Early Proterozoic Calc-Alkaline and Middle Proterozoic Tholeiitic Dyke Swarms from Central–Eastern Argentina: Petrology, Geochemistry, Sr–Nd Isotopes and Tectonic Implications

Abstract

Nb spikes. They have variable e t (Nd) values (−0•5 to 12•1), regions) is characterized by Early Proterozoic (2•0 Ga) calcwhich mainly reflect derivation from a depleted source mantle. alkaline and Middle Proterozoic (1•6 Ga) tholeiitic dyke swarms High-TiO 2 tholeiitic dykes have more enriched IE-PM patterns intruding the crystalline basement involved in the Transamazonian and are characterized by e t (Nd) values (−1•4 to −7•5 ) typical Orogeny (2•2-1•9 Ga). The calc-alkaline dykes have andesitic of an enriched source mantle. Chemical and isotopic data and and rhyolitic compositions and trend east-west, whereas the melting modelling indicate that both calc-alkaline and tholeiitic tholeiitic dykes mainly trend N30°W and are represented by dykes originated by different melting degrees of a heterogeneous basalts with low (0•9-1•7 wt %) and high TiO 2 (up to source mantle, the variable IE enrichment of which may have 3•7 wt %). The calc-alkaline dykes have primitive mantle occurred in Late Archaean to Early Proterozoic times. The emplacement of the calc-alkaline dykes is associated with the (PM)-normalized trace element patterns enriched inRb, Ba, K, La, Ce and Nd, and significant negative Nb and Ti transtensional stage of the Transamazonian Orogeny, whereas the tholeiitic dykes reflect extensional tectonics succeeding the anomalies. These dykes are characterized by e t (Nd) values of −3 to −4, similar to those of the EMI mantle component. Transamazonian event. The calc-alkaline and tholeiitic dykes are similar in emplacement age and characteristics to meta-Low-TiO 2 tholeiitic dykes have low incompatible-element (IE) contents and PM-IE patterns with slightly positive or negative morphosed granites and volcanic rocks outcropping within the

The Río de la Plata Craton: a review of units, boundaries, ages and isotopic signature

“…Sr and e Nd (Mazzucchelli et al 1995) Mantle source IE enriched mantle source IE depleted mantle source (Iacumin et al 2001) EM1 type, dominated by e Nd variation (Mazzucchelli et al 1995) EM2 type, dominated by e Sr variation (Mazzucchelli et al 19952) OIB-type mantle source (Mazzucchelli et al 1995) Tectonic setting Post-collisional extension Anorogenic extension Mataojo Granitic Complex in the Sarandí del Yí Shear Zone at 584 ± 13 Ma (Oyhantçabal et al 2007a) also confirms a pre-Ediacaran age of accretion. Bossi and Cingolani (2009) suggested that the Sarandí del Yí Shear Zone records dextral shearing at 1,200-1,250 Ma, based on a K-Ar age on muscovite from a pegmatite in a thrust plane.…”

“…In the Nico Pérez Terrane of Uruguay, a dike swarm of similar age has not been recognized yet, but numerous gabbro intrusions, like Mahoma, Rospide and Carreta Quemada, could represent this event of mafic post-orogenic magmatism. Iacumin et al (2001) underlined the geochemical similarities between the tholeiitic Florida dike swarm in the Piedra Alta Terrane (1.79 Ga) and the tholeiitic dikes of Tandilia (*1.59 Ga, Teixeira et al 2002; more precise age determinations are still lacking). Both dike swarms are probably coeval and may correspond to anorogenic extension roughly 200 Ma after the Transamazonian orogeny in the Río de la Plata Carton (Teixeira et al 2002).…”

“…Sr and e Nd (Iacumin et al 2001) Positive e Sr and negative e Nd (Mazzucchelli et al 1995) Positive e Sr and negative e Nd (Mazzucchelli et al 1995) Slightly positive e…”

Geocronologia Rb-Sr e Características Geoquímicas dos Diques Máficos da Região de Nova Lacerda e Conquista D’Oeste (MT), Porção Sudoeste do Craton Amazônico

“…Os percentuais dos erros relativos aos elementos traços são considerados: razoá vel com 30%, bom com 20% e ótimo com 10% (e.g., Iacumin et al, 2001;Pinese, 1997). Os coefi cientes de partição sólido/líquido foram extraídos de Iacumin et al (2001) e Bossi et al (1993.…”

“…Na Plataforma Sul-Americana tais pesquisas, principalmente as voltadas para o estudo de diques e intrusivas básicas Meso e Paleoproterozoicos têm propiciado a elaboração de vários trabalhos nas diversas regiões cratônicas existentes, ou seja, no Craton do São Francisco (Bellieni et al, 1991(Bellieni et al, , 1998Bastos Leal et al, 1994;Pinese, 1997;Moraes Brito et al, 1989;Mazzucchelli et al, 2001;D'Agrella et al, 2004;Corrêa da Costa et al, 2006); no Bloco Arqueano Crixás -Goiás (Corrêa da Costa e Girardi, 2004Corrêa da Costa et al, 2006a); no Craton do Rio de La Plata (Bossi et al, 1993;Mazzucchelli et al, 1995;Girardi et al, 1996;Teixeira et al, 1999) e no Craton Amazônico (Rivalenti et al, 1998;Menezes Leal et al, 2006;Teixeira et al, 2006;Girardi et al, 2008). Os trabalhos citados constituem exemplos de estudos de enxames individuais, porém trabalhos tentando estudar comparativamente tais intrusões, visando principalmente comparar fontes mantélicas e implicações tectônicas também têm sido realizados (Iacumin et al, 2001(Iacumin et al, , 2003Girardi, 2006). O enxame de diques de Nova Lacerda e Conquista D'Oeste -MT foram objetos de alguns poucos trabalhos em simpósios e congressos (e.g., Corrêa da Ruiz et al, 2005), que constituem informações pioneiras sobre esses corpos na região SW do Craton Amazônico no Estado do Mato Grosso.…”