赣南南华纪变质沉凝灰岩的碎屑锆石U-Pb年代学及其对裂谷盆地形成时间的限定

Detrital zircon U-Pb dating of Nanhua meta-tuffite in South Jiangxi and constraint on the time limit of the rift basin

江西省宁都某地新元古代浅变质岩风化壳中赋存离子吸附型稀土矿,文章对某矿区内原定青白口纪库里组的2件变质沉凝灰岩样品进行了碎屑锆石LA-ICP-MS U-Pb年代学研究,获得了88组和110组谐和年龄。2件样品的碎屑锆石年龄区间相似,主要分布在:810~780 Ma,峰值年龄为798 Ma(n=55);748~727 Ma,峰值年龄为737 Ma(n=127);691~667 Ma,峰值年龄为680 Ma(n=6),此外还有少量的年龄分布在2.85~1.08 Ga。认为,变质沉凝灰岩样品的沉积时代可能为南华纪,地层应归属为上施组;物源可能来自江南造山带东段(赣东北—皖南—浙西)青白口纪晚期—南华纪的火山-沉积岩;赣南区域上同时期的巨厚海相火山-碎屑沉积可能形成于华南古大陆裂解之后的裂谷盆地,赣南次级裂谷盆地的沉积时限为810~727 Ma。

Ion-adsorption type REE deposits is hosted in regolith of Neoproterozoic epimetamorphic rocks in South Jiangxi,China.LA-ICP-MS U-Pb dating of detrital zircons from two metamorphic tuff samples of the originally identified Kuli Formation of Qingbaikou System in a mine area yielded the harmonic ages of 88 groups and 110 groups respectively.They are predominantly Neoproterozoic and have ages ranging from 810 to 667 Ma with three age peaks at ca 798 Ma(n=55),737 Ma(n=127)and 680 Ma(n=6).There are also a few Meso-to Paleoproterozoic zircon grains with ages scattering from 2.85 Ga to 1.08 Ga.The dating results probably suggest that the sedimentary age of the tuffite may be Nanhua Period.It is speculated that the provenance may be volcanic-sedimentary rocks of late Qingbaikou Period to Nanhua Period in the eastern part of Jiangnan orogenic belt(northeast Jiangxi-southern Anhui-western Zhejiang).The super thick marine volcanic-clastic sediments of the same period in southern Jiangxi might be formed in the rift basin after the breakup of the ancient continent of South China,and the sedimentary time of the secondary rift basin in southern Jiangxi is about 810-727 Ma.