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Martin Reyners - One of the best experts on this subject based on the ideXlab platform.
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three dimensional imaging of impact of a large igneous province with a Subduction Zone
Earth and Planetary Science Letters, 2017Co-Authors: Martin Reyners, Donna Eberhartphillips, Phaedra Upton, David GubbinsAbstract:Abstract How the thickened crust of a large igneous province on an incoming oceanic plate is accommodated at a Subduction Zone remains an open question. New Zealand is one of the few places to study this, as at ca. 105 Ma the ca. 35 km-thick Hikurangi Plateau impacted the Gondwana Subduction Zone in what is now the South Island. Here we report on results from a forty-station portable seismograph array in the southern South Island, designed to delineate the leading edge of the subducted plateau. Three-dimensional images of Vp and Vp/Vs reveal the southwestern part of the plateau was a relatively narrow salient, and the first part to be subducted. The plateau then rotated clockwise about this salient until the southern edge of the plateau was parallel to Subduction strike and Subduction ceased at ca. 100 Ma. Our results suggest that the global-scale plate reorganization event at 105–100 Ma was due to a cessation of Subduction caused by the Hikurangi Plateau choking the Gondwana Subduction Zone, rather than the Subduction of mid ocean ridges as previously proposed. The choking of Gondwana Subduction by the plateau also led to a concentration of slab pull in the adjacent subducted oceanic crust, explaining the episode of basin opening and intraplate magmatism there that occurred at the same time. Our study underlines the havoc caused by impact of a large igneous province with a Subduction Zone.
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Revised Interface Geometry for the Hikurangi Subduction Zone, New Zealand
Seismological Research Letters, 2013Co-Authors: Charles A. Williams, Martin Reyners, Donna Eberhart-phillips, Stephen Bannister, D. Barker, Stuart Henrys, Rupert SutherlandAbstract:Online Material: GMT .grd file and Python script to evaluate interface geometry. The Hikurangi Subduction Zone extends along the eastern North Island of New Zealand southward into the northern portion of the South Island. It has drawn considerable recent attention due to the potential for large and/or tsunamigenic earthquakes, and both shallow and deep slow slip events (SSEs), as discussed in the next section. With such a wide range of seismic and aseismic behavior, the Hikurangi margin is an ideal natural laboratory for testing various types of Subduction Zone models. Furthermore, the possibility of a devastating megathrust earthquake also requires the development of models to evaluate the potential damage caused by such an event. A necessary first step in the development of such models is an accurate representation of the Subduction thrust geometry. Accurate knowledge of the interface geometry is critical in dynamic rupture simulations, in providing the boundary conditions for tsunami simulations, and in geodetic inversions for interseismic coupling, coseismic slip, and SSE slip distributions. Current geodetic inversions (see Wallace et al. [2009] for a summary) make use of the interface geometry defined by Ansell and Bannister (1996), hereafter referred to as AB1996. This geometry was defined using a combination of microearthquake seismicity, the depth of thrust events, the depth of S to P conversions, and deep reflection seismic studies. Combining these datasets, AB1996 were able to define a parametric representation of the thrust interface in terms of a gently tapering conical surface. This representation provided a simple method for querying the depth to the interface at any desired point. The importance of providing an easy‐to‐use description of slab geometry for Subduction Zones worldwide has been recognized, and is being addressed by projects such …
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microseismicity but no tremor accompanying slow slip in the hikurangi Subduction Zone new zealand
Earth and Planetary Science Letters, 2009Co-Authors: E J Delahaye, Martin Reyners, John Townend, G RogersAbstract:Abstract Geodetically-detected episodes of slow slip appear in several Subduction Zones to be accompanied by bursts of low-frequency coherent noise known as seismic tremor, but whether a single physical process governs this association or even whether slow slip is invariably accompanied by tremor remains unresolved. Detailed analysis of broadband seismic data spanning a slow slip episode in the Hikurangi Subduction Zone, New Zealand, reveals that slow slip was accompanied by distinct reverse-faulting microearthquakes, rather than tremor. The timing, location, and faulting style of these earthquakes are consistent with stress triggering down-dip of the slow slip patch, either on the Subduction interface or just below it. These results indicate that tremor is not ubiquitous during Subduction Zone slow slip, and that slow slip in Subduction Zone environments is capable of triggering high-frequency earthquakes near the base of the locked Subduction thrust. In this and other locations (Hawaii, Boso Peninsula) where slow slip is accompanied by triggered microseismicity, the estimated upper extent of the slow slip is shallower (less than ~ 20 km) than in those locations from which tremor has been reported. This suggests that ambient temperature- or pressure-dependent factors govern the character of the seismic response to slow slip on Subduction thrusts and other large faults, with rheological or lithological conditions at shallow depths triggering high-frequency microearthquakes and those at greater depths triggering seismic tremor.
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Plate coupling and the hazard of large Subduction thrust earthquakes at the Hikurangi Subduction Zone, New Zealand
New Zealand Journal of Geology and Geophysics, 1998Co-Authors: Martin ReynersAbstract:Abstract Recent dense deployments of portable seismographs along the Hikurangi Subduction Zone have provided insights into the structure and seismic strain regime of the subducted and overlying plates, and the nature of plate coupling at the shallow part of the plate interface. Beneath Marlborough, the plates appear to be permanently locked, and large Subduction thrust events are not expected. In the Wellington and Wairarapa regions, the plates appear to be strongly coupled over a downdip width of the plate interface of c. 70 km. Subduction thrust earthquakes of about MW 8.0 are estimated for this region. Farther to the northeast, the downdip width of the inferred locked portion of the plate interface progressively decreases, and Subduction thrust events of about MW 6.9 are estimated for the northern part of the Raukumara Peninsula. In the south of the Subduction Zone, changes in coupling arise principally from changes in the thickness of the subducted plate, whereas in the north they are mainly due to ch...
Craig E Manning - One of the best experts on this subject based on the ideXlab platform.
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Subduction-Zone Fluids
Elements, 2020Co-Authors: Craig E Manning, Maria Luce FrezzottiAbstract:Fluids are essential to the physical and chemical processes in Subduction Zones. Two types of Subduction-Zone fluids can be distinguished. First, shallow fluids, which are relatively dilute and water rich and that have properties that vary between Subduction Zones depending on the local thermal regime. Second, deep fluids, which possess higher proportions of dissolved silicate, salts and non-polar gases relative to water content, and have properties that are broadly similar in most Subduction systems, regardless of the local thermal structure. We review key physical and chemical properties of fluids in two key Subduction-Zone contexts—along the slab top and beneath the volcanic front—to illustrate the distinct properties of shallow and deep Subduction-Zone fluids.
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implications for metal and volatile cycles from the ph of Subduction Zone fluids
Nature, 2016Co-Authors: Matthieu E Galvez, James A D Connolly, Craig E ManningAbstract:A thermodynamic model of fluid pH and its variability in Earth’s mantle and subducting crust highlights chemical feedbacks that connect deep Earth to surface processes. Matthieu Galvez and co-authors present thermodynamic predictions of fluid–rock equilibria that tie together models of Subduction-Zone thermal structure, mineralogy and fluid speciation. They find that the pH of fluids in subducted crustal lithologies is uniform and confined to a mildly alkaline range, controlled by rock volatile and chlorine contents, but that the pH of mantle wedge fluids exhibits marked sensitivity to minor variations in rock chemistry. They conclude that this sensitivity of fluid chemistry to carbon, alkali metals and halogens illustrates a feedback between Earth's atmosphere–ocean chemistry and the speciation of Subduction-Zone fluids via the hydrothermally altered oceanic lithosphere. The chemistry of aqueous fluids controls the transport and exchange—the cycles—of metals1,2,3,4,5 and volatile elements3,6,7 on Earth. Subduction Zones, where oceanic plates sink into the Earth’s interior, are the most important geodynamic setting for this fluid-mediated chemical exchange2,6,7,8,9,10. Characterizing the ionic speciation and pH of fluids equilibrated with rocks at Subduction Zone conditions has long been a major challenge in Earth science11,12. Here we report thermodynamic predictions of fluid–rock equilibria that tie together models of the thermal structure, mineralogy and fluid speciation of Subduction Zones. We find that the pH of fluids in subducted crustal lithologies is confined to a mildly alkaline range, modulated by rock volatile and chlorine contents. Cold Subduction typical of the Phanerozoic eon13 favours the preservation of oxidized carbon in subducting slabs. In contrast, the pH of mantle wedge fluids is very sensitive to minor variations in rock composition. These variations may be caused by intramantle differentiation, or by infiltration of fluids enriched in alkali components extracted from the subducted crust. The sensitivity of pH to soluble elements in low abundance in the host rocks, such as carbon, alkali metals and halogens, illustrates a feedback between the chemistry of the Earth’s atmosphere–ocean system14,15 and the speciation of Subduction Zone fluids via the composition of the seawater-altered oceanic lithosphere. Our findings provide a perspective on the controlling reactions that have coupled metal and volatile cycles in Subduction Zones for more than 3 billion years77.
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the chemistry of Subduction Zone fluids
Earth and Planetary Science Letters, 2004Co-Authors: Craig E ManningAbstract:Subduction Zones generate voluminous magma and mediate global element cycling. Fluids are essential to this activity, yet their behavior is perhaps the most poorly understood aspect of the Subduction process. Though many volatile components are subducted, H2O is the most abundant, is preferentially fractionated into the fluid phase, and, among terrestrial volatiles, is by far the most effective solvent. H2O therefore controls the chemical properties of Subduction-Zone fluids. Rising pressure (P) and temperature (T) along Subduction paths yield increased H2O ionization, which enhances dissolved solute concentrations. Under appropriate conditions, silicate solubilities may become so high that there is complete miscibility between hydrous melts and dilute aqueous solutions. Miscible fluids of intermediate composition (e.g., 50% silicate, 50% H2O) are commonly invoked as material-transport agents in Subduction Zones; however, phase relations pose problems for their existence over significant length scales in the mantle. Nevertheless, this behavior provides a key clue pointing to the importance of polymerization of alkali aluminosilicate components in deep fluids. Aqueous aluminosilicate polymers may enhance solubility of important elements even in H2O-rich fluids. Subduction-Zone fluids may be surprisingly dilute, having only two to three times the total dissolved solids (TDS) of seawater. Silica and alkalis are the dominant solutes, with significant Al and Ca and low Mg and Fe, consistent with a role for aqueous aluminosilicate polymers. Trace-element patterns of fluids carrying only dissolved silicate components are similar to those of primitive island-arc basalts, implying that reactive flow of H2O-rich, Cl-poor, alkali-aluminosilicate-bearing fluid is fundamental to element transport in the mantle wedge. Better understanding of the interaction of this fluid with the mantle wedge requires quantitative reaction-flow modeling, but further studies are required to achieve this goal.
Christopher Beaumont - One of the best experts on this subject based on the ideXlab platform.
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Subduction Zone decoupling/retreat modeling explains south Tibet (Xigaze) and other supra-Subduction Zone ophiolites and their UHP mineral phases
Earth and Planetary Science Letters, 2017Co-Authors: J. P. Butler, Christopher BeaumontAbstract:Abstract The plate tectonic setting in which proto-ophiolite ‘oceanic’ lithosphere is created remains controversial with a number of environments suggested. Recent opinions tend to coalesce around supra-Subduction Zone (SSZ) forearc extension, with a popular conceptual model in which the proto-ophiolite forms during foundering of oceanic lithosphere at the time of spontaneous or induced onset of Subduction. This mechanism is favored in intra-oceanic settings where the subducting lithosphere is old and the upper plate is young and thin. We investigate an alternative mechanism; namely, decoupling of the subducting oceanic lithosphere in the forearc of an active continental margin, followed by Subduction Zone (trench) retreat and creation of a forearc oceanic rift basin, containing proto-ophiolite lithosphere, between the continental margin and the retreating Subduction Zone. A template of 2D numerical model experiments examines the trade-off between strength of viscous coupling in the lithospheric Subduction channel and net slab pull of the subducting lithosphere. Three tectonic styles are observed: 1) C, continuous Subduction without forearc decoupling; 2) R, forearc decoupling followed by rapid Subduction Zone retreat; 3) B, breakoff of subducting lithosphere followed by re-initiation of Subduction and in some cases, forearc decoupling (B-R). In one case (BA-B-R; where BA denotes backarc) Subduction Zone retreat follows backarc rifting. Subduction Zone decoupling is analyzed using frictional-plastic yield theory and the Stefan solution for the separation of plates containing a viscous fluid. The numerical model results are used to explain the formation of Xigaze group ophiolites, southern Tibet, which formed in the Lhasa terrane forearc, likely following earlier Subduction and not necessarily during Subduction initiation. Either there was normal coupled Subduction before Subduction Zone decoupling, or precursor slab breakoff, Subduction re-initiation and then decoupling. Rapid deep upper-mantle circulation in the models during Subduction Zone retreat can exhume and emplace material in the forearc proto-ophiolite from as deep as the mantle transition Zone, thereby explaining diamonds and other 10–15 GPa UHP phases in Tibetan ophiolites.
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effect of a retreating Subduction Zone on deformation in simple regions of plate convergence
Journal of Geophysical Research, 1996Co-Authors: Paula Waschbusch, Christopher BeaumontAbstract:Plane strain, two-dimensional, finite element models are used to calculate deformation patterns within model mountain belt systems where Subduction Zone retreat (the process by which space is created between the subducting (“pro”) and overriding (“retro”) lithospheres either by motion of one or both) is active. The model uses Coulomb plastic and thermally activated power law viscous rheologies. Overall deformation is determined by balancing the internal strength of the model layer against the sum of applied boundary stresses plus the gravitational stress induced by mass redistribution within the deforming model. The effect of incorporating retreat in the Subduction setting diffuses deformation, as the moving (retreating) Subduction Zone deforms a larger cross-sectional area of material for a shorter period of time than equivalent models without Subduction Zone retreat. Material is deformed while within the Subduction Zone, but once the material has passed completely through the moving Subduction Zone it is passively appended onto the retrolithosphere and is no longer deformed. Thus, relative to a convergent setting without Subduction Zone retreat, the retreating convergent Zone has an areally extensive Zone of simple deformation. A deformation factor, γ, is derived which characterizes the deformation (shortening) the material experienced within the Subduction Zone. Variable γ is the ratio of convergence rate (rate at which material enters the Subduction Zone) to Subduction rate (rate at which material is subducted). Variables γ and f, the fraction of the layer that is subducted, together determine the dominant style of deformation in the orogenic Zone. Subduction Zone retreat is shown to have significant and predictable effects on the model morphology (e.g., basin or mountain formation) and on the model geology (e.g., its presence suggests lower topography, lower metamorphic grade rocks at the surface, and simpler deformational structures), which agree with observations.
Wouter Pieter Schellart - One of the best experts on this subject based on the ideXlab platform.
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How weak is the Subduction Zone interface
Geophysical Research Letters, 2015Co-Authors: João C. Duarte, Wouter Pieter Schellart, Alexander R CrudenAbstract:Several lines of evidence suggest that Subduction Zones are weak and that the unique availability of water on Earth is a critical factor in the weakening process. We have evaluated the strength of Subduction Zone interfaces using two approaches: (i) from empirical relationships between shear stress at the interface and Subduction velocity, deduced from laboratory experiments; and (ii) from a parametric study of natural Subduction Zones that provides new insights on Subduction Zone interface strength. Our results suggest that Subduction is only mechanically feasible when shear stresses along the plate interface are relatively low (less than ∼35 MPa). To account for this requirement, we propose that there is a feedback mechanism between Subduction velocity, water released from the subducting plate, and weakening of the fore-arc mantle that may explain how relatively low shear stresses are maintained at Subduction interfaces globally.
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Global correlations between maximum magnitudes of Subduction Zone interface thrust earthquakes and physical parameters of Subduction Zones
Physics of the Earth and Planetary Interiors, 2013Co-Authors: Wouter Pieter Schellart, Nicholas RawlinsonAbstract:Abstract The maximum earthquake magnitude recorded for Subduction Zone plate boundaries varies considerably on Earth, with some Subduction Zone segments producing giant Subduction Zone thrust earthquakes (e.g. Chile, Alaska, Sumatra–Andaman, Japan) and others producing relatively small earthquakes (e.g. Mariana, Scotia). Here we show how such variability might depend on various Subduction Zone parameters. We present 24 physical parameters that characterize these Subduction Zones in terms of their geometry, kinematics, geology and dynamics. We have investigated correlations between these parameters and the maximum recorded moment magnitude ( M W ) for Subduction Zone segments in the period 1900–June 2012. The investigations were done for one dataset using a geological Subduction Zone segmentation (44 segments) and for two datasets (rupture Zone dataset and epicenter dataset) using a 200 km segmentation (241 segments). All linear correlations for the rupture Zone dataset and the epicenter dataset (| R | = 0.00–0.30) and for the geological dataset (| R | = 0.02–0.51) are negligible-low, indicating that even for the highest correlation the best-fit regression line can only explain 26% of the variance. A comparative investigation of the observed ranges of the physical parameters for Subduction segments with M W > 8.5 and the observed ranges for all Subduction segments gives more useful insight into the spatial distribution of giant Subduction thrust earthquakes. For segments with M W > 8.5 distinct (narrow) ranges are observed for several parameters, most notably the trench-normal overriding plate deformation rate ( v OPD⊥ , i.e. the relative velocity between forearc and stable far-field backarc), trench-normal absolute trench rollback velocity ( v T⊥ ), Subduction partitioning ratio ( v SP⊥ / v S⊥ , the fraction of the Subduction velocity that is accommodated by subducting plate motion), Subduction thrust dip angle ( δ ST ), Subduction thrust curvature ( C ST ), and trench curvature angle ( α T ). The results indicate that M W > 8.5 Subduction earthquakes occur for rapidly shortening to slowly extending overriding plates (−3.0 ⩽ v OPD⊥ ⩽ 2.3 cm/yr), slow trench velocities (−2.9 ⩽ v T⊥ ⩽ 2.8 cm/yr), moderate to high Subduction partitioning ratios ( v SP⊥ / v S⊥ ⩽ 0.3–1.4), low Subduction thrust dip angles ( δ ST ⩽ 30°), low Subduction thrust curvature ( C ST ⩽ 2.0 × 10 −13 m −2 ) and low trench curvature angles (−6.3° ⩽ α T ⩽ 9.8°). Epicenters of giant earthquakes with M W > 8.5 only occur at trench segments bordering overriding plates that experience shortening or are neutral ( v OPD⊥ ⩽ 0), suggesting that such earthquakes initiate at mechanically highly coupled segments of the Subduction Zone interface that have a relatively high normal stress (deviatoric compression) on the interface (i.e. a normal stress asperity). Notably, for the three largest recorded earthquakes (Chile 1960, Alaska 1964, Sumatra–Andaman 2004) the earthquake rupture propagated from a Zone of compressive deviatoric normal stress on the Subduction Zone interface to a region of lower normal stress (neutral or deviatoric tension). Stress asperities should be seen separately from frictional asperities that result from a variation in friction coefficient along the Subduction Zone interface. We have developed a global map in which individual Subduction Zone segments have been ranked in terms of their predicted capability of generating a giant Subduction Zone earthquake ( M W > 8.5) using the six most indicative Subduction Zone parameters ( v OPD⊥ , v T⊥ , v SP⊥ / v S⊥ , δ ST , C ST and α T ). We identify a number of Subduction Zones and segments that rank highly, which implies a capability to generate M W > 8.5 earthquakes. These include Sunda, North Sulawesi, Hikurangi, Nankai-northern Ryukyu, Kamchatka-Kuril-Japan, Aleutians-Alaska, Cascadia, Mexico-Central America, South America, Lesser Antilles, western Hellenic and Makran. Several Subduction segments have a low score, most notably Scotia, New Hebrides and Mariana.
G Rogers - One of the best experts on this subject based on the ideXlab platform.
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microseismicity but no tremor accompanying slow slip in the hikurangi Subduction Zone new zealand
Earth and Planetary Science Letters, 2009Co-Authors: E J Delahaye, Martin Reyners, John Townend, G RogersAbstract:Abstract Geodetically-detected episodes of slow slip appear in several Subduction Zones to be accompanied by bursts of low-frequency coherent noise known as seismic tremor, but whether a single physical process governs this association or even whether slow slip is invariably accompanied by tremor remains unresolved. Detailed analysis of broadband seismic data spanning a slow slip episode in the Hikurangi Subduction Zone, New Zealand, reveals that slow slip was accompanied by distinct reverse-faulting microearthquakes, rather than tremor. The timing, location, and faulting style of these earthquakes are consistent with stress triggering down-dip of the slow slip patch, either on the Subduction interface or just below it. These results indicate that tremor is not ubiquitous during Subduction Zone slow slip, and that slow slip in Subduction Zone environments is capable of triggering high-frequency earthquakes near the base of the locked Subduction thrust. In this and other locations (Hawaii, Boso Peninsula) where slow slip is accompanied by triggered microseismicity, the estimated upper extent of the slow slip is shallower (less than ~ 20 km) than in those locations from which tremor has been reported. This suggests that ambient temperature- or pressure-dependent factors govern the character of the seismic response to slow slip on Subduction thrusts and other large faults, with rheological or lithological conditions at shallow depths triggering high-frequency microearthquakes and those at greater depths triggering seismic tremor.
