Geochemical characteristics and LA-ICP-MS zircon U-Pb ages of intermediate to mafic dyke swarms in Haxiya area, Golmud, Qinghai Province

Intermediate to mafic dyke swarms are developed in Haxiya area which is located in the north of the Eastern Kunlun orogenic belt. The rocks are mainly composed of diabase, dioriteic lamprophyre and diorite porphyrite, which have K calc-alkaline basalt series features as shown by geochemical analyses. The REE distribution patterns suggest strong fractionation between LREE and HREE and weak negative Eu anomaly, with LREE/HREE being 4.72~8.66 (6.57 on average), and δEu being 0.81~0.98 (0.91 on average), indicating indistinct fractional crystallization of plagioclase. The intermediate to mafic dyke swarms in this area are enriched in LILEs (K, Rb, Cs, Ba, Sr) and depleted in HFSEs (Nb, Ta, Zr, Hf, Ti), showing the characteristics of intraplate basalts with some information of the subduction zone. LA-ICP-MS U-Th-Pb dating shows that zircon ages are relatively scattered, and eight magmatic zircons have yielded a weighted mean 206Pb/238U age of 411.5±7.5Ma, representing the crystallization age of the intermediate to mafic dyke swarms in Haxiya area of Golmud. That age suggests that the tectonic setting of the north of the Eastern Kunlun Block had accomplished the environment conversion from compression of colliding terranes to extension after collision, and eventually entered the intracontinental orogenic stage during Late Silurian-Early Devonian.