【摘要】 北大别岳西地区广泛分布燕山期侵入岩和火山岩。14个岩浆岩样品中锆石LA-ICP-MS U-Pb定年结果显示,这些岩浆岩形成于134~125 Ma之间。以130 Ma为界,岩浆岩可以分为两个期次:早期以石英闪长岩—石英二长闪长岩—似斑状二长花岗岩组合为主;晚期以二长花岗岩—钾长花岗岩组合及脉岩为主。早期岩浆岩含有古元古代(1900~2120 Ma)、新元古代(670~800 Ma)和三叠纪继承锆石;晚期岩浆岩中缺少古元古代继承锆石,以新元古代、三叠纪及140~160 Ma时期的继承锆石为主。高Sr低Y地球化学特征仅出现在早期岩浆岩中,结合继承锆石的年龄特征,表明早期岩浆岩物质来源于加厚的基性下地壳,下地壳的拆沉和岩石圈的减薄发生在约130 Ma;而晚期岩浆岩为以新元古代年龄的中—下地壳在减薄后的环境下发生深熔作用形成。更多还原

【Abstract】 Mesozoic intrusive rocks and volcanic rocks are widely distributed in Yuexi area,North Dabie orogenic belt. Zircon U-Pb dating were carried out using LA-ICP-MS method for fourteen samples,resulting a forming age of 134 ~ 125 Ma. These rocks can be divided into two stages by 130 Ma. The first stage magmatic rocks( > 130 Ma) mainly consist of quartz diorite,quartz monzodiorite and porphyritic monzogranites; while the second stage ones( < 130 Ma) are mostly monzogranites,K-feldspar granites and dyke rocks. The inherited zircons ages in the first stage rocks are made up of Middle Paleoproterozoic( 1900 ~ 2120 Ma),Neoproterozoic( 670 ~ 800Ma),and Triassic; while the second stage rocks are short of inherited zircons of Middle Paleoproterozoic,and have an inherited zircon age composition of Neoproterozoic,Triassic and 140 ~ 160 Ma. Combined the inherited zircon ages composition with the character that magmatic rocks with geochemical features of high Sr,low Y occur only at the early stage,we conclude that the early stage rocks were originated from thickened lower crust,and delamination of the lower crust and thinning of lithosphere happened at ~ 130 Ma; while the late stage rocks results from anatexis of middle to lower crust aged of Neoproterozoic at an after thinning background.更多还原