Dynamic tectonic evolution of western Gondwana margin between 560 and 460 Ma: evidences from the U-Pb and Lu-Hf data on turbidites of NW Argentina

NATALIA HAUSER; PAMELA APARICIO GONZÁLEZ; MAXIMO MATTEINI; OMARINI RICARDO; MARÍA CRISTINA MOYA; MARCIO MARTINS PIMENTEL

Buzios

Congreso; Gondwana 14, Buzios Brasil; 2011

CombinedLA-MC-ICPMS U-Pb isotopic study of zircon from metasediments (Puncoviscana Fm.)and associated igneous rocks from four key areas of the Neoproterozoic to lowerPalaeozoic basement of Eastern Cordillera, NW Argentina, allowed us to unravelthe tectonic history of the western margin of Gondwana between LateNeoproterozoic and Early Palaeozoic times. In theEastern Cordillera, the data suggest that in the Tastil and Sierra de Mojotoro areas,two folded turbidite sequences show maximum depositional ages (MxDA) of 562 Maand 543 Ma respectively. The intrusion of the calc-alkaline Tastil granodiorite(534 Ma) and the Mojotoro porphyry granite (533 Ma) constrained the minimumdepositional age (MnDA). These turbidites must be considered to be the realPuncoviscana Fm. Taking into account the short time for deposition, folding andintrusion as well as the main provenance zircon ages (the Late Brasiliano/EarlyPampean) it is likely that these sequences deposited in a syn-orogenic setting.A collision of a small para- autochthonous block produced the folding of thesequence, and the intrusion of calc-alkaline granites linked with the Tilcarian/PampeanOrogeny.In theSierra de Mojotoro area younger turbidites with MxDA of 534 Ma and 517 Ma wereidentified (Alto de la Sierraand Los Guachos Fm., Aparicio González et al., 2010). These turbidites areyounger than the Puncoviscana Fm. s.sand linked with the Post Tilcarian/Pampean Orogeny. In theEastern Cordillera-Puna boundary, in the El Niño Muerto Hill the MxDA of 496 Mafor the turbidite is constrained by the intrusion of calc-alkaline metadacitesat 483 Ma belonging to the Famatinian arc. The turbidite sequence was depositedduring Late Cambrian to Tremadoc in a N-S elongated narrow basin locatedbetween the Pampean belt and the Arequipa-Antofalla terrain. The collision ofthe para-autochthonous Arequipa-Antofalla terrain with the western margin ofGondwana, after 480 Ma, produced the closure of this basin. In the Calchaquíesvalleys, the metaturbidites of the Río Blanco Valley have a MxDA of ca. 463 Ma.Their association with contemporaneous E-MORB/OIB type basalts and thedominantly Famatinian provenance of zircon population, suggest that thesesediments are post-Caradoc, deposited in an extensional basin to the east ofthe Famatinian arc. The U-Pband Hf isotopic data for zircon grains from the Tastil rocks, El Niño MuertoHill and Río Blanco Valley areas, permitted to characterize three major periodsof magmatism in the sources areas of the detrital zircon grains: i)  Paleoproterozoic (2.0 Ga) event representing reworkingof Archean crust; ii) aMesoproterozoic/Neoproterozoic event (0.95 to 1.2 Ga) with a juvenilecomponent, and iii) a LateNeoproterozoic to Early Paleozoic (0.75 to 0.46 Ga) magmatism, indicatingreworking of Mesoproterozoic to Paleoproterozoic crust. Our datasuggest that the western margin of Gondwana underwent a dynamic tectonicevolution from Neoproterozoic to Early Paleozoic times, with the accretion oftwo continental blocks. This margin was controlled by subduction processes,rapid deposition of syn-orogenic turbiditic sequences, rapid denudation andsynchronous magmatism.