Bending-related faulting and mantle serpentinization at deep-sea trenches

Grevemeyer, Ingo (2012) Bending-related faulting and mantle serpentinization at deep-sea trenches [Talk] In: The Lübeck Retreat, Collaborative Research Centre SFB 574 Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters, 23.05.-25.05.2012, Lübeck.

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The understanding of the Earth’s water cycle is inherently linked to the subduction of water at deep sea trenches. The transfer of water into the deep Earth’s interior is related to the alteration and hydration of the incoming lithosphere. The release of water from subducting lithospheres affects the composition of the mantle wedge, enhances partial melting and triggers intermediate-depth earthquakes. Water is transferred with the incoming plate into the subduction zone as water trapped
in sediments and open void spaces in the igneous crust and as chemically bound water in hydrous minerals in sediments and oceanic crust (Jarrad, 2003). However, if water reaches upper mantle rocks, significant amounts can be transferred into the deep subduction zone as water-bearing mineral serpentine (Peacock, 2004). Serpentinites have nearly the same chemical composition as mantle peridotite except that they contain approximately 13 wt% water in mineral structures. Seismic refraction and wide-angle data were collected at a number of active continental margins in the trench-outer rise to investigate the impact of bending related normal faulting on the seismic
properties of the oceanic lithosphere prior to subduction. Surveys provided data from offshore of Nicaragua (Grevemeyer et al., 2007; Ivandic et al., 2008), Chile (Contreras-Reyes et al., 2008), and Tonga (Contreras-Reyes et al., 2011). At all settings tomographic joint inversion of seismic refraction and wide-angle reflection data yielded anomalously low seismic P-wave velocities in the crust and uppermost mantle seaward of the trench axis. Crustal velocities are reduced by 0.2-0.8 km/s
compared to normal mature oceanic crust. Seismic velocities of the uppermost mantle are 7.4-7.8 km/s and hence 5-12% lower than the typical velocity of mantle peridotite. These systematic changes in P-wave velocity from the outer rise towards the trench axis indicate an evolutionary process in the subducting slab consistent with percolation of seawater through the faulted and fractured lithosphere and serpentinization of mantle peridotites. The observed velocity reduction suggests that mantle
serpentinization reaches 12-25%. Thus, processes occurring in the trench-outer rise affect indeed the Earth’s water cycle and indicate that significant amount of waters are transferred into the subducting lithosphere and hence carried to the deep Earth interior.
Contreras-Reyes, E., Grevemeyer, I., Flueh, E.R., and Reichert, C. (2008), Upper lithospheric structure of the subduction zone
offshore of southern Arauco peninsula, Chile, at 38°S, J. Geophys. Res., 113, B07303, doi:10.1029/2007JB005569.
Contreras-Reyes, E., Grevemeyer, I., Watts, A.B., Flueh, E.R., Peirce, C., Moeller, S., and Papenberg, C., 2011. Deep seismic
structure of the Tonga subduction zone: Implications for mantle hydration, tectonic erosion, and arc magmatism, J. Geophys.
Res., 116, doi:10.1029/2011JB008434.
Grevemeyer, I., Ranero, C.R., Flueh, E., Kläschen, D., Bialas, J. (2007). Passive and active seismological study of bendingrelated
faulting and mantle serpentinization at the Middle America trench. Earth Planet. Sci. Lett. 258, 528-542.
Ivandic, M., Grevemeyer, I., Berhorst, A., Flueh, E.R. and McIntosh, K. (2008), Impact of bending related faulting on the seismic
properties of the incoming oceanic plate offshore of Nicaragua, J. Geophys. Res., 113, B05410, doi:10.1029/2007JB005291.
Jarrad, R.D. (2003). Subduction fluxes of water, carbon dioxid, chlorine, and potassium. Geochemistry, Geophysics,
Geosystems 4: doi: 10.1029/2002GC000392.
Peacock, S.M. (2004). Insight into the hydrogeology and alteration of oceanic lithosphere based on subduction zones and arc
volcanisms. In: Davis E.E, Elderfield, H. (Eds.), Hydrogeology of Oceanic Lithosphere. Cambridge University Press, pp. 659-676.

Document Type: Conference or Workshop Item (Talk)
Research affiliation: OceanRep > SFB 754 > A5
OceanRep > SFB 574
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Related URLs:
Projects: SFB754
Date Deposited: 28 Aug 2012 09:58
Last Modified: 28 Aug 2012 09:58

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