滇西北羊拉地区金沙江古洋盆的穿时碰撞闭合:来自花岗岩年龄的制约
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摘要
金沙江缝合带是特提斯东段重要的缝合带之一,羊拉地区的金沙江缝合带处在青藏高原东构造结东侧,是研究金沙江古洋盆的碰撞闭合过程等构造事件的重要窗口。在前人工作的基础上,通过野外系统观察取样,结合花岗岩侵入体的锆石SHRIMP U-Pb年龄测定结果,对金沙江古洋盆的碰撞闭合过程做初步研究。结果表明,从南部加仁岩体的通吉格花岗闪长岩(加仁岩体之一部分),经中部的路农—里农—江边岩体的花岗闪长岩,到北部的贝吾花岗闪长岩,岩体的侵位年龄分别为通吉格(246.1±3.5)Ma、路农花岗闪长岩(238.1±5.3)Ma、里农花岗闪长岩(239.0±5.7)Ma、江边岗闪长岩(227.9±5.1)Ma和贝吾花岗闪长岩(213.6±6.9)Ma,表明金沙江缝合带的碰撞关闭是从南向北逐渐闭合的,闭合的时限可达33 Ma,但闭合碰撞不是连续而是幕式的,碰撞闭合作用主要发生在约246 Ma、239 Ma、228 Ma、213 Ma 4个幕次。里农大沟还出现222 Ma的辉绿岩脉,与江边岩体时间上较为接近,似乎表明江边岩体侵入时期本区处于局部拉张的构造背景。
The Jinshajiang suture is one of the important sutures in eastern Tethys.The Yangla section of the Jinshajiang suture covers the east syntax of the Tibetan Plateau and is an important window for studying the collision-closing process of the Jinshajiang paleo-oceanic basin.Based on previous investigations and through field sampling and observation,combining with zircon SHRIMP U-Pb dating of granite intrusions,the authors completed the preliminary research on the collision-closure of the Jinshajiang paleo-oceanic basin.The results show that the emplacement ages of the intrusions in the Jinshanjiang basin are 246.1±3.5 Ma for Tongjige granodioprite in the south (apart of the Jiaren intrusion),238.1±5.3 Ma,239.0±5.7 Ma and 227.9±5.1 Ma respectively for Lunong,Linong and Jiangbian granodiorites in the middle,and 213.6±6.9 Ma for the Beiwu granodiorites in the north.Moreover,the collision-closure of the Jinshajiang paleooceanic basin progressed gradually from south to north with closure time ranging up to 33 Ma.The collision,however,occurred episodically and collision-closure mainly developed in four periods at around 246 Ma,239 Ma,228 Ma and 213 Ma,respectively.The diabases outcropped at Linongdagou as～222 Ma diabasic dyke—close to the age of the Jiangbian granodiorite,suggesting that local tensional tectonic background occurred in the Jiangbian-Linong area at around 222 Ma.
The Jinshajiang suture is one of the important sutures in eastern Tethys.The Yangla section of the Jinshajiang suture covers the east syntax of the Tibetan Plateau and is an important window for studying the collision-closing process of the Jinshajiang paleo-oceanic basin.Based on previous investigations and through field sampling and observation,combining with zircon SHRIMP U-Pb dating of granite intrusions,the authors completed the preliminary research on the collision-closure of the Jinshajiang paleo-oceanic basin.The results show that the emplacement ages of the intrusions in the Jinshanjiang basin are 246.1±3.5 Ma for Tongjige granodioprite in the south (apart of the Jiaren intrusion),238.1±5.3 Ma,239.0±5.7 Ma and 227.9±5.1 Ma respectively for Lunong,Linong and Jiangbian granodiorites in the middle,and 213.6±6.9 Ma for the Beiwu granodiorites in the north.Moreover,the collision-closure of the Jinshajiang paleooceanic basin progressed gradually from south to north with closure time ranging up to 33 Ma.The collision,however,occurred episodically and collision-closure mainly developed in four periods at around 246 Ma,239 Ma,228 Ma and 213 Ma,respectively.The diabases outcropped at Linongdagou as～222 Ma diabasic dyke—close to the age of the Jiangbian granodiorite,suggesting that local tensional tectonic background occurred in the Jiangbian-Linong area at around 222 Ma.
引文
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