MODELLO

MARCHESI CLAUDIO¹, GARRIDO CARLOS JESUS², PROENZA JOAQUIN³, GODARD MARGUERITE⁴, GERVILLA FERNANDO¹, BLANCO-MORENO JESUS⁵

presenter's e-mail: claudio@ugr.es

1 - Instituto Andaluz de Ciencias de la Tierra y Departamento de Mineralogía y Petrología, CSIC-Universidad de Granada (Spain)
2 - Departamento de Mineralogía y Petrología, Universidad de Granada (Spain)
3 - Departament de Cristal lografia, Mineralogia i Dipòsits Minerals, Facultat de Geología, Universitat de Barcelona (Spain)
4 - Laboratoire de Tectonophysique, Institute des Sciences de la Terre de l'Eau et de l'Espace de Montpellier, Université Montpellier II (France)
5 - Departamento de Geología, Instituto Superior Minero Metalúrgico de Moa (Cuba)

The Mayarí-Baracoa Ophiolitic Belt (MBOB) is located in the easternmost part of the Northern Cuban Ophiolite Belt. The MBOB comprises the Mayarí-Cristal and Moa-Baracoa massifs, two sets of strongly faulted ultramafic, plutonic, and volcanic complexes. Genetical relationships between the plutonics and volcanics are uncertain due to intense tectonic activity in the area. Mayarí-Cristal massif is made up of mantle tectonites with subordinate intruding mafic dikes and lacking of crustal section. The dikes are composed of diabase chilled-margins and microgabbro cores which display plagioclase-clinopyroxene cumulate texture. The Téneme volcanic Formation is in tectonic contact with Mayarí-Cristal ophiolitic rocks. These volcanics consist mainly of basalts and basaltic andesites and has been interpreted as low-Ti island arc tholeiites.
Moa-Baracoa massif comprises a harzburgite mantle section with minor dunites, a well-developed Moho transition zone with gabbro sills and dikes, and an upper incomplete crustal section constituted by layered gabbros. Sills, dikes and layered gabbros are olivine rich cumulates with low abundance in orthopyroxene. The Quiviján volcanics tectonically overlie the ophiolitic rocks of Moa Baracoa massif and they mainly consist of pillow basalts of back-arc geochemical affinity.
The REE equilibrium concentrations in the liquids coexisting with the cumulate gabbros, as well as their #Mg, have been calculated. The REE patterns of the liquids show an N-MORB shape with (La/Yb)N and (Ce/Sm)N ratios ranging between 0.5-1.0 and 0.6-0.9 respectively. #Mg average value for liquids coexisting with the Moa-Baracoa cumulates is 0.51; such a low value implies that parental magma experienced intense crystal fractionation.
Quiviján volcanics display REE patterns and #Mg comparable to those of the calculated liquids from Moa Baracoa cumulates. On the other hand Téneme volcanics exhibit patterns enriched in LREE and flat to slightly depleted for MREE and HREE which are very different from the calculated liquids coexisting with the Mayarí-Cristal dikes.
These results indicate that cumulate gabbros from Moa Baracoa massif crystallized from a parental mantle-derived magma after which the remaining liquid was extracted and rose to the upper crust where it formed the Quiviján volcanics. Conversely, basing on a limited number of samples of plutonic dikes, Mayarí-Cristal cumulate gabbros and Téneme volcanics do not show any genetical relationship.