Evolution of the Upper Mantle beneath the Pyrenees: Evidence from Orogenic Spinel Lherzolite Massifs

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Abstract
Structural upper portions of the Cabo Ortegal complex display a section of composite upper mantle composed of a continuous sheet of pyroxenite (∼ 3 km long and 300 m thick), within spinel-bearing harzburgite of the Herbeira massif. The sheet contains an alternation of pyroxenite and minor dunite with scarce garnet-rich mafic horizons. These horizons (on a scale of millimetres to 3 m) are generally not zoned but may be locally enriched at the base in olivine, orthopyroxene, and/or spinel. From primary phase compositions it is shown that the peridotites have strong affinities to residual oceanic peridotite tectonites and that the pyroxenites may constitute magma segregates crystallized in dykes or sills intruded into the peridotite.

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