Paragenesis de zeolitas alcalinas en un afloramiento de basaltos olivinicos amigdaloides de Junin de los Andes, Neuquen

VATTUONE,MARIA ELENA,LEAL,PABLO,CROSTA,SABRINA,BERBEGLIA,YANINA,GALLEGOS,ERNESTO Y MARTINEZ, CARMEN

Revista Mexicana de Ciencias Geologicas

Universidad Nacional Autonoma de Mexico

Lugar: Mexico; Año: 2008 vol. 25 p. 483 - 493

ABSTRACT   The optical characteristics, XRD, unit cell, chemistry and crystallization conditions of an alkaline zeolite assemblage were studied. The zeolites have been found infilling amygdales and in the matrix of Tertiary olivine basalts from Junin de los Andes, Patagonia. The secondary minerals (albite, pumpellyite, interestratified chlorite/smectite (C/S), smectite, iddingsite, magnetite and hematite) are replacing phenocrysts of plagioclase, olivine and the matrix of the rocks. Zeolites are sodic, calco-sodic and potassic in composition. Na–chabazite, analcime, Ca-K phillipsite and paulingite are the first zeolites that crystallized. They were followed by acicular-fibrous zeolites as natrolite/Na-gonnardite, thomsonite, mesolite and scolecite. The formation of the first zeolites is consistent with low temperature (<100°C), low pressure (<1kb) and alkaline (pH 9-10) hydrothermal/geothermal meteoric fluids, which were favored by tensional fractures. The aSi decreased during the alteration process and the temperature increased toward 200°C allowing the analcime formation followed by the equilibrium assemblage natrolite/Na-gonnardite-thomsonite-scolecite and mesolite.