The intrusive rocks in the Wukou region, Qinghainanshan area, Qinghai: Zircon U-Pb chronology, geochemistry and geological implications

The present paper deals in detail with the petrology, geochemistry and La-ICP-MS zircon U-Pb chronology of the syenogranite and granodiorite from the Wukou region in the Qinghainanshan area, Qinghai. The syenogranite from the Wukou region gives a zircon ²⁰⁶Pb/²³⁸U age of 253.8 ±3.3 Ma (MSWD=0.96), which may be traced back to the Late Permian. Al₂O₃=(14.13-16.51)×10^-2,K₂O=(1.66-3.59)×10^-2,A/NK=1.15-2.35, A/CNK=0.75-1.03, and TFeO/(TFeO + MgO)=0.53-0.81, all of which are characteristic of metaluminous medium to high-K calc-alkaline granites. Both the syenogranite and granodiorite are enriched in large ion lithophile elements Rb and K, and depleted in high field strength elements Nb, Ta and Ba, noticeably differentiated in light and heavy rare earth elements with right-leaning REE distribution patterns, and moderately negative Eu anomalies (Eu=0.44-0.68), indicating that the intrusive rocks in this area have the origins of the mixting of the crust and mantle magmas. This phase of magmatic thermal event represents the geological records of the tectonic transition between the western Qinling orogenic zone and the southern Qilian orogenic zone in the Qinghainanshan tectonic zone against the background of the northward subduction of the A'nyemaqen oceanic basin during the Late Permian. The timing of the intrusive rocks and determination of the tectonic settings may provide important evidence for the study of the tectonic evolution and dynamic mechanisms of the Qinghainanshan area during the early Indosinian.