HR: 11:50h
AN: V32A-07    [Abstracts]
TI: Recycling deep cratonic lithosphere and generation of intraplate magmatism in the North China Craton
AU: * Gao, S
EM: sgao@263.net
AF: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Lumo Road 388, Wuhan, 430074, China
AU: * Gao, S
EM: sgao@263.net
AF: State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Taibai Road 229, Xi'an, 710069, China
AU: Rudnick, R L
EM: rudnick@geol.umd.edu
AF: Geochemistry Laboratory, Department of Geology, University of Maryland, College Park, MD 20742, United States
AU: Xu, W
EM: xuwl261@sina.com
AF: School of Earth Sciences, Jilin University, Jianshen Road 2199, Changchun, 130061, China
AU: Yuan, H
EM: hlyuan@263.net
AF: State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Taibai Road 229, Xi'an, 710069, China
AU: Liu, Y
EM: yshliu@cug.edu.cn
AF: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Lumo Road 388, Wuhan, 430074, China
AU: Walker, R J
EM: rjwalker@geol.umd.edu
AF: Geochemistry Laboratory, Department of Geology, University of Maryland, College Park, MD 20742, United States
AU: Puchtel, I
EM: ipuchtel@mail.umd.edu
AF: Geochemistry Laboratory, Department of Geology, University of Maryland, College Park, MD 20742, United States
AU: Liu, X
EM: xiaomingliu@263.net
AF: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Lumo Road 388, Wuhan, 430074, China
AU: Liu, X
EM: xiaomingliu@263.net
AF: State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Taibai Road 229, Xi'an, 710069, China
AU: Huang, H
EM: huanghua0913@163.com
AF: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Lumo Road 388, Wuhan, 430074, China
AU: Wang, X
EM: wang-xiaorui@263.net
AF: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Lumo Road 388, Wuhan, 430074, China
AB: Early Cretaceous alkaline picrites and high-magnesium basalts from the North China craton provide evidence for recycling of continental lithosphere by density foundering. Both the picrites and basalts contain xenocrystic olivines with high Fo_92-93 and low CaO (<0.10%), consistent with their derivation from, or interaction with Archean mantle lithosphere. Most importantly, both the picritic and basaltic lavas contain unusual, reversely zoned clinopyroxene phenocrysts whose cores have low MgO, high Na₂O (up to 2.4 wt.%, or 17.3 mol% Jd), and frequently contain ilmenite exsolution lamellae, consistent with their crystallization from an eclogite- derived melt. In contrast, the clinopyroxene mantles have low Na₂O (<0.92 wt.%, or <6.5 mol% Jd) and are lamellae-free, suggesting crystallization from a mantle-derived melt (picrite or basalt). Both the cores and mantles have high Al₂O₃ contents (up to 6.9 wt.%). These observations suggest that both the cores and mantles crystallized from an aluminous melt at mantle depths, but that the cores formed at a significantly greater depth (> 2.5 GPa) than the surrounding mantles (> 1.5 GPa). High Ni/Cr and low 100Mn/Fe of both the picritic and basaltic lavas and correspondingly high Ni and low 100Mn/Fe of magmatic olivines at a given Fo number indicate derivation from a source containing limited or no olivine. High Sr/Y, La_N/Yb_N and Th/U and low Lu/Hf, together with radiogenic initial ⁸⁷Sr/⁸⁶Sr and ¹⁸⁷Os/¹⁸⁸Os ratios and negative epsilon Nd values implicate contributions from melts derived from foundered eclogitic lower continental crust. Modeling results suggest that the basalt source region contained a moderate proportion (20-30%) of eclogite-derived component whereas the source of the picritic lavas contained a substantially greater proportion (70-80%) of a different eclogite-derived component. Collectively, these results suggest that both the basaltic and picritic lavas originated by partial melting of Archean lithospheric mantle that experienced varying degrees of reaction with eclogite-derived melts. Together with previous studies, these findings provide new evidence that thinning of the North China craton was caused by the removal of the lower lithosphere (mantle and lower crust). Recycling and melting of eclogitic lower crust may contribute more to mantle heterogeneity than has previously been recognized.
DE: 1025 Composition of the mantle
DE: 3619 Magma genesis and partial melting (1037)
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8159 Rheology: crust and lithosphere (8031)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting