The mineral thermobarometry proposed in literature is used to calculate the equilibrium temperature and pressure of garnet Iherzolite and websterite xenoliths within the Cenozoic kama-fugite from west Qinling, Gansu P...The mineral thermobarometry proposed in literature is used to calculate the equilibrium temperature and pressure of garnet Iherzolite and websterite xenoliths within the Cenozoic kama-fugite from west Qinling, Gansu Province, China. The results show that the equilibrium temperature and pressure of garnet Iherzolites and websterite and 1127-1266℃, 2.9-3.6 Gpa and 1169 -1248℃, 2.8-3.2 Gpa respectively. The equilibrium peressures reach or exceed the equilibrium peressure of spinel Iherzolites (2.0-3.0 GPa), and fall into the stability range of garnet peridotite. The equilibrium temperature of the xenoliths reach or exceed the ocean geotherm, identical with the melting temperature of kamafugite magma determined by experiments under the conditions of post-orogenic lithosphere extension. So the thermal state of Cenozoic mantle of the west Qinling may be fit to generate the kamafugite magmatism. The research on petrology-mineralogy and geobarothermometry of the xenoliths shows that both garnet Iherzolite and websterite are mantle components of the west Qinling, and may be considered as source rocks of the Cenozoic kamafugite magma.展开更多
The composition of gases trapped in olivine, orthopyroxene and clinopyroxene in Iherzolite xenoliths collected from different locations in eastern China has been measured by the vacuum stepped-heating mass spectrometr...The composition of gases trapped in olivine, orthopyroxene and clinopyroxene in Iherzolite xenoliths collected from different locations in eastern China has been measured by the vacuum stepped-heating mass spectrometry. These xenoliths are hosted in alkali basalts and considered as residues of partial melting of the upper mantle, and may contain evidence of mantle evolution. The results show that various kinds of fluid inclusions in Iherzolite xenoliths have been released at distinct times, which could be related to different stages of mantle evolution. In general, primitive fluids of the upper mantle (PFUM) beneath eastern China are dominated by H2, CO2 and CO, and are characterized by high contents of H2 and reduced gases. The compositions of PFUM are highly variable and related to tectonic settings. CO, CO2 and H2 are the main components of the PFUM beneath cratons; the PFUM in the mantle enriched in potassic metasomatism in the northern part of northeastern China has a high content of H2, while CO2 and SO2 are the dominant components of the PFUM in the Su-Lu-Wan (Jiangsu-Shandong-Anhui) region, where recycled crustal fluids were mixed with deeper mantle components. There are several fluids with distinct compositions beneath eastern China, such as primitive fluids of upper mantle (CO, CO2 and H2), partial melting fluids (CO2 and CO) and metasomatic fluids mixed with recycled crustal fluids (CO2, N2, SO2 and CH4) etc. Fluids of the upper mantle beneath the North China craton are different from that of the South China craton in total gases and chemical compositions: the contents of the reduced gases of the PFUM in the NCC are higher than those in the SCC.展开更多
THE determination of contents of trace (10<sup>-12</sup>—10<sup>-9</sup>) siderophile elements, Re and Os, and osmium isotopic compositions in mantle-derived rocks is very useful. It has been ...THE determination of contents of trace (10<sup>-12</sup>—10<sup>-9</sup>) siderophile elements, Re and Os, and osmium isotopic compositions in mantle-derived rocks is very useful. It has been a new approach to exploring interactions between the mantle and the crust, and the chemical structure of the mantle. This can be done by combination with isotopic dating and tracing展开更多
Xenoliths of garnet and spinel-garnet 1herzolite from Mingxi, Eastern China have been studied in terms of comprehensive methods of mineralogy, petrology, fabrics, mierostructures and infrared spectrum. The temperature...Xenoliths of garnet and spinel-garnet 1herzolite from Mingxi, Eastern China have been studied in terms of comprehensive methods of mineralogy, petrology, fabrics, mierostructures and infrared spectrum. The temperature and pressure equilibration of the xenolith have been calculated using the TEMPEST program with the two-pyroxene geothermometer of Bertrand and Mercier (1985) combined with the geobarometer of Nickel and Green (1985). The temperature and pressure of xenoliths range from^1300 K at 1. 9 GPa (60 km) to ~1500 K at 2. 6 GPa (80 km). The geotherm inferred from xenolith is excellently consistent with the measured surface heat flow (70 mW/m2) in Mingxi. A character of geothermal curve and conductive type suggest that these xenoliths are from the lithosphere, not from the asthenosphere. The geotherm and mierostructures and preferred orientations of minerals in the xenolith are consistent with tecon-ic thinning of the lithosphere in the present-day extensional back-arc environment.展开更多
基金the Major State Basic Research Development Program(G1998040800), the National Natural Science Foundation of China (Grant No. 49973014) and Qinghai-Xizhang Plateau Special Project of Ministry of Land and Resources (200101020404).
文摘The mineral thermobarometry proposed in literature is used to calculate the equilibrium temperature and pressure of garnet Iherzolite and websterite xenoliths within the Cenozoic kama-fugite from west Qinling, Gansu Province, China. The results show that the equilibrium temperature and pressure of garnet Iherzolites and websterite and 1127-1266℃, 2.9-3.6 Gpa and 1169 -1248℃, 2.8-3.2 Gpa respectively. The equilibrium peressures reach or exceed the equilibrium peressure of spinel Iherzolites (2.0-3.0 GPa), and fall into the stability range of garnet peridotite. The equilibrium temperature of the xenoliths reach or exceed the ocean geotherm, identical with the melting temperature of kamafugite magma determined by experiments under the conditions of post-orogenic lithosphere extension. So the thermal state of Cenozoic mantle of the west Qinling may be fit to generate the kamafugite magmatism. The research on petrology-mineralogy and geobarothermometry of the xenoliths shows that both garnet Iherzolite and websterite are mantle components of the west Qinling, and may be considered as source rocks of the Cenozoic kamafugite magma.
基金the Natural Science Foundation of China(grant 40273009).
文摘The composition of gases trapped in olivine, orthopyroxene and clinopyroxene in Iherzolite xenoliths collected from different locations in eastern China has been measured by the vacuum stepped-heating mass spectrometry. These xenoliths are hosted in alkali basalts and considered as residues of partial melting of the upper mantle, and may contain evidence of mantle evolution. The results show that various kinds of fluid inclusions in Iherzolite xenoliths have been released at distinct times, which could be related to different stages of mantle evolution. In general, primitive fluids of the upper mantle (PFUM) beneath eastern China are dominated by H2, CO2 and CO, and are characterized by high contents of H2 and reduced gases. The compositions of PFUM are highly variable and related to tectonic settings. CO, CO2 and H2 are the main components of the PFUM beneath cratons; the PFUM in the mantle enriched in potassic metasomatism in the northern part of northeastern China has a high content of H2, while CO2 and SO2 are the dominant components of the PFUM in the Su-Lu-Wan (Jiangsu-Shandong-Anhui) region, where recycled crustal fluids were mixed with deeper mantle components. There are several fluids with distinct compositions beneath eastern China, such as primitive fluids of upper mantle (CO, CO2 and H2), partial melting fluids (CO2 and CO) and metasomatic fluids mixed with recycled crustal fluids (CO2, N2, SO2 and CH4) etc. Fluids of the upper mantle beneath the North China craton are different from that of the South China craton in total gases and chemical compositions: the contents of the reduced gases of the PFUM in the NCC are higher than those in the SCC.
文摘THE determination of contents of trace (10<sup>-12</sup>—10<sup>-9</sup>) siderophile elements, Re and Os, and osmium isotopic compositions in mantle-derived rocks is very useful. It has been a new approach to exploring interactions between the mantle and the crust, and the chemical structure of the mantle. This can be done by combination with isotopic dating and tracing
文摘Xenoliths of garnet and spinel-garnet 1herzolite from Mingxi, Eastern China have been studied in terms of comprehensive methods of mineralogy, petrology, fabrics, mierostructures and infrared spectrum. The temperature and pressure equilibration of the xenolith have been calculated using the TEMPEST program with the two-pyroxene geothermometer of Bertrand and Mercier (1985) combined with the geobarometer of Nickel and Green (1985). The temperature and pressure of xenoliths range from^1300 K at 1. 9 GPa (60 km) to ~1500 K at 2. 6 GPa (80 km). The geotherm inferred from xenolith is excellently consistent with the measured surface heat flow (70 mW/m2) in Mingxi. A character of geothermal curve and conductive type suggest that these xenoliths are from the lithosphere, not from the asthenosphere. The geotherm and mierostructures and preferred orientations of minerals in the xenolith are consistent with tecon-ic thinning of the lithosphere in the present-day extensional back-arc environment.
