Partial melting experiments were carried on KLB-1 peridotite, a xenolith sample from the Earth＇s upper mantle, at 1.5 GPa and temperatures from 1 300 to 1 600 ℃, with heating time varies from 1 to 30 min. We quantif...Partial melting experiments were carried on KLB-1 peridotite, a xenolith sample from the Earth＇s upper mantle, at 1.5 GPa and temperatures from 1 300 to 1 600 ℃, with heating time varies from 1 to 30 min. We quantify the axial temperature gradient in the deformation-DIA appa- ratus （D-DIA） and constrain the time scale of partial melting by comparing experimental observa- tions with calculated result from pMELTS program. The compositions of the liquid phase and the coexisting solid phases （clinopyroxene, orthopyroxene, and olivine） agree well with those calculated from pMELTS program, suggesting that local chemical equilibrium achieves during partial melting, although longer heating time is required to homogenize the bulk sample. The Mg# （=Mg/（Mg＋Fe） moi.%） of olivines from the 1-minute heating experiment changed continuously along the axial of the graphite capsule. A thermal gradient of 50 ℃/mm was calculated by comparing the Mg# of oli- vine grains with the output of pMELTS program. Olivine grains at the hot end of the graphite cap- sule from the three experiments heated at 1 400 ℃ but with different annealing time show consis- tence on Mg#, indicating that partitioning of Fe2＋ between the olivine grains and the silicate melt happened fast, and partial melting occurs in seconds.展开更多
Due to their high density,the ilmenite-bearing cumulates(IBC)(with or without KREEP)formed during the late-stage lunar magma ocean solidification are thought to sink into the underlying lunar mantle and trigger lunar ...Due to their high density,the ilmenite-bearing cumulates(IBC)(with or without KREEP)formed during the late-stage lunar magma ocean solidification are thought to sink into the underlying lunar mantle and trigger lunar mantle overturn.Geophysical evidence implied that IBC may descend deep inside the Moon and remain as a partially molten layer at the core-mantle boundary(CMB).However,partial melting may have occurred on the mixed mantle cumulates during the sinking of IBC/KREEP and the silicate melt may be positively buoyant,thus preventing the IBC/KREEP layer from sinking to the CMB.Here,we perform thermodynamic simulation on the stability of lunar mantle cumulates at different depths mixed with different amounts of IBC/KREEP from an updated LMO model.The modeling results suggest that the sinking of IBC/KREEP will cause at least 5 wt%partial melting in the shallow(~120 km)and a much larger degree of partial melting in the deep lunar mantle(~420 km).Due to the density contrast with the surrounding mantle,IBC/KREEP-bearing melts could potentially decouple under certain conditions.The modified lunar mantle by sinking of IBC/KREEP can better explain the formation of different kinds of lunar basaltic magma than the primary lunar mantle formed through differentiation of lunar magma ocean.Sinking of IBC/KREEP back into the lunar mantle may introduce plagioclase,clinopyroxene,garnet,and incompatible radioactive elements into the deep lunar mantle,which will further affect the thermal and chemical evolution of the lunar interior.展开更多
基金support by the National Natural Science Foundation of China (No. 41773052)the National Science Foundation of USA (Nos. EAR 1141895, EAR 1045629, and EAR 0968823)
文摘Partial melting experiments were carried on KLB-1 peridotite, a xenolith sample from the Earth＇s upper mantle, at 1.5 GPa and temperatures from 1 300 to 1 600 ℃, with heating time varies from 1 to 30 min. We quantify the axial temperature gradient in the deformation-DIA appa- ratus （D-DIA） and constrain the time scale of partial melting by comparing experimental observa- tions with calculated result from pMELTS program. The compositions of the liquid phase and the coexisting solid phases （clinopyroxene, orthopyroxene, and olivine） agree well with those calculated from pMELTS program, suggesting that local chemical equilibrium achieves during partial melting, although longer heating time is required to homogenize the bulk sample. The Mg# （=Mg/（Mg＋Fe） moi.%） of olivines from the 1-minute heating experiment changed continuously along the axial of the graphite capsule. A thermal gradient of 50 ℃/mm was calculated by comparing the Mg# of oli- vine grains with the output of pMELTS program. Olivine grains at the hot end of the graphite cap- sule from the three experiments heated at 1 400 ℃ but with different annealing time show consis- tence on Mg#, indicating that partitioning of Fe2＋ between the olivine grains and the silicate melt happened fast, and partial melting occurs in seconds.
基金funded by the National Natural Science Foundation of China(41773052,41973058)。
文摘Due to their high density,the ilmenite-bearing cumulates(IBC)(with or without KREEP)formed during the late-stage lunar magma ocean solidification are thought to sink into the underlying lunar mantle and trigger lunar mantle overturn.Geophysical evidence implied that IBC may descend deep inside the Moon and remain as a partially molten layer at the core-mantle boundary(CMB).However,partial melting may have occurred on the mixed mantle cumulates during the sinking of IBC/KREEP and the silicate melt may be positively buoyant,thus preventing the IBC/KREEP layer from sinking to the CMB.Here,we perform thermodynamic simulation on the stability of lunar mantle cumulates at different depths mixed with different amounts of IBC/KREEP from an updated LMO model.The modeling results suggest that the sinking of IBC/KREEP will cause at least 5 wt%partial melting in the shallow(~120 km)and a much larger degree of partial melting in the deep lunar mantle(~420 km).Due to the density contrast with the surrounding mantle,IBC/KREEP-bearing melts could potentially decouple under certain conditions.The modified lunar mantle by sinking of IBC/KREEP can better explain the formation of different kinds of lunar basaltic magma than the primary lunar mantle formed through differentiation of lunar magma ocean.Sinking of IBC/KREEP back into the lunar mantle may introduce plagioclase,clinopyroxene,garnet,and incompatible radioactive elements into the deep lunar mantle,which will further affect the thermal and chemical evolution of the lunar interior.
