In-situ U/Pb rutile dating by LA-ICP-MS: 208Pb correction and prospects for thermochronological applications

The advent of rutile thermometry brought an increasing interest in understanding rutile formation and its temporal evolution. Here we report progress on several fronts of in situ U-Pb rutile geochronology: (1) Matrix matching, necessary for robust in situ dating is fullfilled by calibrating and testing rutile standards (R10 and R19), including the presentation of new TIMS ages for the rutile standard R19. (2) Common lead correction is routinely applied via 208Pb, which is possible due to extremely low Th/U ratios (usually <0.003) in most rutiles. Employing a 213 nm Nd:YAG laser coupled to a quadrupole ICP-MS and using R10 as a primary standard, rutile U/Pb ages for the other rutile standard and four rutile-bearing metamorphic rocks always agree better than 2% with the reported TIMS ages and other dating studies from the same localities. The methods outlined in this contribution should find wide application in thermochronological studies that require age information of single spots, e.g., single-crystal zoning and texturally-controlled dating. With this information we are able to address the effect of shielding of inclusion phases by robust host minerals.