Professor David Chew

Current research applies geochronology to two problems which have attracted much attention in the recent scientific literature: isotopic dating of sedimentation (Neoproterozoic glacial sequences, Phanerozoic sequences with high biostratigraphic resolution) and exhumation mechanisms in orogenic and rift settings as deduced by low temperature thermochronology. The isotopic dating studies are funded by Science Foundation Ireland (06/RF/GEO012), (07/RFP/GEOF207). The first project involves dating sedimentary rocks by three new isotopic methods (applied to a fossil-bearing basin where the age is precisely known). The isotopic ages obtained will be compared with biostratigraphic ages to determine the suitability of each method to dating older, fossil-free sedimentary units. The second project employs precise U-Pb zircon dating of Carboniferous volcanic layers combined with high-resolution biostratigraphy to constrain the onset of Gondwanan glaciation and duration of Gondwanan glacial-interglacial cycles. I also manage the fission track laboratory in Trinity College Dublin. The laboratory was installed during summer 2007 (including all sample preparation equipment) and was funded by SFI and the Petroleum Infrastructure Program. Projects utilizing the laboratory include assessing the utility of low temperature thermochronometers (apatite fission track, (U-Th)-He apatite) in quantifying the thermal structure of the southern Iberian passive margin and investigating the timing of exhumation in tilted rift shoulders in the Tanzanian sector of the East African Rift. The latter research follows on from a recently completed Masters project which I supervised while at the University of Geneva. My PhD research (2001, University College Dublin) and post-doctoral research (University of Geneva, 2003 - 2005) involved investigating the timing of orogenesis in ancient orogenic belts (the Caledonides and proto-Andes respectively), using a combination of fieldwork and a variety of analytical techniques. In particular, much of my work on the Caledonides has involved detailed fieldwork and geochronology on the components of the Grampian orogen along the Fair Head - Clew Bay line, and its continuation into Scotland, the Highland Boundary Fault. My work in the Andes combined whole rock Sr, Nd, Pb and Hf isotopic tracing on magmatic rocks with high-precision geochronology on magmatic rocks (single crystal U-Pb zircon dating by TIMS, SIMS, LA-ICPMS and 40Ar-39Ar dating of K-bearing phases) and metamorphic rocks (Lu-Hf and Sm-Nd garnet dating, U-Pb dating of sphene and monazite). This study demonstrated the presence of an Ordovician magmatic and metamorphic belt in the Peruvian Andes for the first time, and proves the entire western South American margin (> 5000 km) was an active margin in the Early Palaeozoic.

  Earth Science   Geochemistry   Geochronology   Geology   Low temperature thermochronology   Plate Tectonics   Structural Geology

My research involves applying geochronology and isotope geochemistry to a diverse series of questions in the geosciences. It is based mainly around novel method development and applications of laser-ablation (LA) ICP-MS techniques to various geoscience problems, including isotopic dating of sedimentation, sedimentary provenance studies and quantifying the timing and rates of tectonic processes such as mountain building and exhumation. My research group has pioneered U-Pb dating of apatite by the LA-ICP-MS method, and integrating it with both apatite fission-track analysis and apatite trace-element geochemistry to yield protolith compositions in provenance studies. This work was developed in an SFI Investigators Programme grant on applying detrital apatite as a provenance indicator in systems. We have extended our LA-ICP-MS U-Pb dating approaches to undertaking rapid and routine geochronology of U-bearing minerals with appreciable common Pb. We now routinely undertake multi-proxy provenance studies based on U-Pb dating of accessory heavy minerals (e.g. apatite, rutile, titanite, zircon and monazite), in collaboration with leading international research groups and also in Ireland within the SFI iCRAG research centre. Recent research has focussed on developing LA-ICPMS mapping and my group would be recognised as one of the world-leading geoscience laboratories in this field. A key novel development is our U-Pb age mapping approach to dating calcite and zircon. This method is based on selection and pooling of pixels from 2-D elemental and isotopic ratio maps, and is a particularly powerful technique for targeting subdomains in samples with complex geological histories. The U-Pb calcite dating work is funded by an SFI Investigators Program award and has important and novel applications. These include constraining the timing of mineralization in the world-class Irish Zn-Pb mineral province, dating of syn-tectonic carbonate veins in carbonate sequences in orogenic belts, or direct dating of carbonates for key time intervals in Earth history such as Neoproterozoic 'Snowball Earth' glacial episodes.