The mafic-ultramafic belt of the Argentine Precordillera: A geological synthesis

摘要

In central-western Argentina, a mafic-ultramafic belt occurs throughout the western margin of the Precordillera. This belt is interpreted as the suture zone between the Cuyania terrane and the Chilenia terrane, both accreted onto the Gondwana margin during the Early Paleozoic. The belt comprises rocks from different setting and age and can be divided into a northern (28-32 degrees S, present coordinates) and a southern sector (south of 32 degrees S). The northern sector includes MORB (Mid-Ocean-Ridge Basalts)-like metabasalt, metagabbro and minor metadiorite and wehrlite associated to marine sequences. The southern sector comprises serpentinite, ultramafic cumulate, mafic granulite and gneiss not exposed in the north as well as metagabbro, metabasalt and minor metahyaloclastite spatially associated to marine successions. Due to their geological similarities, the southern sector can be correlated with the Argentine Frontal Cordillera mafic-ultramafic belt exposed southwestwards. In the southern sector, the evolution of the belt began during the Late Neoproterozoic, with the generation of continental margin sequences related to MORB magmatism. This extensional regime would be related to the rifting of a continental block, that includes the Cuyania and Chilenia terranes, from southern Laurentia. During the Middle Ordovician-Early Devonian, a second extensional regime occurred along the entire belt, where passive margin successions along with E-MORB magmatism developed on a thinned continental crust. A pre-Devonian deformation phase D1, possibly related to the Ocloyic orogeny, only affected the southern sector of the belt. Whereas a deformation phase D2 is registered throughout the belt and it is related to the collision of the Chilenia terrane against West Gondwana in the Middle-Late Devonian.