Southward extension of the Bangonghu–Nujiang Suture: Evidence from Early Cretaceous intermediate and felsic magmatism in the Gaoligong Orogen, China

Abstract

It remains debated as to whether the Gaoligong Orogen between the Tengchong and Baoshan blocks in Yunnan, China, is the southward extension of the Tibetan Bangonghu–Nujiang Suture (BNS). Here we present new geochronological and petrochemical data for Early Cretaceous magmatic rocks of the Gaoligong Orogen. The LA–ICP–MS U–Pb dating of zircons from diorites, granodiorites, and granites yielded weighted mean 206Pb/238U ages of 120–118, 128–122, and 109–128 Ma, respectively. For the diorites, the εHf(t) values of zircons fall in a range of +1.2 to +5.4 with TDMC ages of 744–979 Ma, for the granodiorites they fall in a range of −9.8 to +2.9 with TDMC ages of 888–1564 Ma, and for the granites the range is −8.0 to −1.1 with TDMC ages of 1101–1488 Ma. They are magnsian, calc-alkaline, enriched in LILEs and LREEs, and have strong negative Nb, Ta, P, and Ti anomalies and high values of Mg#. All these features are indicative of continental arc affinities. The data suggest that the dioritic and granitic magmas were produced by the mixing of variable proportions of mantle- and crust-derived magmas at an active continental margin. The ages and tectonic settings of the diorites, granodiorites, and granites are similar to rocks found within the BNS. Considering the ophiolitic mélange belt, the Middle Jurassic basaltic magmatism, and the marine-facies stratigraphic features of the Gaoligong Orogen are very similar to features in the BNS, we conclude that the Gaoligong Orogen represents the suture between the Tengchong and Baoshan blocks, and is the southward extension of the BNS.