Zircon U-Pb Age,geochemical characteristics and petrogenesis of Paleoproterozoic rhyolites in Ibitiara—Rio de Contas Area,Brazil
Objectives:The aim is to analyze and organize volcanic rocks'timeline and chemical composition in the Ibitiara—Rio de Contas area of the São Francisco Craton,Brazil.This analysis will enhance understanding the origin and tectonic setting in which these rocks evolved.It will offer geochronological and geochemical evidence to gain deeper insights into the geodynamic context of the formation of Paleoproterozoic volcanic rocks in the São Francisco Craton.Methods:The macro and micro characteristics of metamorphic rhyolite ignimbrite in Ibitiara—Rio de Contas were identified using thin sections.The content of major elements was analyzed using X-ray fluorescence spectrometry(XRF),with typical samples collected and analyzed using the laminate method.The content of trace elements was measured using inductively coupled plasma mass spectrometry(LA-ICP-MS).Additionally,zircon LA-ICP-MS U-Pb dating was performed using the LA-ICP-MS and laser ablation system.Result:The paper presents LA-ICP-MS zircon analysis of a Paleoproterozoic(metamorphic)rhyolite ignimbrite in the Ibitiara—Rio de Contas area of the Sao Francisco Craton in Bahia State,Central and eastern Brazil.The analysis revealed U-Pb ages of 1723～1736 Ma,the first time these ages have been reported for this area.The rocks show high levels of silicon,aluminum,and alkali components,and low levels of calcium and magnesium.They also contain enriched large ion lithophile elements(like K,Th,U,Rb,Ba,Sr)and relatively deficient high field strength elements(such as Nb,P,Zr,Hf)and Ti.The rare earth element abundance value is high(Σ.REE is 325x10-6-830x10-6),and light rare earth elements are relatively enriched(La/Yb)N is 3.26～6.57.The rare earth partition curve shows a slight right-leaning and a strong negative Eu anomaly(δEu=0.0460～0.416).The volcanic zircon Ti thermometer indicates a magma temperature range of 706～943℃,with a zircon saturation temperature of 836～992℃.Based on these characteristics,it's suggested that the volcanic magma in this area has a high temperature and shallow origin.This implies it is a calc-alkaline aluminum A-type granite formed in a non-orogenic intracontinental plate rift zone environment.The volcanic magma has undergone crust and mantle partial melting and crystallization differentiation and indicates a trend of silica-rich evolution from west to east.
LA-ICP-MS Zircon U-Pb datinggeochemistryTectonic environmentIbitiara—Rio de Contas AreaSao Francisco CratonBrazil
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维普
