Back to Search Start Over

A Thermal Event in the Ordos Basin: Insights from Illite 40Ar-39Ar Dating with Regression Analysis.

A Thermal Event in the Ordos Basin: Insights from Illite 40Ar-39Ar Dating with Regression Analysis.

Authors :
Wang, Longzhang
Wang, Liyun
Peng, Ping’an
Dai, Tongmo
Liu, Dayong
Source :
Journal of Earth Science; Jun2018, Vol. 29 Issue 3, p629-638, 10p
Publication Year :
2018

Abstract

Four samples from a Permian reservoir in the Ordos Basin of North China were separated into twelve fractions in grain sizes of <0.5, 0.5-1 and 1-2 μm. Using the <superscript>40</superscript>Ar-<superscript>39</superscript>Ar step-heating method, all of the fractions essentially yielded plateau ages ranging from 172.5 to 217.1 Ma. These scattered plateau ages might not have been obtained from pure diagenetic illites but from mixed clay minerals, although the samples were disaggregated using a gentle freeze-thaw cycle to free them of non-clay minerals. A regional thermal event, as suggested by several proxies, led to intensive illitization as a distinct diagenetic process when the Yanshanian Movement triggered magmatism around the entire North China Block during the Jurassic to Cretaceous. Thermal illites formed during a short time period, whereas detrital illites came from various sources. The scattered plateau ages could have resulted from mixed degassing of thermal and detrital illites. Within one sample, the plateau ages decrease with the diminution of grain sizes, but it is difficult to extrapolate to the detrital-illite-free ages. Because the plateau age is a mixture of ages for thermal and detrital illites, this regression analysis studies the dependence of the plateau ages on the synthetic values of contents and ages of detrital illites instead of on the grain sizes. Comparing the samples to one another, the plateau ages show the same trend among the different grain sizes. Weighted by the contents and ages of detrital illites, linear regression analysis revealed the relationship between the plateau ages and the relative weight proportions. Based on iterated calculations, a thermal event age and a set of weight proportions were derived. The regressed thermal event age is 163.3±1.6 Ma, which coincides with regional thermal activities and links to gas accumulation. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
1674487X
Volume :
29
Issue :
3
Database :
Complementary Index
Journal :
Journal of Earth Science
Publication Type :
Academic Journal
Accession number :
130275496
Full Text :
https://doi.org/10.1007/s12583-017-0903-7