Discovery of Early Palaeozoic peraluminous granites the Qingshuihe area of Yunnan Province and constraints on the influence of lithospheric mantle delamination in the Baoshan block

The petrogenesis of the Early Palaeozoic peraluminous granites in the Baoshan block remains controversial.This study applied the comprehensive methods of zircon SHRIMP U-Pb dating, Sr-Nd-Pb isotopic and bulk-rock analyses to probe the genesis and magma source of the granites from the Qingshuihe area in the Baoshan block.The results show that the Qingshuihe granites are consist of two-mica granite and biotite granite.The ages of two-mica granite and biotite granite are 473~462 Ma and 479 Ma, respectively.These rocks belonging to the peraluminous S-type granite(A/CNK > 1.1)have high SiO₂ (67.48%~74.03%)content.The values of(Na₂O+K₂O)-Ca₂O range from 4.47% to 6.46%, exhibiting calc-alkaline characteristics.The two-mica granite and biotite granite have similar chondrite-normalized REE patterns and primitive mantle normalized trace element patterns, such as enriched in LILEs(e.g., Rb, K)and Pb, and depleted in HFSEs, with negative Eu anomalies(δEu=0.31~0.54).The geochemical signatures and Sr-Nd-Pb isotopes indicate that the Qingshuihe granites were derived from anatexis of ancient metasedimentary rocks with small amount of mantle components.The Qingshuihe granites are geochemically comparable to the Shuangmaidi granites and both of them were formed in a post-orogene setting where the thickened lithospheric mantle detached due to the amalgamation of exotic microcontinents onto the East Gondwana margin.