东昆仑五龙沟矿集区中三叠世辉绿岩脉的岩石成因:年代学、地球化学特征及其构造意义

本文对五龙沟矿集区4条辉绿岩脉中的锆石进行LA-ICP-MS U-Pb定年研究，发现其中大部分锆石为捕获锆石，而拥有最新年龄的锆石可代表岩浆结晶时的锆石，其加权平均年龄为（242.8±2.1）Ma，属于中三叠世。这些辉绿岩脉的w（SiO₂）为42.82%~52.94%，w（Na₂O）为1.98%~4.51%，w（K₂O）为0.70%~2.04%，属于钙碱性和高钙碱性系列；4条岩脉中V、Cr、Ni等质量分数与MgO质量分数均呈正相关，且质量分数较小，表明其岩浆演化过程中经历了以橄榄石、辉石为主的分离结晶作用；其微量元素具有相对富集大离子亲石元素（Rb、Ba、Eu）和轻稀土元素，亏损高场强元素的特征，Nb/La为0.39~0.50，Nb/Ta为12.16~16.69，Zr/Hf为45.82~47.06，明显和亏损软流圈地幔来源的岩浆不同。综合分析认为，五龙沟矿集区的中三叠世辉绿岩脉大地构造背景为俯冲环境，是受俯冲板片流体改造的岩石圈地幔部分熔融的产物，并经受了一定的地壳混染。

Petrogenesis of Middle Triassic Diabase Veins in Wulonggou Ore Concentrated Areas Within East Kunlun Orogen: Chronology,Geochemistry and Tectonic Significance

Through a LA-ICP-MS U-Pb dating of zircons from four diabase dykes in Wulonggou ore concentrated areas, we found that the most zircons are the inherited zircons. The zircons with the latest age represent those from the magmatic crystallization of diabase veins with an average age of (242.8±2.1) Ma (the Middle Triassic). The four diabase dykes are calc-alkaline -high calc-alkaline with w(SiO₂) range of 42.82%-52.94%,w(Na₂O) range of 1.98%-4.51% and w(K₂O) range of 0.70%-2.04%. V, Cr, Ni and the other trace elements in the four dikes are positively correlated with MgO mass fraction, and the mass fraction is small. This results indicate that the fractional crystallizations of the olivine and pyroxene occurred during the magmatic process. The trace elements are characterized by relatively rich in LILE (Rb, Ba, Eu), LREE, depleted of HFSE, Nb/La is 0.39-0.50, Nb/Ta is 12.16-16.69, and Zr/Hf is 45.82-47.06. These features are quite different from those of the magma derived from the depleted asthenosphere mantle. In conclusion, the Middle Triassic diabase dikes in Wulonggou ore concentrated areas may be derived from the partial melting of the lithospheric mantle, reconstructed by the subduction plate fluids and contaminated by the crust.