The Petrological Characteristics, Chronology And Tectonic Implications Of The Yushigou Ophiolite Suite, Qinghai Province

The Yushigou ophiolite suite lies in the North Qilian tectonic belt, which has oncebeen the focus of research, where preserved relatively complete rock association.Among the ophiolites in the North Qilian tectonic belt, the Yushigou ophiolite suitepreserves well and completely. It is a nappe which formed by the early Ordovicianophiolite suite and the Carboniferous–Dyas system. From the top to the bottom:Harzburgite, cumular dunite and gabbro and pillow lava. According to the furtherstudy of the North Qilian area on its tectonic system, we can acquire that itsubducted northward under the continental crust.Although the former investigators have done lots of research here, the tectonicevolution history of the Yushigou ophiolite suite is still in debate. Besides, theYushigou ophiolite suite is lack of petrographic characteristics, mineral chemistrycharacteristics and metamorphism.On the basis of integrated field geological survey, carefully petrographicexamination, Chronology characteristic and related literatures, we can draw thefollowing conclusions:1. The petrographic features showed that, the mainly rock combination in this areacontains the serpentine, harzburgite, gabbro, diabase and basalt. The mafic andultra-mafic rocks in Yushigou generally experienced green-schist facies’metamorphism, which contained a mineral combination of chlorite+epidote+albite.2. The consolidation temperature of the rock in the Yushigou ophiolite suite is1050-1150℃and the pressure is1.70-1.85GPa, indicating the forming condition ofthe pyrolite in this area.3. We gain515±2.3Ma LA-ICPMS Zircon U－Pb dating for gabbro fromYushigou ophiolite. So we think that the subduction of oceanic crust in Yushigoumay have come into being in Caledonian.