The Iberian Peninsula is characterized by the outcrops of significant alpine-type pridotite massifs both in the Betic and the Pyrenean orogenic belts, ophiolitic peridote occurrences as well as by several volcanic centres entraining mantle xenoliths (Bodinier and Godard, 2014, Ancochea and Nixon, 1987), allowing a multiple outlook of deep mantle processes occurring in the region. Mantle xenoliths, such as those from the volcanic districts of Calatrava (central Spain), Olot (south-east Spain) and from the Betic locality of Tallante were extensively investigated by various petrological studies, whereas those of the volcano of Cofrentes have been reported, but so far never investigated in detail. They represent a mantle section located between the Betic and Pyrenean belts, in a sector faulted and deformed at least since the Mesozoic (Villaseñor et al., 2018). The study of these xenoliths is therefore very important to complete the lithospheric mapping of the Iberian region. Xenoliths from Cofrentes are extremely fresh, but rarely exceed 1-2 cm in size. Thin section observation, coupled with in situ-major and trace element analyses, show that they are spinel-bearing peridotite characterized by protogranular textures. Using an iterative method that combines the T-P results calculated with various geothermometers and geobarometers, calibrated for ultramafic systems, we obtained that all samples record equilibration temperatures in the range of 610 to 930 °C, and pressure from 13 to 7 Kbar. The xenoliths from Cofrentes, if compared with mantle xenoliths from other Iberian localities (and more in general with xenoliths from other volcanic districts of the circum-Mediterranean area studied by our research group) display the lowest equilibration temperatures, thus suggesting a provenance by a mantle domain equilibrated at relatively shallow conditions, as confirmed by the pressure values. Therefore, it appears that the MOHO beneath Cofrentes is shallower than beneath other volcanic districts, and/or that significant slivers of mantle rocks penetrated at crustal level, a process that has to be explained within the geodynamic evolution of the Iberian margin that was affected by multiple extensional and compressional phases. REFERENCES Bodinier, J.L., Godard, M., (2014): Orogenic, Ophiolitic, and Abyssal Peridotites. In: The Mantle and Core. Treatise on Geochemistry. Carlson, R.W. (ed.), Elsevier, Amsterdam. 3 p. 103–167 Ancochea, E, Nixon, P., (1987). Xenoliths in the Iberian Peninsula. In: Nixon P.H, ed. Mantle Xenoliths. New York: John Wiley & Sons Villaseñor, A., Chevrot S., Harnafi M., et al. (2015): Subduction and volcanism in the Iberia–North Africa collision zone from tomographic images of the upper mantle. Tectonophysics 663, 238-249.
Mantle domains interlayered at crustal depth: evidence provided by peridotite xenoliths from Cofrentes, Iberian peninsula
Bianchini G.;Bonadiman C.
2018
Abstract
The Iberian Peninsula is characterized by the outcrops of significant alpine-type pridotite massifs both in the Betic and the Pyrenean orogenic belts, ophiolitic peridote occurrences as well as by several volcanic centres entraining mantle xenoliths (Bodinier and Godard, 2014, Ancochea and Nixon, 1987), allowing a multiple outlook of deep mantle processes occurring in the region. Mantle xenoliths, such as those from the volcanic districts of Calatrava (central Spain), Olot (south-east Spain) and from the Betic locality of Tallante were extensively investigated by various petrological studies, whereas those of the volcano of Cofrentes have been reported, but so far never investigated in detail. They represent a mantle section located between the Betic and Pyrenean belts, in a sector faulted and deformed at least since the Mesozoic (Villaseñor et al., 2018). The study of these xenoliths is therefore very important to complete the lithospheric mapping of the Iberian region. Xenoliths from Cofrentes are extremely fresh, but rarely exceed 1-2 cm in size. Thin section observation, coupled with in situ-major and trace element analyses, show that they are spinel-bearing peridotite characterized by protogranular textures. Using an iterative method that combines the T-P results calculated with various geothermometers and geobarometers, calibrated for ultramafic systems, we obtained that all samples record equilibration temperatures in the range of 610 to 930 °C, and pressure from 13 to 7 Kbar. The xenoliths from Cofrentes, if compared with mantle xenoliths from other Iberian localities (and more in general with xenoliths from other volcanic districts of the circum-Mediterranean area studied by our research group) display the lowest equilibration temperatures, thus suggesting a provenance by a mantle domain equilibrated at relatively shallow conditions, as confirmed by the pressure values. Therefore, it appears that the MOHO beneath Cofrentes is shallower than beneath other volcanic districts, and/or that significant slivers of mantle rocks penetrated at crustal level, a process that has to be explained within the geodynamic evolution of the Iberian margin that was affected by multiple extensional and compressional phases. REFERENCES Bodinier, J.L., Godard, M., (2014): Orogenic, Ophiolitic, and Abyssal Peridotites. In: The Mantle and Core. Treatise on Geochemistry. Carlson, R.W. (ed.), Elsevier, Amsterdam. 3 p. 103–167 Ancochea, E, Nixon, P., (1987). Xenoliths in the Iberian Peninsula. In: Nixon P.H, ed. Mantle Xenoliths. New York: John Wiley & Sons Villaseñor, A., Chevrot S., Harnafi M., et al. (2015): Subduction and volcanism in the Iberia–North Africa collision zone from tomographic images of the upper mantle. Tectonophysics 663, 238-249.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
