Magmatic activity and tectonic setting of the early stages of the Andean cycle in northern Chile

Abstract

Jurassic and Lower Cretaceous magmatic activity in the present-day CoastalCordillera and the Central Depression of northern Chile is marked by important plutonic and volcanic cycles. The Initial Basics unit of the Coloso Coastal gabbro complex contains the first intrusives into an ensialic marginal basin related to extension, probably due to strike-slip plate motion. These gabbros have affinities with continental tholeiitic basalts. The subsequent Jurassic Volcanic unit, ranging from basalt to andesite in composition, erupted onto the subsiding basin. Simultaneous with and after the eruption of the Volcanic unit, the Late Granitoids unit was intruded. The earliest intrusives of this Late Granitoid unit (GI of the Coastal Cordillera) follow the Initial Basics in time and have similar geochemical source indicators. Geochemical signatures of both the Volcanic unit and the Late Granitoid intrusives suggest that they are related to contemporaneous subduction. Some Late Granitoids (GII of the Central Depression) show evidence of significant crustal contamination much like that of modern Andean magmatism.

Geodynamic controls on the contamination of Cenozoic arc magmas in the southern Central Andes: Insights from the O and Hf isotopic composition of zircon

“…Subduction has been active along the western margin of South America since the earliest Jurassic, with subduction-related magmatism in the Central Andes initiated at $185 Ma (e.g., Pichowiak et al, 1990;Stern, 2004). The study area is located within the Pampean (Chilean) flat-slab segment ($28°-33°S) of the southern Central Andes (Fig.…”

Nazca–South America interactions and the late Eocene–late Oligocene flat‐slab episode in the central Andes

“… Pardo‐Casas and Molnar [1987] showed that the Andean subduction margin was weakly compressional to extensional throughout the Mesozoic and into the Eocene (Figure 2a). Abundant arc volcanism occurred as calc‐alkaline magmatism along the western Cordillera [ Pichowiak et al , 1990; Haschke et al , 2002], as well as the emplacement of the 100–55 Ma Coastal Batholith in Peru [ Atherton , 1990]. Plate reconstructions [ Pilger , 1983; Pardo‐Casas and Molnar , 1987; Tebbens and Cande , 1997; Somoza , 1998] of the Mesozoic and early Cenozoic include the Phoenix Plate as part of a ridge‐ridge‐ridge triple junction with the Pacific and Farallon Plates [ McCarron and Larter , 1998].…”

Geochemistry of Permian to Triassic igneous rocks from northern Chile (28º-30º15’S): Implications on the dynamics of the proto-Andean margin.

“…8b). The first pulses of the well-known early Andean arc are represented by the La Negra Formation and its equivalents (Rogers and Hawkesworth, 1989;Pichowiak et al, 1990;Pichowiak, 1994) but given the signature of the Coastal Cordillera plutonic bodies studied in this work, they may have been the result of the earliest arc activity in the present-day coastal region. Furthermore, recent studies have reported Rhaetian volcanism in the Coastal Cordillera at 20°-22° S (Sepúlveda et al, 2014).…”