摘要
利用EMP独居石定年法佐以LA-ICPMSU-Pb锆石定年法对浙闽武夷山地区5个前寒武纪变质基底岩石及附近5个显生宙花岗岩体进行年龄分析,结果显示独居石多为加里东期的产物且常呈现两期次的生长。前寒武纪变质基底岩石中,万全群杜潭组混合岩为533.0±44.4Ma及451.0±17.7Ma(锆石无年龄群落,但均大于800Ma),八都群堑头组混合岩淡色体为422.0±13.7Ma及360.0±14.9Ma(锆石年龄为436.4±4.7Ma),天井坪组云母石英片岩为443.3±11.3Ma(锆石无年龄群落,但主要散布在450～350Ma),麻源群南山组片麻岩不含独居石,但锆石年龄为859.1±9.2Ma,万全群黄潭组变粒岩不含独居石及可资定年的锆石。显生宙花岗岩的河田岩体(162.3±4.4Ma)及富城岩体(215.3±4.5Ma),均能符合原所预期之晚燕山期及印支期时代;另原认为分属印支期的玮埔(418.7±16.4Ma及360.6±15.3Ma)、海西期的真峰顶(429.3±15.6Ma)及加里东期的宁化(438.2±9.5Ma及348±20Ma)三岩体均获致加里东的年龄,有些并伴有海西期的讯号。这些结果指示:(1)华夏陆块遭受强烈加里东运动的影响,除了有大规模花岗岩侵入外,尚对前寒武基底进行强烈改造;(2)海西期的年龄主要由高铀独居石反应出来,锆石并未明确指出这期事件的事实尚难论断此区历经海西运动,若有此一运动其变质程度亦只影响到独居石;(3)太古代的锆石均为继承锆石,不足以支持武夷山地区有太古代的基底出露;(4)台湾西部大量早元古代的独居石源于武夷山地区的观点尚未落实。
We use EMP monazite, along with LA-ICPMS U-Pb zircon, dating methods to assert on 5 metamorphic rocks from Wuyisahn Precambrian basement and 5 adjacent Phanerozoic granitic rocks. Results reveal that monazites were largely grown in the Caledonian stage and probably overprinted by a younger age at the Hercynian. Among them, 533.0±44.4 Ma and 451.0±17.7 Ma （no age group from zircon but all 〉800 Ma） are obtained for a migmatite of Wanquan Group, 422.0±13.7 Ma and 360.0±14.9 Ma （436.4±4.7 Ma from zircon） for a migmatitic leucosome from Badu Group, and 443.3±11.3 Ma （no age group from zircon but concentrated at 450-350 Ma） for a mica quartz schist from Tienjinping Formation. No monazite was found in gneissic rocks from Mayuan Group and granulite from Wanquan Group, but an age of 859.1±9.2 Ma is obtained from zircon, For Phanerozoic granites, 162.3±4.4 Ma is obtained for Hetien body and 215.3±4.5 Ma for Fuchen body, and 418.7±16.4 Ma and 360.6±15.3 Ma for Weipu, 441.8±12.3 Ma and 350±45 Ma for Ninghua and 429.3±15.6 Ma for Zengfengding bodies, Accordingly, we conclude that （1） Wuyishan basement rocks have been strongly influenced by the Caledonian orogeny leading to not only the granitic intrusion but also the strong modification on these rocks; （2） Hercynian event is only reflected by the high-U monazite but not the zircon ages, indicating that the influence of this orogenesis may be limited if it really existed; （3） the fact that the Archean zircons are mosdy of inherited origin seems not support the existence of such an Archean basement in Wuyishan; （4） the provenance for Paleoproterozoic monazites that are abundant in W Taiwan sediments has not yet been proven to be correlated to the Wuyishan area as suggested earlier.
出处
《高校地质学报》
CAS
CSCD
北大核心
2008年第1期1-15,共15页
Geological Journal of China Universities
