OH-defect content in detrital quartz grains as an archive for crystallisation conditions

Infrared spectra of 433 oriented detrital quartz grains from different large sedimentary reservoirs worldwide are evaluated with respect to their OH-defect concentration (expressed as wt ppm water), which varies between 0 and 160 wt ppm for individual grains. OH-defect contents, averaged over each individual sample, range between 5 and 20 wt ppm defect water, with a mean value around 10 wt ppm. Sand samples tend to have lower average OH-defect contents than older sandstones deposited earlier from a similar source region. Three of the most OH-defect rich grains from our data set were observed in the oldest and the most strongly cemented sandstone investigated (1400 Ma old Dala sandstone from Dalarna/Sweden), suggesting that OH-defects are barely affected during diagenetic conditions even over geological time scales. Furthermore, the average OH-defect content of each sample is well correlated to its maturity. Combined with results from high-pressure experiments in different model systems, the new results may provide an indirect method to estimate the source rock inventory of the upper crust (igneous, hydrothermal or metamorphic) and depth of the sampled crustal section. Results further suggest that provenance analyses of mature sediments and sedimentary rocks could benefit from the analysis of OH-defect content in quartz.