Geochemical and detrital zircon U-Pb geochronological constraints on provenance of the Xiaomei red earth sediments (Bose Basin, Guangxi Province, southern China)
Geochemical and detrital zircon U-Pb geochronological constraints on provenance of the Xiaomei red earth sediments (Bose Basin, Guangxi Province, southern China)
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地球化学和碎屑锆石U-Pb年代学对小梅红土沉积物物源的限制（中国南方广西百色盆地）
DOI：
10.1016/j.palaeo.2017.08.040
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Fang Qian
中科院分区：
文献类型：
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作者：
Cheng Feng;Hong Hanlie;Bae Christopher J.;Li Zhaohui;Algeo Thomas J.;Huang Shengmin;Cheng Liuling;Fang Qian
中国南部的百色盆地处于冬季西风季风的影响范围内，因此有可能出现风尘堆积。珠江支流右江阶地上发育的红土序列记录了更新世气候变化及其与同期全球气候变化的关系。本文采用X射线衍射、X射线荧光、电感耦合等离子体质谱、热电离质谱、碎屑锆石U-Pb定年等方法，研究了小梅红土层序碎屑锆石的地球化学特征和U-Pb年代学。结果表明，红壤沉积物由石英和粘土矿物(高岭石、伊利石、伊利石/蛭石混层)和少量赤铁矿、针铁矿组成。与中国黄土高原(CLP)、上陆壳(UCC)和后太古代澳大利亚页岩(PAAS)相比，活动性元素CaO、MgO、Na2O、K2O、Sr和Ba亏损，而非活动性元素TiO2Al2O3Fe2O3(T)和Zr丰度较高。这些资料表明，小美红壤沉积物经历了强烈的化学风化，与长江中下游宣城和九江红壤段相似。小梅沉积物具有相似的La/Th比值、U/Pb值和Th/Pb值，稀土元素(REE)分布与CLP、UCC和PAAS相似，其低的εND(0)值指示上地壳成因。小梅沉积物的~(147)Sm/~(144)Nd和~(87)Sr/~(86)Sr比值不同于CLP的黄土-古土壤，而与混合良好的河流沉积物相似。小梅沉积物中碎屑状锆石的U-Pb定年结果表明，不同单元的晶体年龄分布略有不同。小梅全剖面的分布与右江地区上二叠-三叠统碎屑岩分布相似，中、上小梅剖面的分布与南中国克拉通上地壳相似。结果表明，小梅红土层序形成于早更新世晚期至中更新世早期(约1.0~0.6m a)，主要来自河流输运的局部风化物质，因此，以往对中国南部红壤沉积物物源的研究高估了东亚冬季风的携沙能力。
The Bose Basin in southern China is within a region influenced by the winter westerly monsoon and, thus, potentially subject to eolian dust accumulation. A red earth sequence developed on terraces of the Youjiang River (a branch of the Pearl River) records information about climate variation during the Pleistocene and its relationship to contemporaneous global climate changes. In this study, geochemical characteristics and U-Pb geochronology of detrital zircons of the red earth sequence at Xiaomei were investigated using X-ray diffraction (XRD), X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), thermal ionization mass spectrometry (TIMS), and detrital zircon U-Pb dating analyses. Our results show that the red earth sediments are composed of quartz and clay minerals (kaolinite, illite, and mixed-layer illite/vermiculite) with minor hematite and goethite. Mobile elements such as CaO, MgO, Na2O, K2O, Sr and Ba are depleted and immobile elements such as TiO2, Al2O3, Fe2O3(t) and Zr are enriched in comparison with loess-paleosols of the Chinese Loess Plateau (CLP), the upper continental crust (UCC), and post-Archean Australian shale (PAAS). These data indicate that the Xiaomei red earth sediments have experienced intense chemical weathering, similar to that of the Xuancheng and Jiujiang red earth sections on the middle to lower reaches of the Yangtze River. The Xiaomei sediments have similar La/Th ratios, U/Pb vs. Th/Pb relationships, and rare earth element (REE) distributions to the CLP, UCC, and PAAS, and their low εNd(0) values are indicative of an upper crustal origin. The147Sm/144Nd and87Sr/86Sr ratios of the Xiaomei sediments are different from loess-paleosols of the CLP but similar to those of well-mixed river sediments. U-Pb dating of detrital zircons in the Xiaomei sediments shows that crystals from different units have slightly different age distributions. The full Xiaomei section yields a distribution similar to that of Upper Permian-Triassic clastic rocks in the Youjiang area, and the distribution of the middle to upper Xiaomei section additionally shows similarities to upper crust of the South China Craton. Our results indicate that the Xiaomei red earth sequence, which dates to the late Early to early Middle Pleistocene (~ 1.0–0.6 Ma), accumulated predominantly from fluvially transported, locally weathered materials and, therefore, that the sediment-carrying capacity of the East Asian winter monsoon has been overestimated in previous provenance studies of red earth sediments in South China.