--> ABSTRACT: Paleocene Igneous Underplating and the Thermal Evolution of the Rockall Trough; Implications for Source Rock Maturation, by P. Clift; #91021 (2010)

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Paleocene Igneous Underplating and the Thermal Evolution of the Rockall Trough; Implications for Source Rock Maturation

CLIFT, PETER

Continental break-up in the NE Atlantic was accompanied by the outpouring of flood basalts in the proto-rift zone, and also on the NW European shelf west of Scotland, especially in the northern Rockall Trough and Wyville-Thomson Ridge area. Backstripping of wells along the eastern side of the Rockall Trough shows extension during the late Paleocene. Discrepancies between the depth and rate of subsidence during the Cenozoic indicate that the present depth to basement is shallower than might be expected from uniform stretching models, suggesting that the rifted crust has been re-thickened by igneous underplating during the late Paleocene. Thicknesses of underplated material vary from 1-2 km in the Erris Trough offshore Ireland, increasing to 5-6 km in the West Lewis Basin offshore the Hebrides, and reaching >7 km close to the Wyville-Thomson Ridge. Deep seismic reflection surveys in this area and the NE Atlantic margins suggest that much of the underplating takes place as gabbroic bodies at the base of the crust. While asthenospheric temperature anomalies underlying the area were probably ca. 150 degrees C during the late Paleocene, decreasing to ca. 50 degrees C for much of the Cenozoic, this only had a modest effect on the regional heatflow. Heatflow substantially increased after 63 Ma and decreased slowly towards the Oligocene (approx. 34 Ma), resulting in temporary substantially increased geothermal gradients, with potential impact on source maturation. This study shows how subsidence analysis can be used in conjunction with fission track and vitrinite data to predict the thermal history of a basin. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.