宁芜盆地中三叠统黄马青组是大别造山带最早剥露的记录

The Earliest Denudation Record of the Dabie Orogenic Belt Evidenced from the Middle Triassic Huangmaqing Formation in the Ningwu Basin

由于后造山期的构造运动改造和巨量剥蚀,大别造山带的初始剥露时间,即开始为周缘盆地提供物源的时间缺乏精确限定。文章对下扬子宁芜盆地中三叠统黄马青组三角洲相陆源碎屑岩进行野外调查,并开展了沉积岩石学和物源分析。结果显示,黄马青组以岩屑石英砂岩、长石岩屑石英砂岩为主,石英含量76%~84%,岩屑含量10%~14%,长石含量6%~11%。岩屑以富含石英的变质岩或变泥质岩岩屑为主,指示变质岩的特殊物源的存在;黄马青组砂岩碎屑锆石年龄主要分布在350~250 Ma、420~400 Ma、900~700 Ma、2000~1600 Ma、2500~2100 Ma等区间,反映了华南板块北缘、华北板块南缘的混合信号,其物源供应主要来自大别造山带南部的宿松杂岩带、华北板块南缘基底及沉积盖层物质;通过与大别造山带周缘中生代沉积记录进行对比,发现在中—晚三叠世各盆地具有物源相似性,认为大别造山带低级变质带的早期折返导致了造山带的初始抬升和剥露,宁芜盆地中三叠统黄马青组至少一部分沉积物来自造山带早期抬升与剥蚀。

Due to post-orogenic multi-stage tectonic events and long-term massive denudation,there are poor precise constraints to limit the initial denudation time of the Dabie orogen,that is,timing of starting to provide a source for the peripheral basins.In this work,we conduct field investigations on the Huangmaqing Formation,a set of Middle Triassic delta facies terrigenous clastic rock in Ningwu Basin,northeastern South China,and presents sedimentologic and provenance analysis.Lithologies of the Huangmaqing Formation are dominated by the litho-quartzose sandstone and feldspathic-litho-quartzose sandstone,with quartz of 76%-84%,lithic fragment of 10%-14%,and feldspar of 6%-11%.Among the lithic fragments,quartz-rich metamorphic rock fragments or metapelite grains rock debris are dominant,indicating the existence of special sources of metamorphic rocks.The detrital zircon age spectrum shows the main peaks at 350-250 Ma、420-400 Ma、900-700 Ma、2000-1600 Ma、2500-2100 Ma.The Susong Complex belt located in the southern orogenic belt is the main source of the Huangmaqing Formation.Compared with the sedimentary records of other early Mesozoic basins around the Dabie orogen,it is found that these basins have similar provenance in the Middle-Late Triassic.The early exhumation of the lower metamorphic belts in the Dabie orogenic belt led to the initial denudation of the orogenic belt.At least part of the sediments of the Huangmaqing Formation were derived from the early uplift and denudation of the orogenic belt.