Minimum Age of Initiation of Collision between India and Asia North of Everest Based on the Subsidence History of the Zhepure Mountain Section1

The collision of India with Asia, one of the most profound tectonic events to have occurred in past 100 m.y., is thought to have had geological, geochemical, and climatological consequences of global extent. Surprisingly the age of initiation of this collision remains poorly constrained. Estimates range from the Late Cretaceous (.65 Ma) to latest Eocene (,40 Ma), with little consensus in between. This paper reviews the stratigraphic section preserved on Zhepure Mountain, on the north flank of Everest (Mount Qomolongma), and its implied subsidence history. Zhepure Mountain lies about 65 km south of the Indus-Yarlung Zangbo suture and contains the most complete and youngest passive margin shelf sediments in the Tethyan Himalayas. On the basis of the subsidence history of the preserved section there is no evidence of acceleration of the subsidence up to the youngest rocks. Therefore, collision-related loading and accelerated subsidence must post-date the youngest sediments preserved, which date from the early Lutetian; hence accelerated subsidence at Zhepure Mountain must post-date about 45.8 Ma. In the Zanskar and Hazara region to the west, the initiation of collision is stratigraphically well constrained as starting in the Late Ypresian (,,52 Ma), implying a significant component of diachroneity to the initiation of this collision.