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中国东部广泛分布着新生代的玄武岩,其地质时代始终是一个争议的问题。本文作者对南京附近地区的两个标准玄武岩组剖面进行了古地磁学研究,使用交变场退磁法检验了样品,证明它们的剩磁稳定性良好,测得江宁方山玄武岩组的I,平均值为8.1×10~(-4)CGSM,D_r=195°29′、J_r=-54°9′,古地磁南极位置为λ_P=192°35′E、Φ_P=76°47′N;六合灵岩山玄武岩组的l,平均值为26.4×10~(-4)CGSM,D_r=354°44′,J_r=42°12′,古地磁北极位置为λ_P=329°38′E、Φ_p=80°36′N,并得出如下结论: (1)六合灵岩山玄武岩组和江宁方山玄武岩组的极性截然不同,灵岩山玄武岩组的岩石磁性全系正向,可能相当于布容期(Brunhes epoch),方山玄武岩组的岩石磁性全属反向,可能相当于松山期(Matuyama epoch); (2)灵岩山玄武岩组测得的古北极相距现今的北极要比方山玄武岩组的近一些,清晰地表明它们的形成时间绝非同一时期,而是灵岩山玄武岩组要晚,方山玄武岩组要早; (3)灵岩山玄武岩组和方山玄武岩组形成时期的岩石产地所处的古纬度都是中纬度地区,属亚热带气候; (4)对比世界各地区一些有关时代的岩石古地磁学数据,参照这两套玄武岩组的上下地层中所含有的古生物化石及岩石学特征,六合灵岩山玄武岩组的地质时代似应为Q_2—Q_3,江宁方?
The Cenozoic basalts are widely distributed in eastern China. The geologic age has always been a controversial issue. The author carried out paleomagnetic studies on two standard basalt formations in the area near Nanjing and used the field demagnetization method to test the samples to prove their good remanence stability. The I, mean The value of the paleomagnetic geomagnetic south pole is 8.1 × 10 ~ (-4) CGSM, D_r = 195 ° 29 ’and J_r = -54 ° 9’. The paleomagnetic polar position is λ_P = 192 ° 35’E and Φ_P = 76 ° 47’N. The average value of l in the basalt group is 26.4 × 10 ~ (-4) CGSM, D_r = 354 ° 44 ’, and J_r = 42 ° 12’. The paleomagnetic polar position is λ_P = 329 ° 38’E and Φ_p = 80 ° 36’N and concluded as follows: (1) The polarities of the Liuhelingyan basalt group and the Jiangning Fangshan basalt group are quite different. The rock magnetism of the Lingyan basalt group is all positive and may be equivalent to Brunhes epoch). The rock magnetism of the Fangshan basalts is all reverse, possibly equivalent to the Matuyama epoch. (2) The Paleosids measured in the Lingyan basalts are closer to the current Arctic than the basalt basalts, Clearly indicate that their formation time is by no means the same period, but rather late Lingyanshan basalt group, Fangshan basalt group early; (3) The paleocontinental latitudes of the rock origin during the formation of the basalts are all in the mid-latitudes and subtropical climate. (4) By comparing the paleomagnetic data of some age-related rocks in different parts of the world with reference to the upper and lower strata of the two basalts Containing the fossils of pelagics and petrology, the geological age of the Liuhelingyan basalt group should be Q_2-Q_3, Jiangning Fang?