华北克拉通清原新太古代表壳岩系变质作用研究

Archean supracrustal series occur as belts, blocks or enclaves of various scales in extensive TTG rocks, where the supracrustal blocks of amphibolite facies commonly show clockwise PT paths with their peak conditions consistent with medium-pressure type or low-pressure type, whereas the enclaves of granulite facies were recognized to mostly reach ultra-high temperature conditions with anti-clockwise PT paths. What tectonic regimes for these metamorphic patterns are widely disputed, and it requires addressing whether they can be originated from an Archean unique vertical tectonic regime. The Qingyuan terrane keeps the “dome and keel” typical of those in other Archean cratons and a number of supracrustal blocks of amphibolite and granulite facies although it has subjected to a high-pressure granulite facies metamorphism during late Paleoproterozoic. Using the quantitative approach of metamorphic phase equilibria and combined with data of petrography, geochemistry and age dating, this project will systematically study the phase relations of metamorphism and ages of the Neoarchean supracrustal rocks in Qingyuan area. We will elucidate the characteristics of spatial distribution of the Paleoproterozoic metamorphic overprinting, and especially, discuss the metamorphic PT paths of supracrustal blocks or enclaves of both amphibolite and granulite facies, including the genetic relations between each other. These studies will provide constraints of metamorphism for discussing the tectonic regimes prevailed in Archean cratons.

太古宙克拉通表壳岩系呈大小不等的块体分布于广泛的TTG质岩石中，其中角闪岩相表壳岩变质作用PT轨迹多为顺时针型，峰期变质条件对应中压相系或者为低压相系，麻粒岩相表壳岩可达到超高温条件，PT轨迹或为逆时针型。对太古宙岩石变质作用的大地构造环境尚有很多争论，但它们是否与太古宙时期特有的垂直构造系统有关，还需要进行深入研究。辽宁清原地区虽然经历了古元古代高压麻粒岩相变质作用叠加，但整体仍然保留着太古宙克拉通中特有的“穹窿-龙骨”构造，发育角闪岩相到麻粒岩相变质的表壳岩块体。本项目拟利用变质相平衡的定量研究方法，结合详细的岩石学、地球化学及同位素年代学结果，系统研究清原新太古代表壳岩的变质相平衡关系和年龄，查明古元古代高压麻粒岩相变质作用的特征与影响范围，阐明新太古代角闪岩相和麻粒岩相表壳岩系的PT轨迹与内在成因联系，为深入讨论新太古代大地构造环境提供变质作用约束。

本项目系统研究了辽北及邻区新太古代表壳岩系和古元古代变质基性岩墙变质作用演化及其大地构造体制。取得了如下进展：（1）基性岩变质相平衡研究取得了重要进展：建立了变质基性岩完整相平衡关系；总结了麻粒岩的研究进展；提出了新的钙质闪石钛温度计。（2）在冀东迁安片麻岩穹窿西缘新太古代表壳岩块体中识别出了超高温泥质和杂砂质麻粒岩，并确定其P–T轨迹为逆时针型，指示太古宙垂直构造过程。（3）辽北清原地区角闪岩相表壳岩和变质基性岩墙变质作用研究，揭示新太古代变质作用为逆时针型，受垂直构造体制控制；古元古代变质作用为顺时针型，受地壳加厚造山过程控制，并首次在吉南夹皮沟地区识别出古元古代变质基性岩墙。（4）在辽北清原地区识别出新太古代晚期超高温麻粒岩相变质作用，其P–T轨迹为逆时针型，指示垂直沉落构造过程。（5）通过辽北及华北克拉通太古宙片麻岩U–Pb–Hf–O–Nd同位素及元素地球化学研究，揭示了地壳垂直生长过程。（6）为了与辽北地块变质作用和大地构造体制进行对比，对冀北红旗营子杂岩多期变质作用、内蒙古集宁超高温麻粒岩、显生宙洋壳俯冲带变质作用及有关的超高压、高岩变质岩进行了系统研究。共发表论文16篇，有10位研究生参与研究。