应钟玉婷副研究员士邀请，伦敦大学学院Pieter Vermeesch教授将于9月2日（下周二）访问我所并在综合楼701会议室做学术报告，欢迎大家参加并积极讨论！

        报告题目：Broken carbonate chronometers

        报 告 人：Pieter Vermeesch教授
        报告时间：9月2日（下周二）上午10:00
        报告地点：综合楼701会议室    

     报告人简介：       

       Pieter Vermeesch is a Professor in Geochronology at University College London (UCL) and serves as the director of the London Geochronology Centre (LGC). He received his BSc degree from Ghent University, followed by an MSc from the Massachusetts Institute of Technology (MIT), and a PhD from Stanford University, specializing in Earth sciences and geochronology throughout his academic training. His research interests include geochronology, thermochronometry, aeolian geomorphology and sedimentary provenance analysis, using the U-Pb, Ar-Ar, fission track, U-Th-He and cosmogenic nuclide methods. As a firm believer in free and open research software, he has developed a number of widely used computer programs (such as IsoplotR, provenance and RadialPlotter) to process

and interpret geochronological data.

报告摘要：

     Carbonate U-Pb dating has become a key tool for Quaternary palaeoclimatology and palaeoanthropology beyond the ~800ka age limit of Th-U disequilibrium dating. U-Pb geochronology is based on the paired radioactive decay of 238U to 206Pb and of 235U to 207Pb. Current carbonate U-Pb data processing algorithms rely mostly on the 206Pb/238U clock and attach little weight to the 207Pb/235U data. A key weakness of this approach is the need to correct the 206Pb/238U data for initial 234U/238U disequilibrium, which may cause an excess (or deficit) in radiogenic 206Pb compared to secular equilibrium. The disequilibrium problem can be elegantly captured by matrix exponentials, using either an assumed initial composition, or a measured set of modern 234U/238U (and optionally 230Th/238U) activity ratios. When coupled with a deterministic Bayesian inversion algorithm, the matrix exponential formulation indicates that disequilibrium corrections work well for relatively young samples but become unreliable beyond 1.5 Ma and impossible beyond 2 Ma. Theoretical models and real world examples from Siberia, South Africa and Israel show that disequilibrium correction of such old samples can do more harm than good. Previous 'Monte Carlo' error propagation methods underestimate these uncertainties by up to an order of magnitude. The 207Pb/235U isochron method is a more accurate and precise alternative to 206Pb/238U geochronology for >2 Ma carbonates that are suspected to have experienced significant levels of initial 234U/238U disequilibrium.