Re–Os isotope constraints on subcontinental lithospheric mantle evolution of southern South America

Petrology and geochemistry of the back-arc lithospheric mantle beneath eastern Payunia (La Pampa, Argentina): Evidence from Agua Poca peridotite xenoliths

“…Schilling et al (2008) demonstrated the ages of the Re-Os model and provided estimations of minimum depletion ages for four samples of Agua Poca xenoliths (AP15, AP78-Z2, AP80, and AP91B). Of these four samples, AP15, AP80, and AP91B are the same samples as studied here and are classified as Groups 1 and 2 for clinopyroxene.…”

“…Moreover, AP80 was determined to have a high 143 Nd/ 144 Nd ratio and to be a Proterozoic Nd-isotope model (Conceição et al, 2005). Schilling et al (2008) pointed out the occurrence of a negative correlation between forsterite olivine contents with 187 Os/ 188 Os ratios, as well as a remarkably good correlation for the Al 2 O 3 versus 187 Os/ 188 Os diagram in the Agua Poca mantle xenoliths, which led to a proposed depletion age of 2.14 Ga. This age approaches the estimated model age of 2 Ga, which is interpreted as the formation of the subcontinental mantle-continental crust assemblage in the region of Central Chile (33°S) by Montecinos et al (2008), based on the Hf isotope analyzes on zircons.…”

“…However, whole rock composition does not usually provide full constraints in the case of multi-stage petrologic evolution, particularly when a later metasomatic event caused petrochemical zoning within the samples. Moreover, the whole rock composition of mantle xenoliths can be affected by an interaction with melts and fluids related to the volcanic event that carried them to the surface (e.g., Dantas et al, 2009;Kempton et al, 1999;Schilling et al, 2008;Stern et al, 1999). Consequently, such events can hinder the unraveling of the petrochemical processes on the pristine subcontinental lithospheric mantle.…”

Ultramafic rocks in the North Patagonian Andes: is their emplacement associated with the Neogene tectonics of the Liquiñe–Ofqui Fault Zone?

“…Another significant occurrence of ultramafic rocks is in the Neogene Taitao ophiolite immediately south of the Chile triple junction, considered to have been emplaced by obduction related to collision of the Chile Ridge with the continental margin (Forsythe and Nelson, 1985;Anma et al, 2006). Ultramafic rock mantle xenoliths are known from Neogene volcanic rocks in the Patagonian Andes and in extra-Andean Patagonia (Schilling et al, 2008), giving an indication of the present composition of the mantle below Patagonia.…”

South Georgia and Gondwana's Pacific Margin: Lost in translation?

“…The basement of the Falkland Plateau, in contrast, consists of older, Proterozoic, metasediments intruded by granitoids that may be as young as Cambrian, exposed at Cape Meredith on the Falkland Islands, possibly also penetrated in DSDP hole 330 on Maurice Ewing Bank, and continuing west beneath the Deseado Massif to be referred to collectively as the Deseado Terrane (Pankhurst et al, 2006;Schilling et al, 2008). On the reconstruction, the basement metasediments of Tierra del Fuego, the North Scotia Ridge and South Georgia are depicted as a Paleozoic-aged autochthonous, probably accretionary, southern rim to the Deseado Terrane (Fig.…”