Paleomagnetism of the Dazhuqu Terrane, Yarlung Zangbo Suture Zone, Southern Tibet (abstract)

Abstract

The Dazhuqu terrane comprises several massifs of mid-Cretaceous ophiolitic rocks with the signature of a supra-subduction zone setting. It is associated with the Zedong (island arc) and Bainang (accretionary wedge) terranes, and with these terranes is interpreted to represent remnants of a Jurassic-Cretaceous south-facing intra-oceanic subduction system. Paleomagnetic investigations have been carried out in order to re-assess paleolatitudes at which the ophiolite was generated. For this purpose, oriented samples were collected from several sections of supra-ophiolite deposits, those ages of which were determined using radiolarian fossils. Sampled lithologies include cherts, siliceous mudstones and volcaniclastics. Conventional alternating field and thermal stepwise demagnetization methods were used to analyze specimens. In three sites, Dazhuqu, Donglhe, and Qunrang, characteristic remanent magnetization have been isolated. Occurrence of anti-parallel magnetization components (Dazhuqu) and a positive conglomerate test (Donglhe) suggest a primary origin for remanence. The results of this study indicate generation of the Dazhuqu terrane ophiolite at equatorial latitudes. Some fragments of the ophiolite have experienced a counter-clockwise rotation.