Serpentinite in Active Suprasubduction-Zone Regions and Preserved Terrestrial Sections: Observations; Modeling; and Implications
Abstract
Exposures of serpentinized mantle of the overriding plate in the trench-proximal regions of nonaccretionary, intraoceanic forearcs have been extensively studied. Deposits of what were formerly called "sedimentary" serpentinite bodies on land are well documented all over the world. The deposits are variously categorized as mylonitized peridotite that was metamorphosed after obduction of an ophiolite section; olistostromes derived from sections of fault-exposed, serpentinized mantle; diapiric intrusions from point sources or along faults (as ridges); and flows from serpentinite mud volcanoes. The structures and compositions of serpentinite exposures help to differentiate between potential origins and protoliths. Theoretical studies of dehydration reactions, coupled with models of the thermal structure of subduction zones, provide constraints on the nature of fluids liberated from the subducting slab for various convergence angles and rates. These fluids are the source for serpentinization of the suprasubduction-zone mantle. The parameters for degree and distribution of serpentinite in such environments must be, however, constrained in each instance by the forcing functions operating within a given convergent margin. Spatial, i.e., down-dip increases in temperature and pressure vary with convergence angle and rate. Whereas most models assume continuous dehydration of the slab, in reality dehydration events are likely episodic and thus temporal effects must also be considered. We know that suprasubduction-zone serpentinization can begin early in the evolution of a convergent margin and that extensive faulting of a forearc region is necessary for emplacement of serpentinite deposits on the seafloor in active margins. Recent studies of Archean exposures of serpentinized peridotitic deposits suggest that the processes we observe in today's active convergent margins likely also took place during the earliest stages of tectonic cycling of the Earth's lithosphere. The implications for such processes help to lend credence to recent hypotheses regarding the link between serpentinization and the potential origins of life on Earth.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.V52A..05F
- Keywords:
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- 0448 BIOGEOSCIENCES / Geomicrobiology;
- 3060 MARINE GEOLOGY AND GEOPHYSICS / Subduction zone processes;
- 3660 MINERALOGY AND PETROLOGY / Metamorphic petrology