Zircon U-Pb ages of granites at Changba and Huangzhuguan in western Qinling and implications for source nature

Mesozoic granitoids are widespread in the Qinling-Dabie-Sulu orogenic belt. Precise U-Pb dating on these granitoids can reveal the evolution of the continental collision orogen and thus provide information on the nature of magma sources. This study presents zircon LA-ICP-MS U-Pb dating and whole-rock geochemical analyses for two intrusions at Changba and Huangzhuguan in western Qinling. Zircon U-Pb ages for central and marginal phases of the Huangzhuguang intrusion are 214±1 Ma and 213±3 Ma, respectively. Zircons from the Changba intrusion yield a dominant cluster with an U-Pb age of 213±2 Ma. Collectively, these ages are younger than ages of 220 to 240 Ma for ultrahigh-pressure metamorphism due to the continental collision between the South China Block and the North China Block, corresponding to syn-exhumation magmatism. Some inherited zircons occur in the Changba intrusion, yielding a weighted mean of ²⁰⁶Pb/²³⁸U ages at 757±14 Ma. This indicates that the Changba intrusion has the crustal source of mid-Neoproterozoic ages and a tectonic affinity to the South China Block. Geochemically, the two intrusuons are both rich in LILE and LREE but depleted in HFSE and HREE, similar to arc-type igneous rocks. The Huangzhuguang intrusion exhibits linear correlations between SiO₂ and the other major oxides, implying chemical evolution from a cognate magma source. It contains mafic enclaves, suggesting possible mixing of felsic-mafic magmas. The Changba granite is rich in Si and K but poor in Fe and Mg as well as has a high value of Fe*, suggesting strong differentiation of granitic magma. Therefore, the two intrusions were derived from the Late Triassic anatexis of the continental crust of different compositions in the northern margin of South China Block. This process may be coupled with exhumation of the subducted continental crust in the stage of late collision.     

Origin of ore-forming fluid in the Piaotang tungsten deposit in Jiangxi Province: Evidence from helium and argon isotopes

The Piaotang tungsten deposit in Jiangxi Province is one of the most important tungsten deposits in the South China Tungsten Metallogenic Province.In this study,we selected wolframite and chalcopyrite from the main mineralizing stage of the Piaotang tungsten deposit,and analyzed the helium and argon isotopic compositions in fluid inclusions of these minerals.The results show a 3He/4He ratio of 0.17 to 0.86 R/Ra,which fall within the range between continental crust(0.01―0.05 R/Ra) and air-saturated water(1 R...     

Hf isotopic composition of zircons from the Huashan-Guposhan intrusive complex and their mafic enclaves in northeastern Guangxi: Implication for petrogenesis

High precision zircon U-Pb dating indicates that main intrusive bodies (Tong'an,Niumiao,Huashan,Lisong),and a mafic microgranular enclave in the Huashan-Guposhan complex were formed at 160-163 Ma.The εHf(t) values of zircons from the Huashan granite vary from -2.8 to +0.3 and those from the Lisong granite vary from -2.3 to +0.3,which are obviously different with those values (+2.6 to +7.4) of the mafic enclaves from the Lisong granite.These Hf isotopic data indicate that the mafic enclaves and host granites...