Uranium-Th-Pb dating of phosphate minerals in very low-grade metasedimentary rocks from the Archean Pilbara Craton, Western Australia, has revealed a long history of deformation and fluid flow during the Paleoproterozoic. However, this technique has not detected evidence for fluid flow along craton margins during Phanerozoic rifting and breakup. We report the use of in situ Th-Pb geochronology of rhabdophane, a hydrous light rare earth element phosphate, to date fluid flow in shale from the 2.76 Ga Mount Roe Basalt from drill hole number 6 of the Archean Biosphere Drilling Program (ABDP6), northwestern Pilbara Craton. Thorium-Pb dating of rhabdophane in carbonaceous shale yields three main populations with weighted mean 208Pb/232Th ages of 152 ± 6 Ma, 132 ± 4 Ma, and 119 ± 4 Ma, which indicates phosphate growth up to 2.64 b.y. after deposition. The rhabdophane ages are coeval with three major breakup events in eastern Gondwana: separation of Southwest Borneo and Argoland from Australia (ca. 156–152 Ma), breakup of Greater India from Australia (ca. 140–135 Ma), and separation of Greater India/India from Antarctica (ca. 123 Ma). The proximity of drill hole ABDP6 to major Mesoarchean faults and shear zones on the craton margin, which are parallel to rift propagation and basin development, points to episodic reactivation of ancient crustal structures >2.8 b.y. after their formation. Our results also highlight the potential of rhabdophane as a U-Th-Pb geochronometer for dating low-temperature (<200 °C) fluid flow and hydrous alteration. The migration of Mesozoic fluids through Archean shales adds weight to questions about the origin of geochemical signals in ancient altered rocks and how to extract information about the early environment and biosphere.

中文翻译：

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Rhabdophane Th-Pb 年龄表明在大印度和澳大利亚 - 南极洲分裂期间西皮尔巴拉克拉通的中太古代结构重新激活

来自西澳大利亚太古代皮尔巴拉克拉通的极低品位变沉积岩中磷酸盐矿物的铀-Th-Pb 年代测定揭示了古元古代期间变形和流体流动的悠久历史。然而，该技术没有检测到在显生宙裂谷和破碎过程中流体沿着克拉通边缘流动的证据。我们报告了使用弹状体（一种含水轻稀土元素磷酸盐）的原位 Th-Pb 年代学，迄今为止，太古宙生物圈钻井计划 (ABDP6) 的 6 号钻孔中 2.76 Ga 罗伊山玄武岩的页岩流体流动，皮尔巴拉克拉通西北部。碳质页岩中弹状体的钍-Pb 定年产生三个主要种群，加权平均 208Pb/232Th 年龄分别为 152±6 Ma、132±4 Ma 和 119±4 Ma，表明沉积后磷酸盐增长高达 2.64。弹纹岩时代与冈瓦纳东部的三个主要分裂事件同时发生：西南婆罗洲和阿尔戈兰与澳大利亚的分离（约 156-152 Ma），大印度与澳大利亚的分裂（约 140-135 Ma），以及大印度洋的分离来自南极洲的印度/印度（约 123 Ma）。钻孔 ABDP6 靠近克拉通边缘的主要中太古代断层和剪切带，与裂谷扩展和盆地发育平行，表明古代地壳结构在其形成后发生了 >2.8 的间歇性再活化。我们的研究结果还突出了弹状体作为 U-Th-Pb 年代计测定低温 (<200 °C) 流体流动和含水蚀变年代的潜力。