Mantle driven cretaceous flare-ups in Cordilleran arcs

Abstract

Listen

Translate article

Continental arcs display episodic magmatism characterized by flare-ups and lulls. Models published to explain these patterns invoke (1) upper plate crustal processes driven by internal feedback; (2) episodic mantle melting processes, or (3) external lower plate tectonic events.This study addresses the role of mantle magmas during flare-ups in Mesozoic Cretaceous continental arcs using geochronological and geochemical data for three Cretaceous arc segments: the western Peninsular Ranges Batholith (wPRB), the Peruvian Coastal Batholith (PCB), and the Chilean Coastal Batholith (CCB).In all three arc segments, bedrock zircon age patterns defining a flare-up from ~125 to 90 Ma characterized by gabbro to granite units with Sri < 0.705, ƐNd from 0 to +7.5, 208Pb/204Pb from 38.2 to 38.7, and 206Pb/204Pb from 18.3 to 18.7. These values project well towards a depleted mantle source. Areal measurements show that gabbro forms ~18% (wPRB), ~24% (PCB), and ~10% (CCB) of exposed plutonic material. AFC modeling indicates that these magmas have experienced fractional crystallization with only minor crustal assimilation (<20–30%), implying that the great majority of these magmas are mantle-derived. Thus the cause of these flare-ups must be episodic mantle processes: crustal melting was not required for triggering the flare-up, and only played a secondary role in modifying melt compositions. It remains unclear if the episodic mantle processes reflect internal feedback(s) or external tectonically driven processes.