Titanium concentration in quartz as a record of multiple deformation mechanisms in an extensional shear zone

Nachlas, William O.; Teyssier, Christian; Bagley, Brian; Mulch, Andreas

doi:10.1002/2013gc005200

Cited by 34 publications

(37 citation statements)

References 102 publications

(204 reference statements)

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“…For example, Figures a and b clearly show that resetting of Ti was not uniform along all grain boundaries (see also Bestmann and Pennacchioni , , Figure a). In addition, Figure suggests that TiO 2 activity was lower adjacent to Ti‐rich phases (i.e., biotite and sphene), similar to previous observations in quartz‐rich rocks [e.g., Nachlas et al ., ]. At distances greater than ∼100 µm from biotite and sphene, preexisting Ti in neighboring quartz grains may have buffered TiO 2 activity.…”

Section: Discussionmentioning

confidence: 99%

Comparison of thermal modeling, microstructural analysis, and Ti‐in‐quartz thermobarometry to constrain the thermal history of a cooling pluton during deformation in the Mount Abbot Quadrangle, CA

Nevitt

Warren

Kidder

et al. 2017

Geochem Geophys Geosyst

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Granitic plutons commonly preserve evidence for jointing, faulting, and ductile fabric development during cooling. Constraining the spatial variation and temporal evolution of temperature during this deformation could facilitate an integrated analysis of heterogeneous deformation over multiple length‐scales through time. Here, we constrain the evolving temperature of the Lake Edison granodiorite within the Mount Abbot Quadrangle (central Sierra Nevada, CA) during late Cretaceous deformation by combining microstructural analysis, titanium‐in‐quartz thermobarometry (TitaniQ), and thermal modeling. Microstructural and TitaniQ analyses were applied to 12 samples collected throughout the pluton, representative of either the penetrative “regional” fabric or the locally strong “fault‐related” fabric. Overprinting textures and mineral assemblages indicate the temperature decreased from 400–500°C to <350°C during faulting. TitaniQ reveals consistently lower Ti concentrations for partially reset fault‐related fabrics (average: 12 ± 4 ppm) than for regional fabrics (average: 31 ± 12 ppm), suggesting fault‐related fabrics developed later, following a period of pluton cooling. Uncertainties, particularly in TiO2 activity, significantly limit further quantitative thermal estimates using TitaniQ. In addition, we present a 1‐D heat conduction model that suggests average pluton temperature decreased from 585°C at 85 Ma to 332°C at 79 Ma, consistent with radiometric age data for the field. Integrated with the model results, microstructural temperature constraints suggest faulting initiated by ∼83 Ma, when the temperature was nearly uniform across the pluton. Thus, spatially heterogeneous deformation cannot be attributed to a persistent temperature gradient, but may be related to regional structures that develop in cooling plutons.

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Section: Discussionmentioning

confidence: 99%

Comparison of thermal modeling, microstructural analysis, and Ti‐in‐quartz thermobarometry to constrain the thermal history of a cooling pluton during deformation in the Mount Abbot Quadrangle, CA

Nevitt

Warren

Kidder

et al. 2017

Geochem Geophys Geosyst

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“…For cases where rutile is absent, Thomas et al [2010] introduced a scaling factor for the dependence of a TiO2 on Ti solubility. Estimating a TiO2 in naturally deformed rocks is difficult because it may vary through time, it may depend on the spatial distribution of Ti buffers within the aggregate [e.g., Nachlas et al, 2014], and the buffering capacity of other Ti-bearing phases (titanite and ilmenite) is not experimentally constrained (but can be estimated, e.g., titanite [Ghent and Stout, 1984;Behr and Platt, 2011] and ilmenite [Ghent and Stout, 1984;Menegon et al, 2011]). We designed our samples with two layers of quartz doped above and below the predicted equilibrium Ti solubility to investigate resetting Ti in quartz during recrystallization in different chemical buffering environments.…”

Section: Discussionmentioning

confidence: 99%

Experimental constraints on the role of dynamic recrystallization on resetting the Ti‐in‐quartz thermobarometer

Nachlas

Hirth

2015

JGR Solid Earth

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We conducted deformation experiments on Ti‐doped quartz aggregates to investigate the effect of crystal‐plastic deformation and dynamic recrystallization on Ti substitution in quartz. Shear experiments were conducted at 1.0 GPa and 900°C at a constant shear strain rate (~5 × 10−6 s−1) for progressively longer intervals of time (24, 48, and 72 h). Equivalent experiments were conducted under hydrostatic stress to compare the effect of deformation relative to static crystallization. A novel quartz‐doping technique is used to synthesize a quartz aggregate consisting of two layers with Ti concentrations above and below the predicted solubility level for the experimental conditions. Samples deformed to progressively higher shear strain by dislocation creep accommodated by a combination of subgrain rotation and grain boundary migration recrystallization show a strengthening of the crystallographic preferred orientation that correlates with a progressive evolution of Ti concentrations. Quartz grains in the highest strain, most strongly recrystallized samples have Ti concentrations that are most similar to undeformed quartz grown in hydrostatic annealing experiments. Cathodoluminescence (CL) analysis of intragrain variations in Ti content reveals core and rim zoning present in the starting material that becomes progressively homogenized with increasing strain—recrystallized quartz in the highest‐strain samples exhibits a uniform CL signal. We conclude that dynamic recrystallization enhances the kinetics of trace element equilibration in quartz, illustrating that Ti‐in‐quartz thermobarometry is capable of recording the conditions of ductile shearing.

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“…In both experimental and natural deformation, Ti concentrations in quartz are often reset during recrystallization (e.g. Behr and Platt, 2011;Kidder et al, 2013;Kohn and Northrup, 2009;Nachlas and Hirth, 2015;Nachlas et al, 2014). While quantifying temperatures using Ti-in-quartz thermobarometry is complicated by uncertainty in Ti 10 activity (Bestmann and Pennacchioni, 2015;Grujic et al, 2011;Nevitt et al, 2017) and differing calibrations (Huang and Audétat, 2012;Thomas et al, 2015), we find that variations in Ti-in-quartz concentrations in Alpine Fault rocks span a range large enough that these issues can be largely bypassed using independent constraints on maximum and minimum temperatures associated with quartz recrystallization.…”

Section: Introductionmentioning

confidence: 86%

Constraints on Alpine Fault (New Zealand) Mylonitization Temperatures and Geothermal Gradient from Ti-in-quartz Thermobarometry

Kidder¹,

Toy²,

Prior³

et al. 2018

Preprint

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Abstract.We constrain the thermal state of the central Alpine Fault using approximately 750 Ti-in-quartz SIMS analyses from a 10 suite of variably deformed mylonites. Ti-in-quartz concentrations span more than an order of magnitude from 0.24 to ~5 ppm, suggesting recrystallization of quartz over a 300° range in temperature. Most Ti-in-quartz concentrations in mylonites, protomylonites, and the Alpine Schist protolith are between 2 and 4 ppm and do not vary as a function of grain size or bulk rock composition. Analyses of 30 large, inferred-remnant quartz grains (>250 µm), as well as late, cross-cutting, chlorite-bearing quartz veins also reveal restricted Ti concentrations of 2-4 ppm. These results indicate that the vast majority of Alpine Fault 15 mylonitization occurred within a restricted zone of pressure-temperature conditions where 2-4 ppm Ti-in-quartz concentrations are stable. This constrains the deep geothermal gradient from the moho to about 8 km to a slope of 5 °/km. In contrast, the small grains (10-40 µm) in ultramylonites have lower Ti concentrations of 1-2 ppm, indicating a deviation from the deeper pressuretemperature trajectory during the latest phase of ductile deformation. These constraints suggest an abrupt, order of magnitude change in the geothermal gradient to an average of about 60 °/km at depths shallower than about 8 km, i.e. within the 20 seismogenic zone. Anomalously, the lowest-Ti quartz (0.24-0.7 ppm) occurs away from the fault in protomylonites, suggesting that the outer fault zone experienced minor plastic deformation late in the exhumation history when more fault-proximal parts of the fault were deforming exclusively by brittle processes.

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Titanium concentration in quartz as a record of multiple deformation mechanisms in an extensional shear zone

Cited by 34 publications

References 102 publications

Comparison of thermal modeling, microstructural analysis, and Ti‐in‐quartz thermobarometry to constrain the thermal history of a cooling pluton during deformation in the Mount Abbot Quadrangle, CA

Comparison of thermal modeling, microstructural analysis, and Ti‐in‐quartz thermobarometry to constrain the thermal history of a cooling pluton during deformation in the Mount Abbot Quadrangle, CA

Experimental constraints on the role of dynamic recrystallization on resetting the Ti‐in‐quartz thermobarometer

Constraints on Alpine Fault (New Zealand) Mylonitization Temperatures and Geothermal Gradient from Ti-in-quartz Thermobarometry

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