西准噶尔克拉玛依花岗岩体地球化学特征及其意义

西准噶尔克拉玛依岩体为二长花岗岩和斜长花岗岩等,为海西中期侵入岩体,具有高钠、铝等特点,A/CNK=0.71~0.78,NK/A为0.8~0.89,为偏铝质钙碱性花岗岩.轻稀土元素中等富集,Eu弱亏损,富集大离子亲石元素,Nb、Ta亏损,富Sr,La/Yb值相对低.多种主微量元素和同位素的综合图解分析表明,该岩体为I型花岗岩,与达拉布特断裂西侧同时期的庙尔沟A型花岗岩具有明显的区别,盆地具有较为年轻的地壳基底.克拉玛依岩体为岛弧花岗岩,晚石炭世准噶尔地区仍存在着洋盆体制.

GEOCHEMICAL CHARACTERISTICS OF THE KARAMAY GRANITOIDS AND THEIR SIGNIFICANCE IN WEST JUNGGAR, XINJIANG

Granitoids types in the Karamay, West Junggar, include monzogranite and granodiorite. The rocks are alkali-rich (K2O Na2O,6.5% on average), and have an average Na2O /K2O value of 1.82, A/CNK value of 0.71~ 0.78 (less than1) and NK/A value of 0.8~0.89 (0.85 on average), attributed to metaluminous calc-alkaline series but closing to calcic. The chemical analysis results of major, rare and trace elements show that the rocks belongs to the I-type graanitoids, with high Sr and positive Ba, Th, U, Zr and Hf anomalies and negative Nb, Ta and Eu anomalies, suggesting island arc rocks characteristics. Combined with the published results of isotopes of the rocks and regional geological data, we suggest that oceanic mechanism and arc systems formed during the early late Carboniferous periods (320~305Ma) and that the basement of the Junggar basin is dominated by juvenile crust.