Quantifying Water Diffusivity and Metamorphic Reaction Rates Within Mountain Belts, and Their Implications for the Rheology of Cratons

Whyte, Andy; Weller, Owen M.; Copley, Alex; St-Onge, M R

doi:10.1029/2021gc009988

Cited by 6 publications

(3 citation statements)

References 66 publications

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“…The composition of the lower crust should therefore act as a sink of water and buffer the water pressure to far below lithostatic over time, except in regions of pervasive water influx and retrogression (Yardley & Valley, 1997). The rates of hydration reactions from natural analogs suggest water can be consumed by dry granulitic rocks at mid‐crustal temperature conditions at ∼10 −8 g/cm 2 /s (Whyte et al., 2021). Without some mechanism that can isolate free water within the fault core from the reactive wall rocks, it is therefore unlikely that a pervasive water phase within the fault zone at 60%–80% of lithostatic pressure is the cause of the frictionally weak faults in the lower crust.…”

Section: Discussionmentioning

confidence: 99%

Weak, Seismogenic Faults Inherited From Mesozoic Rifts Control Mountain Building in the Andean Foreland

Wimpenny

2022

Geochem Geophys Geosyst

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New earthquake focal mechanism and centroid depth estimates show that the deformation style in the forelands of the Andes is spatially correlated with rift systems that stretched the South American lithosphere in the Mesozoic. Where the rifts trend sub‐parallel to the Andean range front, normal faults inherited from the rifts are being reactivated as reverse faults, causing the 30–45 km thick seismogenic layer to break up. Where the rift systems are absent from beneath the range front, the seismogenic layer is bending and being thrust beneath the Andes like a rigid plate. Force‐balance calculations show that the faults inerhited from former rift zones have an effective coefficient of static friction μ′ < 0.2. In order for these frictionally weak faults to remain seismogenic in the lower crust, their wall rocks are likely to be formed of dry granulite. Xenolith data support this view, and suggest that parts of the lower crust are now mostly metastable, having experienced temperatures at least 75–250°C hotter than present. The conditions in the lower crust make it unlikely that highly pressurized free water, or networks of intrinsically weak phyllosilicate minerals, are the cause of their low effective friction, as, at such high temperatures, both mechanisms would cause the faults to deform through viscous creep and not frictional slip. Therefore pre‐existing faults in the Andean forelands have remained weak and seismogenic after reactivation, and have influenced the style of mountain building in South America. However, the controls on their mechanical properties in the lower crust remain unclear.

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Section: Discussionmentioning

confidence: 99%

Weak, Seismogenic Faults Inherited From Mesozoic Rifts Control Mountain Building in the Andean Foreland

Wimpenny

2022

Geochem Geophys Geosyst

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“…Foliations in the rigid lower crust will be inherited from past deformation episodes, with limited overprinting (e.g. St‐Onge & Lucas, 1995; Whyte et al., 2021). In poorly exposed terranes, such features may not be apparent, in which case the thermal characteristics described below will be important in distinguishing this tectonic style from homogeneous thickening.…”

Section: Model Resultsmentioning

confidence: 99%

The controls on the thermal evolution of continental mountain ranges

Copley

Weller

2022

Journal Metamorphic Geology

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This paper examines the controls on the thermal evolution of continental mountain ranges and investigates how pressure (P) and temperature (T) estimates from metamorphic rocks can be used to reconstruct the thermal histories of orogenic belts. We show that one-dimensional models can approximate the temperature structure of most continental mountain belts, and find that the metamorphic conditions typical of such tectonic settings can most easily be achieved by thickening of the mid-to upper-crust above a rigid lower crustal substrate. Homogeneous thickening of the entire lithosphere can only result in these conditions under unusual circumstances. This result implies that thickening above rigid lower crust has been the dominant mode of mountain-building preserved in the rock record. In this situation, modest rates of vertically distributed internal radiogenic heating (1AE0.5 μW/m 3 ) are able to produce typical metamorphic conditions and timescales, without the requirement for an external source of heat. In a given model, peak temperature conditions for rocks originally positioned closely in depth (e.g. 5 km apart) occur at times that can be separated by over 10 Myr, highlighting the spectrum of ages and conditions that can be produced by a single geometrically simple mountain-building event. The direction of approach in P-T space towards the highest-T conditions experienced by a rock (i.e. the curvature of the P-T loop) is the most diagnostic feature that allows the thermal and tectonic history of a mountain belt to be estimated, highlighting the importance of determining prograde P-T paths. Combining estimates of the peak-T conditions with multiple other sources of information (e.g. the timescales of metamorphism or the initial crustal thickness) can also allow the reconstruction of the mountain range evolution under most circumstances. Many configurations of continental mountain-building result in rocks transiently passing through regions with low average thermal gradients (e.g. 10-15 C/km), suggesting that such gradients should not be used to infer the presence of subduction. Analysis of existing P-T loops from the 3.2 Ga metamorphism in the Barberton terrane suggests that mountain-building processes at that time and place were similar to those in present-day mountain ranges, implying that large regions of rigid

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“…Fluids play a major role in rock deformation and failure processes, especially under high temperature and stress conditions found in mid‐ to lower‐crustal detachment shear zones (DSZs, e.g., Gottardi & Hughes, 2022; Menegon et al., 2015; Spruzeniece & Piazolo, 2015; Stenvall et al., 2020; Wehrens et al., 2016). Fluids weaken rocks under stress through multiple physio‐chemical mechanisms, such as pressure‐solution creep (e.g., Gratier et al., 2013; Shimizu, 1995; Wassmann & Stőckhert, 2013), hydrolytic weakening (e.g., Griggs, 1967; Kronenberg & Tullis, 1984; Okazaki et al., 2021; Pongrac et al., 2022; Stünitz et al., 2017), metamorphic reactions and mass transport (e.g., Carter et al., 1990; Ferry, 1994; Hobbs et al., 2010; Labrousse et al., 2010; Whyte et al., 2021), causing departure from experimentally derived failure laws (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Effect of Water‐Rock Ratio on the Stable Isotope Record of Fluid‐Rock‐Deformation Interactions in Detachment Shear Zone

Gottardi,

Mire,

Davis

et al. 2024

Geochem Geophys Geosyst

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Oxygen and hydrogen stable isotope analyses of quartz and muscovite veins from the footwall of the Raft River detachment shear zone (Utah) provide insight into the hydrology and fluid‐rock interactions during ductile deformation. Samples were collected from veins containing 90%–100% quartz with orientations either at a high angle or sub‐parallel to the surrounding quartzite mylonite foliation. Stable isotope analysis was performed on 10 samples and compared with previous quartzite mylonite isotope data sets. The results indicate that the fluid present during deformation of the shear zone was meteoric in origin, with a δ2H value of approximately −100‰ and a δ18O value of approximately −13.7‰. Oxygen stable isotope O18O depletion correlates with the muscovite content of the analyzed rocks. Many of the analyzed samples in this and other studies show an apparent lack of equilibrium between the oxygen and hydrogen isotope systems, which can be explained by hydrogen and oxygen isotope exchange at varying fluid‐rock ratios. Our results suggest that the Raft River detachment shear zone had a low static fluid‐rock ratio (<0.1), yet experienced episodic influxes of fluids through semi‐brittle structures. This fluid was then expelled out into the surrounding mylonite following progressive shearing, causing further 18O‐depletion and fluid‐related embrittlement.

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Quantifying Water Diffusivity and Metamorphic Reaction Rates Within Mountain Belts, and Their Implications for the Rheology of Cratons

Cited by 6 publications

References 66 publications

Weak, Seismogenic Faults Inherited From Mesozoic Rifts Control Mountain Building in the Andean Foreland

Weak, Seismogenic Faults Inherited From Mesozoic Rifts Control Mountain Building in the Andean Foreland

The controls on the thermal evolution of continental mountain ranges

Effect of Water‐Rock Ratio on the Stable Isotope Record of Fluid‐Rock‐Deformation Interactions in Detachment Shear Zone

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