Abstract:

In this paper, we present zircon U-Pb ages, in situ Hf isotopic, wholerock chemical and Nd isotopic data for the Lianyang composite granite in the Nanling region. Zircon LA-ICPMS U-Pb dating of the supplementary intrusion yielded ages of 100104 Ma, which is significantly younger than the predominant intrusion (144 Ma), suggesting that the former (finegrained biotite granite) is unlikely to be residual melts through fractionation of the latter (coarsegrained porphyritic biotite granite). Both of the two rocks show high SiO₂(65%79%), Na₂O+K₂O(6.9%9.5%) and K₂O/Na₂O(1.32.5). They are metaluminous to peraluminous (A/CNK=0.91.2), depleted in Ba, Sr, P and Ti, and enriched in Rb, Pb and LREE. The supplementary intrusion shows highly fractionated characteristics (SiO2 77%79%), with extremely negative Eu anomaly (δEu=0.030.06). The NdHf isotopic data (εNd(t)=-10.6-8.4 for the predominant intrusion, εNd(t)=-9.1-6.6 and εHf(t)=-8.5-1.8 for the supplementary intrusion) suggest that the basement rocks should be dominated by Proterozoic parametamorphic rocks. The Lianyang pluton was formed under an extensional setting during the late Yanshanian in the South China. Based on the comparison with W, Sn and Nb/Tabearing granites, it is suggested that the latestage supplementary intrusion is the most important target for Sn prospection.

Key words: composite granite, U-Pb zircon ages, Nd-Hf isotopes, Nanling region