Mobility of high field strength elements (HFSE) in magmatic-, metamorphic-, and submarine-hydrothermal systems

Abstract

High field strength elements (HFSE) are normally considered as ‘conservative’ elements in most geological settings. However, field and experimental evidence has suggested that these elements are actually mobile in some cases and can be transported by magmatic-, metamorphic-, and submarine-hydrothermal solutions, in particular in those extreme cases such as highly altered hydrothermal ore deposits and highly evolved products of crystal fractionation such as pegmatites or granitic bodies bordering to metamorphic rocks. In this paper, we combine our own data with those from the literature and focus our discussion on HFSE mobility at crustal fluid systems. We suggest that the mobility of HFSE is controlled by a number of factors, including P– T conditions, pH, and solution chemistry. The HFSE mobility can occur in a wide range of P– T conditions, and their solubility is generally enhanced at high pH conditions. The high F contents in the fluids also largely enhance the mobility of HFSE. The mobility of HFSE and formation of hydrothermal minerals such as zircon and titanite offer us a useful tool to directly date related hydrothermal events by U–Pb methods, which otherwise lack suitable minerals for isotope dating.