Submarine Piip Volcano, Western Aleutian Arc: Temporal Evolution from Back-Arc Rift to Island-Arc Stratovolcano
Multi-beam mapping revealed a morphologically complex volcanic edifice and its base, indicating a multi-stage evolution that correlates with prominent changes in the composition of parental magmas. The northwestern and southeastern flanks of the ca. 30 km wide (in the NW-SW direction) massif consist of NE-SW elongated micro plateaus (“wings”), uplifted by ca. 1000-1500 m above the neighboring seafloor. The rocks from the deepest parts of the plateaus and a tilted basement block northwest from the massif are ol-plag-phyric tholeiites with MORB-like compositions (Ba/La=6.0-8.8, Pb/Ce=0.07-0.10, 87Sr/86Sr =0.70256-0.70271), which show very little contribution from a slab-derived fluid to their mantle source. The flank micro plateaus are complicated by NE-SW trending linear ridges and small nested volcanic edifices composed of ol±px±plag-phyric basaltic andesites and high-Mg andesites with an enhanced subduction-related signature (Ba/La=9.2-18.3, Pb/Ce=0.09-0.16, 87Sr/86Sr = 0.70264-0.70279). The central part of the massif is occupied by the ca. 2000 m-high ca. 15 km wide Piip stratovolcano, which reaches a minimum water depth of 500 mbsl in its summit area. Amph-bearing calc-alkaline dacites from the Piip summit have the most pronounced slab-related signature (e.g., Ba/La=18.8-20.7, Pb/Ce=0.17-0.21, 87Sr/86Sr =0.70277-0.70284)
Our new data on Piip Volcano suggest a unique temporal evolution of a single volcano from back-arc rift erupted low viscosity basaltic tholeiitic magmas to island-arc type stratovolcano formed by high-viscosity silicic magmas. The presentation will discuss possible models for the origin of the Piip volcano and its significance to the understanding of the geodynamic evolution of the Aleutian Arc.