腾冲和保山地块广泛分布晚白垩世岩浆岩,主要集中于腾冲地块中部和保山地块西缘的龙陵-象达-平河地区,关于其岩浆起源、成岩构造背景、动力学机制以及其与新特斯洋演化的关系一直以来没有得到很好的约束.本文对滇西保山地块西缘象达岩基晚白垩世花岗进行了详细的岩石学、锆石U-Pb年代学、Hf同位素和全岩地球化学研究.年代学研究结果表明,象达岩基晚白垩世花岗形成于～91 Ma、～83 Ma和～76 Ma;矿物组成和主量元素组成上,象达岩基晚白垩世花岗岩普遍发育白云母,具高SiO2 含量和总碱含量,以及高铝饱和指数(A/CNK>1.21),低P2O5、MgO、TiO2 含量等特征,属于高分异的 S 型花岗岩.微量元素组成特征和富集的锆石Hf同位素组成表明,象达岩基晚白垩世花岗岩是古老的上地壳泥质岩石脱水部分熔融,并经历斜长石、磷灰石和含钛铁矿物分离结晶作用的产物.基于前人对青藏高原和滇西地区班公湖-怒江中特提斯洋演化过程的研究结果,滇西保山地块西缘象达岩基晚白垩世 100～70 Ma的花岗岩应该是新特提斯洋板片俯冲的产物.综合分析显示,腾冲-保山地块晚白垩世岩浆作用具多幕次爆发性特点,这些多幕次的岩浆爆发作用是新特提斯洋壳板片俯冲角度多期次调整的结果.
Genesis and Geotectonic Significance of Late Cretaceous Granites from the Xiangda Batholith on the Western Margin of the Baoshao Terrane of Western Yunnan
Late Cretaceous magmatic rocks are widely distributed in the Tengchong and Baoshan Blocks.They are mainly concentrated in the central part of the Tengchong Block and the Longling-Xiangda-Pinghe area on the western margin of the Baoshan Block.The origin,diagenetic tectonic setting,and dynamic mechanism of these magmatic rocks and their relationship with the evolution of the Neo-Tethys Ocean have not been well constrained.In this study,detailed petrology,zircon U-Pb chronology and Hf isotope,and whole-rock geochemistry of Late Cretaceous granites of the Xiangda batholith in the western margin of the Baoshan Block in Western Yunnan were investigated.The chronological results show that the Late Cretaceous granites of the Xiangda batholith were formed at ca.91 Ma,ca.83 Ma,and ca.76 Ma.In terms of mineral composition and geochemistry,Late Cretaceous granites of the Xiangda batholith generally have muscovite,showing high SiO2 content,total alkali content,aluminum saturation index(>1.21),and low P2O5,MgO,and TiO2,indicating that they belong to highly evolved S-type granites.The elemental and enriched zircon Hf isotope compositions show that the Late Cretaceous granites of the Xiangda batholith are the product of dehydration and partial melting of the ancient upper crust argillaceous rocks.During its formation,it experienced the separation and crystallization of plagioclase,apatite,and titanium-bearing iron minerals.Based on the results of previous studies on the evolution process of the Qinghai-Tibetan Plateau and the Bangong-Nujiang Ocean in Western Yunnan,the Late Cretaceous 100-70 Ma granites of the Xiangda batholith in the western margin of the Baoshan block in Western Yunnan were likely the product of subduction of the Neo-Tethys oceanic plate.Further comprehensive analysis of the tectonic evolution characteristics of the Qinghai-Tibetan Plateau and Western Yunnan since the Cenozoic,as well as the multiple episodes of the Late Cretaceous magmatism in the Tengchong-Baoshan Block,we believe that the multiple episodes of Late Cretaceous magmatism in the Baoshan-Tengchong Block are the result of multiple increases and adjustments in the subduction angle of the Neo-Tethys oceanic crust.
Late CretaceousS-type granitethe western margin of the Baoshan BlockNeo-Tethys Oceanplate subduction
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维普
