Greater India's northern margin prior to its collision with Asia

Abstract

Greater India's northern edge prior to collision with Asia is typically modelled as a rifted passive margin. We argue for a quite different geometry as a consequence of two tectonic episodes that happened sometime before the main impact. Whilst the western segment of India's northern boundary had formed in the Late Triassic as a rifted margin, the central and eastern portions developed between 132 and 110 Ma when the sub‐continent separated from Australia–Antarctica as the inner wall of a dextral ‘scything’ transform fault along the Wallaby–Zenith Fracture Zone off western Australia. Key features would have been (i) the very narrow (20–30 km wide) ocean–continent transition zone marking the sub‐continent's eastern northern boundary, and (ii) similar to the region offshore South Africa's Garden Route coast, Greater India's NE corner may have developed a series of ‘perched’ half grabens due to shearing related to its motion along the Wallaby–Zenith Fracture Zone, from initial break‐up until it passed the Zenith Plateau (ca. 110 Ma). Differences in the development of NW Greater India may be reflected in restriction of ultra‐high pressure metamorphic rocks to the western Himalaya where late Paleocene subduction of the rifted passive margin occurred at sub‐equatorial latitudes beneath the intra‐Tethyan arc. Further east, where the margin developed along the scything transform, the continent–ocean boundary would have been more abrupt and probably less strongly welded. Ophiolite emplacement appears to have been penecontemporaneous along the margin. A subsequent slab break‐off episode then eliminated the original plate boundary. Thereafter, remaining oceanic lithosphere north of the arc sutured to the sub‐continent, albeit rather weakly, was consumed beneath Eurasia, culminating in India–Asia collision.

The youngest marine deposits preserved in southern Tibet and disappearance of the Tethyan Ocean

“…However, we note that the ages of the youngest marine strata underlying any unconformity or at the top of structurally truncated sections remain a maximum age estimates and the apparent different in maximum ages may in fact be due to a different level of erosion instead of the diachronous collision. We also note recent work that suggests the northern margin of Greater Indian was not necessarily relatively linear nor was it a simple continent-ocean boundary (Ali and Aitchison, 2014). The Bartonian to Priabonian Zongpubei Formation indicates that closure of the Tethys seaway in the Eastern Himalaya occurred after Priabonian, which is compatible with the inference of a younger collision age suggested by Aitchison et al (2007) in this region.…”

Paleomagnetic and Geochronologic Results of Latest Cretaceous Lava Flows From the Lhasa Terrane and Their Tectonic Implications

“…This two‐stage continental collision includes the first collision between the TH and the LT at ~59 Ma (DeCelles et al, ; Hu et al, ) and a final collision between the TH and the “remaining Greater India” at no later than ~39 Ma based on the latest initial collision age constructed in Figure a (Huang, Lippert, Dekkers, et al, ; Ma et al, ; van Hinsbergen et al, ; Yang, Ma, Bian, et al, ). Notably, considering potential challenges to different collision models described in Hu et al (), as well as debates on the shapes of the leading edges of the collisional units, especially the TH, more late Cretaceous and Paleocene paleomagnetic investigations from the TH and the LT are needed to further constrain the collision history and paleogeography of Greater India (Ali & Aitchison, , ; Ingalls et al, ; Jagoutz et al, ).…”

Complex rift geometries resulting from inheritance of pre-existing structures: Insights and regional implications from the Barmer Basin rift

“…Ali and Aitchison, 2014) continents may have generated transtension in the region between them during separation (Mascarene Rift of Bastia et al, 2010;Reeves, 2013). Accelerated sea-floor spreading between the Greater Indian and Antarctic continents occurred during the early Cretaceous Period at the expense of rifting in the Somali proto-ocean ( Fig.…”