Evidence for Middle-Late Ordovician subduction and a lower plate setting of the Cuyania Terrane during its accretion to the proto-Andean margin of Gondwana.

VAN STAAL, C.R.,; VUJOVICH GRACIELA IRENE; CURRIE, K.L.,; NAIPAUER MAXIMILIANO

Mar del Plata

Congreso; International Geological Congress on the Southern Hemisphere; 2010

Instituto Nazionale di Oceanografia e di Geofisica Sperimental

Lithostratigraphic and structural analysis of the Caucete Group and the immediately structurally overlying Pie de Palo Complex in the Sierra de Pie de Palo, Argentina, indicate a basement-cover relationship, which we suggest was established during late Early Cambrian (~ 515 Ma) final rifting of Cuyania from Laurentia. The main deformation (Dm) and associated metamorphism indicate conditions typical of the blueschist to high-pressure amphibolite facies conditions, which leaves little doubt that a subduction zone existed between Cuyania and the proto-Andean margin of Gondwana. This provides strong support for the Laurentia-derived microcontinent model of earlier workers. The main structures involve two phases (F1 and F2) of fold nappe formation and associated thrusting; the latter forming by shearing-out of the lower limbs of the inclined to recumbent folds. The style of deformation indicates that strain localization decreased during peak-T metamorphism and imposes a penetrative non-coaxial flow on the rocks involved in the A-subduction of the Cuyania`s leading edge beneath proto-Andean margin. We relate this to widening of the subduction channel after entrance of Cuyania into the trench (star of A-subduction and collision) associated with thermal weakening becoming more prevalent than fabric-related softening.