赣南岐山岩体深熔-幕式岩浆活动:来自锆石U-Pb精细年代学研究

Anatexis-Ceremonies Magmatism Activity of the Qishan Granitic Pluton in Southern Jiangxi:Chronological Study of Zircon U-Pb Precise Dating

武夷山地区加里东期深熔混合岩化-岩浆作用普遍,且两者时代一致或相近,但是加里东期深熔作用的启动时间尚不明确。赣南寻乌县岐山岩体位于武夷山构造带南部,该岩体形成时代缺乏精确的年代学依据。基于锆石LA-ICP-MS U-Pb测年手段,在该岩体中发现两期锆石,早期锆石为深熔成因,晚期为岩浆成因。本次研究获得的晚期锆石形成时代为445~440Ma,具有从外向内年龄渐新的规律,表明该岩体形成于晚奥陶世晚期-早志留世,可能是从源区上升的不同批次岩浆就位的结果,即该岩体为加里东期深熔-幕式、多期次岩浆活动的结果。边缘部位与岩体中心部位分别获得早期深熔锆石加权平均年龄值(458±4Ma)与岩浆锆石加权平均年龄值(460±4Ma),两者在误差范围内一致。表明武夷山地区在加里东早期,大约460Ma左右发生了一期深熔-岩浆活动,为武夷山构造带加里东运动深熔作用的启动时代提供了制约。

The Caledonian anatexis-magmatism activities in the Wuyi mountains region occurred commonly in Caledonian or close Caledonian, but precise starting time is still unknown. The Qishan granitic pluton is located in the southern part of the Wuyishan tectonic belt, and precise dating data for the formation time of the pluton is still absent. Two phase zircons were found in the Qishan granitic pluton, with early zircon being anatexis in origin and the other zircon being magmatic in origin. Using zircon LA-ICP-MS U-Pb dating method yielded an forming age of 445±440Ma for the later zircon from the Qishan granitic pluton, which displays a new change rule that the ages are gradually younger from outside to inside. Our study shows that the pluton formed during the Late Ordovician to Lower Silurian and was likely the product of different magma intrusion from source region, i. e. the product of anatexis- ceremonies magmatism activities. A weighed age of 458 ±4Ma obtained for zircons from the rim and center of the pluton is basically consistent to the weighted age of 460q-4Ma for magmtic zircons, with the deviation within error range. Out study suggests that an anatexis activity occurred in the Wuyi Mountain region at early Ca Ca edonian around 460 Ma, which provided new constraint for the start timing of anatexis triggered by the edonian Movement in the Wuyishan tectonic belt.