新疆肯登高尔铜钼矿区侵入岩年代学、地球化学及其大地构造意义

Geochronology and Geochemistry of the Pluton in the Kendenggaoer Cu-Mo Ore District,Xinjiang and Their Tectonic Implication

肯登高尔铜钼矿床是新疆西天山博罗科努成矿带中一处矽卡岩型矿床,矿体赋存于纳林果勒中酸性侵入体与上石炭统东图津河组钙质粉砂岩夹碳酸盐岩的接触带上。纳林果勒岩体主要由花岗闪长岩与二长花岗岩组成。通过LA-ICP-MS锆石U-Pb同位素定年,获得花岗闪长岩和二长花岗岩的加权平均年龄分别为316.3±3.5Ma和298.9±3.3Ma,表明两者侵位时代分别为晚石炭世和早二叠世。地球化学组成上花岗闪长岩具有高硅和高钠的特征,富集Sr、Rb和Th,亏损Nb、Ta、Yb和Y,无Eu异常,岩石具有埃达克岩的特征,是造山晚期加厚下地壳部分熔融的产物。二长花岗岩具有富硅、富钾、低铝的特征,富集Rb、Th、Nb和Hf,亏损Sr、Ta和Ti,具有明显Eu负异常,岩石为高分异I型花岗岩,是岩石圈伸展减薄背景下,下地壳进一步熔融形成的基性岩浆通过分离结晶作用形成的产物。结合成岩年龄和区域构造背景,推测西天山北缘在晚石炭世进入碰撞造山阶段,在早二叠世向造山后伸展阶段过渡。

The Kendenggaoer skarn Cu-Mo deposit,located in the Boluokenu metallogenic belt,is hosted in contact zone between the Dongtujiinhe Formation and the Nalinguole pluton.The Nalinguole pluton consists of granodiorite and monzogranite.LA-ICP-MS zircon U-Pb dating yielded weighted average ages of 316.3±3.5 Ma for granodiorite and 298.9±3.3 Ma for monzogranite respectively,indicating that the granodiorite intruded in the Late Carboniferous,while the monzogranite intruded in the Early Permian.Geochemically,granodiorite from the Nalinguole pluton is characterized by high contents of SiO2 and Na2 O,enrichment in Sr,Rb and Th and depletion in Nb,Ta,Yb and Y.all samples show no Eu anomalies and are similar to adakites,indicating that they were derived from partial melting of lower crust during late orogenic stage.Monzogranite has high contents of SiO2 and K2 O and low content of Al2 O3.All samples are enriched in Rb,Th,Nb,Hf and depleted in Sr,Ta and Ti,with obvious negative Eu anomalies,suggesting that they were generated by fractional crystallization of basic magma which was derived from further melting of the source region with the lithosphere reduction.Combining with both dating results,it can be inferred that the northwestern margin of Tianshan began to enter collisional orogenic stage in Late Carboniferous and gradually transited into post-orogenic stage in Early-Permian.