东疆星星峡地区淡色花岗岩的成因及其蕴含的古老地壳组成信息

The Central Tianshan Block (CTB), as one of the major microcontinents of the southern Central Asian Orogenic Belt (CAOB), would carry important significances in the definition of the basically tectonic architecture of the CAOB. At present, relatively little is known about the metamorphism, anatexis and differentiation processes of the crustal basements in the microcontinents of the CAOB in response to the accretionary orogeny. The leucogranites scattered in the CTB provide a unique opportunity to understand these processes since they show a close spatial relationship with the Precambrian basements of the CTB and contain abundant information concerning the crustal composition and evolution. In this proposal, we plan to conduct detailed field geological, petrographic, geochronological, and petrogeochemical studies for several leucogranite bodies which were discovered from the Xingxingxia area of the CTB. Combined with the analysis and comparison of previously published data, these new data will be used to reveal the temporal and spatial distribution rule of the leucogranites in the Xingxingxia area, elucidate the magma sources and anatectic types and mechanisms for the different stages of leucogranites, probe the genetic link between the leucogranites and metamorphism and migmatization of the basement rocks of the CTB, and to figure out the information about the age and composition of the ancient crust in the CTB. The results will provide significant insights into the Precambrian crustal formation and evolution of the CTB as well as the understanding of the tectonic evolution of the CAOB.

中天山地块作为中亚造山带南部的主要微陆块之一，在限定造山带的整体构造格架上具有重要作用。然而，目前对这些古老微陆块在增生造山作用中的基底变质、地壳深熔及地壳分异等过程尚不清楚。中天山地块中断续分布的淡色花岗岩与前寒武纪基底岩石在空间上密切相关，蕴含了丰富的地壳组成和演化信息，是深入研究上述问题的理想对象。本项目拟对在中天山地块星星峡地区新发现的几处淡色花岗岩进行详细的野外地质、岩石学、年代学和地球化学研究，并结合已有资料的分析和对比，揭示本区淡色花岗岩的时空分布规律，阐明不同期次淡色花岗岩的源区物质组成和地壳深熔作用的类型与机制，分析其与基底岩石的变质作用和混合岩化之间的成因联系，揭示其蕴含的中天山地块古老地壳时代和组成的重要信息，为中天山地块前寒武纪地壳基底的形成与演化以及中亚造山带的构造演化研究提供新的有力证据。

淡色花岗岩可以由大陆地壳岩石深熔作用形成，或者由原始花岗质岩浆经高程度分离结晶作用形成，因而可以有效反演大陆地壳的组成与演化信息。为了深入认识古老微陆块在增生造山作用中的地壳演化过程，本项目选择中天山微陆块星星峡地区淡色花岗岩为主要研究对象，通过系统的野外地质、岩石学与岩石地球化学研究，获得了如下认识：（1）将星星峡地区淡色花岗岩分为“淡色体”和“侵入体”两种类型，两者具有不同的产状、岩石成因和地壳演化信息；（2）“淡色体”型淡色花岗岩的形成时代为~380 Ma和~310 Ma，分别与其围岩片麻岩的变质年龄一致，是中天山微陆块前寒武纪基底岩石的变质和部分熔融作用的产物；（3）“侵入体”型淡色花岗岩的形成时代为~280 Ma，与同时代的红柳井石英闪长岩的岩浆高度分异演化有关，揭示了共生的高分异花岗岩与堆晶石英闪长岩的具体成因联系，以及原位晶体-熔体分离过程。研究过程还结合中天山微陆块前寒武纪基底岩石的锆石Hf-O同位素研究，揭示了中天山地块中元古代地壳生长事件，以及可能存在的更古老的古元古代地壳，提出了中亚造山带南部微陆块与东欧板块的亲缘性。项目研究成果在ESR、SR、Geology、GSAB、Lithos、GR等国际主流期刊、及中文核心期刊发表论文9篇，并完成1：5万填图2幅，受到国内外研究同行广泛关注和认可。