Geochemical Characteristics and Petrogenesis of Permian Basaltic Rocks in Keping Area, Western Tarim Basin： A Record of Plume-Lithosphere Interaction

ABSTRACT： The two basalt flows in Kupukuziman （库普库兹满） Formation of Keping （柯枰） area are the typical products of Permian magmatism. Based on systematic field investigations, we carried out geochemical studies on representative Keping basalts. The results show that the SiO2 contents in basalts range from 44.69 wt.% to 51.68 wt.%, and the total alkalis range from 4.05 wt.% to 5.5 wt.%, belonging to alkaline basalts. The Ti/Y=468.27-565.35 and TIO2=（2.88-3.82） wt.% compared to those of the high-Ti basalts in Emeishan （峨眉山） large igneous province （LIP） （TIO2=（3.58-5.21） wt.%, Ti/Y〉500, Xiao et al., 2004）. The contents of MgO and compatible elements Cr （12.9-18.6 ppm）, Ni （13.7-22.7 ppm）, and Co （39.6-50.2 ppm） are low, which suggest that the samples have undergone varying grades of fractional crystallization. All the samples have uniform REE and other trace element characteristics, with enriched LREE and LILE relative to HREE and HFS, similar REE patterns without Eu anomaly. The basalts are also show slightly depleted of Ta and Nb. They have higher initial STSr/S6Sr ratios （0.707 211-0.708 300）, lower tNd（t） values （-2.47 to -4.14）, and a narrow range of （208pb/204pb）t=37.535 2-38.297 7, （207pb/204pb）~=15.435 7-15.517 0, and （206Pb/204pb）t=17.206 5-17.874 7 ratios. The Ce/Y versus Zr/Nb diagram shows that the parent magmas were originated from low-degree partial melting of the garnet-lherzolite. The analysis results based on geochemical studies seem all point to the same conclusion that the Keping basalts have formed as a product of the interaction between the plume-derived melts and the lithosphere.Geochemical Characteristics and Petrogenesis of Permian Basaltic Rocks in Keping Area, Western Tarim Basin