伊犁地块早期大陆地壳形成与其亲缘性研究

Yili Block is one of the representative microcontinents within the Tianshan Orogenic Belt. It is a window to reveal the Precambrian tectonic affinities of the microcontinents in the southern Central Asian Orogenic Belt. The Wenquan Complex is the oldest basement rocks exposed in the northern margin of the Yili Block. It is mainly composed of Neoproterozoic intermediate-acid magmatic rocks and clastic sedimentary rocks, which have recorded the Precambrian geological evolution of the Yili Block. In this proposal, we plan to carry out a systematical study of petrology, whole-rock major and trace elements and Sr-Nd isotopes, and zircon U-Pb geochronology for the Neoproterozoic magmatic rocks in order to constrain their petrogenesis and magma source characters, and then to reveal the Neoproterozoic magmatic and geological evolution of the Yili Block. Moreover, whole-rock geochemistry, U-Pb dating and Hf isotopic composition of detrital zircons will be analyzed for the Neoproterozoic clastic sedimentary rocks to constrain the source materials and the provenance. By comparison with the recent studies of Neoproterozoic magmatic and sedimentary rocks exposed in the Central Tianshan Block and the Tarim Craton, the formation process of the Yili Block wll be revealed. Based on these studies, our results will provide close constraints on the tectonic affinity the Yili Block, which will finally improve the researches on the Precambrian geological evolution of the microcontitents and the reconstrution of the tectonic evolution of the southern Central Asian Orogenic Belt.

伊犁地块是天山造山带内一个有代表性的微陆块，是揭示中亚造山带南部众多微陆块构造亲缘性的窗口。温泉杂岩是伊犁地块最古老的岩石，出露于伊犁地块北缘的温泉地区，由新元古代的中-酸性岩浆岩和碎屑沉积岩组成，记录了伊犁地块前寒武纪地质演化历史。本研究拟通过对温泉杂岩中这套新元古代岩浆岩开展详细的岩石学、全岩元素和Sr-Nd同位素地球化学、锆石U-Pb年代学研究，以制约其岩石成因和岩浆源区特征，从而揭示伊犁地块新元古代中-酸性岩浆演化规律，恢复伊犁地块的新元古代地质过程；通过对温泉杂岩中浅变质的碎屑沉积岩开展全岩地球化学、碎屑锆石U-Pb年代学和Hf同位素组成研究，制约其物质源区特征和物质来源。结合已有资料，与中天山和塔里木克拉通开展新元古代岩浆活动和沉积演化综合对比研究，揭示伊犁地块的形成过程，从而制约该地块的构造亲缘性，促进中亚造山带微陆块来源和中亚造山带南部构造演化过程的恢复。

中亚造山带内分布有众多的具有前寒武纪基底的微陆块，其构造起源一直是中亚造山带地质演化研究的核心问题之一。中国天山造山带呈东西向展布于中亚造山带的南部，发育伊犁和中天山2个古老微陆块。已有成果显示，伊犁地块和中天山地块可能存在古元古代地壳物质，其古老陆核主要形成于中元古代（ca.1.4 ~ 1.3 Ga），并在新元古代早期（0.97 ~ 0.85 Ga）发生强烈的地壳改造作用并固结形成统一的结晶基底。我们最新的碎屑锆石研究表明，伊犁地块在1.8 ~ 1.7 Ga和1.6 ~ 1.3 Ga期间发生同时期的地壳生长和改造作用，此后主要以地壳改造为主（1.0 ~ 0.78 Ga）。此外，基于最近的岩浆研究认为中天山地块在中元古代（1.6 ~ 1.3 Ga）经历一期地壳生长事件，随后在新元古代早期开始以地壳的改造作用为主。在中-新元古代时期，伊犁和中天山地块可能都处于大陆地壳伸展环境（0.76–0.71 Ga）。通过与塔里木克拉通及周缘其它主要古老块体的综合对比研究揭示，伊犁地块和中天山地块在前寒武纪时期具有相似的地壳演化过程，但不同于塔里木克拉通及其他这些古老块体。由此认为，伊犁地块和中天山地块与塔里木克拉通不具有亲缘性，而更可能构造起源于相邻的哈萨克斯坦地块。