武夷山地区前寒武纪地层沉积时代研究

武夷山地区前寒武纪地层出露范围大,目前对该地层的形成时代还存在着不同意见。新获得的武夷山地区前寒武纪地层的4个锆石La-ICPMS U-Pb年龄数据,指示万全群的黄潭组和杜潭组分别形成于746.0±6.2Ma和825±18Ma,马面山群东岩组形成于818±14Ma,麻源群大金山组的形成时间晚于879Ma。通过岩性与形成时代对比,认为武夷山地区新元古界的形成时间可以划分为三期,早期由麻源群大金山组和马面山群龙北溪组的陆源碎屑沉积岩构成,形成时限为879—825Ma;中期包括麻源群南山组、马面山群东岩组和大岭组万全群和龙泉群,以及交溪组、迪口组和桃溪组下段,以火山岩—沉积岩系列为主,可以进一步分为两期,即825—800Ma和751—728Ma;晚期由原"天井坪组"主体、桃溪组上段以及楼子坝群下部的沉积岩组成,形成时限为620—542Ma。根据武夷山地区前寒武纪地层的构造变形记录,前寒武纪地层主要记录了3期构造事件,分别为新元古代早期(900—860Ma)的华夏地块与扬子板块的碰撞、新元古代末期(728—620Ma)的挤压构造事件以及加里东运动。

PRECAMBRIAN GEOCHRONOLOGY AND STRATIGRAPHY IN THE WUYISHAN AREA,SOUTH CHINA

The Precambrian strata are widespread in the Wuyishan area,South China. Ongoing debates focuses on the depositional age of Precambrian strata in the wuyishan area. This paper presents four zircon LA-ICPMS U-Pb ages of Precambrian rocks in the Wuyishan area. The new data indicate that the Huangtan and Dutan formations of the Wanquan Group were deposited at 746.0±6.2 Ma and 825±18 Ma,respectively,the Dongyan Formation of the Mamianshan Group was deposited at 818±14 Ma,whereas the Dajinshan Formation of the Mayuan Group was deposited 879 Ma. Three episodes of Neoproterozoic deposition are identified according to lithol stratigraphic and geochronologic data. The early episode is between 879 Ma and 825 Ma,which is characberized by terrigenous sedimentary rocks in the Dajinshan Formation of the Mayuan Group and the Longbeixi Formation of the Mamianshan Group. The middle episode consists of the Nanshan Formation of the Mayuan Group,the Dongyan and the Daling Formation of the Mamianshan Group,the Wanquan and the Longquan groups,and the Jiaoxi,Dikou and Lower Taoxi formations. These deposits are dominated by volcanic-sedimentary rocks and can be further sub divide into two sub-episodes. The early sub-episodes is between 825 Ma and 800 Ma,whereas the later sub-episodes between 751 Ma and 728 Ma. The late episode is between 620Ma and 542 Ma,which is characterized by the sedimentation of the main body of the original Tianjinping Formation,the upper Taoxi Formation,and the lower Louziba Group. Precambrian strata in the Wuyishan area record three episodes tectonic events. They are the early Neoproterozoic collision between the Cathaysian Block and Yangtze Block,the late Neoproterozoic compressional tectonic event and the Caledonian movement.