摘要:
本文利用LA-ICP-MS分析技术,对湘南-桂东北地区寒武纪和奥陶纪沉积岩进行了碎屑锆石U-Pb年代学研究。获得有效年龄数据239组,年龄值变化范围较大(3146~474 Ma),主要集中分布于2633~2473 Ma(峰值2500Ma),1880~1521 Ma(峰值1650 Ma),1146~911 Ma(峰值970 Ma),896~720 Ma(峰值800 Ma)和682~474 Ma(峰值520 Ma)5个时间段。4件样品均记录了古太古代-中太古代年龄信息,同时以1146~911 Ma和896~720 Ma两个时间段年龄最集中,反映全球Grenville造山事件和全球Rodinia超大陆裂解事件对研究区影响显著。此外,本次还获得大量泛非期(520 Ma左右)锆石年龄,认为全球泛非事件对华夏地块及其邻区影响显著,反映华夏地块与冈瓦纳大陆可能有一定亲缘性。结合前人资料,认为研究区位于华夏地块和扬子地块西南段碰撞拼合带,研究区地层同时接受两地块物质沉积,物源主要来自华夏地块。
Abstract:
In this paper, the authors studied detrital zircon geochronology of the Cambrian-Ordovician sedimentary rocks sampled from the southern Hunan to northeastern Guangxi area by using LA-ICP-MS and obtained 239 groups of effective age data, with the ages ranging from 3146 Ma to 474 Ma. Most of the data are concentrated in five periods, i.e., 2633-2473 Ma (peak value around 2500 Ma), 1880-1521 Ma (peak value around 1650 Ma), 1146-911 Ma (peak value around 970 Ma), 896-720 Ma (peak value around 800 Ma) and 682-474 Ma (peak value around 520 Ma). All the four samples recorded Paleoarchean-Mesoarchean information, and their ages are concentrated on 1146-911 Ma and 896-848 Ma, suggesting that the Grenville and Rodinia orogeny events profoundly influenced the study area. Moreover, the authors obtained a large number of ages representing the Pan-African time, implying that the global Pan-African event significantly affected the Cathaysia Block and its adjacent regions. Combined with previous researches, the authors hold that the study area is located in the southeast of the southwestern section of the collision orogenic belt between the Yangtze block and the Cathaysia block. The strata in the study area received material sources from the two blocks with the material from the Cathaysia block being dominant.
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