闽西南晚三叠世文宾山组碎屑锆石U-Pb年龄及地质意义

U-Pb Dating of Detrital Zircons from Late Triassic Wenbinshan Formation in Southwestern Fujian and Its Geological Significance

日益增多的资料表明中国东南沿海并不是后加里东地台,而是由不同地块拼贴而成。闽西南晚三叠世文宾山组具有类磨拉石沉积特征,其盆地沉积物碎屑锆石U-Pb年龄信息,可以为了解盆地源区组成及其变化及区域构造演变过程研究提供约束。闽西南晚三叠世文宾山组碎屑锆石形态学及U-Pb测年分析表明：（1）晚三叠世文宾山组物源复杂,其主要源区是闽西北隆起带;（2）闽西南晚三叠世具有大于2500 Ma的太古宙的源区,华夏古陆可能存在太古宙陆核或东南沿海还存在另一古老基底;（3）980-1190 Ma的碎屑锆石说明晚三叠世闽西南具有G renville期物质来源,它们可能来自另外一个陆块,由于印支期古特提斯洋关闭与华夏地块拼接,并为晚三叠世盆地提供物源;（4）区内印支期岩浆岩带也是晚三叠世沉积的重要物源区。

Increasing data indicate that the SE coastal region of China mainland is not a post-Caledonian platform but a amalgamation of different massives.The Late Triassic Wenbinshan Formation in southwestern Fujian Province is characterized by quasi-mollasse.The U-Pb dating on detrital zircons is employed in this research to a better understanding of the varied provenances and the regional tectonic evolution.The morphological observations of detrital zircons and the U-Pb age dating results reveal four points regarding to the tectonic evolution in southwestern Fujian Province as follows：（1） Late Triassic Wenbinshan Formation has a complicated provenances but mainly derived from northwestern Fujian uplift.（2） Late Triassic sedimentation has an Archaean provenance older than 2.5 Ga which indicates distribution of Archean continent relics on Cathaysia region or another previously unrevealed Archean basement in southeast China.（3） 980-1,190 Ma detrital zircons imply that a Grenville age block served as a provenance area during Late Triassic sedimentation.This block collided with Cathaysia block as a result of the closing of Paleo-Tethys ocean during Late Triassic.（4） The Indosinian magmatic rocks belt in the region formed another part of the provenance during the Late Triassic sedimentation of Wenbinshan Formation.