HR: 1340h
AN: T13A-0442    [Abstracts]
TI: Global 1 deg x1 deg Thermal Model TC1 for the Continental Lithosphere and the Growth Rate of the Continents
AU: * Artemieva, I M
EM: irina@geol.ku.dk
AF: Geological Institute, Copenhagen University, Denmark, Oester Voldgade 10, Copenhagen, DK-1350 Denmark
AB: This study reports a new 1 deg x 1 deg consistent global thermal model TC1 for the continental upper mantle (Artemieva, PEPI, in press) constrained primarily by heat flow data and thus suitable for discrimination between structural/compositional and thermal heterogeneities observed in seismic, gravity, and electromagnetic models. A map of tectono-thermal ages of lithospheric terranes complied for the continents on a 1 deg x1 deg grid forms the basis for the TC1 model. Geotherms for continental terranes of different ages (>3.6 Ga to present) constrained by reliable data on borehole heat flow measurements (Artemieva and Mooney, JGR, 2001, B8) are statistically analyzed as a function of age and show a strong linear correlation with r=0.98. The statistical age relationship of continental geotherms (z=0.04*t+93.6, where z is lithospheric thermal thickness in km and t is age in Ma) is used to estimate lithospheric temperatures in continental regions with no or low-quality heat flow data (ca. 60% of the continents). These data are supplemented by cratonic geotherms based on electromagnetic and xenolith data; the latter indicate the existence of Archean cratons with two characteristic thicknesses, ca. 200 km and >250 km. Statistical analysis of continental geotherms reveals that thick (>250 km) lithosphere is restricted solely to young Archean terranes (3.0-2.6 Ga), while in old Archean cratons (3.6-3.0 Ga) lithospheric roots do not extend deeper than 200-220 km. It is proposed that the former were formed by tectonic stacking and underplating during paleocollisions of continental nuclei and have a limited lateral extent. This conclusion is supported by an analysis of the growth rate of the lithosphere since the Archean, which is constrained by statistical relations between geological ages and lithospheric thermal thickness. Growth models for the lithosphere do not reveal a peak in lithospheric volume at 2.7-2.6 Ga as expected from growth curves for juvenile crust. A pronounced peak in the rate of lithospheric growth (10-18 km3/year) at 2.1-1.7 Ga is the robust feature of the model; the peak correlates with a peak in the growth of juvenile crust and with a consequent global extraction of massif-type anorthosites. It is proposed that large-scale variations in lithospheric thickness at cratonic margins and at paleoterrane boundaries controlled anorogenic magmatism. Emplacement of Proterozoic anorthosites could have been caused by edge-driven convection triggered by a fast growth of the lithospheric mantle at 2.1-1.7 Ga. About 50% of the present continental lithosphere existed by 1.8 Ga.
UR: http://www.lithosphere.info
DE: 8103 Continental cratons
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8125 Evolution of the Earth (0325)
DE: 8130 Heat generation and transport
SC: Tectonophysics [T]
MN: Fall Meeting 2005