Genesis and geodynamic significance of Silurian A-type granites in the Shandan area,southern Longshoushan,Gansu
Igneous rocks in the Longshoushan are of great significance for deducing the geologic and tectonic evolution of the Qilian Mountains belt.In this study,granites from the Shandan area in the southern part of the Longshoushan Mountains in Gansu were selected for petrology,whole-rock geochemistry,zircon U-Pb chronology,and zircon in-situ Lu-Hf isotope studies.LA-ICP-MS zircon U-Pb dating of the Shandan granite yielded an age of 427.2±2.2 Ma,implying that the granite was emplaced during the Middle Silurian.The granites are characterized by high silica-potassium,alkalinity-rich,with A/CNK=1.02-1.17,and low CaO,MgO,and P2O5,showing peraluminous shoshonitic-high potassium calc alkaline.The chondrite-normalized REE patterns of the Shandan granites show enriched light rare earth elements with obvious negative Eu anomalies,whereas the primitive mantle normalized trace element spider diagrams exhibit relatively enrichment of large ionic lithospheric elements(LILE),such as Ba,Th,U,Nd,and Pb,and depletions of high field strength elements(HFSE),such as Nb,La,Ce,and Ti.The estimated zircon saturation temperature of the Shandan granite is 807-1078℃.The zircon grains from the granites have εHf(t)values of-6.51 to-4.30,indicating that the magma might have been derived from partial melting of the Paleoproterozoic crustal material.The study showed that the Shandan granite was peraluminous A2-type and formed in the Early Devonian.Combined with previous research,the Shandan granites were products of crustal remelting,indicating that the North Qilian orogenic belt and the adjacent areas were in a post-collisional extension regime during the Middle-Late Silurian-Early Devonian.
Longshoushan MountainsShandanU-Pb chronology of zirconA2-type granitepost-collision extension
万方数据
维普
