CCSD主孔及周边高压-超高压变质岩的磁性特征及其与深部流体活动关系

The ultra-high pressure metamorphic rocks are interested because they can the carry geological information from the deep lithosphere, and a series of geological and geophysical phenomena during the subduction-exhumation processes is one of the focuses of solid earth sciences. The retrograde metamorphism of UHPM rocks and fluid activities are highly related, and often accompanied by formation of Fe-Ti oxides. Rock magnetic properties can reflect the composition, concentration, grain size and microstructure of the magnetic minerals in the rocks (mainly Fe-Ti oxide, iron sulfide and some Fe bearing silicate), thus the constraints Study of the rock magnetic variation and the deep fluid activities is practical. The study intends to select the eclogites and granitic gneiss with clear contact relationship from the CCSD-MH and it's surrounding area, based on the systematic petrology, mineralogy, H2O concentration （especially the H2O concentration of magnetic minerals, e.g. magnetite） and isotope geochemistry (including H and O isotope) of samples from both sides of the contact area, studying the susceptibility, natural remanent magnetization, hysteresis properties etc. and the differences in composition, concentration, grain size etc. represented by the magnetic properties. The magnetic response of deep fluid activities and the mechanism of mineral transition will be studied, the internal relationship between rock magnetism and fluid activities will be discussed, and the research can provide a basis for the further studies of the mechanism and the origin of magnetism in deep continental crust.

超高压变质岩因其携带岩石圈深部地质信息而受到广泛重视，其中俯冲-折返等一系列复杂过程中的地质、地球物理学现象是固体地球科学的研究热点。超高压变质岩的退变质过程与深部流体活动密切相关，并且常常伴随有铁钛氧化物矿物的生成。岩石磁性与磁性矿物（例如铁钛氧化物、铁硫化物及某些硅酸盐矿物）的成分、含量、颗粒大小及出溶结构等相关，为利用岩石磁性的变异特征研究深部流体活动提供了可能。项目选择大陆科学钻探主孔及其周边具有明确接触关系的各类榴辉岩与花岗质片麻岩为研究对象，在详细的岩相学、矿物学、矿物含水量（尤其是磁性矿物含水量，如磁铁矿）及同位素地球化学（含H、O同位素）研究的基础上，系统研究岩性接触带两侧岩石精细磁性特征及其所代表的磁性矿物的成分、含量及结构等差异。探讨岩石磁性与深部流体活动之间内在的联系，讨论深部流体活动的岩石磁响应特征及其矿物转换机制，为大陆深地壳岩石磁性成因机制研究奠定基础。

超高压变质岩能携带岩石圈深部地质信息，其俯冲-折返一系列复杂过程中的地质、地球物理学现象是固体地球科学的研究热点。超高压变质岩的退变质过程与铁钛氧化物的形成及深部流体活动密切相关，因此我们能利用超高压变质岩的磁性特征来研究深部流体活动。项目选择大陆科学钻探主孔及周边具有接触关系的榴辉岩与花岗质片麻岩为研究对象，在详细的岩石学、矿物学研究的基础上，系统测量岩性接触带两侧岩石磁化率、天然剩磁、磁滞回线特征等磁性特征。研究结果表明，花岗质片麻岩中磁性矿物组合主要为磁铁矿，小部分样品中含有赤铁矿，其中磁铁矿以多畴为主，伪单畴磁铁矿仅在少量样品中出现。和同为完全退变质的角闪岩（完全退变质榴辉岩）相比，花岗质片麻岩具有相似的磁性矿物组合，但其磁铁矿的颗粒明显较大。多畴磁铁矿的形成，可能和超高压变质岩折返过程中，花岗质片麻岩较强的流体活动相关。部分分布于花岗质片麻岩主体岩性段外的样品，具有较高的天然剩余磁化强度，则可能反映了花岗质片麻岩及周围榴辉岩之间的流体交换。该发现为从岩石物理性质变化的角度研究和阐释深部流体活动提供了新的思路。