Ultrahigh-pressure (UHP) nappes provide important opportunities to investigate the processes that exhume rocks from upper mantle depths. Here, we investigate the UHP Tso Morari nappe (TMN) in the Indian Himalaya to test competing models for the construction of UHP nappes via detachment of single, structurally coherent sheets, accretion of multiple sheets, or chaotic accretion of km-scale rock packages. We collected Raman spectroscopy of carbonaceous material (RSCM) temperatures and thin section-scale finite strain, quartz crystallographic preferred-orientation (CPO) and shear-sense data sets from three transects, which we combine with published data to quantify trends across the 120 km by 40 km extent of the TMN. A laterally continuous tectonostratigraphy of metasedimentary rocks overlying granitic orthogneiss, a lack of field evidence for internal shear zones, uniformly high strain (3.4 average lineation-parallel Rs, 65% average lineation-parallel stretching) and CPO intensity (0.64 average cylindricity, 3.80 average J PF), dominant top-to-east kinematics, and overall similar temperature conditions vertically and laterally are all consistent with detachment of the TMN as a single, structurally coherent sheet. The TMN lacks field evidence for partial melting, which is consistent with RSCM and maximum thermobarometric temperatures generally <= 700 degrees C, and limits the importance of diapiric rise as an exhumation mechanism. Distributed top-down-to-east, normal-sense ductile shearing was an important process that facilitated exhumation of the TMN from mid-crustal depths at similar to 51-46 Ma to upper-crustal depths at similar to 45-29 Ma. This extensional shearing was contemporaneous with regional, SW-NE-directed shortening in the Himalayan fold-thrust belt, which could be the consequence of strain partitioning during oblique convergence.

Thermobarometry in the Northern Snake Range metamorphic core complex (Nevada, USA) implies pre-extensional burial of footwall rocks to 21-30 km depths, while geologic field relationships support 7-13 km pre-extensional depths. This has fueled a 40-year-long debate, which has far-reaching implications for how pressure data are interpreted in orogenic settings. Here, we test published models for deep burial by integrating regional cross-section reconstructions with new (n = 95) and published (n = 132) peak temperature measurements, field relationships and published geophysical data. Burial of Neoproterozoic-Cambrian metasedimentary footwall rocks to 21-30 km depths is incompatible with a regional seismic reflection cross-section that interprets the top of Precambrian crystalline basement at 17-20 km depths. Two reconstructed cross-sections define 42 km and 50-65 km of displacement on the master detachment fault and demonstrate that the higher displacement ranges (>66-94 km and >76-102 km, respectively) necessary to exhume rocks from 21 to 30 km depths are not possible without spatially overlapping Cambrian rocks preserved in its footwall and hanging wall. The 22 degrees C/km average Late Cretaceous thermal gradient predicted by thermobarometry is incompatible with the 46 +/- 10 degrees C/km Late Cretaceous peak thermal gradient that we calculate down to 15-20 km pre-extensional depths. Field relationships that rule out large-magnitude shortening invalidate models for deep footwall burial via thrust or reverse faulting. We conclude that there is no scenario for deep burial that is compatible with structural/geophysical constraints, crustal thermal architecture, and field relationships. This necessitates a non-lithostatic interpretation for pressures from the Northern Snake Range, similar to recent interpretations for other Cordilleran metamorphic core complexes.

Documenting the tectono-thermal evolution of the exhumed ductile portions of orogenic systems is critical for interpreting orogen dynamics. Here, we utilize Raman spectroscopy of carbonaceous material thermometry to quantify the thermal architecture of the Salmon River suture zone in west-central Idaho, USA, which records the Cretaceous collision of the Wallowa island arc terrane with North America. We integrate this thermal architecture with published structural interpretations, geochronology, and pressure-temperature -time histories to interpret the evolution of deformation during arc-continent collision in this portion of the North America Cordillera. Mean peak temperatures within four, similar to 1- 3 -km-thick, penetratively deformed thrust sheets in the western part of the suture zone decrease moving structurally downward from 652 +/- 28 degrees C (Pollock Mountain thrust sheet), to 577 +/- 30 degrees C (Rapid River thrust sheet), to 426 +/- 32 degrees C (Morrison Ridge thrust sheet), to 358 +/- 18 degrees C (Heavens Gate thrust sheet). These ductile thrust sheets are separated by 100- 500-m -thick intervals of inverted temperatures that surround the mapped positions of thrust faults. We interpret the western part of the suture zone as a ductile accretionary complex that records the progressive underplating and top - to-the -west translation of ductile thrust sheets that were derived from the Wallowa terrane during ca. 144- 105 Ma collision-related deformation. Accretion of ductile thrust sheets began at similar to 30- 35 km depths and completed at depths of similar to 10- 20 km. Rocks at all structural levels in the suture zone exhibit distributed ductile fabrics, but the inverted thermal gradients that surround the mapped positions of thrust faults suggest that the majority of top to-the -west displacement was accommodated within 100- 500-m-thick, high-strain, thrust -sense ductile shear zones.

Crustal temperature conditions can strongly influence the evolution of deformation during orogenesis. The Sevier hinterland plateau in Nevada and western Utah ("Nevadaplano") experienced a Late Cretaceous episode of shallow-crustal metamorphism and granitic magmatism. Here, we investigate the thermal history of the Nevadaplano by measuring peak thermal field gradients attained in the upper 10-20 km of the crust along an east-west transect through nine ranges in eastern Nevada and western Utah, by integrating Raman spectroscopy of carbonaceous material thermometry and published conodont alteration indices with reconstructed cross sections. Thermal field gradients of 29 +/- 3 degrees C/km were obtained in the House and Confusion Ranges in westernmost Utah. The Deep Creek, Schell Creek, and Egan Ranges in easternmost Nevada yielded elevated gradients of 49 +/- 7 degrees C/km, 36 +/- 3 degrees C/km, and 32 +/- 6 degrees C/km, respectively. Moving westward, the White Pine, Butte, Pancake, and Fish Creek Ranges exhibit gradients typically between similar to 20-30 degrees C/km. The elevated thermal gradients in easternmost Nevada are interpreted to have been attained during ca. 70-90 Ma granitic magmatism and metamorphism and imply possible partial melting at similar to 18 km depths. Our data are compatible with published interpretations of Late Cretaceous lithospheric mantle delamination under the Sevier hinterland, which triggered lower-crustal anatexis and the resulting rise of granitic melts. The lack of evidence for structures that could have accommodated deep burial of rocks in the nearby Northern Snake Range metamorphic core complex, combined with thermal gradients from adjacent ranges that are similar to 1.5-3 times higher than those implied by thermobarometry in the Northern Snake Range, further highlights the debate over possible tectonic overpressure in Cordilleran core complexes. Cross-section retro-deformation defines 73.4 +/- 4.6 km (76 +/- 8%) of extension across eastern Nevada and 15 km of shortening in the Eastern Nevada fold belt.

A widespread unconformity between Ordovician metasedimentary rocks and nonmetamorphosed Mesozoic sedimentary rocks across the Eastern Cordillera of Bolivia provides evidence for significant pre-Late Cretaceous deformation and erosion. In this paper, we refine the middle to late Paleozoic tectonic history of the central Andean segment of Gondwana's western margin. We combine Raman spectroscopy of carbonaceous material (RSCM) thermometry with semi-quantitative deformation temperature estimates from quartz recrystallization microstructures and published illite crystallinity values from Cambrian-Devonian sedimentary rocks that span the Eastern Cordillera of southern Bolivia at-21 degrees S. Estimates of peak temperature and deformation temperature range primarily between-220 and 400 degrees C and show a general increase with depth that defines a metamorphic field gradient between-37 and 47 degrees C/km. Temperatures obtained from Ordovician rocks directly below the unconformity require erosion of a >-5 km overburden prior to the Late Cretaceous, which was likely accomplished by a combination of distributed cleavage development and Paleozoic folding and thrust faulting revealed from cross-section reconstructions. The peak temperature data are incorporated into thermal models along with published illite K\\Ar, zircon (U\\Th)/He, and zircon fission-track cooling ages that refine the timing of Paleozoic orogenesis in the central Andes. We interpret shortening-related flexural subsidence driven by cratonward growth of a pre-Andean orogenic wedge along the western margin of Gondwana, with peak temperature conditions attained during eastward advance of a foreland basin between-420 and 318 Ma during the Devonian Carboniferous Gondwanide Orogeny. Erosional exhumation between-352 and 294 Ma was the result of continued growth and eastward expansion of the associated Transpampean tectonic highland across the Eastern Cordillera. The growth of this pre-Andean contractional orogen coincided with global plate reorganization and the reestablishment of subduction and arc magmatism along the western margin of Gondwana, as indicated by a significant influx of Carboniferous arc-related detritus into the foreland basin system. (c) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

In article number 1907364, Can Ataca, Sefaattin Tongay, and co-workers apply high pressures to a variety of different kinds of 2D halide perovskites in a diamond anvil cell. The results reveal unusual phase transitions and changes in materials properties that are closely tied to the chemistry of the 2D perovskite layers. This study gives unique insights into such pressure-induced changes and extends the understanding of these highly anisotropic layered soft organic perovskite materials under extreme conditions.

The application of high pressure allows control over the unit cell and interatomic spacing of materials without any need for new growth methods or processing while accessing their materials properties in situ. Under these extreme pressures, materials may assume new structural phases and reveal novel properties. Here, unusual phase transition and band renormalization effects in 2D van der Waals Ruddlesden-Popper hybrid lead halide perovskites, which have shown extraordinary optical properties and immense potential in light emission and conversion technologies, are reported. The results show that (CH3(CH2)(3)NH3)(2)(CH3NH3)Pb2Br7 (n = 2) layers undergo two distinct phase transitions related to PbBr6 octahedra, butylammonium (BA), and methylammonium (MA) molecule tilting motion that leads to rather unique/anomalous bandgap variation with pressure. In contrast, (CH3(CH2)(3)NH3)PbBr4 (n = 1) lacks MA molecules and possesses only one pressure-induced phase transition related to PbBr6 octahedra and BA tilting. In this range, the bandgap reduces monotonically, much similar to other inorganic semiconductors and display surprisingly large redshift from 3 to 2.4 eV. Together with theoretical calculations, this study offers unique insights into these pressure-induced changes and extends the understanding of these highly anisotropic layered soft organic perovskite materials under extreme conditions.

Mesozoic crustal shortening in the North American Cordillera's hinterland was related to the construction of the Nevadaplano orogenic plateau. Petrologic and geochemical proxies in Cordilleran core complexes suggest substantial Late Cretaceous crustal thickening during plateau construction. In eastern Nevada, geobarometry from the Snake Range and Ruby Mountains-East Humboldt Range-Wood Hills-Pequop Mountains (REWP) core complexes suggests that the similar to 10-12 km thick Neoproterozoic-Triassic passive-margin sequence was buried to great depths (>30 km) during Mesozoic shortening and was later exhumed to the surface via high-magnitude Cenozoic extension. Deep regional burial is commonly reconciled with structural models involving cryptic thrust sheets, such as the hypothesized Windermere thrust in the REWP. We test the viability of deep thrust burial by examining the least-deformed part of the REWP in the Pequop Mountains. Observations include a compilation of new and published peak temperature estimates (n = 60) spanning the Neoproterozoic-Triassic strata, documentation of critical field relationships that constrain deformation style and timing, and new 40Ar/39Ar ages. This evidence refutes models of deep regional thrust burial, including (1) recognition that most contractional structures in the Pequop Mountains formed in the Jurassic, not Cretaceous, and (2) peak temperature constraints and field relationships are inconsistent with deep burial. Jurassic deformation recorded here correlates with coeval structures spanning western Nevada to central Utah, which highlights that Middle-Late Jurassic shortening was significant in the Cordilleran hinterland. These observations challenge commonly held views for the Mesozoic-early Cenozoic evolution of the REWP and Cordilleran hinterland, including the timing of contractional strain, temporal evolution of plateau growth, and initial conditions for high-magnitude Cenozoic extension. The long-standing differences between peak-pressure estimates and field relationships in Nevadan core complexes may reflect tectonic overpressure.

Documenting the processes that facilitate exhumation of ultra-high pressure (UHP) rocks at convergent margins is critical for understanding orogen dynamics. Here, we present structural and temperature data from the Himalayan UHP Tso Morari nappe (TMN) and overlying nappes, which we integrate with published pressure-temperature-time constraints to refine interpretations for their structural evolution and exhumation history. Our data indicate that the 5.5 km-thick TMN is the upper portion of a penetratively deformed ductile slab, which was extruded via distributed, pure shear-dominated, top-down-to-east shearing. Strain in the TMN is recorded by high-strength quartz fabrics (density norms between 1.74-2.86) and finite strain data that define 63% transport-parallel lengthening and 46% transport-normal shortening. The TMN attained peak temperatures of ~500-600°C, which decrease in the overlying Tetraogal and Mata nappes to ~150-300°C, defining a field gradient as steep as 67°C/km. Within the overlying nappes, quartz fabric strength decreases (density norms between 1.14-1.21) and transport-parallel lengthening and transport-normal shortening decrease to 14% and 18%, respectively. When combined with published 40Ar/39Ar thermochronometry, quartz fabric deformation temperatures as low as ~330°C indicate that the top-to-east shearing that exhumed the TMN continued until ~30 Ma. Peak temperatures constrain the maximum depth of the overlying Mata nappe to 12.5-17.5 km; when combined with published fission-track thermochronometry, this provides further support that the TMN was not underplated at upper-crustal levels until ~30 Ma. The long-duration, convergence-subnormal shearing that exhumed the TMN outlasted rapid India-Asia convergence by ~15 Myr and may be the consequence of strain partitioning during oblique convergence.

Disagreements over how to define shear zones within packages of pervasively recrystallized rock impede our ability to map and correlate these structures. Here, we explore a new approach for delineating the spatial extents of shear zones using quartz petrofabric, temperature, and kinematic data collected from two transects across the Main Central thrust (MCT) in western Bhutan. We calculated cylindricity, a fabric intensity parameter that has been previously interpreted as a proxy for finite strain magnitude, for each sample. Cylindricity values (measured on a scale from 0 to 1) increase upward from 0.11 to 0.47 between 2.3 and 1.3 km below the MCT, vary between 0.55 and 0.93 between 700 m below and 200 m above the MCT, and decrease upward from 0.68 to 0.37 between 2.4 and 11.7 km above the MCT. Fabric intensity increases with proximity to the MCT and defines a similar to 900 m-thick zone of elevated intensity that overlaps spatially with an interval of inverted metamorphism. Our results add to a growing number of recent studies that suggest that spatial patterns of fabric intensity, when integrated with temperature data and kinematic observations, can be used to delineate relative strain patterns across shear zones in the Himalaya and elsewhere.

Here we describe a dual detector system for high-energy X-ray, simultaneous, small and wide-angle X-ray scattering (SAXS and WAXS), designed to extract extended-range pair distribution functions (ER-PDF) for disordered materials. The hardware and software provides continuous reciprocal space coverage over atomic to nanometer length-scales. Details of the varying resolution, splicing of data and normalization on an absolute scale are outlined. In addition, the combination of SAXS and WAXS theory is considered with a view to enabling a direct Fourier transformation of the structure factor spanning multiple length-scales into real space. Important distinctions between the ER-PDF and the pair distance distribution function (PDDF) representations are demonstrated. It is shown that when the SAXS intensity in the structure factor, S(Q), is similar to the WAXS intensity, the contributions to the ER-PDF are minimal. However, when the SAXS S(Q) intensities are substantially stronger than the WAXS, the ER-PDF can provide important structural information on the local, intermediate and nanometer length-scales. Notably, the ER-PDF method provides direct information on particle sizes and their density distributions, overcoming the limitations of PDDF analysis for densely packed systems.

The temperature dependence of the heights of the first and second x-ray diffraction peaks in supercooled water measured down to 244 K are found to display very different behaviours. While the first peak intensity remains essentially constant, the second peak increases strongly with decreasing temperature. In real space this is concomitant with the reduction of the number of non-bonded interstitial molecules between the first and second shells. It is found that although the first O-O shell in supercooled water is unchanged upon supercooling, the variations in intermediate range order are mainly associated with the growth of a predominantly tetrahedral network that is distinctly different from ice-Ih. Moreover, in this temperature regime we find a direct correlation between the height of the second diffraction peak and the intensity changes in the 2nd, 3rd, 4th and 5th peaks in the oxygen-oxygen pair distribution function.

Despite playing a fundamental role in all models of Himalayan tectonics, minimal data constraining the structural evolution, metamorphic history, and offset magnitude of the South Tibetan detachment system (STDS) are available. Here, we integrate petrofabric, finite strain, and kinematic data with metamorphic and deformation temperatures to generate a structural model for the STDS in northwestern Bhutan. We divide the STDS into an ∼2-km-thick lower level that accommodated ∼6–13 km of thinning via ≥30–76 km of simple shear-dominant displacement within Greater Himalayan rocks, and an ∼3-km-thick upper level that accommodated ≥21 km of displacement via an upward decrease (from 44% to 2%) in transport-parallel lengthening within Tethyan Himalayan rocks. Peak metamorphic temperatures in the lower level are ∼650–750 °C, and two distinct intervals of telescoped isotherms in the upper level define a cumulative upward decrease from ∼700 to ∼325 °C. These intervals are separated by an abrupt upward increase from ∼450 to ∼620 °C, which we interpret as the result of post-STDS thrust repetition. Above the upper telescoped interval, temperatures gradually decrease upward from ∼325 to ∼250 °C through a 7-km-thick section of overlying Tethyan Himalayan rocks. Telescoped isotherms lie entirely above the high-strain lower level of the STDS zone, which we attribute to progressive elevation of isotherms during protracted intrusion of granite sills. This study demonstrates the utility of using gradients in fabric intensity and thin section-scale finite strain to delineate shear zone boundaries when field criteria for delineating strain gradients are not apparent.