Shallow forearc mantle dynamics and geochemistry: New insights from IODP Expedition 366

Debret, Baptiste; Albers, Elmar; Walter, B.; Price, Roy E.; Barnes, J.; Beunon, Hugues; Facq, Sébastien; Gillikin, David P.; Mattielli, Nadine; Williams, Helen M.

doi:10.1016/j.lithos.2018.10.038

Cited by 45 publications

(56 citation statements)

References 102 publications

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“…If seismogenesis is temperature controlled, diagenetic and low‐grade metamorphic reactions occurring at temperatures as low as ~60 °C have the potential to create conditions that support stick‐slip behavior (Marcaillou et al, 2008; Moore & Saffer, 2001; Saffer & Tobin, 2011). However, recent estimates of temperature based on oxygen isotope thermometry suggest temperatures as high as 180 °C under Yinazao Seamount at 13‐km depth to slab (Debret et al, 2019), which is consistent with the hypothesis that the updip limit is controlled by the 100–150 °C isotherm.…”

Section: Discussionsupporting

confidence: 64%

Seismicity of the Incoming Plate and Forearc Near the Mariana Trench Recorded by Ocean Bottom Seismographs

Eimer

Wiens

Cai

et al. 2020

Geochem Geophys Geosyst

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Earthquakes near oceanic trenches are important for studying incoming plate bending and updip thrust zone seismogenesis, yet are poorly constrained using seismographs on land. We use an ocean bottom seismograph (OBS) deployment spanning both the incoming Pacific Plate and the forearc to study seismicity near the Mariana Trench. The yearlong deployment in 2012-2013 consisted of 20 broadband OBSs and 5 suspended hydrophones, with an additional 59 short period OBSs and hydrophones recording for 1 month. We locate 1,692 earthquakes using a nonlinear method with a 3D velocity model constructed from active source profiles and surface wave tomography results. Events occurring seaward of the trench occur to depths of~35 km below the seafloor, and focal mechanisms of the larger events indicate normal faulting corresponding to plate bending. Significant seismicity emerges about 70 km seaward from the trench, and the seismicity rate increases continuously towards the trench, indicating that the largest bending deformation occurs near the trench axis. These plate-bending earthquakes occur along faults that facilitate the hydration of the subducting plate, and the lateral and depth distribution of earthquakes is consistent with low-velocity regions imaged in previous studies. The forearc is marked by a heterogeneous distribution of low magnitude (<5 M w ) thrust zone seismicity, possibly due to the rough incoming plate topography and/or serpentinization of the forearc. A sequence of thrust earthquakes occurs at depths~10 km below seafloor and within 20 km of the trench axis, demonstrating that the megathrust is seismically active nearly to the trench. Plain Language Summary Studying earthquakes near oceanic trenches is important forunderstanding subduction zones but can be difficult using only distant land-based instruments. This study uses seismographs designed to work on the seafloor to study earthquakes near the central Mariana Trench. As the subducting plate bends, faults form due to the increased extensional stress. These faults can become pathways for water to penetrate into this subducting plate. Understanding the amount of water stored in the plate is essential for constraining the global water cycle, and the earthquake distribution allows us to determine the distribution of active faults. We found that the earthquakes occur shallower than 35-km depth and within 70 km seaward of the trench. We also study earthquakes occurring along the megathrust, which is the interface between the subducting plate and the overriding plate that is prone to seismic activity. We found that the earthquakes show a patchy distribution, indicating that the megathrust interface is not uniform. This could be related to topographic features on the subducting plate interacting with the plate above. We also observed earthquakes at depths shallower than 10 km below the seafloor, indicating that the megathrust can rupture close to the trench.

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Section: Discussionsupporting

confidence: 64%

Seismicity of the Incoming Plate and Forearc Near the Mariana Trench Recorded by Ocean Bottom Seismographs

Eimer

Wiens

Cai

et al. 2020

Geochem Geophys Geosyst

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“…A possible source is redissolution of anhydrite during fluid ascent. Furthermore, antigorite, which forms at >200°C above the slab at Asùt Tesoru (Debret et al, 2019), and breaks down during serpentinization to generate oxidizing conditions that lead to sulfate production (Debret and Sverjensky, 2017), might explain the high sulfate concentrations in high-pH fluids of Asùt Tesoru and Conical Seamount. This same mechanism of antigorite breakdown could also explain the increase in DIC concentrations at Asùt Tesoru (Figure 2D) and the high alkalinities of 33–62 meq kg −1 in high-pH subsurface pore fluids of Conical Seamount (Shipboard Scientific Party, 1990).…”

Section: Discussionmentioning

confidence: 99%

Origin of Short-Chain Organic Acids in Serpentinite Mud Volcanoes of the Mariana Convergent Margin

et al. 2019

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Serpentinitic systems are potential habitats for microbial life due to frequently high concentrations of microbial energy substrates, such as hydrogen (H 2 ), methane (CH 4 ), and short-chain organic acids (SCOAs). Yet, many serpentinitic systems are also physiologically challenging environments due to highly alkaline conditions (pH > 10) and elevated temperatures (>80°C). To elucidate the possibility of microbial life in deep serpentinitic crustal environments, International Ocean Discovery Program (IODP) Expedition 366 drilled into the Yinazao, Fantangisña, and Asùt Tesoru serpentinite mud volcanoes on the Mariana Forearc. These mud volcanoes differ in temperature (80, 150, 250°C, respectively) of the underlying subducting slab, and in the porewater pH (11.0, 11.2, 12.5, respectively) of the serpentinite mud. Increases in formate and acetate concentrations across the three mud volcanoes, which are positively correlated with temperature in the subducting slab and coincide with strong increases in H 2 concentrations, indicate a serpentinization-related origin. Thermodynamic calculations suggest that formate is produced by equilibrium reactions with dissolved inorganic carbon (DIC) + H 2 , and that equilibration continues during fluid ascent at temperatures below 80°C. By contrast, the mechanism(s) of acetate production are not clear. Besides formate, acetate, and H 2 data, we present concentrations of other SCOAs, methane, carbon monoxide, and sulfate, δ 13 C-data on bulk carbon pools, and microbial cell counts. Even though calculations indicate a wide range of microbial catabolic reactions to be thermodynamically favorable, concentration profiles of potential energy substrates, and very low cell numbers suggest that microbial life is scarce or absent. We discuss the potential roles of temperature, pH, pressure, and dispersal in limiting the occurrence of microbial life in deep serpentinitic environments.

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“…Strontium was extracted using columns loaded with ca. 70 µL of Sr-spec ion exchange resin (Triskem International) following a procedure adapted from Deniel and Pin (2001). The Sr was loaded on single Re filaments with Ta-oxide emitter and analyzed by ThermoScientific Triton-Plus TIMS (thermal ionization mass spectrometry) in the multidynamic acquisition mode at MARUM.…”

Section: Strontiummentioning

confidence: 99%

Fluid–rock interactions in the shallow Mariana forearc: carbon cycling and redox conditions

et al. 2019

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Abstract. Few data exist that provide insight into processes affecting the long-term carbon cycle at shallow forearc depths. To better understand the mobilization of C in sediments and crust of the subducting slab, we investigated carbonate materials that originate from the subduction channel at the Mariana forearc (< 20 km) and were recovered during International Ocean Discovery Program Expedition 366. Calcium carbonates occur as vein precipitates within metavolcanic and metasedimentary clasts. The clasts represent portions of the subducting lithosphere, including ocean island basalt, that were altered at lower blueschist facies conditions and were subsequently transported to the forearc seafloor by serpentinite mud volcanism. Euhedral aragonite and calcite and the lack of deformation within the veins suggest carbonate formation in a stress-free environment after peak metamorphism affected their hosts. Intergrowth with barite and marked negative Ce anomalies in carbonate attest the precipitation within a generally oxic environment, that is an environment not controlled by serpentinization. Strontium and O isotopic compositions in carbonate (87Sr∕86Sr = 0.7052 to 0.7054, δ18OVSMOW = 20 to 24 ‰) imply precipitation from slab-derived fluids at temperatures between ∼130 and 300 ∘C. These temperature estimates are consistent with the presence of blueschist facies phases such as lawsonite coexisting with the carbonates in some veins. Incorporated C is inorganic (δ13CVPDB = −1 ‰ to +4 ‰) and likely derived from the decarbonation of calcareous sediment and/or oceanic crust. These findings provide evidence for the mobilization of C in the downgoing slab at depths of < 20 km. Our study shows for the first time in detail that a portion of this C forms carbonate precipitates in the subduction channel of an active convergent margin. This process may be an important asset in understanding the deep carbon cycle since it highlights that some C is lost from the subducting lithosphere before reaching greater depths.

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Shallow forearc mantle dynamics and geochemistry: New insights from IODP Expedition 366

Cited by 45 publications

References 102 publications

Seismicity of the Incoming Plate and Forearc Near the Mariana Trench Recorded by Ocean Bottom Seismographs

Seismicity of the Incoming Plate and Forearc Near the Mariana Trench Recorded by Ocean Bottom Seismographs

Origin of Short-Chain Organic Acids in Serpentinite Mud Volcanoes of the Mariana Convergent Margin

Fluid–rock interactions in the shallow Mariana forearc: carbon cycling and redox conditions

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