皖南志留系唐家坞组物源分析:来自碎屑锆石年代学和岩石地球化学的制约

分布于皖南泾县地区的唐家坞组为志留系顶部最晚沉积，其沉积时代和物质来源仍存在争议。对其进行了岩相学、岩石地球化学以及锆石U-Pb年代学等综合研究。岩相学特征表明:研究砂岩以波状消光的石英和变质岩屑为主，磨圆度和分选程度较好；岩石地球化学特征显示砂岩的成分成熟度较高，物源区主要以长英质组分为主，并发生了强烈的化学风化或沉积循环；LA-ICP-MS锆石U-Pb测年获得最年轻的单颗粒锆石年龄为424 Ma，可作为唐家坞组沉积时代的下限。结合地层接触关系，限定唐家坞组沉积时代应为志留纪晚期，可能接近华南早古生代造山事件的结束时间。79颗碎屑锆石U-Pb年龄获得主要年龄峰值为981 Ma和756 Ma，次级年龄峰值为2 476 Ma、517 Ma和453 Ma，结合区域上年代学信息，暗示了唐家坞组砂岩的主要物源区为早-中新元古代岩浆岩、新元古代裂谷层序以及震旦纪-奥陶纪沉积岩，同造山期岩浆岩或变质岩也为唐家坞组提供了物源。华南早古生代陆内造山作用导致中奥陶世之前的盆地沉积物、部分盆地基底以及造山期侵入其中的岩浆岩发生强烈的隆升，从而为陆内前陆盆地沉积提供了主要物源，表明华南早古生代造山带与扬子地块东南缘前陆盆地两个构造单元存在盆山物质耦合关系。

Provenance Analysis for the Clastic Rocks in Tangjiawu Formation,South Anhui: Constraints from Detrital Zircon Ages and Geochemistry Characteristics

Provenance and sedimentary age are still debated about Tangjiawu Formation from the South Anhui.The study focused on the petrography,geochemical features and detrital zircon ages of the sandstones in the Tangjiawu For-mation. The sandstones,which are highly rounded and sorted, are essentially composed of metamorphic detritus and quartz with wave extinction. They exhibited relatively high compositional maturity. Their provenances were dominated by felsic materials that had undergone intensive chemical weathering or sedimentary recycling. LA-ICP-MS zircon U-Pb dating yields a youngest age of 424 Ma,which represents the lower limit of deposition age.In addition to the zircon ages,the Tangjiawu Formation uncomfortably overlain by the Devonian Guanshan Formation,suggesting that it should be deposited in Late Silurian that approached to the termination timing of the early Palaeozoic orogenic event. Seventy-nine detrital zircons with discordance <10% display a broadly age spectrum of 2 912 Ma to 424 Ma. Most of the de-trital zircons have U-Pb age grouped between 731 and 1 031 Ma,with two clusters peaking at 981 and 756 Ma. A few populations with peak ages of 2 476 Ma,517 Ma and 453 Ma are present as well. This suggested that the provenances of the Tangjiawu Formation were mainly derived from the early-to middle-Neoproterozoic igneous rocks,Late Neoprot-erozoic rift sequence and Sinian to Ordovician sediments with subordinate synorogenic magmatic or sedimentary rocks. The early Palaeozoic intra-continental orogeny caused the uplifting of the sediments in the pre-middle-Ordovician ba-sins,which mostly contributed to sources of the deposits in the intra-continental foreland basin. The deposition and e-volution of the foreland basin in the South China were controlled by the early Palaeozoic orogeny, reflecting the cou-pled material recycling between the orogen and the foreland basin.