Um Solimate emerald deposit is a unique example for the well-known beryl-related schist type.Where,the Be-mineralization is restricted to NNE-trending quartz veins/lenses and as disseminated emerald grains within the ...Um Solimate emerald deposit is a unique example for the well-known beryl-related schist type.Where,the Be-mineralization is restricted to NNE-trending quartz veins/lenses and as disseminated emerald grains within the altered-metasomatic zones of phlogopite-and graphite-schists.The study of fluid inclusions for the mineralized quartz vein revealed three major groups:(i)aqueous(H_(2)O-NaCl),(ii)aqueous-carbonic(H_(2)O-CO_(2)-[CH_(4)]-NaCl),and(iii)aqueous-hydrocarbonic(H_(2)O-CH_(4))FIs.They have been further classified into five types(namely:types 1,2,3,4 and 5)according to number of phases at the room temperature(20℃)as well as microthermometric measurements.Based upon the study of fluid inclusions,the initial-ore forming fluid was supposed to be of magmatic nature,characterized by a relatively high temperature of homogenization(T_(h,tot):269–485℃)and higher salinity(8.4 wt.%–9.6 wt.%NaCl equiv.),followed by development of aqueous-carbonic inclusions at lower temperature(T_(h,tot):241–355℃)and lower salinity(3.3 wt.%–4.9 wt.%NaCl equiv.)through metamorphic dehydration/decarbonation.Methane-rich FIs were suggested to be formed as a result of local re-equilibration of graphite in reduced environment at the contact aureole of the felsic intrusion.The P-T conditions of ore formation were estimated as modal temperature between(330–370℃)and fluid pressures of about 200 MPa,corresponding to an estimated depth ranges from 7 to 10 km.The formation of emerald is closely associated with multiple events through the ore evolution,the deposition is ascribed to destabilization process of continuous metasomatic interactions and elemental substitutions between felsic-derived Be-bearing fluids with the adjacent mafic-ultramafic rocks at the zone of mineralization.展开更多
Mafic rocks generated from subduction settings have recorded valuable source information about the mantle source.In this study,we present a comprehensive analysis of zircon U–Pb dating,whole-rock major and trace elem...Mafic rocks generated from subduction settings have recorded valuable source information about the mantle source.In this study,we present a comprehensive analysis of zircon U–Pb dating,whole-rock major and trace elements,and Sr–Nd isotopic data for the mafic gabbro located in the Yumen area,on the western part of the Yangtze Block,South China,aiming to constrain the processes of mantle metaso-matism within subduction settings.U–Pb dating results for zircon yield crystallization ages of 800 Ma for type 1 mafic gabbro and 753–734 Ma for type 2 mafic gabbro.Type 1 mafic gabbro exhibits higher SiO_(2)(44.13%–48.93%)and Al_(2)O_(3)content but lower total Fe2O3 and MgO content than type 2 gabbro(SiO_(2):41.02%–43.28%).These gabbros dis-play a high-Mg^(#)signature(52.50–62.81 for type 1,50.89–57.04 for type 2),while they are enriched in significant large-ion lithophile elements(LILEs:Rb,Ba,Sr,K)and depleted in high-field-strength elements(HFSEs:Zr,Hf,Nd,Ta,Ti),which indicates an arc-like element signature.The positive whole-rockεNd(t)values(type 1:3.5–4.4,type 2:5.6–6.3)combined with a narrow range of(^(87)Sr/^(86)Sr)_(i)(type 1:0.7035–0.7043,type 2:0.7035–0.7036)of both gabbro types suggest a depleted lithospheric mantle origin.There-fore,these mafic rocks may derive from a metasomatized spinel lherzolite mantle source(with amphibole)due to the interactions of the deep mantle source and subductionfluid materials.We propose that the long-term metasomatism recorded by mafic gabbro in this study supports the fact that the subduction during the Neoproterozoic contributed to the formation of a metasomatized mantle source in the Yumen area,western Yangtze Block,South China.展开更多
We present petrography and mineral chemistry for both phlogopite,from mantle-derived xenoliths (garnet peridotite,eclogite and clinopyroxene-phlogopite rocks) and for megacryst,macrocryst and groundmass flakes from th...We present petrography and mineral chemistry for both phlogopite,from mantle-derived xenoliths (garnet peridotite,eclogite and clinopyroxene-phlogopite rocks) and for megacryst,macrocryst and groundmass flakes from the Grib kimberlite in the Arkhangelsk diamond province of Russia to provide new insights into multi-stage metasomatism in the subcratonic lithospheric mantle (SCLM) and the origin of phlogopite in kimberlite.Based on the analysed xenoliths,phlogopite is characterized by several generations.The first generation (Phl1) occurs as coarse,discrete grains within garnet peridotite and eclogite xenoliths and as a rock-forming mineral within clinopyroxene-phlogopite xenoliths.The second phlogopite generation (Phl2) occurs as rims and outer zones that surround the Phl1 grains and as fine flakes within kimberlite-related veinlets filled with carbonate,serpentine,chlorite and spinel.In garnet peridotite xenoliths,phlogopite occurs as overgrowths surrounding garnet porphyroblasts,within which phlogopite is associated with Cr-spinel and minor carbonate.In eclogite xenoliths,phlogopite occasionally associates with carbonate bearing veinlet networks.Phlogopite,from the kimberlite,occurs as megacrysts,macrocrysts,microcrysts and fine flakes in the groundmass and matrix of kimberlitic pyroclasts.Most phlogopite grains within the kimberlite are characterised by signs of deformation and form partly fragmented grains,which indicates that they are the disintegrated fragments of previously larger grains.Phl1,within the garnet peridotite and clinopyroxeneephlogopitexenoliths,is characterised bylow Ti and Cr contents (TiO2<1 wt.%,Cr2O3<1 wt.% andMg#=100×Mg/(MgtFe)>92) typical of primary peridotite phlogopite in mantle peridotite xenoliths from global kimberlite occurrences.They formed during SCLM metasomatism that led to a transformation from garnet peridotite to clinopyroxene-phlogopite rocks and the crystallisation of phlogopite and high-Cr clinopyroxene megacrysts before the generation of host-kimberlite magmas.One of the possible processes to generate low-Ti-Cr phlogopite is via the replacement of garnet during its interaction with a metasomatic agent enriched in K and H2O.Rb-Sr isotopic data indicates that the metasomatic agent had a contribution of more radiogenic source than the host-kimberlite magma.Compared with peridotite xenoliths,eclogite xenoliths feature low-Ti phlogopites that are depleted in Cr2O3 despite a wider range of TiO2 concentrations.The presence of phlogopite in eclogite xenoliths indicates that metasomatic processes affected peridotite as well as eclogite within the SCLM beneath the Grib kimberlite.Phl2 has high Ti and Cr concentrations (TiO2 > 2 wt.%,Cr2O3 > 1 wt.% and Mg#=100 × Mg/(Mg + Fe)< 92) and compositionally overlaps with phlogopite from polymict breccia xenoliths that occur in global kimberlite formations.These phlogopites are the product of kimberlitic magma and mantle rock interaction at mantle depths where Phl2 overgrew Phl1 grains or crystallized directly from stalled batches of kimberlitic magmas.Megacrysts,most macrocrysts and microcrysts are disintegrated phlogopite fragments from metasomatised peridotite and eclogite xenoliths.Fine phlogopite flakes within kimberlite groundmass represent mixing of high-Ti-Cr phlogopite antecrysts and high-Ti and low-Cr kimberlitic phlogopite with high Al and Ba contents that may have formed individual grains or overgrown antecrysts.Based on the results of this study,we propose a schematic model of SCLM metasomatism involving phlogopite crystallization,megacryst formation,and genesis of kimberlite magmas as recorded by the Grib pipe.展开更多
We report new petrological, phase equilibria modeling, and fluid inclusion data for pelitic and mafic granulites from Rundv?gshetta in the highest-grade region of the Neoproterozoic Lützow-Holm Complex(LHC),East ...We report new petrological, phase equilibria modeling, and fluid inclusion data for pelitic and mafic granulites from Rundv?gshetta in the highest-grade region of the Neoproterozoic Lützow-Holm Complex(LHC),East Antarctica, and provide unequivocal evidence for fluid-rock interaction and high-temperature metasomatism in the presence of brine fluid. The studied locality is composed dominantly of well-foliated pelitic granulite(K-feldspar+quartz+sillimanite+garnet+ilmenite) with foliation-parallel bands and/or layers of mafic granulite(plagioclase+orthopyroxene+garnet+ilmenite+quartz+biotite). The boundary between the two lithologies is defined by thin(about 1 -20 cm in thick) garnet-rich layers with a common mineral assemblage of garnet+plagioclase+quartz+ilmenite+biotite ? orthopyroxene. Systematic increase of grossular and decrease of pyrope contents in garnet as well as decreasing Mg/(Fe+Mg) ratio of biotite from the pelitic granulite to garnet-rich rock and mafic granulite suggest that the garnet-rich layer was formed by metasomatic interaction between the two granulite lithologies. Phase equilibria modeling in the system NCKFMASHTO demonstrates that the metasomatism took place at 850 -860℃, which is slightly lower than the peak metamorphism of this region, and the modal abundance of garnet is the highest along the metapeliteemetabasite boundary(up to 40%), which is consistent with the field and thin section observations. The occurrence of brine(7.0 -10.9 wt.% Na Cleqfor ice melting or 25.1 -25.5 wt.% NaC leqfor hydrohalite melting) fluid inclusions as a primary phase trapped within plagioclase in the garnet-rich layer and the occurrence of Cl-rich biotite(Cl = 0.22 -0.60 wt.%) in the metasomatic rock compared to that in pelitic(0.15 -0.24 wt.%) and mafic(0.06-0.13 wt.%) granulites suggest infiltration of brine fluid could have given rise to the high-temperature metasomatism. The fluid might have been derived from external sources possibly related to the formation of major suture zones formed during the Gondwana amalgamation.展开更多
Two types of melt pockets, closed melt pocket （CMP） and open melt pocket （OMP）, are recognized from the peridotite xenoliths entrained in the Cenozoic kamafugites in western Qinling （秦岭）, Central China. The Ha...Two types of melt pockets, closed melt pocket （CMP） and open melt pocket （OMP）, are recognized from the peridotite xenoliths entrained in the Cenozoic kamafugites in western Qinling （秦岭）, Central China. The Haoti （好梯） CMPs have a mineral assemblage of olivine＋ clinopyroxene＋amphibole＋K- feldspar, whereas the Baiguan （白关） CMPs are composed of olivine＋clinopyroxene＋Umenite＋carbonate. The components of the OMPs are more complicated. In the Haoti OMPs, there are olivine, ciinopyroxene, glass, low modal abundances of amphibole, K-feldspar （Kfs）, Umenite, sulfide, chlorite, perovskite, chromite and phlogopite. The Baiguan OMPs contain olivine, clinopyroxene, glass, chlorite and chromite. Compositionally, ofivines in the CMPs and OMPs are both apparently depleted in Ni, and those in the OMPs are also depleted in Fe and Mg, and enriched in Ca compared to the primary ones. Ciinopyroxenes display large and systematical compositional variations between the CMPs and OMPs, particularly in Al, Cr, Na, Ca and Ti. Glasses are generally depleted in Si compared to the worldwide glasses in melt pockets, although they still have large variations. Amphiboles and K-feldspars have relatively restricted compositional variations. The petrographical observations and mineral chemistry suggest that the Haoti and Baiguan CMPs were generated by the in-sitn decompression melting of orthopyroxenes, olivines and clinopyroxenes, and by the addition of minor external K-rich and Ca-rich melt/fluids. The OMPs formed during the latest metasomatic event in the lithospheric mantle beneath the western Qinling.展开更多
The Ni-Cu-platinum group element sulfide ore deposits of the Kharaelakh Intrusion,Noril′sk Region,Siberia,represent a large concentration of sulfides associated with a small differentiated intrusion formed at the edg...The Ni-Cu-platinum group element sulfide ore deposits of the Kharaelakh Intrusion,Noril′sk Region,Siberia,represent a large concentration of sulfides associated with a small differentiated intrusion formed at the edge of the Siberian Craton in the roots of the Siberian Trap flood basalt.The deposit is associated with an intrusion that occupies a flanking periclinal structure adjacent to the Noril′sk-Kharaelakh Fault.The intrusion is strongly differentiated and comprises taxitic gabbrodolerites,picritic gabbrodolerites,and gabbrodolerites within the main body which in turn forms a chonolith within a sheet-like intrusion that extends laterally to form extensive undifferentiated sills of gabbrodolerite.The intrusion substantially replaces the stratigraphy of the country rocks,and although it appears to have exploited the axis of structures developed in response to transtension,the intrusion has created space by both mechanical dilation of stratigraphy and magmatic replacement of pre-existing sedimentary rocks.The frontal lobes of the main intrusion have complex apophyses of gabrodolerite on a range of scales that demonstrate replacement of the sedimentary rocks and link to the development of an extensive metamorphic halo in the country rocks.This halo is much narrower over the main body of the intrusion,and these observations have implications for the thermal history of the intrusion.Mg-skarns and breccias are developed in the roof of the main body of the intrusion.Within the intrusion,the taxitic rocks contain vesicles and the blebby sulfides developed in the picritic and taxitic gabbrodolerites appear to have a linkage to volatile phases.Cuprous sulfide mineralization developed at the roof of the Kharaelakh Intrusion is associated with metamorphosed and skarn-bearing country rocks,and appears to have been generated by a combination of sulfide fractionation and associated metasomatism.The geological relationships appear consistent with a chonolith model for the development of the differentiated intrusion and mineralization,but the extent of metasmorphism of the country rocks appears to be related to the unusual thickness of gabbrodolerite apophyses at the flanks of the intrusion rather than metamorphism produced by the passage of mafic magma through the intrusion.Variations in disseminated sulfide compositions and metasomatic textures in the skarns are described,and a model is proposed which balances traditional views on the evolution of the magma conduits with the impact of magmatic fluids transported through the magma column(i.e.transmagmatic fluids).The importance of structures in controlling the nature of the conduit,and the resultant small intrusions with excess sulfide is a feature of many other Ni-Cu sulfide deposits including Voisey′s Bay,and it is suggested that the sulfides are more likely to have beentransported from depth into their final resting place rather than developed by in-situ equilibration of sulfide with fresh magma in the chonolith.展开更多
Two petrologically distinct alkali feldspar syenite bodies （AFS-1 and AFS-2） from Chhotaudepur area, Deccan Large Igneous Province are reported in the present work. AFS-1 is characterized by hypidio-morphic texture ...Two petrologically distinct alkali feldspar syenite bodies （AFS-1 and AFS-2） from Chhotaudepur area, Deccan Large Igneous Province are reported in the present work. AFS-1 is characterized by hypidio-morphic texture and consists of feldspar （Or55Ab43 to Or25Ab71）, ferro-pargasite/ferro-pargasite horn-blende, hastingsite, pyroxene （Wo47, En5, Fs46）, magnetite and biotite. AFS-2 exhibits panidiomorphic texture with euhedral pyroxene （Wo47-50, En22-39, Fs12e31） set in a groundmass matrix of alkali feldspar （Or99Ab0.77 to Or1.33Ab98）, titanite and magnetite. In comparison to AFS-1, higher elemental concentra-tions of Ba, Sr and PREE are observed in AFS-2. The average peralkaline index of the alkali feldspar syenites is w1 indicating their alkaline nature. Variation discrimination diagrams involving major and trace elements and their ratios demonstrate that these alkali feldspar syenites have a shoshonite affinity but emplaced in a within-plate and rifting environment. No evidence of crustal contamination is perceptible in the multi-element primitive mantle normalized diagram as well as in terms of trace elemental ratios. The enrichment of incompatible elements in the alkali feldspar syenites suggests the involvement of mantle metasomatism in their genesis.展开更多
Objective The Sachakou Pb-Zn polymetallic deposit is located in Hetian County, Xinjiang （geographical coordinates of E78° 57＇ 54.30＂-78°59＇ 53.63＂, N34° 39＇ 27.50＂-34° 40＇ 57.21＂）. It be...Objective The Sachakou Pb-Zn polymetallic deposit is located in Hetian County, Xinjiang （geographical coordinates of E78° 57＇ 54.30＂-78°59＇ 53.63＂, N34° 39＇ 27.50＂-34° 40＇ 57.21＂）. It belongs to the West Kunlun orogenic belt on the northwest edge of the Qinghai-Tibet Plateau and is connected to the Sanjiang orogenic belt to the south （Spurlin et al., 2005）. In recent years, a series of Pb-Zn mineralized spots and deposits have been discovered in this area one after another, which is called the Huoshaoyun ore concentration area. Among them, the Sachakou Pb-Zn deposit has reserves up to140 Mt, which has reached a large scale. However, the study on the genesis of deposits in this area has only just begun. This work studied the genesis ofthis Pb-Zn deposit in order to provide new ideas for the genesis of regional deposits and regional prospecting.展开更多
The North China Craton(NCC) represents one of the oldest and largest cratons in the earth with a nearly complete record of Precambrian history. In the northern part of the NCC, the earliest phase of alkaline magmatism...The North China Craton(NCC) represents one of the oldest and largest cratons in the earth with a nearly complete record of Precambrian history. In the northern part of the NCC, the earliest phase of alkaline magmatism occurred in discrete pulses in the Early and Middle Devonian;whereas the next episode of alkaline magmatism took place in the early Mesozoic. The Gucheng pluton is exposed in the northern part of the NCC and forms a composite intrusion, consisting of K-feldspar–bearing clinopyroxenite, clinopyroxene–bearing syenite and alkali-feldspar syenite. Mineral phases in these lithologies include clinopyroxene(Wo43-48En19-35Fs18-38), sanidine(An0 Ab3-11Or89-97), and subordinate titanite, andradite and Na-feldspar. These rocks show homogeneous Sr but variable Nd isotopic compositions, and have relatively high zircon in-situ oxygen isotopes(δ18O=5.2–6.7). The Gucheng plutonic rocks formed through fractional crystallization and accumulation from ultrapotassic magmas, which were originated from partial melting of metasomatic vein systems in the subcontinental lithospheric mantle of the NCC. These vein networks developed as a result of the reactions of fluids derived from subducted pelitic sediments on the downgoing Palaeo-Asian ocean floor with the enriched, subcontinental lithospheric mantle peridotites. SHRIMP U-Pb zircon dating has revealed a crystallization age of 415 Ma for the timing of the emplacement of the Gucheng pluton that marks the early stages of alkaline magmatism associated with the Andean-type continental margin evolution along the northern edge of the NCC facing the Palaeo-Asian Ocean.展开更多
The Qooshchi area lies to northwest of Orumieh Lake in western Azerb ai jan, NW Iran. A basement metamorphic complex, consisting of Precambrian schists and gneisses, has been intruded by gabbros and diorites. Granito...The Qooshchi area lies to northwest of Orumieh Lake in western Azerb ai jan, NW Iran. A basement metamorphic complex, consisting of Precambrian schists and gneisses, has been intruded by gabbros and diorites. Granitoids are grouped into five suites according to their mineralogy, texture and exposed features. Th e main body, pink Qooshchi granite, and apophyse like, myrmekite bearing grani toids are discussed in this paper. On the basis of field observations and micros copic studies, an intensive metasomatism has overprinted the country rocks, espe cially gabbros, transforming them into a more felsic composition. A prior ev ent of intensive deformation and cataclasis preceded the metasomatism, allowing the introduction of hydrothermal fluids. K metasomatism converted plagioclase i nto K feldspar (microcline), myrmekite, and sodic plagioclase as Si metasomati sm replaced the ferromagnesian silicates by quartz. Apophyse like bodies within gabbros, called leucometasomatites, are formed during this process.展开更多
Hydrous Cr-bearing uvarovite garnets are rare in natural occurrences and belong to the ugrandite series and exist in binary solid solutions with grossular and andradite garnets. Here, we report the occurrence of hydro...Hydrous Cr-bearing uvarovite garnets are rare in natural occurrences and belong to the ugrandite series and exist in binary solid solutions with grossular and andradite garnets. Here, we report the occurrence of hydrous uvarovite garnet having Cr_(2)O_(3) upto 19.66 wt% and CaO of 32.12–35.14 wt% in the serpentinized mantle peridotites of Naga Hills Ophiolite(NHO), India. They occur in association with low-Cr diopsides. They are enriched in LILE(Ba, Sr), LREEs, with fractionating LREE-MREE [avg.(La/Sm)_(N) = 2.16] with flat MREE/HREE patterns [avg.(Sm/Yb)_(N) = 0.95]. Raman spectra indicate the presence of hydroxyl(OH^(–)) peaks from 3500 to 3700 cm^(-1). Relative abundances in fluid mobile elements and their close association with clinopyroxenes are suggestive of the formation of uvarovite garnets through low temperature metasomatic alteration of low-Cr diopsides by hydrothermal slab fluids. The high LREE concentration and absence of Eu anomaly in the garnet further attest to alkaline nature of the transporting slab dehydrated fluid rather the involvement of low-p H solution. The chemical characteristics of the hydroxyl bearing uvarovite hosted by the mantle peridotite of NHO deviate from the classical features of uvarovite garnet, and their origin is attributed to the fluid-induced metasomatism of the sub arc mantle wedge in a suprasubduction zone regime.展开更多
Clinopyroxene-enriched upper mantle xenoliths classified as wehrlites are common(~20% of all xenoliths) in the central part of the Nograd-G(o| ")m(o|")r Volcanic Field(NGVF),situated in the northern margin o...Clinopyroxene-enriched upper mantle xenoliths classified as wehrlites are common(~20% of all xenoliths) in the central part of the Nograd-G(o| ")m(o|")r Volcanic Field(NGVF),situated in the northern margin of the Pannonian Basin in northern Hungary and southern Slovakia.In this study,we thoroughly investigated 12 wehrlite xenoliths,two from each wehrlite-bearing occurrence,to determine the conditions of their formation.Specific textural features,including clinopyroxene-rich patches in an olivine-rich lithology,orthopyroxene remnants in the cores of newlyformed clinopyroxenes and vermicular spinel forms all suggest that wehrlites were formed as a result of intensive interaction between a metasomatic agent and the peridotite wall rock.Based on the major and trace element geochemistry of the rock-forming minerals,significant enrichment in basaltic(Fe,Mn,Ti) and high field strength elements(Nb,Ta,Hf,Zr) was observed,compared to compositions of common lherzolite xenoliths.The presence of orthopyroxene remnants and geochemical trends in rock-forming minerals suggest that the metasomatic process ceased before complete wehrlitization was achieved.The composition of the metasomatic agent is interpreted to be a mafic silicate melt,which was further confirmed by numerical modelling of trace elements using the plate model.The model results also show that the melt/rock ratio played a key role in the degree of petrographic and geochemical transformation.The lack of equilibrium and the conclusions drawn by using variable lherzolitic precursors in the model both suggest that wehrlitization was the last event that occurred shortly before xenolith entrainment in the host mafic melt.We suggest that the wehrlitization and the Plio-Pleistocene basaltic volcanism are related to the same magmatic event.展开更多
Here we present new data on the major and trace element compositions of silicate and oxide minerals from mantle xenoliths brought to the surface by the Carolina kimberlite,Pimenta Bueno Kimberlitic Field,which is loca...Here we present new data on the major and trace element compositions of silicate and oxide minerals from mantle xenoliths brought to the surface by the Carolina kimberlite,Pimenta Bueno Kimberlitic Field,which is located on the southwestern border of the Amazonian Craton.We also present Sr-Nd isotopic data of garnet xenocrysts and whole-rocks from the Carolina kimberlite.Mantle xenoliths are mainly clinopyroxenites and garnetites.Some of the clinopyroxenites were classified as GPP–PP–PKP(garnet-phlogopite peridotite,phlogopite-peridotite,phlogopite-K-richterite peridotite)suites,and two clinopyroxenites(eclogites)and two garnetites are relicts of an ancient subducted slab.Temperature and pressure estimates yield 855–1102℃ and 3.6–7.0 GPa,respectively.Clinopyroxenes are enriched in light rare earth elements(LREE)(La_(N)/Yb_(N)=5–62;Ce_(N)/Sm_(N)=1–3;where N=primitive mantle normalized values),they have high Ca/Al ratios(10–410),low to medium Ti/Eu ratios(742–2840),and low Zr/Hf ratios(13–26),which suggest they were formed by metasomatic reactions with CO_(2)-rich silicate melts.Phlogopite with high TiO_(2)(>2.0 wt.%),Al_(2)O_(3)(>12.0 wt.%),and FeOt(5.0–13.0 wt.%)resemble those found in the groundmass of kimberlites,lamproites and lamprophyres.Conversely,phlogopite with low TiO_(2)(<1.0 wt.%)and lower Al_(2)O_(3)(<12.0 wt.%)are similar to those present in GPP-PP-PKP,and in MARID(mica-amphibole-rutile-ilmenite-diopside)and PIC(phlogopite-ilmenite-clinopyorxene)xenoliths.The GPP-PP-PKP suite of xenoliths,together with the clinopyroxene and phlogopite major and trace element signatures suggests that an intense proto-kimberlite melt metasomatism occurred in the deep cratonic lithosphere beneath the Amazonian Craton.The Sr-Nd isotopic ratios of pyrope xenocrysts(G3,G9 and G11)from the Carolina kimberlite are characterized by high ^(143)Nd/^(144)Nd(0.51287–0.51371)and eNd(+4.55 to+20.85)accompanied with enriched ^(87)Sr/^(86)Sr(0.70405–0.71098).These results suggest interaction with a proto-kimberlite melt compositionally similar with worldwide kimberlites.Based on Sr-Nd whole-rock compositions,the Carolina kimberlite has affinity with Group 1 kimberlites.The Sm-Nd isochron age calculated with selected eclogitic garnets yielded an age of 291.9±5.4 Ma(2σ),which represents the cooling age after the proto-kimberlite melt metasomatism.Therefore,we propose that the lithospheric mantle beneath the Amazonian Craton records the Paleozoic subduction with the attachment of an eclogitic slab into the cratonic mantle(garnetites and eclogites);with a later metasomatic event caused by proto-kimberlite melts shortly before the Carolina kimberlite erupted.展开更多
The post-collisional Cenozoic basic volcanic rocks in NE Turkey show temporal variations in whole-rock lithophile element and highly siderophile element(HSE)systematics that are mainly associated with the nature of su...The post-collisional Cenozoic basic volcanic rocks in NE Turkey show temporal variations in whole-rock lithophile element and highly siderophile element(HSE)systematics that are mainly associated with the nature of sub-continental lithospheric mantle(SCLM)sources and parental melt generation.So far,the traditional whole-rock lithophile geochemical data of these basic volcanic rocks have provided important constraints on the nature of SCLM sources.Integrated lithophile element and HSE geochemical data of these basic volcanic rocks also reveal the heterogeneity of the SCLM source,which is principally related to variable metasomatism resulting from previous subduction(s)and post-collisional mantle-crust interactions in an extensional setting.Lithophile element geochemical features suggest that the parental magmas have derived from metasomatized spinel-to garnet-bearing SCLM sources for Eocene and Miocene basic volcanic rocks with subduction signatures whereas originated from spinel-to garnet-bearing SCLM sources for Mio-Pliocene and Plio-Quaternary basaltic volcanic rocks without the subduction signature.Lithophile element and HSE geo-chemistry also reveal that Eocene and Miocene basic vol-canic rocks were affected by more pronounced crustal contamination than the basaltic volcanic rocks of Mio-Pliocene and Quaternary.Furthermore,the integrated lithophile element and HSE compositions of these basic volcanic rocks,together with the regional asymmetric lithospheric delamination model,reveal that the compositional variation(especially due to metasomatism)was significant temporally in the heterogeneity of the SCLM sources from which parental magmas formed during the Cenozoic era.展开更多
The present study focuses on the inorganic geochemical features of the bituminous coal samples from the Raniganj and the Jharia Basins,as well as the anthracite samples from the Himalayan fold-thrust belts of Sikkim,I...The present study focuses on the inorganic geochemical features of the bituminous coal samples from the Raniganj and the Jharia Basins,as well as the anthracite samples from the Himalayan fold-thrust belts of Sikkim,India.The SiO_(2)content(48.05 wt%to 65.09 wt%and 35.92 wt%to 50.11 wt%in the bituminous and anthracite samples,respectively)and the ratio of Al_(2)O_(3)/TiO_(2)(6.97 to 17.03 in the bituminous coal samples and 10.34 to 20.07 in the anthracite samples)reveal the intermediate igneous source rock composition of the minerals.The ratio of the K_(2)O/Al_(2)O_(3)in the ash yield of the bituminous coal samples(0.03 to 0.09)may suggest the presence of kaolinite mixed with montmorillonite,while its range in the ash yield of the anthracite samples(0.16 to 0.27)may imply the presence of illite mixed with kaolinite.The chemical index of alteration values may suggest the moderate to strong chemical weathering of the source rock under sub-humid to humid climatic conditions.The plot of the bituminous coal samples in the A–CN–K diagram depicts the traditional weathering trend of parent rocks,but the anthracite samples plot near the illite feld and are a bit ofset from the weathering trend.This may imply the plausible infuences of the potassium-metasomatism at post coalifcation stages,which is further supported by high K_(2)O/Na_(2)O ratio(29.88–80.13).The Fourier transform infrared spectra further reveal the hydroxyl stretching intensity of illite in the anthracite samples substantiating the efect of the epigenetic potassium-metasomatism.The decrease in total kaolinite intensity/compound intensity of quartz and feldspar may provide additional evidence towards this epigenetic event.展开更多
Phlogopite-amphibole-pyroxenite xenoliths contained in the alkali basic-ultrabasic subvolcanic complex in Langao, Shaanxi Province, are composed of diopside, Ti-rich pargasite, phlogopite apatite, sphene and ilmenite,...Phlogopite-amphibole-pyroxenite xenoliths contained in the alkali basic-ultrabasic subvolcanic complex in Langao, Shaanxi Province, are composed of diopside, Ti-rich pargasite, phlogopite apatite, sphene and ilmenite, which have subsolidus metamorp hism- de formation textures such as triple-points, cataclastic boundaries and kink-bands. Mineral chemical characteristics show that the diopside, Ti-rich pargasite and phlogoPite are derived from the mantle and are the products of mantle metasomatism. Compared with normal mantle-derivedspinel-lherzolites, the xenoliths are enriched in TiO2, Fe2O3, CaO, Na2O and K2O, with apparent depletion in MgO. Chondrite-normalized REE patterns and primordial-mantle normalized trace elements data show that they are enriched in REE (especially LREE) and incompatible trace elements. The petrographic, mineralogical and petrochemical characteristics indicate that the xenoliths are metasomatized mantle xenoliths, which offers the evidence for mantle metasomatism and represents the anomalous mantle beneath the Early Paleozoic rift in northern Daba Mountains. The agents of mantle metasomatism are probably derived from the rising of mantle hot plumes. The processes of metasomatism varied from limited-range fluid metasomatism in deep mantle (＞90 km) to pervasive metasomatism of silicate melt.展开更多
The Pinxiang weathering profile is well developed on Early Triassic dacite lavas of the Baisi Formation. At the top of the profile is developed a red clay zone which is characterized mineralogically by kaolinite, iron...The Pinxiang weathering profile is well developed on Early Triassic dacite lavas of the Baisi Formation. At the top of the profile is developed a red clay zone which is characterized mineralogically by kaolinite, iron oxide minerals, quartz, and a small amount of illite, montmorillonite and vermiculite. In going downwards the red clay zone gives way to a saprolite zone in which plagioclase pseudomorphs have been well preserved although replaced by kaolinite. Beneath the saprolite zone is the saprock zone characterized by less weathering for dacite. At the bottom of the weathering profile is the parent material, dacite, which is composed mainly of plagioclase, quartz, K-feldspar and biotite which have been largely altered into chlorite owing to submarine extrusion of dacite lavas. Some layers in the weathering profile show obvious sodium enrichment and potassium depletion relative to others. In the Al2O3-(CaO*+Na2O)-K2O triangular diagram, the weathering trends of these layers in the middle stage are remarkably deviated from normal ones. Both mineralogy and micro-morphology of these layers indicate such deviation resulted from sodic metasomatism of orthoclase.展开更多
The Longshan orogenic belt is located in the southwestern margin of Ordos Basin at the junction zone between the Western Qinling and Northern Qilian orogenic belt.Voluminous Early Paleozoic magmatism in this area is o...The Longshan orogenic belt is located in the southwestern margin of Ordos Basin at the junction zone between the Western Qinling and Northern Qilian orogenic belt.Voluminous Early Paleozoic magmatism in this area is of key significance for determining the Early Paleozoic tectonic evolution and deep crust-mantle structure.Previous studies mainly focused on the Paleozoic granites;the coeval mafic rocks in this area are still poorly understood.A set of Late Silurian intraplate tholeiitic basalts has been discovered in Longshan area,providing key evidence for the mantle source and deep geodynamic background in this area.The Late Silurian Angou basalt has similar geochemical features as intraplate tholeiitic basalt,with high Na_(2)O/K_(2)O ratios(5.22-8.25),enriched in large ion lithophile elements and LREE.In combination with their relatively evolved Sr-Nd isotopic composition[^(87)Sr/^(86)Sr(i)=0.7128-0.7140;ε_(Nd)(t)=-5.55 to-3.40],it is suggested that it originated from decompression melting of metasomatized enriched mantle in extensional setting.These results indicate that the mantle source in the junction zone of the West Qinling-North Qilian orogenic belt evolved from depleted to enriched with the continuation of Proto-Tethys subduction from the Cambrian to the Silurian.These results are of great significance to understanding the genesis of contemporaneous granite and the crust-mantle interaction in the junction zone between the Western Qinling and Northern Qilian orogenic belt.展开更多
基金conducted through post-doctoral fellowship scheme granted by “TüB?TAK 2221 ” fellowship in Turkey
文摘Um Solimate emerald deposit is a unique example for the well-known beryl-related schist type.Where,the Be-mineralization is restricted to NNE-trending quartz veins/lenses and as disseminated emerald grains within the altered-metasomatic zones of phlogopite-and graphite-schists.The study of fluid inclusions for the mineralized quartz vein revealed three major groups:(i)aqueous(H_(2)O-NaCl),(ii)aqueous-carbonic(H_(2)O-CO_(2)-[CH_(4)]-NaCl),and(iii)aqueous-hydrocarbonic(H_(2)O-CH_(4))FIs.They have been further classified into five types(namely:types 1,2,3,4 and 5)according to number of phases at the room temperature(20℃)as well as microthermometric measurements.Based upon the study of fluid inclusions,the initial-ore forming fluid was supposed to be of magmatic nature,characterized by a relatively high temperature of homogenization(T_(h,tot):269–485℃)and higher salinity(8.4 wt.%–9.6 wt.%NaCl equiv.),followed by development of aqueous-carbonic inclusions at lower temperature(T_(h,tot):241–355℃)and lower salinity(3.3 wt.%–4.9 wt.%NaCl equiv.)through metamorphic dehydration/decarbonation.Methane-rich FIs were suggested to be formed as a result of local re-equilibration of graphite in reduced environment at the contact aureole of the felsic intrusion.The P-T conditions of ore formation were estimated as modal temperature between(330–370℃)and fluid pressures of about 200 MPa,corresponding to an estimated depth ranges from 7 to 10 km.The formation of emerald is closely associated with multiple events through the ore evolution,the deposition is ascribed to destabilization process of continuous metasomatic interactions and elemental substitutions between felsic-derived Be-bearing fluids with the adjacent mafic-ultramafic rocks at the zone of mineralization.
基金The National Natural Science Foundation of China[Grant Nos.42172056,42202048]co-supported this work.
文摘Mafic rocks generated from subduction settings have recorded valuable source information about the mantle source.In this study,we present a comprehensive analysis of zircon U–Pb dating,whole-rock major and trace elements,and Sr–Nd isotopic data for the mafic gabbro located in the Yumen area,on the western part of the Yangtze Block,South China,aiming to constrain the processes of mantle metaso-matism within subduction settings.U–Pb dating results for zircon yield crystallization ages of 800 Ma for type 1 mafic gabbro and 753–734 Ma for type 2 mafic gabbro.Type 1 mafic gabbro exhibits higher SiO_(2)(44.13%–48.93%)and Al_(2)O_(3)content but lower total Fe2O3 and MgO content than type 2 gabbro(SiO_(2):41.02%–43.28%).These gabbros dis-play a high-Mg^(#)signature(52.50–62.81 for type 1,50.89–57.04 for type 2),while they are enriched in significant large-ion lithophile elements(LILEs:Rb,Ba,Sr,K)and depleted in high-field-strength elements(HFSEs:Zr,Hf,Nd,Ta,Ti),which indicates an arc-like element signature.The positive whole-rockεNd(t)values(type 1:3.5–4.4,type 2:5.6–6.3)combined with a narrow range of(^(87)Sr/^(86)Sr)_(i)(type 1:0.7035–0.7043,type 2:0.7035–0.7036)of both gabbro types suggest a depleted lithospheric mantle origin.There-fore,these mafic rocks may derive from a metasomatized spinel lherzolite mantle source(with amphibole)due to the interactions of the deep mantle source and subductionfluid materials.We propose that the long-term metasomatism recorded by mafic gabbro in this study supports the fact that the subduction during the Neoproterozoic contributed to the formation of a metasomatized mantle source in the Yumen area,western Yangtze Block,South China.
基金financially supported by the Program for Development MSU.N.Korotaeva (Lomonosov Moscow State University) assisted with mineral microprobe analysessupported by the Russian President Grant for State Support of Young Russian Scientists (Project No.MK575.2017.5)to A.K.and N.L.+1 种基金by the Russian Foundation for Basic Research (Project No.16-05-00298a)by the Program of Basic Research of the Institute of the Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM), Russian Academy of Sciences
文摘We present petrography and mineral chemistry for both phlogopite,from mantle-derived xenoliths (garnet peridotite,eclogite and clinopyroxene-phlogopite rocks) and for megacryst,macrocryst and groundmass flakes from the Grib kimberlite in the Arkhangelsk diamond province of Russia to provide new insights into multi-stage metasomatism in the subcratonic lithospheric mantle (SCLM) and the origin of phlogopite in kimberlite.Based on the analysed xenoliths,phlogopite is characterized by several generations.The first generation (Phl1) occurs as coarse,discrete grains within garnet peridotite and eclogite xenoliths and as a rock-forming mineral within clinopyroxene-phlogopite xenoliths.The second phlogopite generation (Phl2) occurs as rims and outer zones that surround the Phl1 grains and as fine flakes within kimberlite-related veinlets filled with carbonate,serpentine,chlorite and spinel.In garnet peridotite xenoliths,phlogopite occurs as overgrowths surrounding garnet porphyroblasts,within which phlogopite is associated with Cr-spinel and minor carbonate.In eclogite xenoliths,phlogopite occasionally associates with carbonate bearing veinlet networks.Phlogopite,from the kimberlite,occurs as megacrysts,macrocrysts,microcrysts and fine flakes in the groundmass and matrix of kimberlitic pyroclasts.Most phlogopite grains within the kimberlite are characterised by signs of deformation and form partly fragmented grains,which indicates that they are the disintegrated fragments of previously larger grains.Phl1,within the garnet peridotite and clinopyroxeneephlogopitexenoliths,is characterised bylow Ti and Cr contents (TiO2<1 wt.%,Cr2O3<1 wt.% andMg#=100×Mg/(MgtFe)>92) typical of primary peridotite phlogopite in mantle peridotite xenoliths from global kimberlite occurrences.They formed during SCLM metasomatism that led to a transformation from garnet peridotite to clinopyroxene-phlogopite rocks and the crystallisation of phlogopite and high-Cr clinopyroxene megacrysts before the generation of host-kimberlite magmas.One of the possible processes to generate low-Ti-Cr phlogopite is via the replacement of garnet during its interaction with a metasomatic agent enriched in K and H2O.Rb-Sr isotopic data indicates that the metasomatic agent had a contribution of more radiogenic source than the host-kimberlite magma.Compared with peridotite xenoliths,eclogite xenoliths feature low-Ti phlogopites that are depleted in Cr2O3 despite a wider range of TiO2 concentrations.The presence of phlogopite in eclogite xenoliths indicates that metasomatic processes affected peridotite as well as eclogite within the SCLM beneath the Grib kimberlite.Phl2 has high Ti and Cr concentrations (TiO2 > 2 wt.%,Cr2O3 > 1 wt.% and Mg#=100 × Mg/(Mg + Fe)< 92) and compositionally overlaps with phlogopite from polymict breccia xenoliths that occur in global kimberlite formations.These phlogopites are the product of kimberlitic magma and mantle rock interaction at mantle depths where Phl2 overgrew Phl1 grains or crystallized directly from stalled batches of kimberlitic magmas.Megacrysts,most macrocrysts and microcrysts are disintegrated phlogopite fragments from metasomatised peridotite and eclogite xenoliths.Fine phlogopite flakes within kimberlite groundmass represent mixing of high-Ti-Cr phlogopite antecrysts and high-Ti and low-Cr kimberlitic phlogopite with high Al and Ba contents that may have formed individual grains or overgrown antecrysts.Based on the results of this study,we propose a schematic model of SCLM metasomatism involving phlogopite crystallization,megacryst formation,and genesis of kimberlite magmas as recorded by the Grib pipe.
基金Partial funding for this project was produced by a Grant-in-Aid for Scientific Research (B) from Japan Society for the Promotion of Science (JSPS) (No. 26302009)the NIPR General Collaboration Projects (No. 2634) to Tsunogae
文摘We report new petrological, phase equilibria modeling, and fluid inclusion data for pelitic and mafic granulites from Rundv?gshetta in the highest-grade region of the Neoproterozoic Lützow-Holm Complex(LHC),East Antarctica, and provide unequivocal evidence for fluid-rock interaction and high-temperature metasomatism in the presence of brine fluid. The studied locality is composed dominantly of well-foliated pelitic granulite(K-feldspar+quartz+sillimanite+garnet+ilmenite) with foliation-parallel bands and/or layers of mafic granulite(plagioclase+orthopyroxene+garnet+ilmenite+quartz+biotite). The boundary between the two lithologies is defined by thin(about 1 -20 cm in thick) garnet-rich layers with a common mineral assemblage of garnet+plagioclase+quartz+ilmenite+biotite ? orthopyroxene. Systematic increase of grossular and decrease of pyrope contents in garnet as well as decreasing Mg/(Fe+Mg) ratio of biotite from the pelitic granulite to garnet-rich rock and mafic granulite suggest that the garnet-rich layer was formed by metasomatic interaction between the two granulite lithologies. Phase equilibria modeling in the system NCKFMASHTO demonstrates that the metasomatism took place at 850 -860℃, which is slightly lower than the peak metamorphism of this region, and the modal abundance of garnet is the highest along the metapeliteemetabasite boundary(up to 40%), which is consistent with the field and thin section observations. The occurrence of brine(7.0 -10.9 wt.% Na Cleqfor ice melting or 25.1 -25.5 wt.% NaC leqfor hydrohalite melting) fluid inclusions as a primary phase trapped within plagioclase in the garnet-rich layer and the occurrence of Cl-rich biotite(Cl = 0.22 -0.60 wt.%) in the metasomatic rock compared to that in pelitic(0.15 -0.24 wt.%) and mafic(0.06-0.13 wt.%) granulites suggest infiltration of brine fluid could have given rise to the high-temperature metasomatism. The fluid might have been derived from external sources possibly related to the formation of major suture zones formed during the Gondwana amalgamation.
基金supported by the Special Research Project of the State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences (No. 1008)the National Natural Science Foundation of China (No. 90714008)
文摘Two types of melt pockets, closed melt pocket （CMP） and open melt pocket （OMP）, are recognized from the peridotite xenoliths entrained in the Cenozoic kamafugites in western Qinling （秦岭）, Central China. The Haoti （好梯） CMPs have a mineral assemblage of olivine＋ clinopyroxene＋amphibole＋K- feldspar, whereas the Baiguan （白关） CMPs are composed of olivine＋clinopyroxene＋Umenite＋carbonate. The components of the OMPs are more complicated. In the Haoti OMPs, there are olivine, ciinopyroxene, glass, low modal abundances of amphibole, K-feldspar （Kfs）, Umenite, sulfide, chlorite, perovskite, chromite and phlogopite. The Baiguan OMPs contain olivine, clinopyroxene, glass, chlorite and chromite. Compositionally, ofivines in the CMPs and OMPs are both apparently depleted in Ni, and those in the OMPs are also depleted in Fe and Mg, and enriched in Ca compared to the primary ones. Ciinopyroxenes display large and systematical compositional variations between the CMPs and OMPs, particularly in Al, Cr, Na, Ca and Ti. Glasses are generally depleted in Si compared to the worldwide glasses in melt pockets, although they still have large variations. Amphiboles and K-feldspars have relatively restricted compositional variations. The petrographical observations and mineral chemistry suggest that the Haoti and Baiguan CMPs were generated by the in-sitn decompression melting of orthopyroxenes, olivines and clinopyroxenes, and by the addition of minor external K-rich and Ca-rich melt/fluids. The OMPs formed during the latest metasomatic event in the lithospheric mantle beneath the western Qinling.
基金Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits,MLR
文摘The Ni-Cu-platinum group element sulfide ore deposits of the Kharaelakh Intrusion,Noril′sk Region,Siberia,represent a large concentration of sulfides associated with a small differentiated intrusion formed at the edge of the Siberian Craton in the roots of the Siberian Trap flood basalt.The deposit is associated with an intrusion that occupies a flanking periclinal structure adjacent to the Noril′sk-Kharaelakh Fault.The intrusion is strongly differentiated and comprises taxitic gabbrodolerites,picritic gabbrodolerites,and gabbrodolerites within the main body which in turn forms a chonolith within a sheet-like intrusion that extends laterally to form extensive undifferentiated sills of gabbrodolerite.The intrusion substantially replaces the stratigraphy of the country rocks,and although it appears to have exploited the axis of structures developed in response to transtension,the intrusion has created space by both mechanical dilation of stratigraphy and magmatic replacement of pre-existing sedimentary rocks.The frontal lobes of the main intrusion have complex apophyses of gabrodolerite on a range of scales that demonstrate replacement of the sedimentary rocks and link to the development of an extensive metamorphic halo in the country rocks.This halo is much narrower over the main body of the intrusion,and these observations have implications for the thermal history of the intrusion.Mg-skarns and breccias are developed in the roof of the main body of the intrusion.Within the intrusion,the taxitic rocks contain vesicles and the blebby sulfides developed in the picritic and taxitic gabbrodolerites appear to have a linkage to volatile phases.Cuprous sulfide mineralization developed at the roof of the Kharaelakh Intrusion is associated with metamorphosed and skarn-bearing country rocks,and appears to have been generated by a combination of sulfide fractionation and associated metasomatism.The geological relationships appear consistent with a chonolith model for the development of the differentiated intrusion and mineralization,but the extent of metasmorphism of the country rocks appears to be related to the unusual thickness of gabbrodolerite apophyses at the flanks of the intrusion rather than metamorphism produced by the passage of mafic magma through the intrusion.Variations in disseminated sulfide compositions and metasomatic textures in the skarns are described,and a model is proposed which balances traditional views on the evolution of the magma conduits with the impact of magmatic fluids transported through the magma column(i.e.transmagmatic fluids).The importance of structures in controlling the nature of the conduit,and the resultant small intrusions with excess sulfide is a feature of many other Ni-Cu sulfide deposits including Voisey′s Bay,and it is suggested that the sulfides are more likely to have beentransported from depth into their final resting place rather than developed by in-situ equilibration of sulfide with fresh magma in the chonolith.
基金financial support from Department of Science and Technology, New Delhi in the form of research grant (ESS/16/295/2006) to KRH and NVCR is acknowledged
文摘Two petrologically distinct alkali feldspar syenite bodies （AFS-1 and AFS-2） from Chhotaudepur area, Deccan Large Igneous Province are reported in the present work. AFS-1 is characterized by hypidio-morphic texture and consists of feldspar （Or55Ab43 to Or25Ab71）, ferro-pargasite/ferro-pargasite horn-blende, hastingsite, pyroxene （Wo47, En5, Fs46）, magnetite and biotite. AFS-2 exhibits panidiomorphic texture with euhedral pyroxene （Wo47-50, En22-39, Fs12e31） set in a groundmass matrix of alkali feldspar （Or99Ab0.77 to Or1.33Ab98）, titanite and magnetite. In comparison to AFS-1, higher elemental concentra-tions of Ba, Sr and PREE are observed in AFS-2. The average peralkaline index of the alkali feldspar syenites is w1 indicating their alkaline nature. Variation discrimination diagrams involving major and trace elements and their ratios demonstrate that these alkali feldspar syenites have a shoshonite affinity but emplaced in a within-plate and rifting environment. No evidence of crustal contamination is perceptible in the multi-element primitive mantle normalized diagram as well as in terms of trace elemental ratios. The enrichment of incompatible elements in the alkali feldspar syenites suggests the involvement of mantle metasomatism in their genesis.
基金the 8th Geological Brigade of Aksu,Xinjiang, the Institute of Geology of the Chinese Academy of Geological Sciencesthe Beijing Research Institute of Uranium Geology,CNNC
文摘Objective The Sachakou Pb-Zn polymetallic deposit is located in Hetian County, Xinjiang （geographical coordinates of E78° 57＇ 54.30＂-78°59＇ 53.63＂, N34° 39＇ 27.50＂-34° 40＇ 57.21＂）. It belongs to the West Kunlun orogenic belt on the northwest edge of the Qinghai-Tibet Plateau and is connected to the Sanjiang orogenic belt to the south （Spurlin et al., 2005）. In recent years, a series of Pb-Zn mineralized spots and deposits have been discovered in this area one after another, which is called the Huoshaoyun ore concentration area. Among them, the Sachakou Pb-Zn deposit has reserves up to140 Mt, which has reached a large scale. However, the study on the genesis of deposits in this area has only just begun. This work studied the genesis ofthis Pb-Zn deposit in order to provide new ideas for the genesis of regional deposits and regional prospecting.
基金financially supported by grants from the Nature Science Foundation of China (Grant Nos. 416720634177302941302038 and 41720104009)
文摘The North China Craton(NCC) represents one of the oldest and largest cratons in the earth with a nearly complete record of Precambrian history. In the northern part of the NCC, the earliest phase of alkaline magmatism occurred in discrete pulses in the Early and Middle Devonian;whereas the next episode of alkaline magmatism took place in the early Mesozoic. The Gucheng pluton is exposed in the northern part of the NCC and forms a composite intrusion, consisting of K-feldspar–bearing clinopyroxenite, clinopyroxene–bearing syenite and alkali-feldspar syenite. Mineral phases in these lithologies include clinopyroxene(Wo43-48En19-35Fs18-38), sanidine(An0 Ab3-11Or89-97), and subordinate titanite, andradite and Na-feldspar. These rocks show homogeneous Sr but variable Nd isotopic compositions, and have relatively high zircon in-situ oxygen isotopes(δ18O=5.2–6.7). The Gucheng plutonic rocks formed through fractional crystallization and accumulation from ultrapotassic magmas, which were originated from partial melting of metasomatic vein systems in the subcontinental lithospheric mantle of the NCC. These vein networks developed as a result of the reactions of fluids derived from subducted pelitic sediments on the downgoing Palaeo-Asian ocean floor with the enriched, subcontinental lithospheric mantle peridotites. SHRIMP U-Pb zircon dating has revealed a crystallization age of 415 Ma for the timing of the emplacement of the Gucheng pluton that marks the early stages of alkaline magmatism associated with the Andean-type continental margin evolution along the northern edge of the NCC facing the Palaeo-Asian Ocean.
文摘The Qooshchi area lies to northwest of Orumieh Lake in western Azerb ai jan, NW Iran. A basement metamorphic complex, consisting of Precambrian schists and gneisses, has been intruded by gabbros and diorites. Granitoids are grouped into five suites according to their mineralogy, texture and exposed features. Th e main body, pink Qooshchi granite, and apophyse like, myrmekite bearing grani toids are discussed in this paper. On the basis of field observations and micros copic studies, an intensive metasomatism has overprinted the country rocks, espe cially gabbros, transforming them into a more felsic composition. A prior ev ent of intensive deformation and cataclasis preceded the metasomatism, allowing the introduction of hydrothermal fluids. K metasomatism converted plagioclase i nto K feldspar (microcline), myrmekite, and sodic plagioclase as Si metasomati sm replaced the ferromagnesian silicates by quartz. Apophyse like bodies within gabbros, called leucometasomatites, are formed during this process.
基金the funding received from the Science and Engineering Research Board (SERB), Govt. of India under GAP 3291funded by Ministry of Earth Science (MoES) with project reference number Mo ES/ P.O. (Seismic) 8 (09)-Geochron/2012。
文摘Hydrous Cr-bearing uvarovite garnets are rare in natural occurrences and belong to the ugrandite series and exist in binary solid solutions with grossular and andradite garnets. Here, we report the occurrence of hydrous uvarovite garnet having Cr_(2)O_(3) upto 19.66 wt% and CaO of 32.12–35.14 wt% in the serpentinized mantle peridotites of Naga Hills Ophiolite(NHO), India. They occur in association with low-Cr diopsides. They are enriched in LILE(Ba, Sr), LREEs, with fractionating LREE-MREE [avg.(La/Sm)_(N) = 2.16] with flat MREE/HREE patterns [avg.(Sm/Yb)_(N) = 0.95]. Raman spectra indicate the presence of hydroxyl(OH^(–)) peaks from 3500 to 3700 cm^(-1). Relative abundances in fluid mobile elements and their close association with clinopyroxenes are suggestive of the formation of uvarovite garnets through low temperature metasomatic alteration of low-Cr diopsides by hydrothermal slab fluids. The high LREE concentration and absence of Eu anomaly in the garnet further attest to alkaline nature of the transporting slab dehydrated fluid rather the involvement of low-p H solution. The chemical characteristics of the hydroxyl bearing uvarovite hosted by the mantle peridotite of NHO deviate from the classical features of uvarovite garnet, and their origin is attributed to the fluid-induced metasomatism of the sub arc mantle wedge in a suprasubduction zone regime.
基金This research was financially facilitated by Orlando Vasellisupported by the Bolyai Postdoctoral Fellowship Program,a Marie Curie International Reintegration Grant(Grant No.NAMS-230937)+3 种基金a postdoctoral grant(Grant No.PD101683)of the Hungarian Scientific Research Found(OTKA)to I.J.K.as well as a grant of the Hungarian Scientific Research Found(Grant No.78425)to Cs.supported by a grant from the U.S.National Science Foundation(EAR1624589)to R.J.supported by the GINOP-2.3.2-152016-00009 research program。
文摘Clinopyroxene-enriched upper mantle xenoliths classified as wehrlites are common(~20% of all xenoliths) in the central part of the Nograd-G(o| ")m(o|")r Volcanic Field(NGVF),situated in the northern margin of the Pannonian Basin in northern Hungary and southern Slovakia.In this study,we thoroughly investigated 12 wehrlite xenoliths,two from each wehrlite-bearing occurrence,to determine the conditions of their formation.Specific textural features,including clinopyroxene-rich patches in an olivine-rich lithology,orthopyroxene remnants in the cores of newlyformed clinopyroxenes and vermicular spinel forms all suggest that wehrlites were formed as a result of intensive interaction between a metasomatic agent and the peridotite wall rock.Based on the major and trace element geochemistry of the rock-forming minerals,significant enrichment in basaltic(Fe,Mn,Ti) and high field strength elements(Nb,Ta,Hf,Zr) was observed,compared to compositions of common lherzolite xenoliths.The presence of orthopyroxene remnants and geochemical trends in rock-forming minerals suggest that the metasomatic process ceased before complete wehrlitization was achieved.The composition of the metasomatic agent is interpreted to be a mafic silicate melt,which was further confirmed by numerical modelling of trace elements using the plate model.The model results also show that the melt/rock ratio played a key role in the degree of petrographic and geochemical transformation.The lack of equilibrium and the conclusions drawn by using variable lherzolitic precursors in the model both suggest that wehrlitization was the last event that occurred shortly before xenolith entrainment in the host mafic melt.We suggest that the wehrlitization and the Plio-Pleistocene basaltic volcanism are related to the same magmatic event.
基金supported by FAPDF(Call03/2018Process n°23568.93.50253.24052018)Serrapilheira Institute(Serra-1709-18152)。
文摘Here we present new data on the major and trace element compositions of silicate and oxide minerals from mantle xenoliths brought to the surface by the Carolina kimberlite,Pimenta Bueno Kimberlitic Field,which is located on the southwestern border of the Amazonian Craton.We also present Sr-Nd isotopic data of garnet xenocrysts and whole-rocks from the Carolina kimberlite.Mantle xenoliths are mainly clinopyroxenites and garnetites.Some of the clinopyroxenites were classified as GPP–PP–PKP(garnet-phlogopite peridotite,phlogopite-peridotite,phlogopite-K-richterite peridotite)suites,and two clinopyroxenites(eclogites)and two garnetites are relicts of an ancient subducted slab.Temperature and pressure estimates yield 855–1102℃ and 3.6–7.0 GPa,respectively.Clinopyroxenes are enriched in light rare earth elements(LREE)(La_(N)/Yb_(N)=5–62;Ce_(N)/Sm_(N)=1–3;where N=primitive mantle normalized values),they have high Ca/Al ratios(10–410),low to medium Ti/Eu ratios(742–2840),and low Zr/Hf ratios(13–26),which suggest they were formed by metasomatic reactions with CO_(2)-rich silicate melts.Phlogopite with high TiO_(2)(>2.0 wt.%),Al_(2)O_(3)(>12.0 wt.%),and FeOt(5.0–13.0 wt.%)resemble those found in the groundmass of kimberlites,lamproites and lamprophyres.Conversely,phlogopite with low TiO_(2)(<1.0 wt.%)and lower Al_(2)O_(3)(<12.0 wt.%)are similar to those present in GPP-PP-PKP,and in MARID(mica-amphibole-rutile-ilmenite-diopside)and PIC(phlogopite-ilmenite-clinopyorxene)xenoliths.The GPP-PP-PKP suite of xenoliths,together with the clinopyroxene and phlogopite major and trace element signatures suggests that an intense proto-kimberlite melt metasomatism occurred in the deep cratonic lithosphere beneath the Amazonian Craton.The Sr-Nd isotopic ratios of pyrope xenocrysts(G3,G9 and G11)from the Carolina kimberlite are characterized by high ^(143)Nd/^(144)Nd(0.51287–0.51371)and eNd(+4.55 to+20.85)accompanied with enriched ^(87)Sr/^(86)Sr(0.70405–0.71098).These results suggest interaction with a proto-kimberlite melt compositionally similar with worldwide kimberlites.Based on Sr-Nd whole-rock compositions,the Carolina kimberlite has affinity with Group 1 kimberlites.The Sm-Nd isochron age calculated with selected eclogitic garnets yielded an age of 291.9±5.4 Ma(2σ),which represents the cooling age after the proto-kimberlite melt metasomatism.Therefore,we propose that the lithospheric mantle beneath the Amazonian Craton records the Paleozoic subduction with the attachment of an eclogitic slab into the cratonic mantle(garnetites and eclogites);with a later metasomatic event caused by proto-kimberlite melts shortly before the Carolina kimberlite erupted.
文摘The post-collisional Cenozoic basic volcanic rocks in NE Turkey show temporal variations in whole-rock lithophile element and highly siderophile element(HSE)systematics that are mainly associated with the nature of sub-continental lithospheric mantle(SCLM)sources and parental melt generation.So far,the traditional whole-rock lithophile geochemical data of these basic volcanic rocks have provided important constraints on the nature of SCLM sources.Integrated lithophile element and HSE geochemical data of these basic volcanic rocks also reveal the heterogeneity of the SCLM source,which is principally related to variable metasomatism resulting from previous subduction(s)and post-collisional mantle-crust interactions in an extensional setting.Lithophile element geochemical features suggest that the parental magmas have derived from metasomatized spinel-to garnet-bearing SCLM sources for Eocene and Miocene basic volcanic rocks with subduction signatures whereas originated from spinel-to garnet-bearing SCLM sources for Mio-Pliocene and Plio-Quaternary basaltic volcanic rocks without the subduction signature.Lithophile element and HSE geo-chemistry also reveal that Eocene and Miocene basic vol-canic rocks were affected by more pronounced crustal contamination than the basaltic volcanic rocks of Mio-Pliocene and Quaternary.Furthermore,the integrated lithophile element and HSE compositions of these basic volcanic rocks,together with the regional asymmetric lithospheric delamination model,reveal that the compositional variation(especially due to metasomatism)was significant temporally in the heterogeneity of the SCLM sources from which parental magmas formed during the Cenozoic era.
文摘The present study focuses on the inorganic geochemical features of the bituminous coal samples from the Raniganj and the Jharia Basins,as well as the anthracite samples from the Himalayan fold-thrust belts of Sikkim,India.The SiO_(2)content(48.05 wt%to 65.09 wt%and 35.92 wt%to 50.11 wt%in the bituminous and anthracite samples,respectively)and the ratio of Al_(2)O_(3)/TiO_(2)(6.97 to 17.03 in the bituminous coal samples and 10.34 to 20.07 in the anthracite samples)reveal the intermediate igneous source rock composition of the minerals.The ratio of the K_(2)O/Al_(2)O_(3)in the ash yield of the bituminous coal samples(0.03 to 0.09)may suggest the presence of kaolinite mixed with montmorillonite,while its range in the ash yield of the anthracite samples(0.16 to 0.27)may imply the presence of illite mixed with kaolinite.The chemical index of alteration values may suggest the moderate to strong chemical weathering of the source rock under sub-humid to humid climatic conditions.The plot of the bituminous coal samples in the A–CN–K diagram depicts the traditional weathering trend of parent rocks,but the anthracite samples plot near the illite feld and are a bit ofset from the weathering trend.This may imply the plausible infuences of the potassium-metasomatism at post coalifcation stages,which is further supported by high K_(2)O/Na_(2)O ratio(29.88–80.13).The Fourier transform infrared spectra further reveal the hydroxyl stretching intensity of illite in the anthracite samples substantiating the efect of the epigenetic potassium-metasomatism.The decrease in total kaolinite intensity/compound intensity of quartz and feldspar may provide additional evidence towards this epigenetic event.
文摘Phlogopite-amphibole-pyroxenite xenoliths contained in the alkali basic-ultrabasic subvolcanic complex in Langao, Shaanxi Province, are composed of diopside, Ti-rich pargasite, phlogopite apatite, sphene and ilmenite, which have subsolidus metamorp hism- de formation textures such as triple-points, cataclastic boundaries and kink-bands. Mineral chemical characteristics show that the diopside, Ti-rich pargasite and phlogoPite are derived from the mantle and are the products of mantle metasomatism. Compared with normal mantle-derivedspinel-lherzolites, the xenoliths are enriched in TiO2, Fe2O3, CaO, Na2O and K2O, with apparent depletion in MgO. Chondrite-normalized REE patterns and primordial-mantle normalized trace elements data show that they are enriched in REE (especially LREE) and incompatible trace elements. The petrographic, mineralogical and petrochemical characteristics indicate that the xenoliths are metasomatized mantle xenoliths, which offers the evidence for mantle metasomatism and represents the anomalous mantle beneath the Early Paleozoic rift in northern Daba Mountains. The agents of mantle metasomatism are probably derived from the rising of mantle hot plumes. The processes of metasomatism varied from limited-range fluid metasomatism in deep mantle (＞90 km) to pervasive metasomatism of silicate melt.
文摘The Pinxiang weathering profile is well developed on Early Triassic dacite lavas of the Baisi Formation. At the top of the profile is developed a red clay zone which is characterized mineralogically by kaolinite, iron oxide minerals, quartz, and a small amount of illite, montmorillonite and vermiculite. In going downwards the red clay zone gives way to a saprolite zone in which plagioclase pseudomorphs have been well preserved although replaced by kaolinite. Beneath the saprolite zone is the saprock zone characterized by less weathering for dacite. At the bottom of the weathering profile is the parent material, dacite, which is composed mainly of plagioclase, quartz, K-feldspar and biotite which have been largely altered into chlorite owing to submarine extrusion of dacite lavas. Some layers in the weathering profile show obvious sodium enrichment and potassium depletion relative to others. In the Al2O3-(CaO*+Na2O)-K2O triangular diagram, the weathering trends of these layers in the middle stage are remarkably deviated from normal ones. Both mineralogy and micro-morphology of these layers indicate such deviation resulted from sodic metasomatism of orthoclase.
基金supported by the National Natural Science Foundation of China(42172010,42372071,41102037)。
文摘The Longshan orogenic belt is located in the southwestern margin of Ordos Basin at the junction zone between the Western Qinling and Northern Qilian orogenic belt.Voluminous Early Paleozoic magmatism in this area is of key significance for determining the Early Paleozoic tectonic evolution and deep crust-mantle structure.Previous studies mainly focused on the Paleozoic granites;the coeval mafic rocks in this area are still poorly understood.A set of Late Silurian intraplate tholeiitic basalts has been discovered in Longshan area,providing key evidence for the mantle source and deep geodynamic background in this area.The Late Silurian Angou basalt has similar geochemical features as intraplate tholeiitic basalt,with high Na_(2)O/K_(2)O ratios(5.22-8.25),enriched in large ion lithophile elements and LREE.In combination with their relatively evolved Sr-Nd isotopic composition[^(87)Sr/^(86)Sr(i)=0.7128-0.7140;ε_(Nd)(t)=-5.55 to-3.40],it is suggested that it originated from decompression melting of metasomatized enriched mantle in extensional setting.These results indicate that the mantle source in the junction zone of the West Qinling-North Qilian orogenic belt evolved from depleted to enriched with the continuation of Proto-Tethys subduction from the Cambrian to the Silurian.These results are of great significance to understanding the genesis of contemporaneous granite and the crust-mantle interaction in the junction zone between the Western Qinling and Northern Qilian orogenic belt.
