Mineral Reactions and Controls on Zeolite-facies Alteration in Sandstone of the Central Transantarctic Mountains, Antarctica

Abstract

ABSTRACT Sandstone, mudstone and tuff of the Triassic Fremouw and Falla formations display diagenetic and zeolite-facies mineral assemblages that were controlled by parent material composition, fluid chemistry, permeability and temperature. Diagenetic reactions between sediments and ground water at near-surface temperature and pressure resulted in formation of smectite, chlorite, quartz, heulandite, mordenite and analcime cements and grain replacements. Zeolite-facies alterations, which resulted from simple rock-fluid reactions driven by heat from Jurassic diabase intrusions, converted smectite to illite-rich ordered mixed-layer illite/smectite and produced albite, laumontite, prehnite, epidote and chlorite cements and grain replacements. Organic maturation data suggest that, away from local e fects of the intrusions, temperatures may have been as low as 130° to 160°C, whereas stratigraphic evidence suggests maximum pressures of about 750 bars. Chemical patterns in sandstone near intrusions indicate that, although diabase supplied heat to drive rock-fluid reactions, it did not contribute a significant amount of cations to the hydrochemical system. Mineral and chemical patterns, together with hypothesized mineral reactions, suggest that significant mass transfer of Na+, Ca+2 and Si+4 occurred during alteration, whereas Al+3 mobility was restricted to migration from the reaction site to nearby pore space where Al+3 was incorporated into clay and/or zeolite cements.