Basement evolution of the Sierra de la Ventana Fold Belt: new evidence for Cambrian continental rifting along the southern margin of Gondwana

Abstract

U-Pb sensitive high-resolution ion microprobe data together with geochemical and Nd isotope analyses obtained in the basement complex of the Sierra de la Ventana Fold Belt indicate that the Early Palaeozoic passive margin history of the basin followed Cambrian magmatism related to rifting in a 600 Ma Neoproterozoic crust. The Cambrian episode started with intrusion of 531 AE 4 and 524 AE 5 Ma A-and I-type granites derived from a dehydrated infracrustal source (ENd 530 À3.1 to À5.9), and culminated with eruption of high-Zr peralkaline spherulitic rhyolites derived from an undepleted lithospheric mantle (509 AE 5 Ma; ENd 509 þ0.5 to þ1.0). These rift-related magmatic rocks were covered by shelf sediments deposited along a oncecontinuous passive margin, encompassing the Sierra de la Ventana Fold Belt, the Cape Fold Belt, the Falkland/Malvinas microplate and the Ellsworth Mountains block in Antarctica. The Cambrian rifting event defined the outline shape of the southern part of Gondwana, and can be regarded as the initiation of the supercontinent stage, which lasted until Jurassic break-up. The conjugate continental fragments separated from Gondwana during the Cambrian rifting could be the source for microcontinents with c. 1000 Ma basement rocks that collided with the proto-Andean margin during Ordovician-Silurian times.

The Rio de la Plata craton and the adjoining Pan-African/brasiliano terranes: Their origins and incorporation into south-west Gondwana

“…The basement rocks of the Sierra de la Ventana, which is the southern boundary of the Rio de la Plata craton, include Dom Feliciano age (570- 610 Ma) crustal granites, 530-520 Ma cale-alkaline and A-type granites and 510 Ma peralkaline rhyolites (Rapela et al, 2003;Tohver et al, 2011). The granitic suite of this basement has been correlated with the Cape Granite Suite in southern Africa (Rapela et al, 2003).…”

“…Cambrian rift, which evolved into a sedimentary basin active throughout the Palaeozoic until its inversion in the Permian during the Gondwanan orogeny (Rapela et al, 2003).…”

The Gondwana connections of northern Patagonia

“…The closest comparisons for the Tardugno Granodiorite are with the Pampean granites of the Sierras Pampeanas (pre-deformation granite 537 ± 4 Ma; postdeformational granite 530 ± 4 Ma), the basement of the Sierra de la Ventana (524-531 Ma; Rapela et al 2003) and the basement granitoids beneath the Magallanes basin of southernmost Patagonia (529 ± 8, 521 ± 4, 538 ± 6, 523 ± 7, 522 ± 4, 521 ± 6 Ma; Söllner et al 2000;Pankhurst et al 2003;Hervé et al 2010). The latter in turn may be correlated with Cambrian granites in the Saldania belt of South Africa (summary by Chemale et al 2011), where early S-type granites (550-527 Ma) are followed by I-type granites (540-530 Ma) and then post-tectonic A-type granites (530-500 Ma).…”

“…Provisionally, this could be seen as resulting from readjustment between different crustal domains during compressive deformation contemporaneous with crustal melting. Local response to deformation may also be enhanced by thinned crust in northern Patagonia inherited from the Late Cambrian rifting episode recorded in the Sierra de la Ventana basement (see below and Rapela et al 2003).…”

The Río de la Plata craton and the assembly of SW Gondwana

“…2 and 3a). Farther south, the basement of the Palaeozoic Sierra de la Ventana Fold Belt is composed of 607±5 Ma Brasiliano collisional granites intruded by 531-524 Ma A-type granites, and 509±5 Ma peralkaline rhyolites (U -Pb SHRIMP, Rapela et al, 2003). This indicates that the RPC does not continue below the Sierra de la Ventana fold belt, and its southern limit probably swings to the WNW, sub-parallel to the strike of the Tandilia belt (Fig.…”