浙东南地区晚中生代“祝村组”的解体:相关火山岩形成时代及岩石成因

发布时间：2018-05-12 10:35

本文选题：祝村组 + 地层单元解体　；参考：《岩石学报》2017年01期

【摘要】：浙东南沿海小雄盆地中"祝村组"火山岩的年代学研究表明,其形成时代(128Ma)不仅老于其上覆的上火山岩系(110~88Ma),还老于本应在其下伏的九里坪组(122~120Ma)而与区域内西山头组时代相同(130~128Ma)。"祝村组"火山岩的锆石Hf同位素组成表现出富集的特征并具有古元古代的地壳模式年龄(εHf(t)=-16.4~-13.6,tDM2=2.01~2.09Ga),同样与磨石山群下部地层如西山头组相似。结合火山碎屑岩-流纹岩的岩石组合以及区域地质特征,本研究认为"祝村组"的建组理由不充分,建议将其解体。同时,"祝村组"火山岩富集的Hf同位素组成表明其源区为较为纯粹的古元古代地壳基底物质,进一步暗示相对内陆地区的下岩系早期火山岩形成过程中已有较明显的亏损幔源物质参与,这是以往研究中未明确识别出的。浙东南地区晚中生代火山岩岩石成因中底侵幔源物质贡献比例的升高和火山碎屑岩-流纹岩-双峰式火山岩岩石组合均暗示了逐渐增强的岩石圈伸展应力环境,这可能与古太平洋俯冲板片的后撤作用密切相关。
[Abstract]:A chronological study of the volcanic rocks of the Zhucun formation in the Xiaoxiong Basin, southeast Zhejiang Province, shows that the volcanic rocks formed at the age of 128MaA are not only older than that of the upper volcanic rocks overlying them, but also older than that of the Jiuliping formation, which should be located under it, and is the same as that of the Xishantou formation in the region. " The zircon HF isotopic composition of the volcanic rocks in the Zhucun formation shows the characteristics of enrichment and has the Gu Yuan age of the ancient crustal model (蔚 Hfltntnll-16.4- 13.6t DM2U 2.01U 2.09Ga), which is similar to that of the lower part of the Moshishan Group such as the Xishantou formation. Combined with the rock assemblage of pyroclastic rock and rhyolite and the regional geological characteristics, this study considers that the formation of Zhucun formation is not well-founded, and suggests to disintegrate it. At the same time, the HF isotopic composition of the volcanic rocks enriched in the "Zhucun formation" indicates that the source area is relatively pure Paleoproterozoic crustal basement material. It is further suggested that the depleted mantle source material has been involved in the formation of the early volcanic rocks in the lower rock series, which has not been clearly identified in previous studies. The increase of the contribution ratio of mantle source materials from the late Mesozoic volcanic rocks and the volcanic rock assemblages of pyroclastic rocks, rhyolite and bimodal volcanic rocks in southeastern Zhejiang suggest a gradually enhanced lithospheric extensional stress environment. This may be closely related to the retreat of the paleo-Pacific subduction plate.
【作者单位】：桂林理工大学地球科学学院广西隐伏金属矿产勘查重点实验室;桂林理工大学广西有色金属隐伏矿床勘查及材料开发协同创新中心;南京大学地球科学与工程学院内生金属矿床成矿机制研究国家重点实验室;
【基金】：国家重点研发计划项目(2016YFC0600203) 国家自然科学基金项目(41430208) 桂林理工大学科研启动费资助项目联合资助
【分类号】：P588.14

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