Lithological observations and mineralogical analyses on pyroxene and hornblende megacrysts and pyroxene and hornblende cumulates in xenoliths in the Mesozoic plutons of the Tongling region, Anhui Province, provide evi...Lithological observations and mineralogical analyses on pyroxene and hornblende megacrysts and pyroxene and hornblende cumulates in xenoliths in the Mesozoic plutons of the Tongling region, Anhui Province, provide evidence for the magmatic underplating of mantle-derived alkali-olivine basalt at circa 140 Ma. The pyroxene and hornblende megacrysts and cumulates were formed through the AFC process at depths ranging from 27 to 35 km.展开更多
Some pyrrhotite-chalcopyrite-bearing amphibole megacrysts (including pyroxene megacrysts) were discovered in Mesozoic augite diorite-porphyrite at Caoshan in Tongling area, Anhui Province. The amphibole megacrysts,bel...Some pyrrhotite-chalcopyrite-bearing amphibole megacrysts (including pyroxene megacrysts) were discovered in Mesozoic augite diorite-porphyrite at Caoshan in Tongling area, Anhui Province. The amphibole megacrysts,belonging mainly to pargasite and magnesiohastingsite, are characteristic of the amphibole composition derived from mantle and crystallized in lower crust. In general, the aggregates of pyrrhotite-chalcopyrite take the shapes of cylinder and sphere. Three occurrences have been recognized in the amphibole megacrysts: parallel linear, bunchy and scattered. The unique cylinder-like shape of the aggregates and remarkable Ni-poor sulfides in Caoshan are distinctively different from the spherical Ni-rich sulfides in pyroxene megacrysts and any other kinds of megacrysts. In terms of composition, the amphibole megacrysts and their sulfides in Caoshan are similar to those in the pyroxenite xenoliths in Qilin, Guangdong Province. In terms of origin, the pyrrhotite-chalcopyrites as exsolution products resulted from the subsolidus re-equilibration of sulfide solid solution within amphibole megacrysts. Such pyrrhotite-chalcopyrite-bearing amphibole megacrysts were first discovered inside and outside China. This discovery is important for the study of regional magma evolution and its associated mineralizations and ore sources as well.展开更多
The M?ssbauer spectra of natural megacrystal clinopyroxene are usually fitted by 4 sets of symmetric doublets, A-A', B-B', C-C' and D-D', respectively, in terms of increasing Qs value in literature. Bu...The M?ssbauer spectra of natural megacrystal clinopyroxene are usually fitted by 4 sets of symmetric doublets, A-A', B-B', C-C' and D-D', respectively, in terms of increasing Qs value in literature. But the assignments of those doublets are quite different, except the D-D' doublet assigned to Fe3+at the lattice site M***1 in previous papers. Particularly, the assignment and interpretation of the C-C' doublet are diverse.展开更多
Garnet megacryst with a multiphase inclusion from intraplate alkali basalts of the Shavaryn Tsaram(Tariat,Mongolia)was the object of the study.This unusual aggregate consists of porous glass,Ti-rich biotite,orthopyrox...Garnet megacryst with a multiphase inclusion from intraplate alkali basalts of the Shavaryn Tsaram(Tariat,Mongolia)was the object of the study.This unusual aggregate consists of porous glass,Ti-rich biotite,orthopyroxene,spinel,clinopyroxene,olivine,and ilmenite.Win TWQ 2.32 thermodynamic simulation of this system revealed a few intervals of equilibrium.Pressure and temperature adjustment reflected in the paragenetic minerals of the melt pocket.The capture of already crystallised garnet megacryst was at P=0.8-1 GPa and T=1120-1160℃.Mineral crystallisation inside the melt pocket,accompanied by external inputs,occurred at P=0.75-0.95 GPa;T=790-1120℃.Symplectite assemblage formed in the garnet megacryst due to decomposition at(P=0.55-0.7 GPa;T=850-930℃).The study of the oxygen isotope content in primary garnet and biotite of the melt pocket showed that the δ^(18)O_(VSMOW) values are the same and correspond to that of typical mantle xenoliths.However,the chemical and microcomponent composition of the melt pocket minerals reveals a material that differs from basalts and peridotites.Thus,it has been revealed that the multiphase inclusion in the garnet megacryst formed not only on account of the garnet’s substance,but also due to the entrapped material of the Earth’s interior.展开更多
It is well known that in pyroxene structure, there are two metal sites, M1 and M2.Generally speaking, ferrous iron in each of these sites would normally be expected to give rise to a doublet. However, anomies have bee...It is well known that in pyroxene structure, there are two metal sites, M1 and M2.Generally speaking, ferrous iron in each of these sites would normally be expected to give rise to a doublet. However, anomies have been found in the relative areas of the peaks in the room temperature spectra of some clinopyroxene (CPX) when the above assigninent is folowed. Ac-cording to the calculation of Next Nearest Neighbor configurations of divalent cations in M1,we found that the four configurations of M1 can be divided into two groups. One group is 3Ca configuration that increases with the content of Ca (p. f. u); the other group is made up of three No-3Ca configurations that decrease with the content of Ca. The two groups contribute to the spectrum structure of M1, so in this study we fit two doublets for ferrous iron in M1.Though there were severa reports on Fe3+ in tetrahedral site previously, it wa not sure that Fe3+ occupies the T site is a universal fact in CPX, despite of the content of A1. We found that the Fe3+ in the T site fitted by Medauer spectroscopy is negatively correlated to the Si content in the T site and positively correlated to the Fe3 + in the T site estimated on the suppo-sition that Fe3+ and Al occupy the T site randomly. If it is true, it is important in the model-ing of ion exchange geobarometries and gepthermornetries.展开更多
Helium isotope compositions of the mantle xenoliths and megacrysts in the Cenozoic basalts in the eastern China were measured. The samples were collected from Ludao of Heilongjiang, Huinan and Jiaohe of Jilin, Kuandia...Helium isotope compositions of the mantle xenoliths and megacrysts in the Cenozoic basalts in the eastern China were measured. The samples were collected from Ludao of Heilongjiang, Huinan and Jiaohe of Jilin, Kuandian of Liaoning, Hannuoba of Hebei, Nüshan of Anhui, Dingan of Hainan. The 3He/4He ratios of the mantle xenoliths and megacrysts from the most areas were about 1×10-5 , and were similar to those of the MORB, thus reflecting the characteristics of the MORB-typed depleted mantle. The 3He/4He ratios of the mantle xenoliths from Jiaohe were 4.8×10-6 and the 3He/4He ratios of xenoliths from Hannuoba vary from 0.15×10-6 to 7.4×10-6 , obviously lower than those of the MORB, and even lower than the atmospheric helium isotope ratios, indicating that the continental mantle was strongly replaced in Jiaohe and Hannuoba areas. The helium isotope compositions of the mantle xenoliths and megacrysts in the same region vary in a very wide range. It is inferred that the mantle xenoliths and megacrysts were from different parts of the continental mantle. There were not necessary origin relations between the mantle xenoliths, megacrysts and their host basalts. An extremely high 3He/4He ratio of garnet megacryst from Hannuoba, Hebei was found.展开更多
The garnet megacrysts from Yingfengling basalts are characterlzed by high FeO (】20%), CaO (7.02% -8.16%) and low MgO (5.88%-10.87%). Significant composition variations are observed in these megacrysts, of which Ni, V...The garnet megacrysts from Yingfengling basalts are characterlzed by high FeO (】20%), CaO (7.02% -8.16%) and low MgO (5.88%-10.87%). Significant composition variations are observed in these megacrysts, of which Ni, V, Sc, Co, and HREE are positively correlated with their Mg# and Zr, Hf, Ga, Y, Sr, Nb, Zn and LREE-MREE are negatively correlated with Mg#. Megacryst parent magma is a highly evolved residual melt with strongl depletion in Ti, Sr, Hf, Nb and HREE. This parental magma was generated by more than 60% of crystallization fractionation of clinopyroxene, garnet, plagioclase and ilmenite from quartz tholeiitic magma. It has not erupted to the surface, but stayed at the upper mantle and formed the megacrystic cumulate. Megacrysts and their host basalt are in disequilibrium.展开更多
Abundant megacrysts of clinopyroxene, amphibole, anorthoclase, and phlogopite are found together with deep-seated xenoliths in the Cenozoic basalt of the Tuoyun Basin, Southwest Tianshan. The megacrysts are mainly in ...Abundant megacrysts of clinopyroxene, amphibole, anorthoclase, and phlogopite are found together with deep-seated xenoliths in the Cenozoic basalt of the Tuoyun Basin, Southwest Tianshan. The megacrysts are mainly in the cone sheet formed at the early stage of the volcanic activity. Clinopyroxene megacrysts are located in the lower part of the profile, with amphibole and phlogopite megacrysts in the middle part and anorthoclase megacrysts in the upper part. The crystal integrity, absence of deformation fabric and their relation to the host basalt suggest that they were crystallized from the host magma and quickly transported to the surface. The mineralogical studies imply that the clinopyroxene megacrysts are of Al-augite with higher Al2O3 (>9%). Amphibole megacrysts are kaersutite rich in TiO2 (>4.5%). Sulfide inclusions such as pyrrhotite occur in some clinopyroxene and amphibole megacrysts. Thermodynamic calculations reveal that pyroxene megacrysts formed under the temperature of 1185.85–1199.85°C and the pressure between 1.53 and 1.64 GPa comparable to the crust-mantle boundary and amphibole megacrysts crystallized under the pressure of around 0.85 GPa, temperature about 1000°C comparable to the depth of 30 km. Anorthoclase megacrysts crystallized under the pressure between 0.8–1 GPa, temperature about 900°C. The absence of Ti-rich inclusions such as rutile can be considered as an evidence of quick magma ascending. The P-T conditions estimated via pyroxene megacrysts and phenocrysts compose a P-T path with a steep slope. It can be considered as another evidence of quick magma ascending. However, the estimated temperatures for amphibole megacrysts are markedly lower than those for pyroxene megacrysts given the same pressure. It probably shows that the amphiboles have crystallized at the vanguard of magma and under the volatile-rich condition. Thus, we can conclude that the Cenozoic basalts are produced in an extensional tectonic setting and the processes governing crystallization and ascending of the megacrysts are very complex.展开更多
Hydrogen isotope compositions of mantle-derived amphibole megacrysts from Qilin, Guang dong Province have been obtained by ion micro-probe. δD and H contents are constant both among different samples and within singl...Hydrogen isotope compositions of mantle-derived amphibole megacrysts from Qilin, Guang dong Province have been obtained by ion micro-probe. δD and H contents are constant both among different samples and within single sample, demonstrating that their formation condition is very stable.High δD values suggest the presence of a component recycled from crust which is possibly related to the subduction of Pacific Plate beneath Eurasian Plate in Mesozoic.展开更多
The hydrogen isotope composition of a mantle-derived mica megacryst from Cenozoic basanite from NUshan, Anhui Province has been determined by ion micro probe. The results demonstrate that δD and water content of the ...The hydrogen isotope composition of a mantle-derived mica megacryst from Cenozoic basanite from NUshan, Anhui Province has been determined by ion micro probe. The results demonstrate that δD and water content of the megacryst were heterogeneous on the micro scale, which resulted from reaction with meteoric water after being brought to the surface. The primary δD of mica megacrysts was about-23‰, suggesting the recycled crustal materials in its source. By combining these values with those of other researchers, it is believed that the hydrogen isotope composition of the mantle is heterogeneous at least on the large scale.展开更多
Cenozoic basalts are widely distributed in east- ern China, and some of them contain zircon megacrysts which are considered to be constituent mineral of the sub- continental lithospheric mantle (SCLM) and petrogenetic...Cenozoic basalts are widely distributed in east- ern China, and some of them contain zircon megacrysts which are considered to be constituent mineral of the sub- continental lithospheric mantle (SCLM) and petrogenetically related to mantle metasomatism induced by addition of crustal materials. Using the Laser Ablation Multiple Collec- tor Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICPMS), zircon megacrysts from the Cenozoic ba- salts at Changle in Shandong, Mingxi in Fujian, and Penglai in Hainan provinces have been used for Hf isotopic analyses. The data indicate that there is no significant deviation for the different zircon grains in each locale, except those from Penglai. The obtained 176Hf /177Hf ratios are 0.28302 — 0.28308 for Changle, 0.28297—0.28300 for Mingxi, and 0.28288—0.28293 for Penglai, with corresponding εHf values of 8.7—10.8, 7.0—7.9, and 3.9—5.7, respectively. These data display that there existed some regional heterogeneity, but the Hf model ages clustere in the Phanerozoic. Therefore, it is inferred that metasomatism of the lithospheric mantle be- neath eastern China took place in the Phanerozoic, most probably in the Mesozoic-Cenozoic. However, the formation time of the lithospheric mantle is not clearly constrained based on the present Hf isotopic data.展开更多
We performed a combined study of He–Ar isotopes and element geochemistry for pyroxene megacrysts and mantle xenoliths from Cenozoic basalt in the Changle–Linqu area in western Shandong.The results are used to trace ...We performed a combined study of He–Ar isotopes and element geochemistry for pyroxene megacrysts and mantle xenoliths from Cenozoic basalt in the Changle–Linqu area in western Shandong.The results are used to trace the evolution of subcontinental lithospheric mantle after destruction of the North China Craton.The3He/4He ratios of pyroxene megacrysts,websterite,and dunites are 7.0–7.7 Ra,7.4 Ra,and 7.0–7.7 Ra,respectively.They are related to the origin of host basalts,and are slightly lower than that of mid-ocean ridge basalts(MORB).Their40Ar/36Ar ratios are much lower than that of MORB and close to that of air.The lherzolites and wehrlites represent the fragments of the newly accreted lithospheric mantle,and their REE and trace elements indicate that they experienced melt metasomatism and partial melting.The3He/4He ratios of their olivine are slightly lower than that of MORB,but3He/4He ratios of their clinopyroxene are low(2.3–7.1 Ra)and display an inverse correlation with(La/Yb)N.The40Ar/36Ar ratios of these clinopyroxene are much lower than that of MORB and close to the air ratio.Combining existing studies of petrology,Sr–Nd–Pb isotopes,O isotopes,trace elements,and Mg isotopes,we infer that the juvenile lithospheric mantle in the Changle–Linqu area was metasomatized by oceanic crust-derived melts,which transfer the supracrustal Ar isotope signatures to the mantle sources.The low4He abundance and low3He/4He ratios of clinopyroxene in the lherzolites and wehrlites are ascribed to metasomatism by crustal melts from the subducted Pacific plate.展开更多
This study presents noble gaseous data of the corundum megacrysts from the Cenozoic basalts in Changle, Shandong Province, eastern China. It is known that no noble gaseous data of corundum megacryst have been document...This study presents noble gaseous data of the corundum megacrysts from the Cenozoic basalts in Changle, Shandong Province, eastern China. It is known that no noble gaseous data of corundum megacryst have been documented before. The 3He/4He ratios (1.13-7.37 Ra) of the corundums from Changle vary from atmosphere to MORB values; the 20Ne/22Ne (9.67-10.75) and 21Ne/22Ne (0.0280-0.0372) data define two linear trends on Ne three-isotope diagram, respectively, along the MFL and the correlation line between atmosphere and MORB; the 38Ar/36Ar (0.177-0.194) ratios, the 40Ar/36Ar (280.9 -404.2) ratios and the 128-136Xe/132Xe ration with obvious 129Xe excess are generally higher than at-mospheric component, but the 40Ar/36Ar ratios are much closer to atomospheric ratio. The isotopic compositions of noble gases (particularly for He and Ar) of the corundums are similar to those of py-roxene, anorthoclase megacrysts, and mantle-derived xenoliths from this area, and those of man-tle-derived xenoliths from several areas in eastern China. Therefore, the noble gases trapped in the corundums probably are from mantle source, representing a ‘mixed fluid' produced by the interaction between the lithospheric mantle and fluids releasing from the convective plate. Both the noble gas isotopic compositions and the oxygen isotopic compositions of the solid corundums are not the characteristics of crustal source. These suggest that the corundums crystallized from mantle-derived magmas with minimal crustal contamination.展开更多
基金the NationalNatural Science Foundation of China(Grants 40272034, 40133020)the Ministry of Science and Technology of China(Grant 1999043206) the Korea Science and Engineering Foundation(Grant KOSEF-20005-131-03-02).
文摘Lithological observations and mineralogical analyses on pyroxene and hornblende megacrysts and pyroxene and hornblende cumulates in xenoliths in the Mesozoic plutons of the Tongling region, Anhui Province, provide evidence for the magmatic underplating of mantle-derived alkali-olivine basalt at circa 140 Ma. The pyroxene and hornblende megacrysts and cumulates were formed through the AFC process at depths ranging from 27 to 35 km.
文摘Some pyrrhotite-chalcopyrite-bearing amphibole megacrysts (including pyroxene megacrysts) were discovered in Mesozoic augite diorite-porphyrite at Caoshan in Tongling area, Anhui Province. The amphibole megacrysts,belonging mainly to pargasite and magnesiohastingsite, are characteristic of the amphibole composition derived from mantle and crystallized in lower crust. In general, the aggregates of pyrrhotite-chalcopyrite take the shapes of cylinder and sphere. Three occurrences have been recognized in the amphibole megacrysts: parallel linear, bunchy and scattered. The unique cylinder-like shape of the aggregates and remarkable Ni-poor sulfides in Caoshan are distinctively different from the spherical Ni-rich sulfides in pyroxene megacrysts and any other kinds of megacrysts. In terms of composition, the amphibole megacrysts and their sulfides in Caoshan are similar to those in the pyroxenite xenoliths in Qilin, Guangdong Province. In terms of origin, the pyrrhotite-chalcopyrites as exsolution products resulted from the subsolidus re-equilibration of sulfide solid solution within amphibole megacrysts. Such pyrrhotite-chalcopyrite-bearing amphibole megacrysts were first discovered inside and outside China. This discovery is important for the study of regional magma evolution and its associated mineralizations and ore sources as well.
基金supported by the National Natural Science Foundation Grant 49673186.
文摘The M?ssbauer spectra of natural megacrystal clinopyroxene are usually fitted by 4 sets of symmetric doublets, A-A', B-B', C-C' and D-D', respectively, in terms of increasing Qs value in literature. But the assignments of those doublets are quite different, except the D-D' doublet assigned to Fe3+at the lattice site M***1 in previous papers. Particularly, the assignment and interpretation of the C-C' doublet are diverse.
文摘Garnet megacryst with a multiphase inclusion from intraplate alkali basalts of the Shavaryn Tsaram(Tariat,Mongolia)was the object of the study.This unusual aggregate consists of porous glass,Ti-rich biotite,orthopyroxene,spinel,clinopyroxene,olivine,and ilmenite.Win TWQ 2.32 thermodynamic simulation of this system revealed a few intervals of equilibrium.Pressure and temperature adjustment reflected in the paragenetic minerals of the melt pocket.The capture of already crystallised garnet megacryst was at P=0.8-1 GPa and T=1120-1160℃.Mineral crystallisation inside the melt pocket,accompanied by external inputs,occurred at P=0.75-0.95 GPa;T=790-1120℃.Symplectite assemblage formed in the garnet megacryst due to decomposition at(P=0.55-0.7 GPa;T=850-930℃).The study of the oxygen isotope content in primary garnet and biotite of the melt pocket showed that the δ^(18)O_(VSMOW) values are the same and correspond to that of typical mantle xenoliths.However,the chemical and microcomponent composition of the melt pocket minerals reveals a material that differs from basalts and peridotites.Thus,it has been revealed that the multiphase inclusion in the garnet megacryst formed not only on account of the garnet’s substance,but also due to the entrapped material of the Earth’s interior.
文摘It is well known that in pyroxene structure, there are two metal sites, M1 and M2.Generally speaking, ferrous iron in each of these sites would normally be expected to give rise to a doublet. However, anomies have been found in the relative areas of the peaks in the room temperature spectra of some clinopyroxene (CPX) when the above assigninent is folowed. Ac-cording to the calculation of Next Nearest Neighbor configurations of divalent cations in M1,we found that the four configurations of M1 can be divided into two groups. One group is 3Ca configuration that increases with the content of Ca (p. f. u); the other group is made up of three No-3Ca configurations that decrease with the content of Ca. The two groups contribute to the spectrum structure of M1, so in this study we fit two doublets for ferrous iron in M1.Though there were severa reports on Fe3+ in tetrahedral site previously, it wa not sure that Fe3+ occupies the T site is a universal fact in CPX, despite of the content of A1. We found that the Fe3+ in the T site fitted by Medauer spectroscopy is negatively correlated to the Si content in the T site and positively correlated to the Fe3 + in the T site estimated on the suppo-sition that Fe3+ and Al occupy the T site randomly. If it is true, it is important in the model-ing of ion exchange geobarometries and gepthermornetries.
文摘Helium isotope compositions of the mantle xenoliths and megacrysts in the Cenozoic basalts in the eastern China were measured. The samples were collected from Ludao of Heilongjiang, Huinan and Jiaohe of Jilin, Kuandian of Liaoning, Hannuoba of Hebei, Nüshan of Anhui, Dingan of Hainan. The 3He/4He ratios of the mantle xenoliths and megacrysts from the most areas were about 1×10-5 , and were similar to those of the MORB, thus reflecting the characteristics of the MORB-typed depleted mantle. The 3He/4He ratios of the mantle xenoliths from Jiaohe were 4.8×10-6 and the 3He/4He ratios of xenoliths from Hannuoba vary from 0.15×10-6 to 7.4×10-6 , obviously lower than those of the MORB, and even lower than the atmospheric helium isotope ratios, indicating that the continental mantle was strongly replaced in Jiaohe and Hannuoba areas. The helium isotope compositions of the mantle xenoliths and megacrysts in the same region vary in a very wide range. It is inferred that the mantle xenoliths and megacrysts were from different parts of the continental mantle. There were not necessary origin relations between the mantle xenoliths, megacrysts and their host basalts. An extremely high 3He/4He ratio of garnet megacryst from Hannuoba, Hebei was found.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 49773191) an AusAID Australia-China Institutional Links Program and the State Key Basic Research Program (Grant No. 1999043202)
文摘The garnet megacrysts from Yingfengling basalts are characterlzed by high FeO (】20%), CaO (7.02% -8.16%) and low MgO (5.88%-10.87%). Significant composition variations are observed in these megacrysts, of which Ni, V, Sc, Co, and HREE are positively correlated with their Mg# and Zr, Hf, Ga, Y, Sr, Nb, Zn and LREE-MREE are negatively correlated with Mg#. Megacryst parent magma is a highly evolved residual melt with strongl depletion in Ti, Sr, Hf, Nb and HREE. This parental magma was generated by more than 60% of crystallization fractionation of clinopyroxene, garnet, plagioclase and ilmenite from quartz tholeiitic magma. It has not erupted to the surface, but stayed at the upper mantle and formed the megacrystic cumulate. Megacrysts and their host basalt are in disequilibrium.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40472038 and 40272033)the Extracurriculum Academic Research Programme of China University of Geosciences, Beijing
文摘Abundant megacrysts of clinopyroxene, amphibole, anorthoclase, and phlogopite are found together with deep-seated xenoliths in the Cenozoic basalt of the Tuoyun Basin, Southwest Tianshan. The megacrysts are mainly in the cone sheet formed at the early stage of the volcanic activity. Clinopyroxene megacrysts are located in the lower part of the profile, with amphibole and phlogopite megacrysts in the middle part and anorthoclase megacrysts in the upper part. The crystal integrity, absence of deformation fabric and their relation to the host basalt suggest that they were crystallized from the host magma and quickly transported to the surface. The mineralogical studies imply that the clinopyroxene megacrysts are of Al-augite with higher Al2O3 (>9%). Amphibole megacrysts are kaersutite rich in TiO2 (>4.5%). Sulfide inclusions such as pyrrhotite occur in some clinopyroxene and amphibole megacrysts. Thermodynamic calculations reveal that pyroxene megacrysts formed under the temperature of 1185.85–1199.85°C and the pressure between 1.53 and 1.64 GPa comparable to the crust-mantle boundary and amphibole megacrysts crystallized under the pressure of around 0.85 GPa, temperature about 1000°C comparable to the depth of 30 km. Anorthoclase megacrysts crystallized under the pressure between 0.8–1 GPa, temperature about 900°C. The absence of Ti-rich inclusions such as rutile can be considered as an evidence of quick magma ascending. The P-T conditions estimated via pyroxene megacrysts and phenocrysts compose a P-T path with a steep slope. It can be considered as another evidence of quick magma ascending. However, the estimated temperatures for amphibole megacrysts are markedly lower than those for pyroxene megacrysts given the same pressure. It probably shows that the amphiboles have crystallized at the vanguard of magma and under the volatile-rich condition. Thus, we can conclude that the Cenozoic basalts are produced in an extensional tectonic setting and the processes governing crystallization and ascending of the megacrysts are very complex.
文摘Hydrogen isotope compositions of mantle-derived amphibole megacrysts from Qilin, Guang dong Province have been obtained by ion micro-probe. δD and H contents are constant both among different samples and within single sample, demonstrating that their formation condition is very stable.High δD values suggest the presence of a component recycled from crust which is possibly related to the subduction of Pacific Plate beneath Eurasian Plate in Mesozoic.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 803002 and 49773181).
文摘The hydrogen isotope composition of a mantle-derived mica megacryst from Cenozoic basanite from NUshan, Anhui Province has been determined by ion micro probe. The results demonstrate that δD and water content of the megacryst were heterogeneous on the micro scale, which resulted from reaction with meteoric water after being brought to the surface. The primary δD of mica megacrysts was about-23‰, suggesting the recycled crustal materials in its source. By combining these values with those of other researchers, it is believed that the hydrogen isotope composition of the mantle is heterogeneous at least on the large scale.
基金This work was supported by the National Natural Science Foundation of China (Grants Nos. 49602025, 40325006 and 40025209)“Excellent Youth”of Chinese Academy of Sciences, and Natural Science Foundation of Guangdong (Grant No. 011143).
文摘Cenozoic basalts are widely distributed in east- ern China, and some of them contain zircon megacrysts which are considered to be constituent mineral of the sub- continental lithospheric mantle (SCLM) and petrogenetically related to mantle metasomatism induced by addition of crustal materials. Using the Laser Ablation Multiple Collec- tor Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICPMS), zircon megacrysts from the Cenozoic ba- salts at Changle in Shandong, Mingxi in Fujian, and Penglai in Hainan provinces have been used for Hf isotopic analyses. The data indicate that there is no significant deviation for the different zircon grains in each locale, except those from Penglai. The obtained 176Hf /177Hf ratios are 0.28302 — 0.28308 for Changle, 0.28297—0.28300 for Mingxi, and 0.28288—0.28293 for Penglai, with corresponding εHf values of 8.7—10.8, 7.0—7.9, and 3.9—5.7, respectively. These data display that there existed some regional heterogeneity, but the Hf model ages clustere in the Phanerozoic. Therefore, it is inferred that metasomatism of the lithospheric mantle be- neath eastern China took place in the Phanerozoic, most probably in the Mesozoic-Cenozoic. However, the formation time of the lithospheric mantle is not clearly constrained based on the present Hf isotopic data.
基金supported by the National Basic Research Program of China(2009CB825001)the National Natural Science Foundation of China(90714010)
文摘We performed a combined study of He–Ar isotopes and element geochemistry for pyroxene megacrysts and mantle xenoliths from Cenozoic basalt in the Changle–Linqu area in western Shandong.The results are used to trace the evolution of subcontinental lithospheric mantle after destruction of the North China Craton.The3He/4He ratios of pyroxene megacrysts,websterite,and dunites are 7.0–7.7 Ra,7.4 Ra,and 7.0–7.7 Ra,respectively.They are related to the origin of host basalts,and are slightly lower than that of mid-ocean ridge basalts(MORB).Their40Ar/36Ar ratios are much lower than that of MORB and close to that of air.The lherzolites and wehrlites represent the fragments of the newly accreted lithospheric mantle,and their REE and trace elements indicate that they experienced melt metasomatism and partial melting.The3He/4He ratios of their olivine are slightly lower than that of MORB,but3He/4He ratios of their clinopyroxene are low(2.3–7.1 Ra)and display an inverse correlation with(La/Yb)N.The40Ar/36Ar ratios of these clinopyroxene are much lower than that of MORB and close to the air ratio.Combining existing studies of petrology,Sr–Nd–Pb isotopes,O isotopes,trace elements,and Mg isotopes,we infer that the juvenile lithospheric mantle in the Changle–Linqu area was metasomatized by oceanic crust-derived melts,which transfer the supracrustal Ar isotope signatures to the mantle sources.The low4He abundance and low3He/4He ratios of clinopyroxene in the lherzolites and wehrlites are ascribed to metasomatism by crustal melts from the subducted Pacific plate.
基金the Foundation of State Key Basic Research 973 Program of China (Grant No. 2004CB720503)
文摘This study presents noble gaseous data of the corundum megacrysts from the Cenozoic basalts in Changle, Shandong Province, eastern China. It is known that no noble gaseous data of corundum megacryst have been documented before. The 3He/4He ratios (1.13-7.37 Ra) of the corundums from Changle vary from atmosphere to MORB values; the 20Ne/22Ne (9.67-10.75) and 21Ne/22Ne (0.0280-0.0372) data define two linear trends on Ne three-isotope diagram, respectively, along the MFL and the correlation line between atmosphere and MORB; the 38Ar/36Ar (0.177-0.194) ratios, the 40Ar/36Ar (280.9 -404.2) ratios and the 128-136Xe/132Xe ration with obvious 129Xe excess are generally higher than at-mospheric component, but the 40Ar/36Ar ratios are much closer to atomospheric ratio. The isotopic compositions of noble gases (particularly for He and Ar) of the corundums are similar to those of py-roxene, anorthoclase megacrysts, and mantle-derived xenoliths from this area, and those of man-tle-derived xenoliths from several areas in eastern China. Therefore, the noble gases trapped in the corundums probably are from mantle source, representing a ‘mixed fluid' produced by the interaction between the lithospheric mantle and fluids releasing from the convective plate. Both the noble gas isotopic compositions and the oxygen isotopic compositions of the solid corundums are not the characteristics of crustal source. These suggest that the corundums crystallized from mantle-derived magmas with minimal crustal contamination.
