Wall rock of the Hongge pluton and its age
Wu Gen-yao, Wang Ming-kun and Liu Cheng
The Hongge mafic-ultramafic pluton is situated in the northeastern suburbs of Dukou City, Sichuan. Its wall rocks can be separated into two suites. The immediate one is named Miyi Group, which is divided ascendingly into the Panjiatian, Zhifanggou and Anningcun Formations. The indirect wall rock is named Hongge Group, consisting of Luku, Huangjiashan and Naerba Formations. The mineral assemblages show that the former belongs to metamorphism of medium grade and the latter to the one of lower grade. The strata underlying the Miyi Group are named Yakou Complex, from which the date of 2957 Ma has been got. Previous Miyi Group and Hongge Group were regarded as Upper Sinian, Lower Cambrian and Permian. Ten aspects of evidences (including rock association, ore deposits, geochemistry, stromatolite, deformation, "unconformity", contact metamorphism, etc.) have been put forward, which deny the predecessors' conclusions. Miyi Group may be correlated with Pudeng Formation in Yuanmou region, northern Yunnan. The equivalent of the Yakou Complex is the lower and middle submembers of the Ist member of the Pudeng Formation (granite or granitic gneiss); the Ist member of the Panjiatian Formation may be correlated with the upper submember of the Ist member of the Pudeng Formation, the 2nd, the 3rd and the lower part of the 4th member of the Panjiatian Formation with the 2nd member of Pudeng Formation (marble, dolomitic marble); the middle and upper parts of the 4th member of Panjiatian Formation and the Zhifanggou Formation with the 3rd member of Pudeng Formation. The equivalent of the 4th member of Pudeng Formation is Anningcun Formation.