The lower crustal xenolith of mafic two_pyroxene granulite (the majority) and hypersthene granulite in the Cenozoic basalt at Hannuoba have the characteristics of igneous blastic structure and granulite facies metamor...The lower crustal xenolith of mafic two_pyroxene granulite (the majority) and hypersthene granulite in the Cenozoic basalt at Hannuoba have the characteristics of igneous blastic structure and granulite facies metamorphic recrystallization. Study on the zircon chronology and REE geochemistry of granulite xenolith shows that the underplating of basic magma into the lower crust during late Mesozoic led to the formation of mafic accumulate, which further through metamorphism of granulite facies formed the high_density and high_velocity crustal bottom layer at the lower crust. This suggests that the underplating of mantle magma is the important way for the vertical overgrowth of continental crust since the Phanerozoic and provides new evidence for crust_mantle interaction.展开更多
On the basis of mineral assemblage, mineralogy, petrology, and major, trace ele-mental and isotopic geochemistry of the underplated granulite- and eclogite-facies accumulate, peridotite and pyroxenite xenoliths entrai...On the basis of mineral assemblage, mineralogy, petrology, and major, trace ele-mental and isotopic geochemistry of the underplated granulite- and eclogite-facies accumulate, peridotite and pyroxenite xenoliths entrained in Hannuoba Cenozoic basalts, this work con-strained the petrological constituents for the crust-mantle transitional zone, which is supported by the results of high-temperature and pressure velocity experiments on rocks and geophysics deep survey. Present lower part of lower crust is mainly composed of granulite-facies mafic accumu-lates (dominantly plagioclase websterite) and crust-mantle transitional zone dominantly com-posed of eclogite-facies pyroxenites with or without garnet and spinel lherzolites; Archaean ter-rain granulite is only nominally early lower crust. Magma underplating in the crust-mantle boundary led to the crustal vertical accretion and the formation of the crust-mantle transitional zone, which is a significant mechanism for the chemical adjustment of the crust-mantle boundary since the Phanerozoic.展开更多
Neutron activation analysis after preconcentration of nickel sulfide fire assay was used in measurement of Ru, Ph, Pd, Os, Ir, Pt (i.e. PGE elements) and Au concentrations for basalt, mantle and granulite xenoliths in...Neutron activation analysis after preconcentration of nickel sulfide fire assay was used in measurement of Ru, Ph, Pd, Os, Ir, Pt (i.e. PGE elements) and Au concentrations for basalt, mantle and granulite xenoliths in Hannuoba. The chondrite- and primitive mantle-normalized PGE patterns generally exhibit flat (for Iherzolite), negative slope (for harzburgite),展开更多
In situ Re-Os isotopes of sulfides in peridotitic xenoliths from Cenozoic Hannuoba basalts were analyzed by LAM-MC-ICPMS. The suifides developed two types of occurrences including silicate-enclosed and interstitial. I...In situ Re-Os isotopes of sulfides in peridotitic xenoliths from Cenozoic Hannuoba basalts were analyzed by LAM-MC-ICPMS. The suifides developed two types of occurrences including silicate-enclosed and interstitial. In the enclosed sulfides, 187Os/188Os vary from 0.1124 to 0.1362 and 187Re/188Os from 0.0026 to 1.8027. In the interstitial ones, 187Os/188Os have a range from 0.1174 to 0.1354 and 187Re/188Os from 0.0365 to 1.4469. The oldest age, calculated by TRD for the enclosed sulfides, is 2.1 Ga. An isochron age of 2.3±1.2 Ga is obtained by five grains of enclosed sulfides and primitive mantle. The sulfides used have lower Re-Os isotopic ratio than primitive mantle. Meanwhile, an isochron age of 645±225 Ma is given by all in- terstitial sulfides and the enclosed sulfides with higher Re-Os isotopic ratio due to Re addition after man- tle formation. In addition, the model age of 1.3 Ga recorded by one interstitial sulfide, having similar TDM and TRD, should be meaningful to deep thermal event. The coexistence of different ages, revealed by in situ Re-Os isotope, indicates frequently-occurring mantle events beneath Hannuoba area.展开更多
Lower crustal xenoliths brought up rapidly by basaltic magma onto the earth surface may provide direct information on the lower crust. The main purpose of this research is to gain an insight into the rheology of the l...Lower crustal xenoliths brought up rapidly by basaltic magma onto the earth surface may provide direct information on the lower crust. The main purpose of this research is to gain an insight into the rheology of the lower crust through the detailed study of lower crustal xenoliths collected from the Hannuoba basalt, North China. The lower crustal xenoliths in this area consist mainly of two pyroxene granulite, garnet granulite, and light-colored granulite, with a few exception of felsic granulite. The equilibration temperature and pressure of these xenoliths are estimated by using geothermometers and geobarometers suitable for lower crustal xenoliths. The obtained results show that the equilibration temperature of these xenoliths is within the range of 785–900°C, and the equilibrium pressure is within the range of 0.8–1.2 GPa, corresponding to a depth range of 28–42 km. These results have been used to modify the previously constructed lower crust-upper mantle geotherm for the studied area. The differential stress during the deformation process of the lower crustal xenoliths is estimated by using recrystallized grain-size paleo-piezometer to be in the range of 14–20 MPa. Comparing the available steady state flow laws for lower crustal rocks, it is confirmed that the flow law proposed by Wilks et al. in 1990 is applicable to the lower crustal xenoliths studied in this paper. The strain rate of the lower crust estimated by using this flow law is within the range of 10?13–10?11 s?1, higher than the strain rate of the upper mantle estimated previously for the studied area (10?17–10?13 s?1); the equivalent viscosity is estimated to be within the range of 1017–1019Pa·s, lower than that of the upper mantle (1019–1021 Pa·s). The constructed rheological profiles of the lower crust indicate that the differential stress shows no significant linear relation with depth, while the strain rate increases with depth and equivalent viscosity decrease with depth. The results support the viewpoint of weak lower con展开更多
文摘The lower crustal xenolith of mafic two_pyroxene granulite (the majority) and hypersthene granulite in the Cenozoic basalt at Hannuoba have the characteristics of igneous blastic structure and granulite facies metamorphic recrystallization. Study on the zircon chronology and REE geochemistry of granulite xenolith shows that the underplating of basic magma into the lower crust during late Mesozoic led to the formation of mafic accumulate, which further through metamorphism of granulite facies formed the high_density and high_velocity crustal bottom layer at the lower crust. This suggests that the underplating of mantle magma is the important way for the vertical overgrowth of continental crust since the Phanerozoic and provides new evidence for crust_mantle interaction.
基金the Chinese Academy of Sciences(Gant No.KZCX1-07) the National Natural Scince Foundation of China(Grant No.40234050)
文摘On the basis of mineral assemblage, mineralogy, petrology, and major, trace ele-mental and isotopic geochemistry of the underplated granulite- and eclogite-facies accumulate, peridotite and pyroxenite xenoliths entrained in Hannuoba Cenozoic basalts, this work con-strained the petrological constituents for the crust-mantle transitional zone, which is supported by the results of high-temperature and pressure velocity experiments on rocks and geophysics deep survey. Present lower part of lower crust is mainly composed of granulite-facies mafic accumu-lates (dominantly plagioclase websterite) and crust-mantle transitional zone dominantly com-posed of eclogite-facies pyroxenites with or without garnet and spinel lherzolites; Archaean ter-rain granulite is only nominally early lower crust. Magma underplating in the crust-mantle boundary led to the crustal vertical accretion and the formation of the crust-mantle transitional zone, which is a significant mechanism for the chemical adjustment of the crust-mantle boundary since the Phanerozoic.
文摘Neutron activation analysis after preconcentration of nickel sulfide fire assay was used in measurement of Ru, Ph, Pd, Os, Ir, Pt (i.e. PGE elements) and Au concentrations for basalt, mantle and granulite xenoliths in Hannuoba. The chondrite- and primitive mantle-normalized PGE patterns generally exhibit flat (for Iherzolite), negative slope (for harzburgite),
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40602009 and 40425002)the Research Foundation for Outstanding Young Teachers, China University of Geosciences, Wuhan (Grant No. CUGQNL0510)
文摘In situ Re-Os isotopes of sulfides in peridotitic xenoliths from Cenozoic Hannuoba basalts were analyzed by LAM-MC-ICPMS. The suifides developed two types of occurrences including silicate-enclosed and interstitial. In the enclosed sulfides, 187Os/188Os vary from 0.1124 to 0.1362 and 187Re/188Os from 0.0026 to 1.8027. In the interstitial ones, 187Os/188Os have a range from 0.1174 to 0.1354 and 187Re/188Os from 0.0365 to 1.4469. The oldest age, calculated by TRD for the enclosed sulfides, is 2.1 Ga. An isochron age of 2.3±1.2 Ga is obtained by five grains of enclosed sulfides and primitive mantle. The sulfides used have lower Re-Os isotopic ratio than primitive mantle. Meanwhile, an isochron age of 645±225 Ma is given by all in- terstitial sulfides and the enclosed sulfides with higher Re-Os isotopic ratio due to Re addition after man- tle formation. In addition, the model age of 1.3 Ga recorded by one interstitial sulfide, having similar TDM and TRD, should be meaningful to deep thermal event. The coexistence of different ages, revealed by in situ Re-Os isotope, indicates frequently-occurring mantle events beneath Hannuoba area.
基金Seismic Sciences Joint Foundation (Grant No. 103038)
文摘Lower crustal xenoliths brought up rapidly by basaltic magma onto the earth surface may provide direct information on the lower crust. The main purpose of this research is to gain an insight into the rheology of the lower crust through the detailed study of lower crustal xenoliths collected from the Hannuoba basalt, North China. The lower crustal xenoliths in this area consist mainly of two pyroxene granulite, garnet granulite, and light-colored granulite, with a few exception of felsic granulite. The equilibration temperature and pressure of these xenoliths are estimated by using geothermometers and geobarometers suitable for lower crustal xenoliths. The obtained results show that the equilibration temperature of these xenoliths is within the range of 785–900°C, and the equilibrium pressure is within the range of 0.8–1.2 GPa, corresponding to a depth range of 28–42 km. These results have been used to modify the previously constructed lower crust-upper mantle geotherm for the studied area. The differential stress during the deformation process of the lower crustal xenoliths is estimated by using recrystallized grain-size paleo-piezometer to be in the range of 14–20 MPa. Comparing the available steady state flow laws for lower crustal rocks, it is confirmed that the flow law proposed by Wilks et al. in 1990 is applicable to the lower crustal xenoliths studied in this paper. The strain rate of the lower crust estimated by using this flow law is within the range of 10?13–10?11 s?1, higher than the strain rate of the upper mantle estimated previously for the studied area (10?17–10?13 s?1); the equivalent viscosity is estimated to be within the range of 1017–1019Pa·s, lower than that of the upper mantle (1019–1021 Pa·s). The constructed rheological profiles of the lower crust indicate that the differential stress shows no significant linear relation with depth, while the strain rate increases with depth and equivalent viscosity decrease with depth. The results support the viewpoint of weak lower con
