赣南地区寒武系牛角河组碎屑锆石U-Pb年龄 和Hf同位素特征及其地质意义

通过对赣南地区寒武纪牛角河组变余长石石英砂岩锆石U-Pb年代学和Hf同位素分析表明,牛角河组地层沉积年龄晚于556Ma。LA-ICP-MS U-Pb数据结果显示550～600Ma、700～900Ma、900～1100Ma、1500Ma和2500Ma为五个主要年龄峰值,其中900～1100Ma和700～900Ma两个峰值最显著,表明Rodinia超大陆的裂解聚合在华南地区的响应为赣南地区寒武纪地层提供了主要物源,该物源曾遭受泛非运动的影响,进一步说明华夏地块与冈瓦纳大陆具有一定亲缘性。此次工作中3568Ma锆石的捕获,说明华夏地块可能存在太古宙结晶基底。对具有不同年龄峰值的锆石进行稀土元素分析,其结果表明研究区锆石具有重稀土富集、强Ce正异常、弱或不明显的Eu负异常的地球化学特征,与岩浆锆石特征相似,指示其物源区以岩浆岩为主。此外,Lu-Hf同位素分析显示源区锆石除少数源于新生地壳物质组分熔融产生的岩浆,大多结晶于古老地壳部分熔融产生的岩浆;综合锆石年代学结果,暗示华南地区存在强烈的古元古代到新元古代岩浆活动,其中中元古代末期-新元古代的岩浆事件最甚;而新太古代为一个重要的新生地壳生长时期。

Zircon U-Pb ages and Hf isotope features of rocks from Niujiaohe Formation of Cambrian in the southern Jiangxi area and their geological implications

U-Pb dating and Hf isotope analysis of detrital zircon grains from Niujiaohe Formation rocks in the southern Jiangxi area suggest that the sedimentary time of Niujiaohe Formation strata is 566Ma. LA-ICP-MS U-Pb dating has five peaks: 550~600Ma, 700~900Ma, 900Ma~ 1100, 1500Ma and 2500Ma , of which 900~1100Ma and 700~900Ma are most notable. It implies that the response of South China block to Rodinia supercontinent provided the main source of the Cambrian strata in this area. The source of the area has been affected by pan-African movements, further demonstrating that the Cathaysia block has a certain affinity with Gondwana. The capture of the zircon age at 3568 Ma indicates that the Cathaysia block may have an Archean crustal basement. These zircons show the characteristics of heavy rare earth enrichment, strong Ce positive anomalies, weak or inconsiderable Eu negative anomalies, and similarity to magmatic zircons, indicating that the source resulted from magmatic rocks. Lu-Hf isotope data indicate that a small number of zircons in the source region were crystallized in the magma which were produced by the melting of neo-crustal material components, and most of them were crystallized in the magma produced by the partial melting of ancient crust components. Combined with zircon age data, there was a notable magmatic event during the Neoproterozoic and Paleoproterozoic in southern China, especially the Late Mesoproterozoic-Neoproterozoic time. The Neoarchean is an important period for growth of new crust.