A synthesis of the Peruvian Coastal Batholith: An exploration of temporal histories, causes of compositional diversity, and tectonomagmatic links in arcs

Abstract

The causes for spatial geochemical trends in the central Andes of Peru have been studied since the early 1970s. Along-arc chemical changes observed in the Peruvian Coastal Batholith (PCB) were fundamental to developing models for the evolution of the Pacific margin of South America. However, explanations for these trends and the processes that control magmatic compositional diversity along this arc are not fully understood. In this contribution we use an up-to-date database of high quality geochemical and geochronological data to: 1) assess the evidence for the previously proposed chemical trends, 2) document patterns of episodic magmatism to examine spatial and temporal changes covering a timespan of >170 million years along the PCB segments, 3) investigate PCB-wide variation of the parameters previously studied in the Ica-Pisco plutons, and 4) relate these to the tectonic setting, subduction parameters, magma sources, and crustal assimilation processes. Our results show that the PCB has a clear non-steady-state pattern over variable temporal and spatial scales and that arc magma chemistry covaries with arc magmatic activity. We conclude that the identified diversity in magma chemistry both along- and across-arc is the result of the extent of differentiation, types of assimilated materials, different types of basement, changes in crustal thickness, arc migration, changes in mantle input, and transitioning from depleted to lithospheric mantle resulting from changes in slab dip angle. In order to explain the causes of flare-ups and arc chemical diversity in the PCB we suggest that coupling of external (lower plate) and internal (upper plate) processes in complex ways at different spatial and temporal scales form the final arc diversity.