Miocene and Pleistocene shoshonitic volcanic rocks in the Jingyuhu area, north of the Qinghai-Tibet Plateau

Two periods, Miocene and Pleistocene, of shoshonitic volcanic rocks were recognized in the Jingyuhu area ?northern Qinghai-Tibet plateau. The earlier one is intermediate trachyte series, and the later one is tephrite-basic trachyte series. The two series have different types of phenocryst, chemical composition, trace element pattern and ratio of isotopic element, but they show similar REE patterns. Isotopic characteristics suggest that these rocks were originated from EM II type of mantle, a kind of enriched mantle with the addition of recycled crustal material. The occurrence of the two periods and two series of volcanic rocks suggest that the different periods of Cenozoic volcanic activity on the plateau can be overlapped in space. The volcanic activities occurred along the giant sinistral strike-slip fault along the south margin of Kunlun Mountain, specifically constrained by the second-order faults to the north of the main fault. The deep-cut lithospheric faults here acted as a magma channel, and the occurrence of two periods of eruption represents the reactivity of the fault.