西藏达金海相碎屑岩的组成、地球化学特征及其构造背景

Detrital Modal,geochemical characteristics and tectonic setting of the Dajin marine clastic rocks,Tibet.

达金海相碎屑岩出露于西藏冈仁波齐峰山脚下,长期以来,该套岩石与冈底斯砾岩一起被视为印度-亚洲板块碰撞形成的陆相磨拉石。该套岩石组合是由凝灰质粉砂岩、杂砂岩、含砾杂砂岩和砾岩组成的一套深海-浅海相沉积组合。杂砂岩、砾岩碎屑组成与地球化学组成研究表明,该套岩石组合的形成与岛弧的发展密切相关,源区大地构造背景以岛弧为主,但也存在被动大陆边缘和碰撞构造带(蛇绿混杂带)两个不同构造背景的源区。区域上,在该套岩石组合的北侧存在着冈底斯岛弧带,南侧为雅鲁藏布蛇绿混杂带。这些特征共同表明,达金海相碎屑岩是西藏雅鲁藏布缝合带与冈底斯岛弧带之间的日喀则弧前盆地的一部分。

The Dajin marine clastic rocks outcropped in the Gangriboche Mountain area, western Tibetan, which was previously regarded as a part of nonmarine molasse together with Gangdese conglomerates formed by India-Eurasia collision. So far, detrital assemblage, source area, and tectonic setting of this unit have not been studied in detail. This paper presents detrital modal from statistic petrological data of conglomerates and greywacke as well as geochemical data of the greywacke and siltstones which are used to study and discuss their source area and tectonic setting based on their sedimentary sequences. These data indicate that source area of the Dajin marine deposits is characterized by combination of continental arc, oceanic island arc and passive continental margin, and that the Dajin marine deposits may deposit in a forearc basin.