小兴安岭早白垩世福民河组高硅流纹岩锆石U-Pb定年、地球化学特征及地质意义  

Zircon U-Pb dating,geochemical characteristics and geological implications of Early Cretaceous high-silica rhyolites from Fuminhe Formation in Lesser Xing an Range

作　　者：王奕朋 裴福萍[1] 周皓[1] 焦骥 魏敬洋 宋凯 WANG Yi-peng;PEI Fu-ping;ZHOU Hao;JIAO Ji;WEI Jing-yang;SONG Kai(College of Earth Sciences,Jilin University,Changchun 130061,China)

机构地区：[1]吉林大学地球科学学院,长春130061

出　　处：《世界地质》2021年第2期229-239,255,共12页World Geology

基　　金：国家重点基础研究发展计划项目(2017YFC0601204);吉林大学研究生创新基金项目(101832020CX220)联合资助。

摘　　要：笔者对小兴安岭地区福民河组火山岩进行了岩石学、锆石U-Pb年代学及地球化学的研究,探讨了火山岩的成因和构造背景。福民河组火山岩由粗面岩和流纹岩组成,流纹岩中锆石呈自形-半自形,发育震荡生长环带,并具有较高的Th/U比值(0.41~0.81),表明其为岩浆成因。它们的^(206)Pb/^(238)U加权平均年龄为(105±1)Ma,即形成于早白垩世。福民河组流纹岩具有较高的SiO_(2)含量(71.80%~80.78%),总体属于碱性系列岩石,富集轻稀土元素,亏损Ti、Sr、P、Ba和Eu等元素(δEu=0.13~0.49),其特征与高硅流纹岩相似。福民河组流纹岩与美丰组火山岩具有相似的稀土和微量配分型式,主量元素在哈克图解中呈线性相关,表明福民河组与美丰组火山岩是同源岩浆演化的产物。福民河组粗面岩和流纹岩中的钾长石和石英出现重熔特征,暗示岩浆房经历了新的热源加热。福民河组流纹岩是由早期岩浆形成的晶粥体重新受热,进一步发生分离结晶作用形成。研究表明,小兴安岭地区早白垩世火山岩应形成于古太平洋板块向欧亚大陆之下俯冲-回撤作用的伸展背景。This study reports petrology,zircon U-Pb geochronological and geochemical analysis for volcanic rocks from Fuminhe Formation in Lesser Xing'an Range,to reveal their petrogenesis and tectonic setting.The volcanic rocks collected from Fuminhe Formation are composed of trachytes and rhyolites.Zircons from the rhyolite are euhedral-subhedral in shape and show oscillatory growth zoning,and relatively high Th/U ratios(0.41~0.81),indicating a magmatic origin.The weighted mean of^(206)Pb/^(238)U age for the rhyolite is(105±1)Ma.The results suggested that the rhyolites were formed in Early Cretaceous.The rhyolites from the Fuminhe Formation have high content of SiO_(2)(71.80%~80.78%),belonging to alkaline series.Additionally,they show enrichment of LREEs,depletion of Ti,Ba,P,Sr and Eu(δEu=0.13~0.49),which are similar to those of high-silica rhyolites.The rhyolites from the Fuminhe Formation are similar to the volcanic rocks from the Meifeng Formation in the distribution of trace elements and rare earth elements,and their major elements show linear correlation in Harker diagrams,indicating that volcanic rocks from Fuminhe Formation and Meifeng Formation were derived from the same magma source.The K-feldspar and quartz of the trachytes and rhyolites from Fuminhe Formation show resorption texture,implying that the entire magma chamber was reheated by the later heat source.It is concluded that the rhyolites from the Fuminhe Formation were derived from the reheated early magma mush and experienced further fractional crystallization.The results of this study suggest that Early Cretaceous volcanic rocks in Lesser Xing'an Range formed in an extensional environment related to the rollback of the subducting Paleo-Pacific plate beneath Eurasia.

关 键 词：小兴安岭 高硅流纹岩 晶粥体 福民河组 美丰组 早白垩世 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]