page_title: Paleogeography of the India–Asia collision system
section_title: Synchronous collision hypothesis
hierarchical_section_title: Paleogeography of the India–Asia collision system / Timing of collision onset / Synchronous collision hypothesis
caption_attribution_description: English: Simplified map of the India-Asia collision system at around 59-56 Ma, where the collision between two continents has just started, indicating the orientation of the two transect discussed below. Modified after Hu et al. 2016.
context_page_description: The paleogeography of the India–Asia collision system is the reconstructed geological and geomorphological evolution within the collision zone of the Himalayan orogenic belt. The continental collision between the Indian and Eurasian plate is one of the world's most renowned and most studied convergent systems. However, many mechanisms remain controversial. Some of the highly debated issues include the onset timing of continental collision, the time at which the Tibetan plateau reached its present elevation and how tectonic processes interacted with other geological mechanisms. These mechanisms are crucial for the understanding of Mesozoic and Cenezoic tectonic evolution, paleoclimate and paleontology, such as the interaction between the Himalayas orogenic growth and the Asian monsoon system, as well as the dispersal and speciation of fauna. Various hypotheses have been put forward to explain how the paleogeography of the collision system could have developed. Important ideas include the synchronous collision hypothesis, the Lhasa-plano hypothesis and the southward draining of major river systems.
context_section_description: The synchronous collision hypothesis limits the age of collision onset at 59 Ma by dating the oldest turbidites formed on the passive margin of the India continent, which indicates the incoming of materials from the active Asian continental margin. Geological evidence of rocks younger than 59 Ma and deposited on top of the turbidite sequence can be considered as indicators to reconstruct tectonic evolution after collision had begun. Various evidence documented along NE-SW and NW-SE sections of the India–Asia collision zone synchronize with each other, being in favour of a "one-off" collision.
  Facies changes (NE-SW): stratigraphic correlations of Paleocene to early Eocene across the NE-SW orientation of the Himalayas shows that the change in depositional environment is similar in time, with no unconformity and only a few tens of meters of vertical differences. This suggests that the whole Indian continental margin collided with the Asian continental margin at approximately the same time.
  Detrital zircon age patterns (NW-SE): a transect of paleo-syncollisonal basins (59-56 Ma) on the active Asian continental margin, the point of collision and the passive Indian continental margin is considered. Detrital zircons from these basins shares same age peaks at 50 and 100 Ma. This suggests that the origin of sediments and timing of basin infill along this NW-SE transect is the same, ruling out the possibility of presence of an island arc in between two continental margin and multiple stages of collision.
caption: Simplified map of the India–Asia collision system at around 59-56 Ma, where the collision between two continents has just started, indicating the orientation of the two transects discussed below. Modified after Hu et al. 2016.
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