青海赛什塘铜矿区侵入岩体地球化学及锆石LA-ICPMS U-Pb年代学

Geochemistry and zircon LA-ICPMS U-Pb geochronology of intrusive body in Saishitang copper deposit, Qinghai Province, China

位于青海东部的鄂拉山地区是青藏高原北部重要的构造-岩浆-成矿带。为探讨该区岩浆岩-成矿作用,选取赛什塘矿区石英闪长玢岩和花岗斑岩开展了岩石主量元素、微量元素和锆石U-Pb LA-ICPMS测试。主量元素结果显示:赛什塘铜矿区杂岩体的石英闪长玢岩和花岗斑岩属于偏铝质岩石,具Ⅰ型花岗岩的特征,岩石系列属于高钾钙碱性系列。岩石具弱或无Eu异常,石英闪长岩和花岗斑岩具相似的微量元素特征,稀土元素配分模式一致,具轻稀土富集、重稀土亏损、富集大离子亲石元素和亏损高场强元素特点。矿区岩体锆石阴极发光照相显示:锆石全部具环带结构,显示岩浆锆石特征。锆石U-Pb年代学显示石英闪长玢岩具岩浆环带锆石的27个测试点206Pb/238U加权平均年龄为(223.2±2.2)Ma(MSWD=0.82);花岗斑岩具岩浆环带锆石的21个测试点206Pb/238U加权平均年龄为(219.9±2.6)Ma(MSWD=0.89)。因此,岩体形成于220 Ma左右,为印支晚期岩石圈拆沉作用产生壳-幔混合岩浆的产物。

The Ela Mountain in the east of Qinghai Province is one of the important structural-magmatic- metallogenetic belts of northern Tibet. In order to discuss the magmatic mineralization in the area, quartz diorite porphyrite and granite-porphyry in the Saishitang polymetallic deposit were selected; whole-rock major and trace elements and zircon U-Pb LA-ICPMS ages were analyzed. Geochemically, they both belong to high-potassium calc-alkalic rock series, with no or weak Eu anomaly, and enrichment of LREE, LILE and depletion of HREE, HFSE. The cathodoluminescence images of zircon of intrusive rocks show all that the zircons are magmatic zircons which have zonal structure. The dating of LA-ICP-MS zircon U-Pb of two samples shows that 27 points of oscillatory zoned domains of quartz diorite porphyrite sample yield a group of weighted mean 206pb/238U ages at （223.2±2.2） Ma （MSWD=0.82） and 21 points of oscillatory zoned domains of granite-porphyry sample yield a group of weighted mean 206pb/238U ages at （219.94±2.6） Ma （MSWD=0.89）. The intrusive rocks were formed about 220 Ma, resulted from lithospheric delemination after crustal thickening due to collision between continental plates in late Indosinian.