U-Pb zircon geochronology, geochemistry and tectonic implications of the early Devonian granitoids in the Liuyuan area, Beishan, NW China

Abstract

We present new zircon U-Pb ages, Sr-Nd isotopes, and whole-rock geochemistry of the early Devonian granitoids in the south Beishan area. LA-ICP-MS zircon U-Pb dating indicate that the Huitongshan and Shijinpo granitoids have crystallization ages of 418.5 ± 4.4 Ma (MSWD = 0.31) and 404.4 ± 1.8 Ma (MSWD = 0.20), respectively. Mineralogical and geochemical characteristics suggest that the Huitongshan syenogranites are highly fractionated I-type granites, and the Shijinpo granitoids are A-type granites. They belong to the high-K calc-alkaline and shoshonitic series, and are weakly peraluminous-metaluminous. eNd(t) of the Huitongshan granite vary from –0.4 to –1.0, with TDM2 model ages ranging from 1.20 to 1.25 Ga. While eNd(t) of the Shijinpo granite vary from –1.7 to –2.4, while TDM2 model ages ranging from 1.29 to 1.35 Ga. The Sr-Nd isotopic and geochemical signatures suggest that these granitoids formed through fractional crystallization of magmas derived by partial melting of juvenile crustal source. We interpret that these early Devonian I- and A-type granitoids generated in the subduction setting, probably associated with the upwelling asthenosphere through a slab window.