Isotope (Sr, C) and U–Pb SHRIMP zircon geochronology of marble-bearing sedimentary series in the Eastern Sierras Pampeanas, Argentina. Constraining the SW Gondwana margin in Ediacaran to early Cambrian times

Abstract

Isotope (Sr, C) and U-Pb SHRIMP zircon geochronology of marble-1 bearing sedimentary series in the Eastern Sierras Pampeanas, Argentina. with Sr-isotope composition ca. 0.7075 and 0.7085 that are considered stratigraphically significant. 23The first is inferred early Ediacaran, the second late Ediacaran to early Cambrian. The Sierras de 55The Sr-isotope composition of marbles that remain unmodified after sedimentation has been 56 increasingly used for chemical stratigraphy since the seminal work of Burke et al. (1982). These (and S and O-isotope systematics), to constrain the age 63 of paleoclimatic changes (e.g., Derry et al., 1989Derry et al., , 1992 Jacobsen and Kauffman, 1999; Kuznetsov, 64 1998; Kuznetsov et al., 2013; Montañez et al., 2000; Halverson et al., 2007 Halverson et al., , 2010. 65 We focus here on the Sr, C and O-isotope composition of marbles from the Sierras de , 1998; Vujovich et al., 2004; Casquet et al., 2004 Casquet et al., , 2008 Rapela et al., 2010) high-grade metamorphism from ~490 to 430 Ma (Sims et al., 1998;Pankhurst et al., 1998; Rapela 90 et al., 1998a Rapela 90 et al., , 2007 Dahlquist et al., 2008 (Gordillo, 1984; Gordillo and Bonalumi, 1987; Baldo, 1992; Guereschi and 113 Martino, 2002, 2003). Plutonism, deformation and metamorphism took place in the early Cambrian Rapela 114Pampean orogeny (Rapela et al., 1998b). Metamorphism reached medium to high temperature (600-115 800 °C) and intermediate pressure (4-8 kbar) (Gordillo and Lencinas 1979; Rapela et al., 1998b Rapela et al., , 116 2002 Steenken et al., 2010). Marbles are found as lenticular bodies due to stretching, but they can 117 be followed over long distances with thicknesses from a few centimetres to hundreds of metres. Argentina were recognized in the Sierras de Córdoba (Sierra Grande and in northwestern Sierra 122Chica and Sierra Norte) (Fig. 2) on the basis of detrital zircon ages (Escayola et al., 2007; Rapela et 123 al., 2007 Rapela et 123 al., , 2016. The term Puncoviscana Formation in the literature embraces sedimentary rocks 124 probably older, coeval and younger than the Pampean magmatic arc, with the only constraint that 125 they are older than the unconformably overlying middle to late Cambrian Meson Group (e.g., 126Omarini et al., 1999; Adams et al., 2008 Adams et al., , 2011 Escayola et al., 2011, and references therein). We 127 restrict the term here to that part of the siliciclastic succession that is of relevance to the early 128 history of the Puncoviscana sedimentary basin (e.g., Casquet et al., 2012). These rocks host the 129 magmatic arc in the south (540-530 Ma) and can be coeval with syn-orogenic volcanism (ca. 530 130 Ma) in the north (Escayola et al., 2011). 131The detrital zircon age pattern in the Eastern Sierras Pampeanas is almost bimodal with 132 characteristic peaks at ca. 1000 and 600 Ma. The zircon was interpreted as derived from West 133Gondwana sources in the east (Natal-Namaqua belt and probably the Brasiliano-Panafrican orogen 134 and the...

Review of the Cambrian Pampean orogeny of Argentina; a displaced orogen formerly attached to the Saldania Belt of South Africa?

“…The ocean correlates with the southern extension (present coordinates) of the Clymene Ocean that existed between Amazonia and other Gondwanan blocks (Trindade et al, 2006). Continental collision brought to an end the amalgamation of Gondwana (Rapela et al, 2016;Murra et al, 2016).…”

“…This correlation implies that all belong to an originally extensive sedimentary cover to Mesoproterozoic (Grenvillian s.l.) basement (Murra et al, 2016). The source of these metasedimentary series has been ascribed to the Mesoproterozoic (and Paleoproterozoic) basement of the Western Sierras Pampeanas and further west (Laurentia?)…”

“…This constrained its timing to Early-to-Middle Cambrian (e.g., Aceñolaza and Toselli, 1981). Further work, including precise U-Pb geochronology (for a review see Baldo et al, 2014), has confirmed that the orogeny can also be recognized in the easternmost Sierras Pampeanas, where there are metasedimentary rocks equivalent to the Puncoviscana Formation and regional metamorphism and magmatism has been dated between ca 545 and 520 Ma, i.e., Early Cambrian (Rapela et al, 1998;Otamendi et al, 2004;Schwartz and Gromet, 2004;Escayola et al, 2007;Ianizzotto et al, 2013;Murra et al, 2016). Cambrian magmatism has also been reported from Patagonia (Hervé et al, 2010;Pankhurst et al 2014).…”

Constraints on the depositional age and tectonometamorphic evolution of marbles from the Biharia Nappe System (Apuseni Mountains, Romania)

“…The curve represents the best-fit on measurements of 86 Sr/ 87 Sr in samples dated by biostratigraphy, magnetostratigraphy and astrochronology enabling the user to do a rapid conversion of 86 Sr/ 87 Sr to age and vice versa (McArthur et al 2001). The reliability of Sr-isotope stratigraphy depends on the potential of the tested rocks to preserve depositional isotopic values, but even marbles that have experienced multiphase metamorphism (up to amphibolite-facies conditions) and deformation may retain their depositional (Frank et al 1990;Melezhik 2001Melezhik , 2013Satish-Kumar et al 2008;Murra et al 2011).…”

“…Additional data on the geochemical composition is shown in the Supplementary data (Table S2). Values lower than 0.010 for Mg/Ca and lower than 0.10 for Mn/Sr are indicative for a more or less primary isotopic signal with no or only insignificant alteration (Melezhik et al 2001;Murra et al 2011 Sr isotopic ratio of marine carbonate rocks situated within the continental crust can only increase to higher values due to post-depositional alteration during diagenesis and metamorphism (Brand &Veizer 1980. Consequently, the lowest 87 Sr/ 86 Sr ratios of MR26 (0.707677) and MR13 (0.707655)havebeenacceptedasthebestproxyfortheseawater composition (Table 5 and Fig.…”