Simultaneous determination of zircon U–Pb age and titanium concentration using LA-ICP-MS for crystallization age and temperature

Abstract

Simultaneous determination of zircon U–Pb age and titanium concentration for a single analysis spot gives both the crystallization age and temperature. The crystallization age and temperature pairs in granitic zircons map the time–temperature (t–T) path of granitic magma before its solidification. In laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis, it is challenging to quantitatively analyse a low level of titanium concentration. This study employed two approaches using a quadrupole mass spectrometer equipped with a collision/reaction cell (CRC). In the first approach, the MS/MS mass-shift mode with oxygen reaction gas provided reliable and consistent measurement of titanium as 48Ti16O+. In the second approach, the titanium concentration was determined quantitatively from the signal intensity of 49Ti in the non-gas mode (without the inflow of collision/reaction gas into the CRC). The methods were applied to zircon samples of the Kurobegawa granite (KRG), the Okueyama granite (OKG), the Toki granite (TKG), and the Tono plutonic complex (TCP), and provided U–Pb ages and titanium concentrations consistent with previous studies. The crystallization ages and temperatures collected from individual analysis spots of zircon samples in the KRG, OKG, TKG, and TCP were plotted in the t–T diagrams and enabled us to characterize the rapid cooling paths at thermal conditions of zircon crystallization at the sampling sites.