Coeval interaction between magmas of contrasting composition (Late Carboniferous-Early Permian Santa Eulália-Monforte massif, Ossa-Morena Zone): field relations and geochronological constraints



The Santa Eulália-Monforte massif is a post-kinematic Late Carboniferous-Early Permian (LC-EP) located in the Ossa-Morena Zone (Portugal). This paper examines field relationships between calc-alkaline pinkish granites and mafic-intermediate rocks from the external ring of this composite massif and presents new U-Pb zircon age determinations. In a conservative interpretation, the estimated 206Pb/238U ages of 295.8 ± 1.3 Ma for a sample of the calc-alkaline pinkish granite and of 303.1 ± 3.1 Ma for a sample of gabbro-diorite, point to a short time interval between the crystallization of both magmas, with the mafic and intermediate rocks being the oldest. At the outcrop scale contacts of the mafic-intermediate rocks with the host pinkish granite are sharp and corroborate this age relationship but, do not justify why the host-enclave contacts often have curved and irregular shapes indicative of liquid-liquid interaction. However, with a full analysis of the distribution of the obtained U-Pb zircon ages and respective Th/U ratios seems to be possible to admit that the distinct compositionally magmas were roughly contemporaneous. The ages obtained are also important because they fit the LC-EP Iberian calc-alkaline within the time interval in which the Iberian orocline was formed and took place the subduction of the Paleotethyan oceanic plate under the Eurasian active margin. Taking this geodynamic setting as reference, the LC-EP Iberian calc-alkaline magmatism can be interpreted as most probably related to the Cimmerian cycle instead of the traditionally accepted model that ascribe a closer connection with the Variscan cycle.


Iberian Massif, Late Carboniferous-Early Permian, calc-alkaline bimodal plutonism, Zircon dating, Variscan and Cimmerian cycles

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Geologica Acta (ISSN-1695-6133)
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