Abstract
New isotopic studies on mantle xenoliths from Santa Cruz Province, southern Patagonia, Argentina, reveal that at least three discrete subcontinental lithospheric mantle (SCLM) domains—the Deseado Massif, Tres Lagos, and Pali Aike—form the southernmost part of South America. Re-Os systematics yield early Paleoproterozoic (up to 2.5 Ga) SCLM formation ages (rhenium depletion ages, TRD) for Pali Aike spinel peridotites, while samples from the Deseado Massif and Tres Lagos indicate a younger SCLM origin with Neoproterozoic to Mesoproterozoic (0.9–1.3 Ga) and Mesoproterozoic to late Paleoproterozoic (1.3–1.9 Ga) TRD ages, respectively. Hf-Sr-Nd isotopic compositions indicate metasomatic overprinting of the majority of the samples, which, however, has not affected the Os isotopic system. Based on similar formation ages, the geological evolution of the Deseado Massif is most likely connected to the evolution of the Namaqua-Natal belt of South Africa. TRD ages from SCLM domains underneath Tres Lagos and Pali Aike indicate a common origin with crustal sections from Shackleton Range, Antarctica, positioning the southern tip of South America closer to west Antarctica in the reconstructed Rodinia supercontinent than previously assumed.
Highlights
The origin of the Patagonian continental terrane is highly debated
The formation of ancient continental terranes is related to the formation of their underlying subcontinental lithospheric mantle (SCLM) roots, as continental crust is formed by the extraction of melt of a mantle section that has experienced variable degrees of partial melting
Bulk-rock major element analyses show that samples from Pali Aike (POKA, SA, El Ruido (ELRU)) and Tres Lagos have mean Al2O3 contents and Mg# [Mg/(Mg + Fetot)] of 1.46 wt% and 0.91, respectively, and are generally more depleted than mantle xenoliths found in the Deseado Massif with mean Al2O3 contents and Mg# of 2.08 wt% and 0.90, respectively
Summary
The origin of the Patagonian continental terrane is highly debated. Whether Patagonia is a uniform part of the southernmost South American continental plate or an assemblage of fragments with different mantle roots is a matter of controversy (Stern et al, 1999; Pankhurst et al, 2006; Ramos, 2008; Schilling et al, 2008; Wang et al, 2008). The formation of ancient continental terranes is related to the formation of their underlying subcontinental lithospheric mantle (SCLM) roots, as continental crust is formed by the extraction of melt of a mantle section that has experienced variable degrees of partial melting. This residual depleted lithospheric mantle coevally forms the root of the overlying continental crust (e.g., Griffin et al, 1999a, and references therein; Pearson, 1999). Hf-Nd-Sr isotopic data obtained from leached clinopyroxene (cpx) separates of those samples analyzed for Os isotopic composition are presented to provide better insight into the origin and complex history of South Patagonia
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