内蒙古中部达茂旗地区三叠纪花岗岩和钾玄岩的地球化学、年代学和Hf同位素特征

Geochemistry,Geochronology and Hf isotopic compositions of Triassic granodiorite-diorite and shoshonite from the Damaoqi area,central Inner Mongolia,China

内蒙古索伦山缝合带南侧达尔罕茂明安联合旗北部分布有车根达来花岗闪长岩-闪长岩和西别河火山岩。车根达来花岗闪长岩为高钾或中钾钙碱性系列岩石,化学成分相当于埃达克岩。闪长岩为中钾钙碱性系列岩石,呈大小不等的包体产于花岗闪长岩中,化学成分相当于正常岛弧深成岩。但是,花岗闪长岩[εHf(t)=-4.56～-1.56]和闪长岩[εHf(t)=-5.01～-1.88]锆石Hf同位素组成指示其源区为古老的(镁铁质)陆壳或富集地幔。锆石SHRIMPU-Pb定年给出车根达来花岗闪长岩的年龄为245Ma±1Ma,闪长岩包体的形成年龄为239Ma±2Ma。西别河火山岩为钾玄岩,喷发年龄为224Ma±2Ma。火山岩以大量的、年龄分散的捕虏晶(260～1556Ma)为特征,指示了大陆背景。这些三叠纪侵入岩和火山岩形成于古亚洲洋闭合(中晚二叠世)之后,没有明显的构造变形,应为中亚造山带的造山后演化的岩浆岩记录。

We report new geochemical data and SHRIMP zircon ages for the Chegendalai granodiorite-diorite and the Xibiehe volcanic rocks, from the northern Damaoqi area south of the Permian Solenker suture. The Chegendalal granodiorites are high-K or medium-K calc-alkaline rocks and are compositionally similar to adakite. Diorite at Chegendalai is a medium-K calc-alkaline, normal island arc-like plutonic rocks, and occurs as variable-sized xenolith in granodiorite. However, Hf isotopic compositions of zircons from the granodiorite [εHf（t）=-4.56～-1.56] and diorite [εHf（t）=-5.01～-l.88] indicate that the magmas originated form partial melting of an old mafic crust or enriched mantle and suggest a continental setting for magma genesis. The Chegendalal granodiorite has a SHRIMP zircon age of 245±1 Ma, and a diorite within granodiorite from the same outcrop is dated at 239±2 Ma. The Xibiehe volcanic rocks belongs to shoshonitic series, and the eruption time is determined at 224±2 Ma. This volcanic rocks contains zircon variably sourced xenocrysts of ca. 260-1556 Ma, indicating a continental setting. These Triassic rocks, which were formed in a continental setting, generally undeformed and postdated closure of the Paleo-Asian Ocean （Mid-Late Permian）, are therefore interpreted to record the post-orogenic （or post-tectonic） evolution of the Central Asian Orogenic Belt.