Crustal xenoliths from Tallante (Betic Cordillera, Spain); insights into the crust-mantle boundary

The volcano of Tallante (Pliocene) in the Betic Cordillera (Spain) exhumed a heterogeneous xenolith association, including ultramafic mantle rocks and diverse crustal lithologies. The latter include metagabbroids and felsic rocks characterized by quartz-rich parageneses containing spinel + or - garnet + or - sillimanite + or - feldspars. Pressure-temperature estimates for felsic xenoliths overlap (at 0.7-0.8 GPa) those recorded by the mantle-derived peridotite xenoliths. Therefore, we propose that an intimate association of interlayered crust and mantle lithologies characterizes the crust-mantle boundary in this area. This scenario conforms to evidence provided by the neighbouring massifs of Ronda and Beni Bousera (and by other peri-Mediterranean deep crust/mantle sections) where exhumation of fossil crust-mantle boundary reveals that this boundary is not sharp. The results are discussed on the basis of recent geophysical and petrological studies emphasizing that in non-cratonic regions the crust-mantle boundary is often characterized by a gradational nature showing inter-fingering of heterogeneous lithologies. Silica-rich melts formed within the crustal domains intruded the surrounding mantle and induced metasomatism. The resulting hybrid crust-mantle domains thus provide suitable sources for exotic magma types such as the Mediterranean lamproites.