On the genetic classification and tectonic implications of the Early Yanshanian granitoids in the Nanling Range, South China

摘要

Early Yanshanian (Jurassic) granitoids are widespread in the Nanling Range of South China, and areassociated with numerous non-ferrous and rare metal mineral deposits. These granitoids consistmainly of slightly peraluminous biotite monzogranites and K-feldspar granites that are closely associated in time and space with subordinate amphibole-bearing granites and muscovite- andgarnet-bearing granites. In most previous studies, the biotite-bearing granites were classified as crustaltransformation-type (corresponding to the S-type) granites which were interpreted to be derived fromthe regional Paleoproterozoic meta-sedimentary rocks. In this paper, we re-analyze the geochemicalcharacteristics of a number of representative Early Yanshanian Nanling granitoids. There exists a clearnegative correlation between SiO_2 and P_2O_5for the studied granitoids. The Early Yanshanian Nanlinggranitoid suites (including amphibole-bearing granodiorites -> biotite monzogranites -> K-feldspar granites--two-mica (muscovite) granites) are metaluminous to slightly peraluminous l-type or fractionatedl-type granites. They were derived predominantly from Proterozoic igneous protoliths. The juvenilecrust and/or newly mantle-derived materials might also have been involved in some of these granites.In addition, the I- and fractionated l-type granites are closely associated in time and space with minoramount of A-type felsic and mafic volcanic and intrusive rocks as well as alkaline rocks. All these rocksconstitute a typical assemblage of anorogenic, intraplate magmatism, suggesting a dominant lithospheric extensional regime for the Nanling Range and neighboring region during the Early Yanshanianperiod.