The Las Matras tonalitic–trondhjemitic pluton, central Argentina: Grenvillian-age constraints, geochemical characteristics, and regional implications

Abstract

The N-S trending belt with Grenvillian-age rocks developed in central western Argentina represents the basement of an allochthonous terrane derived from Laurentia during the Early Paleozoic. The Las Matras pluton (36Њ46 H S, 67Њ07 H W) is located at the southern extension of this belt in the Las Matras Block. It consists of a low-Al tonalitic to trondhjemitic facies characteristic of an arc magmatism. Isotopic studies yielded Grenvillian Rb-Sr (1212^47 Ma) and Sm-Nd (1188^47 Ma) ages which, due to the undeformed and non-metamorphosed character of the pluton, are interpreted to represent a crystallization age of around 1200 Ma. Although this age is slightly older than available dates from other exposures of the same belt, and the undeformed feature is also distinctive for Las Matras, the depleted Sr and Nd isotopic signatures of the pluton agree with those from other magmatic rocks involved in that belt. The differences found between Las Matras and the northern exposures indicate that this belt with Grenvillian-age rocks comprises regions of non-homogeneous evolution. Although the correlation of the Lower Paleozoic platform carbonates from the sedimentary cover of the Grenvillian-age basement rocks suggests the surroundings of the Southern Grenville Province (Texas and northern Mexico) as the probable detachment site for the Argentine belt, comparison of magmatic and tectonic processes involved in these basement rocks does not indicate similar evolutions. This fact can suggest an independent evolution of the Argentine belt prior to amalgamation to the Laurentian Grenville orogen. ᭧

Early Gondwanan connection for the Argentine Precordillera terrane

“…Similarity of Pb isotope ratios between the xenoliths of the Precordillera and rocks of the extensive Grenvillian age-equivalent belts throughout Gondwana cannot be ruled out because such comparisons were not made by Kay et al [22], and, in fact, Wareham et al [43] reported close similarity of Pb and Nd isotope characteristics of Grenvillian-age rocks of Laurentia and the Precordillera to Mesoproterozoic rocks in East and West Antarctica, Natal, and the Falkland Islands. A recent isotopic study of Grenvillian-age basement in the southern part of the western Sierras Pampeanas reveals signi¢cant isotopic di¡erences from the Laurentian Grenville [44]. Thus, the widely held assumption of dominantly Grenvillian-age basement of Laurentian af¢nity for the Precordillera may be untrue.…”

Erosion Surface and Granitic Morphology in the Sierra de Lihuel Calel, Province of La Pampa, Argentina

“…The ignimbrites overlie the basement integrated by igneous and metamorphic rocks of Late Proterozoic to Early Paleozoic age (Linares et al 1980;Tickyj et al 1999;Sato et al 2000).…”

Evolução estrutural da Sierra de Umango, Sierras Pampeanas Ocidentais, Noroeste da Argentina

“…Matras, ocorre uma faixa N-S de rochas de idades mesoproterozóicas grenvilianas, pertencentes ao embasamento do Terreno Cuyania (Sato et al, 2000). Incluem as serras de Toro Negro, Umango, Maz e Espinal ao norte; Sierra de La Huerta/Sierra…”

“…Valle Fértil e Sierra de Pie de Palo na porção central; e blocos de San Rafael e Las Matras ao sul (Sato et al, 2000) (Figura 1).…”

“…Terreno exótico Cuyania (Sato et al, 2000;Varela et al, 2003aVarela et al, , 2003bSato et al, 2004;Porcher et al, 2004;Vujovich et al, 2004) ou Occidentalia (Dalla Salda et al, 1992a;Varela et al, 1996Varela et al, , 2000.…”