THE GUARGUARAZ COMPLEX AND THE NEOPROTEROZOIC-CAMBRIAN

LÓPEZ DE AZAREVICH V., ESCAYOLA M., AZAREVICH M., PIMENTEL M., TASSINARI C.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier

Lugar: Amsterdam, The Netherlands; Año: 2009 vol. 28 p. 333 - 344

0895-9811

The Guarguaraz Complex, in western Argentina, comprises a metasedimentary assemblage,associated with mafic sills and ultramafic bodies intruded by basaltic dikes, which wereinterpreted as Ordovician dismembered ophiolites. Two kinds of dikes were recognized, agroup associated with the metasediments and other ophiolite-related. Both have N-MORBsignatures, with eNd between +3.5 and +8.2, indicating a depleted source, and Grenville modelages between 0.99-1.62 Ga. A whole-rock Sm-Nd isochron yielded an age of 655±76 Ma forthese mafic rocks, which is compatible with cianobacteria and acritarchae recognized in theclastic metasedimentary platform sequences, that indicate a Neoproterozoic (Vendian)-Cambrian age of deposition.The Guarguaraz metasedimentary – ophiolitic Complex represents, therefore, a remnant of anoceanic basin developed to the west of the Grenville-aged Cuyania terrane during theNeoproterozoic. The southernmost extension of these metasedimentary sequences in Cordóndel Portillo, might represent part of this platform and not fragments of the Chilenia terrane.An extensional event related to the fragmentation of Rodinia is represented by the mafic andultramafic rocks. The Devonian docking of Chilenia emplaced remnants of ocean floor andslices of the Cuyania terrane (Las Yaretas Gneisses), in tectonic contact with theNeoproterozoic metasediments, marking the Devonian western border of Gondwana.Keywords: Vendian- Cambrian platforms, mafic sills and dismembered ophiolites, N-MORBsignatures, Mesoproterozoic model ages, Cuyania and Chilenia terranes.