桐柏增生造山带早古生代中酸性侵入岩岩石成因与陆壳增长

Accretionary orogens are viewed as the main sites of continental crust growth. However, it is not well known on the mechanism and geodynamic settings of continental crust generation during orogenic evolution. The Early Paleozoic geological units of the Tongbai orogen record the southward accretionary process of the North China Block, and thus it provides an optimal area to address the issue on growth of continental crust. The Taoyuan and Huanggang batholiths are two main Early Paleozoic plutons in the Tongbai orogen, which are composed of biotite granites, trondhjemites, granodiorites, quartz diorites, and diorites with some mafic enclaves. This project will carry out an integrated study of petrology, geochronology, whole-rock major and trace elements and Sr-Nd-Pb isotopes, in situ mineral major and trace elements as well as zircon Hf-O isotopes for the Taoyuan and Huanggang plutons, with aims to: 1) reveal the precise formation ages, nature of sources, evolutionary processes of magma and geodynamic settings and 2) perceive the potential information of new crustal addition. Combined with previous studies on modern magmatic arcs, this project will discuss the mechanism of continental crust generation in accretionary orogens.

增生造山带被认为是大陆地壳增长的重要场所，然而目前关于造山过程中大陆地壳的形成机制以及动力学背景缺乏清晰的认识。桐柏造山带内的早古生代地质单元记录了华北板块向南增生过程，是研究大陆地壳增长的理想场所。桃园和黄岗岩体是桐柏造山带内两个最重要的早古生代岩体，主要由黑云母花岗岩、奥长花岗岩、花岗闪长岩、石英闪长岩和闪长岩等组成，并含有暗色包体。本项目拟通过对桃园与黄岗岩体开展详细的岩石学、年代学、全岩主微量元素和Sr-Nd-Pb同位素、矿物微区主微量元素以及锆石Hf-O同位素分析，揭示这些岩体的精确形成时代、源区性质、岩浆演化过程以及形成的动力学背景，并甄别其中可能蕴含的新生地壳信息。结合前人对现代岩浆弧的研究，本项目将探讨增生造山带内的陆壳形成机制。

本项目选取桐柏造山带桃园和黄岗岩基为研究对象，通过详细的岩石学，全岩地球化学，锆石U-Pb年代学以及Hf-O同位素分析，结合区域地质背景，准确限定了这两个岩基不同岩性单元的形成时代，系统探讨了其源区性质、形成过程和动力学背景。在总结前人资料的基础上，阐明了花岗岩类岩石形成与大陆地壳生长和岩石圈演化关系，通过对比增生造山带内不同块体内陆壳增长方式的异同，明确提出洋弧地体的增生是大陆地壳增长的主要方式。