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Title: Expedition 366 Scientific Prospectus: Mariana Serpentine Mud Volcanism
International Ocean Discovery Program (IODP) Expedition 366 has two primary science objectives. The first objective is devoted to coring a series of sites at the summit and flanks of three large (up to 50 km diameter and 2 km high) serpentinite mud volcanoes in the Mariana forearc (within 100 km west of the Mariana Trench). This objective addresses the broad scientific aim of examining processes of mass transport within the subduction zone of a nonaccretionary convergent margin. In detail, the plan is to recover mudflow materials to (1) examine processes of mass transport and geochemical cycling within the forearc of a nonaccretionary convergent margin; (2) ascertain the spatial variability of slab-related fluids within the forearc environment as a means of tracing dehydration, decarbonation, and water-rock reactions in subduction and suprasubduction zone environments; (3) study the metamorphic and tectonic history of this nonaccretionary forearc region; (4) investigate the physical properties of the subduction zone in relation to dehydration reactions and seismicity; (5) document microbial activity associated with subduction zone material from great depth; and (6) explore linkages among these subduction-related processes, including seismicity, while placing the effects of these processes within a historical context. The second objective establishes long-term seafloor observatory sites more » by emplacing cased boreholes at summit (conduit) holes in three mud volcanoes (at Expedition 366 proposed Sites MAF-11A, MAF-9B, and MAF-15A) and removing the circulation obviation retrofit kit (CORK) body from Ocean Drilling Program Hole 1200C. These activities set the foundation for future deployments of sensors and samplers with the possibility of deploying a CORK-Lite structure within the boreholes. CORK-Lites provide a framework for conducting temporal observations that will allow one to “take the pulse of subduction” in an active nonaccretionary convergent plate margin and establish a platform for in situ experimentation. « less
Authors:
; ;
Award ID(s):
1326927
Publication Date:
NSF-PAR ID:
10230629
Journal Name:
Scientific prospectus
Volume:
366
ISSN:
2332-1385
Sponsoring Org:
National Science Foundation
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Their positions adjacent to or atop fault scarps on the forearc are likely related to the regional extension and vertical tectonic deformation in the forearc. Serpentinite mudflows at these volcanoes include serpentinized forearc mantle clasts, crustal and subducted Pacific plate materials, a matrix of serpentinite muds, and deep-sourced formation fluid. Mud volcanism on the Mariana forearc occurs within 100 km of the trench, representing a range of depths and temperatures to the downgoing plate and the subduction channel. These processes have likely been active for tens of millions of years at this site and for billions of years on Earth. At least 10 active serpentinite mud volcanoes have been located in the Mariana forearc. Two of these mud volcanoes are Conical and South Chamorro Seamounts, which are the furthest from the Mariana Trench at 86 and 78 km, respectively. Both seamounts were cored during Ocean Drilling Program (ODP) Legs 125 and 195, respectively. Data from these two seamounts represent deeper, warmer examples of the continuum of slab-derived materials as the Pacific plate subducts, providing a snapshot of how slab subduction affects fluid release, the composition of ascending fluids, mantle hydration, and the metamorphic paragenesis of subducted oceanic lithosphere. Data from the study of these two mud volcanoes constrain the pressure, temperature, and composition of fluids and materials within the subduction channel at depths of about 18 to 19 km. Understanding such processes is necessary for elucidating factors that control seismicity in convergent margins, tectonic and magma genesis processes in the forearc and volcanic arc, fluid and material fluxes, and the nature and variability of environmental conditions that impact subseafloor microbial communities. 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The new 2G Enterprises superconducting rock magnetometer (liquid helium free) revealed relatively high values of both magnetization and bulk magnetic susceptibility of discrete samples related to ultramafic rocks, particularly in dunite. Magnetite, a product of serpentinization, and authigenic carbonates were observed in the mudflow matrix materials. In addition to coring operations, Expedition 366 focused on the deployment and remediation of borehole casings for future observatories and set the framework for in situ experimentation. Borehole work commenced at South Chamorro Seamount, where the original-style CORK was partially removed. Work then continued at each of the three summit sites following coring operations. Cased boreholes with at least three joints of screened casing were deployed, and a plug of cement was placed at the bottom of each hole. Water samples were collected from two of the three boreholes, revealing significant inputs of formation fluids. 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Expedition 366 focused on data collection from cores recovered from three serpentinite mud volcanoes that define a continuum of subduction-channel processes to compare with results from drilling at the two previously cored serpentinite mud volcanoes and with previously collected gravity, piston, and remotely operated vehicle push cores across the trench-proximal forearc. Three serpentinite mud volcanoes (Yinazao, Fantangisña, and Asùt Tesoro) were chosen at distances 55 to 72 km from the Mariana Trench. Cores were recovered from active sites of eruption on their summit regions and on the flanks where ancient flows are overlain by more recent ones. Recovered materials show the effects of dynamic processes that are active at these sites, bringing a range of materials to the seafloor, including materials from the crust of the Pacific plate, most notably subducted seamounts (even corals). 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