Variations of OH defects and chemical impurities in natural quartz within igneous bodies

Alexander Potrafke,Roland Stalder,Thomas Ludwig,Karel Breiter,Rolf Dieter Neuser

doi:10.1007/s00269-020-01091-w

Abstract

In this study, we present the first systematic dataset on natural variations of OH defect and trace element contents in quartz within igneous bodies. Samples were derived from bore holes of two plutonic bodies from the Krušné Hory/Erzgebirge (German–Czech border), representing typical A-type (Cínovec/Zinnwald granite cupola) and S-type (Podlesí Stock) granite intrusions. Fourier Transform Infrared spectroscopy of quartz was used to investigate the sample set with regard to its OH defect speciation and content. For Zinnwald quartz, IR absorption spectra reveal different lithologies due to changes of the OH defect inventory, enabling a subdivision of the granitic body: (1) hydrothermal greisen quartz of the uppermost part of the intrusion have low OH defect contents (average of 15 µg/g H2O); (2) zinnwaldite granite quartz vary strongly in defect content and show the highest content of the dataset (10–70 µg/g H2O); (3) quartz from an underlying biotite granite have slightly lower, but very uniform contents down to the bottom of the borehole at 1600 m (average 20 µg/g H2O). Infrared spectra of Podlesí quartz reveal a gradual increase in total defect water content with increasing depth over 350 m (30–55 µg/g H2O). Lithium contents in quartz samples from the uppermost part of the Zinnwald intrusion correlate with the occurrence of Li-specific OH defects, while cathodoluminescence (CL) images do not show specific differences. Our findings evidence the potential of OH defects in quartz as a tool to decipher differentiation trends in igneous bodies, and the application of their eroded material for provenance analyses.

Highlights

Quartz (SiO2) is a major constituent of felsic igneous rocks such as granites, as well as of metamorphic and sedimentary rocks
We present the first systematic dataset on OH defects in quartz from borehole sections of two localities to monitor variations in selected granitic bodies
For each sample five oriented quartz wafers were prepared for IR spectroscopy following the protocol described by Stalder and Konzett (2012), adding up to a total of 75 (Zinnwald) and 25 (Podlesí) crystals (Table 1)

Summary

Introduction

Quartz (SiO2) is a major constituent of felsic igneous rocks such as granites, as well as of metamorphic and sedimentary rocks. Institut für Mineralogie und Petrographie, Universität Innsbruck, Innrain 52f, 6020 Innsbruck, Austria. Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany usually makes up the principal component due to its high resistance to chemical and mechanical weathering. Quartz does not form solid solution series, it is capable of incorporating significant amounts of trace elements such as P5+, Ti4+, Ge4+, Al3+, Fe3+, B3+, Li+, Na+, K+ and H+ (Bambauer 1961, 1963; Kats 1962; Aines and Rossman 1984; Müller and Koch-Müller 2009). Participation of hydrogen in the substitution mechanism leads to the formation of hydroxyl dipoles (OH) with the oxygen anions from the quartz lattice. Trace element incorporation in general and OH defect formation in particular is a function of physico-chemical parameter such as pressure, temperature, Page 2 of 16

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Results

Discussion

Conclusion