The extent of Greater India, II. Palaeomagnetic data from the Ladakh Intrusives at Kargil, northwestern Himalayas

Abstract

The Ladakh Intrusives at Kargil (central Ladakh, northwestern Himalayas), immediately north of the Indus-Tsangpo suture zone, have been studied palaeomagnetically. These intrusives were emplaced before and during the early Tertiary with final closure of the isotopic systems between 49 and 45 m.y. ago. Six different magnetization components have been identified, on basis of which a two-stage collision model is proposed. Two magnetically very “soft” components are present in most of the samples examined. They represent (1) a recent field component, and (2) an eastwards directed component streaking towards the plane of the east-west-oriented foliation pattern. Two other magnetically rather “soft” components are present in some of the samples only. One of these components (3) indicates a palaeolatitude of the sampled area at about 23°N and suggests crustal shortening in south-central Asia over more than 10° of latitude after final collision of the Ladakh island arc, then already united with the Indian subcontinent. The other soft component (4) may be related to younger phases of the Himalayan Orogeny (Mio-Pliocene or younger). Two magnetically very “hard” components (5 and 6) indicate a palaeolatitude of the sampled area at 7–10°N. These components were acquired shortly before final closure of the isotopic systems, but after initial collision (pre-Middle Eocene) of the Indian subcontinent with the Ladakh island arc along the Indus-Tsangpo suture zone. This palaeolatitude of the sampled area is in good agreement with palaeolatitudinal control of the Indian plate from DSDP core data and indicates that after their initial collision, this combined Indian subcontinent—Ladakh island arc block moved northwards over a total distance of about 25° of latitude. Declination control of the various magnetization components suggests that after initial collision the sampled area followed the counterclockwise rotation of the Indian plate, which subsequently reversed to a clockwise rotation after final collision with Asia.