Mantle driven cretaceous flare-ups in Cordilleran arcs

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 similar to 125 to 90 Ma characterized by gabbro to granite units with Sri < 0.705, epsilon Nd from 0 to +7.5, Pb-208/Pb-204 from 38.2 to 38.7, and Pb-206/Pb-204 from 18.3 to 18.7. These values project well towards a depleted mantle source. Areal measurements show that gabbro forms -18% (wPRB), similar to 24% (PCB), and similar to 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. (C) 2018 The Authors. Published by Elsevier B.V.