Subduction zone metamorphic pathway for deep carbon cycling: I. Evidence from HP/UHP metasedimentary rocks, Italian Alps

Cook-Kollars, J.; Bebout, Gray E.; Collins, Nathan; Angiboust, Samuel; Agard, Philippe

doi:10.1016/j.chemgeo.2014.07.013

Cited by 95 publications

(116 citation statements)

References 121 publications

(236 reference statements)

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“…Bebout 1995Bebout , 2007bBebout , 2014Hilton et al, 2002;Jarrard, 2003;Dasgupta and Hirschmann, 2010;Dasgupta, 2013). The complexity and related uncertainty of these estimates are evident in the large ranges of published input flux estimates presented in Table 1 (also see Cook-Kollars et al, 2014). The combination of the uncertainties in the inputs and outputs results in a wide range in the estimates of volcanic arc return efficiency (16 -80% arc return of the C entering trenches; Table 1).…”

Section: Introductionmentioning

confidence: 91%

“…The coupling of external fluid-ingress and decarbonation within subducting slabs has been described in some studies of HP rocks (e.g., John et al, 2008;Ague and Nicolescu, 2014), and the opposite has also been described, with carbonation occurring along major intraslab fluid conduits (Beinlich et al, 2010;John et al, 2012). Closed-and open-system scenarios can produce drastically differing degrees of forearc devolatilization (Gorman et al, 2006; see the discussion by Cook-Kollars et al, 2014), pointing to the need for "ground-truthing" by detailed study of devolatilization and fluid mobility in exposures of HP/UHP-metamorphosed oceanic lithologies.…”

Section: Introductionmentioning

confidence: 94%

“…We integrate field and petrologic observations, theoretical calculations of devolatilization history (using the Perple_X software; Connolly, 2005), and O and C isotope data for these rocks, largely focusing on carbonate (and decarbonation history) but with some attention paid to the minor reduced C that could reside in the metabasalts. A companion paper (Cook-Kollars et al, 2014) A C C E P T E D M A N U S C R I P T (Martin and Tartarotti, 1989;Martin et al, 2008). These UHP eclogites contain pillow breccia with carbonate mineralogy varying from calcite to magnesite and often associated with chalcopyrite deposits.…”

Section: Introductionmentioning

confidence: 97%

“…Theoretical studies have calculated phase stabilities for sediments, oceanic crust, and ultramafic lithologies associated with inputs into subduction zones (Molina and Poli, 2000; A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 5 Kerrick and Connolly, 1998Connolly, , 2001aProyer, 2003;Connolly, 2005;Gorman et al, 2006;Cook-Kollars et al, 2014). Kerrick and Connolly (2001a) calculated mineral assemblages and volatiles concentrations for a wide range of sediment compositions, along subduction-zone P-T paths for modern margins, examining a closed-system model where decarbonation in subducting sediments allows CO 2 to be expelled from sediments without the influence of infiltrating, externally-derived H 2 O fluids.…”

Section: Introductionmentioning

confidence: 99%

“…The decarbonation and overall C loss history of deeply subducting AOC is particularly key to understanding subduction C cycling as this lithology could convey one-half to two-thirds of the subduction C input inventory into trenches (Table 1; see Dasgupta and Hirschmann, 2010; Dasgupta, 2013;Cook-Kollars et al, 2014). The C subduction input in carbonated ultramafic rocks is likely far smaller, but still a significant flux (see Alt et al, 2013; (Platt, 1986;Desmons et al, 1999a,b;Jolivet et al, 2003;Zheng, 2012), affording a more thorough assessment of prograde metamorphic devolatilization history (see Bebout, 2007a;Bebout et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

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Subduction zone metamorphic pathway for deep carbon cycling: II. Evidence from HP/UHP metabasaltic rocks and ophicarbonates

et al. 2015

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Exposures of low-grade metabasalts and ophicarbonates in the Northern Apennines, and their high- and ultrahigh-pressure metamorphic equivalents in the Western and Ligurian Alps and Tianshan (representing an overall peak P- T range of ~ 0.2-3.0. GPa, 200-610. °C), allow investigation of the effects of prograde metamorphic devolatilization, and other fluid-rock interactions, on degrees of retention and isotopic evolution of C in subducting oceanic crust and associated mantle rocks. Such work can inform models of C cycling at convergent margins, helping to constrain the efficiency of return of initially subducted C via arc volcanism and the fraction of this subducted C entering the deeper mantle beyond arcs. In the metabasaltic rocks, the preservation of finely disseminated carbonate with δ13C overlapping that of seafloor-altered protoliths, and the minimal mineralogical evidence of decarbonation, indicates large degrees of carbonate retention in this suite extending to UHP conditions similar to those beneath modern volcanic fronts. For many of the metabasalts, the δ18O of this carbonate can be explained by closed-system equilibration with silicate phases (e.g., garnet, clinopyroxene) during HP/UHP metamorphism. Larger volumes of carbonate preserved in interpillow regions and as breccia-filling largely escaped decarbonation, showing little or no evidence for reaction with adjacent metabasalt. Calculated devolatilization histories demonstrate that, in a closed-system model, carbonate in metabasaltic rocks can largely be preserved to depths approaching those beneath volcanic fronts (80-90km). Modeling of open-system behavior indicates that episodic infiltration of such rocks by H2O-rich fluids would have greatly enhanced decarbonation. Trends in O-C isotope composition of carbonate in some metabasaltic suites likely reflect effects of infiltration by externally-derived fluid with or without resulting decarbonation. Most carbonated ultramafic rocks similarly show little mineralogical evidence for decarbonation, consistent with calculated reaction histories, and have δ13C largely overlapping that of seafloor equivalents. However, the high-grade ophicarbonates show more restricted ranges in δ18O consistent with some control by infiltrating fluids, likely during subduction. This combination of field, petrographic, and isotopic evidence, together with calculated decarbonation histories, is consistent with minimal loss of CO2 from these rocks via decarbonation during forearc metamorphism. Combining our results with those of Cook-Kollars et al. (2014; Chemical Geology) for associated W. Alps metasedimentary rocks, we suggest that the majority of the CO2 (perhaps 80-90%, considering the full range of rock types) could be retained through forearcs in more intact volumes of subducting sediment, basalt, and ophicarbonate experiencing closed- or limited open-system conditions. Deep in forearcs and beneath arcs, decarbonation (and also carbonate dissolution) could be enhanced in shear zones and highly fractured volumes experiencin...

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Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Subduction zone metamorphic pathway for deep carbon cycling: II. Evidence from HP/UHP metabasaltic rocks and ophicarbonates

et al. 2015

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Probing the transition between seismically coupled and decoupled segments along an ancient subduction interface

Angiboust

Kirsch

Oncken

et al. 2015

Geochem Geophys Geosyst

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The transition zone at the downdip end of seismic coupling along subduction interfaces is often the site of megathrust earthquake nucleation and concentrated postseismic afterslip, as well as the focus site of episodic tremor and slip features. Exhumed remnants of the former Alpine subduction zone found in the Swiss Alps allow analyzing fluid and deformation processes near the transition zone region (30-40 km paleodepth). The Dent Blanche Thrust (DBT) is a lower blueschist-facies shear zone interpreted as a fossilized subduction interface where granitic mylonites overlie a metamorphosed accretionary wedge. We report field observations from the DBT region where multiple, several tens of meters thick foliated cataclastic networks are interlayered within the basal DBT mylonites. Petrological results and microstructural observations indicate that the various cataclasis events took place at near-peak metamorphic conditions (400-5008C, 1.1-1.3 GPa) during subduction of the Tethyan seafloor in Eocene times (42-48 Ma). Some of these networks exhibit mutual crosscutting relationships between mylonites, foliated cataclasites, and vein systems indicating mutual overprinting between brittle deformation and ductile creep. Whole-rock chemical compositions, in situ 40 Ar age data of recrystallized phengite, and Sr isotopic signatures reveal that DBT rocks also underwent multiple hydrofracturing and metasomatic events via the infiltration of fluids mainly derived from the oceanic metasediments underneath the DBT. From the rock fabrics, we infer strain rate fluctuations of several orders of magnitude beyond subduction strain rates (10 212 s 21) accompanied by fluctuation of supralithostatic and quasi-lithostatic fluid pressures (1 k > 0.95). DBT brittle-plastic deformation switches highlight the diversity of deformation processes and fluid-rock interactions in the transition zone region of the subduction interface.

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A revised budget for Cenozoic sedimentary carbon subduction

Clift

2017

Reviews of Geophysics

110

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Carbon plays a pivotal role in governing the climate and biosphere of Earth, yet quantification of carbon's long‐term cycling from the mantle to the surface remains contentious. Sedimentary carbon represents a significant part of the budget and can be recycled to the mantle if underthrust in subduction zones. I estimate that ~60 megaton per year (Mt/yr) is presently being subducted below the outer fore arc, 80% in the form of carbonate carbon, significantly more than previously estimated. Sedimentary carbon represents around two thirds of the total carbon input at the trenches. An additional 7 Mt/yr is averaged over the Cenozoic as a result of passive margin subduction during continental collision (~83% CaCO3). This revision brings the input and output budgets within the range of uncertainty. Degassing from arc volcanoes and fore arcs totals ~55 Mt/yr. When carbon in hydrothermal veins in the altered oceanic crust and serpentinized upper mantle is accounted for, a net flux to the mantle appears likely. The efficiency of carbon subduction is largely controlled by the carbonate contents of the sediment column and is partly linked to the latitude of the trench. Accretionary margins are the biggest suppliers of carbon to the mantle wedge, especially Java, Sumatra, Andaman‐Burma, and Makran, reflecting the inefficiency of offscraping, the thickness of the subducting sediment, and the trench length. The western Pacific trenches are negligible sinks of sedimentary carbon. Increases in deep‐sea carbonate in the Oligocene and middle Mesozoic had a large impact on the subduction budget, increasing it greatly compared to earlier times.

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Subduction zone metamorphic pathway for deep carbon cycling: I. Evidence from HP/UHP metasedimentary rocks, Italian Alps

Cited by 95 publications

References 121 publications

Subduction zone metamorphic pathway for deep carbon cycling: II. Evidence from HP/UHP metabasaltic rocks and ophicarbonates

Subduction zone metamorphic pathway for deep carbon cycling: II. Evidence from HP/UHP metabasaltic rocks and ophicarbonates

Probing the transition between seismically coupled and decoupled segments along an ancient subduction interface

A revised budget for Cenozoic sedimentary carbon subduction

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