Abstract
The subduction of seamounts and ridge features at convergent plate boundaries plays an important role in the deformation of the overriding plate and influences geochemical cycling and associated biological processes. Active serpentinization of forearc mantle and serpentinite mud volcanism on the Mariana forearc (between the trench and active volcanic arc) provides windows on subduction processes. Here, we present (1) the first observation of an extensive exposure of an undeformed Cretaceous seamount currently being subducted at the Mariana Trench inner slope; (2) vertical deformation of the forearc region related to subduction of Pacific Plate seamounts and thickened crust; (3) recovered Ocean Drilling Program and International Ocean Discovery Program cores of serpentinite mudflows that confirm exhumation of various Pacific Plate lithologies, including subducted reef limestone; (4) petrologic, geochemical and paleontological data from the cores that show that Pacific Plate seamount exhumation covers greater spatial and temporal extents; (5) the inference that microbial communities associated with serpentinite mud volcanism may also be exhumed from the subducted plate seafloor and/or seamounts; and (6) the implications for effects of these processes with regard to evolution of life.This article is part of a discussion meeting issue ‘Serpentine in the Earth system’.
Highlights
For example, if carbon dioxide is present in the hydrating fluid, serpentinization can release methane
Our observation of an intact section of Cretaceous reef exposed in the Mariana Trench inner slope shows, for the first time, that large expanses of impinging seamounts can remain undeformed at first contact
ODP and IODP drill cores from five serpentinite mud volcanoes contain a range of subducted plate and seamount lithologies
Summary
Recent (2016) expeditions to the western Pacific’s Mariana Trench region, on the United States’ National Ocean and Atmospheric Administration’s Office of Exploration and Research (NOAA OER) ‘Deepwater Exploration of the Marianas’ [1,2] and the International Ocean Discovery Program (IODP) Expedition 366 [3], provided a deeper understanding of the potential for widespread recycling of components of the subducting oceanic lithospheric plate and of seamounts on it. The faults permit fluids originating from the subduction channel to permeate the forearc mantle and erupt to form immense (up to 50 km diameter and 2.5 km high) serpentinite mud volcanoes [4,5]. As the Pacific lithospheric plate and features on it approach the trench, lithospheric bending creates an outer trench bulge about 60–120 km east of the trench This decreases the effective elastic plate thickness [16,17,18] so that normal faulting creates uplifted blocks with intervening troughs and/or trenchward, down-stepping half-grabens. Deep faults, penetrating to the subduction channel [20], provide pathways for fluids from the down-going plate to hydrate and serpentinize the forearc mantle [4,5,24,25,26]. The Mariana forearc serpentinite mud volcanoes episodically [3,4] tap the subduction channel at a range of depths and temperatures (table 1), providing windows into aspects of physical, chemical and biological processes that affect the subducted Pacific Plate as it moves downward and the overlying forearc lithosphere [5]
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