Publication: Use of thermal modeling to assess the tectono-metamorphic history of the Lugo
and Sanabria gneiss domes, Northwest Iberia
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Publication Date
2009
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Societe géologique de France
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Abstract
The Lugo and Sanabria domes in Northwest Iberia have well constrained metamorphic and structural histories.
Both occur in the Iberian autochthon and resulted from late-Variscan extensional collapse following crustal thickening
related to the Variscan collision. The two domes developed beneath large thrust sheets, are cored by
sillimanite-orthoclase anatectic gneiss, preserve evidence of a steep thermal gradient (1 oC MPa-1), and exhibit a distinct
decrease in metamorphic grade to the east in the direction of nappe movement. Geochronological evidence indicates
that the lower crust melted within 30 Ma of initial crustal thickening and that dome formation occurred within
50 Ma.
The histories of the two domes are considered as the basis for one-dimensional finite-difference models of thermal
response to changes in crustal thickness. Results from thermal models suggest that thickening was limited to the
crust, provide a numeric explanation for timing and nature of granite magmatism, and indicate that high-temperature
metamorphism and crustal anatexis may result directly from thermal relaxation, eliminating the need for significant
mantle thermal contribution. Also, the models show that small differences in thickness of large, wedge-shaped thrust
sheets can explain distinct P-T paths experienced by different limbs of the domes.