Abstract:

East Kunlun Orogen is a natural site to study the magma mixing and mingling, where a lot of granitic magmatic rocks outcropped with widely developed mafic microgranular enclaves in it. Taking the Xiangjiananshan granitic batholith in eastern section of East Kunlun Orogen as the object, the paper has studied the field geological characteristics of mafic microgranular enclaves developed in the batholith, in order to research the magma mixing and mingling and the magma dynamics process. The enclaves have fine grained to medium coarse grained texture, and contain phenocrysts like plagioclase, amphibole, quartz, mafic minerals edged quartz, and K feldspar, which stretch across the host rocks and enclaves occasionally. The enclaves often contain back veins, and the contact boundaries between the enclaves and host rocks are sharp or transitional. The above characteristics suggest that the mafic microgranular enclaves are the products of magma mixing and mingling, in which an interchange of material have taken place in the processes. The textures of enclaves vary from fine grain to coarse grain, and dispersive to completely mixed, indicating that the proportions of magma mixing become bigger and the temperature differences between the two magmas become smaller. The temperature differences between the two magmas have a great influence on the formation of enclaves. Research on the morphology of enclaves shows that they have different stretch degrees, resulting from interactions among viscosity, temperature, flow rate, etc. The plastic deformation degree increases with the stretch degree of the enclaves. The enclaves have different longaxis directions, mainly divided into two categories, one with approximately directions representing the magma flow direction, one with no fixed direction or with several different directions at the same outcrop representing the magma partial stirring and convection. When injected into the acidic magma represented by the host rocks, the basic magma represented by the enclaves came into rotating and flowing, and partial stirring of the acidic magma may have occurred, which produced the directionalities of the minerals on the enclave edges and in the host rocks. The phenomena of enclave in enclave and different types of enclaves in the same outcrop indicate a multiple magma mixing and mingling. Field geological characteristics of mafic microgranular enclaves in Xiangjiananshan granitic batholith have provided important evidences for the magma mixing and mingling and the magma dynamics process.

Key words: East Kunlun Orogen, granite, Xiangjiananshan granitic batholith, mafic microgranular enclave, magma mixing