Remnants of a Cretaceous intra-oceanic subduction system within the Yarlung^Zangbo suture (southern Tibet) Jonathan C. Aitchison a ; *, Badengzhu b , Aileen M. Davis a , Jianbing Liu a , Hui Luo a , John G. Malpas a , Isabella R.C. McDermid a , Hiyun Wu b , Sergei V. Ziabrev a , Mei-fu Zhou a a Tibet Research Group, Department of Earth Sciences, University of Hong Kong, Pokfulam Rd, Hong Kong, SAR, China b Geological Team No 2, Tibetan Geological Survey, Lhasa, Tibet, China Received 10 April 2000; received in revised form 21 September 2000; accepted 23 September 2000 Abstract Extensive field investigations along the Yarlung^Zangbo suture zone in southern Tibet reveal the presence of now fragmented remnants of a south-facing intra-oceanic subduction system. This system developed within Tethys during the Cretaceous. The associated arc, forearc ophiolite, and subduction complex were emplaced onto the leading edge of India at the end of the Cretaceous. Rapid sedimentation in oblique-slip basins and disruption of water-saturated sediments into me ¨lange was widespread and concomitant with ophiolite emplacement. We describe the tectonic entities that developed during this previously unrecognized phase of Tethys^Tibet evolution and present a new model for the evolution of this portion of Tibet. ß 2000 Elsevier Science B.V. All rights reserved. Keywords: Xizang China; Cretaceous; Tethys; Indus^Yarlung Zangbo suture zone; island arcs; ophiolite; subduction zones; melange 1. Introduction The Yarlung^Zangbo suture zone (YZSZ) marks where the Tethys Ocean was consumed as India approached and ultimately collided with Asia. The most widely accepted tectonic model for this event is one in which the entire N^S ex- tent of the Tethyan oceanic crust was subducted along the southern margin of the Lhasa terrane. Existing models for India^Asia collision suggest the existence of a south-facing subduction system along the continental margin of Asia at which the northern margin of Tethys was consumed [1,2]. We note, the early suggestion by Allegre et al. [3] of the existence within Tethys of a `hypothet- ical island arc which would have to have been completely obliterated'. Prost et al., [4], presented three models two of which allowed for the possi- bility of intra-Tethyan subduction. Searle et al., [2], however, suggested that an important di¡er- ence between Tibet and the western Himalaya was the absence of evidence for the former existence of an intra-oceanic island arc in Tibet. Detailed in- vestigation of the YZSZ during the past four summer ¢eld seasons reveals the presence of rem- 0012-821X / 00 / $ ^ see front matter ß 2000 Elsevier Science B.V. All rights reserved. PII:S0012-821X(00)00287-9 * Corresponding author. Tel.: +852-28598047; Fax: +852-25176912; E-mail: jona@hku.hk Earth and Planetary Science Letters 183 (2000) 231^244 www.elsevier.comGlocateGepsl