Zircon U–Pb–Hf isotopic and geochemical characteristics of the Xierzi biotite monzogranite pluton, Linxi, Inner Mongolia and its tectonic implications

摘要

The opening, subduction and final closure of the Paleo-Asian Ocean led to the formation of the Central Asian Orogenic Belt. Controversy has long surrounded the timing of final closure of the Paleo-Asian Ocean. Here we present zircon U–Pb ages and petrological, geochemical and in situ Hf isotope data for the Xierzi biotite monzogranite pluton, Linxi, SE Inner Mongolia. U–Pb dating of zircon by LA-ICP-MS yields a middle Permian emplacement age (268.7?±?2.3?Ma) for the Xierzi pluton that is dominated by biotite monzogranites with high SiO 2 (71.2–72.8?wt.%), alkali (Na 2 O?+?K 2 O?=?8.05–8.44?wt.%), Al 2 O 3 (14.4–15.2?wt.%) and Fe 2 O 3 T relative to low MgO contents, yielding Fe 2 O 3 T /MgO ratios of 2.87–3.44, and plotting within the high-K calc-alkaline field on a SiO 2 vs. K 2 O diagram. The aluminum saturation indexes (A/CNK) of the biotite monzogranites range from 1.06 to 1.19, corresponding to weakly to strongly peraluminous. They are enriched in rare earth elements (REE), high field strength elements (HFSEs; Zr, Hf), and large ion lithophile elements (LILEs; Rb, U, Th). The LREEs are enriched relative to the HREEs, with a distinct negative Eu anomaly in a chondrite–normalized REE diagram. Geochemically, the Xierzi biotite monzogranite is classified as an aluminous A-type granite, with all samples plotting within the A 2 -type granite field on a Y/Nb vs. Rb/Nb diagram. Zircon ε Hf ( t ) values and two-stage modal ages of the zircons within the pluton range from?+4.80 to?+13.65 and from 983 to 418?Ma, respectively, indicating that the primary magma was generated through partial melting of felsic rocks from juvenile crust. Consequently, these results demonstrate that the Xierzi pluton formed under the post-orogenic extensional setting after arc–continent collision in the middle Permian. Graphical abstract Display Omitted Highlights ? Zircon U–Pb ages and petrological, geochemical and in situ Hf isotope data of the Xierzi biotite monzogranite pluton in Inner Mongolia are presented. ? The primary magma of the Xierzi biotite monzogranite was generated through partial melting of felsic rocks from Phanerozoic juvenile crust. ? The biotite monzogranite formed during post-orogenic extension following arc–continent collision in the middle Permian.