Blueschist metamorphism in an active subduction zone

Maekawa, Hirokazu; Shozul, Masaya; Ishll, Teruaki.; Fryer, Patricia; Pearce, Julian A.

doi:10.1038/364520a0

Cited by 165 publications

(102 citation statements)

References 18 publications

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“…The estimate assumes (1) that the subducting Pacific plate is a smooth surface (i.e., has carried no subducted seamounts down, although the drilling results show it has), (2) that the trench itself is unperturbed by interaction with subducting seamounts and thus subtends a smooth curve that is an average of the thalweg position ) (bathymetry maps; e.g., Figure F1) (however, there are significant perturbations associated with impact from Pacific seamounts entering the trench), (3) that the plate subducts along the shortest perpendicular to a tangent of that average curve and that the distance of the seamount summit from the trench can be determined by measuring along that perpendicular, (4) that the angle of convergence between the Pacific plate and the trench lies along that perpendicular (though it does not), and (5) that paragenesis models using equilibrium assemblages of metamorphic minerals in subduction-channel-derived rocks recovered from coring and drilling on these two edifices do not fit a graphic model for depth to slab beneath the seamounts. The paragenesis models are described fully in Maekawa et al (1993), , and Gharib (2006). Therefore, we used the depths of the three seamounts cored during this expedition, as estimated by MCS data, to fit a line defining a depth versus distance from the curve representing an average of the trench position and extrapolated that line to the distances of the summits of Conical and South Chamorro Seamounts as measured along the perpendicular to the tangent of the average trench-curve to establish an estimate for the depths to slab beneath those seamounts.…”

Section: Coring Resultsmentioning

confidence: 99%

“…Critical parameters of the deep-sourced fluid from five Mariana serpentinite mud volcanoes. Depth-to-slab was determined by seismic reflection profile for Yinazao, Fantangisña, and Asùt Tesoro Seamounts (Oakley et al, 2007(Oakley et al, , 2008Oakley, 2008), and by equilibrium mineral assemblages in metamafic clasts for South Chamorro and Conical Seamounts (Maekawa et al, 1993;Gharib, 2006). Distance to trench and temperature of slab from Hulme et al (2010).…”

Section: Introductionmentioning

confidence: 99%

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Mariana Convergent Margin and South Chamorro Seamount

Fryer¹,

Wheat²,

Williams³

et al. 2018

Proceedings of the International Ocean Discovery Program

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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.At least 19 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 farthest from the Mariana Trench at 86 and 78 km, respectively. Both seamounts were cored during Ocean Drilling Program 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 up to 19 km. Understanding such processes is necessary for elucidating factors that control seismicity in convergent margins, tectonic and magma genesis processes in the volcanic arc and backarc areas, fluid and material fluxes, and the nature and variability of environmental conditions that impact subseafloor microbial communities.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 ...

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Section: Coring Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mariana Convergent Margin and South Chamorro Seamount

Fryer¹,

Wheat²,

Williams³

et al. 2018

Proceedings of the International Ocean Discovery Program

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show abstract

“…In the Mariana and Izu-Bonin forearc, two serpentinite seamounts were drilled during Ocean Drilling Program Legs 125 [Fryer and Mottl, 1992] and 195 ( M. Salisbury et al, Leg 195 scientific prospectus: Mariana convergent margin/West Philippine Sea seismic observatory, available at http://www-odp.tamu.edu/publications). These seamounts form as MVs, composed of undercompacted serpentine mudflows, or as horst blocks of serpentinized ultramafics that diapirically intruded the leading edge of the overlying plate [Maekawa et al, 1993]. As many as 100 up to 30-km-wide and 2-km-high features have been reported from the Mariana forearc as being 50 -120 km behind the trench axis [Fryer et al, 1985].…”

Section: A40 Marianasmentioning

confidence: 99%

Significance of Mud Volcanism

Kopf

2002

Reviews of Geophysics

746

646

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Mud volcanism and diapirism have puzzled geoscientists for ∼2 centuries. They have been described onshore and offshore in many places on Earth, and although they occur in various tectonic settings, the majority of the features known to date are located in compressional tectonic scenarios. This paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described. Mud volcanoes show variable geometry (up to tens of kilometers in diameter and several hundred meters in height) and a great diversity regarding the origin of the fluid and solid phases. Gas (predominantly methane), water, and mud may be mobilized at subbottom depth of only a few meters but, in places, can originate from several kilometers depth (with minor crustal or mantle input). The possible contribution of mud extrusion to global budgets, both from quiescent fluid emission and from the extrusive processes themselves, is important. In regions where mud volcanoes are abundant, such as the collision zones between Africa and Eurasia, fluid flux through mud extrusion exceeds the compaction‐driven pore fluid expulsion of the accretionary wedge. Also, quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and, hence, to greenhouse climate.

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“…These processes are well known by sedimentologists and neotectonics specialists, as they are responsible for intrusive sediments and seismically-induced mud and sand volcanoes. This process is suggested to explain some of the blueschisteclogite-serpentine associations of California and even, perhaps, the coesite rocks of the Italian Alps (see Barriga et al 1992;Maekawa et al 1993). …”

Section: Subduction and Fluids: Subduction-induced Mantle Convectionmentioning

confidence: 99%

The water inventory of the Earth: fluids and tectonics

Fyfe¹

1994

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Abstract:As the human population continues to expand, to approach ten billion, there will be an increasing demand upon all Earth's resources. Of particular importance will be resources related to energy, soil and water, all of which involve geofluids. Problems associated with waste disposal also involve systems for protecting near-surface water quality. There is an urgent need to quantify the fluid inventory and fluid dynamics of the near surface, while understanding volatiles and their deep recycling is fundamental to our understanding of the major dynamic processes of the Earth.

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Blueschist metamorphism in an active subduction zone

Cited by 165 publications

References 18 publications

Mariana Convergent Margin and South Chamorro Seamount

Mariana Convergent Margin and South Chamorro Seamount

Significance of Mud Volcanism

The water inventory of the Earth: fluids and tectonics

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