扬子板块北缘花山群沉积时代及其对Rodinia超大陆裂解的制约

发布时间：2018-05-26 20:05

本文选题：扬子板块 + 大洪山　；参考：《地质学报》2017年11期

【摘要】：出露于扬子板块北缘大洪山地区的花山群自下而上由一套以砾岩为主的粗碎屑沉积和一套以砂质板岩为主的细碎屑沉积组成,伴随有拉斑玄武质岩浆活动。花山群整体变质程度不高,形成构造环境复杂,对其构造属性及其与区内所谓的花山"蛇绿混杂岩"的时空关系一直存有争议,它们对新元古代Rodinia超大陆在扬子板块北缘的汇聚-裂解响应具有重要的制约意义。笔者在花山群六房咀组下部细砂岩中采集玄武质熔结凝灰岩夹层样品1件,碎屑岩样品2件,在上覆地层南华系莲沱组采集碎屑岩样品1件;对玄武质熔结凝灰岩进行了SHRIMP锆石U-Pb同位素测年,对碎屑岩样品进行了LA-MC-ICPMS锆石U-Pb同位素测年。获得玄武质熔结凝灰岩锆石U-Pb年龄814.7±7.3 Ma;花山群的碎屑锆石U-Pb年龄谱存在三个明显的峰值:~900 Ma、~2050Ma和~2650 Ma,最显著峰值为~2650 Ma,上覆莲沱组碎屑岩年龄谱的三个峰值为:~900 Ma、~2050 Ma和~2500 Ma,最显著峰值为~2050Ma,三件碎屑岩样品均与扬子板块的碎屑锆石U-Pb年龄统计峰值一致。花山群的碎屑源区可能包括下伏中元古代打鼓石群、太古宙鱼洞子杂岩以及崆岭杂岩。结合前人年代学研究资料和区域构造成果分析,花山群沉积时代应为820~815Ma,形成于伸展构造背景,与花山"蛇绿混杂岩"不是同期同构造背景的产物;花山"蛇绿混杂岩"与花山群沉积建造依次反映了扬子板块北缘由挤压构造背景向伸展构造背景的转换过程。花山群中的碎屑沉积物与基性火山岩、火山碎屑岩属于裂解背景下形成的同时代沉积-火山建造;结合前人在扬子板块周缘发现的大量约820 Ma酸性—基性岩浆活动记录以及同时代(820~800 Ma)的沉积地层,推测花山群形成于Rodinia超大陆裂解背景之下,与超级地幔柱活动有关。
[Abstract]:The Huashan Group, which is exposed to the northern margin of the Yangtze plate, consists of a set of coarse clastic deposits dominated by conglomerates and a set of fine clastic deposits dominated by sandy slate from the bottom to the top, accompanied by Black Tortoise magmatic activity. The whole metamorphic degree of Huashan Group is not high, and the tectonic environment is complex. The tectonic attributes and their spatiotemporal relationship with the so-called "ophiolite melange" in Huashan region have always been disputed. They are of great significance to the converging-pyrolysis response of the Neoproterozoic Rodinia supercontinent in the northern margin of the Yangtze plate. In this paper, 1 sample of Black Tortoise melt tuff intercalation, 2 samples of clastic rock and 1 sample of clastic rock are collected in the fine sandstone of the lower part of Liufangzui formation in Huashan Group, and in the Liantuo formation of the South China Series in the overlying strata. SHRIMP zircon U-Pb isotope dating and LA-MC-ICPMS zircon U-Pb isotope dating of clastic rock samples were carried out for Black Tortoise melt-formed tuff. The zircon U-Pb age of Black Tortoise melt-formed tuff is 814.7 卤7.3Ma.The U-Pb age spectrum of clastic zircon in Huashan group has three distinct peak values of 2050Ma and 2650Ma, with the most significant peak value of 2650 Ma, and the three peaks of the clastic age spectrum of the Shangwuliantuo formation is: 0900 Ma2050 2050Ma. the most significant peak value is 2650Ma. the three peaks of the clastic age spectrum of the Shangwuliantuo formation are: 900Ma2050. Ma and Xian2500 Ma.The most significant peak value is 2050Ma.The three samples of clastic rock are in agreement with the U-Pb age peak of the Yangtze plate's detrital zircon. The detrital sources of the Huashan Group may include the Lower Proterozoic Dagu Group Archean Yudong Zi complex and the Kongling complex. Based on previous chronological data and analysis of regional tectonic achievements, the sedimentary age of Huashan Group should be 820 ~ 815 Ma.It was formed in the extensional tectonic setting and was not the product of the same tectonic setting as the Huashan "ophiolite". The "ophiolite melange" in Huashan and the sedimentary formation of the Huashan Group in turn reflect the transformation process from the compressional tectonic setting to the extensional tectonic setting of the northern Yangtze plate. The clastic sediments and basic volcanic rocks in the Huashan Group belong to the contemporaneous sedimentation-volcanic formation formed in the pyrolysis background. Combined with a large number of acid-basic magma activity records of 820 Ma and sedimentary strata of 820 Ma and 800 Ma found by predecessors around the Yangtze plate, it is inferred that the Huashan Group was formed in the Rodinia supercontinental pyrolysis background, which is related to the super-mantle plume activity.
【作者单位】：中国地质调查局天津地质调查中心;湖北省区域地质矿产调查所;
【基金】：中国地质调查局项目(编号DD20160343-06) 湖北省国土资源厅项目“神农架群岩石地层序列和年代格架研究”联合资助成果
【分类号】：P542

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