“The crystalline basement of the Catamarca Andes (27° 15' - 27° 40' South), Argentina: geochronology and geodynamic implications”.

OTAMENDI J.; CRISTOFOLINI E; MOROSINI AUGUSTO; ESCRIBANO F.; GALLI, ANDREA C.; BARZOLA MATÍAS; ARMAS, PAULA

SANTIAGO

Congreso; XVI Congreso Geológico de Chile.; 2023

Sociedad Geológica de Chile,

The crystalline basement of Laguna Amarga Metamorphic Complex (LAMC) occurs as a mosaic of fault-bounded blocks in the Cenozoic eruptive volcanic field of the Andes of Catamarca. These basement blocks are located between the Cazadero Grande River and the Valle Ancho depression, around 150 km of Fiambalá, Catamarca. The outcrops have been mapped based on the correlation of the rock types and structural evidence as a new stratigraphic nomenclature (LAMC), and subdivide in Cazadero Grande and Los Aparejos associations. The Cazadero Grande Association is characterized by amphibolite-facies metasedimentary rocks and ortho-amphibolites, grouped in three lithological units: 1) Aguada de Tambillo Unit, composed of metamorphosed siliciclastic rocks, including gneisses, quartzites, and cherts; 2) Puesto Verde Unit, constituted by marbles and calcsilicate gneisses; and 3) El Quemadito Unit, dominated by ortho-amphibolites. The Los Aparejos metamorphic association is divided into two granulite-facies lithostratigraphic units: 1) Lagunas Frías Unit, consisting of metapelitic and metapsammitic migmatites with subordinate marbles; and 2) Pirca Negra Unit, formed by meta-mafic rocks. The combination of a petrological-structural analysis, and detrital-metamorphic zircon ages is relevant to the stratigraphic correlation of the LAMC at a regional scale. In order to know the age of the metamorphic peak and the ages of inheritance associated with their provenance areas, zircons from five metasedimentary rocks of siliciclastic protoliths (paragneiss, metagreywacke, metaquartzite, leucosome and schollen of metatexite,) were dated by U-Pb isotopes (LA-MC-ICPMS). Zircons occur in all samples as long prismatic to slightly elongated crystals with straight or rounded edges that are 50-200 μm long and 25-70 μm thick. In cathodoluminescence images, the grains display oscillatory or sector-zoned, dark or bright cores surrounded by rims up to 30 μm thick, often truncated by homogeneous or oscillatory dark rims. In all samples, the U-Pb zircon age distributions show that the dominant populations make well-defined clusters. In three samples the analyses on homogeneous zircon rims give a concordant age peak at 389 Ma. These younger peaks record a metamorphic event (metamorphic cycle happened under amphibolite to granulite facies at mean P-T condition) and the evolution to the nappe system that affected the entire LAMC during Middle Devonian. Analysis of zircons core in all samples are concordant with a statistically strong constrained age range between 1000 and 1370 Ma (concord age peaks 1119-1082-1071-1065-1031 Ma). The Late Mesoproterozoic ages (1100-1000 Ma) are interpreted as inheritance ages of their sedimentary protolith. The absence of typical zircon age of Gondwana landmasses (650-600 Ma; Late Neoproterozoic Basiliano-Pan-African orogenic ages), makes impossible a Gondwana provenance for the detritus that formed the LAMC protoliths. Consequently, the origin of the detritus that constructed the metamorphic sequence is consistent with a Laurentian affinity source area linked with the southern Appalachian Grenvillian and the Granite-Rhyolite Igneous Province. Also the lack of paleo-Proterozoic ages demonstrates that the LAMC is disconnected from the Arequipa-Antofalla terrane and the MARA block. Based on the prevalence of Mesoproterozoic (Grenvillian) detrital ages and the analogous petrological (P-T-t) and structural style features, we consider that the LAMC shows similarities in the geological evolution to the exotic Cuyania composite terrane transferred from Laurentia to the western Gondwana.The LAMC study has key implications for understating the evolution of the Paleozoic basement between the Famatinian arc and the Andes cordillera. A narrow area separate the Mesoproterozoic blocks from the Ordovician arc exposed in the Sierra de Las Planchadas. The region between the Chaschuil River and Los Aparejos valleys may represent a geodynamic boundary zone among the autochthonous Famatinian arc and the allochthonous Cuyania terrane, and considered as the northward continuation of the Valle Fértil lineament. In line with this interpretation, the northern boundary of the allochthonous terrane would extend beyond 28° South latitude