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on wide-ranging discussions with members of the LIPs community around the
world, we have identified three themes that seem to resonate. Other themes
can be developed as interest and potential coordinators arise. Expand the Database: Archean to Present The recognition of pre-Mesozoic LIPs is complicated by: 1) erosion which removes the flood basalt component and exposes the plumbing system, 2) deformation, 3) plate tectonics which fragments older LIPs. A campaign will be organized in order to expand the study (particularly U-Pb dating) of pre-Mesozoic LIPs. In the Proterozoic this will focus on sill provinces and dyke swarms, and in the Archean work will focus on correlating between greenstone belts. Along with integrated paleomagnetic and geochemical study, these data will contribute to defining paleocontinental reconstructions and facilitate the reconstruction of fragmented LIPs, thereby allowing a more complete understanding of LIP distributions in time and space. Contact: Richard Ernst rernst@NRCan.gc.ca The Great Plume Debate: Developing Critical Tests Proposed Symposium There is currently vigorous debate regarding the origin of LIPs, mainly between a deep-mantle plume model, and alternative top-down (lithospheric plate) control (includes rift generated, cratonic edge convection mechanisms). Meteorite impact models are also proposed. A workshop is being planned in order to evaluate the current data pertaining to the origin of LIPs, in order to design critical tests for resolving the debate. It is forty years since Wilson first suggested that the Hawaiian Islands were produced by the oceanic lithosphere moving over a stationary “hot spot” in the mantle, and thirty years since Morgan suggested that plumes exist in the Earth’s mantle and may play an important role in convection. Flood basalts, volcanic continental margins, large oceanic plateaux and age progressive aseismic ridges, along with smaller-volume seamount and ocean island chains, have all been attributed to mantle plumes. The tendency over the last decade has been to focus research on those features of large igneous provinces (LIPs) and “hot spots” that can be explained by plume theory and to ignore those features that cannot. Does this mean that the plume hypothesis has become an a-priori assumption? Are there observations that can not be explained by the plume hypothesis? Do these observations require modification of the plume hypothesis, do they mean that the model does not apply to some “hot spot” volcanism or does it mean that the plume hypothesis should be abandoned altogether? What are the alternative hypotheses and what predictions do they make that can be used to test their validity? What is the current status of the plume hypothesis? The model has been widely applied by Earth scientists in many subdisciplines and there is a tendency for it to have become all things to all men. However, the fluid mechanics of low Reynolds number plumes is well understood, and as a consequence, mantle plume theory can make a number of readily testable predictions that can be used to evaluate it. What are these predictions and how can they be tested? We propose to convene a symposium on LIPs and “hot spots” to be called “The Great Plume Debate”. The Conveners will be Ian Campbell and Gillian R. Foulger. The meeting will be held at a LIP, either the Deccan, the Karoo or the Parana. The objectives of the symposium will be, for both the plume- and alternative hypotheses, to: • Deliver clear definitions of the hypotheses, • Set out the predictions of the hypotheses, • Test those predictions against field observations and laboratory measurements, • Clarify which observations are consistent with the various hypotheses and which are not, • To evaluate the link between LIPs and mass extinctions • To evaluate the role of LIPs in the formation of diamonds, nickel, platinum and copper-uranium deposits. The symposium will be cross disciplinary and will attract a wide range of Earth scientists including tectonophysicists, seismologists, fluid dynamists, geochemists, geochronologists, paleontologists volcanologists, economic geologists, sedimentologists, and field geologists. A major product will be a clearly focused statement of what the most important research avenues for the future are, that can potentially make first order advances in our understanding of the origin of LIPs and “hotspots” and their relationship to mantle convection. Contact: Ian Campbell Ian.Campbell@anu.edu.au or Gillian R. Foulger gfoulger@usgs.gov LIPs and Climate Change / Extinction Events The dramatic climatic effects of LIPs will be evaluated including the proposed link with extinction events. A particular focus will be the largest LIPs through time, and detailed comparison with the climatic record, particularly that preserved in the isotopic (Sr, O and C) composition of marine carbonates, and in the faunal/flora record. Contact: Paul Wignall wignall@earth.leeds.ac.uk |
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