Abstract:
The volatization of Rhenium (Re) from melts of natural basalt, dacite and a synthetic composition in the CaO-MgO-Al2O3-SiO2 system has been investigated at 0.1 MPa and 1250-1350 °C over a range of fO2 conditions from log fO2 = -10 to -0.68. Experiments were conducted using open top Pt crucibles doped with Re and Yb. Analysis of quenched glasses by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) normal to the melt/gas interface showed concentration profiles for Re, to which a semi-infinite one-dimensional diffusion model could be applied to extract diffusion coefficients (D). The results show Re diffusivity in basalt at 1300 °C in air is log DRe = -7.2 ± 0.3 cm2/s and increases to log DRe = -6.6 ± 0.3 cm2/s when trace amounts of Cl were added to the starting material. At fO2 conditions below the nickel-nickel oxide (NNO) buffer Re diffusivity decreases to log DRereducing = - 7.6 ± 0.2 cm2 / s and to log DRedacite = - 8.4 ± 0.2 cm2 / s in dacitic melt. In the CMAS composition, log DReCMAS = - 7.5 ± 0.1. The diffusivity of Re is comparable to Ar and CO2 in basalt at 500 MPa favoring its release as a volatile. Our results support the contention that subaerial degassing is the cause of lower Re concentrations in arc-type and ocean island basalts compared to mid-ocean ridge basalts. © 2006 Elsevier Inc. All rights reserved.
