Application of the TitaniQ geothermometer to the mafic layering of the Ronda peridotites (Betic Cordilleras)

Abstract

The titanium-in-quartz geothermometer (TitaniQ) is being nowadays successfully applied to quartz-bearing crustal rocks, mineral deposits or even to quartz mylonites. To examine further the validity of the thermometer we have analysed by electron microprobe the Ti concentration of quartz inclusions within garnets from a garnet-pyroxenite of the Sierra Bermeja massif (Ronda peridotites, Betic Cordilleras). The analysed pyroxenite shows a granoblastic texture consisting mainly of clinopyroxene crystals and partially kelyphitized garnet. Clinopyroxene and plagioclase inclusions in garnet yielded equilibrium conditions for the Grt-Cpx-Pl assemblage in the range of 1025-825 ºC and 1.7-1.5 GPa. The Ti mean content in quartz inclusions is 178 ± 21 ppm, which corresponds to quartz crystallization temperatures of ca. 995 ± 15 ºC (at 1.7 GP) and 820 ± 15 ºC (at 1 GPa). According to the obtained data and the concordance, within limits, with the results from conventional geothermobarometry, we propose that although quartz is far from being a main mineral in mantle rocks, its Ti-in-quartz composition can be used to unravel reliable crystallization temperatures and may be considered a useful geothermometer in quartz-bearing pyroxenites.