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首页> 外文期刊>Journal of Asian earth sciences >Initiation of the intra-cratonic Cuddapah basin: Evidence from Paleoproterozoic (1995 Ma) anorogenic porphyritic granite in Eastern Dharwar Craton basement
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Initiation of the intra-cratonic Cuddapah basin: Evidence from Paleoproterozoic (1995 Ma) anorogenic porphyritic granite in Eastern Dharwar Craton basement

机译：克拉通内Cuddapah盆地的形成：来自东Dharwar Craton地下室的古元古代（1995 Ma）造山斑岩的证据

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摘要

Initiation of large intra-cratonic sedimentary basins has been constrained by dating the magmatic rocks intercalated in the sedimentary sequence; one such major basin in southeastern India is the Paleoproterozoic Cuddapah Basin. Near-basal Cuddapah sediments, deposited over the Eastern Dharwar Craton basement, are interlayered with mafic lavas and intruded mafic-ultramafic sills (1885 ±3 Ma) being evidence for mantle melting. One of the expected major consequences of the asthenospheric upwelling on the lithosphere, apart from crustal doming, would have been partial melting of the cratonic tonalite-granodiorite crust and generation of granitic melts with anorogenic geochemical characteristics, the precise dating of which would constrain the timing of the basin initiation. From the southeastern part of the eroded basin, being the only exposed part into the basement below the sediment cover, we report presence of exactly such intrusive porphyritic granite. Petrological and geochemical characteristics of these anorogenic metaluminous granites strongly support partial melting (～10-12%) of the cratonic tonalite-diorite crust most likely due to basaltic underplating. The crystallization time of this granite, sampled from SE of SriKalahasti, was determined on magmatic zircons and yielded a precise ~(207)Pb/~(206)Pb weighted mean age of 1995 ±11 Ma. As the felsic crustal melting phase significantly predated the 1885 ±3 Ma-aged mafic sills emplacement, early events include significant erosion of the previously uplifted basement followed by sedimentation (＞1500m) before mafic volcanism and sill emplacement. This history broadly suggests active rift basin evolution from a non-extensional setting progressing to passive extension.
机译：大型克拉通内沉积盆地的形成已受到对沉积序列中插层岩浆岩年代的限制。印度东南部的这样一个主要盆地是古元古代Cuddapah盆地。沉积在东部Dharwar Craton地下室之上的近基底Cuddapah沉积物与镁铁质熔岩夹层，侵入的镁铁质-超镁铁基岩（1885±3 Ma）是地幔融化的证据。除了地壳隆起以外，岩石圈软流圈上升的预期主要后果之一将是克拉通斜长石-斜辉闪石地壳的部分熔融和具有厌食地球化学特征的花岗岩熔体的产生，其精确定年将限制时间。盆地萌生从侵蚀盆地的东南部开始，它是沉积物覆盖层下方地下室中唯一暴露的部分，我们报告确实存在这种侵入性的斑状花岗岩。这些矿成矿性金属花岗岩的岩石学和地球化学特征强烈支持了克拉通的斜长石-闪长岩地壳的部分熔融（〜10-12％），这很可能是由于玄武质的底层沉积所致。该花岗岩的结晶时间是从岩浆锆石上从斯里兰卡卡拉哈斯蒂（SriKalahasti）的SE取样确定的，精确的〜（207）Pb /〜（206）Pb加权平均年龄为1995±11 Ma。由于长英质地壳熔融阶段明显早于1885年±3 Ma年龄的基性基岩的侵袭，早期事件包括对先前隆起的基底的严重侵蚀，随后在基性质火山作用和基岩侵袭之前沉积（> 1500m）。这段历史广泛地表明了主动裂谷盆地从非伸展环境向被动伸展的演变。

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