The San Blas Pluton: An example of Carboniferous plutonism in the Sierras Pampeanas, Argentina

Abstract

AbstraetNew geoehronologieal and geoehemieal data are reported for the San BIas Pluton (SBP), in the northwestern Sierra de Velaseo, Sierras Pampeanas, whieh intrudes Ordovieian granitoids developed during the Famatinian orogeny. A precise Carboniferous age of 340 ± 3 Ma is established by U-Pb dating of zireon using a sensitive high-resolution ion mieroprobe (SHRIMP). The SBP illustrates several petrologieal and geoehemieal eharaeteristies of previously reported Carboniferous granitoids in the Sierras Pampeanas. Their generation is eonsistent with a regional reheating of the erust at approximately 342 Ma, whieh resulted in the forn1ation of relatively large amounts of granitie melts that were emplaeed in higher erustallevels along master fractures (older master shear zones ofLower Paleozoie age). The SBP can be ehemieally defined as a typieal A-type granitoid related to posteollisonal or postorogenie magmatism. Its high REE eontent and extraordinarily high U and Th eoneentrations may have eeonomie signifieanee. Many previously published Devonian and Carboniferous K-Ar dates are reset Ordovieian ages, but the existenee of other Carboniferous bodies in the Sierra de Velaseo eannot be diseounted until detailed mapping of the whole Sierra is eompleted.

Extensional Carboniferous magmatism at the western margin of Gondwana: Las Lozas valley, Catamarca, Argentina

“…1), to the north of the Mississippian rhyolites reported in Cazadero Grande by Martina et al (2011) and to the west of the coeval granites of the Sierras Pampeanas (Dahlquist et al, 2006(Dahlquist et al, , 2013Grosse et al, 2009). The Las Lozas rocks, previously mapped as Ordovician and considered to be part of the Famatinian magmatic system (Turner, 1967;Mpodozis et al, 1997;Rubiolo et al, 2001;Coira et al, 2005), were recently assigned by Cisterna et al (2013) and Zappettini et al (2015) to the Lower Pennsylvanian based on a zircon U-Pb SHRIMP age (320±2 Ma).…”

“…The geodynamic setting of the Carboniferous magmatism in the region remains controversial. It has been considered product of crustal reheating during final phase of Famatinian orogeny (e.g., Grissom et al, 1998;Llambias et al, 1998;Höckenreiner et al, 2003;Grosse et al, 2009) or part of the Achalian orogen (e.g., Sims et al,1998;Siesgesmund et al, 2004;Dahlquist et al, 2006. Meanwhile Dahlquist et al, 2010 proposed that those Carboniferous granites represent a new tectonothermal event, considering their field and geochemical characteristics, indicative of an extensional within-plate setting and noncompressive tectonic regime and not syn-kinematic emplacement as has been invoked for Devonian granite of Sierras de Cordoba or San Luis (Sims et al,1998;Siesgesmund et al, 2004).…”

International Lateinamerika-Kolloquium 2009

“…This slightly younger age, combined with the geochemical and isotopic trend towards more primitive mantle compositions in the SG melt supports the idea of cumulative degree of assimilation of mantle-derived components with time in the Carboniferous granites of the Sierra de Velasco . One of the youngest and most primitive products of this evolution could be the San Blas granite (340 ± 3 Ma; Dahlquist et al 2006). Conventional U-Pb determinations on monazite from HG and SG are identical in age with that of the main zircon growth phase at 350 ± 2 Ma .…”

Edades de metamorfismo en las unidades con bajo grado de la region central del Famatina: la impronta del ciclo orogenico ocloyico (Ordovicico).Metamorphic ages of low-grade units in the central region of Famatina: The signature of the Ocloyic Orogeny (Ordovician).

“…7; Rapela et al, 1998;Sims et al, 1998;Sato et al, 2003;Höckenreiner et al, 2003). Aun cuando no se conozca la cinemática precisa de varias de estas fajas miloníticas es clara su vinculación con el magmatismo achaliano que habría determinado la intrusión de cuerpos graníticos de 'tipo A' comunes en contextos extensionales (e.g., 340±3 Ma, Granito San Blas, Dahlquist et al, 2005bDahlquist et al, , 2006a. La edad K-Ar de ca.…”