Distribution of Zeolites in Lavas of Southeastern Parana Basin, State of Rio Grande Do Sul, Brazil

Abstract

Zeolites collected from the pile of Jurassic-Cretaceous plateau lavas in southeastern Parana Basin, Brazil are, in order of decreasing abundance: heulandite, scolecite, stilbite, laumontite, mesolite, mordenite, analcime, chabazite, and thomsonite. The lava pile is zeolitized into three zones on a regional scale with laumontite as the index mineral for the basal zone, scolecite for the intermediate zone, and a quartz, siliciczeolites assemblage for the upper zone. Laumontite is restricted to the bottom 100 m of basic lavas at the bottom of the pile where the temperature was sufficiently high (>100°C) to produce this mineral. Scolecite without laumontite formed in the basic lavas of the intermediate zone. In the upper zone, the radically different composition of acidic lavas yielded an impoverished assemblage of quartz and silicic low-calcium zeolites like mordenite and heulandite-stilbite. Parana volcanism occurred in an environment of a continental spreading center; a high flow of heat common to such spreading centers may have promoted hydrothermal circulation and zonal, rather than random, zeolitization of the lava pile.