Convergence between the Indian and Asian plates has reshaped large parts of Asia, changing regional climate and biodiversity. Yet geodynamic models fundamentally diverge on how convergence was accommodated since the India-Asia collision. Here we report paleomagnetic data from the Burma Terrane, at the eastern edge of the collision zone and famous for its Cretaceous amber biota, to better determine the evolution of the India-Asia collision. The Burma Terrane was part of a Trans-Tethyan island arc and stood at a near-equatorial southern latitude at ~95 Ma, suggesting island endemism for the Burmese amber biota. The Burma Terrane underwent significant clockwise rotation between ~80-50 Ma, causing its subduction margin to become hyper-oblique. Subsequently, it was translated northward on the Indian Plate, by an exceptional distance of at least 2000 km, along a dextral strike-slip fault system in the east. Our reconstructions are only compatible with geodynamic models involving a first collision of India with a near-equatorial Trans-Tethyan subduction system at ~60 Ma, followed by a later collision with the Asian margin. Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:
Blueschist-and eclogite-facies high-to ultrahigh-pressure (HP/UHP) metamorphic rocks occur in the southern Tianshan Belt. Their deformation and metamorphic history is important for understanding the Paleozoic tectonics of the Central Asian Orogenic Belt. Our study focuses on the structural analysis and geochronology of the HP metamorphic rocks and the surrounding rocks in the Kekesu Section in the southern Chinese Tianshan. Geometric and kinematic analyses indicate three ductile deformation events: a top-to-the-north thrusting, a top-to-the-south shearing, and a dextral wrenching. New 40 Ar/ 39 Ar laser probe plateau ages were obtained on white mica from retrograde blueschist ( and Ma; 1j) and greenschist-facies metasediments ( Ma; 1j). These ages are interpreted as 316 ע 2 ע133 1 3 2 3 ע 1 the time of retrograde recrystallization during exhumation of the HP metamorphic rocks. New structural and isotopic data, in conjunction with previous results, suggest that (1) the collision event occurred during the latest Devonian to earliest Carboniferous, resulting in HP/UHP metamorphism and the top-to-the-north thrusting; (2) the postcollisional exhumation of the HP/UHP metamorphic rocks and extensive retrograde metamorphism under greenschistfacies conditions took place in the Mid-Late Carboniferous and are correlated with south-dipping normal faulting; and (3) Permian ductile dextral shearing and associated granitic intrusion and fluid activity severely overprinted the earlier fabrics.
In the Neuquén Basin of Argentina, ’beef' (bedding-parallel veins of fibrous calcite) is widespread within Late Jurassic black mudstones. A typical vein consists of two grey inner zones and two white outer zones. The inner zones contain inclusions of wall rock and hydrocarbons. Calcite fibres are perpendicular to the margins. In the outer zones, the angle between fibre and margin varies from about 45° at the vein tips to 90° in the centre. Imprints of fossils are offset, proving that the fibres have grown antitaxially. We infer that the veins opened in two phases. During Phase 1, the opening was vertical, against gravity. During Phase 2, the veins resisted tectonic shortening, so that shear stresses acted at the margins. The senses of shear account for the fibre angles. At outcrop, igneous intrusive rocks have cut and metamorphosed the veins. From burial curves, maturity calculations, growth strata, and ages of igneous intrusions, we estimate that the inner zones of the beef formed in the oil window, during the Aptian to Albian, and that the outer zones formed in the gas window, during the Cenomanian to Campanian. We infer that the beef is evidence for fluid overpressure during hydrocarbon generation.
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