[S-MP47_1PO1] Physics and Chemistry of Minerals

[SMP47-P21] Provenance study of quartz grains in aeolian desert sediments using cathodoluminescence method

*Risa MASUDA¹, Mototaka SANEYOSHI¹, Hirotsugu NISHIDO¹, K. TSOGTBAATAR², T. CHINZORIG², B. MAINBAYAR² (1.Okayama University of Science, 2.Mongolian Academy of Sciences, Mongolia)

Cathodoluminescence (CL), the emission of light caused by electron irradiation, has been widely applied in earth science, most extensively used in sedimentology. In such studies CL has the advantage that it can reveal characteristics which are invisible using transmitted light, e.g. growth zones of the crystals such as silica and carbonate minerals. In the case of quartz, its CL spectral feature is so complicated to be simply used for the identification of the provenance due to many emission centers related to various types of structural defects. In this study, we have conducted to clarify the luminescence centers in quartz selected from desert sediments using SEM-CL and evaluate quantitative ratios of the emission components of the CL spectra by the deconvolution method. The quartz grains (#60-80 mesh size) in the aeolian sediments collected from Djadokhta formation (upper Cretaceous) in the Gobi desert were fixed on the slide glass with low-luminescent epoxy resin, of which surfaces were polished with 1 micron diamond paste. Color CL images were obtained using a cold-cathode type Luminoscope with a cooled-CCD camera. CL spectroscopy was made by a SEM-CL system, which is comprised of SEM (JEOL: JSM-5410LV) combined with a grating monochromator (OXFORD: Mono CL2). The CL emitted from the samples was dispersed by a grating monochromator (1200 grooves/mm), and recorded by a photon counting method using a photomultiplier tube. All CL spectra were corrected for total instrumental response, which was determined using a calibrated standard lamp.All samples show dark blue CL emission, and exhibit two broad bands at 400 nm in a blue region and at 600-650 nm in a red region. CL spectra corrected for total instrumental response were converted into energy units for spectral deconvolution using a Gaussian curve fitting, because Gaussian curve in energy units can be assigned to one specific type of emission center (Stevens-Kalceff, 2009). The deconvoluted components can be assigned to the emission centers related to trivalent Fe at 1.65 eV, NBOHC at 1.89 eV, tetravalent Ti at 2.75 eV and trivalent Al at 3.19 eV by referring to Stevens-Kalceff (2009). We employed 10 grains randomly selected from collected 80 grains for each sample, and determined quantitative ratios of the emission components for these quartz grains using their integral intensities. We discuss variations of characteristic components among the sediments based on the results by a statistical analysis.