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  

Disintegration of Late Mesozoic Zhucun Formation in southeastern Zhejiang:Geochronology and petrogenesis of the related volcanic rocks

作　　者：刘磊[1,2,3] 徐夕生[3] 夏炎[3] 梁琼丹[1,2] 裴小利[1,2] LIU Lei XU XiSheng XIA Yan LIANG QiongDan PEI XiaoLi(Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, College of Earth Sciences, Guilin University of Technology, Guilin 541004, China Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials in Guangxi, Guilin University of Technology, Guilin 541004, China State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China)

机构地区：[1]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541004 [2]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,桂林541004 [3]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,南京210023

出　　处：《岩石学报》2017年第1期115-126,共12页Acta Petrologica Sinica

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

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。The once designated Zhucun Formation in Xiaoxiong basin is investigated to be geochronologically earlier （128Ma） not only than the overlying upper volcanic series （110~88Ma）, but also than the underlying Jiuliping Formation （122~120Ma）, but coeval to the Xishantou Formation （130~128Ma）. Zircon Hf isotopic compositions of the studied Zhucun Formation rhyolitic tuff show enriched characteristics with Paleoproterozoic crustal model ages （εHf（t）=-16.4^-13.6, tDM2=2.01~2.09Ga）, also similar to the Lower Moshishan Group, such as the Xishantou Formation. Note these and the pyroclastic-rhyolitic volcanic rock assemblages and other regional geological features, the foundation basis of the Zhucun Formation is considered to be insufficient, and the Formation should be disintegrated. On the other hand, the enriched zircon Hf isotopic compositions of the studied Zhucun Formation rhyolitic tuff show that it was derived mainly from partial melting of the Paleoproterozoic crustal basement, further indicating that the Lower Moshishan Group volcanic rocks inland were derived with depleted-mantle derived material contribution, which was barely noticed in previous studies. The increased depleted-mantle derived material contribution in the volcanic petrogenesis and the pyroclastic-rhyolitic-bimodal volcanic assemblages both imply increased lithospheric extension, plausibly caused by rollback of the subducted paleo-Pacific slab.

关 键 词：祝村组 地层单元解体 构造背景制约 晚中生代 中国东南部 

分 类 号：P588.14[天文地球—岩石学]