Temporal Evolution of the Mariana Arc: Mantle Wedge and Subducted Slab Controls Revealed with a Tephra Perspective

Abstract:

Tephra recovered by deep-sea drilling from forearc to backarc across the Mariana volcanic arc system record the last 34 million years of the Arc’s evolution. Major and trace element abundances and Sr-Nd-Pb-Hf isotope ratios have been determined for tephra with high temporal precision and an average resolution of ∼1 million years. Temporal variations of source-sensitive radiogenic isotopes and large-ion lithophile elements (LILE) are decoupled from the steady trends of silica and other archetypical crust-forming major elements. Modeling confirms the temporal isotopic and elemental abundance trends are controlled by subducted slab and mantle sources. Pb and Sr fluxes can be linked to fluids from altered oceanic crust (AOC), Nd is influenced by contributions from the mantle wedge and partial slab melts, while Hf mostly derives from the subarc mantle. Most plausibly, the K₂O increase and fluctuations thereafter can be linked to a collision of the Mariana Arc with the leading trace of the Cretaceous-aged Western Pacific Seamount Province. The Province is inferred to have arrived at the Mariana Trench at ∼15-16 Ma coincident with the termination of spreading in the Parece Vela Backarc Basin. A short period of slab melting followed, possibly induced by slab rollback that peaked at ∼8-9 Ma and ended with the incipient rifting in the Mariana Trough at ∼7 Ma. Individual periods of Arc formation (52-24, 22-11, and 10-0 Ma) are characterized by a distinctive melee of source materials which is not repeated through time. Mariana Arc crustal growth has occurred through the addition of predominantly mafic and silicic melts formed during relatively short time intervals traceable via the chemically-distinctive subducted slab inputs.