Early Mesozoic unroofing pattern of the Dabie Mountains (China): Constraints from the U-Pb detrital zircon geochronology and Si-in-white mica analysis of synorogenic sediments in the Jianghan Basin
Early Mesozoic unroofing pattern of the Dabie Mountains (China): Constraints from the U-Pb detrital zircon geochronology and Si-in-white mica analysis of synorogenic sediments in the Jianghan Basin
复制标题
DOI：
10.1016/j.chemgeo.2009.06.012
复制
发表时间：
2009-08
期刊：
影响因子：
3.9
通讯作者：
Yuejun Wang;Guochun Zhao;X. Xia;Yanhua Zhang;W. Fan;C. Li;X. Bi;San-zhong Li
中科院分区：
文献类型：
--
作者：
Yuejun Wang;Guochun Zhao;X. Xia;Yanhua Zhang;W. Fan;C. Li;X. Bi;San-zhong Li
本文报道了大别造山带以南江汉盆地同造山期沉积物中碎屑锆石U-Pb年代学和白色云母硅分析的结果。研究结果为大别山早中生代沉积物的物源和去顶模式提供了新的认识。上三叠统碎屑白色云母的Si含量为3.09 ~ 3.34atoms pfu，下、中侏罗世为3.06 ~ 3.59atoms pfu。下侏罗统砂岩中的碎屑白色云母主要为多硅质云母，且完全来自大别高压-超高压岩石。7个样品的碎屑锆石U-Pb定年结果表明，这些同造山沉积物的物源从晚三叠世到早、中侏罗世发生了明显的变化。上三叠统砂岩中锆石U-Pb年龄群分别为~420- 450 Ma、~750- 820 Ma、~1050- 1200 Ma和~ 2500 Ma，并含有少量吕梁期（~1700- 2000 Ma）成分。侏罗系砂岩的锆石年龄以吕梁期（~1700- 2000 Ma）为主，加里东期（~420- 450 Ma）和格林维尔期（~1050- 1200 Ma）次之。结合已有的地质资料，大别高压-超高压岩石可能于早侏罗世（~ 190 Ma）开始出露地表。江汉盆地南部的江南地体（又称“江南古陆”）是上三叠统沉积物的主要来源，而古元古代扬子地壳物质（上覆于现今大别杂岩之上）是江汉盆地侏罗纪沉积物的重要物源。
This paper presents the results of an integrated U-Pb detrital zircon geochronology and Si-in-white mica analysis for synorogenic sediments in the Jianghan Basin to the south of the Dabie Orogen. The results provide an improved understanding of the provenance of these sediments and the unroofing pattern of the early Mesozoic Dabie Mountain. Si contents of detrital white micas range from 3.09 to 3.34atoms pfu for the upper Triassic sandstones whereas 3.06 to 3.59atoms pfu for the lower and middle Jurassic sandstones. The majority of detrital white micas in the lower Jurassic sandstones is phengitic and originated exclusively from the Dabie high- to ultrahigh- pressure rocks. The U-Pb dating results of the detrital zircons for seven samples suggest that these synorogenic sediments have a significant change of provenance from late Triassic to early and middle Jurassic. For the upper Triassic sandstone, the U-Pb age clusters of these zircons are characterized by ~420-450Ma, ~750-820Ma, ~1050-1200Ma and ~2500Ma with minor Luliangian (~1700–2000Ma) components. In contrast, the zircon ages of the Jurassic sandstones are dominated by the Luliangian (~1700–2000Ma) ages with only minor Caledonian (~420-450Ma) and Greenville (~1050-1200Ma) ages. In combination with other available geological data, it can be concluded that the Dabie HP-UHP rocks might initially be exposed to the surface at the beginning of early Jurassic (~190Ma). The Jiangnan terrain (also named “Jiangnan old continental in Chinese) to the south of the Jianghan basin provided the predominant supply of upper Triassic sediments, whereas the Paleoproterozoic Yangtze crustal materials (overlying the present Dabie Complex at the time) were the important provenance of the Jurassic sediments in the Jianghan basin.