An Integrated Tectono-Magmatic Model for the Evolution of the Southern Peruvian Andes (13-20°S) since 55 Ma

Abstract

The definition and characterization of the Oligocene-Miocene Crucero Supergroup of the southern Peru Inner Arc domain provide a previously unavailable lithostratigraphic framework for the clarification of the geodynamic context of magmatism across the southern Peruvian transect. We integrate new lithostratigraphic, petrologic, and 40 Ar/ 39 Ar geochronologic data for these volcanic and hypabyssal rocks with published information to establish a geotectonic model for the transect since 55 Ma.The early Eocene to Early Miocene tectono-magmatic history of the region was controlled by the evolution of a flat-subduction regime, which was initiated at ~52 Ma with the onset of rapid convergence, terminating the magmatic and hydrothermal activity of the Toquepala superunit of the Coastal Batholith. Collision of the flat slab with the leading edge of the Brazilian Shield lithospheric mantle at 39-40 Ma resulted in catastrophic failure of the overriding plate and crustal-scale, NE-directed ramping, generating the "Incaic" Zongo-San Gaban tectonothermal zone in the proto-Cordillera Oriental. Failure of the flat slab (~37 Ma), its progressive foundering into the asthenosphere (from ~37 to 20 Ma), and the upwelling of asthenosphere in its wake are inferred to have generated an eastward-migrating thermal anomaly that severely weakened the lower crust. This resulted in the resumption of Main Arc magmatism in the protoCordillera Occidental (~32 Ma) in an axial regime of transtension, followed at 29 Ma by quasiinstantaneous broadening of the arc to a width of ~200 km. Further continentward arc expansion into the Inner Arc at ~25 Ma, generating the mixed crust-and mantle-derived suites of the Picotani Group, resulted in a 360-km-wide swath of magmatism. Termination of magmatism in the Inner Arc at ~22 Ma reflected the waning stages of anomalous mantle flow associated with foundering of the slab, and was accompanied by substantial uplift and crustal thickening.The subsequent evolution of the transect was initiated and prompted by the broad zone of thermally weakened lower crust. Ductile shortening of the lower crust from ~22 to 17 Ma generated widespread crustal thickening and uplift across the orogen, and was accompanied by the antithetic oceanward subduction of Brazilian Shield lithosphere beneath the Inner Arc and the initiation of thrusting and folding along the Sub-Andean zone. Delamination and, probably, detachment of the Brazilian Shield from its lithospheric mantle root, as well as partial melting of this root, yielded enriched mafic melts that ascended into the orogenic crust and contributed both thermally and through the release of volatiles to the generation of the Quenamari Group.We emphasize the spatial association of the Crucero Supergroup and comparable suites of the Bolivian Cordillera Oriental with the Bolivian Orocline, and delimit a ~250-km amagmatic longitudinal zone separating the sites of anatexis in southern Peru and northern Bolivia. This is inferred to represent the zone of maximum orthogonal convergence thro...

The time-space distribution of Eocene to Miocene magmatism in the central Peruvian polymetallic province and its metallogenetic implications

“…31-26 Ma) all along the Peruvian margin has been proposed by Séb-rier and Soler (1991). Magmatism in this period was restricted but has been reported from southern Peru (Sandeman et al, 1995;Clark et al, 1990), although it appears to have been most important in the southern Peruvian Cordillera Oriental and Altiplano (Sébrier and Soler, 1991;Sandeman et al, 1995) as well as the Precordillera of northern Chile (Trumbull et al, 2006). These relationships suggest a regional geodynamic control on the reduction of magma output.…”

“…The Oligocene and Miocene phases of uplift and contractile deformation in the Central Andes have been summarized by numerous authors (Tosdal et al, 1984;Sébrier and Soler, 1991;Sandeman et al, 1995;Benavides, 1999;Oncken et al, 2006). Within the study area, important mid-Miocene deformation has been constrained to between $14.5 and 5.2 Ma by Farrar and Noble (1976) for areas south of Cerro de Pasco.…”

“…Much of the detailed work on the Cenozoic volcanic arcs in Perú has been carried out in northern (e.g., Noble et al, 1990), south central (e.g., Noble et al, 1979a) or southern Perú (Sébrier and Soler, 1991;Sandeman et al, 1995) whereas only limited data are available for central Perú (Noble et al, 1979b(Noble et al, , 1999a In this segment of the Andes, the largest volumes of volcanic rocks were deposited west of the Cordillera Occidental and thus west of the area concerned herein, a notable exception being the early Oligocene Astabamba Formation composed of andesitic and dacitic volcanic rocks which crops out west of Hunacayo (Fig. 2, Mégard, 1968).…”

“…Hornblende from one of these rocks yielded a plateau age of 77.8 ± 1.3 Ma (Table 3 Cenozoic contractional deformation, crustal thickening and uplift in the Andes are related to the balance between upper plate motion and slab roll-back velocity, but not to net convergence . The deformation has been defined as a series of orogenic phases (e.g., Mégard, 1984;Sébrier and Soler, 1991;Sandeman et al, 1995;Jaillard and Soler, 1996;Benavides, 1999) which, however, vary in timing both along and across the orogen . Within the study area, the late Paleocene to Eocene Incaic orogenic phase formed a fold and thrust belt with the most intense deformation between the rigid block represented by the coastal batholith and the Marañón arch tectonic high constituting the western border of the South American continent at that time (Benavides, 1999).…”

Sedimentary Crust and Metallogeny of Granitoid Affinity: Implications from the Geotectonic Histories of the Circum‐Japan Sea Region, Central Andes and Southeastern Australia

“…9), although its genesis has been a matter of discussion (e.g. Sillitoe, 1981;Kay & Kay, 1993;Sandeman et al, 1995).…”