Laser 40Ar/39Ar Isochron Dating on Leizhou Quaternary Volcanic Rocks
详细信息
- 责任者：Li Weiran (Laboratory of Orogenic Belts and Crustal Evolution ; School of Earth and Space Sciences ; Peking University ; Beijing 100871 ; China) ; Ji Jianqing
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(8)
- 关键词：火山岩 ; volcanic rocks ; 氩—氩计时 ; Ar-Ar dating ; 雷州半岛 ; Leizhou Peninsula
- 页码：p.2775-2788
- 图表：9 illus., 6 tables, 20 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
Leizhou area is one of the most important distribution areas of Cenozoic volcanic rocks. Volcanic activities in this area concentrate in mid to late Pleistocene. Researchers dated Leizhou volcanic rocks mainly by K-Ar method and the results indicate the isotopic ages vary from 0. 38Ma to 3. 04Ma. However,according to the stratigraphic sequence,Leizhou Quaternary volcanic rocks overlie the layers of 1. 87Ma and 0. 76Ma. Therefore,the ages of volcanic rocks must be younger than the underlying layers,which indicates the error of ages dated by K-Ar method. This paper dates samples taken from Leizhou area by laser 40Ar/39Ar dating method. The results show that ages mainly center on 0. 18Ma,indicating the eruptions occurred approximately 180000a ago. We can also infer that,to young samples,the isotopic ages dated by K-Ar method and apparent ages dated by 40Ar/39 Armethod are all older than the real ages. By comparison,isochron ages by 40Ar/39Ar method are more reliable. Furthermore,reliable ages calculated with phenocryst and matrix from the same sample (phenocryst-matrix isochron) must base on the fact that the phenocryst and matrix are congenetic. To determine whether they are congenetic or not,this paper proposes as the first time to compare the uniformity of initial 36 Ar/38Ar value of samples before irradiated by neutron,thus testing the reliability of phenocryst-matrix isochron. Based on that,isochron dating method could be extended to all the other datings on congenetic and isochronic samples from the same district.
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