Revealing the continental margin of Gondwana: the Ordovician arc of the Cordón de Lila (northern Chile)

Abstract

The tectonic evolution of the proto-Andean

Reinterpretation of the Ordovician rotations in NW Argentina and Northern Chile: a consequence of the Precordillera collision?

“…A crustal discontinuity between the Western and Eastern Puna has been proposed by several authors (Ramos and Coira 2008), evidenced either as interpreted ophiolite remnants (Coira et al 1982;Allmendinger et al 1983;Blasco et al 1996) or as a major strike-slip boundary (Coira et al 1999), being an extensional retroarc setting (Astini 2008) the more accepted alternative nowadays. Although there are outcrops of peridotites, basaltic flows and pillow lavas of the Salar de Pocitos and Calalaste Ranges interpreted inicially as the opening of an oceanic basin (Allmendinger et al 1983;Ramos 1988;Blasco et al 1996), new geochemical results indicate that they were generated in an extensional arcbackarc setting (Balhburg et al 1987;Balhburg and Furlong 1996;Zimmermann et al 1999Zimmermann et al , 2009Balhburg and Zimmerman 1999) emplaced in a thin crust. Another inconsistency is that the sence of movement (taking into account the paleomagnetic results of Forsythe et al 1993) makes the basin wider and deeper to the south while the sedimentation is younger to the north but the paleocurrents are south-north directed (Niemeyer 1989;Balhburg 1990aBalhburg , b, 1991.…”

Neoproterozoic to Lower Palaeozoic successions of the Tandilia System in Argentina: implication for the palaeotectonic framework of southwest Gondwana

“…In typical continental arc environments, such a trend is visible in volcaniclastic sedimentary rock (Floyd and Leveridge 1987) and observed in an Ordovician arc environment in northwest Argentina (Zimmermann and Bahlburg 2003;Zimmermann et al 2009a). Tectonic processes in foreland basins or retro-arc basin could exhume basement material, including mafic sources, as observed in Ordovician arc terranes and today in northwest Argentina, with a trend of decreasing geochemical arc signals away from the subduction zone (Bahlburg 1998;Zimmermann and Bahlburg 2003;Zimmermann et al 2009a). A distal position to the proposed active continental margin to the west and south of the Río de la Plata craton (Cawood 2005;Chew et al 2008) could explain the typical UCC (after McLennan et al 2006) and enriched Nb (*20 ppm) and Ti ([1%) values in some samples.…”

“…Absolute concentrations of the compatible elements Ti, Nb and Ta are often used to determine an arc derivation in magmatic rocks (Hofmann 1988(Hofmann , 1997. In typical continental arc environments, such a trend is visible in volcaniclastic sedimentary rock (Floyd and Leveridge 1987) and observed in an Ordovician arc environment in northwest Argentina (Zimmermann and Bahlburg 2003;Zimmermann et al 2009a). Tectonic processes in foreland basins or retro-arc basin could exhume basement material, including mafic sources, as observed in Ordovician arc terranes and today in northwest Argentina, with a trend of decreasing geochemical arc signals away from the subduction zone (Bahlburg 1998;Zimmermann and Bahlburg 2003;Zimmermann et al 2009a).…”

“…The detritus is therefore composed of felsic and less fractionated source(s). Selected trace elements and their ratios can be used to test a possible arc signature for most of the samples of the Cerro Negro Formation (after Floyd and Leveridge 1987;McLennan et al 1990McLennan et al , 1993Zimmermann et al 2009a). In Table 2, geochemical values for those samples indicating an arc derivation for detrital mixes are shadowed in grey.…”

Bandas de cataclastitas en el Plutón Tambillo: Manifestaciones de la orogénesis oclóyica en el cordón de Lila, norte de Chile

“…1). La unidad estratificada más antigua corresponde a basaltos y brechas volcánicas dacíticas con intercalaciones de turbiditas, del TremadocianoArenigiano medio y se incluye dentro del Complejo ígneo-sedimentario del Cordón de Lila (CISL; Niemeyer, 1989;Damm et al, 1990;Zimmermann et al, 2010). El CISL se observa intruido, a su vez, por varios cuerpos plutónicos de edad ordovícica: Monzogranito Tucúcaro, Sienita Tilopozo, Granodiorita Pingo-Pingo y Monzogranito Tambillo (Mpodozis et al, 1983).…”