Karoo ignous province; environmental perturbation; Large Igneous Province; eruption dynamics; Central Atlantic Magmatic Province; U-Pb dating; mass extinction; Toarcian oceanic anoxic event; micro-baddeleyite; basalt; Triassic Jurassic boundary; geochronology
Broderick C., Wotzlaw J.F., Frick D.A., Gerdes A., Ulianov A., Günther D., Schaltegger U. (2015), Linking the thermal evolution and emplacement history of an upper-crustal pluton to its lower-crustal roots using zircon geochronology and geochemistry (southern Adamello batholith, N. Italy), in Contributions to Mineralogy and Petrology
, 170(3), 28.
Schaltegger U., Ulianov A., Müntener O., Ovtcharova M., Peytcheva I., Vonlanthen P., Vennemann T., Antognini M., Girlanda F. (2015), Megacrystic zircon with planar fractures in miaskite-type nepheline pegmatites formed at high pressures in the lower crust (Ivrea Zone, southern Alps, Switzerland), in American Mineralogist
, 100(1), 83-94.
Zeh A., Ovtcharova M., Wilson A.H., Schaltegger U. (2015), The Bushveld Complex was emplaced and cooled in less than one million years - results of zirconology, and geotectonic implications, in Earth and Planetary Science Letters
, 418, 103-114.
Jourdan F., Hodges K., Sell B., Schaltegger U., Wingate M.T.D., Evins L.Z., Söderlund U., Haines P.W., Phillips D., Blenkinsop T. (2014), High-precision dating of the Kalkarindji large igneous province, Australia, and synchrony with the Early-Middle Cambrian (Stage 4-5) extinction, in Geology
, 42(6), 543-546.
Schaltegger U., Wotzlaw J.-F., Ovtcharova M., Chiaradia M., Spikings R. (2014), Mass spectrometry in earth sciences: The precise and accurate measurement of time, in Chimia
, 68(3), 124-128.
High-precision and high-accuracy U-Pb dates of volcanic zircon from ash beds provide invaluable information for the temporal quantification of environmental perturbation and biotic response in the geological past. We have previously demonstrated that in selected cases, catastrophic biotic change as well as post-extinction biological recovery, and dynamics and tempo of biotic post-extinction recovery can be dated with better than ± 100 ka uncertainty of the 206Pb/238U zircon date. In the present project we aim to develop high-precision U-Pb dating of the mineral baddeleyite (ZrO2) in basalts from Large Igneous Provinces (LIP's), such as the Central Atlantic Magmatic Province (CAMP) or the Karoo igneous province. These two huge volcanic systems are thought to be the triggers for the end-Triassic climatic deterioration and mass extinction, and the early Toarcian global marine anoxia, respectively. High-precision U-Pb dating of magmatic baddeleyite in these basalts will allow temporal cross-calibration between volcanism on one hand, and global environmental and biotic disturbance on the other hand at a 50 - 100 ka level of precision and accuracy. By avoiding the widely used 40Ar/39Ar chronometer, we avoid the necessity to propagate systematic uncertainties associated with decay constants and standard or tracer compositions, respectively, into the final dates due to the comparison of two decay schemes, and therefore can compare dates at the level of analytical precision. In addition, we plan to analyze trace elements and Hf isotopes from the same dated volume of baddeleyite, for helping with the detailed interpretation of the U-Pb dates, and for gaining information about the melt source. We also intend to explore oxygen isotope analysis as a tool to quantify the degree of post-crystallization open-system behaviour of baddelyite grains.Separation and isotopic analysis of 20-40 µm small baddeleyite grains from basalts will be challenging and will request several efforts in adapting existing and developing new techniques in our laboratory. We anticipate that a majority of basalts will show a certain amount micro-baddeleyites, or, in case of more evolved compositions, of micro-zircon. The newly developed techniques will be applied to two cases: 1) The high-resolution intercalibration between the very short-lived CAMP volcanism in Morocco, US and Canada, with existing high-precision data for the environmental perturbation at the end of the Triassic causing mass extinction; and 2) the intercalibration between the lower Toarcian marine anoxic event with the eruption dynamics of the long-lived Karoo igneous province in Lesotho/South Africa. Basalts will be sampled from sections that are well characterized in terms of the paleomagnetism, sample selection is therefore carried out in close collaboration with specialists from France, Italy, The Netherlands and Australia. By high-precision dating some important paleomagnetic reversals of global importance will be calibrated to better than ±50 to 100 ka. Total durations of LIP volcanism, as well as their eruption dynamics over time will be reconstructed with high-precision methods by the first time. In conclusion, the project will deliver the following new knowledge about Earth's history:1.Establish absolute durations of volcanic activity at high resolution and reconstruct the eruption dynamics of two fundamentally different LIP's: CAMP (single activity peak of short duration) and Karoo (multi-peak activity over an extended period of time).2.Offer a new approach for dating basalt flows at ± 50-100 ka precision, which allows to directly date eruption dynamics of LIP's. Together with the obtained Hf isotope information from dated baddeleyite and potentially from geochemical information from whole rocks, the temporal variations of the melt sources may be interpreted in terms of plate tectonics. 3.Establish a precise relationship between the eruption dynamics and the highest environmental stress leading to the biotic response: end-Triassic mass extinction and lower Toarcian anoxic event, respectively (high-precision data for marine environmental and biotic crises established in former projects). These data will discriminate between models of pre-volcanic peak extinction versus maximum environmental stress and extinction during the peak volcanic activity.4.Calibrate the E23r magnetic interval at at the Triassic-Jurassic boundary, and the "van Zjil" magnetic reversal in the Toarcian at a ±50-100 ka level, used for global correlation of terrestrial sedimentary and volcanic deposits.5.Contribute to further quantify the apparent 0.8% offset between 40Ar/39Ar and 206Pb/238U dates.