Discovery of 1.79 Ga dacite porphyry in the Taiyueshan Mts:Constraints on the genesis of the southern rift system in the North China Craton
The volcanic rocks of the Xiong'er Group mainly distribute in the southern North China Craton(NCC),and the main eruption peak time is ca.1.75～1.80Ga.As a distinctive large-scale magmatic activity of the Earth's middle age in the NCC,its formation time,temporal and spatial distribution and geodynamic background is still controversial,that hinders further research of tectonic evolution of the NCC during the Early Mesoproterozoic.In this study,Mesoproterozoic dacite porphyry is distinguished in the Taiyueshan Mts in central NCC.It intrudes into the surrounding Paleoproterozoic gneissic granitoids with weak metamorphism and deformation.The SHRIMP and LA-ICP-MS zircon U-Pb age of the dacite porphyry is ca.1.79Ga,which is consistent with the formation time of the Xiong'er volcanic rocks.90％zircon grains show two age peaks of～1.92Ga and～2.16Ga,which are speculated to be captured from surrounding rocks.The dacites belong to shoshonite series with SiO2 content from 65.12％to 66.11％,alkali content(K2O+Na2O)from 6.85％to 7.28％,A/CNK ratios of 0.91～1.05,and Na2O/K2O ratios of 0.48～0.54.They have a high content of REE with depletion in HFSE such as Nb,Ta,Zr and Hf,and enrichment in LILE such as Rb,Ba,and La,which is completely consistent with the geochemical characteristics of Xiong'er dacite-rhyolite porphyry in the southern part of NCC.Currently,more scholars believe that the Xiong'er Group was formed in a trigeminal rift system,indicating the background of within-plate extension.This dacite porphyry connects the Xiong'er Group volcanic rock series in the Zhongtiaoshan area with the Hangaoshan Group and Xiaoliangling volcanic rock series in the Lüliang area.They complete the northern branch of the Xiong'er trigeminal rift system,recording the initial Mesoproterozoic rifting in the central part of the NCC.
Dacite porphyryXiong'er volcanic-intrusive rocksTrigeminal riftTaiyueshan MtsNorth China Craton
万方数据
维普
