INVESTIGADORES
BECCHIO Raul Alberto
congresos y reuniones científicas
Título:
New U-Pb and Nd-Sm data for the Ordovician Magmatism on the Eastern Border of the Southern
Autor/es:
VIRAMONTE, J.M., VIRAMONTE, J.G., BECCHIO, RAÚL, PIMENTEL, M.M, AND ROBERTO MARTINO
Lugar:
La Plata
Reunión:
Congreso; XVI Congreso Geológico Argentino; 2005
Institución organizadora:
Asociación Geológica Argentina
Resumen:
During upper Cambrian to lower Ordovician times, in the southwestern margin of Gondwana, subduction of oceanic litosphere took place and tholeiitic mafic magmas were produced. These magmas probably accumulated at the base of the crust and also intruded it producing an important thermal anomaly which induced extensive crustal melting, indicated by the generation of migmatites and production of large volumes of felsic magmas (Becchio et al.,1999; Lucassen et al., 2000). This is suggested by the Sm-Nd isotopic characteristics of the mafic and felsic rocks investigated here, as well as by the U-Pb inheritance pattern observed for most granitoids. The mafic rocks present εNd (T) values ranging from + 2.3 to + 2.5, compatible with a depleted mantle source, whereas the granitoids, rhyolites and dacites have negative εNd (T) values (- 3.2 to 7.5), TDM values between 1.5 and 1.8 Ga and zircon inheritance ages between ca. 1.4 and 1.9 Ga, suggestive of extensive melting of Proterozoic continental crust.Between ca. 485 and 470 Ma silicic magmas derived from crustal anatexitic process and small volumes of mantle derived arc-tholeiite basaltic magmas reached the surface forming the volcanic layers interbedded with sediments and constituting the bimodal volcano-sedimentary unit. The rhyolites and dacites most probably represent extrusive counterparts of the large syenogranite and leucogranite bodies, emplaced at deeper levels in the crust. Upper Ordovician deformation is expressed along narrow, west-vergent ductile shear zones, thrusting deeper structural levels (plutonic unit and high grade metamorphic rocks) on top of shallow level rock units (volcano-sedimentary units).The data presented here and more in development will allow us to give a paleogeographic interpretation for this part of southwestern margin of Gondwana.
