Heulandite-group zeolites in volcaniclastic deposits of the southern Basin and Range province, Mexico
Munch, Philippe; Cocheme, Jean-Jacques
European Journal of Mineralogy Volume 5 Number 1 (1993), p. 171 - 180
published: Mar 4, 1993
manuscript accepted: Oct 13, 1992
manuscript received: Oct 17, 1991
ArtNo. ESP147050501019, Price: 29.00 €
Abstract Volcanogenic sandstones and conglomerates of the molassic Báucarit Formation of northern Mexico, Sonora State, fill intermontane extensional basins generated by the Miocene Basin and Range tectonics. Their cements consist of heulandite-group zeolites (up to 40% of rock volume), smectites and calcite or silica minerals. Heulandite-group zeolites have been distinguished by their thermal stability and chemical composition. The calcium content of all the heulandite-group minerals, clinoptilolite included, is very high, frequently exceeding 50 % of the total exchangeable cations. These calcic heulandite-group zeolites have been formed by reaction of acidic ashes and lithic fragments with interstitial water. Minor compositional changes have been observed and two kinds of variations have been distinguished: (i) variation from one basin to another; (ii) variation between heulandite cementing sandstones and heulandite replacing glassy volcanic fragments, the latter being more siliceous than the former. These two kind of variations are related to the strong influence of the chemical composition of source materials, although the second one might also be controlled by the permeability of the sandstones and by the rate of temperature increase. The presence of heulandite suggests a widespread hydrothermal activity and a steep geothermal gradient in the region during the Miocene.