内蒙古集宁-卓资地区古元古代变质-深熔岩石流变组构及行为研究

The rheological study on the nature rocks from continental lower crust is one of the effective ways to reveal the crustal deformation, material exchange of crust and mantle, as well as the deep lithosphere dynamic process. This project mainly focuses on the khondalites and mafic granulites in the Jining-Zhuozi area, located in eastern part of Paleoproterozoic Orogenic Belt of North China Craton (so-called ‘Paleoproterozoic Khondalitic Belt’ in some literatures), and plans to carry out the systematic researches on field investigation, petrography, mineralogy, geochemistry, geochronology and micro-fabric analysis, in order to understanding the macro-micro structural deformation patterns, rock rheological behavior and genetic mechanism during granulite-facies metamorphic-anataxis processes in the different rock types with different partial melting degrees. The purposes of this study are also that, to identify the constraint relationship between the solid(residual)-liquid(melt) ratio, distribution features and mineral deformation throughout the entire metamorphic-anataxis process; to explain the influence of the rock rheological strength and properties at the different stages of initial melting, migration and aggregation of the molten melt; to reveal the constrain of the anataxis during the exhumation of the continental lower crustal rocks in the orogenic domain; to preliminarily reconstruct the rheological framework of the Paleoproterozoic Orogenic Belt of North China Craton and study its tectonic evolution.

大陆下地壳岩石流变学研究是深入了解地壳变形、壳-幔物质交换以及岩石圈深部动力学过程的有效途径和手段。本项目以华北克拉通古元古代造山带（孔兹岩带）东段的集宁-卓资地区出露的孔兹岩和基性麻粒岩作为主要研究对象，结合野外宏观构造解析、岩相学、矿物学、地球化学、同位素年代学和显微变形组构分析等综合方法，研究不同岩石类型、不同熔融程度的麻粒相变质-深熔作用与岩石宏-微观构造变形样式、岩石流变行为及成因机制；揭示造山变质-深熔作用过程中熔体-固体分布特点和矿物-岩石变形之间的相互制约关系；查明熔体形成、迁移、聚集等不同演化阶段对岩石流变强度和性质的影响；探讨造山体系中深熔作用对下地壳岩石剥露过程的制约；初步建立华北克拉通古元古代造山带流变结构及研究其演化过程。

大陆下地壳岩石流变学研究是深入了解地壳变形，壳-幔物质交换以及岩石圈深部动力学过程的有效途径和手段。本项目以华北克拉通古元古代造山带东段集宁-凉城地区出露的高级变质深熔岩石作为主要研究对象，结合野外宏观构造解析、岩相学、矿物学、地球化学、同位素年代学和显微变形组构分析等综合方法，研究了不同岩石类型、不同熔融程度的深熔岩石宏微观构造变形样式及成因机制，建立了古元古代造山带东段深熔下地壳结构剖面，揭示了造山演化过程中的变质-深熔作用及矿物-岩石变形之间的相互制约关系。研究结果表明，古元古代造山带东段深熔下地壳由深至浅依次包括残余-堆晶岩带（凉城带）、高级深熔岩带（大榆树带）和初级深熔岩带（大-小什字带）。造山演化过程为阴山陆块与鄂尔多斯陆块在1.95Ga发生陆陆碰撞，持续地壳加厚发生变质深熔作用，导致其强度显著下降。熔融弱化的下地壳发生近水平的渠道流。熔体在差应力作用下挤压排出，并向上迁移，而熔融残余的物质与早期结晶的斜长石、辉石等矿物发生动力堆晶作用,形成造山带下地壳相对“干”体系的残余-堆晶岩带。向上迁移的熔体，进一步汇聚形成富熔体层（高级深熔岩带或岩浆带），该层是造山后伸展-隆升的应变集中带。造山带伸展垮塌阶段，隆滑过程造成在堆晶岩带与高级深熔岩带接触部位形成强的剪切应变带，使该部位进一步熔体排出，岩石固体格架形成进而发生韧性剪切变形。在造山带伸展-隆升阶段，由于软流圈（幔源）物质的底垫（上涌），进一步加热“干”的下地壳，使之发生超高温变质作用（1.92Ga）。在深熔下地壳水平层流的构造体制下，造山带深熔下地壳岩石的变形机制主要受位错蠕变，扩散蠕变和颗粒流动来调节。随着地壳层次的加深，岩石变质深熔程度逐渐增加，变质深熔岩中固液相的比例不断变化。其变形机制也会相应调整，导致形成不同构造样式的变质深熔片麻岩。