Numerical modeling of thermal structure, circulation of H2O, and magmatism–metamorphism in subduction zones: Implications for evolution of arcs

2007 ◽  
Vol 11 (1-2) ◽  
pp. 109-119 ◽  
Author(s):  
Hikaru Iwamori ◽  
Chris Richardson ◽  
Shigenori Maruyama
Keyword(s):  
Numerical Modeling ◽  
Subduction Zones ◽  
Thermal Structure

scholarly journals Large submarine earthquakes that occurred worldwide in a 1-year period (June 2013 to June 2014) – a contribution to the understanding of tsunamigenic potential

2015 ◽  
Vol 15 (10) ◽  
pp. 2183-2200 ◽  
Author(s):  
R. Omira ◽  
D. Vales ◽  
C. Marreiros ◽  
F. Carrilho
Keyword(s):  
Numerical Modeling ◽  
Subduction Zones ◽  
Source Parameters ◽  
Tsunami Generation ◽  
Earthquake Parameters ◽  
Shallow Earthquakes ◽  
Earthquake Source Parameters ◽  
Tsunami Numerical Modeling ◽  
Submarine Earthquakes ◽  
Earthquake Model

Abstract. This paper is a contribution to a better understanding of the tsunamigenic potential of large submarine earthquakes. Here, we analyze the tsunamigenic potential of large earthquakes which have occurred worldwide with magnitudes around Mw = 7.0 and greater during a period of 1 year, from June 2013 to June 2014. The analysis involves earthquake model evaluation, tsunami numerical modeling, and sensors' records analysis in order to confirm the generation of a tsunami (or lack thereof) following the occurrence of an earthquake. We also investigate and discuss the sensitivity of tsunami generation to the earthquake parameters recognized to control tsunami occurrence, including the earthquake location, magnitude, focal mechanism and fault rupture depth. Through this analysis, we attempt to understand why some earthquakes trigger tsunamis and others do not, and how the earthquake source parameters are related to the potential of tsunami generation. We further discuss the performance of tsunami warning systems in detecting tsunamis and disseminating the alerts. A total of 23 events, with magnitudes ranging from Mw = 6.7 to Mw = 8.1, have been analyzed. This study shows that about 39 % of the analyzed earthquakes caused tsunamis that were recorded by different sensors with wave amplitudes varying from a few centimeters to about 2 m. Tsunami numerical modeling shows good agreement between simulated waveforms and recorded waveforms, for some events. On the other hand, simulations of tsunami generation predict that some of the events, considered as non-tsunamigenic, caused small tsunamis. We find that most generated tsunamis were caused by shallow earthquakes (depth < 30 km) and thrust faults that took place on/near the subduction zones. The results of this study can help the development of modified and improved versions of tsunami decision matrixes for various oceanic domains.

Warm thermal structures in subduction zones lead to ample dehydration at the depths of deep slow slip and tremor and resultant transformations in viscous rheology 

2021 ◽  
Author(s):  
Cailey Condit ◽  
Victor Guevara ◽  
Melodie French ◽  
Adam Holt ◽  
Jonathan Delph
Keyword(s):  
Subduction Zones ◽  
Thermal Structure ◽  
Fluid Pressure ◽  
Plate Boundary ◽  
Pore Fluid ◽  
Seismogenic Zone ◽  
Plate Interface ◽  
Dehydration Reactions ◽  
Episodic Tremor And Slip ◽  
Increased Strength

&lt;p&gt;Feedbacks amongst petrologic and mechanical processes along the subduction plate boundary play a central role influencing slip behaviors and deformation styles. Metamorphic reactions, resultant fluid production, deformation mechanisms, and strength are strongly temperature dependent, making the thermal structure of these zones a key control on slip behaviors.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Firstly, we investigate the role of metamorphic devolatilization reactions in the production of Episodic Tremor and Slip (ETS) in warm subduction zones. Geophysical and geologic observations of ETS hosting subduction zones suggest the plate interface is fluid-rich and critically stressed, which together, suggests that this area is a zone of near lithostatic pore fluid pressure. &amp;#160;Fluids and high pore fluid pressures have been invoked in many models for ETS. However, whether these fluids are sourced from local dehydration reactions in particular lithologies, or via up-dip transport from greater depths remains an open question. We present thermodynamic models of the petrologic evolution of four lithologies typical of the plate interface along predicted pressure&amp;#8211;temperature (P-T) paths for the plate boundary along Cascadia, Nankai, and Mexico which all exhibit ETS at depths between 25-65 km. Our models suggest that 1-2 wt% H&lt;sub&gt;2&lt;/sub&gt;O is released at the depths of ETS along these subduction segments due to punctuated dehydration reactions within MORB, primarily through chlorite and/or lawsonite breakdown. These reactions produce sufficient in-situ fluid across this narrow P-T range to cause high pore fluid pressures. Punctuated dehydration of oceanic crust provides the dominant source of fluids at the base of the seismogenic zone in these warm subduction margins, and up-dip migration of fluids from deeper in the subduction zone is not required to produce ETS-facilitating high pore fluid pressures. These dehydration reactions not only produce metamorphic fluids at these depths, but also result in an increased strength of viscous deformation through the breakdown of weak hydrous phases (e.g., chlorite, glaucophane) and the growth of stronger minerals (e.g., garnet, omphacite, Ca-amphibole). Lastly, we present preliminary data on viscosity along warm subduction paths showing the locations of these dehydration pulses correlate with viscosity increases in mafic lithologies along the shallow forarc.&lt;/p&gt;

Exhumation of subducted mafic rocks in a dynamically evolving thermal structure: constraints from phase equilibria modelling

2021 ◽  
Author(s):  
Rilla C. McKeegan ◽  
Victor E. Guevara ◽  
Adam F. Holt ◽  
Cailey B. Condit
Keyword(s):  
Phase Equilibria ◽  
Subduction Zone ◽  
Subduction Zones ◽  
Mantle Wedge ◽  
Dynamic Models ◽  
Thermal Structure ◽  
Temporal Dependence ◽  
Subduction Channel ◽  
Mafic Rocks ◽  
Point Of No Return

&lt;p&gt;The dominant mechanisms that control the exhumation of subducted rocks and how these mechanisms evolve through time in a subduction zone remain unclear. Dynamic models of subduction zones suggest that their thermal structures evolve from subduction initiation to maturity. The series of metamorphic reactions that occur within the slab, resultant density, and buoyancy with respect to the mantle wedge will co-evolve with the thermal structure. We combine dynamic models of subduction zone thermal structure with phase equilibria modeling to place constraints on the dominant controls on the depth limits of exhumation. This is done across the temporal evolution of a subduction zone for various endmember lithologic associations observed in exhumed high-pressure terranes: sedimentary and serpentinite m&amp;#233;langes, and oceanic tectonic slices.&lt;/p&gt;&lt;p&gt;Initial modeling suggests that both serpentinite and sedimentary m&amp;#233;langes remain positively buoyant with respect to the mantle wedge throughout all stages of subduction (up to 65 Myr), and for the spectrum of naturally constrained ratios of mafic blocks to serpentinite/sedimentary matrix. In these settings, exhumation depth limits and the &amp;#8220;point of no return&amp;#8221; (c. 2.3 GPa) are not directly limited by buoyancy, but potentially rheological changes in the slab at the blueschist-eclogite transition stemming from: the switch from amphibole-dominated to pyroxene-dominated rheology and/or dehydration embrittlement. These mechanisms may increase the possibility of brittle failure and hence promote detachment of the slab top into the subduction channel. For the range of temperatures recorded by exhumed serpentinite m&amp;#233;langes, the locus of dehydration for altered MORB at the slab top coincides with the point of no return (2.3 GPa) between 35 and 40 Myr, suggesting a strong temporal dependence on deep exhumation in the subduction channel.&amp;#160;&lt;/p&gt;&lt;p&gt;Tectonic slices composed of 50% mafic rocks and 50% serpentinized slab mantle show a temporal dependence on the depth limits of positive buoyancy. For the range of temperatures recorded by exhumed tectonic slices, the upper pressure limit of positive buoyancy is ~2 GPa, and is only crossed between ~30 and 40 Myr after subduction initiation. Some exhumed tectonic slices record much higher pressures (2.5 GPa); thus, other mechanisms or lithologic combinations may also play a significant role in determining the exhumation limits of tectonic slices.&amp;#160;&lt;/p&gt;&lt;p&gt;Future work includes constraining how the loci of dehydration vary through time for different degrees of oceanic crust alteration, how exhumation limits and mechanisms may change with different subducting plate ages, and calculating how initial exhumation velocities may vary through time. Further comparison with the rock record will constrain the parameters that control the timing and limits of exhumation in subduction zones.&lt;/p&gt;

The thermal structure of subduction zones constrained by seismic imaging: Implications for slab dehydration and wedge flow

2006 ◽  
Vol 241 (3-4) ◽  
pp. 387-397 ◽  
Author(s):  
Geoffrey A. Abers ◽  
Peter E. van Keken ◽  
Erik A. Kneller ◽  
Aaron Ferris ◽  
Joshua C. Stachnik
Keyword(s):  
Subduction Zones ◽  
Seismic Imaging ◽  
Thermal Structure ◽  
Wedge Flow ◽  
Slab Dehydration

scholarly journals Shear heating reconciles thermal models with the metamorphic rock record of subduction

2018 ◽  
Vol 115 (46) ◽  
pp. 11706-11711 ◽  
Author(s):  
Matthew J. Kohn ◽  
Adrian E. Castro ◽  
Buchanan C. Kerswell ◽  
César R. Ranero ◽  
Frank S. Spear
Keyword(s):  
Heat Flow ◽  
Subduction Zones ◽  
Thermal Structure ◽  
Metamorphic Rocks ◽  
Shear Stresses ◽  
Thermal Models ◽  
Average Value ◽  
Temperature Conditions ◽  
Mechanical Models ◽  
Shear Heating

Some commonly referenced thermal-mechanical models of current subduction zones imply temperatures that are 100–500 °C colder at 30–80-km depth than pressure–temperature conditions determined thermobarometrically from exhumed metamorphic rocks. Accurately inferring subduction zone thermal structure, whether from models or rocks, is crucial for predicting metamorphic reactions and associated fluid release, subarc melting conditions, rheologies, and fault-slip phenomena. Here, we compile surface heat flow data from subduction zones worldwide and show that values are higher than can be explained for a frictionless subduction interface often assumed for modeling. An additional heat source––likely shear heating––is required to explain these forearc heat flow values. A friction coefficient of at least 0.03 and possibly as high as 0.1 in some cases explains these data, and we recommend a provisional average value of 0.05 ± 0.015 for modeling. Even small coefficients of friction can contribute several hundred degrees of heating at depths of 30–80 km. Adding such shear stresses to thermal models quantitatively reproduces the pressure–temperature conditions recorded by exhumed metamorphic rocks. Comparatively higher temperatures generally drive rock dehydration and densification, so, at a given depth, hotter rocks are denser than colder rocks, and harder to exhume through buoyancy mechanisms. Consequently––conversely to previous proposals––exhumed metamorphic rocks might overrepresent old-cold subduction where rocks at the slab interface are wetter and more buoyant than in young-hot subduction zones.

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