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Isotopic and geochemical constraints on the origin of the sea of Japan
Goldschmidt Conference Abstracts 2006
A455
Metal-silicate fractionation in the deep magma ocean and light elements in the core
Isotopic and geochemical constraints on the origin of the sea of Japan
E. OHTANI, T. SAKAI, T. KAWAZOE, T. KONDO
S. OKAMURA1, R.J. ARCULUS2, Y.A. MARTYNOV3
Faculty of Science, Tohoku University, Sendai 980-8578, Japan ([email protected]) It has been believed that a giant impact occurred in the final stage of accretion of the earth. The effect of the impact on fractionation of the Earth has been discussed recently by several authors (Rubie, 2003; Wood and Haliday, 2005), although this process was originally introduced for explaining the origin of the Moon. We may expect a magma ocean extended into the deep lower mantle or even total melting of the early Earth as the results of the giant impact because of the energetic nature of the impact. Since it has been suggested that the reaction and equilibrium were achieved at the bottom of the magma ocean (e.g., Rubie, 2003), the metallic iron and Mg-perovskite (and/or post-perovskite phase) were in equilibrium in the deep magma ocean. We have conducted high pressure and temperature experiments on the reactions between iron and Mg-perovskite, and iron and post-perovskite using both the multi-anvil and laser heated diamond anvil cell (LHDAC). Multi-anvil experiments revealed that the solubility of O and Si in molten iron coexisting with Mg-perovskite is 2.23 wt% and 1.70 wt%, respectively, at 27 GPa and 3040 K and it has a strong positive temperature dependency (Kawazoe and Ohtani, 2006). Our LHDAC experiments indicate that the solubility of both O and Si in metallic iron increases significantly with increasing pressure, and those coexisting with post-perovskite phase at 135 GPa and 3000 K are 6.3 wt% and 4.0 wt%, respectively, which are consistent with the solubility in metallic iron coexisting with perovskite (Takafuji, 2005). These experiments revealed that significant amounts of O and Si, which explain the core density deficit, can be dissolved into metallic iron at the bottom of the magma ocean with the deep lower mantle or CMB depths. A depletion of Si in the mantle can also be produced by dissolution of Si into the metallic core during the core separation stage.
References Kawazoe, T., Ohtani, E., 2006. PCM, in press. Rubie et al., 2003. EPSL 205, 239–255. Wood, B.J., Haliday, A.J., 2005. Nature 437, 1345–1348. Takafuji et al., 2005. GRL 32, L06313. doi:10.1029/2005GL022773. doi:10.1016/j.gca.2006.06.916
1
Sapporo Campus, Hokkaido Education University, Japan ([email protected]) 2 Department of Earth and Marine Sciences, Australian National University, Australia ([email protected]) 3 Far East Geological Institute, Russia ([email protected]) Sikhote-Alin and Sakhalin (SAS) are located in the Russian Far East Flank of the northernmost part of the Sea of Japan. Magmatism in this region preceded, was concurrent with, and continued after the extension and sea floor-spreading that formed the Sea of Japan. The Sr–Nd–Pb isotopic and trace element systematics between the Eocene-Oligocene basalt and Early-Mid Miocene basalt suggest that the sites of magma generation beneath the SAS region have moved from the subduction-related, EMII-like mantle lithosphere deeper into MORB-type asthenosphere as spreading progressed in the Sea of Japan. The post-Sea of Japan opening Mid Miocene-Pliocene lavas exhibit wide ranges in trace element abundances that vary between two distinct end member types. The minor Mid Miocene–Pliocene alkali basalts have OIB-like trace element and Sr– Nd–Pb isotope compositions, similar to the Cenozoic alkali basalts from the Sino-Korean Craton, consistent with melting of asthenospheric mantle at depth. By contrast, the Mid Miocene– Pliocene tholeiites form the other extreme with HFSE concentrations that are much lower than those of elements of similar incompatibility. The wide range of incompatible-element abundances in the Mid Miocene–Pliocene basalts defines coherent trends consistent with a mantle mixing between an isotopically enriched FOZO-type asthenospheric mantle and an isotopically enriched EMI-type subcontinental lithospheric mantle. The appearance of the FOZO- and EMI-type components in the post-opening Mid Miocene-Pliocene basalts may reflect mantle flow into the region through asthenospheric injection under the Sino-Korean Craton that led to thinning of the subcontinental lithosphere via partial delamination. It is likely that the Japan Sea opening and associated magmatism in the back-arc basin were triggered by lateral migration of the FOZO-type asthenospheric mantle from beneath northeast China toward the Japan arc during late stages of Tethyan closure by the India–Asia collision. doi:10.1016/j.gca.2006.06.917
A455
Metal-silicate fractionation in the deep magma ocean and light elements in the core
Isotopic and geochemical constraints on the origin of the sea of Japan
E. OHTANI, T. SAKAI, T. KAWAZOE, T. KONDO
S. OKAMURA1, R.J. ARCULUS2, Y.A. MARTYNOV3
Faculty of Science, Tohoku University, Sendai 980-8578, Japan ([email protected]) It has been believed that a giant impact occurred in the final stage of accretion of the earth. The effect of the impact on fractionation of the Earth has been discussed recently by several authors (Rubie, 2003; Wood and Haliday, 2005), although this process was originally introduced for explaining the origin of the Moon. We may expect a magma ocean extended into the deep lower mantle or even total melting of the early Earth as the results of the giant impact because of the energetic nature of the impact. Since it has been suggested that the reaction and equilibrium were achieved at the bottom of the magma ocean (e.g., Rubie, 2003), the metallic iron and Mg-perovskite (and/or post-perovskite phase) were in equilibrium in the deep magma ocean. We have conducted high pressure and temperature experiments on the reactions between iron and Mg-perovskite, and iron and post-perovskite using both the multi-anvil and laser heated diamond anvil cell (LHDAC). Multi-anvil experiments revealed that the solubility of O and Si in molten iron coexisting with Mg-perovskite is 2.23 wt% and 1.70 wt%, respectively, at 27 GPa and 3040 K and it has a strong positive temperature dependency (Kawazoe and Ohtani, 2006). Our LHDAC experiments indicate that the solubility of both O and Si in metallic iron increases significantly with increasing pressure, and those coexisting with post-perovskite phase at 135 GPa and 3000 K are 6.3 wt% and 4.0 wt%, respectively, which are consistent with the solubility in metallic iron coexisting with perovskite (Takafuji, 2005). These experiments revealed that significant amounts of O and Si, which explain the core density deficit, can be dissolved into metallic iron at the bottom of the magma ocean with the deep lower mantle or CMB depths. A depletion of Si in the mantle can also be produced by dissolution of Si into the metallic core during the core separation stage.
References Kawazoe, T., Ohtani, E., 2006. PCM, in press. Rubie et al., 2003. EPSL 205, 239–255. Wood, B.J., Haliday, A.J., 2005. Nature 437, 1345–1348. Takafuji et al., 2005. GRL 32, L06313. doi:10.1029/2005GL022773. doi:10.1016/j.gca.2006.06.916
1
Sapporo Campus, Hokkaido Education University, Japan ([email protected]) 2 Department of Earth and Marine Sciences, Australian National University, Australia ([email protected]) 3 Far East Geological Institute, Russia ([email protected]) Sikhote-Alin and Sakhalin (SAS) are located in the Russian Far East Flank of the northernmost part of the Sea of Japan. Magmatism in this region preceded, was concurrent with, and continued after the extension and sea floor-spreading that formed the Sea of Japan. The Sr–Nd–Pb isotopic and trace element systematics between the Eocene-Oligocene basalt and Early-Mid Miocene basalt suggest that the sites of magma generation beneath the SAS region have moved from the subduction-related, EMII-like mantle lithosphere deeper into MORB-type asthenosphere as spreading progressed in the Sea of Japan. The post-Sea of Japan opening Mid Miocene-Pliocene lavas exhibit wide ranges in trace element abundances that vary between two distinct end member types. The minor Mid Miocene–Pliocene alkali basalts have OIB-like trace element and Sr– Nd–Pb isotope compositions, similar to the Cenozoic alkali basalts from the Sino-Korean Craton, consistent with melting of asthenospheric mantle at depth. By contrast, the Mid Miocene– Pliocene tholeiites form the other extreme with HFSE concentrations that are much lower than those of elements of similar incompatibility. The wide range of incompatible-element abundances in the Mid Miocene–Pliocene basalts defines coherent trends consistent with a mantle mixing between an isotopically enriched FOZO-type asthenospheric mantle and an isotopically enriched EMI-type subcontinental lithospheric mantle. The appearance of the FOZO- and EMI-type components in the post-opening Mid Miocene-Pliocene basalts may reflect mantle flow into the region through asthenospheric injection under the Sino-Korean Craton that led to thinning of the subcontinental lithosphere via partial delamination. It is likely that the Japan Sea opening and associated magmatism in the back-arc basin were triggered by lateral migration of the FOZO-type asthenospheric mantle from beneath northeast China toward the Japan arc during late stages of Tethyan closure by the India–Asia collision. doi:10.1016/j.gca.2006.06.917