High-sensitivity U–Pb rutile dating by secondary ion mass spectrometry (SIMS) with an O2+ primary beam
Abstract We present a secondary ionization mass spectrometry (SIMS) technique for U–Pb geochronology of rutile at high spatial resolution and sensitivity using an O2+ primary ion beam coupled with surficial O2 gas deposition (O2 flooding). The O2+ beam is ~ 10 × more intense than conventionally applied O− or O2− beams at the same lateral resolution. Natural and synthetic rutile was determined to be conductive under O2+ bombardment, permitting higher excavation (sputter) rates than conventional SIMS using negatively charged O-beams without detrimental effects of sample charging. The main advantage of O2+ is rapid sputtering at shallow primary ion penetration depths. This minimizes the contri…
The effect of titanite and other HFSE-rich mineral (Ti-bearing andradite, zircon, eudialyte) fractionation on the geochemical evolution of silicate melts
Abstract We present trace element data for HFSE-rich minerals (titanite, eudialyte, Ti-bearing andradite, zircon) from plutonic rocks of the Eocene Tamazeght complex, High Atlas Mountains, Morocco. In most lithologies significant amounts of titanite are present and as such, titanite fractionation played a major role in the evolution of the HFSE budget of the whole complex. By combining our data with published titanite–melt partition coefficients we explore the effects of titanite fractionation on the evolution of geochemical parameters (Zr/Hf, Nb/Ta, La/Lu and Th/U ratios) during differentiation of silicate melts in detail. Based upon this, we further discuss the genetic relationships betwe…