Geochemistry and Sr-Nd-Pb Isotopes of the Granites from the Hashitu Mo Deposit of Inner Mongolia, China: Constraints on Their Origin and Tectonic Setting

摘要

The Hashitu molybdenum deposit is located in the southern part of the Great Hinggan Range,NE China.Molybdenum mineralization is hosted by and genetically associated with monzogranite and porphyritic syenogranite.Sr-Nd-Pb isotopes of the intrusions show that the porphyritic syenogranite has initial^(87)Sr/^(86)Sr ratios of 0.70418-0.70952,ε_(Nd)(t)values of 1.3 to 2.1(t=143Ma),^(206)Pb/^(204)Pb ratios of 19.191-19.573,^(207)Pb/^(204)Pb ratios of 15.551-15.572,and^(208)Pb/^(204)Pb ratios of38.826-39.143.The monzogranite has initial^(87)Sr/^(86)Sr ratios of 0.70293-0.71305,ε_(Nd)(t)values of 1.1 to2.0(t=147 Ma),^(206)Pb/^(204)Pb ratios of 19.507-20.075,^(207)Pb/^(204)Pb ratios of 15.564-15.596,and^(208)Pb/^(204)Pb ratios of 39.012-39.599.The calculated Nd model ages(T_(DM))for monzogranite and porphyritic syenogranite range from 866 to 1121 Ma and 795 to 1020 Ma,respectively.The granitic rocks in the Hashitu area have the same isotope range as granites in the southern parts of the Great Hinggan Range.The isotope composition indicates that these granites are derived from the partial melting of a juvenile lower crust originating from a depleted mantle with minor contamination by ancient continental crust.The integrating our results with published data and the Late Mesozoic regional tectonic setting of the region suggest that the granites in the Hashitu area formed in an intra-continent extensional setting,and they are related to the thinning of the thickened lithosphere and upwelling of the asthenosphere.