CATHODOLUMINESCENCE OF QUARTZ FROM SANDSTONES - INTERPRETATION OF THEUV RANGE BY DETERMINATION OF TRACE-ELEMENT DISTRIBUTIONS AND FLUID-INCLUSION P-T-X PROPERTIES IN AUTHIGENIC QUARTZ

Quartz overgrowths from Keuper sandstones of the Paris basin were exam ined using cathodoluminescence (CL) microscopy and spectroscopy couple d with a scanning electron microscope (SEM). With the use of standard cold CL equipment, it was observed that the emission of authigenic qua rtz is much less intense than that of detrital quartz grains, but a re versal of intensity was observed with scanned CL in the 200-800 nm ran ge. The main CL emission band of diagenetic quartz is at 330-340 nm in the UV range, with other bands in the visible range. The determinatio n of trace element distributions in authigenic quartz by in situ analy ses and by SIMS imagery reveals the correlation of the 330-340 nm emis sion band with the highest Al and Li contents. The cathodoluminescence emission of diagenetic quartz in the UV range appears to be influence d by the coupled substitution of Al and Li into the crystal. Two expla nations are suggested: (i) Al, Li, or both serve as activators, and (2 ) the incorporation of Al and Li causes lattice defects that lead to a n enhancement of the intrinsic luminescence. Trace element analyses an d fluid-inclusion studies revealed that quartz overgrowths precipitate d from a fluid that partially originated from an Li-enriched primary b rine derived from eastern Triassic evaporites of the Paris basin. The specific CL emission band in the UV range can be linked to the diagene tic environment. The chemistry of the fluids appears to be the essenti al parameter, whereas precipitation temperatures do not influence the occurrence of such emissions.