New evidence concerning the Plio-Pleistocene landscape evolution of southern Santa Cruz region

The Late Pliocene mafic lavas from the Camusú Aike volcanic field (∼50°S, Argentina): Evidence for geochemical variability in slab window magmatism

“…Recently, Mejia et al (2004) published a paleomagnetic study of the Plio-Pleistocene mafic lavas of southern Patagonia in which they report two 40 Ar-39 Ar dates of lavas from the CAVF of 2.98G0.03 Ma and 3.02G0.04 Ma, in close agreement with our data. The 40 Ar-39 Ar age determinations from our work and Mejia et al (2004) contrast with a single 40 Ar-39 Ar age of 0.67G0.56 Ma quoted by Strelin et al (1999) for a lava flow from the central portion of the NW-SE-elongated lava field. Unfortunately, the possible cause of the mismatch between these data cannot be evaluated because of the lack of the analytical details for the latter 40 Ar-39 Ar determination.…”

“…These volcanic rocks lie atop the Meseta Pampa Alta, a widespread high plain located south of the upper Río Santa Cruz valley that slopes to the southeast with a w1% gradient. According to Strelin et al (1999), this meseta is a proglacial plain emerging east of the moraine deposits of the Pampa Alta glaciation, 10 km west of the CAVF. Within the study area, the Meseta Pampa Alta attains elevations of 700-420 m above sea level (a.s.l.)…”

Fossil localities of the Santa Cruz Formation (Early Miocene, Patagonia, Argentina) prospected by Carlos Ameghino in 1887 revisited and the location of the Notohippidian

“…The EeW oriented valley contrasts with the smooth topography of the plateaus (mesetas) that surround it, especially to the south (Meseta Pampa Alta, Strelin et al, 1999;and Pampa de Monte León, Panza, 2002). The oldest unit recognized is the Early Miocene marine Monte León Formation , that is restricted to the east and to the topographically lower portion of the Río Santa Cruz valley.…”

“…The estimated thickness of SCF in the valley is 250 m, although our observations are confined to the well exposed first 100 basal meters from the base. At its western end, the valley broadens and becomes a colossal glacial trough with Lago Argentino at its apex (Strelin et al, 1999). There, older units crop out due the Neogene Andean uplift.…”

“…Throughout its course on the river, the SCF is covered unconformably by late Miocene-Pleistocene sedimentary deposits of fluvial and glacial origin and by Plio-Pleistocene basaltic lava flows (Strelin et al, 1999;Panza, 2002). In the western portion of the valley, the late Cenozoic sedimentary cover is composed of a complex assemblage of glacial, fluvial and lacustrine sediments (Strelin et al, 1999). To the east the cover consists of well-sorted fluvial gravels of the terrace systems associated to the valley formation history (Panza, 2002).…”