摘要
阜平 (超 )群是华北克拉通中段变质基底的代表性“地层”。阜平大柳树黑云斜长片麻岩常规微量锆石U -Pb法 ( 2 80 0 +2 30- 150 )Ma的年龄 ,既是阜平 (超 )群底部可能为中太古代、也是华北克拉通变质基底为一统太古宙的主要年龄依据。然而 ,阜平 (超 )群传统的地层、年龄和性质一直不断地受到后续研究者质疑 ,现已为许多文献证实不是有序的群级地层而是中 -下地壳性质的杂岩。阜平杂岩的片麻岩种类繁多 ,除了一些学者提出的构造成因的龙泉关片麻岩、TTG质的阜平片麻岩、同构造的片麻状花岗岩等以外 ,本文作者还认为阜平杂岩中的湾子(富铝 )片麻岩可与晋蒙孔兹岩对比。在晋蒙孔兹岩获得了古元古代的沉积年龄之后 ,湾子孔兹岩系是否也可能是古元古代的 ?为证实这个问题 ,本文在阜平杂岩中选取了有代表性的两种片麻岩———阜平大柳树黑云斜长片麻岩 (狭义阜平片麻岩 )和陈庄寒巴的夕线石二云母钾长片麻岩 (湾子孔兹岩 )———分别进行了单颗粒锆石U Pb法测年。结果前者得到 1) ( 2 4 84± 37)Ma不一致线上交点年龄 ,被认为是阜平片麻岩深成结晶年龄 ;2 ) ( 2 332± 7)Ma的谐和年龄 ,可能是持续时间较长的深成作用的结束年龄 ,也可能是深熔作用的年龄。后者得到 1) ( 2 32 6± 30 )Ma的不一致上交点年龄 ,?
The Fuping Complex is located in the basement of the central part of the North China Craton and consists of diverse gneisses and supracrustal assemblage and syntectonic granites (2.0 Ga±). The complex was previous considered as a uniform stratigraphic sequence named the Fuping Group, and assigned to the uniform Archaean based on the conventional multi grains zircon U Pb age of (2 800 +230 -150 )Ma from the biotite plagioclase gneiss of the Lower Group. However, this age was viewed as unreliable because of the scatter of the data points and the large error. And the sequence has also been queried because the plutonic orthogneisses were treated as part of the supracrustal rocks. Besides, the Wanzi series in the Fuping Group is composed of felsic and pelitic gneisses, calc silicates and marble, which the authors thought it as the equivalent of the Palaeoproterozoic khondalite in the Northern granulite belt of North China Craton. In order to verify this opinion, two different kinds of gneiss in the Fuping Complex were analyzed using the method of TIMS U Pb single zircon. The zircons (sample No. F103) from biotite plagioclase gneiss of the Lower Fuping Group yield an up intercept age of 2 484 Ma and a concordia age of 2 332 Ma, interpreted as crystallization and anatexis timing, respectively. The zircons (sample No. F101) from sillimanite mica potashfeldspar gneiss yield an up intercept ages of 2 326 Ma and a near concodia age of 1833 Ma, interpreted as the age of detrital zircon and the age of metamorphism, respectively. Based on the age of detrital zircon in the Fuping Complex, it is concluded that the basement of the central North China Craton formed during the Palaeoproterozoic.
出处
《前寒武纪研究进展》
2000年第3期129-139,共11页
Progress in Precambrian Research
基金
国家自然科学基金资助项目!(No .4 9972 0 65)
关键词
阜平杂岩
湾子孔兹岩
锆石年龄
年代学
片麻岩
Central part of North China Craton
Fuping complex
Wanzi paragneiss (khondalite)
Palaeoproterozoic and Archean
zircon age
China
