austrheim & Bjørn Jamtveit (2018). Self-induced serpentine deformation and its effect on weathering. Full text in Research Archive
• Marguerite Godard, Patrizia Fumagalli, Bjørn Jamtveit & Bénédicte Ménez (2018). Geological reactive systems from the mantle to the abyssal sub-seafloor: Preface. Lithos. ISSN 0024-4937. 323, p. 1–3. doi: 10.1016/j.lithos.2018.10.019. Full text in Research Archive
• Claire Olga Maryse Aupart, Kristina Grete Dunkel, Luiza Angheluta-Bauer, Håkon Austrheim, Benoit Ildefonse & Anders Malthe-Sørenssen [Show all 7 contributors for this article] (2017). Grain size distribution evolution in shear zones: a study case in the Leka Ophiolite Complex (LOC). Full text in Research Archive
• Dániel Keszthelyi, Dag Kristian Dysthe & Bjørn Jamtveit (2015). Compaction of North Sea Chalk - A new micromechanical mechanism of pore collapse and a statistical mechanical upscaling to predict Ekofisk subsidence. Full text in Research Archive
• Dániel Keszthelyi, Bjørn Jamtveit & Dag Kristian Dysthe (2015). Compaction creep of carbonate rocks. Full text in Research Archive
• Dániel Keszthelyi, Dag Kristian Dysthe & Bjørn Jamtveit (2015). The mysterious subsidence of the seafloor due to oil production – How to predict it with a simple model? EGU Blogs. Full text in Research Archive
• Ole Ivar Ulven, Håkon Olav Austrheim, Andreas Beinlich, Jörn-Erik Hövelmann & Bjørn Jamtveit (2015). Subarctic physicochemical weathering of serpentinized peridotite. Full text in Research Archive
• Dániel Keszthelyi, Dag Kristian Dysthe & Bjørn Jamtveit (2015). Model of compaction in carbonates. Full text in Research Archive
• Dániel Keszthelyi, Bjørn Jamtveit & Dag Kristian Dysthe (2015). A model of compaction creep in carbonates. Full text in Research Archive
• Dániel Keszthelyi, Bjørn Jamtveit & Dag Kristian Dysthe (2015). Compaction creep by pore failure and pressure solution applied to a carbonate reservoir. Full text in Research Archive
• Dániel Keszthelyi, Dag Kristian Dysthe & Bjørn Jamtveit (2015). Compaction of the Ekofisk oil reservoir - On small- and on large-scale. Full text in Research Archive
• Dániel Keszthelyi, Dag Kristian Dysthe & Bjørn Jamtveit (2015). Compaction of North-sea chalk by pore-failure and pressure solution. Full text in Research Archive
• Dániel Keszthelyi, Dag Kristian Dysthe & Bjørn Jamtveit (2015). A simple model of compaction in carbonates. Full text in Research Archive
• Dag Kristian Dysthe, Maya Kobchenko, Andreas Hafver, Hamed Panahi, Bjørn Jamtveit & Francois Marie Paul L Renard (2014). Temporal and spatial characteristics of drainage fracture networks in elastic media with internal fluid generation. Full text in Research Archive
• Kristina G. Dunkel, Kerstin Drivdal, Håkon Olav Austrheim, Torgeir Bjørge Andersen & Bjørn Jamtveit (2014). Faulting and Serpentinisation of Peridotites in the Leka Ophiolite. Full text in Research Archive
• Dániel Keszthelyi, Bjørn Jamtveit & Dag Kristian Dysthe (2014). Compaction of North-sea chalk. Full text in Research Archive
• Dániel Keszthelyi, Dag Kristian Dysthe & Bjørn Jamtveit (2014). Compaction of the Ekofisk oil reservoir - On small- and on large-scale. Full text in Research Archive
• Dániel Keszthelyi, Dag Kristian Dysthe & Bjørn Jamtveit (2014). Compaction of a producing reservoir. Full text in Research Archive
• Håkon Olav Austrheim, Andreas Beinlich, Oliver Plümper, Jörn-Erik Hövelmann & Bjørn Jamtveit (2010). Naturally sequestered CO2 in ultramafic rocks – field examples from Norway. Full text in Research Archive

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