Transcript PPT
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?