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Carbon Cycling in Subduction Zones

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					         Carbon Cycling in
         Subduction Zones
implications for mantle-exosphere exchange
                          C




                      C




            Rajdeep Dasgupta
Modern-day fluxes and reservoirs of carbon




      http://earthobservatory.nasa.gov/Library/CarbonCycle
Modern-day fluxes and reservoirs of carbon
sediment
  crust
 mantle
             sediment                         basalt                        peridotite




(Sciutto and Ottonello, 1995; Kerrick & Connolly, 2001; Sleep and Zahnle, 2001; Jarrard, 2003; Alt, 2004)
Carbonated basalts




          (Yaxley and Green, 1994; Yaxley and Brey, 2004; Dasgupta et al., 2004, 2005)
Carbonated sediments




             (Thomsen and Schmidt, 2008; Tsuno and Dasgupta, submitted)
Carbonated peridotite




          (Wallace and Green, 1988; Falloon and Green, 1989; Dasgupta and Hirschmann, 2006)
How do we get carbon out of the slab in modern
subduction zones?

●    Fluid infiltration induced decarbonation of basalts and sediments
     (Molina and Poli, 2000; Connolley, 2005; Gormann et al., 2006; Poli et al., 2009)




                                (Gormann et al., 2006)
How do we get carbon out of the slab in modern
subduction zones?
●    Mantle wedge plume/ intrusions and sediment detachment ?




                                                       (Currie et al., 2007)




                                                      (Gerya and Yuen, 2003)
      Deep subduction of carbon in ancient past ?
                                     DT
Radiogenic heat production




                                                        (Sizova et al., 2010)




      Modern-style subduction may have initiated at 3.2-2.5 Ga, with T
      hotter than the present mantle by as much as ~175-200 oC
Subduction zone cycling of carbon through time

 • Modern Earth observes efficient ingassing
   of exosphere carbon and there is likely a
   net influx of surficial carbon into the deep
   mantle
 • More than 3 b.y. of the Earth’s history
   likely have seen inefficient ingassing of
   carbon to the interior
 • The residence of carbon in the mantle
   must have increased through time
Questions related to subduction zone carbon cycling
 • How variable is the behavior of carbonated sediments in
   subduction zones through space and time?

 • What is the influence of slab released carbon on mantle
   wedge melting? How does it alter the role of water and
   halogens on wedge melting?

 • What is the nature of metasomatic interaction between slab
   released (carbonated) melt and mantle wedge peridotite?

 • What is the carbon content of primary arc magmas? – how
   do we determine that?

 • What is the back-arc carbon flux? How does it differ from
   that of arc and MOR?

 • What is the behavior of reduced carbon?

				
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