摘要
内蒙古东部出露的锡林格勒杂岩主要由中元古代原岩为火成岩的黑云母片麻岩和斜长角闪岩透镜体组成。片麻岩显示轻稀土元素富集的中等分异特征 ,具明显的Eu负异常 ,其不相容元素特征与平均地壳类似但相对亏损Ba和Sr。斜长角闪岩构成一条Sm -Nd等时线 ,其年龄值为12 0 2± 6 5Ma ,εNd(1.2 0Ga)值为 6 .8。角闪岩的亏损地幔模式年龄 (tDM,1.2 6～ 1.32Ga)与其Sm -Nd同位素等时线年龄接近。角闪岩的Rb -Sr同位素等时线年龄为 393± 14Ma ,其87Sr/ 86 Sr初始比值为 0 .70 379± 0 .0 0 0 0 7,此Rb -Sr等时线年龄与本区出露的篮片岩Ar-Ar年龄 (～ 383Ma)一致 ,记录了中亚造山带东南部洋壳俯冲结束后由大陆碰撞造山引起的变质作用事件。黑云母片麻岩的Rb -Sr同位素等时线年龄为 2 79.5± 6 .4Ma ,87Sr/ 86 Sr初始比值为 0 .70 85 1± 0 .0 0 0 10 ,此Rb -Sr等时线年龄与本区广泛分布的早二叠世火山岩的Rb -Sr等时线年龄 (～ 2 77± 15Ma)一致 ,因此可能是由大规模岩浆活动诱发的变质作用的记录。锡林格勒杂岩因此不仅记录了Rodinia超大陆聚合的地质事件 ,并且通过对比研究本地区蛇绿岩和晚古生代岩浆岩的演化历史 ,可以恢复从Ro dinia超大陆聚合 (～ 1.2 0Ga)到古亚洲洋关闭 (～ 4 30Ma)、大陆碰撞造山 (～
The metamorphic rocks in Xilingele complex mainly consist of biotite gneisses with plagioclase amphibolite lenses. The gneisses show medium fractionated LREE-enriched pattern with obvious negative Eu anomalies. Their incompatible trace element concentrations are similar to the average continental crust but with depletions of Ba and Sr. One Sm-Nd isochron for amphibolites yields an age of 1 202 ±64 Ma with ε_(Nd)(t) value of +6.8. The Rb-Sr isochron for amphibolites yields an isochron age of 393 ±14 Ma with an initial ^(87)Sr/^(86)Sr ratio of 0.703 79. This Rb-Sr isochron age is consistent with the Ar-Ar age ((～383) Ma) of the blueschists in this region, and is ～40 Ma younger than the Rb-Sr isochron age of Hegenshan ophiolite. It probably recorded the metamorphism caused by the continental collision after the closure of the Paleo-Asian Ocean, which finally led to the continental collision of the north China craton with the Siberian craton. The Rb-Sr isochron for the gneisses yields an age of 279 ±6.4 Ma with an initial ^(87)Sr/(^(86)Sr) ratio of 0.708 51, which is consistent with the age of volcanic rocks (～277 Ma) most-widely distributed in this region. Such coincidence probably implies that the metamorphism recorded in the studied gneisses was caused by magmatic processes during Early Permian. The geochemistry of the Xilingele complex thus recorded not only the Rodinia accretion processes, but also the closure event of the Paleo-Asian Ocean (～430 Ma), continental collision (～390 Ma) and post-collisional magmatism ((～280 Ma)) by comparing the ophiolites and magmatic rocks in this region.
出处
《高校地质学报》
CAS
CSCD
2004年第3期343-355,共13页
Geological Journal of China Universities
基金
国家重大基础研究项目 (973项目
编号 2 0 0 1CB4 0 980 7)资助
