Growth related zonations in authigenic and hydrothermal quartz characterized by SIMS-, EPMA-, SEM-CL- and SEM-CC-imaging

Abstract

AbstractAuthigenic quartz overgrowths and hydrothermal quartz crystals from locations in Oman and Switzerland have been investigated with SIMS, EPMA, SEM-CL and SEM-CC. All techniques reveal similar zonation patterns with SEM-CL having the best resolution followed by SEM-CC, EPMA and finally SIMS. The observed zonations reflect chemical and/or physical changes during growth in the precipitation environment or disequilibrium precipitation at the crystal surface (i.e. sectoral and intrasectoral zonation). Based on the total Al content, two types of authigenic quartz are distinguishable. When the Al concentration is <500 μg g–1the predominant CL emission is at ~630 nm; in such quartzes, SEM-CL and SEM-CC are directly correlated, and signal intensities drop as a function of increasing Al concentration. In contrast, authigenic quartz with Al concentrations between 500 μg g–1and 1000 μg g–1has CL emission maxima at both ~630 nm and ~380—400 nm, at which point the panchromatic SEM-CL and SEM-CC intensities become decoupled.