CHARACTERISTICS AND TECTONIC SETTING OF LATE PALEOZOIC PLUTONS IN THE SOUTH OF WESTERN JUNGGAR

Abundant Late Paleozoic granitoid, which emplaced during Early Carboniferous Visean to Early Permian Artinskian with zircon U-Pb ages ranging from 337 to 276 Ma, is distributed along both sides of the Dalabute fault in the south of Western Junggar. Based on the previous published geological and geochemical data about the granitoid in this area, this paper concludes the changing tendency of the granitoid from early to late: 1) In corresponding to the rock type change from diorite to granite and alkali feldspar granite, the genetic types show the variation of adakitic granite → arc I-type granite → A-type granite. 2) The rock series present a regular variation of CA → HKCA → SH, with the ratios of Na₂O/K₂O turning from Na₂O/K₂O > 1 to Na₂O/K₂O < 1, correspondingly. 3) The ∑REE, δEu, L/H and contents of Sr and Yb of the granitoid vary regularly, with relatively enriched LILE but depleted HFSE, such as Nb, Ta, etc. 4) All the granitoid have high εNd (t) and low (⁸⁷Sr/⁸⁶Sr)i values, with young Nd-model ages. 5) On the discrimination diagram for tectonic setting, that of the granitoid turns from compressional setting associated with subduction-collisional to extensional setting of postcollision. All of these suggest that the granitoid should be resulted from the transition from compression to extension. The early magmatism is probably related to the breakup of the subducted slab.