Petrogenesis and geological significance of the Early Mesozoic mafic dyke swarms in Zhongzaohuo area, East Kunlun orogenic belt

The Zhongzaohuo mafic dyke swarms in East Kunlun are principally composed of dioritic porphyrite with minor lamprophyre, porphyritic diabase, and diabase. The LA-ICP-MS zircon U-Pb dating indicates that the mafic dykes were emplacedat(249 ± 1) Ma. The mafic dykes are enriched in LILE and depleted in HFSE. The rocks have higher total REE, with slightly enriched LREE(∑REE=99.9×10^-6~173.9×10^-6, (La/Yb)_N=3.5~9.3). Source region analysis shows that mafic magma resulted from the fluid from subducted ocean crust and the mantle metasomatism, and partial melting played a dominant role in magma evolution, while crustal contamination and fractional crystallization played a limited role in magmatic differentiation. Tectonic setting analysis shows that the formation of the rocks was related to subduction; in combination with the tectonic evolution of East Kunlun, the authors hold that the formation process of mafic dyke swarms in this paper is as follows: in early Triassic, as the result of northward subduction of Paleo-Tethys Ocean, fluids from the subduction slab were dehydrated and mantle peridotite experienced metasomatism, which promoted the mantle peridotite partial melting into mafic magma; the magma was affected by the dynamic background of the back-arc extension, and then it migrated upward to the upper crust along the fissures to form the mafic dykes.