印度尼西亚苏门答腊岛Sarudik地区A型花岗岩锆石U-Pb年龄及其构造意义

A-type granite of granite complex in Sarudik area,Sumatra:Zircon U-Pb ages and its tectonic implication

苏门答腊岛位于印度尼西亚西缘,大地构造位置处于印度-澳大利亚板块向欧亚板块俯冲的前缘地区,实武牙复式花岗岩体是该岛规模较大的花岗岩体,至今仍缺少高精度年代学研究,制约了对其岩石成因和区域构造演化的深入认识。本文对Sarudik地区实武牙岩体黑云母二长花岗岩进行了LAICP-MS锆石U-Pb年龄测定,获得其年龄值为225.3±0.8Ma,表明成岩时代为晚三叠世。前人岩石地球化学研究指示其为A1型花岗岩,结合苏门答腊岛区域地质研究结果,晚三叠世实武牙地区总体处于陆内伸展环境,实武牙复式岩体Sarudik地区黑云母二长花岗岩是中-晚三叠世苏门答腊岛局部地壳伸展减薄、岩浆上侵的产物。

Sumatra is located in the most west of Indonesia and is subject to the subduction of the India- Australia Plate beneath the Eurasian Plate. Sibolga, one of the largest granites in Sumatra, still lacks high- precision geochronological research, which prevents the advance of knowledge in its petrogenesis and tectonic evolution. Biotite monzogranite from Sarudik area, Sumatra was assigned to granite of A1 type by previous geochemical research. The present study conducted LA-ICP-MS Zircon U-Pb age analysis on the identical granite,yielding an age of 225.3 - 0.8 Ma and indicating its formation in late Triassic. Combined with the results from previous study,it is proposed that Sibolga and adjacent areas were dominated by within-plate tectonic environment during late Triassic period, which coincides with the results from regionally geological studies. It is further concluded that late Triassic Al-type granite in study area is associated with locally crust extending and thinning throughout Sumatra during mid-late Triassic.