Geochronology and Geochemistry of Cihua Neoproterozoic High-Mg Andesites in Jiangnan Orogen and Their Tectonic Implications
Zhang Yuzhi
Wang Yuejun
Guo Xiaofei
Gan Chengshi
Xing Xiaowan
Song Jingjing
Abstract：It is generally accepted that the Jiangnan orogenic belt led to the amalgamation of the Yangtze with Cathaysia blocks during the Neoproterozoic period.However,its tectonic evolution and amalgamation timing are still in debate.This paper pres-ents a set of new geochronological and geochemical data for the newly-identified Neoproterozoic high-Mg volcanics from Cihua (Jiangxi).LA-ICP-MS zircon U-Pb dating of the representative sample yields a weighted mean age of 832±12 Ma (n=16, MSWD=0.12),representing the eruption age of the andesite.Geochemical results indicate that they can be classified as high-Mg andesites with SiO2 ranging from 57.67% to 61.33%,MgO from 3.51% to 4.29% and Mg-number from 52 to 57.Their chondrite-normalized REE patterns exhibit a left-sloping pattern with enriched LREEs relative to HREEs.On the primitive mantle-normalized multi-element patterns,these samples have strong enrichment in LILE and depletion in HFSE with marked negative Nb-Ta,Ti and positive Th anomalies,similar to those of the typical arc volcanics.The generation of the volcanic rocks might have been attributed to an interaction of the subducted melt/fluid or sediment with the overlying refractory mantle,sug-gesting the central Jiangnan orogen was still on the subduction till ~832 Ma.It is concluded that the Jiangnan orogen consists of several branches with distinct amalgamation evolution.
Keywords：Cihua high-Mg andesitezircon U-Pb datingNeoproterozoic subductioncentral Jiangnan orogengeochemistry
Publication Date：2015-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：15( 1781-1795 )