Geochemistry, Zircon U-Pb Chronology, Lu-Hf Isotopic Compositions and Geological Significance of the Hangmuduo Granite in Riduo Area of Eastern Gangdise Belt

The Paleocene magmatic rocks in the Gangdese belt are considered to be the product of the demise of the New Tethys Ocean to the collision between India and Eurasia. The volcanic rocks and the contemporaneous acidic intrusive rocks of the Dianzhong Formation of the Linzizong group are typical paleocene magmatic assemblages of the eastern Gangdise belt, which is an important indictor to the geodynamic background of the Gangdisebelt. Previus researchers have done much work on the volcanic rocks of the Dianzhong Formation of the Linzizong group, but few on the contemporaneous intrusions. There are still disputes on its genesis and evolution. This paper studied the Paleocene Hangmuduo granite in Riduo area of eastern Gangdise belt with the bulk-rock geochemistry, zircon U-Pb geochronology, and Lu-Hf isotope in order to shed light on this issue. The results showed that the zircon U-Pb ages of the three granites samples are (62.6±0.6) Ma,(64.9±0.7) Ma and (62.2±0.7) Ma respectively, in accordance with the ages of the Dianzhong Formation of the Linzizong group. Geochemically, the rocks show the characteristics of high SiO₂ (72.23%-76.02%), Al₂O₃ (12.73%-14.72%) and K₂O(2.19%-4.84%); low MgO (0.01%-0.52%) and TiO₂(0.12%-0.24%); high differentiation(DI 86.35%-95.02%) and pera luminous (A/CNK1.01-1.26), belonging to S-type granites. However, the zircon Lu-Hf isotope results show that the εHf (t) value is mainly between-10.64 and 10.79, and the two-stage model age(t_DM2) is between 443 and 1810 Ma. It suggests that the source of the Hangmuduo granitic pluton is mainly the partial melting of the juvenile crust and has the characteristics of I-typegranite. the identification of trace elements of Hangmuduo granite shows the enrichment of LILE (Rb, K, Th and U) and the depletion of HFSE (Nb, Ta, P and Ti), with the light rare earth-enriched rare earth distribution model petrologically and geochemically, which is in consistent with clastic sedimentsin Riduo basin from late Jurassic to late Cretaceous. Combined with the previous research in Gangdese belt, it is held that the Hangmuduo granite had been derived from the partial melting of clastic sediments under the co-collision from the rapid weathering of the Yeba volcanic arc in Riduo basin, which has similar lithological and geochemical characteristics to juvenile crust. Meanwhile, a small amount of ancient crystallization basement mingled and formed S-type granite with the arc magmatic characteristics through crystallization differentiation.