摘要
通过对桂北地区新元古代四堡群鱼西组顶部的板岩(SB01)和丹洲群白竹组底部的底砾岩(DZ01)开展碎屑锆石U-Pb年代学和Hf同位素研究,约束华南新元古代南华裂谷盆地沉积超覆的时限。四堡群鱼西组板岩和丹洲群白竹组底砾岩具有相似的碎屑锆石U-Pb年龄谱系,主要分布在820~900 Ma、900~1400 Ma、1450~2200 Ma和2350~2700 Ma;表明两者具有相似的物源,主要来自于扬子陆块东南缘新元古代岩浆岩,华夏陆块Grenville期造山事件的产物和太古宙基底,以及与Columbia超大陆聚合和裂解事件相当的地质体。四堡群鱼西组板岩中锆石ε(t)值为-13.63~6.92,二阶段Hf模式年龄(t)为1318~3129 Ma;丹洲群白竹组底砾岩中锆石ε(t)值为-25.37~12.89,t为901~3998 Ma。Hf同位素特征显示,四堡群源区物质以古老地壳物质的再循环为主,新生地壳物质相对较少;而丹洲群源区物质既有新生地壳物质,也有古老地壳物质的再循环。丹洲群白竹组底砾岩最年轻一组碎屑锆石的加权平均年龄为824.9±8.0Ma,而四堡群鱼西组板岩最年轻一组碎屑锆石的加权平均年龄为823.0±8.4 Ma,结合前人的研究,限定丹洲群沉积下限为~820 Ma,同时约束南华裂谷盆地沉积超覆作用的启动时限为~820 Ma。
U-Pb ages and Hf isotopic compositions of detrital zircon from the basal conglomerate of the Baizhu Formation of the Danzhou Group(DZ01), and from the slate in the top of the Yuxi Formation of the Sibao Group(SB01)in the northern Guangxi were analyzed by using LA-ICP-MS method, aiming to constrain the timing of sedimentary overlap in the Neoproterozoic Nanhua rift basin in South China. The slate of the Yuxi Formation and the basal conglomerate of the Baizhu Formation have similar detrital zircon age spectra, mainly distributed in 820–900 Ma,900–1400 Ma, 1450–2200 Ma and 2350–2700 Ma. The two samples have similar provenance, mainly the Neoproterozoic magmatic rocks in the southeastern margin of the Yangtze Block, the products of the Grenville orogenic event in the Cathaysian Block and the Archean basement, as well as geological bodies equivalent to the Columbia supercontinent polymerization and cracking period. The ε(t) values and corresponding two-stage Hf model ages(t) of detrital zircon grains from the slate sample in the Yuxi Formation of the Sibao Group range from-13.63 to 6.92 and 1318 to 3129 Ma, respectively. The ε(t) values and tof detrital zircon from the basal conglomerate sample in the Baizhu Formation of the Danzhou Group vary from-25.37 to 12.89 and 901 to 3998 Ma, respectively. The Hf isotope results show that the detritus of the Sibao Group is dominated by the recycled ancient crustal material, whereas the contribution of juvenile crustal material is relatively small. In contrast, the source materials of the Danzhou Group include both the juvenile crustal materials and the recycled ancient crustal materials. The weighted average age of the youngest zircon grains from the basal conglomerate of the Baizhu Formation in the Danzhou Group is 824.9±8.0 Ma, while the youngest zircon population from the slate of the Yuxi Formation in the Sibao Group is 823.0±8.4 Ma. Combined with previous results, the initial depositional age of the Danzhou Group is ca. 820 Ma, indicating that the sedimentary overlap in Nanhua rift basin began at ca. 820 Ma.
作者
秦亚
冯佐海
吴杰
白玉明
邢全力
薛云峰
QIN Ya;FENG Zuohai;WU Jie;BAI Yuming;XING Quanli;XUE Yunfeng(Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials in Guangxi,Guangxi Key Laboratory of Hidden Metallic Ore Exploration,Guilin University of Technology,Guilin 541004,Guangxi,China)
出处
《大地构造与成矿学》
EI
CAS
CSCD
北大核心
2022年第5期968-992,共25页
Geotectonica et Metallogenia
基金
国家自然科学基金项目(41572191、41702211、42072259)
广西自然科学基金项目(2018GXNSFAA281248、2019GXNSFDA245009)联合资助。
