Evidence for strain rate variation and an elevated transient geothermal gradient during shear zone evolution in the Cordillera Blanca, Peru

Hughes, Cameron; Jessup, Micah J.; Shaw, Colin A.; Newell, Dennis L.

doi:10.1016/j.tecto.2020.228610

Cited by 11 publications

(58 citation statements)

References 67 publications

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“…We consider two field‐based data sets that quantify deformation conditions precisely enough to assign specific strain rates to specific deformation conditions (Behr & Platt, 2011; Lusk & Platt, 2020). Strain rates from these studies are consistent with previous estimates measured or modeled in tectonically active midcrustal to lower‐crustal regions (Hirth et al., 2001; Hughes et al., 2020; Lu & Jiang, 2019; Pfiffner & Ramsay, 1982; Sassier et al., 2009). For both these studies, electron backscatter diffraction crystallographic data were used to calculate dynamically recrystallized grain size and infer active slip system(s) and deformation mechanism(s).…”

Section: Methodssupporting

confidence: 89%

“…We do not use naturally constrained strain rate and deformation data from the RGD (Dunlap et al., 1997; Hirth et al., 2001), the Ailao Shan–Red River shear zone (ARSZ; Boutonnet et al., 2013; Sassier et al., 2009), nor the Cordillera Blanca shear zone (CBSZ; Hughes et al., 2019, 2020). In the RGD, Hirth et al.…”

Section: Methodsmentioning

confidence: 99%

“…Using an assumed value for the stress exponent, based on experimental work of Gleason and Tullis (1995) and Luan and Paterson (1992), they incorporated field‐based data to constrain other parameters. Since then, several additional studies have calculated strain rates and deformation conditions directly from the rock record, potentially providing further constraints (Behr & Platt, 2011; Hughes et al., 2020; Kidder et al., 2012; Lusk & Platt, 2020; Sassier et al., 2009; Stipp et al., 2002). Given the increase in available experimental and field‐based data as well as advances in our understanding of thermobarometry and grain size evolution in strained rocks, a reevaluation of quartz dislocation creep flow law parameters is warranted.…”

Section: Introductionmentioning

confidence: 99%

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Natural and Experimental Constraints on a Flow Law for Dislocation‐Dominated Creep in Wet Quartz

Lusk

Platt

2021

JGR Solid Earth

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Constitutive relationships (i.e., flow laws) relate strain rate () to differential stress (σ), temperature (T), pressure (P), water fugacity ( H O 2 f ), and material properties for a given deformation mechanism. As one of the most abundant minerals in the crust, quartz is thought to control crustal rheology and is commonly used to model and predict the viscous behavior of the middle and lower crust (e.g., Brace & Kohlstedt, 1980;Hirth et al., 2001). At these depths, quartz deforms by dislocation creep, a thermally activated process that is driven by the nucleation, buildup, and motion of dislocations, resulting in viscous flow. Dislocation creep

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Section: Methodssupporting

confidence: 89%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Natural and Experimental Constraints on a Flow Law for Dislocation‐Dominated Creep in Wet Quartz

Lusk

Platt

2021

JGR Solid Earth

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“…The CBSZ δ 2 H mica values imply that meteoric water migrated to the BDTZ at depths of 8-13 km (Hughes et al, 2020) during CBSZ formation and resulted in δ 2 H mica values that are inconsistent with hydrogen derived from structurally deep portions of the footwall. Available constraints on CBSZ formation depth, the onset of faulting, and exhumation rates delimit the onset of meteoric water infiltration to between 5.4 Ma and 3.0 Ma (Giovanni et al, 2010;Margirier et al, 2016Margirier et al, , 2018Hughes et al, 2020). Collectively, these relationships suggest that a meteoric-hydrothermal network closely resembling the modern fault and fracture-driven spring network was active during formation of the shear zone mica fish in the Miocene-Pliocene (Fig.…”

Section: Origin Of Fluids Within the Shear Zonementioning

confidence: 94%

“…Samples >230 m into the footwall at Gatay were 15‰-50‰ higher than samples <130 m but were still less than primary igneous δ 2 H values. This pattern could be explained by juxtaposition of rock-buffered portions of the shear zone against meteorically altered portions during exhumation (e.g., Mulch et al, 2005;Gébelin et al, 2011), changing time-integrated fluid-rock ratios, structural and/or thermal permeability barriers, or the introduction of magmatic fluids during overlap of deformation and batholith crystallization in the central CBSZ (Hayba and Ingebritsen, 1997;Hughes et al, 2019Hughes et al, , 2020Petford and Atherton, 1992;Margirier et al, 2018).…”

Section: Origin Of Fluids Within the Shear Zonementioning

confidence: 99%

Miocene to modern hydrothermal circulation and high topography during synconvergent extension in the Cordillera Blanca, Peru

Grambling

Jessup

Newell

et al. 2021

Geology

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The Cordillera Blanca detachment in the highest elevations of the Peruvian Andes has been accommodating synconvergent extension since the late Miocene. Stable isotope analysis of synkinematic mica from its exhumed footwall shear zone provides new constraints on deep meteoric-hydrothermal circulation during ductile deformation and regional paleoelevation. Muscovite and biotite that deformed and/or grew synkinematically in the shear zone have δ2H values of −131‰ to −58‰ and −149‰ to −98‰ (versus Vienna standard mean ocean water, VSMOW), respectively. The δ2H value difference between coexisting muscovite and biotite is consistent with equilibrium fractionation of the same fluid at the same temperature. Calculated δ2H values of water (−107‰ to −78‰) in equilibrium with these micas are indistinguishable from those of present-day, deeply circulated (9–11 km) hot spring waters emanating from the fault. Such low-δ2H fluids indicate circulation of meteoric water to the depths of the brittle-ductile transition that cannot be explained by other mechanisms. Average recharge paleoelevation for water entering the shear zone based on hydrogen isotopes was 3400 + 500/–700 m (1σ). This is near, but ~500 m below, the present-day mean elevation of the catchments feeding modern hot springs of 3965 ± 880 m, and ~700 m below the 4200 + 700/–900 m mean recharge elevation derived from δ2H values of modern surface and thermal water. The consistency between modern and ancient fault-assisted hydrothermal systems and elevation suggests that high topography, steep relief, and meteoric-hydrothermal circulation have persisted throughout the history of the Cordillera Blanca detachment system.

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Influence of Creep Compaction and Dilatancy on Earthquake Sequences and Slow Slip

Yang

Dunham

2022

Preprint

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Fluids influence fault zone strength and the occurrence of earthquakes, slow slip events, and aseismic slip. We introduce an earthquake sequence model with fault zone fluid transport, accounting for elastic, viscous, and plastic porosity evolution, with permeability having a power-law dependence on porosity. Fluids, sourced at a constant rate below the seismogenic zone, ascend along the fault. While the modeling is done for a vertical strike-slip fault with 2D antiplane shear deformation, the general behavior and processes are anticipated to apply also to subduction zones. The model produces large earthquakes in the seismogenic zone, whose recurrence interval is controlled in part by compaction-driven pressurization and weakening. The model also produces a complex sequence of slow slip events (SSEs) beneath the seismogenic zone. The SSEs are initiated by compaction-driven pressurization and weakening and stalled by dilatant suctions. Modeled SSE sequences include long-term events lasting from a few months to years and very rapid short-term events lasting for only a few days; slip is ˜1-10 cm. Despite ˜1-10 MPa pore pressure changes, porosity and permeability changes are small and hence fluid flux is relatively constant except in the immediate vicinity of slip fronts. This contrasts with alternative fault valving models that feature much larger changes in permeability from the evolution of pore connectivity. Our model demonstrates the important role that compaction and dilatancy have on fluid pressure and fault slip, with possible relevance to slow slip events in subduction zones and elsewhere.

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Evidence for strain rate variation and an elevated transient geothermal gradient during shear zone evolution in the Cordillera Blanca, Peru

Cited by 11 publications

References 67 publications

Natural and Experimental Constraints on a Flow Law for Dislocation‐Dominated Creep in Wet Quartz

Natural and Experimental Constraints on a Flow Law for Dislocation‐Dominated Creep in Wet Quartz

Miocene to modern hydrothermal circulation and high topography during synconvergent extension in the Cordillera Blanca, Peru

Influence of Creep Compaction and Dilatancy on Earthquake Sequences and Slow Slip

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