First Evidence of Late Paleoproterozoic/Early Mesoproterozoic Sediment Deposition and Magmatism in the Central Aravalli Orogen (NW India)

IF 1.5 4区 地球科学 Q2 GEOLOGY
Journal of Geology Pub Date : 2020-02-13 DOI:10.1086/707235
P. Kaur, A. Zeh, N. Chaudhri, Jaideep K. Tiwana
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引用次数: 16

Abstract

The nature and stratigraphic position of the Beawar gneiss unit (BGU) within the central Aravalli orogen (NW India) remain unresolved. These rocks are currently assigned to the South Delhi Supergroup, assumed to be deposited at 1200–1000 Ma. This interpretation is challenged by new results of petrography, combined with U-Pb dating, Hf isotope analyses of zircon, and whole-rock geochemistry. These data reveal that the BGU consists of both ortho- and paragneisses and that the protoliths were formed and/or deposited at the boundary between the late Paleoproterozoic and early Mesoproterozoic at ca. 1600 Ma. U-Pb ages of detrital zircon grains from a paragneiss sample indicate a maximum deposition age of 1614±14 Ma and major age peaks at 2528, 1916, 1840, 1725, and 1617 Ma. These ages, in combination with Hf isotope data, suggest that the source area consisted mainly of felsic magmatic rocks similar to those exposed within the Aravalli orogen and in the Bundelkhand Craton and/or in terranes within the Central Indian Tectonic Zone. A single detrital zircon with an Eoarchean crystallization age of ca. 3630 Ma and Hf model age of 4.05 Ga point to the existence of the Hadean crust. Magmatic zircon in an orthogneiss sample yields an upper-intercept age of 1581±24 Ma, indicating granite emplacement during the early Mesoproterozoic. Combined geochemical and Hf isotope data suggest that the orthogneiss protolith was a strongly peraluminous S-type granite, formed by melting of surrounding country rocks perhaps within a convergent setting. U-Pb ages (980–960 Ma) of zircon overgrowths and monazite grains suggest that all the rocks were affected by a Grenvillian metamorphic overprint during the assembly of Rodinia.
印度西北部Aravalli造山带中部晚古元古代/早中元古代沉积与岩浆作用的首个证据
印度西北部Aravalli造山带中部的Beawar片麻岩单元(BGU)的性质和地层位置仍未确定。这些岩石目前被划分为南德里超群,假定沉积于1200-1000 Ma。岩石学的新结果,结合U-Pb测年、锆石Hf同位素分析和全岩地球化学,对这种解释提出了挑战。这些资料表明,北古陆既有正长岩,也有副长岩,其原岩形成和沉积于大约1600 Ma的古元古代晚期和中元古代早期之间。副辉岩碎屑锆石U-Pb年龄显示,最大沉积年龄为1614±14 Ma,主要年龄峰为2528、1916、1840、1725和1617 Ma。这些年龄结合Hf同位素数据表明,烃源区主要由长英质岩浆岩组成,类似于Aravalli造山带和Bundelkhand克拉通和/或印度中部构造带的地体中暴露的岩浆岩。单一碎屑锆石的结晶年龄约为3630 Ma,模式年龄为4.05 Ga,表明冥古宙地壳的存在。正长岩样品的岩浆锆石上截年龄为1581±24 Ma,表明花岗岩侵位时间为中元古代早期。地球化学和Hf同位素数据表明,正长石原岩是一种强过铝s型花岗岩,可能是在会聚环境中由周围围岩熔融形成的。锆石生长体和独居石颗粒的U-Pb年龄(980 ~ 960 Ma)表明,所有岩石在Rodinia组合期间都受到了Grenvillian变质套印的影响。
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来源期刊
Journal of Geology
Journal of Geology 地学-地质学
CiteScore
3.50
自引率
5.60%
发文量
0
审稿时长
3 months
期刊介绍: One of the oldest journals in geology, The Journal of Geology has since 1893 promoted the systematic philosophical and fundamental study of geology. The Journal publishes original research across a broad range of subfields in geology, including geophysics, geochemistry, sedimentology, geomorphology, petrology, plate tectonics, volcanology, structural geology, mineralogy, and planetary sciences. Many of its articles have wide appeal for geologists, present research of topical relevance, and offer new geological insights through the application of innovative approaches and methods.
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