Constraints of ductile shear deformation on rock geochemical behavior-an example from the Bashikaogong ductile shear zone in the northern Altyn Tagh

The constraints of ductile shear deformation on rock geochemical behaviors have long been a subject discussed by geologists. Take for example the Bashikaogong oblique thrust ductile shear zone that forms the boundary between the northern Altyn Tagh-Hongliugou-Lapeiquan subduction-collision complex zone and the northern Altyn Tagh block, the authors estimate the influences of ductile shear deformation on the rock volume loss and compositional variation by comparing the geochemical compositions of tectonite of different deformation intensities before and after deformation of granodiorite in the Bashikaogong ductile shear zone and determine the isocon line slopes. The calculation shows that the volume losses of mylonitized granodiorite and granodioritic mylonite during mylonitization are 21% and 31% respectively. The mass balance analysis and isocon diagram indicate that the loss of SiO2 is largest, while Al2O3, K2O and Ba, Rb and Sr lose to different extent, showing that they are mobile components in the rock. MnO, P2O5 and Sc, which are located at or near the isocon line, are immobile components. The variation of mobile components in the rock was caused by fluid infiltration, while the variation of immobile components resulted from the volume loss during mylonitization.