西藏改则县错果错地区则弄群火山岩岩石地球化学特征及其构造意义

GEOCHEMICAL CHARACTERISTICS AND TECTONIC SIGNIFICANCE OF ZENONG GROUP VOLCANIC ROCKS IN CUOGUOCUO AREA OF GAIZE, TIBET

错果错地区晚侏罗—早白垩世则弄群火山岩主要由酸性火山熔岩及其火山碎屑岩组成,总体上具有高Si低Al,富K贫Na,低Sr低Y(Yb)及强不相容元素和LREE相对富集,Nb、Ta呈负异常,特别是Sr、P、Ti为强烈的负异常,以及δEu负异常明显等特点,揭示了错果错地区的则弄群长英质火山岩很可能是幔源基性岩浆的热量促使地壳物质脱水发生重熔的产物,暗示其形成的大地构造背景很可能与班公湖—怒江洋南向的俯冲作用有关。

Late Jurassic- Early Cretaceous Zenong Group volcanic rocks are mainly composed of acidic volcanic lava and its pyroclastic rocks in Cuoguocuo area. The geochemistry result show that volcanic rocks of Zenong Group are characterized by high Si O2,K,low Al,Na,Y（Yb） content, strong incompatible elements,relative enrichment of LREE, Nb, Ta negative anomalies, Sr, P, Ti strong negative anomalies, δEu significant negative anomalies, that feature reveals the felsic volcanic rocks of Zenong Group might be products of the dehydration and remelting of crustal materials caused mainly by the heat of the mantle basic magma with the participation of some mantle materials. The tectonic setting of the magmatic rocks of Zenong Group was probably associated with the southward subduction of the Bangong Lake-Nujiang River Tethys oceanic crust.