Quaternary intraplate magmatism formed several volcanic islands and seamounts,including Dokdo(DD),Ulleungdo(UD),Simheungtack(ST),Anyongbok,and Isabu in the southwest of the East Sea back-arc basin.In this study,we pre...Quaternary intraplate magmatism formed several volcanic islands and seamounts,including Dokdo(DD),Ulleungdo(UD),Simheungtack(ST),Anyongbok,and Isabu in the southwest of the East Sea back-arc basin.In this study,we present whole-rock geochemical,zircon U–Pb age,and in situ O–Hf isotope data for the submerged volcanic rocks from DD,UD,and ST to provide new insights into the eruption timing of these volcanoes and constrain the magma evolution processes.All samples used in this study were trachytes and exhibited ferroan,alkalic,and metaluminous to weakly peraluminous characteristics.They showed light rare earth element(REE)-enriched patterns with(La/Yb)N ratios of 25.3–31.7 and mostly negative Eu anomalies in a chondrite-normalized REE plot.In addition,they were enriched in large-ion lithophile elements and high field strength elements;they exhibited positive Pb anomalies and strongly negative Ba,Sr,P,and Ti anomalies.The zircons yielded a weighted-mean 206Pb/238U age of 2.61,0.348–0.704,and 2.76–2.94 Ma for the DD,UD,and ST trachytes,respectively.All zircons exhibited lowerδ^(18)O values than normal depleted mantle values,regardless of the crystallization age and spatial distribution of volcanoes.Theδ^(18)O values showed no correlation with U contents or Th/U ratios,indicating that the lowδ^(18)O signatures were of primary magmatic origin.The Hf isotopic compositions of the zircons were relatively heterogeneous but predominately characterized by positive eHf values.Binary O–Hf mixing modeling revealed that low-δ^(18)O rocks with positive eHf values from the UD and ST volcanoes were derived from a hybrid source of recycled juvenile crustal materials with low-δ^(18)O and positive eHf signatures and an enriched mantle source with normalδ^(18)O and negative eHf values.The juvenile oceanic crust in the source was likely metasomatized by seawater at high temperatures prior to melting.In contrast,the felsic magma that formed the DD volcanoes may have assimilated with regional basement rocks(Triassic–Jurassic granitoids),resulting in increasedδ^(18)O values and decreased eHf values relative to those of the UD and ST volcanoes.Our study highlights the significant contribution of recycled oceanic crust materials to the generation of the Quaternary magmas.展开更多
Systematical experimental study has been carried out on liquation (liquid seperation) of granitic silicate melt containing tungsten and tin at the conditions of 850℃ and 150 MPa. The experiments were conducted in rap...Systematical experimental study has been carried out on liquation (liquid seperation) of granitic silicate melt containing tungsten and tin at the conditions of 850℃ and 150 MPa. The experiments were conducted in rapid quenched high-pressure vessel system.Two kinds of glass, used as starting meterial, were made from Dengfuxian coarse porphyritic biotite granite enriched in W (0. 45 wB% ) and Sn (0. 50 wB%) and Dachang granular biotitemuscovite granite enriched in W (0. 16 wB% ) and Sn (0. 13 wB%). The results of the experiments indicate that the quenched product glass contains no newly-formed minerals through observation under 200 times microscope and with determination of the X-rays diffraction. The final glass of each run consists of both lightedolor and dark-color parts which represent two phases of liquid-separated melt. The color of the light gIass varies with the composition of the systems. In the granite-KF-H2O and granite-NaCl-H2O systems, the light glass is colorless.In the granite-KP-H2O system, the light part is lightly brown. In the Rranite-LiF-H2O system, the light glass appears milkwhite. The color of the dark glass hardly varies with the different compositions of the systems, and appears darkbrown or grew-black. In tbe quenched glass, the dark part is dominant and takes a portion of more than 80 percent. The data of the compositions for the two portions of glass contains relatively much silica and less Fe2O3,FeO, TiO2, MgO, CaO. On the contact line between two phases of glass, there does not exist gradually varying zone of the composition, which indicates that complete liquid separation has taken place.展开更多
Lithological observations and mineralogical analyses on pyroxene and hornblende megacrysts and pyroxene and hornblende cumulates in xenoliths in the Mesozoic plutons of the Tongling region, Anhui Province, provide evi...Lithological observations and mineralogical analyses on pyroxene and hornblende megacrysts and pyroxene and hornblende cumulates in xenoliths in the Mesozoic plutons of the Tongling region, Anhui Province, provide evidence for the magmatic underplating of mantle-derived alkali-olivine basalt at circa 140 Ma. The pyroxene and hornblende megacrysts and cumulates were formed through the AFC process at depths ranging from 27 to 35 km.展开更多
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 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
Mount Cameroon is a Plio-Quaternary volcanic massif, without a centralcrater, made up of more than 140 pyroclastic cones. It is one of theactive volcanoes of the Cameroon Volcanic Line. Mount Cameroon meltinclusions a...Mount Cameroon is a Plio-Quaternary volcanic massif, without a centralcrater, made up of more than 140 pyroclastic cones. It is one of theactive volcanoes of the Cameroon Volcanic Line. Mount Cameroon meltinclusions are found in microdroplets trapped in the early minerals (olivines)from the pyroclastic products. The analysis of these melt inclusions allowedus to find primitive liquids compared to lavas. Major elements study ofthe magmatic inclusions, trapped in the most magnesian olivines (Mg#84-86) of Mount Cameroon revealed “primitive” liquids of basanite and alkalibasalt type with variable composition compared to the much more uniformbasalts of the magmatic series of Mount Cameroon. The study of thesetrapped liquids shows that: (1) the original primitive lavas did not undergothe process of evolution by FC, but rather underwent fundamentally (orexclusively) the process of partial melting;(2) the emitted lavas, evolvedessentially by FC;(3) the variations in the trace element contents of theprimitive liquids directly reflect a variation in the rate of partial melting ofa homogeneous mantelic source. The very high La/Yb ratios of the MountCameroon melt inclusions (> 20) characterize a garnet lherzolite source.Spectra of the melt inclusions show a negative anomaly or depletion in K,Rb and Ba as those of HIMU. The “primitive” liquids and lavas of MountCameroon represent a co-genetic sequence formed by varying degrees ofpartial melting of a source considered as homogeneous.展开更多
1. Introduction Porphyry Cu-(Mo-Au) deposits, hereafter termed as porphyry Cu deposits, are typical magmatic-hydrothermal systems spatially and genetically associated with shallow,intermediate to felsic porphyritic in...1. Introduction Porphyry Cu-(Mo-Au) deposits, hereafter termed as porphyry Cu deposits, are typical magmatic-hydrothermal systems spatially and genetically associated with shallow,intermediate to felsic porphyritic intrusions. These deposits exhibit well-developed alteration zoning and are characterized by veinlet-disseminated mineralization.展开更多
Primary or parental magmas act as probes to infer eruption and source temperatures for both mid-ocean ridge （MOR） and‘hot-spot＇ magmas （tholeiitic picrites）. The experimental petrogenetic constraints （＇inverse...Primary or parental magmas act as probes to infer eruption and source temperatures for both mid-ocean ridge （MOR） and‘hot-spot＇ magmas （tholeiitic picrites）. The experimental petrogenetic constraints （＇inverse＇ experiments） argue for no significant temperature differences between them. However, there are differences in major, minor and trace elements which characterise geochemical, not thermal, anomalies beneath ‘hot-spots＇. We suggest that diapiric upwelling from interfaces （redox contrasts） between old subducted slab and normal MOR basalt source mantle is the major reason for the observed characteristics of island chain or ‘hot-spot＇ volcanism. Intraplate basalts also include widely distributed volcanic centres containing lherzolite xenoliths, i.e. mantle-derived magmas. Inverse experiments on olivine basalt, alkali oli- vine basalt, olivine basanite, olivine nephelinite, olivine melilitite and olivine leucitite （lamproite） determined liquidus phases as a function of pressure, initially under anhydrous and CO2-absent conditions. Under C- and H-absent conditions, only tholeiites to alkali olivine basalts had O1 ＋ Opx 4-Cpx as high-pressure liquidus phases. Addition of H20 accessed olivine basanites at 2.5-3 GPa, ,- 1,200 ℃, but both CO2 and H20 were necessary to obtain saturation with O1, Opx, Cpx and Ga at 2.5-3.5 GPa for olivine nephelinite and olivine melilitite. The forward and inverse experimental studies are combined to formulate a petrogenetic grid for intraplate, ‘hot-spot＇ and MOR magmatism within the plate tectonics paradigm. The asthenosphere is geochemically zoned by slow upward migration of incipient melt. The solidus and phasestabilities of lherzolite with very small water contents （〈3,000 ppm） determine the thin plate behaviour of the oceanic lithosphere and thus the Earth＇s convection in the form of plate tectonics. There is no evidence from the parental magmas of MOR and ‘hot-spots＇ to support the ＇deep mantle thermal plume＇ hypothesis. The preferred alternative is the presence of old subducted slabs, relatively buoyant and oxidised with respect to MORB source mantle and suspended or upwelling in or below the lower asthenosphere （and thus detached from overlying plate movement）.展开更多
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
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
Numerous Indosinian igneous rocks in the North Qaidam(NQ)provide crucial insights into the tectonic evolution of the Paleo-Tethys Ocean.This paper presents a comprehensive study of the petrography,mineralogy,geochemis...Numerous Indosinian igneous rocks in the North Qaidam(NQ)provide crucial insights into the tectonic evolution of the Paleo-Tethys Ocean.This paper presents a comprehensive study of the petrography,mineralogy,geochemistry,zircon U-Pb geochronology,and Hf isotope composition of dioritic rocks from the eastern NQ.Zircon U-Pb dating results indicate that the dioritic rocks were formed during the Middle Triassic(244-240 Ma).The rocks exhibit high-K calc-alkaline characteristics with variable SiO_(2)(55.25-65.39 wt%)and elevated K_(2)O+Na_(2)O(4.81-6.94 wt%)contents.They show enrichment in LILEs(Rb,Ba,K)and depletion in HFSEs(Nb,Ta,Ti),with slight negative Eu anomalies(Eu/Eu*=0.89-0.97).Zirconε_(Hf)(t)values(−20.93 to+5.60)and T_(DM2)ages(0.85-1.72 Ga)suggest mixed sources.Petrographic and mineralogical analysis reveals that the plagioclase phenocrysts exhibit disequilibrium textures(including reverse zoning),primarily composed of andesine and labradorite,with a small amount of oligoclase.The clinopyroxenes are all augites and have high crystallization temperatures(1111-1151℃).These features,particularly the reverse zoning of plagioclase,support a petrogenetic model involving mantle-derived magma underplating that induced melting of ancient lower crust,followed by mixing of underplated basaltic magma with crust-derived felsic magma.Our results indicate formation in a back-arc extensional setting during subduction of the Zongwulong Paleo-Tethys Ocean.展开更多
The Duanfengshan deposit is a newly discovered large pegmatitic-type Nb-Ta deposit in the central section of the Jiangnan orogenic belt,South China.There are three types of pegmatite in the Duanfengshan area:microclin...The Duanfengshan deposit is a newly discovered large pegmatitic-type Nb-Ta deposit in the central section of the Jiangnan orogenic belt,South China.There are three types of pegmatite in the Duanfengshan area:microcline pegmatite,microcline-albite pegmatite and albite pegmatite.Although several geological,geochronological and geochemical studies of this deposit have been carried out,the relationships between the evolution degree of different types of pegmatites and mineralization are still unclear.We address this problem through systematic petrographic and geochemical studies of muscovite and feldspars from two representative pegmatite veins,the No.328 microcline-albite pegmatite vein,and the No.610 albite pegmatite vein.The results of electron probe microanalysis(EPMA)and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)analyses of muscovite and K-feldspar reveal that K/Rb ratios decrease with increasing Rb,Cs,Ga,Nb and Ta contents alongside decreasing Ba and Sr contents,suggesting that magmatic differentiation played a dominant role in rare metal mineralization.A comparison of the analytical results of this study with those from rare metal pegmatites globally suggests that the No.610 vein has a high mineralization potential,whereas the No.328 vein has relatively low mineralization potential.The results from this study may be applied to the evaluation of mineralization potential for other pegmatite veins in the Duanfengshan area and other rare metal pegmatite fields with similar geological settings.展开更多
A-type rocks have drawn considerable attention in the past few decades due to their distinctive mineralogical and geochemical fingerprints and prospective utility for geodynamic reconstruction of the lithosphere.A com...A-type rocks have drawn considerable attention in the past few decades due to their distinctive mineralogical and geochemical fingerprints and prospective utility for geodynamic reconstruction of the lithosphere.A comprehensive study,involving zircon U-Pb geochronology,wholerock elemental and Sr-Nd-Pb isotopic geochemistry,was undertaken to elucidate the origin and evolutionary process for syenites from the Daguiping area in the North Daba mountains,South Qinling belt.The syenites revealed an Ordovician igneous crystallization age of 454.4±17 Ma,coeval with the neighboring mafic rocks.All samples show high SiO_(2),LREEs,and HFSEs(Nb,Ta,Zr and Hf)contents,with negative to slightly positive Eu(Eu/Eu^(*)=0.78-1.08)anomalies.The geochemical characteristics of the Daguiping syenites imply that they are of A_1-type magmatic affinity,which is confirmed by their high total alkali levels(8.57 wt.%-11.94 wt.%),Zr+Nb+Ce+Y contents(738.00 ppm-1734.78 ppm),and 10000×Ga/Al ratios(3.25-4.22),as well as low Y/Nb ratios(0.30-0.40).Our samples exhibit a wide range of initial^(87)Sr/^(86)Sr ratios of 0.701943 to 0.709802 and a narrow range of^(143)Nd/^(144)Nd ratios of 0.512205-0.512246 withε_(Nd)(t)values from+3.0 to+3.8.These rocks display(^(206)Pb/^(204)Pb)_(initial),(^(207)Pb/^(204)Pb)_(initial),and(^(208)Pb/^(204)Pb)_(initial)ratios range from 17.96 to 18.62,15.55 to 15.59,and 36.87 to 38.22,respectively.All of the isotopic data indicate that the syenites were essentially mantle-derived.A cogenetic source for the Daguiping syenites and coeval mafic rocks in the South Qinling belt is supported by their uniform Sr-Nd-Pb isotope data and linear major/trace elemental changes,with prolonged fractional crystallization considered as the essential mechanism for these geochemical discrepancies.Mass-balance and Rayleigh fractionation modeling estimate~85 vol%fractional crystallization involving amphibole,clinopyroxene,plagioclase,Kfeldspar,biotite,Fe-Ti oxide,and quartz,to reproduce the compositional varieties between a coeval mafic rock and the Daguiping syenites.The Daguiping syenites and associated alkaline rocks were likely related to a rifting episode triggered by asthenospheric upwelling,which led to the South Qinling detaching from the South China Block along the Mianlue suture during the Early Paleozoic.展开更多
The Shuangwang Au deposit in the western Qinling Orogen is hosted by a WNW-ESE-trending breccia belt that is structurally controlled by the northern limb of the Yindonggou fold.Igneous rocks area in the deposit are pa...The Shuangwang Au deposit in the western Qinling Orogen is hosted by a WNW-ESE-trending breccia belt that is structurally controlled by the northern limb of the Yindonggou fold.Igneous rocks area in the deposit are part of the Xiba pluton,which comprises granodiorite and monzogranite that contains mafic microgranular envlaves(MMEs),and later mineralized granitic porphyry dikes.The mineralized granitic porphyry dikes were controlled by the same structures that controlled the ore bodies.Zircon LA-ICP-MS U-Pb dating yields ages of 220.0±1.9 Ma for the granodiorite,and 217.9±1.9 Ma for the granitic porphyry,which is consistent with the mineralization ages reported in previous studies(220-218 Ma).Together with the similarity of alteration mineral assemblages between ore and mineralized granitic porphyry,we suggest that the mineralization was controlled by structure and Xiba pluton.The geochemical data show that the granodiorite and granitic porphyry are subalkaline and the MMEs are alkaline in composition.All samples have similar chondrite-normalized rare earth element patterns with enrichment of light rare earth elements.The granodiorite and MMEs are depleted in Nb,Ta,Sr,P,and Ti and enriched in U,K,Pb,Zr,and Hf.The granitic porphyry is enriched in large-ion lithophile elements but depleted in high-field-strength elements.The granodiorite and MMEs have low whole-rockεNd(t)values(−10.90 to−2.32)and(^(87)Sr/^(86)Sr)i ratios(0.7000-0.7285),similar to coeval Triassic granites in the western Qinling Orogen.The(^(87)Sr/^(86)Sr)i ratios of the granitic porphyry have been affected by fluid metasomatism that results in higher(^(87)Sr/^(86)Sr)i values.The geochronological,geochemical,and isotopic evidence suggest that the Xiba pluton formed by partial melting of thickened lower crust that had been intruded by alkaline mafic magma,as documented by the MMEs,which were derived from a source metasomatized by subduction-related fluids.The granodioritic and granitic porphyry magmas were relatively oxidized(fayalite-magnetite-quartz[FMQ]to magnetite-hematite(MH)buffer conditions;zircon Ce^(4+)/Ce^(3+)=72-813;log(fO_(2))=−22 to−8).We propose that magma mixing between lower crust and mantle-derived mafic magma was triggered by the tectonic transition from a collisional to post-collision setting,which provided the metals,S,fluids,and increase in magma oxygen fugacity that enabled the formation of the Shuangwang Au deposit.Since the Late Triassic,the western Qinling Orogen evolved from a syn-collisional compressional to post-collisional extensional environment.The mineralization of the Shuangwang Au deposit involved early formation of a tectonic breccia in the compressional stage.Subsequently,hydrothermal fluids derived from a magma ascended,migrated,mixed,and precipitated ores in the tectonic breccia during the later extensional stage to form the Shuangwang Au deposit.展开更多
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
基金This research was supported by a project on the sustainable research and development of Dokdo(Grant No.PG52911)which is funded by the Ministry of Oceans and Fisheries,South Korea.
文摘Quaternary intraplate magmatism formed several volcanic islands and seamounts,including Dokdo(DD),Ulleungdo(UD),Simheungtack(ST),Anyongbok,and Isabu in the southwest of the East Sea back-arc basin.In this study,we present whole-rock geochemical,zircon U–Pb age,and in situ O–Hf isotope data for the submerged volcanic rocks from DD,UD,and ST to provide new insights into the eruption timing of these volcanoes and constrain the magma evolution processes.All samples used in this study were trachytes and exhibited ferroan,alkalic,and metaluminous to weakly peraluminous characteristics.They showed light rare earth element(REE)-enriched patterns with(La/Yb)N ratios of 25.3–31.7 and mostly negative Eu anomalies in a chondrite-normalized REE plot.In addition,they were enriched in large-ion lithophile elements and high field strength elements;they exhibited positive Pb anomalies and strongly negative Ba,Sr,P,and Ti anomalies.The zircons yielded a weighted-mean 206Pb/238U age of 2.61,0.348–0.704,and 2.76–2.94 Ma for the DD,UD,and ST trachytes,respectively.All zircons exhibited lowerδ^(18)O values than normal depleted mantle values,regardless of the crystallization age and spatial distribution of volcanoes.Theδ^(18)O values showed no correlation with U contents or Th/U ratios,indicating that the lowδ^(18)O signatures were of primary magmatic origin.The Hf isotopic compositions of the zircons were relatively heterogeneous but predominately characterized by positive eHf values.Binary O–Hf mixing modeling revealed that low-δ^(18)O rocks with positive eHf values from the UD and ST volcanoes were derived from a hybrid source of recycled juvenile crustal materials with low-δ^(18)O and positive eHf signatures and an enriched mantle source with normalδ^(18)O and negative eHf values.The juvenile oceanic crust in the source was likely metasomatized by seawater at high temperatures prior to melting.In contrast,the felsic magma that formed the DD volcanoes may have assimilated with regional basement rocks(Triassic–Jurassic granitoids),resulting in increasedδ^(18)O values and decreased eHf values relative to those of the UD and ST volcanoes.Our study highlights the significant contribution of recycled oceanic crust materials to the generation of the Quaternary magmas.
文摘Systematical experimental study has been carried out on liquation (liquid seperation) of granitic silicate melt containing tungsten and tin at the conditions of 850℃ and 150 MPa. The experiments were conducted in rapid quenched high-pressure vessel system.Two kinds of glass, used as starting meterial, were made from Dengfuxian coarse porphyritic biotite granite enriched in W (0. 45 wB% ) and Sn (0. 50 wB%) and Dachang granular biotitemuscovite granite enriched in W (0. 16 wB% ) and Sn (0. 13 wB%). The results of the experiments indicate that the quenched product glass contains no newly-formed minerals through observation under 200 times microscope and with determination of the X-rays diffraction. The final glass of each run consists of both lightedolor and dark-color parts which represent two phases of liquid-separated melt. The color of the light gIass varies with the composition of the systems. In the granite-KF-H2O and granite-NaCl-H2O systems, the light glass is colorless.In the granite-KP-H2O system, the light part is lightly brown. In the Rranite-LiF-H2O system, the light glass appears milkwhite. The color of the dark glass hardly varies with the different compositions of the systems, and appears darkbrown or grew-black. In tbe quenched glass, the dark part is dominant and takes a portion of more than 80 percent. The data of the compositions for the two portions of glass contains relatively much silica and less Fe2O3,FeO, TiO2, MgO, CaO. On the contact line between two phases of glass, there does not exist gradually varying zone of the composition, which indicates that complete liquid separation has taken place.
基金the NationalNatural Science Foundation of China(Grants 40272034, 40133020)the Ministry of Science and Technology of China(Grant 1999043206) the Korea Science and Engineering Foundation(Grant KOSEF-20005-131-03-02).
文摘Lithological observations and mineralogical analyses on pyroxene and hornblende megacrysts and pyroxene and hornblende cumulates in xenoliths in the Mesozoic plutons of the Tongling region, Anhui Province, provide evidence for the magmatic underplating of mantle-derived alkali-olivine basalt at circa 140 Ma. The pyroxene and hornblende megacrysts and cumulates were formed through the AFC process at depths ranging from 27 to 35 km.
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 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.
文摘Mount Cameroon is a Plio-Quaternary volcanic massif, without a centralcrater, made up of more than 140 pyroclastic cones. It is one of theactive volcanoes of the Cameroon Volcanic Line. Mount Cameroon meltinclusions are found in microdroplets trapped in the early minerals (olivines)from the pyroclastic products. The analysis of these melt inclusions allowedus to find primitive liquids compared to lavas. Major elements study ofthe magmatic inclusions, trapped in the most magnesian olivines (Mg#84-86) of Mount Cameroon revealed “primitive” liquids of basanite and alkalibasalt type with variable composition compared to the much more uniformbasalts of the magmatic series of Mount Cameroon. The study of thesetrapped liquids shows that: (1) the original primitive lavas did not undergothe process of evolution by FC, but rather underwent fundamentally (orexclusively) the process of partial melting;(2) the emitted lavas, evolvedessentially by FC;(3) the variations in the trace element contents of theprimitive liquids directly reflect a variation in the rate of partial melting ofa homogeneous mantelic source. The very high La/Yb ratios of the MountCameroon melt inclusions (> 20) characterize a garnet lherzolite source.Spectra of the melt inclusions show a negative anomaly or depletion in K,Rb and Ba as those of HIMU. The “primitive” liquids and lavas of MountCameroon represent a co-genetic sequence formed by varying degrees ofpartial melting of a source considered as homogeneous.
基金supported by the National Natural Science Foundation of China (Grant No. 42225204)the Fundamental Research Funds for the Central Universities (Grant No. 2652023001)the Program of Introducing Talents of Discipline to Universities (Grant No. B18048)。
文摘1. Introduction Porphyry Cu-(Mo-Au) deposits, hereafter termed as porphyry Cu deposits, are typical magmatic-hydrothermal systems spatially and genetically associated with shallow,intermediate to felsic porphyritic intrusions. These deposits exhibit well-developed alteration zoning and are characterized by veinlet-disseminated mineralization.
基金the support of the Department of Geology/School of Earth Sciences at University of Tasmaniathe Research School of Earth Sciences, Australian National UniversityAt University of Tasmania, ‘Earth Sciences’ and ‘Centre for Ore Deposits and Exploration Studies (CODES)’
文摘Primary or parental magmas act as probes to infer eruption and source temperatures for both mid-ocean ridge （MOR） and‘hot-spot＇ magmas （tholeiitic picrites）. The experimental petrogenetic constraints （＇inverse＇ experiments） argue for no significant temperature differences between them. However, there are differences in major, minor and trace elements which characterise geochemical, not thermal, anomalies beneath ‘hot-spots＇. We suggest that diapiric upwelling from interfaces （redox contrasts） between old subducted slab and normal MOR basalt source mantle is the major reason for the observed characteristics of island chain or ‘hot-spot＇ volcanism. Intraplate basalts also include widely distributed volcanic centres containing lherzolite xenoliths, i.e. mantle-derived magmas. Inverse experiments on olivine basalt, alkali oli- vine basalt, olivine basanite, olivine nephelinite, olivine melilitite and olivine leucitite （lamproite） determined liquidus phases as a function of pressure, initially under anhydrous and CO2-absent conditions. Under C- and H-absent conditions, only tholeiites to alkali olivine basalts had O1 ＋ Opx 4-Cpx as high-pressure liquidus phases. Addition of H20 accessed olivine basanites at 2.5-3 GPa, ,- 1,200 ℃, but both CO2 and H20 were necessary to obtain saturation with O1, Opx, Cpx and Ga at 2.5-3.5 GPa for olivine nephelinite and olivine melilitite. The forward and inverse experimental studies are combined to formulate a petrogenetic grid for intraplate, ‘hot-spot＇ and MOR magmatism within the plate tectonics paradigm. The asthenosphere is geochemically zoned by slow upward migration of incipient melt. The solidus and phasestabilities of lherzolite with very small water contents （〈3,000 ppm） determine the thin plate behaviour of the oceanic lithosphere and thus the Earth＇s convection in the form of plate tectonics. There is no evidence from the parental magmas of MOR and ‘hot-spots＇ to support the ＇deep mantle thermal plume＇ hypothesis. The preferred alternative is the presence of old subducted slabs, relatively buoyant and oxidised with respect to MORB source mantle and suspended or upwelling in or below the lower asthenosphere （and thus detached from overlying plate movement）.
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.
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 China Geological Survey Project(DD20190069 and DD20221636)Science and Technology Plan Project in Shaanxi Province,China(2023-JC-ZD-14,2023-JC-YB-236,2024JC-YBQN-0249,and 2022JQ-286).
文摘Numerous Indosinian igneous rocks in the North Qaidam(NQ)provide crucial insights into the tectonic evolution of the Paleo-Tethys Ocean.This paper presents a comprehensive study of the petrography,mineralogy,geochemistry,zircon U-Pb geochronology,and Hf isotope composition of dioritic rocks from the eastern NQ.Zircon U-Pb dating results indicate that the dioritic rocks were formed during the Middle Triassic(244-240 Ma).The rocks exhibit high-K calc-alkaline characteristics with variable SiO_(2)(55.25-65.39 wt%)and elevated K_(2)O+Na_(2)O(4.81-6.94 wt%)contents.They show enrichment in LILEs(Rb,Ba,K)and depletion in HFSEs(Nb,Ta,Ti),with slight negative Eu anomalies(Eu/Eu*=0.89-0.97).Zirconε_(Hf)(t)values(−20.93 to+5.60)and T_(DM2)ages(0.85-1.72 Ga)suggest mixed sources.Petrographic and mineralogical analysis reveals that the plagioclase phenocrysts exhibit disequilibrium textures(including reverse zoning),primarily composed of andesine and labradorite,with a small amount of oligoclase.The clinopyroxenes are all augites and have high crystallization temperatures(1111-1151℃).These features,particularly the reverse zoning of plagioclase,support a petrogenetic model involving mantle-derived magma underplating that induced melting of ancient lower crust,followed by mixing of underplated basaltic magma with crust-derived felsic magma.Our results indicate formation in a back-arc extensional setting during subduction of the Zongwulong Paleo-Tethys Ocean.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.42102110,U2444204,42472111 and U2344220).
文摘The Duanfengshan deposit is a newly discovered large pegmatitic-type Nb-Ta deposit in the central section of the Jiangnan orogenic belt,South China.There are three types of pegmatite in the Duanfengshan area:microcline pegmatite,microcline-albite pegmatite and albite pegmatite.Although several geological,geochronological and geochemical studies of this deposit have been carried out,the relationships between the evolution degree of different types of pegmatites and mineralization are still unclear.We address this problem through systematic petrographic and geochemical studies of muscovite and feldspars from two representative pegmatite veins,the No.328 microcline-albite pegmatite vein,and the No.610 albite pegmatite vein.The results of electron probe microanalysis(EPMA)and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)analyses of muscovite and K-feldspar reveal that K/Rb ratios decrease with increasing Rb,Cs,Ga,Nb and Ta contents alongside decreasing Ba and Sr contents,suggesting that magmatic differentiation played a dominant role in rare metal mineralization.A comparison of the analytical results of this study with those from rare metal pegmatites globally suggests that the No.610 vein has a high mineralization potential,whereas the No.328 vein has relatively low mineralization potential.The results from this study may be applied to the evaluation of mineralization potential for other pegmatite veins in the Duanfengshan area and other rare metal pegmatite fields with similar geological settings.
基金jointly supported by the Natural Science Foundation of China(Nos.42172056,41772052)。
文摘A-type rocks have drawn considerable attention in the past few decades due to their distinctive mineralogical and geochemical fingerprints and prospective utility for geodynamic reconstruction of the lithosphere.A comprehensive study,involving zircon U-Pb geochronology,wholerock elemental and Sr-Nd-Pb isotopic geochemistry,was undertaken to elucidate the origin and evolutionary process for syenites from the Daguiping area in the North Daba mountains,South Qinling belt.The syenites revealed an Ordovician igneous crystallization age of 454.4±17 Ma,coeval with the neighboring mafic rocks.All samples show high SiO_(2),LREEs,and HFSEs(Nb,Ta,Zr and Hf)contents,with negative to slightly positive Eu(Eu/Eu^(*)=0.78-1.08)anomalies.The geochemical characteristics of the Daguiping syenites imply that they are of A_1-type magmatic affinity,which is confirmed by their high total alkali levels(8.57 wt.%-11.94 wt.%),Zr+Nb+Ce+Y contents(738.00 ppm-1734.78 ppm),and 10000×Ga/Al ratios(3.25-4.22),as well as low Y/Nb ratios(0.30-0.40).Our samples exhibit a wide range of initial^(87)Sr/^(86)Sr ratios of 0.701943 to 0.709802 and a narrow range of^(143)Nd/^(144)Nd ratios of 0.512205-0.512246 withε_(Nd)(t)values from+3.0 to+3.8.These rocks display(^(206)Pb/^(204)Pb)_(initial),(^(207)Pb/^(204)Pb)_(initial),and(^(208)Pb/^(204)Pb)_(initial)ratios range from 17.96 to 18.62,15.55 to 15.59,and 36.87 to 38.22,respectively.All of the isotopic data indicate that the syenites were essentially mantle-derived.A cogenetic source for the Daguiping syenites and coeval mafic rocks in the South Qinling belt is supported by their uniform Sr-Nd-Pb isotope data and linear major/trace elemental changes,with prolonged fractional crystallization considered as the essential mechanism for these geochemical discrepancies.Mass-balance and Rayleigh fractionation modeling estimate~85 vol%fractional crystallization involving amphibole,clinopyroxene,plagioclase,Kfeldspar,biotite,Fe-Ti oxide,and quartz,to reproduce the compositional varieties between a coeval mafic rock and the Daguiping syenites.The Daguiping syenites and associated alkaline rocks were likely related to a rifting episode triggered by asthenospheric upwelling,which led to the South Qinling detaching from the South China Block along the Mianlue suture during the Early Paleozoic.
基金supported by the Natural Science Foundation of Shaanxi Province(2023-JC-YB-222)National Natural Science Foundation of China(41872219)+1 种基金Opening Foundation of Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Natural Resources(DBY-KF-19-12)Research on metallogenic structure and metallogenic structural plane of Shuangwang gold deposit(220227220347,220227230756).
文摘The Shuangwang Au deposit in the western Qinling Orogen is hosted by a WNW-ESE-trending breccia belt that is structurally controlled by the northern limb of the Yindonggou fold.Igneous rocks area in the deposit are part of the Xiba pluton,which comprises granodiorite and monzogranite that contains mafic microgranular envlaves(MMEs),and later mineralized granitic porphyry dikes.The mineralized granitic porphyry dikes were controlled by the same structures that controlled the ore bodies.Zircon LA-ICP-MS U-Pb dating yields ages of 220.0±1.9 Ma for the granodiorite,and 217.9±1.9 Ma for the granitic porphyry,which is consistent with the mineralization ages reported in previous studies(220-218 Ma).Together with the similarity of alteration mineral assemblages between ore and mineralized granitic porphyry,we suggest that the mineralization was controlled by structure and Xiba pluton.The geochemical data show that the granodiorite and granitic porphyry are subalkaline and the MMEs are alkaline in composition.All samples have similar chondrite-normalized rare earth element patterns with enrichment of light rare earth elements.The granodiorite and MMEs are depleted in Nb,Ta,Sr,P,and Ti and enriched in U,K,Pb,Zr,and Hf.The granitic porphyry is enriched in large-ion lithophile elements but depleted in high-field-strength elements.The granodiorite and MMEs have low whole-rockεNd(t)values(−10.90 to−2.32)and(^(87)Sr/^(86)Sr)i ratios(0.7000-0.7285),similar to coeval Triassic granites in the western Qinling Orogen.The(^(87)Sr/^(86)Sr)i ratios of the granitic porphyry have been affected by fluid metasomatism that results in higher(^(87)Sr/^(86)Sr)i values.The geochronological,geochemical,and isotopic evidence suggest that the Xiba pluton formed by partial melting of thickened lower crust that had been intruded by alkaline mafic magma,as documented by the MMEs,which were derived from a source metasomatized by subduction-related fluids.The granodioritic and granitic porphyry magmas were relatively oxidized(fayalite-magnetite-quartz[FMQ]to magnetite-hematite(MH)buffer conditions;zircon Ce^(4+)/Ce^(3+)=72-813;log(fO_(2))=−22 to−8).We propose that magma mixing between lower crust and mantle-derived mafic magma was triggered by the tectonic transition from a collisional to post-collision setting,which provided the metals,S,fluids,and increase in magma oxygen fugacity that enabled the formation of the Shuangwang Au deposit.Since the Late Triassic,the western Qinling Orogen evolved from a syn-collisional compressional to post-collisional extensional environment.The mineralization of the Shuangwang Au deposit involved early formation of a tectonic breccia in the compressional stage.Subsequently,hydrothermal fluids derived from a magma ascended,migrated,mixed,and precipitated ores in the tectonic breccia during the later extensional stage to form the Shuangwang Au deposit.
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.
