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Title: Age constraints on the Late Cretaceous alkaline magmatism on the West Iberian Margin
Authors: Miranda, Rui
Valadares, Vasco
Terrinha, Pedro
Mata, João
Azevedo, Maria do Rosário
Gaspar, Miguel
Kullberg, José Carlos
Ribeiro, Carlos
Keywords: Geochronology
Alkaline magmatism
Wesy Iberian Margin
Late Cretaceous
Issue Date: 2009
Publisher: Elsevier Publisher
Citation: Miranda, Rui; Valadares, Vasco; Terrinha, Pedro; Mata, João; Azevedo, Maria do Rosário; Gaspar, Miguel; Kullberg, José Carlos; Ribeiro, Carlos. Age constraints on the Late Cretaceous alkaline magmatism on the West Iberian Margin, Cretaceous Research, 30, 3, 575-586, 2009.
Abstract: The onshore sector of theWest Iberian Margin (WIM) was the locus of several cycles of magmatic activity during the Mesozoic, the most voluminous of which was of alkaline nature and occurred between 70 and 100 Ma. This cycle took place in a post-rift environment, during the 35 counter-clockwise rotation of Iberia and initiation of the alpine compression. It includes the subvolcanic complexes of Sintra, Sines, and Monchique, the volcanic complex of Lisbon and several other minor intrusions, covering an area of approximately 325 km2. Previous cycles were tholeiitic and transitional in nature, occuring around 200 Ma and 130–135 Ma, respectively. New LA-ICP-MS U-Pb, 40Ar/39Ar, K-Ar and Rb-Sr ages on several intrusions distributed along the onshore WIM are presented, which combined with reviously published data allows us to constrain the duration of the Late Cretaceous alkaline cycle to circa 22 Ma (94–72 Ma) and define two pulses of magmatic activity. The first one (94–88 Ma) occurred during the opening of the Bay of Biscay and consequent rotation of Iberia and clusters above N38 200 . The second pulse (75–72 Ma) has a wider geographical distribution, from N37 to N39 . This final pulse occurred during the initial stages of the Alpine orogeny in Iberia that led to the formation of the Pyrenees and Betics and to tectonic inversion of the Mesozoic basins. Isotope and trace element geochemistry point to a sublithospheric source for the alkaline magmatism that clearly distinguishes it from the previous cycles which had an important lithospheric mantle component. Also, it allows the discrimination between the two different alkaline pulses in terms of trace element abundance and residual mantle minerology. It is speculated that these differences might be the result of distinct magma ascent rates due to either more or less favourable tectonic settings that avoided or allowed the interaction with metasomatized lithosphere and equilibration with K rich minerals like amphibole and/or phlogopite.
Type: article
Appears in Collections:CGE - Publicações - Artigos em Revistas Internacionais Com Arbitragem Científica

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