Serpentinite Mud Volcanism and Exhumation of Forearc- and Lower Plate Material in the Mariana Convergent Margin System (IODP Expedition 366)
Abstract
Serpentine seamounts located in the forearc region of a subduction zone represent an excellent natural laboratory for studying the geochemical processes acting along convergent plate margins as well as the forearc structure and the related fault patterns. Active serpentinite mud volcanoes are currently restricted only to the Izu-Bonin-Mariana system, where old (presumably Cretaceous) oceanic lithosphere is subducting in the absence of an accretionary prism.
IODP Expedition 366 recovered cores from three serpentinite mud volcanoes at increasing distances from the Mariana trench (Yinazao, Fantangisña and Asùt Tesoro). Most of the material consists of serpentinite mud containing lithic clasts from the underlying forearc crust and mantle as well as from the subducting Pacific plate. Pelagic sediments and volcanic ash deposits underlying the mud volcanos were also recovered. Recycled materials from the subducted slab are found at all three mud volcanoes and consist of metavolcanics rocks, metamorphosed pelagic sediments including cherty limestone as well as fault rocks. Preliminary investigation of lithic clasts from the furthest Asùt Tesoro Seamount revealed metavolcanics as well as serpentinized ultramafics with well-preserved primary mineral assemblages. In contrast, recovered ultramafic clasts from the adjacent Fantangisña Seamount display higher degrees of serpentinization with matrix composed of mesh and bastite textures. Interestingly, andraditic garnet occurs throughout the matrix, indicating serpentinization temperatures of at least 225 °C. Petrological analysis of metabasalt clasts from the flank of Fantangisña shows changes in the mineral composition within the different core intervals. The composition of clinopyroxene varies between aegirine-augite and omphacite, but augite is also present. The presence of phengite with Si content of up to 3.5 a.p.f.u. as well as the Na-content in pyroxene indicate minimum pressure of 0.7 GPa at ~250 °C. Furthermore, providing a detailed characterization of the fluids composition and transport would allow the better constraining of the tectonic and metamorphic history as well as the physical properties of the subducting Pacific Plate. Obtaining data on that point is in progress and will be presented additionally.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMT018.0012M
- Keywords:
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- 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGY;
- 8104 Continental margins: convergent;
- TECTONOPHYSICS;
- 8413 Subduction zone processes;
- VOLCANOLOGY;
- 8488 Volcanic hazards and risks;
- VOLCANOLOGY