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.

中文翻译：

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阿拉瓦利造山带中部（印度西北部）古元古代晚期/中元古代早期沉积物沉积和岩浆作用的第一个证据

阿拉瓦利造山带中部（印度西北部）内的 Beawar 片麻岩单元 (BGU) 的性质和地层位置仍未得到解决。这些岩石目前属于南德里超群，假定沉积于 1200-1000 Ma。这种解释受到岩石学新结果的挑战，结合 U-Pb 测年、锆石 Hf 同位素分析和全岩地球化学。这些数据表明，BGU 由正片麻岩和副片麻岩组成，并且原岩形成和/或沉积在大约 20 年的古元古代晚期和中元古代早期之间的边界处。1600 马。副片麻岩样品碎屑锆石的 U-Pb 年龄表明最大沉积年龄为 1614±14 Ma，主要年龄峰值在 2528、1916、1840、1725 和 1617 Ma。这些年龄，结合 Hf 同位素数据，表明源区主要由长英质岩浆岩组成，类似于在阿拉瓦利造山带和邦德尔坎德克拉通和/或印度中部构造带内的地体中出露的岩浆岩。具有约 1 年始太古代结晶年龄的单个碎屑锆石。3630 Ma 和 4.05 Ga 的 Hf 模型年龄表明冥河地壳的存在。正方麻岩样品中岩浆锆石的上截距年龄为 1581±24 Ma，表明花岗岩在中元古代早期就位。结合地球化学和 Hf 同位素数据表明，正方麻岩原岩是一种强过铝质 S 型花岗岩，由周围的围岩熔化形成，可能是在会聚环境中。