RT Journal Article
T1 Sm–Nd isotope geochemistry and tectonic setting of the metasedimentary rocks fromthe basal allochthonous units of NW Iberia (Variscan suture, Galicia)
A1 Fuenlabrada Pérez, José Manuel
A1 Arenas Martín, Ricardo
A1 Díez Fernández, Rubén
A1 Sánchez Martínez, Sonia
A1 Abati Gómez, Jacobo
A1 López Carmona, Alicia
AB The basal units of the allochthonous complexes of NW Iberia are formed by thick metasedimentary rock sequencesintruded by granitoids, ranging in composition from calc-alkaline (c. 493 Ma) to minor alkaline–peralkaline massifs (c. 475–470 Ma), and mafic rocks. The granitoids were transformed into variably deformedothogneisses and the associated mafic rocks were transformed into amphibolites, blueschists andeclogites during eo-Variscan high-P metamorphism dated at c. 370 Ma. Two different superimposedmetasedimentary rock sequences can be distinguished. The lower sequence (maximum depositional age atc. 560 Ma) is mainly composed of metagreywackes, while the upper sequence (maximum depositional ageat c. 500 Ma) consists of mica schists and other minor types. Major and trace element geochemistry of themetagreywackes of the lower sequence suggests that they were generated in relation to a peri-Gondwananarc system built on the thinned continental margin, although some chemical transition to passive margingreywackes is also observed. This sedimentary sequence was probably deposited in an Ediacaran–Early Cambrianback-arc setting or retro-arc setting, closer to the thinned platform of the continental margin. The geochemicalfeatures of the sedimentary rocks of the upper sequence suggest some affinity with passive marginsediments; they were probably deposited closer to the continental domain and to certain distance from themost active zones of the magmatic arc. The Nd model ages of 23 analysed samples are Paleoproterozoic andrange between 1782 Ma and 2223 Ma (average value 1919 Ma). The Nd model ages are slightly younger inthe upper sequence than in the lower sequence, but altogether they define a single population, and thereforethe two metasedimentary rock sequences can be clearly related. Sedimentation probably took place withinthe same basin located in the continental platform of Gondwana, the main source areas of these sedimentaryrocks did not change during the Late Neoproterozoic and Cambrian times. The Nd model ages are very oldand they seem to be compatible with Paleoproterozoic or Archean source areas, with only minor participationof younger sources probably represented by intrusive Cadomian–Pan-African granitoids.
PB Elsevier Science B.V., Amsterdam
SN 0024-4937
YR 2012
FD 2012
LK https://hdl.handle.net/20.500.14352/42430
UL https://hdl.handle.net/20.500.14352/42430
LA eng
DS Docta Complutense
RD 26 ago 2024