Abstract:

 Field geological investigation along two routes  of RutogShiquanhe and DuobuzaGertse across the Bangong Lake suture was carried out. Among the samples collected, two mafic dykes of gabbro and diabase from the Rutog ophiolite belt display flatten chondritenormalized rare earth element patterns, typical of oceanicridge basalt. Their zircon UPb ages of 1819±26 Ma (MSWD=115) and 1844±44 Ma (MSWD=22) dated by LAICPMS technique indicate that the Bangong Lake middle Tethys oceanic basin was opened during the Late EarlyJurassic Epoch. Meanwhile, olivine diabase samples collected from the ShiquianheGertse ophiolite belt have high K2O (149%156%) and Al2O3 (1476%1521%) contents with high Fe2O3/FeO ratios (173249), and are rich in large ion lithophile elements (Rb,Ba,Th,Sr) and light rare earth elements (LREE). They display oceanic island basalt (OIB) affinity in tectonic discrimination diagrams for mafic magmatic rock. Formation age of 1762±90 Ma (MSWD=31) yielded by zircon UPb LAICPMS technique shows that the Middle Tethys oceanic basin opened during the Late EarlyJurassic Epoch had become a relatively matured oceanic basin after an opening period of about 10 Ma.

Key words: zircon UPb ages, mafic dykes, ophiolite, Bangong Lake suture, Tibet Plateau