中天山卡瓦布拉克地区彩霞山花岗岩体年龄及成因

Age and Petrogenesis of the Caixiashan Granitic Pluton in the Kawabulake Area,Central Tianshan

彩霞山花岗岩体位于中天山南缘的卡瓦布拉克地区,由糜棱岩化二长花岗岩和斑状钾长花岗岩组成,其LA-ICP-MS锆石U-Pb年龄分别为(330.0±3.6)Ma、(333.3±3.6)Ma;其锆石εHf(t)分别为5.23~0.87和10.85^-5.81,tDM2分别为1.28~1.00Ga和1.7~0.65Ga。地球化学分析结果显示,二长花岗岩和斑状钾长花岗岩的A/CNK、Na2O+K2O值分别为6.40、45.91和4.17、33.19,均属于高钾钙碱性过铝质I型花岗岩。富集轻稀土元素,具有强烈的铕负异常(δEu=2.76~4.14)。糜棱岩化二长花岗岩同构造侵位的显微构造特征揭示卡瓦布拉克韧性剪切带至少在早石炭世晚期处于活动状态。结合区域地质资料,认为彩霞山花岗岩体形成于南天山洋向北俯冲的活动大陆边缘环境,代表中天山南缘晚古生代岩浆弧的一部分。

The Caixiashan granitic pluton,which consists of mylonitized monzonitic granite and porphyritic moyite,is located in the Kawabulake area of the southern Central Tianshan. The LA-ICP-MS zircon U-Pb dating results show that those granitoids were formed at( 330. 0±3. 6) Ma and( 333. 3 ± 3. 6) Ma respectively. The εHf( t) values of mylonitized monzonitic granite vary from 5. 23 to 0. 87 with the tDM2 values of 1. 28-1. 00 Ga,while the εHf( t) values of porphyritic moyite vary from 10. 85 to-5. 81 with tDM2 values of 1. 7-0. 65 Ga. Geochemical analyses indicate that the A/CNK,Na2 O+K2 O ratios are 6. 40 and 45. 91 for the mylonitized monzonitic granite and 4. 17 and 33. 19 for the porphyritic moyite,and respectively. Both of them belong to the high-K calc-alkaline peraluminous I-type granite. They have relatively enriched in LREE with obviously negative Eu anomalies(δEu = 2. 76-4. 14). Microstructural features of syntectonic emplacement for themylonitized monzonitic granite indicate that the Kawabulake ductile shear zone was in an active state at least during the late agee of Early Carboniferous. Integrating with the regional geological data,It is believed that the Caixiashan pluton was formed in an active continental margin arc setting caused by the norward subduction of the South Tianshan Ocean and it represents a part of the Late Paleozoic magmatic arc in southern margin of the Central Tianshan.