TY - JOUR
T1 - Early carboniferous wrenching, exhumation of high-grade metamorphic rocks and basin instability in SW Iberia
T2 - Constraints derived from structural geology and U-Pb and 40Ar- 39Ar geochronology
AU - Pereira, M. Francisco
AU - Chichorro, Martim
AU - Silva, J. Brandão
AU - Ordóñez-Casado, Berta
AU - Lee, James K.W.
AU - Williams, Ian S.
PY - 2012/8/10
Y1 - 2012/8/10
N2 - New U-Pb and 40Ar- 39Ar geochronology and structural data from high- to medium grade metamorphic shear zones of the Ossa-Morena Zone, and structural data from Early Carboniferous basins (Ossa-Morena Zone and South-Portuguese Zone), place additional constraints on the Variscan tectonics in SW Iberia. A zircon U-Pb age of 465±14Ma (Middle Ordovician) measured on migmatite from the Coimbra-Cordoba shear zone is interpreted as the age of protolith crystallization. This age determination revises the information contained in the geological map of Portugal, in which these rocks were considered to be Proterozoic in age.This paper describes the evolution of Variscan wrench tectonics related to the development of shear zones, exhumation of deep crustal rocks and emplacement of magma in the Ossa-Morena Zone basement. In the Coimbra-Cordoba shear zone (transpressional), migmatites were rapidly exhumed from a depth of 42.5. km to 16.6. km over a period of ca. 10. Ma in the Viséan (ca. 340-330. Ma), indicating oblique slip exhumation rates of 8.5 to 10.6. mm/yr (Campo Maior migmatites) and 3.2. mm/yr (Ouguela gneisses) respectively. In the Évora Massif, the gneisses of the Boa Fé shear zone (transtensional) were exhumed from 18.5 to 7.4. km depth in the period ca. 344-334. Ma (Viséan), with exhumation oblique slip rates of 2.8 to 4.2. mm/yr. At the same time, the Early Carboniferous basins of SW Iberia were filled by turbidites and olistoliths, composed mostly of Devonian rocks. The presence of olistoliths indicates significant tectonic instability during sedimentation with large-scale mass movement, probably in the form of gravity slides. Deformation and metamorphism dated at 356 ± 12. Ma, 321 ± 13. Ma and 322 ± 29. Ma respectively suggests that Variscan wrench movements were active in SW Iberia during the Early Carboniferous for a period of at least 35. Ma.
AB - New U-Pb and 40Ar- 39Ar geochronology and structural data from high- to medium grade metamorphic shear zones of the Ossa-Morena Zone, and structural data from Early Carboniferous basins (Ossa-Morena Zone and South-Portuguese Zone), place additional constraints on the Variscan tectonics in SW Iberia. A zircon U-Pb age of 465±14Ma (Middle Ordovician) measured on migmatite from the Coimbra-Cordoba shear zone is interpreted as the age of protolith crystallization. This age determination revises the information contained in the geological map of Portugal, in which these rocks were considered to be Proterozoic in age.This paper describes the evolution of Variscan wrench tectonics related to the development of shear zones, exhumation of deep crustal rocks and emplacement of magma in the Ossa-Morena Zone basement. In the Coimbra-Cordoba shear zone (transpressional), migmatites were rapidly exhumed from a depth of 42.5. km to 16.6. km over a period of ca. 10. Ma in the Viséan (ca. 340-330. Ma), indicating oblique slip exhumation rates of 8.5 to 10.6. mm/yr (Campo Maior migmatites) and 3.2. mm/yr (Ouguela gneisses) respectively. In the Évora Massif, the gneisses of the Boa Fé shear zone (transtensional) were exhumed from 18.5 to 7.4. km depth in the period ca. 344-334. Ma (Viséan), with exhumation oblique slip rates of 2.8 to 4.2. mm/yr. At the same time, the Early Carboniferous basins of SW Iberia were filled by turbidites and olistoliths, composed mostly of Devonian rocks. The presence of olistoliths indicates significant tectonic instability during sedimentation with large-scale mass movement, probably in the form of gravity slides. Deformation and metamorphism dated at 356 ± 12. Ma, 321 ± 13. Ma and 322 ± 29. Ma respectively suggests that Variscan wrench movements were active in SW Iberia during the Early Carboniferous for a period of at least 35. Ma.
KW - Basin instability
KW - Ossa-morena zone
KW - South Portuguese Zone
KW - Timing of deformation
KW - Variscan belt
KW - Wrench tectonics
UR - http://www.scopus.com/inward/record.url?scp=84864027341&partnerID=8YFLogxK
U2 - 10.1016/j.tecto.2012.06.020
DO - 10.1016/j.tecto.2012.06.020
M3 - Article
SN - 0040-1951
VL - 558-559
SP - 28
EP - 44
JO - Tectonophysics
JF - Tectonophysics
ER -