内蒙古图林凯蛇绿岩中埃达克岩SHRIMP测年:早古生代洋壳消减的证据

SHRIMP Dating of Adakites in the Tulingkai Ophiolite, Inner Mongolia: Evidence for the Early Paleozoic Subduction

内蒙古图林凯蛇绿岩中,新发现了埃达克岩,岩性包括石英闪长岩、奥长花岗岩、斜长岩和英安岩。它们是温都尔庙—图林凯早古生代消减带的一种岩浆岩标志。精确的SHRIMP U-Pb测年表明:①石英闪长岩侵位于约467±13Ma,说明温都尔庙古洋壳的消减可能始于约467±13Ma或更早。随后不久,这一岩石经历了约451±18Ma的高级变质和部分熔融事件。②英安岩喷发于约459±8Ma,奥长花岗岩形成略晚,约451±7Ma,最后形成了斜长岩的岩墙,其时代约为429±7Ma。据此认为,温都尔庙—图林凯古洋壳在早古生代时期,经历了愈38Ma的消减事件。

The newly recognized adakites in the Tulingkai ophiolite, Inner Mongolia, lithologically including quartz diorite, trondhjemite, anorthosite and dacite, are magmatic markers of the Early Paleozoic Ondor Sum-Tulingkai subduction zone. The rocks are precisely dated using SHRIMP. The quartz diorite intruded at 467± 13 Ma, implying that the oceanic subduction started at this time or earlier. Shortly afterwards, at about 451± 18 Ma, the high-grade metamorphism and/or partial melting took place. The dacite erupted at 459 ± 8 Ma, the trondhjemite intruded at 451 ± 7 Ma, and finally, the anorthosite dike was formed at 429 ± 7 Ma. It is therefore suggested that the time interval of the Early Paleozoic subduction of the Ondor Sum-Tulingkai oceanic crust is over 38 Ma.