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Miocene Magmatism and Tectonics of The Miocene magmatism and tectonics of the easternmost sector of the Calama-Olacapato-El Toro fault system in Central Andes at 24° S: Insights into the evolution of the Eastern Cordillera R. Mazzuoli, L. Vezzoli, R. Omarini, V. Acocella, A. Gioncada, M. Matteini, A. Dini, H. Guillou, N. Hauser, A. Uttini, et al. To cite this version: R. Mazzuoli, L. Vezzoli, R. Omarini, V. Acocella, A. Gioncada, et al.. Miocene magmatism and tectonics of the easternmost sector of the Calama-Olacapato-El Toro fault system in Central Andes at 24° S: Insights into the evolution of the Eastern Cordillera. Geological Society of America Bulletin, Geological Society of America, 2008, 120 (11-12), pp.1493-1517. 10.1130/B26109.1. hal-03193227 HAL Id: hal-03193227 https://hal.archives-ouvertes.fr/hal-03193227 Submitted on 9 Apr 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Miocene magmatism and tectonics of the easternmost sector of the Calama–Olacapato–El Toro fault system in Central Andes at ~24°S: Insights into the evolution of the Eastern Cordillera R. Mazzuoli† Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy L. Vezzoli Dipartimento di Scienze Chimiche e Ambientali, Università degli Studi dell’Insubria, Como, Italy R. Omarini Facultad de Ciencias Naturales, Universidad Nacional de Salta, CONICET, Argentina V. Acocella Dipartimento di Scienze Geologiche, Università Roma Tre, Roma, Italy A. Gioncada Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy M. Matteini CNPq, Institute of Geosciences, University of Brasilia, Brasilia, Brazil A. Dini Istituto di Geoscienze e Georisorse, CNR, Pisa, Italy H. Guillou Laboratoire des Sciences du Climat et de l’Environnement CNRS, Gif-sur-Yvette, France N. Hauser Facultad de Ciencias Naturales, Universidad Nacional de Salta, CONICET, Argentina A. Uttini Dipartimento di Scienze Chimiche e Ambientali, Università degli Studi dell’Insubria, Como, Italy S. Scaillet Laboratoire des Sciences du Climat et de l’Environnement CNRS, Gif-sur-Yvette, France ABSTRACT rocks. The emplacement of the intrusion was fractional crystallization and crustal assimila- controlled by N-S–striking strike-slip faults tion moderately modifi ed magma composition The Miocene Las Burras–Almagro– in a context of oblique convergence; the vol- during its residence in the crust. The products El Toro magmatic complex lies ~300 km to the canism, which occurred along WNW-ESE– of the younger magmatic phase (ca. 11–6 Ma) east of the Central Andes volcanic arc, in the and N-S–striking extensional faults, relates have higher Ba/Nb (24–42) and La/Ta (24–30) easternmost sector of the transverse Calama– to the Calama–Olacapato–El Toro fault and 87Sr/86Sr (0.706738–0.708729) and lower Olacapato–El Toro fault zone. The magmatic zone. Two magmatic phases were recognized. 143Nd/144Nd (0.512433–0.512360). The results rocks of the Las Burras–Almagro–El Toro Intrusive and volcanic rocks of the older of EC-AFC modeling exclude a signifi cant complex comprise a monzogabbro to mon- magmatic phase (ca. 14–13 Ma) are charac- role for the upper crust in the generation of zogranite laccolith like intrusion and basaltic terized by Ba/Nb (7–14), La/Ta (11–18), and the most primitive magmas of this phase. andesite to dacite volcanic rocks that include isotopic ratios (87Sr/86Sr: 0.704339–0.705281, Their compositions can be explained by (1) seven lithostratigraphic members. New Rb-Sr 143Nd/144Nd: 0.512713–0.512598), which are contamination of the primary magmas hav- dates indicate that the intrusive rocks are intraplate characteristics. The source of the ing originated in a depleted mantle with a ca. 14 Ma, and K-Ar dates suggest emplace- older magmas was isotopically depleted litho- mafi c crust, or (2) the contribution of isoto- ment ages of ca. 12.8–6.4 Ma for the volcanic spheric mantle rich in K, Rb, and Th. Energy pically enriched mantle zones. Shallow dif- constrained–assimilation and fractional crys- ferentiation and moderate contamination by †E-mail: [email protected] tallization (EC-AFC) modeling indicates that continental crust can explain the composition GSA Bulletin; November/December 2008; v. 120; no. 11/12; p. 1493–1517; doi: 10.1130/B26109.1; 16 fi gures; 5 tables; Data Repository item 2008123. For permission to copy, contact [email protected] 1493 © 2008 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/120/11-12/1493/3397494/i0016-7606-120-11-1493.pdf by CEA Saclay DSM/LSCE Bibliotheque - MME Aptel user on 09 April 2021 Mazzuoli et al. of the intermediate and evolved products fault system (~24°S) is the longest of these the Pacifi c coast as far as 400–600 km inland of the younger phase. The variation of the transverse structures in the Central Andes, with (Fig. 1B; Allmendinger et al., 1983; Salfi ty, magma source characteristics at 11 Ma is inferred transtensive sinistral motion (Riller 1985; Marrett et al., 1994). Although the data- discussed in the frame of the complex geo- and Oncken, 2003), and is identifi ed by the base for the geometric and kinematic features dynamical setting in this region. alignment of magmatic centers (e.g., Matteini of these transverse faults is limited, they have et al., 2002a, 2002b; Fig. 1B). The study area been interpreted as old, probably Paleozoic, Keywords: Central Andes, Eastern Cordillera, is the easternmost portion of this fault, within left-lateral structures that were reactivated backarc magmatism, volcanic stratigraphy, geo- the Eastern Cordillera, and comprises the Mio- by the oblique convergence between the chronology, structural geology. cene Las Burras–Almagro–El Toro magmatic Nazca and South American plates (Riller et complex (Figs. 1B and 1C). The Las Burras– al., 2001; Riller and Oncken, 2003). Exten- INTRODUCTION Almagro–El Toro magmatism is of particular sive Miocene–Quaternary magmatic activity interest because of (1) its position ~300 km east developed along these fault systems in arc and An understanding of the structural context of the arc and ~600 km east of the trench, and backarc settings and formed transverse vol- and the petrochemical features of magmas is (2) its occurrence within the Eastern Cordillera, canic chains. Magmatism related to the NW- crucial in defi ning the geodynamic evolution which was characterized by Miocene–Quater- SE–trending Calama–Olacapato–El Toro fault of an area. Tectono-magmatic relationships are nary compression (Marrett and Strecker, 2000; system (~24°S; Fig. 1B) has occurred between well established in divergent oceanic and conti- Riller and Oncken, 2003). Our reconstruction, 17 Ma and the Quaternary, with maximum nental settings, and enable defi nition of consis- integrating stratigraphic, structural, volcanolog- activity between 10 and 5 Ma (Kay et al., 1999; tent geodynamic scenarios (e.g., Gudmundsson, ical, petrographic, geochemical, and geochrono- Petrinovic et al., 1999, 2005; Matteini et al., 1998; Ebinger and Casey, 2001); in contrast, logical data sets, relates to the geology of the 2002a, 2002b; Hongn et al., 2002; Haschke and knowledge of the tectonic evolution at conver- area and the genesis, evolution, and emplace- Ben-Avraham, 2005). This intense magmatic gent settings is more limited. It is commonly ment mechanisms of the magmas so far behind activity occurred concomitantly with a strong accepted that, at continental active margins, the main arc. uplift and deformation in the northern Puna the main arc location depends on the dip of the and the Eastern Cordillera and coincided with slab and the thermal regime in the slab-wedge GEOLOGICAL SETTING an eastward shift of the compression from the confi guration (e.g., Stern, 2002). At shallow plateau to the foreland (Gubbels et al., 1993). crustal levels, in oblique convergence settings, The Cenozoic Andean Cordillera and mag- The volcanic belt along the Calama–Olacap- the volcanoes along the arc are controlled by the matic arc are the result of moderately oblique ato–El Toro structure comprises stratovolca- activity of strike-slip faults related to the parti- convergence between the Farallon-Nazca and noes (mainly in the western Puna) and large tioning of deformation (Glazner, 1991; Tikoff South American plates (angle of ~20° between calderas with widespread ignimbrite sheets and Teyssier, 1992; Tobisch and Cruden, 1995; the plate motion vector and the plate boundary and intrusions (mainly in the eastern Puna). Tikoff and de Saint Blanquat, 1997; de Saint normal; Dewey and Lamb, 1992; Scheuber and The magmatic products are variable in age Blanquat et al., 1998). However, the shallow Reutter, 1992; Fig. 1A). Complex and wide- and in geochemical characteristics from the structural control on volcanoes behind the arc, spread arc magmatic activity has accompanied active volcanic arc to the Eastern Cordillera. where extensional, strike-slip, or compressional the evolution of the Andean margin since Meso- The variations refl ect different magma sources structures may form complex deformation pat- zoic time. In the Central Andes the Jurassic–Cre- and crustal thicknesses (Matteini et al., 2002a, terns, is less well constrained. The Andean oro- taceous volcanic arc was emplaced in the present b). The Pliocene–Quaternary monogenetic and gen is a spectacular example of convergence, Coastal Cordillera and Chilean Precordillera. mainly basaltic-andesite centers emplaced in mountain building, and magmatism in an active The arc migrated progressively eastward to the the Altiplano-Puna Plateau may relate to litho- ocean-continent subduction setting, and hence present Western Cordillera during the Miocene spheric delamination (e.g., Coira and Kay, represents an ideal site for investigating prob- to Quaternary (Fig.
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