A new kinematic evolutionary model for the growth of a duplex - an example from the Rangit duplex, Sikkim Himalaya, India

The Lesser Himalayan duplex (LHD) is a prominent structure through much of the Lesser Himalayan fold-thrust belt In the Darjeeling - Sikkim Himalaya a component of the LHD is exposed in the Rangit window as the Rangit duplex (RD). The RD consists of ten horses of the upper Lesser Himalayan Sequence (Gondwana, Buxa, Upper Daling). The duplex varies from hinterland-dipping in the north, through an antiformal stack in the middle to foreland-dipping in the south. The Ramgarh thrust (RT) is the roof thrust and, based on a balanced cross-section, the Main Himalayan Sole thrust is the floor thrust at a depth of similar to 10 km and with a dip of similar to 3.5 degrees N. Retrodeformation suggests that the RD initiated as a foreland-dipping duplex with the Early Ramgarh thrust as the roof thrust and the RT as the floor thrust The RT became the roof thrust during continued duplexing by a combination of footwall imbrication and concurrent RT reactivation. This kinematic history best explains the large translation of the overlying MCT sheets. The restoration suggests that RD shortening is similar to 125 km, and the original Gondwana basin extended similar to 142 km northward of its present northernmost exposures within the window. (C) 2009 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.