HR: 11:35h
AN: T32A-06    [Abstracts]
TI: Lithospheric Controls on the Rifting of Continents at Slow Rates of Extension
AU: * Armitage, J J
EM: jja103@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, University of Southampton, European Way, Southampton, SO15 5RR, United Kingdom
AU: Henstock, T J
EM: then@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, University of Southampton, European Way, Southampton, SO15 5RR, United Kingdom
AU: Minshull, T A
EM: tmin@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, University of Southampton, European Way, Southampton, SO15 5RR, United Kingdom
AU: Hopper, J R
EM: hopper@geo.tamu.edu
AF: Texas A&M University, Department of Geology and Geophysics, College Station, TX 77843, United States
AB: The North Atlantic Igneous Province (NAIP) has escaped a simple explanation for its vast size and thickness. The region has a complicated history with many sedimentary basins that may or may not contain oceanic lithosphere and that pre-date the NAIP by between 20 and 100 Ma. Should these regions of pre-thinned lithosphere be ignored however in models that hope to explain the presence of the NAIP? We use the major and rare earth composition of melts generated within our dynamic model of extension of the lithosphere to predict seismic velocities within the emplaced igneous material. Previous models of the North Atlantic make the case clear for the presence of an exhaustible thermal anomaly that lay under the lithosphere. We test models with a 200 m°C, 50 km thick thermal anomaly beneath 125 km thick lithosphere to the sensitivity to regions of pre-thinning. The mantle potential temperature is 1325 m°C. The aim is to assess the importance of such failed rift basins. Extensional events that have stretching factors more than 3 to 4; pre-date the rift by 20 to 40 Myrs; and are less than 150 km from the centre of extension of a successful rift, have the effect of reducing the viscosity of the upper lithosphere, creating a region where the flow of mantle material can reach shallower depths. For an exhaustible thermal anomaly to have an affect, it must be advected above the solidus before it loses significant amounts of heat to the surroundings. There are two ways to achieve this, have a fast rate of rifting or introduce a pre-thinned region. We suggest that for enhanced melting leading to the formation of the NAIP, on or off axis pre-thinning is likely requirement, given the half rates of extension are slow. We suggest that the pre- thinning caused by the formation of the Hatton-Rockall Trough is enough, when combined with a 200 m °C thermal anomaly, to explain the magmatism of the Southeast Greenland Hatton Bank conjugate system. Such pre-thinning leads to asymmetric melt regions that crystallise to form underplate with seismic velocities of more than 7 km s^-1.
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 8178 Tectonics and magmatism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting