P-T evolution of MORB-derived amphibolites in the Paleozoic basement of the Aluminé Igneous-Metamorphic Complex, Neuquén, Argentina: Decoding its genesis, and pre-Andean regional correlations

URRAZA I. A.; DELPINO S.H.; GRECCO, L.E.

GEOLOGICA ACTA

UNIV BARCELONA

Lugar: Barcelona; Año: 2019 vol. 17 p. 1 - 23

1695-6133

Amphibolites included in the metapelitic sequence andas xenoliths in intrusive magmatic rocks outcropping in the southern sector ofthe Alumine Igneous-Metamorphic Complex, are studied in detail in order todetermine its primitive genesis and its subsequent metamorphic evolution.  Field evidence and whole-rock geochemistryindicate that these rocks were derived from a MORB type protolith, and wereinitially emplaced as tectonic wedges into the metapelitic sequence that mainlyformed the accretionary prism associated to a pre-Andean SO-NE subduction setting.Phase relationships, geochemistry of index minerals and geothermobarometry,indicate the development of at least two metamorphic events (M11.9-3.9 kbar, 677-745ºC and M2 5.5-6.4 kbar) framed in a counterclockwiseP-T path, comparable to those previously determined for the metapelitic country-rocksand metatroctolites outcropping in the same sector of AlumineIgneous-Metamorphic Complex. Based on regional proximity and the agreement inthe petrological, geochemical, geochronological andstructural data, we strongly suggest that the Ñorquinco rocks belong to the easternprolongation of the Western Series of the Coastal Cordillera of Chile, towardsthe center-west of Argentinean territory.