2-D thermal modeling of HT-LP metamorphism in NW and Central Iberia: Implications for Variscan magmatism, rheology of the lithosphere and orogenic evolution (original) (raw)
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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 °C 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, ...
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The pre‐Mesozoic geodynamic evolution of SW Iberia has been investigated on the basis of detailed structural analysis, isotope dating, and petrologic study of high‐pressure (HP) rocks, revealing the superposition of several tectonometamorphic events: (1) An HP event older than circa 358 Ma is recorded in basic rocks preserved inside marbles, which suggests subduction of a continental margin. The deformation associated with this stage is recorded by a refractory graphite fabric and noncoaxial mesoscopic structures found within the host metasediments. The sense of shear is top to south, revealing thrusting synthetic with subduction (underthrusting) to the north. (2) Recrystallization before circa 358 Ma is due to a regional‐scale thermal episode and magmatism. (3) Noncoaxial deformation with top to north sense of shear in northward dipping large‐scale shear zones is associated with pervasive hydration and metamorphic retrogression under mostly greenschist facies. This indicates exhuma...