Middle Permian-Early Trias-sic mafic magmatic events in Kaixinling zone, Tuotuo River area, Qinghai Province, and their geological significance

The Middle Permian-Early Triassic tectonic background of Kaixinling zone in Tuotuo River area is an important factor affecting the metallogenic regularity and prospecting direction analysis. The geochemical study of Middle Permian basalt and geochro-nologic data of gabbro from Nuoribagaribao Formation are expected to put constraint on the ore-forming geotectonic background of Middle Permian-Early Triassic in this area. The gabbro with zircon U-Pb age of 247.0±1.7Ma has established an important magmat-ic event and filled the blank of magmatic activity in Early Triassic. This event might have been caused by the subduction and collision during the evolution of the Longmu Co-Shuanghu suture zone and the Kekexili-Jinsha River suture zone. Geochemistry of Middle Permian basalt is consistent with the tholeiitic magma series, which is characterized by high Mg and Fe, low alkali, enrichment of LREE and partial enrichment of HFSE. It has relatively high Zr (>70×10-6 in average) and Zr/Y (5.2~7.0), similar to things of the continental basalt. The depleted Nb, Ta, Zr, Hf, Ti and low Nb/La ratios (0.1~0.3) imply the contamination of crustal components.Various discrimination diagrams show that the basalt was formed in a continental-rift environment and the volcanism was closely re-lated to the regional mineralization. New data from gabbro and basalt are presented in this paper to demonstrate the metallogenic geo-tectonic background of Kaixinling area.