Chronology and geochemistry of the Aruhan granodiorite in Inner Mongolia and their implications for the evolution of the Paleo-Asian Ocean
The Aruhan granodiorite intrusion in Xiwuqi,Inner Mongolia,is exposed along the central and eastern parts of the Hegenshan suture zone.LA-ICP-MS zircon U-Pb dating shows that the ages of the granodiorite are ran-ging from 332±3 to 327±1 Ma,suggesting emplacement during the Early Carboniferous.The Aruhan granodiorite is characterized by high contents of SiO2(65.20％to 68.27％),Al2O3(15.61％to 17.35％),Sr(472×10-6 to 552×10-6)and low contents of MgO(1.16％to 1.61％),Yb(0.86×10-6 to 1.13×10-6),Y(7.29×10-6 to 11.42×10-6,with Na2O/K2O and Sr/Y ratios ranging from 2.56 to 4.35 and 43.45 to 75.68,respectively.The total REE is low(44.73×10-6 to 88.11×10-6),the fractionation of REE is significant[(La/Yb)N=6.65～13.85],and the anomaly of Eu(δEu=0.79 to 1.07)is not obvious.The geochemical characteristics of the whole-rock indicate that the Aruhan granodiorite belongs to typical high-SiO2 island arc adakites(O-type)series,formed in an environment of active continental marginal arc.The source of the maga might be the product of partial melting of subducting oceanic crust with oceanic sediments,which reacts with overlying mantle peridotite.Crystallization differentiation and contamination by crustal materials might occurre during its emplacement.This discovery may support the fact that the central and eastern parts of the Hegenshan Ocean was not yet closed during the Early Car-boniferous.Combined with the regional research,we preliminarily believe that the Hegenshan Ocean may have un-dergone bidirectional subduction and abatement during the Early Carboniferous,which is different from the previous view that the Hegenshan Ocean underwent unidirectional subduction and abatement northward only.
Hegenshan suture zoneadakitebidirectional subduction of the Hegenshan OceanEarly Carbonifer-ousactive continental margingranodioriteXiwuqi
万方数据
维普
