CHANDIGARH: Timing of collision between Indian and Tibetan plate has been a matter of concern for all the geologist, said Dr Ritesh Arya, a renowned international Geologist while speaking in a Scientific Programme “ Age and depositional environment of Siwalik and Siwalik-equivalent sediments” held on September 7.
He said that various dates have been proposed by various workers mostly based on radio active dating of the igneous rock samples and many 3 D graphic models proposed to show the movement and final collision. And a sort of concensus appears to have been achieved about initial and final collision between 55 milion years to 40 million years.
Present paper is based on collection of fossils of plants molluscs from Kasauli-Subathu in Himachal Pradesh and Ladakh Tethyan sediments and establishing thier role in bio and lithostratigraphic correlation which show that these were homotaxial formation.
Plant fossils of Combretum Syzygium Garcinia Gluta Palm collected from Kasauli show that today these plants are not found in Himalayas and are confined to Indonesia Malaysia and Andaman Nicobar island, says Dr Arya.
Paleolatitudinal position of the Kasauli and equivalent formation therefore at the time of deposition must be around 4-11 degrees north of equator. Since Kasauli sediments are Lower Miocene in age. This also implies that Himalayas were not born at that time and it might have taken couple of more million years of Indian plate to reach its present latitude of 33 degrees.
The Batholiths (granites ) of Ladakh has intruded into these fossiliferous horizons along the present day suture. Hence the age of the collision which subsequently led to the origin of Himalayas has to much younger then 20 million years.
Time of initial collision of the 2 plates has to be definately less then 18 million years, says he.