TY - JOUR
T1 - A reinterpretation of the Nevado-Filábride and Alpujárride Complexes (Betic Cordillera)
T2 - Field, petrography and U-Pb ages from orthogneisses (western Sierra Nevada, S Spain)
AU - Gómez-Pugnaire, M. Teresa
AU - Galindo-Zaldívar, J.
AU - Rubatto, D.
AU - González-Lodeiro, F.
AU - López Sánchez-Vizcaíno, V.
AU - Jabaloy, A.
PY - 2004
Y1 - 2004
N2 - We investigated gneisses from the upper sequence of the Nevado-Filábride Complex in the western Sierra Nevada, close to the contact with the Permo-Triassic Alpujárride Complex. Despite intense deformation, the occurrence of skarn-like lenses (epidote + amphibole + garnet + quartz) and abundant post-magmatic hydrothermal tourmaline in both the gneisses and adjacent metasediments strongly suggests that an originally intrusive contact is preserved. High-pressure assemblages are not preserved in the dated gneisses due to intense retrograde overprinting during exhumation. Nevertheless, thermobarometry performed in adjacent skarn rocks and metapelites indicates maximum temperatures and pressures ranging from 605 ± 74 to 715 ± 72 °C and from 11.0 ± 2.5 to 14.5 ± 2.5 kbar. SHRIMP ion microprobe U-Pb analyses were performed on zircons from one gneiss. The zircon crystals display igneous oscillatory-zoned domains, with an age of 301 ± 7 Ma (95% c.l.), rimmed by dark, unzoned overgrowths of metamorphic origin (mean age of 16.5 ± 0.4 Ma). The former age is interpreted as dating the crystallisation of the granitic protolith of the gneiss. This implies a pre-Permian age for the Nevado-Filábride marbles, traditionally considered to be Triassic, and a Palaeozoic age for the complete sequence of the upper part of the Complex. Accordingly, in western Sierra Nevada, the observed succession from the Nevado-Filábride Complex to the Alpujárride Complex (Permo-Triassic phyllites and Triassic marbles) can be considered normal from a stratigraphic point of view. Therefore, the present-day contact between the two complexes, the Mecina Fault in Sierra Nevada, is interpreted as a normal fault generated during exhumation rather than a thrust structure. The age of the metamorphic zircon overgrowths (16.5 ± 0.4 Ma) is likely to be related to de compression, as suggested by titanite inclusions found in zircon. Titanite postdates rutile, the high-pressure Ti-rich phase. This indicates exhumation of the Nevado-Filábride Complex significantly after the Alpujárride Complex (∼18 Ma).
AB - We investigated gneisses from the upper sequence of the Nevado-Filábride Complex in the western Sierra Nevada, close to the contact with the Permo-Triassic Alpujárride Complex. Despite intense deformation, the occurrence of skarn-like lenses (epidote + amphibole + garnet + quartz) and abundant post-magmatic hydrothermal tourmaline in both the gneisses and adjacent metasediments strongly suggests that an originally intrusive contact is preserved. High-pressure assemblages are not preserved in the dated gneisses due to intense retrograde overprinting during exhumation. Nevertheless, thermobarometry performed in adjacent skarn rocks and metapelites indicates maximum temperatures and pressures ranging from 605 ± 74 to 715 ± 72 °C and from 11.0 ± 2.5 to 14.5 ± 2.5 kbar. SHRIMP ion microprobe U-Pb analyses were performed on zircons from one gneiss. The zircon crystals display igneous oscillatory-zoned domains, with an age of 301 ± 7 Ma (95% c.l.), rimmed by dark, unzoned overgrowths of metamorphic origin (mean age of 16.5 ± 0.4 Ma). The former age is interpreted as dating the crystallisation of the granitic protolith of the gneiss. This implies a pre-Permian age for the Nevado-Filábride marbles, traditionally considered to be Triassic, and a Palaeozoic age for the complete sequence of the upper part of the Complex. Accordingly, in western Sierra Nevada, the observed succession from the Nevado-Filábride Complex to the Alpujárride Complex (Permo-Triassic phyllites and Triassic marbles) can be considered normal from a stratigraphic point of view. Therefore, the present-day contact between the two complexes, the Mecina Fault in Sierra Nevada, is interpreted as a normal fault generated during exhumation rather than a thrust structure. The age of the metamorphic zircon overgrowths (16.5 ± 0.4 Ma) is likely to be related to de compression, as suggested by titanite inclusions found in zircon. Titanite postdates rutile, the high-pressure Ti-rich phase. This indicates exhumation of the Nevado-Filábride Complex significantly after the Alpujárride Complex (∼18 Ma).
KW - Betic Complexes
KW - Hercynian magmatism
KW - High-pressure metamorphism
KW - SHRIMP U-Pb geochronology
KW - Zircon
UR - http://www.scopus.com/inward/record.url?scp=33645766785&partnerID=8YFLogxK
M3 - Article
SN - 0036-7699
VL - 84
SP - 303
EP - 322
JO - Schweizerische Mineralogische und Petrographische Mitteilungen
JF - Schweizerische Mineralogische und Petrographische Mitteilungen
IS - 3
ER -