Abstract:

We present a discrimination scheme for cathodoluminescence (CL) spectra of quartz as a tool in provenance studies. We analyzed > 1000 quartz crystals from 58 samples of different plutonic, volcanic, metamorphic, and pegmatitic rocks. The technique is based on the measurement of the relative intensity of the two main emission centers in visible light at 470–490 nm and 600–640 nm. The results confirm a red, violet, or bright to medium blue luminescence for volcanic phenocrysts, mainly bright blue colors for felsic plutonic and high-temperature metamorphic quartz, as well as brown to dark blue CL for quartz of low-temperature metamorphic origin. These and additional results for mafic plutonic (dark blue) and pegmatitic quartz (bright blue) lead to a possible discrimination with the following rock grouping: (1) volcanic quartz, (2) low-temperature metamorphic and mafic plutonic quartz, and (3) felsic plutonic, high-temperature metamorphic, and pegmatitic quartz. In the proposed scheme, 87% of the spectra are classified correctly. The three quartz groups can be taken as an estimate for the amount of volcanic, metamorphic, and plutonic quartz in sediments, unless major input from plutonic, high-temperature metamorphic, or pegmatitic quartz has taken place. Hence, despite criticism within the literature during the last decades, the CL colors of detrital quartz still can be used as provenance indicators. We finally conclude that the measurement of wavelength spectra is a fast and straightforward method to determine quartz-bearing source rocks of siliciclastic sediments.

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