新疆东准噶尔绿石沟高Ba-Sr石英二长岩的锆石U-Pb年龄、成因及地质意义

Zircon U-Pb age and petrogenesis of the Lushigou high Ba-Sr quartz-monzonite in East Junggar,Xinjiang,and its geological significance

绿石沟岩体位于东准噶尔琼河坝矿集区,向东侵入到绿石沟铜矿赋矿围岩中泥盆统北塔山组火山岩中。LA-ICP-MS锆石U-Pb测年显示该岩体形成于354±1Ma,为早石炭世。其主要岩石类型为石英二长岩,含有大量的基性微粒包体,具有较高的硅、钙、钾含量(SiO_2=62.31%~65.31%,CaO=3.71%~4.89%,K_2O=2.85%~3.54%),属高钾钙碱性系列。铝含量较高(Al_2O_3=15.44%~16.29%),属准铝质(A/CNK=0.93~0.99,A/NK=1.68~1.96)Ⅰ型花岗岩。稀土元素总量较低(ΣREE=90.82×10^(-6)~111.36×10^(-6)),轻稀土元素相对富集,Eu呈弱的负异常(δEu=0.68~0.87)。富集大离子亲石元素(K、Rb、Ba、Sr等),亏损高场强元素(Nb、Ta、P、Ti等),具有高Ba(758×10^(-6)~1113×10^(-6))、Sr(401.8×10^(-6)~512.5×10^(-6))含量和高的(La/Yb)_N、Sr/Y值,显示出高Ba-Sr花岗岩的特征,应是幔源基性岩浆与壳源岩浆混合的产物,可能形成于俯冲环境向造山后环境的构造转换阶段。

The Lüshigou pluton is located in the Qiongheba ore concentration area in East Junggar. This pluton intruded into the host rock of the Lüshigou copper deposit. LA-ICP-MS U-Pb dating of zircons from this pluton yielded an early Carboniferous age of 354±1 Ma. The main rock type of the pluton is quartz-monzonite with many mafic-ultral mafic enclaves inside. These quartz-monzonites have high SiO2 （62.31%～65.31%）, Al2O3 （15.44%～16.29%）, CaO （3.71%～4.89%） and K2O （2.85%～3.54%） contents, exhibiting high-K calc-alkaline and metaluminous characteristics （A/CNK=0.93～0.99,A/NK=1.68～1.96）, and belonging to I-type granite. The total REE values of them are low （90.82×10^-6～111.36×10^-6） with relative enrichment of LREE and Eu negative anomaly （δEu=0.68～0.87）. The primitive mantle normalized trace element patterns are characterized by the enrichment of the LILE （K, Rb, Ba, Sr） and depletion of the HFSE （Nb, Ta, P, Ti）. The quartz-monzonite has high Ba （758×10^-6～1 113×10^-6）, Sr （401.8×10^-6～512.5×10^-6） values with high （La/Yb）N, Sr/Y ratios, distinct Nb, Ta and Ti depletion, and are comprehensively called high Ba-Sr granitoid. These characters indicate that the Lüshigou pluton was probably formed by the magma-mixing of the mantle-derived mafic magma and crustal partial melting magma during the tectonic transition period from subduction to post-orogenic setting in the late Paleozoic.