摘要
本文给出的滹沱群下亚群青石村组玄武岩Ｒｂ－Ｓｒ、Ｓｍ－Ｎｄ全岩等时线年龄为２０４５．８±１７和２３６９±３０Ｍａ（Ｚ），角门石４０Ａｒ－３９Ａｒ坪年龄和最高视年龄为１３６４±１９和１９３２±１９Ｍａ（１）；中亚群河边村组玄武岩Ｒｂ－Ｓｒ全岩等时线年龄图的投点呈完全离散状，Ｓｍ－Ｎｄ全岩等时线年龄为２３２２±３１Ｍａ（２），角门石４０Ａｒ－３９Ａｒ坪年龄和最高视年龄为１３６０和１７４２±１７Ｍａ（１）。根据上述Ｒｂ－Ｓｒ、Ｓｍ－Ｎｄ数据与已知青石村组、河边村组单颗粒锆石Ｕ－Ｐｂ法确定的成岩年龄２４５０±１０和２４００±２０Ｍａ（２）的明显差别，４０Ａｒ－３９Ａｒ均揭示为较典型受扰动的年龄谱和较发育的透人性构造、晚期岩脉等地质证据，认为Ｒｂ－Ｓｒ、Ｓｍ－Ｎｄ是重设的同位素体系。
This paper reports on the geochronological study of Precalnbrian metamorphicbasement in Wutaishan region, in which whole rock Rb-Sr and Sin-Nd methords, hornblende40Ar-39Ar method are used and significant data are gained from the Early Proterozoic HutuoGroup.U-Pb single zircon age determination with 205Pb/235U mixed spike for basaltic rocks fromQingshicun (HQ) and Hebiancun (HH). Formations of Hutuo Group had supplied the reliable a2450±10 and a 2400±20Ma(2) age, respectively (Wang, R. Z. et al., 1996a, b). They weretherfore belived to reflect primary ages irrespective of their subsequent geological history.Whereas it is common to find rocks with bath the Rb-Sr and Sin-Nd whole rock ages youngerthan their times of practise as determined by U-Ph on zircon from Wutaishan area. Their Rb-Srand Sm-Nd whole-rock equivalents are 3-16% younger and bear no consistent relationship withstratigraphy. Basaltic rock samples have an Rb-Sr whole rock isochron age of 2046±17Ma(2),a Sm-Nd whole rock isochron age of 2369±30Ma(2) from the HQ is Obtained. While the samelithology amples as the Ho are scattered on the Rb-Sr plot, Sm-Nd isochron yields an age of2322±31Ma(2) for the HH. The author concludes that bath the Rb-Sr and Sm-Nd whole-rockisotopic systems can be reset under low-grade hydrothermal and metamorphic coditions in thearea.The samples measured with 40Ar-39 Ar incremental heating technique on the massspectrometer give a plateau age of 1364±19Ma (1), a older age of 1932±19Ma (1) forhornblende of the HQ and a plateau age of 1360Ma(1) and older age of 1742±17Ma(1) forhornblende of the HH. Abovementioned results indicate that may represent the main threetectonothermal events occuring in the area, and, the later ductile activatities took place at about1930, 1740 and 1360Ma ago respectively.
出处
《前寒武纪研究进展》
1997年第1期35-43,共9页
Progress in Precambrian Research
基金
国家自然科学基金!49273179
关键词
玄武岩
铷-锶
体系
同位素体系
钐-钕体系
Hutuo Group, basaltic rocks, Rb-Sr system, Sm-Nd-system, isotope systemresetting
