摘要
The South China Block is characterized by the large-scale emplacement of felsic magmas and giant ore deposits during the Yanshanian. We present zircon Hf isotopic compositions, whole-rock major and trace element compositions of the Fengshun complex, located in eastern Guangdong Province, South China. The Fengshun complex is a multi-stage magmatic intrusion. It is composed of two main units, i.e., the Mantoushan（MTS） syeno-monzogranites, alkali feldspar granites and the Hulutian（HLT） alkali feldspar granites. LA-ICPMS zircon dating shows that the complex emplaced in 166–161 and 139±2 Ma, respectively. Geochemically, the MTS granites show relatively various geochemical compositions with low REE contents（87.76×10-6–249.71×10-6）, Rb/Sr ratios（1.19–58.93）, pronounced Eu negative anomaly（0.01–0.37） and low Nb/Ta ratios（2.40–6.82）. In contrast, the HLT granites exhibit relatively stable geochemical characteristics with high REE contents（147.35×10-6– 282.17×10-6）, Rb/Sr ratios（2.05–10.30） and relatively high Nb/Ta ratios（4.45–13.00）. The isotopic data of the MTS granites display relatively enriched values, with ISr varying from 0.708 2 to 0.709 7, εNd（t） from-7.8 to-6.9 and εHf（t） from-7.4 to-3.2, in comparison with those of the HLT which are ISr=0.703 05–0.704 77, εNd（t）=-5–-3.4 and εHf（t）=-0.7–1.8）. The two-stage model ages of the MTS granites（T2DM（Nd）=1.51–1.59 Ga and T2DM（Hf）=1.26–1.48 Ga） are also higher than those of the HLT granites（T2DM（Nd）=1.21–1.34 Ga and T2DM（Hf）=0.96–1.10 Ga）. Thus the MTS and HLT granites might originate from different sources. The former is more likely derived from partial melting of Meso-Proterozoic basement triggered by upwelling of asthenosphere and/or underplate of the basaltic magma and then extensive fractional crystallisation, similar to the genesis of Early Yanshanian granitoids of the EW-trending tectono-magmatism belt in the Nanling range. In comparison, the latter might have involved with asthenosphere component, similar to the Early Cretaceous granitoids of NE-NNE-trending granitoid-volcanic belt in coastal region, southeastern China. We propose that the MTS granites were mainly formed in Paleo-Tethyan post-orogenic extensional tectonic setting whereas the HLT granites were formed in the back-arc extensional tectonic setting. The period at 139 Ma represents the initial time of roll-back of the paleo-Pacific Plate in SE-trending.
The South China Block is characterized by the large-scale emplacement of felsic magmas and giant ore deposits during the Yanshanian. We present zircon Hf isotopic compositions, whole-rock major and trace element compositions of the Fengshun complex, located in eastern Guangdong Province, South China. The Fengshun complex is a multi-stage magmatic intrusion. It is composed of two main units, i.e., the Mantoushan（MTS） syeno-monzogranites, alkali feldspar granites and the Hulutian（HLT） alkali feldspar granites. LA-ICPMS zircon dating shows that the complex emplaced in 166–161 and 139±2 Ma, respectively. Geochemically, the MTS granites show relatively various geochemical compositions with low REE contents（87.76×10-6–249.71×10-6）, Rb/Sr ratios（1.19–58.93）, pronounced Eu negative anomaly（0.01–0.37） and low Nb/Ta ratios（2.40–6.82）. In contrast, the HLT granites exhibit relatively stable geochemical characteristics with high REE contents（147.35×10-6– 282.17×10-6）, Rb/Sr ratios（2.05–10.30） and relatively high Nb/Ta ratios（4.45–13.00）. The isotopic data of the MTS granites display relatively enriched values, with ISr varying from 0.708 2 to 0.709 7, εNd（t） from-7.8 to-6.9 and εHf（t） from-7.4 to-3.2, in comparison with those of the HLT which are ISr=0.703 05–0.704 77, εNd（t）=-5–-3.4 and εHf（t）=-0.7–1.8）. The two-stage model ages of the MTS granites（T2DM（Nd）=1.51–1.59 Ga and T2DM（Hf）=1.26–1.48 Ga） are also higher than those of the HLT granites（T2DM（Nd）=1.21–1.34 Ga and T2DM（Hf）=0.96–1.10 Ga）. Thus the MTS and HLT granites might originate from different sources. The former is more likely derived from partial melting of Meso-Proterozoic basement triggered by upwelling of asthenosphere and/or underplate of the basaltic magma and then extensive fractional crystallisation, similar to the genesis of Early Yanshanian granitoids of the EW-trending tectono-magmatism belt in the Nanling range. In comparison, the latter might have involved with asthenosphere component, similar to the Early Cretaceous granitoids of NE-NNE-trending granitoid-volcanic belt in coastal region, southeastern China. We propose that the MTS granites were mainly formed in Paleo-Tethyan post-orogenic extensional tectonic setting whereas the HLT granites were formed in the back-arc extensional tectonic setting. The period at 139 Ma represents the initial time of roll-back of the paleo-Pacific Plate in SE-trending.
基金
financially supported by the China Geological Survey(No.1212011220014)
the Chinese National Natural Science Foundation(No.41172063)
