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

Abstract

Tephras recovered by deep-sea drilling from fore-arc to back-arc locations across the Mariana Volcanic Arc record the last 34 Myr of the system’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 inter-tephra layer interval of � 1 Myr. Temporal variations of source-sensitive radiogenic isotopes and large-ion lithophile elements (LILE) are mostly decoupled from unchanging modes observed in silica and, with the exception of K, other archetypical crust-forming major elements. Modeling confirms that the temporal isotopic and elemental abundance trends are controlled by subducted slab and mantle sources. The Pb and Sr fluxes can be linked to fluids from altered oceanic crust (AOC), and are influenced by contributions from the mantle wedge and slab partial melts, whereas Hf mostly derives from the sub-arc mantle. Most plausibly, a K2O increase and fluctuations at � 10 Ma can be linked to collision of the leading trace of the Cretaceous-aged Western Pacific Seamount Province with the arc. This is inferred to have arrived at the Mariana Trench at � 15–16 Ma, coincident with the termination of spreading in the Parece Vela back-arc basin. A short period of slab melting followed, possibly induced by slab rollback that peaked at � 8–9 Ma and ended with incipient rifting in the Mariana Trough at � 7 Ma. Each of the periods of arc formation (52–24, 22–11 and 10–0 Ma) is characterized by a distinctive mixture of source materials that 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 their chemically distinctive subducted slab inputs.