Magmatic sources and tectonic setting of Gondwana margin Ordovician magmas, northern Puna of Argentina and Chile

Abstract

Understanding the sources of Ordovician magmatic rocks in the broad western Faja Eruptiva Occidental and eastern Faja Eruptiva Oriental magmatic belts in the northern Puna of Argentina and Chile is important to Ordovician geodynamic models for westernGondwana evolution and Gondwana-Laurentian terrane interactions. A critical evaluation of existing chemical and age data, along with new major trace element data, and field observations leads to a working model in which magmatism in the western belt progressively occurred in an active to waning arc to collisional regime, whereas that in the eastern belt occurred in an oblique fault regime transitional to a subduction zone to the south. The model is hampered by data gaps in all areas, and particularly by lack of ages in western and southern regions. The best understood area is the northern Faja Eruptiva Oriental where dacitic and mafic units with published ages of 476-467 Ma occur in linear fault-controlled trends. Their chemistry is consistent with dacitic magma sources being dominated by sedimentary-type protoliths melted in association with emplacement of mantle-derived alkaline mafic magmas. These dacitic units represent lava-dome complexes emplaced contemporaneously with outer shelf and slope basin sedimentation. Farther south where deeper crustal levels are exposed, volcanic/subvolcanic units grade into poorly studied plutonic facies. Trondhjemitic bodies are reported to the east. Contemporaneous units in the Faja Eruptiva Occidental are plutons and mafic to rhyolitic lavas in sequences of volcaniclastic sediments. Chemical signatures in the poorly dated Cordón de Lila lavas and Choschas dioritic to leucogranodioritic pluton in Chile are consistent with emplacement in a magmatic arc on thinned continental or oceanic crust. Mafic volcanic units in volcanic-sedimentary sequences just to the east could represent arc volcanism behind the front. An Arenig-Llanvirn change to bimodal and predominantly silicic magmatism, the emplacement of shoshonitic and mafic andesitic flows with weak arc signatures followed by alkaline dikes in the eastern Faja Eruptiva Occidental, and the formation of the Faja Eruptiva Oriental dacitic-mafic sequences could signal a change to a very oblique subduction regime. This change would be roughly contemporaneous with the arrival of the Laurentia-derived Precordillera terrane to the south. A post-Arenig-Llanvirn compressional regime seems required to explain Ocloyic deformation in the east and late plutons to the west. The nature of the eastern boundary of a periGondwana Arequipa terrane and the existence of a peri-Gondwana Famatina-Puna Oriental terrane remain unclear.

Teleseismic tomography of the southern Puna plateau in Argentina and adjacent regions

“…These eruptions are postulated to be related to crustal and mantle lithospheric delamination events that led to decompression melting in the mantle producing the basaltic melts that triggered the crustal melting producing the hybrid magmas that erupted to produce these ignimbrites (e.g., Kay et al 1994Kay et al , 19992011a).…”

Ordovician back arc foreland and Ocloyic thrust belt development on the western Gondwana margin as a response to Precordillera terrane accretion

“…This is the case of the Northwestern Basin (southern extent of the central Andean basin), where a complete spectrum of Ordovician back arc foreland systems is represented [Astini, 2003], atop Cambrian passive margin sandstones and tightly folded high-level Pampean metasediments (Puncoviscana Formation). The Ordovician rocks exposed in the Famatina belt are chemically, lithologically, and paleontologically largely equivalent to those represented in the coeval arc of western Puna [Bock et al, 2000;Astini, 2003;Benedetto, 2003] and known as the ''Faja eruptiva de la Puna Occidental'' Niemeyer, 1989;Coira et al, 1999]. There, a largely volcano-sedimentary succession is overlain by an epiclastic deep-water section that partly records postorogenic arc unroofing stages and eastward progradation toward the craton [Bahlburg, 1990[Bahlburg, , 1991Bahlburg and Furlong, 1996].…”

Outlining the thermal posdepositional evolution of the Ordovician successions of northwestern Argentina by clay mineral analysis, chlorite geothermometry and Kübler index.

“…We will adopt the widely accepted stratigraphic nomenclature that assigned the upper Cambrian-Ordovician strata from Cordillera Oriental and the siliciclastic levels from the northeastern Puna to the Santa Victoria Group (Turner, 1964), which consists of the Santa Rosita (upper Cambrian-Tremadocian) and the Acoite (upper Tremadocian?-Floian) formations (Rubiolo et al, 2001;Astini, 2003;Buatois and Mángano, 2003;Voldman et al, 2016). In the Puna region, the fossiliferous siliciclastic marine sediments assignable to Upper Cambrian, Tremadocian to Floian interdigitate with synsedimentary lavas and subvolcanic intrusives of the Eastern Puna Eruptive Belt (Méndez et al, 1973;Giuliano et al, 2013b) that were grouped into the Magmatic-Sedimentary Cochinoca-Escaya Complex (Coira et al, 1999;Coira et al, 2001).…”

“…The Magmatic-Sedimentary Cochinoca-Escaya Complex (Coira et al, 2001) comprises sandstonepelite succession along with syndepositional bimodal volcanic and subvolcanic rocks; mainly dacitic lavas, hyaloclastites, domes-cryptodomes and minor basic-spilitic lavas, massive and in pillows (Coira and Koukharsky, 1991), with gabbro-basalt sills and dikes (Coira et al, 1999(Coira et al, , 2009). The type locality of this units located to the southwest of the study area, in the western flank of Sierra de Quichagua and the Eastern flank of Sierra de Queta (Coira et al, 2001).…”