中祁连拉脊山混杂带的岩石组成和增生造山过程

This study is focused on the Lajishan mélange to aim at the problem of the early Paleozoic tectonic evolution of the Central Qilian belt. Based on detailed field investigation and the large scale geological mapping, we will identify the characteristics of rock assemblages, spatial distribution and structure styles of the matrix and blocks in the Lajisha mélange. Using the sedimentology, structural geology, petrology and geochemistry, zircon SHRIMP (LA-ICPMS) U-Pb dating, muscovite Ar-Ar isotopic dating and Sr-Nd-Hf isotopic tracer methods, We intend to disclose the petrogenesis and tectonic setting, and determine the formation ages, and meanwhile probe into the ancient tectonic framework and dynamic mechanism of the early Paleozoic Lajishan mélange. This study has important significance for revealing the accretionary orogenic process of the Lajishan mélange in early Paleozoic era, on the other hand, it will provide valuable informations and geological evidences for the comprehensive and reasonable establishment of the tectonic evolution model of the Central Qilian belt.

针对早古生代中祁连大地构造演化问题，拟以中祁连拉脊山混杂带为研究对象，在详细的野外地质调查和重要区段大比例尺科研地质填图的基础上，查清拉脊山混杂带中基质和岩块的岩石组成、空间分布和变质变形特征；利用沉积学、构造地质学、岩石地球化学、锆石SHRIMP（LA-ICPMS）U-Pb定年和Sr-Nd-Hf同位素示踪等手段，研究混杂带中基质和岩块的成因、形成环境和时限，探索拉脊山混杂带早古生代的古构造体系及其动力学机制；揭示拉脊山混杂带增生造山过程，为全面地、合理地建立中祁连早古生代大地构造演化模式提供重要的资料。

拉脊山是否存在着早古生代洋盆，以及古洋盆消减极性和增生造山过程方面存在着较大的分歧；项目主要研究了拉脊山构造带的岩石组成、不同性质的岩石形成环境和时代。在详细地地质调查和研究基础上，查清了拉脊山混杂带主要由基质和岩块，以及侵入于混杂带中的花岗岩组成，其中岩块包括超基性岩、基性岩和中-基性火山岩，灰岩和硅质岩；基质主要由强变形的泥岩和粉砂岩组成。岩石矿物、地球化学、同位素和年代学等研究表明火山岩形成于476～460Ma，具有岛弧型、洋中脊型和洋岛型玄武岩特征；花岗岩为I型花岗岩，形成于438-452Ma。在青石坡组粉砂质板岩中获大量碎屑锆石年龄为455±3Ma，限定了青石坡组最大沉积时代为晚奥陶纪早期，而非前寒武纪；探讨了拉脊山古洋盆的消减和俯冲增生造山过程。项目中获得的数据和成果，将有助于开展区域大比例尺地质填图和成矿地质背景的调查和研究，为全面地、合理地建立祁连早古生代大地构造演化模式提供重要的资料。