Geochemistry and Genesis of the S-Type, Cordierite-Andalusite-Bearing Capillitas Batholith, Argentina

Abstract

The Ordovician Famatinian-age magmatic cordierite-andalusite-bearing Capillitas batholith, in the Pampean Ranges of northwestern Argentina, encompasses a coarsely porphyritic to equigranular two-mica monzogranite with equigranular, fine-grained, late leucogranitic muscovite-rich facies. This batholith exhibits sharp, discordant contacts with low-pressure biotiteandalusite-cordierite schists of the La Cébila Formation, locally developing biotite-cordieritemuscovite-bearing contact hornfels aureoles.The two-mica monzogranite contains cordierite, andalusite, and sillimanite, although cordierite and andalusite are more abundant in the leucogranitic equigranular facies. These minerals are not homogeneously distributed and the three minerals are found together only locally. The presence of biotite-rich xenoliths with a high amount of anhydrous aluminum silicates (andalusite, sillimanite) and cordierite, exhibiting textures similar to those of the host monzogranites, suggest that, at least in part, they have been incorporated into the magma and reequilibrated. The pressure during emplacement was probably 4 kbar under near-solidus temperature, thus preserving the anhydrous aluminum-silicate stability under high H 2 O activity.The major-element data indicate a peraluminous calc-alkalic trend with compositional gaps. They attest to the existence of two distinct magma pulses. The chondrite-normalized REE patterns and multi-element spidergrams point to a probable origin by crustal (metasediment?) anatexis for both pulses. Peraluminous granitic magma cannot be a primary melt of metaluminous quartz-amphibolite, since there is a great geochemical homogeneity of all the granitoids. Igneous xenoliths are absent and the isotopic compositions of the granitoids correspond to those of metasedimentary sources. Both major and trace elements point to a collisional tectonic environment of an inner-continental magmatic arc.

High T/P evolution and metamorphic ages of the migmatitic basement of northern Sierras Pampeanas, Argentina: Characterization of a mid-crustal segment of the Famatinian belt

“…The magmatic activity in the study area and nearby ranges can be enclosed in two major events: LowerMiddle Ordovician (Famatinian) and Late Devonian -Early Carboniferous (Achalian). The former and more important is characterized by the Capillitas Batholith, the main granitoid body that crops out in the area and is representative of the Ordovician peraluminous S-type Famatinian magmatism (Toselli et al, 1996;Pankhurst et al, 2000;Rossi et al, 2002). In addition, several coeval I-type and S-type plutons complete the Ordovician magmatic groups (Knüver, 1983;Toselli, 1992;Rapela et al, 2005;Büttner et al, 2005).…”

Successive reactivation of older structures under variable heat flow conditions evidenced by K–Ar fault gouge dating in Sierra de Ambato, northern Argentine broken foreland

“…The metamorphic basement in mainly formed by the Ancasti Formation, with sedimentation ages between 680 and 570 Ma (Rapela et al, 2007;Murra et al, 2011) and a metamorphic episode between ~477 and 470 Ma (UePb geochronology on monazite grains, Larrovere et al, 2011). The igneous activity is Middle to Late Ordovician (Knüver, 1983;Toselli, 1992;Toselli et al, 1996;Pankhurst et al, 2000;Rossi et al, 2002;Rapela et al, 2005) and Devonian-early Carboniferous (Knüver, 1983;Toselli, 1983;Indri and Barber, 1987;Toselli, 1992) (Fig. 1).…”

The Ordovician Las Chacritas pluton (Sierra de Humaya, NW Argentina): origin and emplacement triggered by lateral shortening and magmatic stoping at mid-crustal level

“…The accretionary wedge zone is located in the west side of the Sierra de Valle Fértil and consists of metamorphic rocks with strong isothermal decompression paths (Vujovich 1994;Baldo et al 2001;Otamendi et al 2008;Casquet et al 2012). The arc zone consists of calc-alkaline batholiths composed of I-, S-and transitional I/S-type granitoids with εNd 470 values of ~−4 to −5.5, ~−4.5 to −8.5 and ~−4 to −6, respectively (Toselli et al 1996;Pankhurst et al 1998;Saavedra et al 1998;Dahlquist and Galindo 2004;Grosse et al 2011). In the westernmost region of the Famatinian arc, mafic magmatism with a wide isotopic range (εNd 470 ~−5.5 to 4.5) has been reported as well as granulite facies migmatites (Pankhurst et al 2000;Otamendi et al 2008Otamendi et al , 2009Otamendi et al , 2010Casquet et al 2012).…”

“…In the retro-arc zone to the east, minor isolated granitoid plutons that intruded into metasedimentary host rocks represent the innermost documentation of the Famatinian magmatism (Toselli et al 1983;Llambías et al 1998;Pankhurst et al 2000;Dahlquist et al 2012). A plethora of geochemical, isotopic and geochronologic studies (Knüver 1983;Reissinger 1983;Toselli et al 1983Toselli et al , 1996Rapela et al 1990;Toselli 1992;Llambías et al 1998;Pankhurst et al 1998Pankhurst et al , 2000Saavedra et al 1998;Rossi et al 2002;Sato et al 2003;Cisterna 2003;Cisterna et al 2004;Dahlquist and Galindo 2004;Büttner et al 2005;Dahlquist et al 2005Dahlquist et al , 2007Dahlquist et al , 2008Dahlquist et al , 2012Dahlquist et al , 2013López de Luchi et al 2007;Fernández et al 2008;Morosini et al 2009;Otamendi et al 2009Otamendi et al , 2012Ducea et al 2010;Chernicoff et al 2010;Sola and Becchio 2010;Grosse et al 2011;Steenken et al 2011;Casquet et al 2012) attempted to unravel the origin and geotectonic evolution of the Famatinian magmatism. The core works focus on the regional evolution of granitic batholiths from the main Famatinian magmatic arc (Sierras de Capillitas, Velasco, Chepes, Famatina and Valle Fértil), whereas less attention was given to the more...…”