HR: 13:45h
AN: V43G-01 INVITED     [Abstracts]
TI: Constraints on Mantle Thermal Variations from the Sedimentary Record of Large Igneous Provinces
AU: * Clift, P D
EM: p.clift@abdn.ac.uk
AF: University of Aberdeen, Department of Geology and Petroleum Geology, Kings College, Aberdeen, AB24 3UE United Kingdom
AB: One of the characteristics of all models for mantle plumes, whether they are deep or shallow rooted is the presence of anomalously hot asthenosphere underlying the lithospheric plate, the melting of which is believed to produce large igneous provinces (LIP). Surface uplift is driven by the upward flow of mantle, as well as a lower density caused by excess heat and melt extraction. Shallowing of the seafloor around Iceland, Hawaii and regions of French Polynesia are characteristic of modern plume activity and should be preserved in the sediment cover of old LIPs. Removal of the LIP from over the plume would result in more subsidence than observed in regular oceanic crust. However, studies of the sedimentary cover from a range of seamounts, plateaus and ridges of various ages from all major ocean basins do not always show this greater than expected subsidence. Drill sites from the North Atlantic margins show the clearest consistent evidence for subsidence anomalies that could be caused by mantle temperature anomalies of around 100?C for a 100 km thick plume layer. However, several examples (e.g., Walvis Ridge, Rio Grande Ridge, Iceland-Faeroe Ridge, MIT Guyot, Hess Rise, 90East Ridge) show no resolvable differences with the normal oceanic crust and preclude major thermal anomalies under them at or shortly after the time of their emplacement. Most unusually in some LIPs (e.g., Ontong Java, Manihiki, Magellan and Shatsky Rises) subsidence is slower than for normal oceanic lithosphere, suggesting either colder than normal mantle temperatures, or more likely the emplacement of a buoyant lithospheric root under the magmatic province at the time of its formation caused by melt extraction. Gradual emplacement of the LIP crust may also slow the net basement subsidence. In these slow subsiding examples the sediments do not preclude or require hotter than normal mantle involved with LIP generation, but instead indicate that the lithosphere in these provinces was formed by processes that are quite different from those operating at mid ocean ridges. It is not clear why the buoyant depleted root under Hawaii disperses with time after magmatism, yet those under the Pacific plateaus do not, although this implies differences in viscosity that could be temperature related.
UR: http://www.mantleplumes.org/SedTemp.html
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8162 Rheology--mantle
DE: 3022 Marine sediments--processes and transport
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting