Browsing by Author "Villaseca, Carlos"
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- Geochemical comparison of circular plutonic complexes with extrusive rocks from Sal Island (Cape Verde)Publication . Garcia-Rodriguez, Maria; Villaseca, Carlos; Ignacio, Cristina; Orejana, David; Mata, João; Caldeira, RitaABSTRACT: Sal island is located in the northeast and is the oldest of the Cape Verde archipelago, with magmatic activity starting ~25 Ma ago. It presents a series of circular plutons that could represent the subvolcanic roots of the exposed extrusive rocks. In this work we compare the geochemical characteristics of melagabbro-gabbro of circular (~16.3 Ma) intrusions in the Old Eruptive Complex, with basaltic and nephelinitic lavas of equivalent age (~15.8 and 14.2 Ma, Torres et al., 2010). This comparison allows observing a geochemical overlap between basalts and gabbros, and the similarity between trends of part of the samples in Harker-type diagrams and REE patterns. However, this compositional overlap is incomplete, with considerable differences and absence of fractionated (intermediate) lava types related to these terms of the circular complexes. This partial but incomplete overlap of the compositional fields of the plutonic and volcanic trends argues against the possibility of a direct genetic relationship between the two.
- The old central igneous complexes of Sal, Boa Vista and Maio islands: Implications for 17 Ma of isotopic evolution of the Cape Verde archipelagoPublication . Villaseca, Carlos; Orejana, David; Huertas, Maria J.; Ancochea, Eumenio; Ignacio, Cristina; Mata, João; Caldeira, Rita; Garcia-Rodriguez, Maria; Moreno, Juan A.; Perez-Soba, CeciliaABSTRACT: The central igneous complexes of the easternmost islands (Sal, Boa Vista and Maio) preserve some of the most ancient outcropping rocks of the Cape Verde (CV) archipelago. These Early to Middle Miocene (about 25 to 12 Ma) complexes show marked isotopic differences between mafic rocks from the northern (Sal and Boa Vista) and the southern Maio Island, the latter showing lower 143Nd/144Nd, 206Pb/204Pb, 207Pb/204Pb, and higher 87Sr/86Sr ratios. The main mantle plume composition beneath Cape Verde is here considered to be dominated by the FOZO component. Our data supports previous models suggesting the incorporation to plume components of minor DMM mantle sources in the northern CV island alignment, whereas mixing with the EM1 pole is prevalent on the southern CV islands. These isotopic differences are evident since the early stages of Cape Verde magmatism. The Late Miocene to Holocene time period (7 to 1.7 Ma) is characterized by the irruption of silica-undersaturated and carbonatite magmas with a relatively homogeneous isotopic composition and highly radiogenic Pb signatures (206Pb/204Pb up to 20.6 in carbonatitic rocks and 20.2 in silicate rocks) throughout most of the Cape Verde archipelago. During this transitional stage, the input of this new HIMU mantle component overprinted the previous mixing of the main FOZO plume component with shallow mantle members (DMM, EM1) of minor contribution.