大兴安岭北段高地林场满克头鄂博组火山岩年代学、地球化学特征及其构造意义

Geochronology and geochemical characteristics of volcanic rocks of Manketou ebo Formation in Gaodi forest farm,northern Great Xing an Range,and their tectonic implications

对大兴安岭北段高地林场地区满克头鄂博组火山岩进行LA-ICP-MS锆石U-Pb定年和岩石地球化学研究,以限定其岩石成因及成岩构造背景。定年结果显示:火山岩年龄为(149±1)Ma,形成于晚侏罗世。岩石地球化学特征具有高硅、富碱、贫钙、贫镁,为高钾钙碱性弱过铝质岩石;稀土总量(ΣREE)为124.32×10^(-6)~189.41×10^(-6),LREE/HREE比值为8.72~16.35,轻重稀土明显分馏。岩浆具有壳源特征,来源于浅部地壳物质的部分熔融。综合区域地质背景,研究区满克头鄂博组火山岩为蒙古-鄂霍次克洋闭合后造山伸展环境下形成的。

LA-ICP-MS zircon U-Pb dating and whole-rock geochemistry were conducted for the volcanic rocks of Manketou ebo Formation in the Gaodi forest farm area,northern Great Xing an Range,with the aims of constraining their petrogenesis and tectonic setting.The dating results show that the eruptive age of the volcanic rock is(149±1)Ma,i.e.Late Jurassic.In terms of geochemical characteristics,the studied samples are characterized by high silicon,rich alkali,poor calcium,and poor magnesium,belonging to high potassium calc-alkaline weak peraluminous rocks.They have total rare earth element(ΣREE)contents of 124.32×10^(-6)~189.41×10^(-6)and LREE/HREE ratios of 8.72~16.35,indicating a significant fractionation between LREE and HREE.Their magmas originated from the partial melting of shallow crustal materials.Combined with regional geological background,the authors propose that the volcanic rocks of the Manketou ebo Formation were formed in the post-orogenic extensional setting after the closure of Mongolia--Okhotsk Ocean.