扬子北部三峡地区南沱组冰碛岩的物源特征:锆石年龄和地球化学证据

发布时间：2018-06-06 05:54

本文选题：扬子陆块 + 南沱组　；参考：《地球科学》2016年10期

【摘要】：扬子陆块新元古代地层发育完整并广泛分布,三峡地区南沱组冰碛岩是扬子北部南华纪的冰成杂砾岩,不整合地覆盖在新元古代黄陵花岗岩之上.南沱组冰碛岩成分复杂,分选性差,缺乏可对比的标志,其沉积时代和物源组成研究较少且存在争议.对南沱组冰碛岩开展锆石U-Pb定年工作,得到最年轻的锆石年龄为706±7 Ma,印证了南沱组沉积时代应不早于700Ma的说法,并可与Marinoan冰期对应.所获得锆石U-Pb年龄谱峰值主要分为~3.0Ga,2.5~2.3Ga,2.05~1.95Ga和900~700Ma,反映了扬子陆块4次地壳再造事件,其中古元古代和太古代年龄与崆岭杂岩相似,900~800Ma和800~700Ma的锆石年龄与附近黄陵花岗岩和扬子北缘岩体一致.冰碛砂岩的微量元素和同位素组成分异明显,可能是扬子北缘岩体、黄陵花岗岩和崆岭杂岩不同程度混合的结果.南沱组冰碛岩中包裹的花岗质砾石表现出不同的微量元素特征,具有偏低的稀土含量和亏损的重稀土组成,结合其锆石U-Pb年龄和Sr-Nd同位素特征,这些花岗质砾石主体可能来自于附近黄陵花岗岩和崆岭岩基.南沱组冰碛岩的物质组成特征反映了新元古时期,扬子地区强烈的裂谷岩浆作用所导致的北高南低的地势环境.
[Abstract]:The Neoproterozoic strata of the Yangtze block are well developed and widely distributed. The moraine rock of Nantuo formation in the three Gorges area is an ice conglomerate of the Nanhua period in the northern part of Yangzi, which is unconformably covered on the neoproterozoic Huangling granite. The moraine rocks of Nantuo formation are complex in composition, poor in sorting and lack of comparable markers, and there are few researches on sedimentary age and provenance composition in Nantuo formation. Zircon U-Pb dating was carried out for the moraine rocks of Nantuo formation, and the youngest zircon age was 706 卤7 Ma, which confirmed that the sedimentary age of Nantuo formation should not be earlier than 700Ma, and could correspond to Marinoan glacial age. The peak values of zircon U-Pb age spectrum are mainly divided into 3. 0 Ga, 2. 5, 2. 3, 2. 05 and 1. 95 Ga and 900, 700 Ma, which reflect the 4 crustal reconstruction events in the Yangtze continent block. The zircon ages of Gu Yuan and Archean are similar to those of the Kongling complex and the zircon ages of 800~700Ma and Huangling granites are consistent with those of the nearby Huangling granites and the northern margin of Yangtze. The trace elements and isotopic compositions of moraine sandstone are distinct, which may be the result of the mixing of the northern Yangtze margin, Huangling granite and Kongling complex to different degrees. The granitic gravels in the moraine rocks of the Nantuo formation show different trace element characteristics, with low rare earth content and depleted heavy rare earth composition, combined with the zircon U-Pb age and Sr-Nd isotopic characteristics. These granitic gravel bodies may be derived from nearby Huangling granite and Kongling rock bases. The material composition characteristics of moraine rocks in Nantuo formation reflect the strong rift magmatism in Yangzi area in the Neoproterozoic.
【作者单位】：中国科学技术大学地球和空间科学学院;中国地质大学地球科学学院;
【基金】：国家自然科学基金项目(Nos.40973042;41090372) 中央高校基本科研业务费专项资金
【分类号】：P597.3;P588.2

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