柴北缘超高压变质带大陆深俯冲及造山带垮塌过程岩浆作用及大陆地壳生长

This project will focus on studies of magmatic activity during continental subduction and orogeny collapse and in the North Qaidam ultrahigh-pressure metamorphic belt and its significance in continental growth. Through detailed investigations of petrology, element and isotopic geochemistry, metamorphism, phase equilibrium modeling, isotopic geochronology and high-pressure-temperature melting experiment, by using various techniques including in situ element and isotopic analysis for minerals, isotopic dating for zircon, sphene, rutile and allanite, we will try to unveil rock types of syn-collisional and post-collisional magmatism in the North Qaidam UHP belt and their spatio-temporal relationships with the UHP metamorphism, to understand mechanism of decompression melting of the deep-subducted continental crust and geochemical behaviors of rocks during anatexis, and to determine characters of mantle and mantle-crust reactions during orogenic collapse and extension. This study will not only play key roles in understanding characters, time-space evolution and rock-forming mechanism of magmatic activity in the process of continental deep-subduction, exhumation and orogen collapse, but also have theoretical significance in unveiling evolutional process of orogenesis from continental subduction - exhumation, to orogen collapse and unrooting, mechanism of anatexis and decompression melting, crust-mantle reactions and growth of continent crust.

本立项将以柴北缘超高压变质带为研究地区，通过岩石学、岩石地球化学、变质作用和相平衡分析、同位素年代学，以及高温高压熔融实验等方面研究，利用矿物微区元素、同位素原位分析技术以及锆石、榍石、金红石和褐帘石原位定年等手段，查明柴北缘超高压变质带中同碰撞和碰撞后岩浆作用的类型及其与超高压变质的时空关系，了解深俯冲大陆地壳减压熔融机理和深熔过程中岩石和矿物的地球化学行为，确定造山带垮塌和伸展过程中地幔的性质和壳幔相互作用特征。该项研究不仅对于了解大陆俯冲、折返和造山带垮塌过程岩浆作用的特征、时空演化和岩浆成因机制将起关键作用，而且对于揭示从大陆俯冲－折返到造山带去根和垮塌的演化过程、深熔和减压熔融机制、壳幔相互作用以及大陆地壳的生长过程等科学问题都具有重要的理论意义。

本项目对柴北缘超高压变质带与造山有关的岩浆岩的岩石学、地球化学、变质作用和相平衡分析、同位素年代学进行了深入研究，其目的是揭示大陆俯冲碰撞和造山带垮塌的动力学机制以及大陆地壳熔融、壳幔相互作用和大陆地壳生长的机理。项目取得了多项研究成果，在SCI检索期刊发表标注本项目的论文15篇，其中13篇SCI检索论文发表在国际著名的期刊 (如Earth Science Review, GCA, Lithos, Tectonics 等)，论文被SCI引用190次，并有多篇论文正在评审和撰写中，达到了预期的成果。重要研究成果包括：(1) 查明了柴北缘超高压变质带与俯冲碰撞有关的岩浆岩的分布、岩石类型、地球化学特征；(2) 揭示了同俯冲/碰撞和碰撞后岩浆作用发生的机理及其与超高压变质的时空关系; (3) 确定了3个主要阶段的岩浆作用：435-420 Ma，410-400 Ma，390-360 Ma，分别代表大陆俯冲阶段，折返阶段和造山带去根和垮塌过程的岩浆作用；(4) 确定了大陆俯冲过程中洋壳折返熔融形成埃达克岩的过程；(5) 揭示了大陆造山带从大洋俯冲、大陆碰撞造山到造山带垮塌的演化过程；(6) 确定了同碰撞和碰撞后岩浆作用特征和鉴别标志。