【摘要】 <正> 前言我国东部中生代火山岩系地层非常发育,随着我国科学技术的发展,对广泛分布的火山岩系地层进行了深入的研究。在地层、古生物、岩石、大地构造、同位素地质等方面都已取得了大量资料,为火山岩系地层时代的确定、划分和对比提供了有力的依据,这不仅在理论上有重大意义,而且有很大实际价值。自1973年以来,我们对宁芜、庐枞地区作了系统的年代学工作,并对测定得到的部分年龄数据作过报道,同时对长江中下游其它几个火山岩盆地,浙江、福建以及冀北、辽西等地区的中生代火山岩系,进行了剖面观察和年龄测定工作。下面就同位素地质年龄测定和研究,来讨论这套火山岩系地层的时代。更多还原

【Abstract】 on the basis of the geological investigation and the geochronological determination of several Mesozoic volcanic basins along both sides of the middle-lower reaches of the Changjiang River. Zhejiang and Fujian Provinces and Yan-Liao region in North China, the following conclusions are obtained:(1) Most of the paleontologists unanimously, consider that the Mesozoic rocks in East China, both the "Jiande group" in south and "Tehol group" in north and their corresponding groups may be biostratigraphically correlated, i.e. they all belong to the same geological age, and the data from radiometrics also support this viewpoint.(2) Paleontologically, there are different viewpoints on the geological age of the volcanic rocks in East China. Some researchers hold that they belong to Cretaceous, but others, to Jurassic. Recent advance on geochronology and paleontology shows that the Mesozoic volcanic rock series in East China should belong to Cretaceous, not upper Jurassic. The isotopic age determination is roughly estimated at 137—110 m.y., such as 133—118m.y. of "Jiande group" in Zhejiang Province, 130 m.y. of "Nanyuan formation" in Fujian Province, 126.8—109.7m.y. of "Longwangshan formation" to "Gushan formation" in Nanjing-Wuhu basin, 132—108 m.y. of "Zhuanqiao formation" to "Fushan formation" in Lu-Zong basin, 139—132 m.y. of "Lingxiang formation" and "Dasi formation" in eastern Hupei area, ca. 120m.y. of "Qingshan group" in Shandong Province, 145—113 m.y. of "Jehol group" in northern Hebei Province. etc.; all these show that it is more reasonable to assign the strata of the Mesozoic volcanic rocks to the Cretaceous.(3) The Cretaceous in East China may be divided into three parts; the lower, middle and upper series. For example, the lower Cretaceous series is represented by the "Jiande group" in south and "Jehol group" in north, the-middle series by the "Yongkang group" in south and. "Huushan group" in north, and the upper series by the "Jujiang group" in south, "Wangshi group" in north, respectively.According to the radiometric data available the lower boundary of the Cretaceous is dated at 137—135 m.y., and that of the middle Cretaeeous is in the range of 108—105 m.y. with reference to the data of volcanic and intrusive rocks genetically connected with the late phase of Yanshan orogeny, we suggest that the age for the boundary between middle and upper Cretaceous should be 88—85 m.y. According to the ages of granite porphyry (70.5 m.y.) intruded into the Nanxiong formation and Eogene basalt (61m.y.) intercalated in Buxing formation, we consider that the upper boundary of Cretaceous may be referred to 65 m.y.更多还原