Argon Accumulation And The Crustal Degassing Flux Of40Ar In The Great Artesian Basin, Australia
Journal Article: Argon Accumulation And The Crustal Degassing Flux Of40Ar In The Great Artesian Basin, Australia
AbstractMeasurements of the40Ar/36Ar ratio of dissolved argon from groundwaters in the Great Artesian Basin (GAB), Australia, indicate the accumulation of significant radiogenic40Ar. This radiogenic40Ar cannot be supplied by in situ production (40K-decay in the hydrologically conductive Hooray Sandstone) or by the dissolution of Hooray Sandstone with a finite K40Ar age. As was found earlier for the4He 1, the magnitude of the radiogenic40Ar in the GAB requires a crustal degassing flux of40Ar to be entering the aquifer. Within the errors of the data and assumptions regarding the composition and structure of the eastern Australian continental crust, this degassing flux approaches and may be equivalent to the whole crustal production of40Ar. A flux of this magnitude is in agreement with40Ar degassing estimates derived from atmospheric models. These measurements constitute the first direct measure of the40Ar continental degassing flux. The distribution of radiogenic40Ar from crustal degassing in the aquifer is discontinuous with time, distance, and4He. This suggests that the crustal degassing processes for40Ar and4He are local, time dependent, and decoupled. This can be understood in terms of (1) the mineral and lithologic distribution of K, U, Th; (2) the release of4He and40Ar from the solid phase to the fluid phase by recoil, diffusion, and dissolution; (3) the release of4He and40Ar by stress fracturing; (4) the variability of tectonic and hydraulic stress; and (5) the separation of differentially released4He and40Ar by the rapid rate ( > 10-6 cm2 s-1; > 0.1 cm yr-1) of crustal fluid transport required by metamorphism and crustal degassing. This further suggests that the crustal degassing process may be tectonically and hydraulically linked with other continental-scale fluid processes.
- T. Torgersen, B. M. Kennedy, H. Hiyagon, K. Y. Chiou, J. H. Reynolds and W. B. Clarke
- Published Journal
- Earth and Planetary Science Letters, 1989
T. Torgersen,B. M. Kennedy,H. Hiyagon,K. Y. Chiou,J. H. Reynolds,W. B. Clarke. 1989. Argon Accumulation And The Crustal Degassing Flux Of40Ar In The Great Artesian Basin, Australia. Earth and Planetary Science Letters. (!) .