HR: 08:50h
AN: V51F-04    [Abstracts]
TI: Diamonds From the Asthenosphere and Transition Zone: Remnants of Subducted Crustal Material in the Deep Earth's Mantle
AU: * Tappert, R
EM: rtappert@ualberta.net
AF: University of Alberta, Department of Earth and Atmospheric Sciences, 1-26 Earth Science Building, Edmonton, AB T6G2E3 Canada
AU: Stachel, T
EM: tstachel@ualberta.ca
AF: University of Alberta, Department of Earth and Atmospheric Sciences, 1-26 Earth Science Building, Edmonton, AB T6G2E3 Canada
AU: Harris, J W
EM: j.harris@ges.gla.ac.uk
AF: University of Glasgow, Division of Earth Sciences, Gregory Building, Glasgow, G128QQ United Kingdom
AU: Muehlenbachs, K
EM: karlis.Muehlenbachs@ualberta.ca
AF: University of Alberta, Department of Earth and Atmospheric Sciences, 1-26 Earth Science Building, Edmonton, AB T6G2E3 Canada
AU: Ludwig, T
EM: tl@min.uni-heidelberg.de
AF: Heidelberg University, Institute for Mineralogy, Im Neuenheimer Feld 236, Heidelberg, 69120 Germany
AU: Brey, G P
EM: brey@em.uni-frankfurt.de
AF: Frankfurt University, Institute for Mineralogy Senckenberganlage 28, Frankfurt, 60054 Germany
AB: The presence of majoritic garnet inclusions in diamonds from the Jagersfontein kimberlite in South Africa shows that the diamonds formed at depths of up to 550 km in source rocks of basaltic composition. Negative europium anomalies in all recovered majoritic garnets link these basaltic sources to subducted oceanic crust. A narrow range of isotopically light carbon compositions (δ¹³C: -17 to -24‰) of the host diamonds suggests that diamond formation in the asthenosphere and transition zone is principally different to the formation of diamonds from the shallower lithosphere, which at Jagersfontein have a broad carbon isotopic range from -1 to -24‰ with a pronounced mode at -4‰. The narrow range in carbon isotopic composition of diamonds from the asthenosphere and transition zone suggests that they directly reflect the isotopic signature of their carbon source. The isotopically light carbon composition of these diamonds is, therefore, consistent with derivation from organic matter within a subducting slab and most likely related to an early Mesozoic subduction event that transferred oceanic crust into the deep mantle beneath the Kaapvaal craton. Accumulation of subducted oceanic crust in the deep mantle may have also caused the late Cretaceous kimberlite volcanism on the Kaapvaal craton, which ultimately brought the deep diamonds from Jagersfontein to the Earth's surface.
DE: 1025 Composition of the mantle
DE: 1030 Geochemical cycles (0330)
DE: 1038 Mantle processes (3621)
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005