Analyses of the Rock Magnetic Fabric in Eastern Part of Southern Altay Margin Area, Xinjiang

Abstract

The magnetic fabric represents rock's susceptibility anisotropy. Magnetic fabric analytic method has been widely used in geology for structural deformation analysis. Magnetic fabric of the rocks in eastern part of southern Altay margin area, Xinjiang, northwest of China, shows that they have a high value of P, indicating that their magnetic anisotropy is prominent. E value of the rocks in the Sa'erbulake-Kekesayi brittle compressional cleavage belt and Mayin'ebo ductile shear-compressional belt was found to be greater than zero; magnetic foliation well developed and lineation developed only in a part of samples; implying that compressional deformation was well developed in the area. The sense of maximum compressive stress across the NW trending structural belts was NE (NEE) and there was partly a shear deformation along the belts with left-lateral shearing. In Dalaweizi-Areletebie shear rheomorphic belt and Xibodu-Fuyun deep ultra-ductile crystalloblast mylonite belt, rocks' magnetic fabric showed well developed magnetic foliation and lineation, and their E value was either above zero or below zero, giving indications that these two belts were subjected to shear deformation, and that the sense of maximum compressive stress of Dalaweizi-Areletebie belt was NE (NEE) trending indicating a left-lateral shearing, but the sense of maximum compressive stress of Xibodu-Fuyun belt was SN trending showing a right-lateral shearing. Magnetic fabric analysis revealed that the value of P of some altered-mineralized deformed rocks from Halasu Cu-deposit and Kalaxiange'er-Laoshankou area belonging to the Dalaweizi-Areletebie belt was very low, displaying that there were late mineralization and alteration weakened and isotropic susceptibility in the area. Combining with the regional structure analysis, we suggested that the three belts, i.e., the belts of Sa'erbulake-Kekesayi, Dalaweizi-Areletebie and Mayin'ebo, constituted a complete plate (micro landmass) condensation zone underthrusted by the Kalatongke island arc toward northeast to the Keketuhai-Qinghe magmatic arc and collision of the two arcs; and that the Xibodu-Fuyun belt was probably a relict (or a thin fault piece) of a micro-landmass with pre-Sinian crystalline basement reformed strongly in the Paleozoic.