Staff directory
Jean-Paul Liégeois
Earth Sciences
Geodynamics and mineral resources
Geodynamics and mineral resources
Publication details
Carlier, G, Lorand, G, Liégeois, J.P., Fornari, M, Soler, P.r, Carlotto, V & Cardenas, J. 2005. ‘Potassic-Ultrapotassic Mafic Rocks Delineate Two Lithospheric Mantle Blocks Beneath The South Peruvian Altiplano’. Geology 33: 601-604. Boullder : Geological Society of America. DOI: 10.1130/G21643.1. I.F. 3.887.
Article in a scientific Journal / Article in a Journal
The Altiplano of Southern Peru displays a large spectrum of Cenozoic potassic (K) and ultrapotassic (UK) mafic rocks that delineate two deep lithospheric mantle blocks that have experienced different depletion and enrichment events. Phlogopite lamproites indicate that the Eastern Altiplano block is underlain by a metasomatized, harzburgitic mantle, of Palaeoproterozoic to Archaean age (TDM = 1130-2485 Ma; Nd = -5.0 to -11.4; 87Sr/86Sri = 0.7100-0.7159). Beneath the Western Altiplano block, the presence of a younger (TDM = 837-1259 Ma; Nd = +0.6 to -6.3; 87Sr/86Sri = 0.7048-0.7069), metasomatized lherzolitic mantle is deduced from multiple occurrences of diopside-rich K-UK lavas (leucitites, leucite-bearing tephrites, olivine and diopside trachybasalts). A third suite of young (< 2 Ma), K-UK rocks outlines the active Cusco-Vilacanota Fault System separating the Western and Eastern Altiplano blocks; this third suite, composed of diopside phlogopite lamproites and augite kersantites, minettes and trachybasalts, sampled a composite mantle source probably including an asthenospheric component (TDM = 612-864 Ma; Nd = -1.1 to -3.5; 87Sr/86Sri = 0.7051-0.7062), in addition to lithospheric components inherited from the Eastern and Western Altiplano blocks. The spatial distribution of the south Peruvian K-UK magmatism suggests that K-UK melts reached the surface through re-using older translithospheric weakness zones extending at least to the depth of magma generation. These latter were reactivated by a dextral transpressional regime imposed on the two rigid lithospheric blocks by the Andean orogen.