青海东昆仑尕林格铁多金属矿床辉石闪长岩U-Pb年代学及地球化学特征

Zircon U-Pb geochronology and geochemistry of pyroxene diorite in Galinge iron-polymetallic deposit,East Kunlun

对青海尕林格矿区与成矿有关的辉石闪长岩的地球化学特征研究显示,该辉石闪长岩属于偏铝质、钙碱性系列岩石,明显富集活泼不相容元素Th、U和轻稀土元素,相对亏损高场强元素Nb、Ta、Ti和P,具弱的负Eu异常(δEu介于0.924~0.962)。岩石εHf(t)值为-3.79^-1.70,二阶段模式年龄为TDM2为1 223~1 339 Ma。尕林格闪长岩锆石LA-ICP-MS U-Pb加权平均年龄为228±2 Ma(MSWD=0.32),为晚三叠世。综合前人研究成果,认为在巴颜喀拉地块与东昆仑地块碰撞-后碰撞转换阶段俯冲的阿尼玛卿洋壳板片发生断离,引起地幔物质上涌至古老的下地壳底部,使其发生部分熔融并混入部分幔源物质,形成尕林格辉石闪长岩石。

The paper discusses the pyroxene diorite which is closely related to ore-forming bodies in Galinge deposit. Geochemical characteristics show that the pyroxene diorite in Galinge belongs to calc-alkaline and metaluminous series. The trace element is enriched in more mobile incompatible elements（ e. g. Th,U） and LREE,relatively depleted in high field strength elements（ e. g. Nb,Ta,Ti and P）,and exhibits weak negative Eu anomalies（ δEu = 0. 924 ~ 0. 962）. The zircon εHf（ t） values- 3. 79 ^- 1. 70,all yield relatively ancient model ages（ TDM2）,ranging from 1 223 to 1 339 Ma. Zircon LA-ICP-MS U-Pb dating for the pyroxene diorite yields age of Galinge is 228 ± 2 Ma（ MSWD = 0. 32）,indicating the Late Triassic. Combined with previous research about the regional geological background, we propose that anemaqen oceanic crust was already subducted and break-off during a period of change in the tectonic setting of the EKO from compression to extension,and it in-duced the upwelling of deep asthenosphere and the addition of mantle-derived material,providing enhanced heat and triggering the partial melting of overlying ancient lower crust,eventually forming the Galinge pyroxene diorite.