巴西伊比蒂亚拉—里奥德孔塔斯地区古元古代火山岩年代学、地球化学特征及其成因
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本文为国家重点研发计划项目“环太平洋和非洲成矿域战略性矿产信息及成矿规律“(编号:2021YFC2901804)及地质调查项目”武夷成矿带战略性矿产调查(编号:DD20240067)、美洲和大洋洲国际合作地质调查”(编号:DD20230129)和江南陆块南缘成矿带(东段)战略性矿产调查(编号:DD20240066)资助的成果


Zircon U- Pb Age, geochemical characteristics and petrogenesis of Paleoproterozoic rhyolites in Ibitiara—Rio de Contas Area,SFC, Brazil
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    摘要:

    本文首次报道了巴西中东部圣弗朗西斯科克拉通巴伊亚州内伊比蒂亚拉—里奥德孔塔地区古元古代(变)流纹质熔结凝灰岩LAICPMS锆石UPb年龄为1723~1736 Ma。该类岩石地球化学特征上具有高硅、富碱和低钙镁、过铝质特点;富集大离子亲石元素(如K、Th、U、Rb、Ba、Sr)和相对亏损高场强元素(如Nb、P、Zr、Hf)以及Ti明显亏损。稀土元素含量较高(∑REE为325× 10-6~830×10-6),轻稀土元素相对富集((La/Yb)N为 3. 26~6. 57,稀土配分曲线呈现略右倾,强烈Eu负异常(δEu = 0. 0460~0. 416)的海鸥型;火山岩锆石Ti温度计得出岩浆温度为706~943℃,锆石饱和温度836~992℃。这些特征表明该区火山岩岩浆具有高温、浅成就位特征,为钙碱性铝质A型花岗岩类岩浆,形成于非造山型陆内板块裂谷带环境。该火山岩岩浆经历了壳幔部分熔融、结晶分异过程,并有西部火山岩向东部富硅演化的趋势。

    Abstract:

    The aim is to analyze and organize volcanic rocks’ timeline and chemical composition in the Ibitiara—Rio de Contas area of the So 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 So 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 So 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 (∑REE is 325×10-6-830×10-6), 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.

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沈莽庭,叶海敏,王天刚,范飞鹏,孙建东,徐鸣,吴大天.2024.巴西伊比蒂亚拉—里奥德孔塔斯地区古元古代火山岩年代学、地球化学特征及其成因[J].地质论评,70(4):2024040012,[DOI].
SHEN Mangting, YE Haiming, WANG Tiangang, FAN Feipong, SUN Jiangdong, XU Ming, WU Datian.2024. Zircon U- Pb Age, geochemical characteristics and petrogenesis of Paleoproterozoic rhyolites in Ibitiara—Rio de Contas Area,SFC, Brazil[J]. Geological Review,70(4):2024040012.

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  • 收稿日期:2024-04-10
  • 最后修改日期:2024-07-11
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  • 在线发布日期: 2024-07-20
  • 出版日期: 2024-07-15