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 ?
Radiogenic heat production
DT
(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?