Zircon SHRIMP U-Pb ages of gneissic granites in Jiamusi massif, northeastern China.
Zircon SHRIMP U-Pb ages of gneissic granites in Jiamusi massif, northeastern China.
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作者：
Wu Fu
佳木斯花岗质岩体分布广泛，可分为花岗质片麻岩和片麻状花岗岩两大类。花岗质片麻岩经历了500 Ma的角闪岩-麻粒岩相变质作用，具有与基底马山群相同的片麻状构造。片麻状花岗岩以岩浆结晶组构为特征，无后期变质迹象。这些片麻状花岗岩形成于新元古代，但锆石SHRIMP U-Pb测年结果表明，它们侵位于晚古生代，侵位时间为270~254 Ma。部分岩石中的继承锆石颗粒或核支持它们主要是马山群基底岩石部分熔融的产物。矿物组合、化学成分分析表明，这些花岗岩与佳木斯地块与周围微大陆或陆块的碰撞作用有关，或与佳木斯地块内部陆块的碰撞作用有关。
The Jiamusi massif in northeastern China is characterized by the widespread granitic intrusions, which can be divided into two major types, granitic gneisses and gneissic granites. The granitic gneisses had undergone the amphibolite to granulite facies metamorphism of 500 Ma, and have the same gneissic structures as those of Mashan Group of basement. The gneissic granites are characterized by magmatic crystallized fabric and did not show any sign of later stage metamorphism. Though these gneissic granites were thought formed in Neo Proterozoic, our zircon SHRIMP U Pb dating results suggest that they were emplaced in Late Paleozoic of 270～254 Ma. The inherited zircon grains or cores in some of these rocks support that they resulted mainly from the partial melting of the basement rocks of Mashan Group. The mineral associations, chemical compositions of analyzed samples suggested that these granites were related to the suturing between the Jiamusi Massif and surrounding micro continents or terranes, or to the collision of terranes within the Jiamusi Massif.