Mesozoic–Cenozoic Evolution of the Western Margin of South America: Case Study of the Peruvian Andes

Abstract

Based on the structural style and physiographic criteria, the Central Andes of Peru can be divided into segments running parallel to the Pacific coast. The westernmost segment, the Coastal Belt, consists of a Late Jurassic–Cretaceous volcanic arc sequence that was accreted to the South American craton in Cretaceous times. The Mesozoic strata of the adjacent Western Cordillera represent an ENE-vergent fold-and-thrust belt that formed in Eocene times. Tight upright folds developed above a shallow detachment horizon in the West, while more open folds formed above a deeper detachment horizon towards the East and in the neighboring Central Highlands. A completely different style with steeply dipping reverse faults and open folds affecting the Neoproterozoic crystalline basement is typical for the Eastern Cordillera. The Subandean Zone is characterized by mainly NE-vergent imbricate thrusting which occurred in Neogene times. A quantitative estimate of the shortening of the orogen obtained from balanced cross-sections indicates a total shortening of 120–150 km (24%–27%). This shortening was coevel with the Neogene westward drift of South America, occurred at rates between 3 and 4.7 mm/year and was responsible for the high elevation of the Peruvian Andes

Arc and Slab-Failure Magmatism in Cordilleran Batholiths I – The Cretaceous Coastal Batholith of Peru and its Role in South American Orogenesis and Hemispheric Subduction Flip

“…To the east we see no evidence of another magmatic belt of the appropriate age that might be interpreted as a Cretaceous arc, so there is no reason a priori for subduction beneath South America to have been easterly during most of the Cretaceous. This model is similar to that proposed recently by Pfiffner and Gonzalez (2013).…”

“…The belt is well developed between the Tapacocha zone and the Marañon complex and places western basinal facies rocks over more easterly platformal facies rocks. The structure ranges from tightly folded and isoclinal with steep axial fabrics to shallowly dipping beds with shallowly dipping northeast-vergent thrust faults (Pfiffner and Gonzalez 2013;Scherrenberg et al 2014). The thrust belt continues southward into Bolivia (McQuarrie 2002).…”

“…The Coastal batholith includes medium-K, high-K and shoshonitic compositions and is consistently enriched in largeion lithophile elements (LILE) ( Figure 4e). LILE-enrichment and negative Ta anomalies on extended element nor- Marañon Fold-Thrust Belt During deposition and deformation of rocks within the Huarmey-Cañete basin, as well as during the subsequent emplacement of the Coastal batholith, all of which are located west of the Tapacocha zone, thinly bedded siliciclastic and limey rocks accumulated to the east in the West Peruvian basin ( Figure 5) to a thickness of at least 4000 m in the western off-shelf facies and about half that farther east on the west-facing platform (Wilson 1963;Scherrenberg et al 2012;Pfiffner and Gonzalez 2013). The rocks span most of the Cretaceous ( Figure 5) and there were no significant breaks in sedimentation until the uppermost Cretaceous when the platformal sequence was disconformably overlain by a thin sequence of calcareous marl capped by red cross-bedded sandstone, collectively interpreted to represent foredeep fill (Scherrenberg et al 2012).…”

“…Emerging from the jungles of the Amazon are rocks of the Subandean region, an area of Tertiary basins overlying thick sequences of Phanerozoic rocks and basement, which to the west become progressively involved in thick-skinned basement-involved thrusts and thin-skinned thrusts (Mathalone and Montoya 1995;Pfiffner and Gonzalez 2013). Farther southwest, in the Cordillera Oriental, lies the Marañon complex (Figure 1), which is a northwest-trending belt of Late Neoproterozoic to Paleozoic metamorphic rocks, including ~600 Ma orthogneiss, cut by Ordovician plutons, interpreted to represent part of a magmatic arc (Chew et al 2007), and overlain by two sequences of metamorphosed Paleozoic rocks: an older sequence deposited and metamorphosed between 450 and 420 Ma; and a younger sequence deposited after 320 Ma and metamorphosed at 310 Ma (Cardona et al 2009).…”

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

“…The latter become much wider towards the SE, opening into the Altiplano of Bolivia and Chile. The structure of the Peruvian Andes is illustrated with a SW-NE cross-section running between 11° and 13°S (see Figure 22A) that is based on [201].…”