Andonaegui Moreno, Pilar and Castiñeiras García, Pedro and González Cuadra, Pablo and Arenas Martín, Ricardo and Sánchez Martínez, Sonia and Abati Gómez, Jacobo and Díaz García, Florentino and Martínez Catalán, José Ramón (2012) The Corredoiras orthogneiss (NW Iberian Massif): Geochemistry and geochronology of the Paleozoic magmatic suite developed in a peri-Gondwanan arc. Lithos, 128-131 . pp. 84-99. ISSN 0024-4937
The Corredoiras orthogneiss belongs to the intermediate pressure upper units of the Órdenes Complex (Variscan belt, NW Spain), mainly composed by granodioritic orthogneisses, with small bodies of tonalitic orthogneisses, amphibole-rich orthogneisses and metagabbronorites. In this work we study their chemical and isotopic composition, to gain insight into the linkage between plate tectonics and magmatism and to improve the knowledge of the paleogeographic evolution of the European Variscan Belt. Granodioritic and tonalitic orthogneisses range from intermediate to felsic rocks, with K2O/Na2O ratios≈1, typical of calc-alkaline rocks, and high Na2O content, characteristic of I-type granites. Metagabbronorites are basic rocks, but some of them are contaminated by interaction with the felsic magmas, showing enrichment in SiO2, Na2O and K2O. All Corredoiras metaigneous rocks are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE), resulting in a high LILE/HFSE ratio. These geochemical features are the most characteristic of magmas related to subduction zones; furthermore all orthogneisses display significant negative anomalies in Ta, Nb and Zr, which together with their low contents in Y and Yb match up with granitoids generated in volcanic arcs or subduction zones. SHRIMP U–Pb zircon dating provides a concordia age of 492±3 Ma. Granodioritic orthogneiss has negative εNd(492 Ma) values (−2.2 to −3.6) and high (87Sr/86Sr)i ratios (0.707 to 0.708), on the other hand tonalitic orthogneisses and metagabbronorites have positive εNd(492 Ma) (1.0 to 2.4) and low (87Sr/86Sr)i (0.703 to 0.705), suggesting that granodioritic orthogneisses have a clear crustal influence in their generation, whereas tonalitic orthogneisses and metagabbros can be related to basic magmas extracted from the mantle or from a basic lower continental crust. The Corredoiras chemical characteristics permit us to interpret that this rocks were probably generated in an ensialic island arc and may represent a peri-Gondwanan fragment drifted away to open the Rheic Ocean.
|Uncontrolled Keywords:||Geochemistry, Geochronology, Metaigneous rocks, Magmatic arc, Northern Gondwana margin, Iberian Massif|
|Subjects:||Sciences > Geology > Petrology|
Sciences > Geology > Geochemistry
|Deposited On:||14 Mar 2012 11:39|
|Last Modified:||14 Mar 2012 11:39|
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