A Kinetic Explanation for Combined Potassium Gains and Radiogenic 40Argon Losses of Diagenetic Illite-Rich Clay Separates

Geosciences

Abraham Lerman¹  Norbert Clauer² 

[1] Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL 60208, USA;Institut des Sciences de la Terre et de l’Environnement, Université de Strasbourg (UdS/CNRS), F-67084 Strasbourg, France;

关键词: burial diagenesis;    illitization;    K gain;    radiogenic ⁴⁰Ar loss;    K-Ar ages;    K-Ar two process model;   

DOI  :  10.3390/geosciences12050186

来源: DOAJ

【 摘 要 】

In this study, a kinetic model sketches the concomitant K gain and radiogenic ⁴⁰Ar loss of clay separates recovered from progressively buried sediments. Published K-Ar ages of clay separates from the Mahakam Delta, the Texas Gulf Coast, and the North Sea were used to constrain the modeling. As compared with analytical results, the model simulates changes relative to depth or to deposition time of the K-Ar ages from fine- and coarse-grained clay crystals. The decrease in the K-Ar ages of detrital-rich coarse-grained fractions (>2 μm) is bracketed with depth by K addition rates between 0.2 and 3.5%/Ma and slightly higher ⁴⁰Ar release rates between 0.5 and 4.5%/Ma. The former rate varies from 3.5 to 6%/Ma in the fine-grained fractions (<0.4 μm) and the latter rate varies from 0.7 to 6%/Ma in the same fractions. In fact, the K addition and the radiogenic ⁴⁰Ar release rates record independent processes on different material sizes and types. Small K addition and ⁴⁰Ar escape rates of about 1%/Ma also simulate analytical cases in which the mean K-Ar ages of the finer grained fractions remain about constant with increasing depth, confirming that the relationship between K-Ar age and stratigraphic depth cannot represent a temporary “steady state”, but a continuing dynamic process at a smaller rate. In turn, the modeled results help quantifying the illitization reactions in size separates consisting of authigenic and detrital clay materials from sediments covering stratigraphic intervals from 10 to 1000 Ma.

【 授权许可】

Unknown