This study demonstrates how the response of ultramafic lithologies to infiltrating H20-CO2 fluids depends on the primary mineralogy. This has major implications on fluid flow through the lower crust and upper mantle as mineral reactions control the permeability and rheology. The studied samples are from the hanging wall of a 2 kilometer-long transtensional shear zone within ultramafic-mafic rocks in the Reinfjord Ultramafic Complex (RUC), part of the Seiland Igneous Province (SIP) in Northern Norway.Fluid-rock interaction surrounding shear zones with abundant pseudotachlylites is highly variable and depends on bulk rock compositions. Thermodynamic modelling demonstrates that mineral reactions involving hydration and carbonation differ between dunitic rocks and the pyroxenitic dykes which intersect them. Alteration of dunitic rocks results in the formation of dominantly magnesite-anthophyllite-talc and talc-magnesite assemblages causing approximately 12% volume expansion. This results in a sharp reaction front contacts with the host rock. When the alteration zones cross the dunite-pyroxenite boundary the associated alteration has a more gradual boundary towards the unaltered rock and the alteration zone widens by approximately 40%. In contrast to the simpler dunite alteration assemblage, the pyroxenetic dykes are altered to a complex mixture of cummingtonite-anthophyllite, magnetite and chlorite. Additionally, orthopyroxene is completely pseudomorphed by a mixture of cummingtonite and magnetite, whereas olivine xenocrysts are partly preserved and surrounded by a magnesite-anthophyllite assemblage. Other, open cavity-like areas are filled by chlorite, amphibole, and Mg-MgCa carbonates, indicating volume reduction during alteration of the pyroxene.Accordingly, dunite alteration effectuates a significant volume expansion, and are therefore only altered locally during seismic creep events. The pyroxenites are near volume neutral throughout interaction with the same fluids, and are thus more homogeneously altered. The formation of chlorite in hybrid compositions, such as the dykes in the lower crust, may create weak permeable zones that are consequently exploited as pathways for fertile mantle fluids and will hence also be the locus of ore bearing fluids moving to the upper crust. Increased understanding of fluid mediated metamorphism increases our current knowledge on fluid flow and strain localization in the lower crust. We further suggest that the hydrothermal assemblages are closely related to deformation leading to the formation of grain size sensitive creep in olivine facilitated carbonation of olivine and clinopyroxene to form orthopyroxene and dolomite and associated pseudoctacylites in the peridotites (Sørensen et al., 2019) , commonly associated with volatile rich mafic dykes (Ryan et al., 2022). Either the ductile magnesite-chlorite-talc assemblages formed at the same time in a shear-related heat gradient or they formed during cooling and continued CO2 infiltration from depth through the shearzones. Ryan E J, et al. 2022 Infiltration of volatile-rich mafic melt in lower crustal peridotites provokes deep earthquakes. J. Struct. Geol. (https://doi.org/10.1016/j.jsg.2022.104708)Sørensen, B.E., et al., 2019 In situ evidence of earthquakes near the crust mantle boundary initiated by mantle CO2 fluxing and reaction-driven strain softening. Earth and Planetary Science Letters (https://doi.org/10.1016/j.epsl.2019.115713 )

<p>Planar deformation features are a common feature in shock-deformed olivine, both experimentally in conditions corresponding to crustal shear zones [1] and impact structures e.g., [2] and in deep crustal shear zones [3, 4].  Hence, the identification of different planes associated with the shock deformation is essential to access the stress levels during deformation, important feature during studies of earthquake deformation.  A combination of optical and EBSD data combined to infer which of the possible crystallographic planes and EPMA to study trace elements to investigate planar deformation features and grain size reduction in olivine. Samples originate from the Reinfjord Ultramafic Complex, exposing lower crustal earthquakes induced by with CO<sub>2</sub> bearing magmatic volatiles causing reaction facilitated grainsize reduction and weakening [3, 4].  First, calculated plane traces are compared with the observed plane traces in the free open source Matlab ® toolbox MTEX  [5], then the dip and dip direction of the observations of planes in the optical microscope.  Our results demonstrate: 1) That several planes are active during high stress deformation of lower crustal olivine rich rocks. 2) Some planes develop recrystallization features, whereas others develop later and do not develop recrystallization features. 3) Our results shows that these new olivine grains are a mix of grains with an orientation relationship with the host grains and grains that are far of the orientation of the host grain. 3) Further investigation using trace element mapping shows that P (Phosphorous) is a marker of fluid involvement in the recrystallization. P is mobilized preferably along grain boundaries and sub-grain boundaries involving twist, shown by zones of local P enrichment.</p><p>By looking at several grains we found that the developed fractures highly depend on the orientation of the host grain with respect to the external stress field.  Using the demonstrated methodology, it should be possible to map out the relative abundance of planar deformation features along different crystallographic planes in high stress deformed olivine and other transparent silicates.  The method can be refined by calculation of the exact thickness of the sample using interference colours calculated using the code published by [6] now available in MTEX.  This will enable the calculation of exact plane inclinations extracted from multifocal optical images that can be compared with crystallographic planes calculated in MTEX from the EBSD data. Further combination of trace elements reveals that fluid mobilisation is involved in the recrystallization process.</p><p> </p><p> </p><p>[1]   Druiventak A, Trepmann C A, Renner J and Hanke K  2011  <em>Earth Planet. Sci. Lett.</em> <strong>311</strong> 199‑211</p><p> [2]  Stöffler D, Keil K and Edward R D S  1991  <em>Geochim. </em><em>Cosmochim. Acta</em> <strong>55</strong> 3845-3867</p><p> [3]  Ryan E J, <em>et al.</em>  2021  Infiltration of volatile-rich mafic melt in lower crustal peridotites provokes deep earthquakes.  <em>J. Struct. Geol.</em> 2022</p><p>[4]       Sørensen, B.E., et al., In situ evidence of earthquakes near the crust mantle boundary initiated by mantle CO2 fluxing and reaction-driven strain softening. Earth and Planetary Science Letters, 2019.</p><p>[5] Bachmann F, Hielscher R and Schaeben H  2010  <em>Solid State Phenomena</em> <strong>160</strong> 63-68</p><p>[6] Sørensen B E  2013  <em>Eur. J. Mineral.</em> <strong>25</strong> 5-10</p><p> </p>

We provide here in situ evidence from a network of well-preserved extensional shear zones cutting a rift related lower crustal Reinfjord Ultramafic Complex, Seiland Igneous Province, that formed in the late Ediacaran. Our results can explain seismic events well below the seimic zone of continental rifts and associated CO2 emissions. Processses leading to catastrophic failure of the weakened rocks led to extremely high strain rates and the formation of pseudotachylites can be traced from a netwok og mm-m scale steeply dipping transtensional shearzones associated with gabbronoritc dykes to a 2km long low angle extensional shearzone. Deformation, initiated through a priming of the dyke-host rock interface by magmatic fluids, exploits subgrains and microfractures in olivine, with reactive CO2-bearing fluids leading to volume expanding reactions such as olivine + diopside + CO2 = Dolomite + enstatite, enhancing olivine grain fracturing. Fragmentation of the olivine grains and addition of weaker phases facilitated strain localization and local increases in strain rate by two orders of magnitude. Catastrophic failure of the weakened rocks led to extremely high strain rates and the formation of pseudotachylites in several cyclic events. The frictional heat raised the temperature above the dolomite forming reaction, causing release of CO2 and H2O along the fault, but also in the surrounding mafic-ultramafic rocks, forming veins around the shearzone. Fluid-rock interaction surrounding shear zones is highly variable and depends on bulk rock compositions. Thermodynamic modelling demonstrates that mineral reactions involving hydration and carbonation differ between dunitic rocks and the pyroxenitic dykes which intersect them. Alteration of dunitic rocks results in the formation of dominantly magnesite-anthophyllite-talc and talc-magnesite assemblages causing approximately 12% volume expansion, resultinig in a sharp reaction front contacts with the host rock. When the alteration zones cross the dunite-pyroxenite boundary the associated alteration has a more gradual boundary towards the unaltered rock and the alteration zone widens by approximately 40%. In contrast to the simpler dunite alteration assemblage, the pyroxenenitic dykes are altered to a complex mixture of cummingtonite-anthophyllite, magnetite and chlorite. Additionally, orthopyroxene is completely pseudomorphed by a mixture of cummingtonite and magnetite, whereas olivine xenocrysts are partly preserved and surrounded by a magnesite-anthophyllite assemblage. Other, open cavity-like areas are filled by chlorite, amphibole, and Mg-MgCa carbonates, indicating volume reduction during alteration of the pyroxene.Accordingly, dunite alteration effectuates a significant volume expansion, and are therefore only altered locally during seismic creep events. The pyroxenites are near volume neutral throughout interaction with the same fluids, and are thus more homogeneously altered. The formation of chlorite in hybrid compositions, such as the dykes in the lower crust, may create weak permeable zones that are consequently exploited as pathways for fertile mantle fluids and will hence also be the locus of ore bearing fluids moving to the upper crust. We conclude that catastrophic failure along shear zones in lower crustal continental rifts is possible without remote stress events in the presence of pre-existing heterogeneities and volatiles. These zones also acted and transport conduits for volatiles from the lower crust to atmosphere.

Exploration for mineral resources offshore requires a detailed understanding and assessment of similar onshore mineral systems. The island of Bjornoya in the Barents Sea presents a unique opportunity to investigate structurally controlled sulfide-bearing (Pb + Zn + Cu + Au) mineral systems in a tectonic and lithological setting relevant for the surrounding subsea domain. We applied geophysical methods including the interpretation of magnetic and gravity data, field mapping, photogrammetry, and stress-tensor analyses to describe the structural setting and estimate the relative timing of structural and oreforming events. We show that fault linkage between N-S-striking normal faults and NW-SE-striking oblique-slip transtensional faults provided fluid pathways for mineralising fluids in the mid- to late Paleozoic, probably during the Carboniferous, leading to widespread structurally controlled vein mineralisation of sphalerite and galena on southeastern Bjornoya. Migration of the ore-forming fluids on Bjornoya depended on movement along active faults causing seismic pumping, while the ore precipitated following the reduction of sulfate to sulfide by hydrocarbons or hydrogen gas. The characteristic structural setting of mineralisations and ore deposits on Bjornoya may act as an analog model in the search for primary targets of fluid pathways with potential for mineral resources offshore.

We document well-preserved extensional shear zones in a rift-related lower-crustal magmatic conduit system, the Reinfjord Ultramafic Complex. Deformation along the shear zones led to seismic events below the seismogenic zone of continental rifts (10-15 kbar and 850-1150 ?), similar to events observed along the East African Rift today. Processes leading to failure of the weakened rocks caused extremely high strain. We mapped pseudotachylytes along a network of millimeter to meter -scale transtensional shear zones associated with gabbronoritic dykes, and a 2 km long low-angle extensional shear zone. Deformation, initiated through priming of the rock by magmatic fluids, exploited subgrains and microfractures in olivine, with CO2-bearing fluids leading to volume expanding reactions (olivine + diopside + CO2 = dolomite + enstatite), enhancing olivine fracturing. Fragmentation of the olivine grains and the addition of weaker phases facilitated strain localization and increased the strain rate by two orders of magnitude through grain size reduction (Sorensen et al., 2019). Sudden failure under transient brittle conditions formed pseudotachylytes. We conclude that failure along shear zones in lower crustal continental rifts is possible without remote stress events, in the presence of pre-existing textural and structural heterogeneities and events of volatile fluid infiltration.

The permeability structure of a fault zone is strongly dependent on the occurrence of meso-scale fracture patterns within the damage zone. Here, structural analyses of Virtual Outcrop Models (VOM) integrated with Discrete Fracture Network (DFN) modelling are used to constrain the relationship between meso-scale fracture patterns and the bulk permeability of a regional-scale fault zone. The Goddo Fault Zone (GFZ, Bømlo – Norway) is a long-lived extensional fault zone cutting across a granodioritic body developed during the long-lasting rifting of the North Sea. Fracture geometrical characteristics and the spatial variation of fracture intensity derived from VOM structural analysis were adopted as input for stochastic DFN models representing selected portions of the GFZ to constrain the variability of the structural permeability tensor K related to the mesoscopic fracture pattern. The intensity of fault-related fracture set(s), and the associated structural permeability computed with DFN models, likely exhibits a decreasing power-law trend within the damage zone with increasing distance from the fault cores. The orientation of the maximum K tensor component is controlled by the intersection direction of the dominant fracture sets. These results highlight the fundamental role of mesoscopic fracture patterns in controlling the bulk petrophysical properties of large fault zones.

We document the tectonic and metamorphic evolution of thrust nappes of the eastern island of Elba. The area exposes a natural cross section of the Northern Apennines hinterland, from the metamorphic basement units to the overlying continent- and ocean-derived nappes. We integrated mapping, analysis of structures and microstructures, and the interpretation of drill core logs with lithostratigraphic, metamorphic, and geochronological constraints, producing a novel geological map of eastern Elba (1:5'000 scale). We show that the area experienced polyphase Oligocene - Pliocene contractional tectonics marked by in-sequence and out-of-sequence thrusting accompanied by folding and overprinted by faulting in the Pliocene. Magmatism occurred during contraction with post-magmatic thrusting ultimately coupling HP-LT and LP-HT units. Drill core logs allow for the first time the reconstruction of the N-dipping character of the Zuccale Fault, which represents the youngest (late Miocene - early Pliocene) large-scale structure in the area.

The E‐vergent Northern Apennines formed by Oligocene‐Miocene convergence and westward subduction of Adria beneath Europe. Extension ensued in the Mid‐Late Miocene reflecting lower plate roll‐back and causing opening of the back‐arc Northern Tyrrhenian Sea. Post‐orogenic extension is commonly advocated as the main driver of the exhumation of the belt's inner domain high‐pressure/low‐temperature (HP‐LT) rock units. The Acquadolce Subunit of the Eastern Elba nappe stack contains HP‐LT rocks recording peak blueschist conditions of 1.5–1.8 GPa at 320°C–370°C loosely dated to the Oligocene‐Early Miocene. It is sandwiched by two Late Miocene, out‐of‐sequence top‐to‐the E thrusts between Jurassic LP serpentinites on top and HT–LP contact metamorphosed marbles at its base. We document widespread W‐verging ductile asymmetries within the Acquadolce Subunit, which correspond to top‐to‐the W extensional shearing for the nappe stack current orientation. This allowed for early syn‐orogenic exhumation from blueschist‐ to greenschist‐facies conditions, wherein coeval W‐directed extension at the top of the exhuming units acted synchronously with E‐directed thrusting at their base causing exhumation by extrusion in an overall contractional setting. The basal, E‐vergent thrusting is, however, challenging to document as the wedge has since been reworked by Late Miocene, E‐verging compressive tectonics, contact metamorphism, and later extension, obliterating much of the evidence supporting exhumation by extrusion during the early stages of wedge build‐up. Syn‐orogenic exhumation by extrusion from deep structural levels within the orogenic wedge is a viable mechanism to account for other exhumed HP‐LT units in the inner part of the belt.

The detailed characterization of internal fault zone architecture and petrophysical and geomechanical properties of fault rocks is fundamental to understanding the flow and mechanical behaviour of mature fault zones. The Goddo normal fault (Bømlo – Norway) accommodated c. E-W extension related to North Sea Rifting from Permian to Early Cretaceous times [1]. It represents a good example of a mature, iteratively reactivated and thus long-lived (seismogenic?) fault zone, developed in a pervasively fractured granitoid basement at upper crustal conditions in a regional extensional setting. Field characterization of the fault zone’s structural facies and analysis of background fracture patterns in the protolith have been integrated with in-situ petrophysical and geomechanical surveys of the recognized fault zone architectural components. In-situ air-permeability and mechanical directional tests (performed with NER TinyPerm III air-minipermeameter and DRC GeoHammer, L-type Schmidt hammer, respectively) have allowed for the quantification of the permeability tensor and mechanical properties (UCS and elastic modulus) within each brittle structural facies. Mechanical properties measured parallel to fault rock fabric of cataclasite- and gouge-bearing structural facies differ by up to one order of magnitude from those measured perpendicularly to it (~10 MPa vs. 100-200 MPa in UCS, respectively). Accordingly, permeability of cataclasite- and gouge-bearing facies is several orders of magnitude larger when measured parallel to fault-rock fabric than that perpendicular to it (10-0-10-1 D vs. 10-2-10-3 D, respectively). Virtual outcrop models (VOMs) of the fault zone were obtained from high-resolution UAV-photogrammetry. Field measurements of fracture orientations were used for calibration of the VOMs to construct a statistically robust fracture dataset. The results of VOMs structural analysis allowed for the quantification of fracture intensity and geometrical characteristics of mesoscopic fracture patterns within the different domains of the fault zone architecture. Results from field, VOMs structural analysis, and in-situ petrophysical investigations have been integrated into a realistic 3D fault zone model with the software 3DMove (Petex). This model can be used to investigate the influence of mesoscopic fracture patterns, related to either the fault zone or the background fracturing, on the hydro-mechanical behaviour of a mature fault zone. In addition, the evolution of the hydro-mechanical properties through time can be assessed by integrating the progressive development of brittle structural facies and fracture sets developed during the incremental strain and stress history into the model. This contribution proposes a geologically-constrained method to quantify the geometry of 3D fault zones, as a possible tool for models to be adopted in stress-strain analysis, hydraulic characterization and in the mechanical analysis of fault zones. [1] Viola, G., Scheiber, T., Fredin, O., Zwingmann, H., Margreth, A., & Knies, J. (2016). Deconvoluting complex structural histories archived in brittle fault zones. Nature communications, 7, 13448.

The Acquadolce Subunit on the Island of Elba, Italy, records blueschist facies metamorphism related to the Oligocene–early Miocene stages of continental collision in the Northern Apennines. The blueschist facies metamorphism is represented by glaucophane‐ and lawsonite‐bearing metabasite associated with marble and calcschist. These rock types occur as lenses in a schistose complex representing foredeep deposits of early Oligocene age. Detailed petrological analyses on metabasic and metapelitic protoliths, involving mineral and bulk‐rock chemistry coupled with P–T and P–T–X(Fe2O3) pseudosection modelling using PERPLE_X, show that the Acquadolce Subunit recorded nearly isothermal exhumation from peak pressure–temperature conditions of 1.5–1.8 GPa and 320–370°C. During exhumation, peak lawsonite‐ and possibly carpholite‐ or stilpnomelane‐bearing assemblages were overprinted and partially obliterated by epidote‐blueschist and, subsequently, albite‐greenschist facies metamorphic assemblages. This study sheds new light on the tectonic evolution of Adria‐derived metamorphic units in the Northern Apennines, by showing (a) the deep underthrusting of continental crust during continental collision and (b) rapid exhumation along ‘cold’ and nearly isothermal paths, compatible with syn‐orogenic extrusion.

The coupling of CO2 emissions and tectonic activity in active plate margins is becoming increasingly prominent, as remote sensing techniques make this relationship readily observable on a global scale. However, direct observations of the processes that link emissions and seismicity are lacking. This study documents observations from the deep part of an ancient continental rift system, now exposed at the Earth’s surface. We demonstrate how volatiles and preexisting magma chamber structures affect the influx of new magma and how magma induced deformation plays a key role during the shift from initial plume related magmatism to rifting, by altering the rock rheology and facilitating strain localization. The outcrops are comprised of ultramafic cumulates, intersected by mafic dykes. The ultramafic cumulates consist of three units: the central series, upper layered series and the lower layered series, with the central series being the youngest and partly replacing the upper and lower layered series. The dykes intersecting the upper layered series are partially remolten and replaced by the influx of the central series cumulates. This is especially evident in mafic dykes in wherlitic cumulates of the upper layered series. Younger melts of the central series used the contact between the dykes and host wehrlite as a pathway. The heating caused partial melting of the mafic dyke, which acted as a lubricant during deformation. In addition to the lubrication effect of the melt, volatiles within the mafic dykes, including CO2 react with the mafic minerals within the host ultramafic rocks, leading to fracturing and brecciation, and locally followed by diffusion creep in the finer-grained material. PT-estimates indicate that this brecciation took place under lower crustal/upper mantle conditions. Hence, conditions of deformation can shift from low strain rate plastic creep to ultrafast localized seismic creep in a short time due to local structural and compositional inhomogeneities.

The detailed characterization of internal fault zone architecture and petrophysical and geomechanical properties of fault rocks is fundamental to understanding the flow and mechanical behaviour of mature fault zones. The Goddo normal fault (Bømlo – Norway) accommodated c. E-W extension related to North Sea Rifting from Permian to Early Cretaceous times [1]. It represents a good example of a mature, iteratively reactivated and thus long-lived (seismogenic?) fault zone, developed in a pervasively fractured granitoid basement at upper crustal conditions in a regional extensional setting. Field characterization of the fault zone’s structural facies and analysis of background fracture patterns in the protolith have been integrated with in-situ petrophysical and geomechanical surveys of the recognized fault zone architectural components. In-situ air-permeability and mechanical directional tests (performed with NER TinyPerm III air-minipermeameter and DRC GeoHammer, L-type Schmidt hammer, respectively) have allowed for the quantification of the permeability tensor and mechanical properties (UCS and elastic modulus) within each brittle structural facies. Mechanical properties measured parallel to fault rock fabric of cataclasite- and gouge-bearing structural facies differ by up to one order of magnitude from those measured perpendicularly to it (~10 MPa vs. 100-200 MPa in UCS, respectively). Accordingly, permeability of cataclasite- and gouge-bearing facies is several orders of magnitude larger when measured parallel to fault-rock fabric than that perpendicular to it (10-0-10-1 D vs. 10-2-10-3 D, respectively). Virtual outcrop models (VOMs) of the fault zone were obtained from high-resolution UAV-photogrammetry. Field measurements of fracture orientations were used for calibration of the VOMs to construct a statistically robust fracture dataset. The results of VOMs structural analysis allowed for the quantification of fracture intensity and geometrical characteristics of mesoscopic fracture patterns within the different domains of the fault zone architecture. Results from field, VOMs structural analysis, and in-situ petrophysical investigations have been integrated into a realistic 3D fault zone model with the software 3DMove (Petex). This model can be used to investigate the influence of mesoscopic fracture patterns, related to either the fault zone or the background fracturing, on the hydro-mechanical behaviour of a mature fault zone. In addition, the evolution of the hydro-mechanical properties through time can be assessed by integrating the progressive development of brittle structural facies and fracture sets developed during the incremental strain and stress history into the model. This contribution proposes a geologically-constrained method to quantify the geometry of 3D fault zones, as a possible tool for models to be adopted in stress-strain analysis, hydraulic characterization and in the mechanical analysis of fault zones. [1] Viola, G., Scheiber, T., Fredin, O., Zwingmann, H., Margreth, A., & Knies, J. (2016). Deconvoluting complex structural histories archived in brittle fault zones. Nature communications, 7, 13448.

This study aims to understand the process behind the worldwide connection between deep crustal/upper mantle earthquakes and CO2 emissions along faults in rift zones. We do this by studying CO2-induced mineral reactions that facilitate strain localization in peridotites from an ancient rift zone in the Seiland Igneous Province (SIP), North Norway. Strain localization in association with hydration processes is well documented in all types of tectonic settings and has major implications for rheological behavior in active plate margin processes. The implications of CO2-bearing fluids are less studied, though experiments have shown how CO2 can influence the flow laws of olivine by imposing a brittle and more localized type of deformation. This study documents narrow shear zones observed within ultramafic rocks from the Seiland Igneous Province (SIP) comprising large volumes (>20,000 km(3)) of mafic, ultramafic, silicic and alkaline melts that were emplaced into the lower continental crust (25-30 km) between 570 and 560 Ma under an extensional regime. The extensional shear zones are mm cm-scale and contain extremely fine-grained material with a distinct shape preferred orientation (SPO), but weak to absent crystallographic preferred orientation. The shear zones offset dykes across numerous micro-faults that are documented in areas close to a major fault zone cutting through the area. Within the shear zones, olivine and clinopyroxene react to form orthopyroxene and dolomite at approximately 11 kb and 850 degrees C according to the reaction: 2 Olivine + Clinopyroxene + 2 CO2 = Dolomite + 2 Orthopyroxene This reaction formed coronas of orthopyroxene and dolomite between olivine and clinopyroxene in the shear zones. In addition, large olivine grains proximal to the shear zones show a microfabric with subgrain walls decorated by rounded grains of dolomite and more irregular and elongated grains of orthopyroxene. Clinopyroxene grains are separated from the enstatite and dolomite by at least hundreds of microns, suggesting material transport within the shear zone. The shear zones thus provide a unique insight into the interplay between CO2-metasomatism and reaction accommodated strain softening. Carbonation-driven cracking and mineral reaction also serves to reduce grain size, making grain boundary sliding an efficient process, further enhancing the rheological contrast between the shear zone and the host rock. The sudden decrease in rock strength could lead to rapid deformation and triggered pseudotachylite formation during earthquake events in the near proximity of the micro-shear zones. Our observations match the relations between CO2 emissions and earthquakes observed in present rift environments such as the East African rift and in New Zealand, and underline the importance of active shear zones as fluid conduits in the lower crust and upper mantle. (C) 2019 The Authors. Published by Elsevier B.V.