Geologic processes at convergent plate margins control geochemical cycling, seismicity, and deep biosphere activity in subduction zones and suprasubduction zone lithosphere.International Ocean Discovery Program Expedition 366 was designed to address the nature of these processes in the shallow to intermediate depth of the Mariana subduction channel.Although no technology is available to permit direct sampling of the subduction channel of an intraoceanic convergent margin at depths up to 19 km, the Mariana forearc region (between the trench and the active volcanic arc) provides a means to access materials from this zone.Active conduits, resulting from fractures in the forearc, are prompted by along-and across-strike extension that allows slab-derived fluids and materials to ascend to the seafloor along associated faults, resulting in the formation of serpentinite mud volcanoes.Serpentinite mud volcanoes of the Mariana forearc are the largest mud volcanoes on Earth.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 the Mariana forearc and for billions of years on Earth.
Abstract In late 2016, the IODP Expedition 366 drilled 21 holes on summits and flanks of three serpentinite mud volcanoes (SMVs) of the Mariana Forearc: Yinazao (Blue Moon), Fantangisña (Celestial), and Asùt Tesoru (Big Blue). The drilling reached the forearc sediments underneath the SMVs only at Site U1498 where, according to data from this study, the biostratigraphic age of Fantangisña appears to be well constrained, with a pelagic cover on top of the serpentine mud flows of 0.44 Ma and an age of the forearc sediments of 11.21 Ma. With an estimated age of at least 10.77 Myr this is, to our knowledge, the oldest mud volcano ever dated. To link the age of the edifice with its eruptive dynamics, we performed rheological tests of natural samples of serpentine mud from the Fantangisña SMV for the first time. These experiments not only confirm the highly viscous characteristic of the mud breccia but also identify different muds' mineralogical compositions (i.e., serpentine‐rich vs. serpentine‐poor sediments) and water contents as being responsible for the main rheological variations. The viscosity from the rheological data, together with the physical properties of the mud breccia and the clasts measured onboard IODP366, under several assumptions, allow us to estimate of flow velocities and a depth of the mud source at ∼8.4 km below seafloor. Moreover, comparison of erupted mud breccia volumes from bathymetry, seismic data, and calculations shows how the SMV evolution is linked to episodic events, highlighting that Fantangisña has actively been expelling sediments during 2.41% of its life span.
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’.
Color reflectance data were measured on section halves using an integration sphere and a UV-VIS spectrophotometer mounted on the Section Half Multisensor Logger (SHMSL). Spectral counts are recorded in the range of 380 to 700 nm, covering the visible spectrum, and binned in ~2 nm bins. Spectral data are reduced from spectra and recorded in tristimulus XYZ values, CieLAB L*a*b* values, and other units.
Mud volcanoes in the Mediterranean Sea have been subject of scientific research since the 1970s and contributed to the understanding of these seafloor features and their role in the subduction budgets worldwide. Recently, the need to better characterize the connection of these mud volcanoes with the deeper lithologies of the accretionary prism and its implications led to expedition POS410 (2011) and SO278 (2020). During these expeditions, mud volcanoes which had been investigated in ODP Leg 160 (1996) were resampled and complemented with new sites along the Mediterranean Ridge accretionary complex. We present pore water data from six mud volcanoes and two brine pools in and around the Olimpi Mud Volcano Field (OMVF). The data highlight strong depletion in Cl (<200 mM), Na (∼200 mM), Mg and K (with concentrations ∼0 mM) and striking water isotope ratios (δ18O of +9.79‰ V-SMOW and δD of −26.33‰ V-SMOW), indicating dehydration of clay minerals at depth. At five locations, the interstitial waters are characterized by extremely high salinities (Cl > 5000 mM and Na >6500 mM), therefore drastically expanding the previous reports of highly saline pore waters in the OMVF. The measurements further reveal that Gelendzhik mud volcano, located in the western part of the OMVF along a major strike-slip fault, shows an unusual pore water downcore profile and its water isotopes signature differ strongly from the other structures (δ18O of +13.63‰ and δD of +1.83‰). Upon further investigation through XRF scans and hydrates stability calculations we tied the anomalous low salinity values of the Gelendzhik MV pore waters results from the presence of gas hydrates in the sediments. This is the first, indirect evidence of gas hydrates in the OMVF, several years after this hypothesis was formulated by De Lange and Brumsack (1998) and then quickly discarded.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
