With mineral-melt thermobarometers,reconstruction of P-T-depth history of magmas can be established for vol-canic rocks.The pillow lava of Hantangang River Basalt is suitable for the study as it bears narrow compositi...With mineral-melt thermobarometers,reconstruction of P-T-depth history of magmas can be established for vol-canic rocks.The pillow lava of Hantangang River Basalt is suitable for the study as it bears narrow compositional range resulting from little or no fractional crystallization or crustal assimilation and shows evidence of rapid magma ascent.The established thermodynamic model covers the pathway from the magma source depth to the eruption.The model shows that the pillow lava originated at the depths of~85-100 km by fluid ascent from a stagnant slab.This range corresponds to the depth that encompasses the uppermost asthenosphere to the lowermost lithosphere corresponding to the upper garnet to the lower spinel sta-bility fields of the mantle.Subsequently,the melt rose to~66-71 km depth where a primary magma reservoir was generated possibly due to existence of a possible local discontinuity within the upper mantle.The magma uprose rapidly from~61 to~20 km or even to a shallower depth with crystallization of dendritic clinopyroxene and titano-magnetite,due to dehydration of magma.Magma ascent slowed down near the surface possibly due to the volcanic channel split into two or more toward the vents.The model can be applied to other volcanic areas composed of less evolved rocks.展开更多
Magmatic Ni-Cu-(PGE) sulfide and Fe-Ti oxide deposits in plume-related large igneous provinces(LIPs)are commonly related to low-Ti and high-Ti series magmas, respectively, but the major factors that control such a rel...Magmatic Ni-Cu-(PGE) sulfide and Fe-Ti oxide deposits in plume-related large igneous provinces(LIPs)are commonly related to low-Ti and high-Ti series magmas, respectively, but the major factors that control such a relationship of metallogenic types and magma compositions are unclear. Magma fOcontrols sulfur status and relative timing of Fe-Ti oxide saturation in mafic magmas, which may help clarify this issue. Taking the Emeishan LIP as a case, we calculated the magma fOof the high-Ti and low-Ti picrites based on the olivine-spinel oxygen barometer, and the partitioning of V in olivine. The obtained fOof the high-Ti series magma(FMQ + 1.1 to FMQ + 2.6) is higher than that of the low-Ti series magma(FMQ-0.5to FMQ + 0.5). The magma fOof the high-Ti and low-Ti picrites containing Fo > 90 olivine reveals that the mantle source of the high-Ti series is likely more oxidized than that of the low-Ti series. The results using the ’lambda REE’ approach show that the high-Ti series may have been derived from relatively oxidized mantle with garnet pyroxenite component. The S contents at sulfide saturation(SCSS) of the two series magmas were calculated based on liquid compositions obtained from the alpha Melts modeling, and the results show that the low-Ti series magma could easily attain the sulfide saturation as it has low fOwith S being dominantly as S. In contrast, the oxidized high-Ti series magma is difficult to attain the sulfide saturation, but could crystallize Fe-Ti oxides at magma MgO content of ~7.0 wt.%. Thus, contrasting magma fOof low-Ti and high-Ti series in plume-related LIPs may play an important role in producing two different styles of metallogeny.展开更多
The Baibokoum syenitic pluton(BSP),located in southern Chad,to the NE of the Adamawa-Yadédomain,is one of the few strongly potassic magmatic bodies in the southern part of the Central African Fold Belt(CAFB)in Ch...The Baibokoum syenitic pluton(BSP),located in southern Chad,to the NE of the Adamawa-Yadédomain,is one of the few strongly potassic magmatic bodies in the southern part of the Central African Fold Belt(CAFB)in Chad.It has been previously studied petrologically,but its petrogenesis has remained poorly known.Petrographic and whole-rock geochemical data presented in this article highlight their magma genesis and geodynamic evolution.The BSP consists of medium-to coarse-grained syenites associated with minor microdiorites,which occur as syn-plutonic dikes and mafic microgranular enclaves(MME)coarse-and medium-grained syenites outcrop respectively to the core and the border of the BSP.The syenite displays high-K and alkaline to trans-alkaline affinity.Petrographic and geochemical data suggest that medium-to coarse-grained syenites are from single magma source that evolved and differentiated by fractional crystallization in a magma reservoir.REE profiles show enriched LREEs(La_(N)/Yb_(N)=6.19-45.55)while HREEs show an almost flat profile(Dy_(N)/Yb_(N)=1.0-2.23),and the La/Sm and Sm/Yb ratios have led to propose that the aforementioned rocks derived from the partial melting of a garnet-spinel-lherzolite mantle source.Negative Nb and Ta anomalies indicate that this mantle source was modified by the addition of subduction-related material.Th/Yb ratios associated with high Ba/La ratios indicate that enrichment of the source could be related to slab-derived fluids.The parental magma of the BSP was generated by partial melting of the metasomatized lithospheric mantle that was modified into arc-magmatism material in a subduction setting.Its emplacement took place in two successive stages:a static stage of fractional crystallization and crystal settling in a deep magma source and a dynamic stage in a shear deformation setting during which stratified magma rises towards the upper crust,with evolved syenite magma being emplaced first and diorite later.The emplacement of the BSP was probably controlled by the evolution of the Tcholliré-Banyo Fault and M'BéréShear Zone during the Pan-African orogeny.展开更多
The three most crucial factors for the formation of large and super-large magmatic sulfide deposits are： （1） a large volume of mantle-derived mafic-ultramafic magmas that participated in the formation of the deposi...The three most crucial factors for the formation of large and super-large magmatic sulfide deposits are： （1） a large volume of mantle-derived mafic-ultramafic magmas that participated in the formation of the deposits; （2） fractional crystallization and crustal contamination, particularly the input of sulfur from crustal rocks, resulting in sulfide immiscibility and segregation; and （3） the timing of sulfide concentration in the intrusion. The super-large magmatic Ni-Cu sulfide deposits around the world have been found in small mafic-ultramafic intrusions, except for the Sudbury deposit. Studies in the past decade indicated that the intrusions hosting large and super-large magmatic sulfide deposits occur in magma conduits, such as those in China, including Jinchuan （Gansu）, Yangliuping （Sichuan）, Kalatongke （Xinjiang）, and Hongqiling （Jilin）. Magma conduits as open magma systems provide a perfect environment for extensive concentration of immiscible sulfide melts, which have been found to occur along deep regional faults. The origin of many mantle-derived magmas is closely associated with mantle plumes, intracontinental rifts, or post-collisional extension. Although it has been confirmed that sulfide immiscibility results from crustal contamination, grades of sulfide ores are also related to the nature of the parental magmas, the ratio between silicate magma and immiscible sulfide melt, the reaction between the sulfide melts and newly injected silicate magmas, and fractionation of the sulfide melt. The field relationships of the ore-bearing intrusion and the sulfide ore body are controlled by the geological features of the wall rocks. In this paper, we attempt to demonstrate the general characteristics, formation mechanism,tectonic settings, and indicators of magmatic sulfide deposits occurring in magmatic conduits which would provide guidelines for further exploration.展开更多
Magma mingling has been identified within the continental margin of southeastern China.This study focuses on the relationship between mafic and felsic igneous rocks in composite dikes and plutons in this area,and uses...Magma mingling has been identified within the continental margin of southeastern China.This study focuses on the relationship between mafic and felsic igneous rocks in composite dikes and plutons in this area,and uses this relationship to examine the tectonic and geodynamic implications of the mingling of mafic and felsic magmas.Mafic magmatic enclaves(MMEs)show complex relationships with the hosting Xiaocuo granite in Fujian area,including lenticular to rounded porphyritic microgranular enclaves containing abundant felsic/mafic phenocrysts,elongate mafic enclaves,and back-veining of the felsic host granite into mafic enclaves.LA-ICP-MS zircon U-Pb analyses show crystallization of the granite and dioritic mafic magmatic enclave during ca.132 and 116 Ma.The host granite and MMEs both show zircon growth during repeated thermal events at-210 Ma and 160-180 Ma.Samples from the magma mingling zone generally contain felsic-derived zircons with well-developed growth zoning and aspect ratios of 2-3,and maficderived zircons with no obvious oscillatory zoning and with higher aspect ratios of 5-10.However,these two groups of zircons show no obvious trace element or age differences.The Hf-isotope compositions show that the host granite and MMEs have similarε(Hf)(t)values from negative to positive which suggest a mixed source from partial melting of the Meso-Neoproterozoic with involvement of enriched mantlederived magmas or juvenile components.The lithologies,mineral associations,and geochemical characteristics of the mafic and felsic rocks in this study area indicate that both were intruded together,suggesting Early Cretaceous mantle—crustal interactions along the southeastern China continental margin.The Early Cretaceous magma mingling is correlated to subduction of Paleo-Pacific plate.展开更多
The major and trace elements and Sr-Nd-Pb isotopes of Miocene host granitoid rocks and their mafic microgranular enclaves（MMEs） were studied to understand the petrogenesis of MMEs in the Kashan complex, which is par...The major and trace elements and Sr-Nd-Pb isotopes of Miocene host granitoid rocks and their mafic microgranular enclaves（MMEs） were studied to understand the petrogenesis of MMEs in the Kashan complex, which is part of the Urumieh-Dokhtar magmatic belt（Iran）. The host rocks consist of quartz-diorite and tonalite associated with a dioritic intrusion. The enclaves show microgranular texture and the same mineralogy as their respective host with plagioclase, quartz and biotite. MMEs have a diorite to quartz-diorite composition and show geochemical characteristics mostly between their granitoid host and the diorite intrusion. Chondrite-normalized REE patterns of all samples are moderately fractionated [（La/Yb）N=2.1 to 12.9]. The MMEs display in part small negative Eu anomalies（Eu/Eu＊=0.54 to 0.99）, with enrichment of LILE and depletion of HFSE. The enclaves show emplacement depth of -4 to 6 km which is comparable with the host rocks. Moreover, the Hornblende-plagioclase equilibrium temprature of MMEs yields average temperatures of 795℃ which is slightly higher than the host ones. Identical mineral compositions and Nd-Sr-Pb isotopic features of MME-host granitoid pairs indicate interactions and parallel evolution of MME and enclosing granitoid in the Kashan plutons. Additionally, the geochemical and isotopic investigations of host and dioritic intrusions suggest a common source for their genesis. A thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower crust to generate Kashan granitoid rocks.展开更多
The ultramafic dikes in the Tarim large igneous province（Tarim LIP）, exposed in the Xiaohaizi area in the northwestern Tarim Basin of northwestern China, have porphyritic textures, and the olivine and clinopyroxene ...The ultramafic dikes in the Tarim large igneous province（Tarim LIP）, exposed in the Xiaohaizi area in the northwestern Tarim Basin of northwestern China, have porphyritic textures, and the olivine and clinopyroxene are as the major phenocryst phases. The groundmass therein consists of clinopyroxene, plagioclase and Fe-Ti oxides, with the cryptocrystalline texture. The olivine phenocrysts in one typical ultramafic dike have Fo（Mg/（Mg＋Fe）） numbers ranging from 73 to 85, which are not in equilibrium with the olivine（Mg# of 89） from the host rock crystalized. Combined with microscope observation, both the olivine and clinopyroxene phenocrysts as well as some Fe-Ti oxides in the ultramafic rock are accounted as cumulates. The liquid（parental magma） composition of SiO2 of 45.00 wt.%–48.82 wt.%, MgO of 9.93 wt.%– 18.56 wt.%, FeO of 5.85 wt.%–14.17 wt.%, CaO of 7.54 wt.%–11.52 wt.%, Al2O3 of 8.70 wt.%–11.62 wt.% and TiO2 of 0.00 wt.%–3.43 wt.% in the Xiaohaizi ultramafic rock was estimated by mass balance, and the results show a reasonable liquid proportion in the cumulate-bearing ultramafic dike（ca. 45%–60% in the whole rock）. The estimated parental magma composition corresponds to a melting temperature of 1 300–1 550 oC, which is equal or higher than those of a normal asthenosphere mantle, supporting the involvement of a mantle plume. Combined with other previous studies, an evolution model for the formation processes of the Xiaohaizi ultramafic dike of the Tarim LIP is proposed.展开更多
For skarn type deposits , there are two lands of skarns , skarn formed by filtrating-diffusing metasomatism and vein skarn formed by filling . The vein skarn , discussed this paper and considered to be magmatic genesi...For skarn type deposits , there are two lands of skarns , skarn formed by filtrating-diffusing metasomatism and vein skarn formed by filling . The vein skarn , discussed this paper and considered to be magmatic genesis , is characterized by: (1) occurring as vein with distinct boundaries with country rocks , yet just the same even in marble easy to be replaced ; (2) composed of a mineral assemblage similar to that of granite ,containing pegmatite as wen as coarse skarn mineral pockets ,and sometimes transited with dike rocks ; (3) dear crystalline feature of deposition ; (4) sideronitic texture ; (5) stowing vesicular, bean-like and flow structures ; (6) very common liquid immiscibility; (7) vertical zoning of gravitational differentiation caused by volatile concentration upwards; (8) associated and transited with non-copper ore bodies of magmatic genesis and tungsten-bearing quartz veins of silicate magmatic genesis rich in volatile ; (9) melt inclusions . Two origins of skam magma . originated by assimilation of silicate magma at its emplacemeot or below it and generated owe to assimilation of deep magma ,corrosion of carbonate strata and liquation , are presented .展开更多
Petro Gram is an Excel?based magmatic petrology program that generates numerical and graphical models.Petro Gram can model the magmatic processes such as melting,crystallization,assimilation and magma mixing based on ...Petro Gram is an Excel?based magmatic petrology program that generates numerical and graphical models.Petro Gram can model the magmatic processes such as melting,crystallization,assimilation and magma mixing based on the trace element and isotopic data.The program can produce both inverse and forward geochemical models for melting processes(e.g.forward model for batch,fractional and dynamic melting,and inverse model for batch and dynamic melting).However,the program uses a forward modeling approach for magma differentiation processes such as crystallization(EC:Equilibruim Crystallization,FC:Fractional Crystallization,IFC:Imperfect Fractional Crystallization and In-situ Crystallization),assimilation(AFC:Assimilation Fractional Crystallization,Decoupled FC-A:Decoupled Fractional Crystallization and Assimillation,A-IFC:Assimilation and Imperfect Fractional Crystallization)and magma mixing.One of the most important advantages of the program is that the melt composition obtained from any partial melting model can be used as a starting composition of the crystallization,assimilation and magma mixing.In addition,Petro Gram is able to carry out the classification,tectonic setting,multi-element(spider)and isotope correlation diagrams,and basic calculations including Mg^#,Eu/Eu^*,εSrandεNdwidely used in magmatic petrology.展开更多
The contents of major element composition of the phenocrysts and the matrix glass as well as the spinel inclusions and the melt inclusion in the phenocrysts of the basalt dredged from Station 133 of the Okinawa Trough...The contents of major element composition of the phenocrysts and the matrix glass as well as the spinel inclusions and the melt inclusion in the phenocrysts of the basalt dredged from Station 133 of the Okinawa Trough are determined by electron microprobe. The results show that the basalt is a dor- galite consisting of phenocrysts of bytownite, chrysolite, clinopyroxene and magnetite as well as labradorite microcrystal, matrix glass and a few bits of broken vein quartz. Glassy melt inclusion and chromohercynite or chrompleonaste exist in bytownite and chrysolite. The formation of the spinels is re- lated to partial melting of mantle. The melt inclusions stand for a primary alkali dorgalitic magma, whose composition corresponds to olivine gabbro. The basaltic magma was generated from partial melting of spinel-lherzolite of the upper mantle and evolved in a process of 'alkali dorgalitic magma-trachy- basaltic magma-basdaltic trachytic magma-trachytic magma'. Assimilation and hybridization of crustal material may exist during magma upwelling in every evolutionary stage.展开更多
The Tafresh granitoids are located at the central part of the Urumieh-Dokhtar Magmatic Arc(UDMA)in Iran.These rocks,mainly consisting of diorite and granodiorite,were emplaced during the Early Miocene.They are compose...The Tafresh granitoids are located at the central part of the Urumieh-Dokhtar Magmatic Arc(UDMA)in Iran.These rocks,mainly consisting of diorite and granodiorite,were emplaced during the Early Miocene.They are composed of varying proportions of plagioclase+K-feldspar+hornblende±quartz±biotite.Discrimination diagrams and chemical indices of amphibole phases reveal a calc-alkaline affinity and fall clearly in the crust-mantle mixed source field.The estimated pressure,derived from Al in amphibole barometry,is approximately 3 Kb.The granitoids are I-type,metaluminous and belong to the calc-alkaline series.They are all enriched in light rare earth elements and large ion lithophile elements,depleted in high field strength elements and display geochemical features typical of subduction-related calc-alkaline arc magmas.Most crystal size distribution(CSD)line patterns from the granitoids show a non-straight trend which points to the effect of physical processes during petrogenesis.The presence of numerous mafic enclaves,sieve texture and oscillatory zoning along with the CSD results show that magma mixing in the magma chamber had an important role in the petrogenesis of Tafresh granitoids.Moreover,the CSD analysis suggests that the plagioclase crystals were crystallized in a time span of less than 1000 years,which is indicative of shallow depth magma crystallization.展开更多
基金supported by the 2021 Research Project for UNESCO Hantangang River Global Geopark supported by Gyeonggi Provincial Office(Grant No.20210606641-00)Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(No.2019R1A6A1A03033167).
文摘With mineral-melt thermobarometers,reconstruction of P-T-depth history of magmas can be established for vol-canic rocks.The pillow lava of Hantangang River Basalt is suitable for the study as it bears narrow compositional range resulting from little or no fractional crystallization or crustal assimilation and shows evidence of rapid magma ascent.The established thermodynamic model covers the pathway from the magma source depth to the eruption.The model shows that the pillow lava originated at the depths of~85-100 km by fluid ascent from a stagnant slab.This range corresponds to the depth that encompasses the uppermost asthenosphere to the lowermost lithosphere corresponding to the upper garnet to the lower spinel sta-bility fields of the mantle.Subsequently,the melt rose to~66-71 km depth where a primary magma reservoir was generated possibly due to existence of a possible local discontinuity within the upper mantle.The magma uprose rapidly from~61 to~20 km or even to a shallower depth with crystallization of dendritic clinopyroxene and titano-magnetite,due to dehydration of magma.Magma ascent slowed down near the surface possibly due to the volcanic channel split into two or more toward the vents.The model can be applied to other volcanic areas composed of less evolved rocks.
基金supported by grants from the National Natural Science Foundation of China (Nos. 41902077, 41730423 and 41921003)China Postdoctoral Science Foundation Grant (No. 2019M653103)Science and Technology Planning of Guangdong Province, China (2020B1212060055)。
文摘Magmatic Ni-Cu-(PGE) sulfide and Fe-Ti oxide deposits in plume-related large igneous provinces(LIPs)are commonly related to low-Ti and high-Ti series magmas, respectively, but the major factors that control such a relationship of metallogenic types and magma compositions are unclear. Magma fOcontrols sulfur status and relative timing of Fe-Ti oxide saturation in mafic magmas, which may help clarify this issue. Taking the Emeishan LIP as a case, we calculated the magma fOof the high-Ti and low-Ti picrites based on the olivine-spinel oxygen barometer, and the partitioning of V in olivine. The obtained fOof the high-Ti series magma(FMQ + 1.1 to FMQ + 2.6) is higher than that of the low-Ti series magma(FMQ-0.5to FMQ + 0.5). The magma fOof the high-Ti and low-Ti picrites containing Fo > 90 olivine reveals that the mantle source of the high-Ti series is likely more oxidized than that of the low-Ti series. The results using the ’lambda REE’ approach show that the high-Ti series may have been derived from relatively oxidized mantle with garnet pyroxenite component. The S contents at sulfide saturation(SCSS) of the two series magmas were calculated based on liquid compositions obtained from the alpha Melts modeling, and the results show that the low-Ti series magma could easily attain the sulfide saturation as it has low fOwith S being dominantly as S. In contrast, the oxidized high-Ti series magma is difficult to attain the sulfide saturation, but could crystallize Fe-Ti oxides at magma MgO content of ~7.0 wt.%. Thus, contrasting magma fOof low-Ti and high-Ti series in plume-related LIPs may play an important role in producing two different styles of metallogeny.
文摘The Baibokoum syenitic pluton(BSP),located in southern Chad,to the NE of the Adamawa-Yadédomain,is one of the few strongly potassic magmatic bodies in the southern part of the Central African Fold Belt(CAFB)in Chad.It has been previously studied petrologically,but its petrogenesis has remained poorly known.Petrographic and whole-rock geochemical data presented in this article highlight their magma genesis and geodynamic evolution.The BSP consists of medium-to coarse-grained syenites associated with minor microdiorites,which occur as syn-plutonic dikes and mafic microgranular enclaves(MME)coarse-and medium-grained syenites outcrop respectively to the core and the border of the BSP.The syenite displays high-K and alkaline to trans-alkaline affinity.Petrographic and geochemical data suggest that medium-to coarse-grained syenites are from single magma source that evolved and differentiated by fractional crystallization in a magma reservoir.REE profiles show enriched LREEs(La_(N)/Yb_(N)=6.19-45.55)while HREEs show an almost flat profile(Dy_(N)/Yb_(N)=1.0-2.23),and the La/Sm and Sm/Yb ratios have led to propose that the aforementioned rocks derived from the partial melting of a garnet-spinel-lherzolite mantle source.Negative Nb and Ta anomalies indicate that this mantle source was modified by the addition of subduction-related material.Th/Yb ratios associated with high Ba/La ratios indicate that enrichment of the source could be related to slab-derived fluids.The parental magma of the BSP was generated by partial melting of the metasomatized lithospheric mantle that was modified into arc-magmatism material in a subduction setting.Its emplacement took place in two successive stages:a static stage of fractional crystallization and crystal settling in a deep magma source and a dynamic stage in a shear deformation setting during which stratified magma rises towards the upper crust,with evolved syenite magma being emplaced first and diorite later.The emplacement of the BSP was probably controlled by the evolution of the Tcholliré-Banyo Fault and M'BéréShear Zone during the Pan-African orogeny.
基金supported by 973 Program(2007CB411408)National Natural Science Foundation of China(NSFC) projects (40730420 and 40973038)Chinese Academy of Sciences(KZCX2-YW-Q04)
文摘The three most crucial factors for the formation of large and super-large magmatic sulfide deposits are： （1） a large volume of mantle-derived mafic-ultramafic magmas that participated in the formation of the deposits; （2） fractional crystallization and crustal contamination, particularly the input of sulfur from crustal rocks, resulting in sulfide immiscibility and segregation; and （3） the timing of sulfide concentration in the intrusion. The super-large magmatic Ni-Cu sulfide deposits around the world have been found in small mafic-ultramafic intrusions, except for the Sudbury deposit. Studies in the past decade indicated that the intrusions hosting large and super-large magmatic sulfide deposits occur in magma conduits, such as those in China, including Jinchuan （Gansu）, Yangliuping （Sichuan）, Kalatongke （Xinjiang）, and Hongqiling （Jilin）. Magma conduits as open magma systems provide a perfect environment for extensive concentration of immiscible sulfide melts, which have been found to occur along deep regional faults. The origin of many mantle-derived magmas is closely associated with mantle plumes, intracontinental rifts, or post-collisional extension. Although it has been confirmed that sulfide immiscibility results from crustal contamination, grades of sulfide ores are also related to the nature of the parental magmas, the ratio between silicate magma and immiscible sulfide melt, the reaction between the sulfide melts and newly injected silicate magmas, and fractionation of the sulfide melt. The field relationships of the ore-bearing intrusion and the sulfide ore body are controlled by the geological features of the wall rocks. In this paper, we attempt to demonstrate the general characteristics, formation mechanism,tectonic settings, and indicators of magmatic sulfide deposits occurring in magmatic conduits which would provide guidelines for further exploration.
基金supported by the Chinese NSF(41602213,90914004)China University of Geosciences(Beijing)(2011TDL001)the Guangzhou Marine Geological Survey(GZH20110205)
文摘Magma mingling has been identified within the continental margin of southeastern China.This study focuses on the relationship between mafic and felsic igneous rocks in composite dikes and plutons in this area,and uses this relationship to examine the tectonic and geodynamic implications of the mingling of mafic and felsic magmas.Mafic magmatic enclaves(MMEs)show complex relationships with the hosting Xiaocuo granite in Fujian area,including lenticular to rounded porphyritic microgranular enclaves containing abundant felsic/mafic phenocrysts,elongate mafic enclaves,and back-veining of the felsic host granite into mafic enclaves.LA-ICP-MS zircon U-Pb analyses show crystallization of the granite and dioritic mafic magmatic enclave during ca.132 and 116 Ma.The host granite and MMEs both show zircon growth during repeated thermal events at-210 Ma and 160-180 Ma.Samples from the magma mingling zone generally contain felsic-derived zircons with well-developed growth zoning and aspect ratios of 2-3,and maficderived zircons with no obvious oscillatory zoning and with higher aspect ratios of 5-10.However,these two groups of zircons show no obvious trace element or age differences.The Hf-isotope compositions show that the host granite and MMEs have similarε(Hf)(t)values from negative to positive which suggest a mixed source from partial melting of the Meso-Neoproterozoic with involvement of enriched mantlederived magmas or juvenile components.The lithologies,mineral associations,and geochemical characteristics of the mafic and felsic rocks in this study area indicate that both were intruded together,suggesting Early Cretaceous mantle—crustal interactions along the southeastern China continental margin.The Early Cretaceous magma mingling is correlated to subduction of Paleo-Pacific plate.
文摘The major and trace elements and Sr-Nd-Pb isotopes of Miocene host granitoid rocks and their mafic microgranular enclaves（MMEs） were studied to understand the petrogenesis of MMEs in the Kashan complex, which is part of the Urumieh-Dokhtar magmatic belt（Iran）. The host rocks consist of quartz-diorite and tonalite associated with a dioritic intrusion. The enclaves show microgranular texture and the same mineralogy as their respective host with plagioclase, quartz and biotite. MMEs have a diorite to quartz-diorite composition and show geochemical characteristics mostly between their granitoid host and the diorite intrusion. Chondrite-normalized REE patterns of all samples are moderately fractionated [（La/Yb）N=2.1 to 12.9]. The MMEs display in part small negative Eu anomalies（Eu/Eu＊=0.54 to 0.99）, with enrichment of LILE and depletion of HFSE. The enclaves show emplacement depth of -4 to 6 km which is comparable with the host rocks. Moreover, the Hornblende-plagioclase equilibrium temprature of MMEs yields average temperatures of 795℃ which is slightly higher than the host ones. Identical mineral compositions and Nd-Sr-Pb isotopic features of MME-host granitoid pairs indicate interactions and parallel evolution of MME and enclosing granitoid in the Kashan plutons. Additionally, the geochemical and isotopic investigations of host and dioritic intrusions suggest a common source for their genesis. A thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower crust to generate Kashan granitoid rocks.
基金funded by the National Basic Research of China (Nos. 2011CB808902 and 2007CB411303)the National Natural Science Foundation of China (Nos. 41541018, 40930315 and 41072048)+1 种基金the Doctoral Program of Higher Education of China (No. 20110101110001)the State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, CAS (No. 201208)
文摘The ultramafic dikes in the Tarim large igneous province（Tarim LIP）, exposed in the Xiaohaizi area in the northwestern Tarim Basin of northwestern China, have porphyritic textures, and the olivine and clinopyroxene are as the major phenocryst phases. The groundmass therein consists of clinopyroxene, plagioclase and Fe-Ti oxides, with the cryptocrystalline texture. The olivine phenocrysts in one typical ultramafic dike have Fo（Mg/（Mg＋Fe）） numbers ranging from 73 to 85, which are not in equilibrium with the olivine（Mg# of 89） from the host rock crystalized. Combined with microscope observation, both the olivine and clinopyroxene phenocrysts as well as some Fe-Ti oxides in the ultramafic rock are accounted as cumulates. The liquid（parental magma） composition of SiO2 of 45.00 wt.%–48.82 wt.%, MgO of 9.93 wt.%– 18.56 wt.%, FeO of 5.85 wt.%–14.17 wt.%, CaO of 7.54 wt.%–11.52 wt.%, Al2O3 of 8.70 wt.%–11.62 wt.% and TiO2 of 0.00 wt.%–3.43 wt.% in the Xiaohaizi ultramafic rock was estimated by mass balance, and the results show a reasonable liquid proportion in the cumulate-bearing ultramafic dike（ca. 45%–60% in the whole rock）. The estimated parental magma composition corresponds to a melting temperature of 1 300–1 550 oC, which is equal or higher than those of a normal asthenosphere mantle, supporting the involvement of a mantle plume. Combined with other previous studies, an evolution model for the formation processes of the Xiaohaizi ultramafic dike of the Tarim LIP is proposed.
文摘For skarn type deposits , there are two lands of skarns , skarn formed by filtrating-diffusing metasomatism and vein skarn formed by filling . The vein skarn , discussed this paper and considered to be magmatic genesis , is characterized by: (1) occurring as vein with distinct boundaries with country rocks , yet just the same even in marble easy to be replaced ; (2) composed of a mineral assemblage similar to that of granite ,containing pegmatite as wen as coarse skarn mineral pockets ,and sometimes transited with dike rocks ; (3) dear crystalline feature of deposition ; (4) sideronitic texture ; (5) stowing vesicular, bean-like and flow structures ; (6) very common liquid immiscibility; (7) vertical zoning of gravitational differentiation caused by volatile concentration upwards; (8) associated and transited with non-copper ore bodies of magmatic genesis and tungsten-bearing quartz veins of silicate magmatic genesis rich in volatile ; (9) melt inclusions . Two origins of skam magma . originated by assimilation of silicate magma at its emplacemeot or below it and generated owe to assimilation of deep magma ,corrosion of carbonate strata and liquation , are presented .
文摘Petro Gram is an Excel?based magmatic petrology program that generates numerical and graphical models.Petro Gram can model the magmatic processes such as melting,crystallization,assimilation and magma mixing based on the trace element and isotopic data.The program can produce both inverse and forward geochemical models for melting processes(e.g.forward model for batch,fractional and dynamic melting,and inverse model for batch and dynamic melting).However,the program uses a forward modeling approach for magma differentiation processes such as crystallization(EC:Equilibruim Crystallization,FC:Fractional Crystallization,IFC:Imperfect Fractional Crystallization and In-situ Crystallization),assimilation(AFC:Assimilation Fractional Crystallization,Decoupled FC-A:Decoupled Fractional Crystallization and Assimillation,A-IFC:Assimilation and Imperfect Fractional Crystallization)and magma mixing.One of the most important advantages of the program is that the melt composition obtained from any partial melting model can be used as a starting composition of the crystallization,assimilation and magma mixing.In addition,Petro Gram is able to carry out the classification,tectonic setting,multi-element(spider)and isotope correlation diagrams,and basic calculations including Mg^#,Eu/Eu^*,εSrandεNdwidely used in magmatic petrology.
基金This work was supported by the Youth Oceanic Science Foundation of State Oceanic Administration of China under contract!No. 94-2
文摘The contents of major element composition of the phenocrysts and the matrix glass as well as the spinel inclusions and the melt inclusion in the phenocrysts of the basalt dredged from Station 133 of the Okinawa Trough are determined by electron microprobe. The results show that the basalt is a dor- galite consisting of phenocrysts of bytownite, chrysolite, clinopyroxene and magnetite as well as labradorite microcrystal, matrix glass and a few bits of broken vein quartz. Glassy melt inclusion and chromohercynite or chrompleonaste exist in bytownite and chrysolite. The formation of the spinels is re- lated to partial melting of mantle. The melt inclusions stand for a primary alkali dorgalitic magma, whose composition corresponds to olivine gabbro. The basaltic magma was generated from partial melting of spinel-lherzolite of the upper mantle and evolved in a process of 'alkali dorgalitic magma-trachy- basaltic magma-basdaltic trachytic magma-trachytic magma'. Assimilation and hybridization of crustal material may exist during magma upwelling in every evolutionary stage.
文摘The Tafresh granitoids are located at the central part of the Urumieh-Dokhtar Magmatic Arc(UDMA)in Iran.These rocks,mainly consisting of diorite and granodiorite,were emplaced during the Early Miocene.They are composed of varying proportions of plagioclase+K-feldspar+hornblende±quartz±biotite.Discrimination diagrams and chemical indices of amphibole phases reveal a calc-alkaline affinity and fall clearly in the crust-mantle mixed source field.The estimated pressure,derived from Al in amphibole barometry,is approximately 3 Kb.The granitoids are I-type,metaluminous and belong to the calc-alkaline series.They are all enriched in light rare earth elements and large ion lithophile elements,depleted in high field strength elements and display geochemical features typical of subduction-related calc-alkaline arc magmas.Most crystal size distribution(CSD)line patterns from the granitoids show a non-straight trend which points to the effect of physical processes during petrogenesis.The presence of numerous mafic enclaves,sieve texture and oscillatory zoning along with the CSD results show that magma mixing in the magma chamber had an important role in the petrogenesis of Tafresh granitoids.Moreover,the CSD analysis suggests that the plagioclase crystals were crystallized in a time span of less than 1000 years,which is indicative of shallow depth magma crystallization.
