GSA Bulletin; July 1997; V

Geodynamic evolution and tectonostratigraphic terranes of northwestern Argentina and northern Chile Heinrich Bahlburg* Geologisch-Paläontologisches Institut, Ruprecht-Karls-Universität, Im Neuenheimer Feld 234, 69120 Heidelberg, Germany Francisco Hervé Departamento de Geología, Universidad de Chile, Casilla 13518, Correo 21, Santiago, Chile ABSTRACT pothesis is difficult to reconcile with the Paleo- one should bear in mind that the Paleozoic rocks of zoic tectonostratigraphic evolution of the the central Andes are not as well and systemati- In Ordovician time, Gondwana in the area southern Central Andean region. cally studied as the Appalachian mountain range, of northwestern Argentina and northern for example, or many other more accessible oro- Chile had a west-facing active margin. The INTRODUCTION gens. Some data compiled in Table 1 should there- evolution of this margin culminated in the fore be considered preliminary. In the interpreta- Oclóyic orogeny at the end of Ordovician Recently proposed paleotectonic reconstruc- tion of stratigraphic and radiometric data we used time. This orogeny was caused by the collision tions of Neoproterozoic and early Paleozoic time the time scale of Harland et al. (1989). We apply of the allochthonous Arequipa-Antofalla ter- suggest that the Laurentian craton was located the data to evaluate earlier models of terrane ac- rane with this margin. The early Paleozoic close to Antarctica and South America at these cretion in the southern Central Andes (e.g., Dalziel evolution of northwestern Argentina and times (Dalziel, 1991; Moores, 1991; Hoffman, and Forsythe, 1985; Ramos et al., 1986; Hervé et northern Chile contrasts markedly with the 1991). The clockwise movement of Laurentia al., 1987; Ramos, 1988; Bahlburg and Breitkreuz, accretionary history of central Argentina and around South America during early Paleozoic time 1991; Forsythe et al., 1993) and the hypothesis of central Chile, where the Precordillera and is interpreted to have resulted in repeated plate tec- Dalziel et al. (1994), and propose a new terrane Chilenia terranes docked in the Late Ordovi- tonic interaction of the two continents (Dalziel et map for the region. cian and Late Devonian periods, respectively. al., 1994). Furthermore, Dalla Salda et al. (1992a) An inspection of the available stratigraphic and Dalziel et al. (1994) proposed that the early PALEOZOIC RECORD and geochronological data on sedimentary, Paleozoic Famatinian orogenic belt of the Andes volcanic, and plutonic units of the southern in southwestern South America, and the Late Figure 4 synthesizes the available data on sed- Central Andes of northern Chile and north- Ordovician–Early Silurian Oclóyic orogen within imentary, magmatic, and metamorphic events in western Argentina reveals a lull in magmatic the Famatinian belt, may have originated jointly and metamorphic activity lasting for ~100 m.y., with the Taconic orogenic belt from the collision from Early Silurian to early Late Carbonifer- of eastern Laurentia and southwestern South ous time. This is interpreted as corresponding America, during the latter part of Ordovician time to a tectonic scenario in which the present An- (Fig. 1). Accordingly, the Late Ordovician rifting dean margin was a passive margin of Gond- off of Laurentia after the Taconic orogenic pulse is wana. This passive margin developed in re- thought to have left behind the Precambrian Are- sponse to the rifting off of a part of the quipa massif in southern Peru, related basement Arequipa-Antofalla terrane; the present loca- units in northern Chile, and probably the western tion of this block is unknown. Late Carbonif- part of northwestern Argentina (Figs. 2 and 3). The erous time marks the renewed onset of sub- recognition of tectonostratigraphic terranes in cen- duction, initiating the Andean plate tectonic tral Argentina and central Chile (Ramos et al., setting still prevalent today. Recently pro- 1986) has invited the tentative extrapolation of this posed models explain the Late Ordovician accretionary history to the regions farther north in orogeny by the collision of Laurentia with northwestern Argentina, northern Chile, southern western South America during Laurentia’s Bolivia, and southern Peru (Ramos, 1988). How- clockwise motion around South America and ever, in this contribution we suggest a significantly away from its position in the Neoproterozoic different accretionary history of the southern Cen- supercontinent. In its present form, this hy- tral Andes that is based on our own work and a compilation of the available information on Paleo- zoic stratigraphy and the radiometric ages of mag- Figure 1. Present-day location of the Taconic *Present address: Geologisch-Paläontologisches matic and metamorphic events of northern Chile and Famatinian orogens, and the study area in Institut, Westfälische Wilhelms-Universität, Correns- strasse 24, D-48149 Münster, Germany. E-mail: and northwestern Argentina (Figs. 2, 3, and 4). the southern Central Andes (adapted from [email protected] With regard to the radiometric ages in particular, Dalla Salda et al., 1992a). GSA Bulletin; July 1997; v. 109; no. 7; p. 869–884; 12 figures; 1 table. 869 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/869/3382721/i0016-7606-109-7-869.pdf by guest on 30 September 2021 BAHLBURG AND HERVÉ tion and equivalents of variable metamorphic 72°W 71° 70° 69° 68° 67° 66° 65°W grade (Figs. 2, 3, and 4). It acquired its first meta- Sierras Cordillera 10°N morphic overprint in the Early Cambrian Pam- Arequipa Pampeanas Occidental Northern pean orogeny (Willner et al., 1987; Mon and Sierras 0° Andes 18 Salar de Hongn, 1996). In the Cordillera Oriental and PERU Subandinas Atacama Basin ° Transamazonian Cordillera Chilean 10 S shield Sierras Pampeanas (Figs. 2, 3, and 4), these rocks Oriental Precordillera ° Central were intruded in Middle Cambrian time by the 20 Andes Altiplano, Cordillera post-tectonic peraluminous Santa Rosa de Tastil Puna de la Costa 30° study Southern ° area 18 S and Cañaní granitoids (Figs. 3, 4, and Table 1; Andes African Salars 40° Bachmann et al., 1987; Damm et al., 1990). Arica shield Belén northern- The Puncoviscana Formation and the Middle southern Puna 50° V boundary Cambrian plutons are overlain in the Cordillera N alle Longitudinal Oriental with an angular unconformity by the shallow marine, partly tidally influenced quartz- CHILE Salar de Uyuni sandstones and shales of the Late Cambrian Mesón Group (Figs. 3 and 4). The Mesón Group 20° Iquique has a minimum thickness of 1000 m and was de- posited on a -west-facing marine platform 8 (Kumpa and Sanchez, 1988) interpreted to be BOLIVIA part of an epeiric sea east of the continental mar- Choja gin (Sanchez and Salfity, 1990; Gohrbrandt, 21 1992). With an erosional unconformity (Fig. 4, Irúyica event, Turner and Méndez, 1979), the 20 22° Mesón Group is overstepped to the east and west Tocopilla 9 PACIFIC OCEAN PACIFIC 16 by the sandstones and shales of the Early Ordovi- Calama cian Santa Victoria Group (Figs. 3 and 4) which 15 12 received sediment mainly from the east. The Mejillones San Pedro 10 thickness of the Santa Victoria Group is esti- Salar de 14 Humahuaca mated as approximately 4500 m (Turner, 1960; 23 Atacama 3 8 Moya, 1988). Antofagasta 5 In Early Ordovician time, (Tremadocian and 13 northern Puna 6 24° Arenigian), a magmatic arc was farther to the CHILE 2 10 17 Jujuy west in the western Puna region and south of the Salar de Atacama in northern Chile (Fig. 2). It 22 Salta led to the formation of basaltic to andesitic lavas 19 of volcanic arc geochemical affinity, and associ- Puna Atacama Fault Zone Cachi ated volcaniclastic apron deposits of approxi- 1 11 mately 3500 m thickness (Las Vicuñas and 19 Zone Aguada de la Perdíz formations, Complejo Ígneo- 19 southern10 A ° 26 Sedimentario del Cordón de Lila (Figs. 3 and 4; T I N Koukharsky et al., 1988; Niemeyer, 1989; Breit- alle Longitudinal kreuz et al., 1989; Bahlburg, 1990; Moya et al., Chañaral 4 V 7 A R G E N 1993). Graptolites and trilobites present in clas- Atacama Fault tic intercalations date the volcanic rocks as Tremadocian and Arenigian (e.g., Garcia et al., Figure 2. Distribution and areal extent of morphostructural units in the southern Central An- 1962; Coira and Nullo, 1987; Bahlburg et al., des. Numbers refer to outcrops indicated on the map of Figure 3 and are included here for ori- 1990; Moya et al., 1993). Cogenetic calc-alkaline entation purposes only. intrusive activity is recorded in the Choschas granodiorite (502 ± 7 Ma) in the Complejo Ígneo-Sedimentario del Cordón de Lila in north- northern Chile and northwestern Argentina. It Silurian to Early Carboniferous, and Late ern Chile and in Archibarca granite (485 ± 15 Ma) illustrates that magmatic and metamorphic ac- Carboniferous–Permian time. in the western reaches of the southern Puna tivity occurred mainly in the Ordovician and Late (Figs. 3, 4, and Table 1; Mpodozis et al., 1983; Carboniferous–Permian periods. These peaks of Evolution During Cambrian and Palma et al., 1986; Niemeyer, 1989; Rapela et activity are separated from each other by a pe- Ordovician Time al., 1992). Crustal extension in the region of the riod of tectonic, magmatic, and metamorphic Faja Eruptiva de la Puna Oriental farther to the quiescence ranging from Early Silurian to early The oldest and easternmost stratigraphic unit east in the northern Puna (Figs. 2 and 3) is indi- Late Carboniferous time. The Paleozoic evolu- considered here is represented in the Cordillera cated by minor volumes of basaltic pillow lavas tion is presented according to this temporal Oriental of northwestern Argentina (Fig. 2) by and sills of within-plate geochemical affinity three-fold division into Cambrian-Ordovician, the metaturbidites of the Puncoviscana Forma- (Coira and Koukharsky, 1991). 870 Geological Society of America Bulletin, July 1997 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/7/869/3382721/i0016-7606-109-7-869.pdf by guest on 30 September 2021 GEODYNAMIC EVOLUTION, ARGENTINA AND CHILE 72°W 71° 70° 69° 68° 67° 66° 65°W 10°N Arequipa Northern 0° Andes Figure 3.

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