Cyclical variations of fluid sources and stress state in a shallow megathrust-zone mélange

Cerchiari, Anna; Remitti, Francesca; Mittempergher, Silvia; Festa, Andrea; Lugli, Federico; Cipriani, Anna

doi:10.1144/jgs2019-072

Cited by 28 publications

(37 citation statements)

References 71 publications

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“…Fluid inclusions are dense within quartz of high luminescence suggesting rapid growth due to advective input of an external fluid during a drop in fluid pressure (Raimbourg et al (2021)). In the Apennines, Cerchiari et al (2020) document two types of carbonate veins, with shear veins that have a Eu anomaly indicative of a fluid source hotter than the ambient temperature as well as opening mode veins with fluid in apparent thermodynamic equilibrium with local lithologies. Yamaguchi et al (2012) describe stable isotopic data for two distinct types of veins in the Mugi mélange and argue for episodic seismic cycles and punctuated changes in the physicochemical character of the vein-forming fluids.…”

Section: Relationship Between Local Mass Redistribution By Dpc and External Fluid Advectionmentioning

confidence: 99%

Constraints on Element Mobility During Deformation Within the Seismogenic Zone, Shimanto Belt, Japan

Ramirez¹,

Smye

Fisher

et al. 2021

Geochem Geophys Geosyst

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Subduction interfaces exhibit a variety of slip behaviors, including megathrust and slow earthquakes. Field observations are consistent with crack‐seal deformation, in which tensile cracks are sealed by fluid‐transported solute. However, there are few constraints on the mass fluxes and length and time scales of such deformation and attendant increases in cohesion within the seismogenic zone. Here, we present a systematic geochemical investigation of mass transport associated with development of crack‐seal veins in the Shimanto Belt—an accretionary complex that preserves a record of plate boundary slip behavior at temperatures relevant to the seismogenic zone: 150–350°C. These mélanges show evidence for shear across decameter‐scale zones of deformation dominated by anastomosing scaly fabrics and pervasive veins. We use meso‐ and microstructural observations with geochemical observations of scaly fabrics and crack‐seal veins to evaluate the role of silica redistribution in healing fracture porosity along the plate interface and modulating slip behavior. Crack‐seal veins contain primarily quartz with albite and calcite, and vein textures provide evidence for partial sealing. Bulk rock analyses determined that the amount of phyllosilicates, specifically illite and chlorite, increases with temperature. A simple mass‐balance model based on the immobile chemical component TiO2 shows a systematic trend in mobility for all three mélanges and increased element mobility as a function of temperature. Scaly fabrics and veins show compositional evidence for locally sourced mineral redistribution. This study supports a model where development of scaly slip surfaces and fracture healing through temperature‐dependent mineral redistribution can impact slip behavior and fluid flow along the subduction plate interface.

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Section: Relationship Between Local Mass Redistribution By Dpc and External Fluid Advectionmentioning

confidence: 99%

Constraints on Element Mobility During Deformation Within the Seismogenic Zone, Shimanto Belt, Japan

Ramirez¹,

Smye

Fisher

et al. 2021

Geochem Geophys Geosyst

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“…This mechanism supports the idea that forces acting in the same direction of fluid motion, parallel to the subduction interface, may result in dilatational features (Shapiro et al, 2018). Nevertheless, the presence of (1) burial-related oblique (ptygmatic) veins cutting and being cut by veins oriented parallel to the main foliation and (2) amphibole needles oriented perpendicular to the vein margins suggests that the orientation of the least principal compressive stress (σ 3 ) must in fact be variable with time, switching between subparallel to subvertical on the subduction interface fault (e.g., Meneghini and Moore, 2007;Ujiie et al, 2018;Cerchiari et al, 2020). The apparent diversity of deformation patterns affecting the rocks along the subduction interface can likely be reconciled considering the evolution of the stress regime at the seismic-cycle time scale (e.g., Magee and Zoback, 1993).…”

Section: Nature and Mechanisms Of Fluid-rock Interaction Processesmentioning

confidence: 99%

“…Last, we postulate that several distinct pulses contributed to the final state recorded in the exposure, as evidenced by crack-seal textures and cross-cutting relationships resulting from the studied hydrofracture events (e.g., Figs. 5B, 6D-6F; Ramsay, 1980;Bachmann et al, 2009;Cerchiari et al, 2020). To precisely evaluate the amount of material deposited after a single pulse event, further fluid-rock experimental work is needed to refine (1) our understanding of the kinetics of fluid precipitation in vein systems and (2) the quantification of the physico-chemical parameters acting during vein-filling processes.…”

Section: Nature and Mechanisms Of Fluid-rock Interaction Processesmentioning

confidence: 99%

Multiple veining in a paleo–accretionary wedge: The metamorphic rock record of prograde dehydration and transient high pore-fluid pressures along the subduction interface (Western Series, central Chile)

et al. 2020

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High pressure–low temperature metamorphic rocks from the late Paleozoic accretionary wedge exposed in central Chile (Pichilemu region) are characterized by a greenschist-blueschist lithological association with interbedded metasediments that reached peak burial conditions of ∼400 °C and 0.8 GPa during late Carboniferous times. We herein combine new extensive field observations, structural measurements, and geochemical and petrological data on vein and matrix material from Pichilemu transitional greenschist-blueschist facies rocks. The studied veins were first filled by albite, followed by quartz and calcite as well as glaucophane and winchite. Field, structural, and microscopic zoning patterns show that these rocks underwent a protracted sequence of prograde vein-opening events, which have been largely transposed to the main foliation before and during underplating in the basal accretion site near 25–30 km depth. While some of the earliest albite-filled vein sets may have formed after prograde breakdown of sub–greenschist facies minerals (<250 °C), our thermodynamic modeling shows that relatively minor amounts of fluid are produced in the subducted pile by dehydration reactions between 250 and 400 °C along the estimated geothermal gradient. It also confirms that the formation of interlayered blueschist and greenschist layers in Pichilemu metavolcanics is a consequence of local bulk composition variations, and that greenschists are generally not formed due to selective exhumation-related retrogression of blueschists. The early vein sets are a consequence of prograde internal fluid production followed by sets of hydrofractures formed at near-peak burial that are interpreted as a record of external fluid influx. We postulate that such a fractured sequence represents a close analogue to the high-Vp/Vs regions documented by seismological studies within the base of the seismogenic zone in active subduction settings.

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“…All in all, a fault zone should be considered an extremely dynamic system, characterized by specific physicochemical conditions during each of the faulting stages (Figure 3; e.g., Cerchiari et al, 2020; Wibberley et al, 2008). For example, the redox state associated with faulting and accompanying fluid flow varies enormously during seismic slip events (Ishikawa et al, 2008; Yamaguchi et al, 2011).…”

Section: Formation Of Fault Rocks and Processes During Faultingmentioning

confidence: 99%

Faulting Processes Unveiled by Magnetic Properties of Fault Rocks

Yang

Chou

Ferré

et al. 2020

Reviews of Geophysics

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As iron-bearing minerals-ferrimagnetic minerals in particular-are sensitive to stress, temperature, and presence of fluids in fault zones, their magnetic properties provide valuable insights into physical and chemical processes affecting fault rocks. Here, we review the advances made in magnetic studies of fault rocks in the past three decades. We provide a synthesis of the mechanisms that account for the magnetic changes in fault rocks and insights gained from magnetic research. We also integrate nonmagnetic approaches in the evaluation of the magnetic properties of fault rocks. Magnetic analysis unveils microscopic processes operating in the fault zones such as frictional heating, energy dissipation, and fluid percolation that are otherwise difficult to constrain. This makes magnetic properties suited as a "strain indicator," a "geothermometer," and a "fluid tracer" in fault zones. However, a full understanding of faulting-induced magnetic changes has not been accomplished yet. Future research should focus on detailed magnetic property analysis of fault zones including magnetic microscanning and magnetic fabric analysis. To calibrate the observations on natural fault zones, laboratory experiments should be carried out that enable to extract the exact physicochemical conditions that led to a certain magnetic signature. Potential avenues could include (1) magnetic investigations on natural and synthetic fault rocks after friction experiments, (2) laboratory simulation of fault fluid percolation, (3) paleomagnetic analysis of postkinematic remanence components associated with faulting processes, and (4) synergy of interdisciplinary approaches in mineral-magnetic studies. This would help to place our understanding of the microphysics of faulting on a much stronger footing. Plain Language Summary The Earth's surface is riddled with faults that largely contribute to landscape evolution and human activities. Some of these faults produce earthquakes of different magnitudes including some with catastrophic consequences. Understanding faulting mechanisms benefits society when predictions about rupture are made. Fault zones preserve an excellent record of chemical and physical processes involved in failure. Among other analytical methods, magnetic studies prove to be an emergent and untapped source of information on these processes. These methods, focused on prefaulting, synfaulting, and postfaulting mineral changes, have resulted in significant advances in our understanding of the conditions of faulting. In this review, we present an extensive account of the state of knowledge and highlight current challenges and future avenues of fault magnetism research.

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Cyclical variations of fluid sources and stress state in a shallow megathrust-zone mélange

Cited by 28 publications

References 71 publications

Constraints on Element Mobility During Deformation Within the Seismogenic Zone, Shimanto Belt, Japan

Constraints on Element Mobility During Deformation Within the Seismogenic Zone, Shimanto Belt, Japan

Multiple veining in a paleo–accretionary wedge: The metamorphic rock record of prograde dehydration and transient high pore-fluid pressures along the subduction interface (Western Series, central Chile)

Faulting Processes Unveiled by Magnetic Properties of Fault Rocks

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