Paleomagnetism and geochemistry from the Upper Cretaceous Tres Picos Prieto locality (43ºS), Patagonian Plateau Basalts

Abstract

ABSTRACT.A paleomagnetic study on nine samples from lavas from the Upper Cretaceous Tres Picos Prieto locality (43º50'S and 70º3'W), Patagonian Plateau Basaltic Province, revealed that a ca. 300 m thick pile of basalts accumulated during three discrete (i.e., temporally separated) volcanic episodes. The chemistry of these lavas shows characteristics compatible with both subduction and intraplate magmatism, with the former having a more important contribution in the younger lavas. Overall, we interpret these rocks to be transitional basalts generated in a supra-subduction environment. The Late Cretaceous to Cenozoic Patagonian Plateau Basaltic Province crops out from eastern Patagonia to the cordillera, and their genesis have been associated with different tectonic processes, even for spatially separated rocks of the same age. Considering that the development of the magmatic province is contemporary with the stage of westward drift of South America, we propose that magma generation and upwelling due to rapidly shearing asthenosphere inducing circulatory flow associated to asperities in the lithosphere-asthenosphere interface (shear-driven upwelling) can be evaluated as a further potential mechanism to account for many outcrops of these backarc to intraplate lavas.

Paleomagnetic evidence of earliest Paleocene deformation in Calama (∼22°S), northern Chile: Andean-type or ridge-collision tectonics?

“…4) would be incompatible with the hypothesis of the KeT event in northern Chile as related to an oceanic plateeboundary collision, prevailing thus the alternative of Andean-type noncollisional deformation in northern Chile, as discussed in the Introduction of the paper. Nevertheless, it is worth noting that the case of a southern interception of the oceanic ridge with the trench would allow the possibility of analyzing the origin of all the Late Cretaceous to Eocene plateau basalts in Patagonia (Ramos and Kay, 1992;Zaffarana et al, 2012) in terms of upward flow of sub-slab asthenosphere.…”

First geochemical and geochronological characterization of Late Cretaceous mesosilicic magmatism in Gastre, Northern Patagonia, and its tectonic relation to other coeval volcanic rocks in the region

“…1; Demant, Suárez & De La Cruz, 2007). The porphyritic rocks from Gastre bear a geochemical signature typical of subductionderived magmas, which is also found in the Tres Picos Prieto basalts (especially in the upper section; Zaffarana, Lagorio & Somoza, 2012) and in the volcanic rocks from the Coihaique Alto region (Demant, Suárez & De La Cruz, 2007). Therefore, it is put forth that the porphyritic rocks from Gastre could represent an eastward shift in the position of the magmatic arc at 42°S, as they were erupted c. 270 km away from the axis of the magmatic arc (represented by the outcrops of the Northern Patagonian Batholith; Fig.…”

“…In turn, the Late Cretaceous rocks from the Tres Picos Prieto Formation display distinctly lower ratios of La/Ta (18-27) and of Ta/Hf (0.14-0.22), as well as Ba/La < 20 and Ba/Nb < 40 (Fig. 5), showing a geochemical signature transitional between arc and intraplate magmas (Zaffarana, Lagorio & Somoza, 2012).…”

“…A regional analysis of the location and geochemical features of the Cretaceous to Palaeogene magmatic rocks of Northern (Sun & McDonough 1989) are shown for comparison, together with data from the Pilcaniyeu belt (Rapela et al 1988;Aragón et al 2011;Iannelli et al 2017), the Casa de Piedra Volcanic Complex averaged with the El Toro Formation (data from Demant, Suárez & De La Cruz, 2007), the Morro Negro basalts averaged with the Tres Picos Prieto Formation (data from De La Cruz, 2007 andZaffarana, Lagorio & and Lonco Trapial Formation (unpub. data).…”

“…1). (Rapela et al 1988;Aragón et al 2011;Iannelli et al 2017), Casa de Piedra Volcanic Complex (Demant, Suárez & De La Cruz, 2007), El Toro Formation (Demant, Suárez & De La Cruz, 2007), Morro Negro basalts (Demant, Suárez & De La Cruz, 2007), Tres Picos Prieto Formation (Zaffarana, Lagorio & Somoza, 2012) and Lonco Trapial Formation (unpub. data) are shown for comparison; the chosen rocks had SiO 2 content less than 70 %.…”