Gabbroic and poikilitic shergottites are intrusive igneous rocks on Mars,providing significant insights into the igneous processes within the Martian crust.However,questions remain regarding the chemical signatures of...Gabbroic and poikilitic shergottites are intrusive igneous rocks on Mars,providing significant insights into the igneous processes within the Martian crust.However,questions remain regarding the chemical signatures of their source reservoirs and the petrogenetic links among shergottites of different subtypes.In this study,we present petrological and mineralogical analyses of the intermediate shergottite Northwest Africa(NWA)12241.Quantitative textural analysis and pyroxene chemistry indicate that,despite minor differences such as the accumulation of intermediate-sized olivine and smaller pyroxene oikocrysts,NWA 12241 has experienced a similar emplacement history as typical poikilitic and gabbroic shergottites.The estimated parent melt of NWA 12241 is consistent with derivation from an intermediate source reservoir,resulting from the mixing of enriched and depleted mantle end-members at depth,prior to magma ascent.Similar emplacement histories of variable poikilitic and gabbroic shergottites suggest the common presence of multiple staging magma chambers with different compositions at the crust–mantle boundary,coupled with prolonged ponding at this depth.Our study highlights that,in addition to magma mixing and assimilation,magmatic differentiation and cooling conditions at shallow depths are crucial processes leading to textural and compositional variations among shergottites of different subtypes.展开更多
The Dharwar Craton in India,as one of the oldest cratons in the world,preserves key information of early continental crust evolution.However,a~3.0 Ga tectonothermal event was previously recognized only in the Western ...The Dharwar Craton in India,as one of the oldest cratons in the world,preserves key information of early continental crust evolution.However,a~3.0 Ga tectonothermal event was previously recognized only in the Western Dharwar Craton,and the coeval tectono-thermal event has been rarely reported in the Central Dharwar Block.In this study,zircon U-Pb dating of the gabbroic diorite xenolith from Neoarchean Closepet batholith yields an age of 2995±13 Ma,confirming the~3.0 Ga magmatism in the Central Dharwar Block.The gabbroic diorite is characterized by low SiO_(2)(52.62%-53.42%)and high MgO(5.38%-5.42%),Cr(48-70)×10^(-6),and Ni(115-124)×10^(-6),with relative enrichment in LILEs and LREE and depletion in HFSEs as well as negative Nd(ε_(Nd)(t)=−4.8 to−4.5)and Hf(ε_(Hf)(t)=−6.64 to−2.36)isotopes,indicating an enriched mantle source.Furthermore,geochemical signatures of zircon,clinopyroxene,and hornblende indicate that this magmatism occurred in an environment with water enrichment and high oxygen fugacity,similar to the island-arc setting,suggesting that the gabbroic diorite was produced by partial melting of enriched mantle source under a subduction zone.Additionally,the mafic magmatism in the Dharwar Craton evidently decreased from 3.2 to 3.0 Ga,accompanied by a transition of crustal components from Na-rich to K-rich,implying that a significant tectonic regime shift had already happened in the Dharwar Craton around~3.0 Ga.Considering the enriched isotopic composition of the gabbroic diorite and previous studies on the Dharwar Craton from 3.2 to 3.0 Ga,it suggests that the Dharwar Craton might have undergone a vertical-to-lateral tectonic transition beginning at~3.2 Ga and lasting until~3.0 Ga,and the subduction related to the plate tectonic probably started in a specific scale.展开更多
Nine pieces of gabbroic xenoliths from Hannuoba were examined for their major and trace elements and Nd,Sr and Pb isotopes.The results show that the gab-broic xenoliths are of more mafic basaltic composition .Their ab...Nine pieces of gabbroic xenoliths from Hannuoba were examined for their major and trace elements and Nd,Sr and Pb isotopes.The results show that the gab-broic xenoliths are of more mafic basaltic composition .Their abundances show narrow variations in major elements.The trace element contents are highly variable in contrast with those of host basalts and lherzolite xenoliths.The gabbroic xenoliths are rich in Nd(0.51159-0.51249),Sr(0.70491-0.70768) and low in radiogenic Pb(16.283-17.046, 15.191-15.381 and 36.999-37.476),significantly different from basalts and lherzolites in isotopic space.The calculated Nd and Pb model ages are about 3.0-3.5 Ga.The rocks have relatively low equilibrium T(-850℃) and P(0.8-0.9 Gpa).They could be inter-preted to be the product of upper mantle melting at the boundary between the lower crust and the upper mantle.Their chemical and isotopic variations can be ascribed to different degrees of melting,segregation and long-term evolution.展开更多
High-Mg andesites(HMAs)typically originate in subduction-related tectonic settings,including active continental margins and island arcs,and studies of HMAs can constrain the tectonic evolution of the South China Block...High-Mg andesites(HMAs)typically originate in subduction-related tectonic settings,including active continental margins and island arcs,and studies of HMAs can constrain the tectonic evolution of the South China Block and Paleo-Tethyan Ocean.This paper presents new chronological and geochemical data for high-Mg gabbroic diorites in the Funing area,southern South China.The gabbroic diorites yield ages of 254-249 Ma,and have moderate SiO2 contents(51.3%-57.8%),high MgO contents(4.6%-10.2%)and Mg^(#)values(52-75),enrichment in large-ion lithophile elements and light rare earth elements,and depletion in high-field-strength elements-collectively displaying geochemical signatures typical of sanukites.The gabbroic diorites have radiogenic initial Sr and Pb isotopic compositions,and negativeεNd(t)andεHf(t)values.These characteristics distinguish the Funing gabbroic diorites from subduction-related igneous rocks in the Paleo-Pacific tectonic domain.Instead,they are isotopically similar to HMAs and basalts along the Paleo-Tethys suture.We propose the high-Mg gabbroic diorites and basaltic andesites in Funing area share a common mantle source,linked to subduction and rollback of the Paleo-Tethyan plate beneath the South China Block,which triggered back-arc rifting and partial melting of the metasomatized lithospheric mantle during the Late Permian to Early Triassic.展开更多
The Dharwar Craton(DC)in India consists of three distinct Archean blocks.Previous research suggests that the Central Dharwar Block(CDB)experienced a geological history(3.3-2.5 Ga)comparable to the Western Dharwar Crat...The Dharwar Craton(DC)in India consists of three distinct Archean blocks.Previous research suggests that the Central Dharwar Block(CDB)experienced a geological history(3.3-2.5 Ga)comparable to the Western Dharwar Craton(WDC).However,3.0-2.7 Ga geological records are missed in the CDB.This study identified the 2.85 Ga gabbroic xenoliths within the Closepet batholith in the CDB.The~2.85 Ga inherited zircons and zircon Hf model ages in CDB further provide evidence for this significant magmatic event.The gabbroic xenoliths are characterized by E-MORB REE patterns and Nb,Ta,and Ti depletions,together with high radiogenic isotopic signatures,including zircon Hf(ε_(Hf)(t)_(min)=-3.2),whole-rock Nd(ε_(Nd)(t)=-0.8-0.7),and Pb isotopes(κ=4.9-7.9),indicating derivation from a slightly enriched mantle source.Additionally,they have high Nb(4.41 to 4.73 ppm),low Ti/V(23.4 to 22.5),and elevated Th/Yb(0.38 to 0.61).All these suggest a subduction-related back-arc basin setting.Coupled with widespread early Neoarchean subduction-related igneous rocks in the DC,the 2.85 Ga gabbroic magmatism signifies that the DC had transitioned into a tectonic stage dominated by lateral movement of continental blocks around 2.85 Ga,corresponding to global~2.85 Ga magmatic events.展开更多
Magmatic oxide deposits in the～260 Ma Emeishan Large Igneous Province（ELIP）,SW China and northern Vietnam,are important sources of Fe,Ti and V.Some giant magmatic Fe-Ti-V oxide deposits, such as the Panzhihua,Hongg...Magmatic oxide deposits in the～260 Ma Emeishan Large Igneous Province（ELIP）,SW China and northern Vietnam,are important sources of Fe,Ti and V.Some giant magmatic Fe-Ti-V oxide deposits, such as the Panzhihua,Hongge,and Baima deposits,are well described in the literature and are hosted in layered mafic-ultramafic intrusions in the Panxi region,the central ELIP.The same type of ELIP- related deposits also occur far to the south and include the Anyi deposit,about 130 km south of Panzhihua,and the Mianhuadi deposit in the Red River fault zone.The Anyi deposit is relatively small but is similarly hosted in a layered mafic intrusion.The Mianhuadi deposit has a zircon U-Pb age of～260 Ma and is thus contemporaneous with the ELIP.This deposit was variably metamorphosed during the Indosinian orogeny and Red River faulting.Compositionally,magnetite of the Mianhuadi deposit contains smaller amounts of Ti and V than that of the other deposits,possibly attributable to the later metamorphism.The distribution of the oxide ore deposits is not related to the domal structure of the ELIP.One major feature of all the oxide deposits in the ELIP is the spatial association of oxide-bearing gabbroic intrusions,syenitic plutons and high-Ti flood basalts.Thus,we propose that magmas from a mantle plume were emplaced into a shallow magma chamber where they were evolved into a field of liquid immiscibility to form two silicate liquids,one with an extremely Fe-Ti-rich gabbroic composition and the other syenitic.An immiscible Fe-Ti-（P） oxide melt may then separate from the mafic magmas to form oxide deposits.The parental magmas from which these deposits formed were likely Fe-Ti-rich picritic in composition and were derived from enriched asthenospheric mantle at a greater depth than the magmas that produced sulfide-bearing intrusions of the ELIP.展开更多
Emplacement ages, geochemical characteristics and analysis of continental dynamics on gabbroic intrusions in Luodian County, Guizhou Province, have been discussed based on studies of isotopic chronology （the whole-ro...Emplacement ages, geochemical characteristics and analysis of continental dynamics on gabbroic intrusions in Luodian County, Guizhou Province, have been discussed based on studies of isotopic chronology （the whole-rock Sm-Nd and Rb-Sr isochron methods）, major elements, trace elements and PGE. Intrusive activities of the gabbroic intrusions in the study area took place during the Late Yanshanian Orogenic Movement （the Cretaceous Period）, as indicated by the Sm-Nd isochron ages （t）=（99.6±4.5） （2σ） Ma and by the Rb-Sr isochron ages t=（97±1.6） （2σ） Ma. The gabbroic intrusions are attached to mafic rocks in cal-alkaline basaltic series. They occurred as dikes and might be formed under an extensional background of the continent. Differentiation of their magmatic crystallization resulted in obvious zonation of petrography. In the gabbroic intrusions of this study, large ion lithophile elements and LREE are enriched, and the chondrite-normalized REE distribution pattern is leftward inclined without anomalies of JCe or JEu, and there are high concentrations of PGE and ratios of Pd/Ir （averaging 4.21）. All of these imply that their source areas may be basaltic magma in the upper mantle with high-level partial melting, derived from EMl-type enriched mantle. It is different from Emeishan basalt, which may be related to the upper mantle at low-grade partial melting. Emplacement mechanism of the gabbroic intrusions in this study may suppose to be asthenosphere upheaving as an isolated hot wave in the presence of mantle fluid, resulting in basaltic magma intruded into the continental crust as a diapiric intrusion. Therefore, uplifting of faulting-block and extensional deformation could take place in the shallow part of the continental crust while vertical amassing and accretion of magmatic materials in the deep part of the continental crust. These special processes could supposed to be a special background of continental dynamics for this large-scale epithermal metallogenic domain, such as Au, As, Sb and Hg deposits, and vertical uplifting of the Yunnan-Guizhou Plateau in the Cretaceous Period.展开更多
The Bethampudi layered anorthosite complex at the border zone of Archaean supracrustal rocks of Khammam district, Eastern Ghats shows normal stratification predominantly in the form of rhythmic layering and often exhi...The Bethampudi layered anorthosite complex at the border zone of Archaean supracrustal rocks of Khammam district, Eastern Ghats shows normal stratification predominantly in the form of rhythmic layering and often exhibits of zebra layering. Graded bedding and cumulate structures are also noticed. The rocks of the study area are classified based on petrography into anorthositic rocks, gabbroic rocks and ultramafic rocks and amphibolites. The field relations and major element composition suggest that these anorthosite rocks are of calc-alkaline in nature and petrogenitically related to the gabbroic rocks by the fractional crystallization at ℃.展开更多
基金supported by the National Natural Science Foundation of China(Nos.42473049,42241108,and 42273040)the Guangdong Basic and Applied Basic Research Foundation(No.2024A1515011311)the Open Project for Innovative Platform of Meteoritical Research,Shanghai Science and Technology Museum。
文摘Gabbroic and poikilitic shergottites are intrusive igneous rocks on Mars,providing significant insights into the igneous processes within the Martian crust.However,questions remain regarding the chemical signatures of their source reservoirs and the petrogenetic links among shergottites of different subtypes.In this study,we present petrological and mineralogical analyses of the intermediate shergottite Northwest Africa(NWA)12241.Quantitative textural analysis and pyroxene chemistry indicate that,despite minor differences such as the accumulation of intermediate-sized olivine and smaller pyroxene oikocrysts,NWA 12241 has experienced a similar emplacement history as typical poikilitic and gabbroic shergottites.The estimated parent melt of NWA 12241 is consistent with derivation from an intermediate source reservoir,resulting from the mixing of enriched and depleted mantle end-members at depth,prior to magma ascent.Similar emplacement histories of variable poikilitic and gabbroic shergottites suggest the common presence of multiple staging magma chambers with different compositions at the crust–mantle boundary,coupled with prolonged ponding at this depth.Our study highlights that,in addition to magma mixing and assimilation,magmatic differentiation and cooling conditions at shallow depths are crucial processes leading to textural and compositional variations among shergottites of different subtypes.
基金funded by the National Science Foundation of China(grant Nos.41890831 and 41772189)the Most Special Fund from State Key Laboratory of Continental Dynamics,Northwest University,Xi’an,China(grant No.201210133).
文摘The Dharwar Craton in India,as one of the oldest cratons in the world,preserves key information of early continental crust evolution.However,a~3.0 Ga tectonothermal event was previously recognized only in the Western Dharwar Craton,and the coeval tectono-thermal event has been rarely reported in the Central Dharwar Block.In this study,zircon U-Pb dating of the gabbroic diorite xenolith from Neoarchean Closepet batholith yields an age of 2995±13 Ma,confirming the~3.0 Ga magmatism in the Central Dharwar Block.The gabbroic diorite is characterized by low SiO_(2)(52.62%-53.42%)and high MgO(5.38%-5.42%),Cr(48-70)×10^(-6),and Ni(115-124)×10^(-6),with relative enrichment in LILEs and LREE and depletion in HFSEs as well as negative Nd(ε_(Nd)(t)=−4.8 to−4.5)and Hf(ε_(Hf)(t)=−6.64 to−2.36)isotopes,indicating an enriched mantle source.Furthermore,geochemical signatures of zircon,clinopyroxene,and hornblende indicate that this magmatism occurred in an environment with water enrichment and high oxygen fugacity,similar to the island-arc setting,suggesting that the gabbroic diorite was produced by partial melting of enriched mantle source under a subduction zone.Additionally,the mafic magmatism in the Dharwar Craton evidently decreased from 3.2 to 3.0 Ga,accompanied by a transition of crustal components from Na-rich to K-rich,implying that a significant tectonic regime shift had already happened in the Dharwar Craton around~3.0 Ga.Considering the enriched isotopic composition of the gabbroic diorite and previous studies on the Dharwar Craton from 3.2 to 3.0 Ga,it suggests that the Dharwar Craton might have undergone a vertical-to-lateral tectonic transition beginning at~3.2 Ga and lasting until~3.0 Ga,and the subduction related to the plate tectonic probably started in a specific scale.
文摘Nine pieces of gabbroic xenoliths from Hannuoba were examined for their major and trace elements and Nd,Sr and Pb isotopes.The results show that the gab-broic xenoliths are of more mafic basaltic composition .Their abundances show narrow variations in major elements.The trace element contents are highly variable in contrast with those of host basalts and lherzolite xenoliths.The gabbroic xenoliths are rich in Nd(0.51159-0.51249),Sr(0.70491-0.70768) and low in radiogenic Pb(16.283-17.046, 15.191-15.381 and 36.999-37.476),significantly different from basalts and lherzolites in isotopic space.The calculated Nd and Pb model ages are about 3.0-3.5 Ga.The rocks have relatively low equilibrium T(-850℃) and P(0.8-0.9 Gpa).They could be inter-preted to be the product of upper mantle melting at the boundary between the lower crust and the upper mantle.Their chemical and isotopic variations can be ascribed to different degrees of melting,segregation and long-term evolution.
基金supported by the National Natural Science Foundation of China (42473063)Guike AD24010023, the Seventh Guangxi Zhuang Autonomous Region Bagui Scholars Program (to LIU Xijun)the Guangxi Natural Science Foundations of China (2025GXNSFBA069054)
文摘High-Mg andesites(HMAs)typically originate in subduction-related tectonic settings,including active continental margins and island arcs,and studies of HMAs can constrain the tectonic evolution of the South China Block and Paleo-Tethyan Ocean.This paper presents new chronological and geochemical data for high-Mg gabbroic diorites in the Funing area,southern South China.The gabbroic diorites yield ages of 254-249 Ma,and have moderate SiO2 contents(51.3%-57.8%),high MgO contents(4.6%-10.2%)and Mg^(#)values(52-75),enrichment in large-ion lithophile elements and light rare earth elements,and depletion in high-field-strength elements-collectively displaying geochemical signatures typical of sanukites.The gabbroic diorites have radiogenic initial Sr and Pb isotopic compositions,and negativeεNd(t)andεHf(t)values.These characteristics distinguish the Funing gabbroic diorites from subduction-related igneous rocks in the Paleo-Pacific tectonic domain.Instead,they are isotopically similar to HMAs and basalts along the Paleo-Tethys suture.We propose the high-Mg gabbroic diorites and basaltic andesites in Funing area share a common mantle source,linked to subduction and rollback of the Paleo-Tethyan plate beneath the South China Block,which triggered back-arc rifting and partial melting of the metasomatized lithospheric mantle during the Late Permian to Early Triassic.
基金financially supported by the National Natural Science Foundations of China(41890831,41421002)the MOST Special Fund from the State Key Laboratory of Continental Dynamics,Northwest University(201210133)。
文摘The Dharwar Craton(DC)in India consists of three distinct Archean blocks.Previous research suggests that the Central Dharwar Block(CDB)experienced a geological history(3.3-2.5 Ga)comparable to the Western Dharwar Craton(WDC).However,3.0-2.7 Ga geological records are missed in the CDB.This study identified the 2.85 Ga gabbroic xenoliths within the Closepet batholith in the CDB.The~2.85 Ga inherited zircons and zircon Hf model ages in CDB further provide evidence for this significant magmatic event.The gabbroic xenoliths are characterized by E-MORB REE patterns and Nb,Ta,and Ti depletions,together with high radiogenic isotopic signatures,including zircon Hf(ε_(Hf)(t)_(min)=-3.2),whole-rock Nd(ε_(Nd)(t)=-0.8-0.7),and Pb isotopes(κ=4.9-7.9),indicating derivation from a slightly enriched mantle source.Additionally,they have high Nb(4.41 to 4.73 ppm),low Ti/V(23.4 to 22.5),and elevated Th/Yb(0.38 to 0.61).All these suggest a subduction-related back-arc basin setting.Coupled with widespread early Neoarchean subduction-related igneous rocks in the DC,the 2.85 Ga gabbroic magmatism signifies that the DC had transitioned into a tectonic stage dominated by lateral movement of continental blocks around 2.85 Ga,corresponding to global~2.85 Ga magmatic events.
基金supported by the Research Grant Council of Hong Kong(HKU707012P)to MFZfrom a Chinese National "973" project (2011CB808903)+1 种基金a "CAS Hundred Talents" project under Chinese Academy of Sciences to CYWSouth African National Science Foundation Grant SA/China Project 67220 to SP and MFZ
文摘Magmatic oxide deposits in the～260 Ma Emeishan Large Igneous Province（ELIP）,SW China and northern Vietnam,are important sources of Fe,Ti and V.Some giant magmatic Fe-Ti-V oxide deposits, such as the Panzhihua,Hongge,and Baima deposits,are well described in the literature and are hosted in layered mafic-ultramafic intrusions in the Panxi region,the central ELIP.The same type of ELIP- related deposits also occur far to the south and include the Anyi deposit,about 130 km south of Panzhihua,and the Mianhuadi deposit in the Red River fault zone.The Anyi deposit is relatively small but is similarly hosted in a layered mafic intrusion.The Mianhuadi deposit has a zircon U-Pb age of～260 Ma and is thus contemporaneous with the ELIP.This deposit was variably metamorphosed during the Indosinian orogeny and Red River faulting.Compositionally,magnetite of the Mianhuadi deposit contains smaller amounts of Ti and V than that of the other deposits,possibly attributable to the later metamorphism.The distribution of the oxide ore deposits is not related to the domal structure of the ELIP.One major feature of all the oxide deposits in the ELIP is the spatial association of oxide-bearing gabbroic intrusions,syenitic plutons and high-Ti flood basalts.Thus,we propose that magmas from a mantle plume were emplaced into a shallow magma chamber where they were evolved into a field of liquid immiscibility to form two silicate liquids,one with an extremely Fe-Ti-rich gabbroic composition and the other syenitic.An immiscible Fe-Ti-（P） oxide melt may then separate from the mafic magmas to form oxide deposits.The parental magmas from which these deposits formed were likely Fe-Ti-rich picritic in composition and were derived from enriched asthenospheric mantle at a greater depth than the magmas that produced sulfide-bearing intrusions of the ELIP.
文摘Emplacement ages, geochemical characteristics and analysis of continental dynamics on gabbroic intrusions in Luodian County, Guizhou Province, have been discussed based on studies of isotopic chronology （the whole-rock Sm-Nd and Rb-Sr isochron methods）, major elements, trace elements and PGE. Intrusive activities of the gabbroic intrusions in the study area took place during the Late Yanshanian Orogenic Movement （the Cretaceous Period）, as indicated by the Sm-Nd isochron ages （t）=（99.6±4.5） （2σ） Ma and by the Rb-Sr isochron ages t=（97±1.6） （2σ） Ma. The gabbroic intrusions are attached to mafic rocks in cal-alkaline basaltic series. They occurred as dikes and might be formed under an extensional background of the continent. Differentiation of their magmatic crystallization resulted in obvious zonation of petrography. In the gabbroic intrusions of this study, large ion lithophile elements and LREE are enriched, and the chondrite-normalized REE distribution pattern is leftward inclined without anomalies of JCe or JEu, and there are high concentrations of PGE and ratios of Pd/Ir （averaging 4.21）. All of these imply that their source areas may be basaltic magma in the upper mantle with high-level partial melting, derived from EMl-type enriched mantle. It is different from Emeishan basalt, which may be related to the upper mantle at low-grade partial melting. Emplacement mechanism of the gabbroic intrusions in this study may suppose to be asthenosphere upheaving as an isolated hot wave in the presence of mantle fluid, resulting in basaltic magma intruded into the continental crust as a diapiric intrusion. Therefore, uplifting of faulting-block and extensional deformation could take place in the shallow part of the continental crust while vertical amassing and accretion of magmatic materials in the deep part of the continental crust. These special processes could supposed to be a special background of continental dynamics for this large-scale epithermal metallogenic domain, such as Au, As, Sb and Hg deposits, and vertical uplifting of the Yunnan-Guizhou Plateau in the Cretaceous Period.
文摘The Bethampudi layered anorthosite complex at the border zone of Archaean supracrustal rocks of Khammam district, Eastern Ghats shows normal stratification predominantly in the form of rhythmic layering and often exhibits of zebra layering. Graded bedding and cumulate structures are also noticed. The rocks of the study area are classified based on petrography into anorthositic rocks, gabbroic rocks and ultramafic rocks and amphibolites. The field relations and major element composition suggest that these anorthosite rocks are of calc-alkaline in nature and petrogenitically related to the gabbroic rocks by the fractional crystallization at ℃.
