泰国北部晚泥盆世后碰撞岩浆岩:对特提斯演化的启示

Late Devonian Post⁃Collisional Magmatic Rocks in Northern Thailand:Implication for the Tethyan Evolution

东南亚特提斯构造带的研究主要集中在晚古生代古特提斯的演化,而对于原特提斯演化的研究非常薄弱.对泰国北部花岗岩和角闪辉长岩进行了锆石U-Pb年代学、地球化学及锆石Lu-Hf同位素研究.这些岩浆岩的加权平均年龄为367~361 Ma,时代为晚泥盆世.泰北花岗岩属高钾钙碱性A2型花岗岩,具备LILE相对富集,HFSE相对亏损的地球化学特征,具明显的Nb、Ta、Sr和Ti的负异常.Hf同位素具有正εHf(t)值(+5.43~+10.91),T_(DM2)年龄在1015.0~668.9 Ma之间,来源于年轻的镁铁质下地壳.角闪辉长岩具高含量的Al_(2)O_(3)、Zr和Nb,低含量的TiO_(2)、Ni,LILE相对富集和HFSE相对亏损,明显的Nb和Ta负异常,类似于岛弧钙碱性玄武岩特征.正的εHf(T)值(+1.24~+9.11)和高的Mg^(#)(50.0~64.8)表明其来源于亏损的地幔楔.根据泰国北部岩浆岩U-Pb年龄、Hf同位素及地球化学特征,认为它们形成于晚泥盆世后碰撞伸展构造背景下,可以与缅甸东部、云南西南部同期原特提斯地质记录对比,该成果为滇西南及东南亚地区原特提斯演化提供了依据.

The studies of the Tethys tectonic belt in Southeast Asia mainly focus on the evolution of the Paleo-Tethys in the Late Paleozoic,while the studies of the Proto-Tethys evolution immediately are pretty weakThe present study focuses on zircon U-Pb geochronology,geochemistry and zircon Lu-Hf isotopes of granites and hornblende gabbros from northern Thailand.These magmatic rocks yielded zircon U-Pb weighted mean age of 367-361 Ma.The geologic age is the Late Devonian.The northern Thailand granites are the high-K calc-alkaline A2 type granites,with the geochemical characteristics of relatively enriched LILE and relatively depleted HFSE,with obvious negative anomalies of Nb,Ta,Sr and Ti.The Hf isotopes have positiveεHf(t)values(+5.43-+10.91)with T_(DM2) ages of 1015.0-668.9 Ma,indicating a juvenile mafic lower crust source.The hornblende gabbros showhigh Al_(2)O_(3)、Zr and Nbcontents,but low contents of TiO_(2) and Ni,with the geochemical characteristics ofrelatively enriched LILE and relatively depleted HFSE,with the distinctly negative Nb and Ta anomalies,similar to the characteristics of island arc calc-alkaline basalts.PositiveεHf(t)values(+1.24-+9.11)and high Mg^(#)(50.0-64.8)indicate that it originates from the depleted mantle wedge.Based on the U-Pb age,Hf isotope and geochemical characteristics of the magmatic rocks in northern Thailand,it is believed that they were formed in the Late Devonian post-collisional extension-related tectonic setting,which can be compared with the corresponding the Proto-Tethys geological records in eastern Myanmar and southwestern Yunnan.The results provide evidence for the evolution of the Proto-Tethys in southwest Yunnan and Southeast Asia.