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Chemical and mineralogical characterisation of illite-smectite: implications for episodic tectonism and associated fluid flow, central Australia

机译:伊利石-蒙脱石的化学和矿物学特征:对偶发构造和相关流体流动的影响,澳大利亚中部

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摘要

The Warburton-Cooper-Eromanga basins of central-eastern Australia contain a number of reactivated fracture-fault networks that relate to a complex and poorly understood thermal and tectonic evolution. Authigenic illite was sampled from two prominent features of the Warburton-Cooper basins: the Gidgealpa-Merrimelia-Innamincka Ridge, composed of anticlinal imbricate thrust fault blocks, and the synclinal Nappamerri Trough. These sample sets were investigated using a combination of clay mineralogical, trace element and stable isotope analyses to deduce the palaeofluid chemistry associated with past tectonothermal perturbations. The Nappamerri Trough hosts the highly radiogenic Big Lake Suite granite and part of one of Australia\u27s larger on-shore oil and gas reserves. Calculated fluid stable isotope values from the trough, in conjunction with calculated palaeotemperatures, indicate an influx of evolved high-latitudinal meteoric waters under an extremely high geothermal gradient (~100°Ckm) and high water/rock ratios consistent with an extensional environment. Such high water/rock ratios resulted in intense alteration of the granite during which it underwent substantial enrichment in the heat-producing elements (HPE), particularly Th. This hydrothermal system is interpreted to result from continent-wide transmission of tensional stress originating from episodic rifting of the eastern Australian margin in the mid Cretaceous, as dated by Sm-Nd, Rb-Sr and Ar-Ar. The Gidgealpa-Merrimelia-Innamincka Ridge, by contrast, is marked by a lower, but still elevated, palaeogeothermal gradient (~42°Ckm) and calculated fluid isotopic values compatible with evolved basinal fluids of meteoric origin under low water/rock ratio conditions. Distinct trace element compositions of residue and leachate aliquots further indicate two periods of fluid flow with unique chemical compositions. In light of previous geochronology, these events are interpreted as westward extensions of widespread crustal tensional stress that affected much of central and eastern Queensland in the Carboniferous and Late Triassic. Integrated analyses of authigenic illite provide evidence for three periods of fluid flow and elevated thermal regime associated with regional tectonism during the Carboniferous, Late Triassic and Cretaceous. Our data further show that due to the extremely high geothermal gradient and water/rock ratios, Cretaceous fluid flow had profound effects on the surrounding geology, which may have formed/enhanced two of Australia\u27s most significant energy resources.
机译:澳大利亚中东部的沃伯顿-库珀-埃罗曼加盆地包含许多重新活化的断裂-断裂网络,这些断裂-断裂网络与复杂且鲜为人知的热演化和构造演化有关。自Warburton-Cooper盆地的两个突出特征取样了自生伊利石:由反斜纹岩性逆冲断层块组成的吉德阿尔帕-梅里梅利亚-Innamincka山脊和向斜Nappamerri槽。使用粘土矿物学,痕量元素和稳定同位素分析相结合的方法研究了这些样品组,以推论与过去构造热扰动有关的古流体化学。 Nappamerri槽拥有高放射性的Big Lake Suite花岗岩,并且是澳大利亚较大的陆上石油和天然气储藏之一的一部分。从槽中计算出的流体稳定同位素值,再加上计算出的古温度,表明在极高的地热梯度(〜100°Ckm)和高水/岩石比(与扩张环境一致)的条件下,涌入了高纬度的演化水。如此高的水/岩石比导致花岗岩发生强烈变化,在此期间,花岗岩经历了发热元素(HPE)尤其是Th的大量富集。该热液系统被解释为是由白垩纪中期澳大利亚东部边缘的间歇性裂谷引起的张应力在整个大陆范围内传播所引起的,如Sm-Nd,Rb-Sr和Ar-Ar年代。相比之下,吉德阿尔巴-梅里米利亚-因南辛卡山脊的特征是较低的但仍然升高的古地热梯度(〜42°Ckm),并且计算出的流体同位素值与低水/岩石比条件下流变演化的盆地流体兼容。残留物和沥出液等分试样的不同微量元素组成进一步表明了两个具有独特化学组成的流体流动时期。根据以前的年代学,这些事件被解释为广泛的地壳拉应力向西扩展,影响了石炭纪和晚三叠纪的昆士兰州中部和东部的大部分地区。对自生伊利石的综合分析为石炭纪,晚三叠纪和白垩纪的三个时期的流体流动和与区域构造有关的热态升高提供了证据。我们的数据进一步表明,由于极高的地热梯度和水/岩石比,白垩纪流体流动对周围的地质产生了深远的影响,这可能已经形成/增强了澳大利亚两个最重要的能源。

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