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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°C/km average Late Cretaceous thermal gradient predicted by thermobarometry is incompatible with the 46 ± 10°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. Key Points: Strain compatibility demonstrates that the detachment displacement necessary to exhume footwall rocks from 21 to 30 km depths is not possibleThe 22°C/km gradient predicted by thermobarometry is incompatible with the Late Cretaceous thermal gradient of 46 ± 10°C/km that we calculateA non‐lithostatic interpretation for pressure data from the Northern Snake Range is required, similar to other Cordilleran core complexes [ABSTRACT FROM AUTHOR]

Cordilleran orogens are complex tectonic systems, strongly influenced by lithospheric deformation and exhumation. However, in the type region of the Central Andes, the timing and mechanisms of deformation and mountain building remain poorly constrained, especially for the high‐elevation Puna Plateau of NW Argentina. We use geologic mapping, structural cross‐sections, low‐temperature thermochronology, and U‐Pb dating of ash and detrital zircons to elucidate the history and style of orogenic deformation in the Antofalla region of the Puna Plateau. Cooling ages of major reverse fault hanging walls and dated growth strata indicate that crustal shortening activated major reverse faults during the Eocene and continued out‐of‐sequence through the Early Miocene. This protracted period of shortening, which resulted in the filling of the Antofalla Basin, was followed by a transient episode of upper‐crustal E‐W extension on a major normal fault system during the Late Miocene. Pliocene to Quaternary time saw E‐W shortening return to the region. Our structural cross‐section permits only a low magnitude of shortening (∼15–25%), which stands in contrast to the 60‐km thick crust. Triassic to Cretaceous cooling ages from footwall rocks and minor structures indicate that the entire region experienced little exhumation or sedimentation during the Mesozoic, perhaps retaining a crust thickened during multiple episodes of Paleozoic orogenesis. The crust may also reflect lower‐crustal thickening due to the growth of a lithospheric drip during the Late Miocene. Key Points: Combination of structural mapping, thermochronology, and U‐Pb chronostratigraphy reveals four phases of Cenozoic deformationExhumation due to horizontal shortening was underway by the Eocene (∼45 Ma), ∼20 Myr earlier than previously inferred for the regionShortening propagated out‐of‐sequence, westward from the Calalaste Range into the Antofalla Basin until ∼15 Ma [ABSTRACT FROM AUTHOR]

Documenting the processes that facilitate exhumation of ultrahigh‐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 and 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 and 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. Key Points: Deformation temperatures combined with thermochronometry indicate that the shearing that exhumed the Tso Morari nappe continued until ~30 MaTop‐to‐east shearing outlasted rapid India‐Asia convergence by ~15 Myr and may be a result of strain partitioning in the western HimalayaThe exhumation of the Tso Morari nappe is generally consistent with models of UHP exhumation that emphasize piston forcing or recirculation [ABSTRACT FROM AUTHOR]

The Northern Patagonian Andes have been constructed through multiple mechanisms that range from tectonic inversion of extensional structures of Early to Middle Jurassic age in the Main Andes to Oligocene in the Precordilleran region. These have acted during two distinctive orogenic stages, first in late Early Cretaceous and later in Miocene times Late Oligocene extension separates these two contractional periods and is recorded by half-grabens developed in the retroarc region. The last contractional stage coexists with an eastward foreland expansion of the late Miocene arc whose roots are presently exposed as minor granitic stocks and volcanic piles subordinately in the Main Andes, east of the present arc. As a consequence of this orogenic stage a foreland basin has developed, having progressed from 18 Ma in the main North Patagonian Andes, where the mountain front was flooded by a marine transgression corresponding to the base of the Ñirihuau Formation, to 11 Ma in the foreland area. Cannibalization of this foreland basin occurred initially in the hinterland and then progressed to the foreland zone. Blind structures formed a broken foreland at the frontal zone inferred from growth strata geometries. During Pliocene to Quaternary times most of the contractional deformation was dissipated in the orogenic wedge at the time when the arc front retracted to its present position. [ABSTRACT FROM AUTHOR]

The Patagonian Andes record a period of Cretaceous-Neogene orogenesis that began with the compressional inversion of a Late Jurassic rift called the Rocas Verdes basin. Detrital zircon ages from sediment that filled the southern part of the basin provide a maximum depositional age of ∼148 Ma, suggesting that the basin opened approximately simultaneously along its length during the Late Jurassic. Structural data and U-Pb isotopic ages on zircon from granite plutons near the Beagle Channel (55°S) show that basin inversion involved two stages of shortening separated by tens of millions of years. An initial stage created a small (∼60 km wide) thrust wedge that placed the basaltic floor of the Rocas Verdes basin on top of adjacent continental crust prior to ∼86 Ma. Structures and metamorphic mineral assemblages preserved in an exhumed middle to lower crustal shear zone in Cordillera Darwin suggest that this obduction was accompanied by south directed subduction of the basaltic crust and underthrusting of continental crust to depths of ∼35 km beneath a coeval volcanic arc. A subsequent stage of out-of-sequence thrusting, culminating in the Paleogene, shortened basement and Upper Jurassic igneous rock in the internal part of the belt by at least ∼50 km, forming a bivergent thrust wedge. This latter period coincided with the exhumation of rocks in Cordillera Darwin and expansion of the fold-thrust belt into the Magallanes foreland basin. This orogen provides an important example of how orogenesis initiated and led to continental underthrusting and obduction of basaltic crust during closure of a quasi-oceanic rift basin. [ABSTRACT FROM AUTHOR]

Field mapping, structural analysis, and geochronologic data from northwestern Nepal reveal major normal right-slip motion along a previously unrecognized west-northwest striking system of shear zones that we term the Gurla Mandhata-Humla fault system (GMH). The GMH obliquely cuts across the Greater Himalayan Crystalline sequence and into the Lesser Himalayan imbricate thrust belt via two right-step-over structures. The average slip direction on the GMH parallels the strike of the Himalayan orogen. Motion along this fault system has resulted in an apparent left separation of the South Tibet Detachment, Main Central thrust zone, and Lesser Himalayan imbricate thrust belt along a north striking segment of the fault system. We estimate a minimum of 21 km of net slip on the southern branch of the GMH by restoring the trace of the Main Central thrust zone parallel to the average slip direction on the fault. Taking into account slip estimates from the northern branch of the GMH yields a minimum net slip estimate of 24.4 to 32.4 km for the GMH. The 232Th/208Pb ion microprobe monazite ages from leucogranite bodies indicate that motion on the GMH occurred after 15 Ma. Its initiation immediately followed crustal thickening between the Main Central thrust zone and Indus-Yalu suture zone. Motion on the GMH is contemporaneous with arc-normal contraction in the southernmost Himalayan orogen. These observations can be explained by a model that involves foreland propagating structural systems facilitating arc-normal contraction in the foreland and arc-parallel extension in the hinterland that work together to maintain the arcuate shape of the Himalayan orogen. [ABSTRACT FROM AUTHOR]

The Balakot Formation of the Himalayan foreland basin in Pakistan was originally described as a >8 km thick clastic red bed succession within which are stratigraphically intercalated four gray marl bands containing fossils dated at 55-50 Ma. On this basis, and the reported conformable contact with the underlying Paleocene Patala Formation, the Balakot Formation red beds were interpreted as tidal facies dated at 55-50 Ma, by >20 Myr the oldest foreland basin sediments eroded from the metamorphic orogen. However, our new detailed structural mapping shows the Balakot Formation to be in tectonic contact with the underlying Patala Formation, and the marl bands to be structurally intercalated with the red beds. Hence neither the nature of the Balakot Formation lower contact nor the intercalated marl bands can be used to date the red beds. Our Ar/Ar dating of 257 individual detrital white micas from the Balakot Formation red bed sandstones shows that the red bed succession must be younger than 37 Ma, and we thus conclude that the first exposed foreland basin continental sediments eroded from the metamorphic mountain belt were deposited after 37 Ma, at least 15 Myr later than previously believed. These new structural, stratigraphic, and isotopic data from the Balakot Formation provide new constraints to the early tectonic evolution of the mountain belt, result in reassessment of the facies and provenance of the Balakot Formation, and force reconsideration of models of orogenesis, basin evolution, and the timing and diachroneity of India-Asia collision that are based on the original documentation of the Balakot Formation. [ABSTRACT FROM AUTHOR]