Igneous intrusions were emplaced prior to and contemporaneous with horizontal shortening of the crust in the Late Cretaceous to late Eocene magmatic arc in north Chile (21°45′-22°30′S). Temporally changing major and trace elements of magmatic rocks from this paleo-arc system chronicled gradual crustal thickening prior to and substantial crustal thickening contemporaneously with crustal shortening. Balanced structural cross sections indicate a minimum of 9 km of arc-normal shortening that occurred simultaneously with dextral arc-parallel movements accounting for orogen-parallel lengthening of ∼10 km. This shortening produced ∼5.4 km of tectonic crustal thickening and resulted in a minimum of ∼42 km late Eocene Andean crustal thickness. Temporal and spatial geochemical changes diagnostic of crustal thickening indicate that the remainder (∼2.6 km) was accommodated by basaltic underplating at or near the base of the arc crust prior to and during transpression. The ratio of tectonic to magmatic crustal thickening is ∼2:1. Whole-crustal magmatic addition rates during the ∼12 m.y. duration of arc transpression are ∼35 km3 per kilometer of model arc length per million years. Mafic underplating may have thickened the Andean crust considerably, but most pre-Neogene crustal thickening was due to discrete episodes of tectonic shortening.
CITATION STYLE
Haschke, M., & Günther, A. (2003). Balancing crustal thickening in arcs by tectonic vs. magmatic means. Geology, 31(11), 933–936. https://doi.org/10.1130/G19945.1
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