HR: 15:15h
AN: V53D-07 INVITED    [Abstracts]
TI: Cooling Rates in the Lower Crust of the Oman Ophiolite: Ca in Olivine, Revisited
AU: * VanTongeren, J A
EM: jvantong@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory - Columbia University, 61 Rt 9W, Palisades, NY 10964, United States
AU: Kelemen, P B
EM: peterk@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory - Columbia University, 61 Rt 9W, Palisades, NY 10964, United States
AU: Hanghoj, K
EM: khanghoj@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory - Columbia University, 61 Rt 9W, Palisades, NY 10964, United States
AB: Debate over the mechanism of accretion of the layered gabbros of the lower oceanic crust has been centered on the gabbro glacier and the sheeted sills models. In the gabbro glacier model it is proposed that the lower oceanic crust (below the sheeted dikes) crystallizes in a single shallow melt lens and is then transported ductilely downward. Conversely, in the sheeted sills model the lower oceanic crust is formed in several melt lenses and crystallizes in situ. The thermal profile of the crust, specifically the roles of hydrothermal circulation and cooling rate, is a key component in distinguishing between these two models. Results from Ca in olivine in this study show no systematic variation of cooling rate with depth in the lower crust of the Khafifah section in the Wadi Tayin massif of the Oman ophiolite. Additionally, very high cooling rates recorded near the base of the crust suggest that hydrothermal circulation plays an important role in the removal of heat throughout the crust. On the basis of these results it can be concluded that the sheeted sills model is a thermally viable mechanism for accretion of oceanic lower crust. Ca in olivine results for the oceanic lower crust are also compared with other magmatic systems such as layered mafic intrusions and arc lower crust to quantify relative cooling rates among these different systems. Perhaps surprisingly, large layered intrusions, such as the Bushveld Complex, are found to cool at approximately the same rate as oceanic lower crust.
DE: 3614 Mid-oceanic ridge processes (1032, 8416)
DE: 3616 Hydrothermal systems (0450, 1034, 3017, 4832, 8135, 8424)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting