Crystallization conditions of authigenic quartz from salt of the Zechstein basin inferred from their triple oxygen isotope composition

The triple oxygen isotope composition of authigenic quartz allows reconstructing formation temperature and isotopic composition of the fluid with which the quartz had equilibrated [1]. We studied authigenic quartz grains from salt deposits of the Zechstein evaporitic basin to estimate the formation temperature and δ18O of the saline brine. Chemically purified authigenic quartz was analyzed by means of high precision laser fluorination isotope ratio mass spectrometry.

In the triple oxygen isotope space, additional (compared to δ18O only) information is gained about the equilibrium conditions during crystallization or diagenesis of the quartz. The coexisting fluid deviated from modern ocean water composition in that it was enriched in δ18O in order to account for a valid equilibration temperature. By assuming the mineralizing fluid was fractionated evaporitic water, it is possible to reconstruct the diagenetic environment in which the quartz formed. Utilizing the calibration of [2], the diagenetic temperature and local water δ18O value can be determined by high precision analysis of authigenic quartz minerals (pseudo-single-phase thermometer).

[1] Pack, A. and Herwartz, D. (2014) The triple oxygen isotope composition of the Earth mantle and understanding Δ17O variations in terrestrial rocks and minerals, Earth and Planetary Science Letters 390: 138-145.

[2] Sharp, Z.D., Gibbons, J.A., Atudorei, V., Pack, A., Sengupta, S., Shock, E.L., and Knauth, L.P. (2016) A calibration of the triple oxygen isotope fractionation in the SiO2–H2O system and applications to natural samples, Geochimica et Cosmochimica Acta 186: 105-119.