Structure of the Xigaze Ophiolite, Yarlung Zangbo Suture Zone, southern Tibet, China: Genetic implications

Abstract

Three massifs in the Xigaze area (Southern Tibet, China), have been preserved from the intense deformation observed everywhere else in the Yarlung Zangbo Suture Zone. These massifs have similar lithologies and display a remarkable homogeneity in the attitude of most magmatic and tectonic structures such as lava flow planes, dolerite dikes and sills, and foliation planes in peridotites. This indicates that these ophiolites are only slightly dismembered, inasmuch as they locally display complete sequences from pillow lavas at the top to fresh Cr‐diopside‐bearing harzburgites at the base. Gabbroic rocks are rare and are present as screens between dolerite intrusives or in small‐sized pockets at the limit between mafic and ultramafic rocks. One of the most important feature of this ophiolite is the occurrence of dolerite sills and dikes throughout the whole sequence indicating that this ophiolite results from to two successive magmatic events with (1) creation of the crustal part of the oceanic lithosphere with deposition of minor cumulates in small magma chambers over mantle residual rocks and (2) intrusion of dolerite sills and dikes throughout the whole sequence.