A U-PB CA-ID-TIMS DATE FOR THE WRANGELLIA LARGE IGNEOUS PROVINCE IN THE KLUANE RANGE, YUKON

The eruption of the Wrangellia Large Igneous Province (LIP) has long been suggested as the cause of Carnian (early Late Triassic) biotic revolution and Earth-system change, but there is uncertainty surrounding its timing and duration. Published U-Pb, Ar-Ar and K-Ar radioisotopic dates for the Wrangellia LIP have a broad range of uncertainties (0.53 to 13.5 Myr), making them too imprecise to test this hypothesis. In the Yukon, the four published radioisotopic dates span from 224 ± 8 Ma to 232.2 ± 1 Ma. Improvements in analytical methods, such as the use of chemical abrasion in IDTIMS zircon geochronology, have reduced uncertainties, allowing us to place more precise geochronologic constraints on the timing of Wrangellia magmatism.

In this study, we used high-precision U-Pb chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-IDTIMS) to date a Wrangellia gabbro from the Yukon to investigate the timing of volcanism. A sample of the Maple Creek gabbro—interpreted to be a feeder for the extrusive Wrangellia Nikolai flood basalts—was collected in the Tatamagouche Creek area of the Kluane Range, Yukon. Our analysis produced a date of 230.7 ± 0.08 Ma for the Maple Creek Gabbro. This date overlaps within uncertainty with a U-Pb age of 230.91 ± 0.33 Ma from a volcanic ash bed in southern Italy that stratigraphically overlies evidence for Carnian environmental and climatic perturbations. Our results indicate that the Wrangellia LIP was active during this period of Earth-system change. The large uncertainties associated with previous radioisotopic dates, coupled with improvements in analytical methods make our new U-Pb date for the Maple Creek gabbro the most precise geochronologic constraint on the timing of the Wrangellia LIP.