The Late Permian Emeishan Large Igneous Province (ELIP) is commonly regarded as being located in the western part of the Yangtze craton, SW China, with an asymmetrical shape and a small area. This area, however, is ju...The Late Permian Emeishan Large Igneous Province (ELIP) is commonly regarded as being located in the western part of the Yangtze craton, SW China, with an asymmetrical shape and a small area. This area, however, is just a maximum estimation because some parts of the ELIP were not recognized or dismembered and destroyed during the Triassic to Cenozoic tectonism. In this paper, the chemostratigraphical data of the Zongza block, the Garze-Litang belt and the Songpan-Garze block suggest that the Late Permian basalts in these areas have remarkable similarities to the ELIP basalts in petrography and geochemistry. Flood basalts in the Sanjiangkou area are composed of the lower part of the low-Ti (LT) tholeiite and the upper part of the high-Ti (HT) tholeiite, which is the same as the flood basalts on the western margin of the Yangtze craton. Flood basalts in the Zongza and Songpan-Garze areas, which are far from the Yangtze craton, consist of HT tholeiite only. This is the same as the flood basalts within the Yangtze craton. Therefore we argue that these contemporary basalts all originated from the Emeishan mantle plume, and the ELIP could have a significant westward extension with an outcropped area of over 500,000 km2. This new scenario shows that the LT tholeiite occurs on the western margin of the Yangtze craton, while the HT tholeiite overlying the LT basalts occupies the whole area of the ELIP.展开更多
A suite of continental flood basalts sampled over a vast exposure and stratigraphic thickness in the Emeishan large igneous province （LIP）, SW China was investigated for laser microprobe ^40Ar/^39Ar dating. There ar...A suite of continental flood basalts sampled over a vast exposure and stratigraphic thickness in the Emeishan large igneous province （LIP）, SW China was investigated for laser microprobe ^40Ar/^39Ar dating. There are two ^40Ar/^39Ar age groups for these basalts, corresponding to 259-246 Ma and 177-137 Ma, respectively. A well-defined isochron gives an eruption age of huge quantities of mafic magmas at 258.9±3.4 Ma, which is identical to previous dating and paleontological data. Much younger ^40Ar/^39Ar ages for some basalts with Iow-greenschist metamorphic facies probably recorded a late thermo-tectonic event caused by collision between the Yangtze and Qiangtang continental blocks during the Mesozoic, which resulted in the reset of argon isotope system. The ^40Ar/^39Ar age data, we present here, combined with previous dating and paleontological data, suggest relatively short duration （about 3 Ma） of mafic volcanism, which have important implication on mantle plume genesis of the Emeishan continental flood basalts in the LIP.展开更多
Electronic microprobe analyses for olivine, clinopyroxene and Cr-spinel in picrites, which we have discovered recently in the Emeishan continental flood basalt province (ECFBP), show that the olivine is rich in Mg, an...Electronic microprobe analyses for olivine, clinopyroxene and Cr-spinel in picrites, which we have discovered recently in the Emeishan continental flood basalt province (ECFBP), show that the olivine is rich in Mg, and that Cr-spinel is rich in Cr. Based on the olivine-melt equilibrium, the primary parental melt compositions are calculated. The high-Mg olivine-hosted picrite can be regarded as parental melt. Thus, the melting temperature and pressure are estimated: T=1600℃ and P=4.5 GPa. It suggests that the picrites are connected with the activity of mantle plumes. Their major element composition is comparable to many other CFBs by their high Fe8, (CaO/Al2O3)8 and low Na8, indicating a high pressure. All rocks display a similar chondrite-normalized REE patterns, i.e., enrichment of LREE, relative depletion of HFSE and absence of negative Nb and Ta but depletion in P and K. Some incompatible element ratios, such as La/Ta, La/ Sm, (La/Nb)PM, (Th/Ta)PM, are in a limited range, show that they were derived from the mantle plume, and there was no or little crustal contamination during magma ascent en route to the surface. They were generated by 7% partial melting of garnet peridotite. The axis of the plume might be located beneath Lijiang Town, Yunnan province.展开更多
The Woniusi flood basalts from the Baoshan terrane,SW China,represent a significant eruption of volcanic rocks which were linked to the Late Paleozoic rifting of the Cimmeria from the northern margin of East Gondwana....The Woniusi flood basalts from the Baoshan terrane,SW China,represent a significant eruption of volcanic rocks which were linked to the Late Paleozoic rifting of the Cimmeria from the northern margin of East Gondwana.However,the precise mechanism for the formation and propagation of the rifting is still in debate.Here we report 40 Ar/39 Ar dating,whole-rock geochemistry,and Sr-Nd-Pb isotopes for the Woniusi basalts from the Baoshan terrane of SW China,with the aim of assessing if a mantle plume was related to the formation of the continent Cimmeria.40 Ar/39 Ar dating of the Woniusi basalts yielded ages of 279.3±1.1 Ma and 273.9±1.5 Ma,indicating they were emplaced during the Early Permian.Whole-rock geochemistry shows that these basalts have subalkaline tholeiitic affinity,low Ti O2(1.2-2.2 wt%),and fractionated chondrite-normalized LREE and nearly flat HREE patterns[(La/Yb)N=2.86-5.77;(Dy/Yb)N=1.21-1.49]with noticeable negative Nb and Ta anomalies on the primitive mantle-normalized trace element diagram.Theε(Nd)(t)values(-4.76 to+0.92)and high(206 Pb/204 Pb)i(18.40-18.66)along with partial melt modeling indicates that the basalts were likely derived from a sub-continental lithospheric mantle(SCLM)source metasomatized by subduction-related processes.On the basis of a similar emplacement age to the Panjal basalts and Qiangtang mafic dykes and flood basalts in the Himalayas,combined with a tectonic reconstruction of Gondwana in the Early Permian,we propose that the large-scale eruption of these basalts and dykes was related to an Early Permian mantle plume that possibly initiated the rifting on the northern margin of East Gondwana.展开更多
The detailed structures of the plumbing system of the early Permian Tarim flood basalt were investigated by 3-D seismic imaging.The images show that the Tarim flood basalt mainly erupted from central volcanoes distrib...The detailed structures of the plumbing system of the early Permian Tarim flood basalt were investigated by 3-D seismic imaging.The images show that the Tarim flood basalt mainly erupted from central volcanoes distributed展开更多
Since continental sediments （in addition to the marine geological record） offer important means of deciphering environmental changes, the sediments hosted by the successive flows of the continental flood basalt prov...Since continental sediments （in addition to the marine geological record） offer important means of deciphering environmental changes, the sediments hosted by the successive flows of the continental flood basalt provinces of the world should be treasure houses in gathering the palaeoclimatic data. Palaeosols developed on top of basalt flows are potentially ideal for palaeoenvironmental reconstructions because it is easy to determine their protolith geochemistry and also they define a definite time interval. The present paper summarizes the nature of the basalt-hosted palaeosols formed on the flood basalts provinces from different parts of the ~lobe havin~ different ages.展开更多
Rift formation is a crucial topic in global tectonics. The Yemen rift-related area is one of the most important provinces, being connected to the rifting processes of the Gulf of Aden, the Red Sea and Afar Triangle. I...Rift formation is a crucial topic in global tectonics. The Yemen rift-related area is one of the most important provinces, being connected to the rifting processes of the Gulf of Aden, the Red Sea and Afar Triangle. In this paper, a review of the Yemen volcanic province and its relations with the Red Sea rifting are presented. Tertiary continental extension in Yemen resulted in the extrusion of large volumes of effusive rocks. This magmatism is divided in the Oligo-Miocene Yemen Trap Series (YTS) separated by an unconformity from the Miocene-Recent Yemen Volcanic Series (YVS). Magmas of the YTS were erupted during the synrift phase and correlate with the first stage of sea-floor spreading of the Red Sea and the Gulf of Aden (30 - 15 Ma), whereas the magmas of the YVS were emplaced during the post rift phase (10 - 0 Ma). A continental within plate character is recognized for both the YTS and YVS basalts. The YTS volcanic rocks are contemporaneous with, and geochemically similar to, the Ethiopian rift volcanism, just as the volcanic fields of the YVS are geochemically alike to most of the Saudi Arabian volcanics. YTS and YVS have analogous SiO2 ranges, but YVS tend to have, on average, higher alkalis and MgO contents than YTS. Fractional crystallization processes dominate geochemical variations of both series. Primitive magmas (MgO > 7.0%) are enriched in incompatible elements and LREEs with respect to primitive mantle, but YVS are more enriched than YTS. To first order, the different geochemical patterns agree with different degrees of partial melting of an astenospheric mantle source: 25% - 30% of partial melting for YTS and 10% - 3% for YVS. Secondly, the higher degree of enrichment in incompatible elements of YVS reflects also greater contribution of a lithospheric mantle component in their source region.展开更多
The voluminous Choke Shield basalts and flood basalts are distributed in the central Ethiopian Plateau.They are tholeiitic in composition and have OIB-like geochemical features.The ca.23 Ma Choke Shield basalts have S...The voluminous Choke Shield basalts and flood basalts are distributed in the central Ethiopian Plateau.They are tholeiitic in composition and have OIB-like geochemical features.The ca.23 Ma Choke Shield basalts have SiO_(2)(47.1 wt.%-59.6 wt.%),MgO(1.01 wt.%-7.8 wt.%),Na_(2)O+K_(2)O(2.7 wt.%-8.4 wt.%),and display right inclined REE patterns((La/Yb)N=21.4-24.2) with enrichment of Nb,Ta,Zr,Hf and Pb in the primitive mantle-normalized trace element diagrams.They show low initial ^(87)Sr/^(86)Sr ratios(0.703 47-0.703 77) and high ε_(Nd)(t) values(+4.4 to+5.0).In comparison,the 24Ma high-Ti(HT1) flood basalts have SiO_(2)(38.9 wt.%-50.8 wt.%),MgO(3.9 wt.%-11.4 wt.%),Na_(2)O+K_(2)O(1.6 wt.%-5.8 wt.%), and display right inclined REE patterns((La/Yb)N=24-130.3) with enrichment of Nb,Ta,Zr,Hf,and Pb.They also show low initial ^(87)Sr/^(86)Sr ratios(0.703 30-0.704 44) and highε_(Nd)(t) values(+2.2 to+5.3).Both types of basalts were contaminated by minor crustal materials and underwent fractional crystallization of clinopyroxene,plagioclase,olivine,and minor Fe-Ti oxide.The Choke Shield basalts were generated by 1%-5% melting of garnet-spinel to phlogopite-bearing spinel lherzolite in a shallow zone of the mantle plume,while the flood basalts were formed by <20% melting of amphibole-bearing garnet to garnet-spinel lherzolite in a deeper zone of the same mantle plume.The mantle source beneath the central Ethiopian Plateau was significantly heterogeneous during the Tertiary.It was characterized by EMI and EMII end-members that were formed by the metasomatism of the different components.展开更多
Proterozoic volcanic rocks of the western part from the North Qilian Mountains are the products of continental rift volcanism, belonging to continental flood basalts, the petrogeochemistry of which apears to suggest t...Proterozoic volcanic rocks of the western part from the North Qilian Mountains are the products of continental rift volcanism, belonging to continental flood basalts, the petrogeochemistry of which apears to suggest that they are derived from sub-lithospheric mantle plume sources, but that they also show evidence of continental lithosphere components involvement. Their formation is the consequences of plume-lithosphere interactions and is precursive to the opening of the North Qilian Early-Paleozoic ocean basin.展开更多
The detailed structures of the volcanic edifice and plumbing system of the early Permian Tarim flood basalt were investigated by three-dimensional seismic imaging. The images show that the Tarim flood basalt erupted f...The detailed structures of the volcanic edifice and plumbing system of the early Permian Tarim flood basalt were investigated by three-dimensional seismic imaging. The images show that the Tarim flood basalt erupted from central volcanoes distributed along major faults. The uppermost magma formed a single lava lobe with a volume of *0.74 km3 and an aspect ratio of 50,implying a sheet flow eruption with a high effusion rate. At the subsurface level, all central volcanoes, irrespective of size, had a separate pipe-like feeder vent. Only thirteen dikes were identified at shallow depths of \100 m below the lava surface; deeper dikes were even rarer. The pipelike plumbing system and the paucity of dilational dikes were different from the typical plumbing system of flood basalt provinces on Earth, which are normally buoyancycontrolled dike–sill networks. A gas-driven vigorous eruption can be inferred from the imaged structure, which means that the Tarim flood basalt may have carried and released a large proportion of volcanic gas, similar to some mafic volcaniclastic deposit-bearing continental flood basalt provinces.展开更多
The West Congo Belt contains in its rocks of Neoproterozoic age from Nemba complex outcropping in the Moumba River. This West Congo belt is made up of a crustal segment of the Arcuaï-West Congo orogen which exten...The West Congo Belt contains in its rocks of Neoproterozoic age from Nemba complex outcropping in the Moumba River. This West Congo belt is made up of a crustal segment of the Arcuaï-West Congo orogen which extends from southwest Gabon to the northeast of Angola. This study aims to constrain the geochemical signature Nemba complex of West Congo belt from the petrograhic and geochemical study on the whole rock. The petrographic data from this study show the Moumba metabasites are made up of amphibolites, metagabbros, epidotites and greenschists interstratified in the Eburnean metasediments and affected by mesozonal to epizonal metamorphism characterized by the retromorphosis of intermediate amphibolite facies minerals into greenschist facies. Whole-rock geochemical data indicate that these metabasites are continental flood basalts (CFB) of basic nature and transitional affinity emplaced in intraplate context. These continental flood basalts are generated from magma originating from a significantly enriched shallow mantle plume and this magma then contaminated by the continental crust during their ascent. The reconstruction of tectonic signature suggests that West Congo belt would result from closure of an ocean basin with subduction phenomena. This collision would be marked by the establishment of ophiolite complex. We show that this model is incompatible with the CFB nature of metabasites and the orogenic evolution of Neoproterozoic. It does not seem that we can evoke a genetic link with a subduction of oceanic crust, because the paleogeography of Neoproterozoic (Rodinia) is marked by intracontinental rifts linked to opening of Rodinia. We therefore suggest the non-existence of ophiolitic complex in western Congo belt and reject the collisional model published by certain authors. We confirm the currently available intracontinental orogen model.展开更多
Thermal conductivity and mineral composition of flood basalt in Al Hashimiyya city were correlated. Representative thin sections were optically analyzed for their mineral constituents and micro fractures. Findings of ...Thermal conductivity and mineral composition of flood basalt in Al Hashimiyya city were correlated. Representative thin sections were optically analyzed for their mineral constituents and micro fractures. Findings of this study will contribute to a comprehensive understanding of the correlation between selected petrological characteristics of basalts and their heat conduction properties. It found that a 10% increase of opaque and ferromagnesian minerals volume in the studied basalts leads to a thermal conductivity increasing by 0.4 W•m−1•K−1. This may considerably contribute to provide an alternative to direct measurements of the thermal conductivity in Jordan basalts if a sufficient mineralogical data set is achievable. Thus, the prediction of thermal conductivity through modal mineral composition may become a significant feature for efficient geothermal system exploration in basaltic rocks. The results can be brought together into a petrophysical and hydrogeothermal model for better reservoir characterization. Such models will improve the assessment of the basalt’s suitability as a geothermal reservoir for cooling and heating utilizations.展开更多
文摘The Late Permian Emeishan Large Igneous Province (ELIP) is commonly regarded as being located in the western part of the Yangtze craton, SW China, with an asymmetrical shape and a small area. This area, however, is just a maximum estimation because some parts of the ELIP were not recognized or dismembered and destroyed during the Triassic to Cenozoic tectonism. In this paper, the chemostratigraphical data of the Zongza block, the Garze-Litang belt and the Songpan-Garze block suggest that the Late Permian basalts in these areas have remarkable similarities to the ELIP basalts in petrography and geochemistry. Flood basalts in the Sanjiangkou area are composed of the lower part of the low-Ti (LT) tholeiite and the upper part of the high-Ti (HT) tholeiite, which is the same as the flood basalts on the western margin of the Yangtze craton. Flood basalts in the Zongza and Songpan-Garze areas, which are far from the Yangtze craton, consist of HT tholeiite only. This is the same as the flood basalts within the Yangtze craton. Therefore we argue that these contemporary basalts all originated from the Emeishan mantle plume, and the ELIP could have a significant westward extension with an outcropped area of over 500,000 km2. This new scenario shows that the LT tholeiite occurs on the western margin of the Yangtze craton, while the HT tholeiite overlying the LT basalts occupies the whole area of the ELIP.
基金supported by a Youth Foundation from the former Ministry of GeologyMineral Resources and an 0utstanding Youth Foundation from the National Natural Science Foundation of China(grant 40425014).
文摘A suite of continental flood basalts sampled over a vast exposure and stratigraphic thickness in the Emeishan large igneous province （LIP）, SW China was investigated for laser microprobe ^40Ar/^39Ar dating. There are two ^40Ar/^39Ar age groups for these basalts, corresponding to 259-246 Ma and 177-137 Ma, respectively. A well-defined isochron gives an eruption age of huge quantities of mafic magmas at 258.9±3.4 Ma, which is identical to previous dating and paleontological data. Much younger ^40Ar/^39Ar ages for some basalts with Iow-greenschist metamorphic facies probably recorded a late thermo-tectonic event caused by collision between the Yangtze and Qiangtang continental blocks during the Mesozoic, which resulted in the reset of argon isotope system. The ^40Ar/^39Ar age data, we present here, combined with previous dating and paleontological data, suggest relatively short duration （about 3 Ma） of mafic volcanism, which have important implication on mantle plume genesis of the Emeishan continental flood basalts in the LIP.
基金the National Key Fundamental Research Project(No.G1999043205) the National National Science Foundation of China(Nos.40273020 , 40172026) Program of Excellent Young Scientists of the Ministry of Land and Resources.
文摘Electronic microprobe analyses for olivine, clinopyroxene and Cr-spinel in picrites, which we have discovered recently in the Emeishan continental flood basalt province (ECFBP), show that the olivine is rich in Mg, and that Cr-spinel is rich in Cr. Based on the olivine-melt equilibrium, the primary parental melt compositions are calculated. The high-Mg olivine-hosted picrite can be regarded as parental melt. Thus, the melting temperature and pressure are estimated: T=1600℃ and P=4.5 GPa. It suggests that the picrites are connected with the activity of mantle plumes. Their major element composition is comparable to many other CFBs by their high Fe8, (CaO/Al2O3)8 and low Na8, indicating a high pressure. All rocks display a similar chondrite-normalized REE patterns, i.e., enrichment of LREE, relative depletion of HFSE and absence of negative Nb and Ta but depletion in P and K. Some incompatible element ratios, such as La/Ta, La/ Sm, (La/Nb)PM, (Th/Ta)PM, are in a limited range, show that they were derived from the mantle plume, and there was no or little crustal contamination during magma ascent en route to the surface. They were generated by 7% partial melting of garnet peridotite. The axis of the plume might be located beneath Lijiang Town, Yunnan province.
基金supported by the National Natural Science Foundation of China(NSFC)(No.41703030)Natural Science Foundation of Jiangxi Province(No.20192BAB213024)+1 种基金China Scholarship Council(No.201808360273)the research grant of Shandong Key Laboratory of Depositional Mineralization&Sedimentary Minerals,Shandong University of Science and Technology(No.DMSM20190029)。
文摘The Woniusi flood basalts from the Baoshan terrane,SW China,represent a significant eruption of volcanic rocks which were linked to the Late Paleozoic rifting of the Cimmeria from the northern margin of East Gondwana.However,the precise mechanism for the formation and propagation of the rifting is still in debate.Here we report 40 Ar/39 Ar dating,whole-rock geochemistry,and Sr-Nd-Pb isotopes for the Woniusi basalts from the Baoshan terrane of SW China,with the aim of assessing if a mantle plume was related to the formation of the continent Cimmeria.40 Ar/39 Ar dating of the Woniusi basalts yielded ages of 279.3±1.1 Ma and 273.9±1.5 Ma,indicating they were emplaced during the Early Permian.Whole-rock geochemistry shows that these basalts have subalkaline tholeiitic affinity,low Ti O2(1.2-2.2 wt%),and fractionated chondrite-normalized LREE and nearly flat HREE patterns[(La/Yb)N=2.86-5.77;(Dy/Yb)N=1.21-1.49]with noticeable negative Nb and Ta anomalies on the primitive mantle-normalized trace element diagram.Theε(Nd)(t)values(-4.76 to+0.92)and high(206 Pb/204 Pb)i(18.40-18.66)along with partial melt modeling indicates that the basalts were likely derived from a sub-continental lithospheric mantle(SCLM)source metasomatized by subduction-related processes.On the basis of a similar emplacement age to the Panjal basalts and Qiangtang mafic dykes and flood basalts in the Himalayas,combined with a tectonic reconstruction of Gondwana in the Early Permian,we propose that the large-scale eruption of these basalts and dykes was related to an Early Permian mantle plume that possibly initiated the rifting on the northern margin of East Gondwana.
文摘The detailed structures of the plumbing system of the early Permian Tarim flood basalt were investigated by 3-D seismic imaging.The images show that the Tarim flood basalt mainly erupted from central volcanoes distributed
文摘Since continental sediments （in addition to the marine geological record） offer important means of deciphering environmental changes, the sediments hosted by the successive flows of the continental flood basalt provinces of the world should be treasure houses in gathering the palaeoclimatic data. Palaeosols developed on top of basalt flows are potentially ideal for palaeoenvironmental reconstructions because it is easy to determine their protolith geochemistry and also they define a definite time interval. The present paper summarizes the nature of the basalt-hosted palaeosols formed on the flood basalts provinces from different parts of the ~lobe havin~ different ages.
文摘Rift formation is a crucial topic in global tectonics. The Yemen rift-related area is one of the most important provinces, being connected to the rifting processes of the Gulf of Aden, the Red Sea and Afar Triangle. In this paper, a review of the Yemen volcanic province and its relations with the Red Sea rifting are presented. Tertiary continental extension in Yemen resulted in the extrusion of large volumes of effusive rocks. This magmatism is divided in the Oligo-Miocene Yemen Trap Series (YTS) separated by an unconformity from the Miocene-Recent Yemen Volcanic Series (YVS). Magmas of the YTS were erupted during the synrift phase and correlate with the first stage of sea-floor spreading of the Red Sea and the Gulf of Aden (30 - 15 Ma), whereas the magmas of the YVS were emplaced during the post rift phase (10 - 0 Ma). A continental within plate character is recognized for both the YTS and YVS basalts. The YTS volcanic rocks are contemporaneous with, and geochemically similar to, the Ethiopian rift volcanism, just as the volcanic fields of the YVS are geochemically alike to most of the Saudi Arabian volcanics. YTS and YVS have analogous SiO2 ranges, but YVS tend to have, on average, higher alkalis and MgO contents than YTS. Fractional crystallization processes dominate geochemical variations of both series. Primitive magmas (MgO > 7.0%) are enriched in incompatible elements and LREEs with respect to primitive mantle, but YVS are more enriched than YTS. To first order, the different geochemical patterns agree with different degrees of partial melting of an astenospheric mantle source: 25% - 30% of partial melting for YTS and 10% - 3% for YVS. Secondly, the higher degree of enrichment in incompatible elements of YVS reflects also greater contribution of a lithospheric mantle component in their source region.
基金supported by China Commerce Ministry (foreign-aid project (2007)420)China Geological Survey (Nos. DD20190443, DD20160109)。
文摘The voluminous Choke Shield basalts and flood basalts are distributed in the central Ethiopian Plateau.They are tholeiitic in composition and have OIB-like geochemical features.The ca.23 Ma Choke Shield basalts have SiO_(2)(47.1 wt.%-59.6 wt.%),MgO(1.01 wt.%-7.8 wt.%),Na_(2)O+K_(2)O(2.7 wt.%-8.4 wt.%),and display right inclined REE patterns((La/Yb)N=21.4-24.2) with enrichment of Nb,Ta,Zr,Hf and Pb in the primitive mantle-normalized trace element diagrams.They show low initial ^(87)Sr/^(86)Sr ratios(0.703 47-0.703 77) and high ε_(Nd)(t) values(+4.4 to+5.0).In comparison,the 24Ma high-Ti(HT1) flood basalts have SiO_(2)(38.9 wt.%-50.8 wt.%),MgO(3.9 wt.%-11.4 wt.%),Na_(2)O+K_(2)O(1.6 wt.%-5.8 wt.%), and display right inclined REE patterns((La/Yb)N=24-130.3) with enrichment of Nb,Ta,Zr,Hf,and Pb.They also show low initial ^(87)Sr/^(86)Sr ratios(0.703 30-0.704 44) and highε_(Nd)(t) values(+2.2 to+5.3).Both types of basalts were contaminated by minor crustal materials and underwent fractional crystallization of clinopyroxene,plagioclase,olivine,and minor Fe-Ti oxide.The Choke Shield basalts were generated by 1%-5% melting of garnet-spinel to phlogopite-bearing spinel lherzolite in a shallow zone of the mantle plume,while the flood basalts were formed by <20% melting of amphibole-bearing garnet to garnet-spinel lherzolite in a deeper zone of the same mantle plume.The mantle source beneath the central Ethiopian Plateau was significantly heterogeneous during the Tertiary.It was characterized by EMI and EMII end-members that were formed by the metasomatism of the different components.
文摘Proterozoic volcanic rocks of the western part from the North Qilian Mountains are the products of continental rift volcanism, belonging to continental flood basalts, the petrogeochemistry of which apears to suggest that they are derived from sub-lithospheric mantle plume sources, but that they also show evidence of continental lithosphere components involvement. Their formation is the consequences of plume-lithosphere interactions and is precursive to the opening of the North Qilian Early-Paleozoic ocean basin.
基金supported by the National Basic Research Program of China(2010CB808906)the National Natural Science Foundation of China(41272368)to WT
文摘The detailed structures of the volcanic edifice and plumbing system of the early Permian Tarim flood basalt were investigated by three-dimensional seismic imaging. The images show that the Tarim flood basalt erupted from central volcanoes distributed along major faults. The uppermost magma formed a single lava lobe with a volume of *0.74 km3 and an aspect ratio of 50,implying a sheet flow eruption with a high effusion rate. At the subsurface level, all central volcanoes, irrespective of size, had a separate pipe-like feeder vent. Only thirteen dikes were identified at shallow depths of \100 m below the lava surface; deeper dikes were even rarer. The pipelike plumbing system and the paucity of dilational dikes were different from the typical plumbing system of flood basalt provinces on Earth, which are normally buoyancycontrolled dike–sill networks. A gas-driven vigorous eruption can be inferred from the imaged structure, which means that the Tarim flood basalt may have carried and released a large proportion of volcanic gas, similar to some mafic volcaniclastic deposit-bearing continental flood basalt provinces.
文摘The West Congo Belt contains in its rocks of Neoproterozoic age from Nemba complex outcropping in the Moumba River. This West Congo belt is made up of a crustal segment of the Arcuaï-West Congo orogen which extends from southwest Gabon to the northeast of Angola. This study aims to constrain the geochemical signature Nemba complex of West Congo belt from the petrograhic and geochemical study on the whole rock. The petrographic data from this study show the Moumba metabasites are made up of amphibolites, metagabbros, epidotites and greenschists interstratified in the Eburnean metasediments and affected by mesozonal to epizonal metamorphism characterized by the retromorphosis of intermediate amphibolite facies minerals into greenschist facies. Whole-rock geochemical data indicate that these metabasites are continental flood basalts (CFB) of basic nature and transitional affinity emplaced in intraplate context. These continental flood basalts are generated from magma originating from a significantly enriched shallow mantle plume and this magma then contaminated by the continental crust during their ascent. The reconstruction of tectonic signature suggests that West Congo belt would result from closure of an ocean basin with subduction phenomena. This collision would be marked by the establishment of ophiolite complex. We show that this model is incompatible with the CFB nature of metabasites and the orogenic evolution of Neoproterozoic. It does not seem that we can evoke a genetic link with a subduction of oceanic crust, because the paleogeography of Neoproterozoic (Rodinia) is marked by intracontinental rifts linked to opening of Rodinia. We therefore suggest the non-existence of ophiolitic complex in western Congo belt and reject the collisional model published by certain authors. We confirm the currently available intracontinental orogen model.
文摘Thermal conductivity and mineral composition of flood basalt in Al Hashimiyya city were correlated. Representative thin sections were optically analyzed for their mineral constituents and micro fractures. Findings of this study will contribute to a comprehensive understanding of the correlation between selected petrological characteristics of basalts and their heat conduction properties. It found that a 10% increase of opaque and ferromagnesian minerals volume in the studied basalts leads to a thermal conductivity increasing by 0.4 W•m−1•K−1. This may considerably contribute to provide an alternative to direct measurements of the thermal conductivity in Jordan basalts if a sufficient mineralogical data set is achievable. Thus, the prediction of thermal conductivity through modal mineral composition may become a significant feature for efficient geothermal system exploration in basaltic rocks. The results can be brought together into a petrophysical and hydrogeothermal model for better reservoir characterization. Such models will improve the assessment of the basalt’s suitability as a geothermal reservoir for cooling and heating utilizations.
