CATHODOLUMINESCENCE INVESTIGATIONS AND TRACE-ELEMENT ANALYSIS OF QUARTZ BY MICRO-PIXE - IMPLICATIONS FOR DIAGENETIC AND PROVENANCE STUDIES IN SANDSTONE

Hot-cathodoluminescence (CL) microscopy and high-resolution trace-elem ent analyses by Particle Induced X-ray Emission (micro-PIXE) using the proton microprobe have been applied to samples of quartz arenite in o rder to obtain information about their diagenetic environment and the provenance of quartz detritus. The occurrence of an intensely zoned or ange-brown cement generation within quartz overgrowths in quartzitic l enses from the Fontainebleau Sand (Oligocene, Paris Basin) coincides w ith increased Fe concentrations of up to 192 ppm. In contrast, the Fe content of a nonluminescing generation within the same overgrowths is significantly lower, This finding suggests that the CL is either activ ated by the Fe itself or caused by defects induced by the incorporatio n of Fe into the structure. Detrital grains of quartz from sandstone s amples of different ages and locations (Wiehengebirgsquarzit, Upper Ju rassic, northwestern Germany; Fontainebleau Sand, Oligocene, Paris Bas in) yield a good correlation between CL color and Fe and Ti concentrat ions, with Fe (up to 455 ppm) being more abundant in red-brown-lumines cing grains and Ti (up to 298 ppm) confined to grains with blue-violet luminescence. Ti is universally present in quartz from plutonic and e xtrusive igneous rocks, but rarely observed in quartz from metamorphic rocks. This supports the general contention that the blue-violet-lumi nescing quartz was formed under higher temperatures than the quartz wi th brown luminescence, an observation important for studies of sandsto ne provenance. Concerning the mechanisms of CL activation, these resul ts do not unequivocally prove that the observed colors are activated b y the elements sought. Despite the advantages of the microanalytical t echnique, the observed trace-element contents may still reflect submic roscopic inclusions rather than element incorporation into the structu re.