广西鹰扬关群基性火山岩的锆石U-Pb年龄及其地质意义

U-Pb Zircon Geochronology of Basic Volcanic Rocks of the Yingyangguan Group in Hezhou,Guangxi,and Its Tectonic Implications

TIMS锆石U-Pb定年结果表明,广西贺州下龙地区鹰扬关群浅变质基性火山岩形成于819±11Ma,表明鹰扬关群火山岩是华南新元古代裂谷盆地中最早的火山活动,并确定了华南震旦系的底界年龄为819±11Ma。桂北地区震旦纪裂谷盆地底部火山岩与其不整合覆盖的花岗岩的年龄非常接近,表明区域在约820 Ma经历了非常快速的大规模地壳抬升、去顶和裂谷盆地沉降,支持华南约825 Ma地幔柱模式。

A TIMS U-Pb zircon analysis indicates that the Yingyangguan basic volcanic rocks in Hezhou, Guangxi, were formed at 819 ±11 Ma. This means that the Yingyangguan volcanic rocks represent the first magma event in the Neoproterozoic rift basin in South China. It is suggested that 819±11 Ma is the limit age of Sinian in South China. The age of the Neoproterozoic granitoids in northern Guangxi is very close to that of spilitic and mafic-ultramafic rocks unconformably covering the granitoids, which suggests that this area underwent a process of rapid crustal uplifting, unloading and rift basin subsidence at about 820 Ma. It can be considered as part of a wider continental rift system produced by a starting mantle plume beneath South China during the Neoproterozoic breakup of Rodinia. This supports the model of mantle plume about 825 Ma in South China.