New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase m...New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase metamorphic history, with peak Barrovian metamorphism at (32 2±0 4)Ma and a later high\|temperature, low\|pressure event (620℃, 400MPa) at (22 7±0 2)Ma.. Emplacement and crystallization of the Everest granite subsequently occurred at 20 5～21 3Ma. The monazite crystallization ages that differ by 10Ma are recorded in two structurally adjacent rocks of different lithology, which have the same post collisional p—T history.. Scanning electron microscopy reveals that the younger monazite is elaborately shaped and grew in close association with apatite at grain boundaries and triple junctions, suggesting that growth was stimulated by a change in the fluid regime. The older monazite is euhedral, is not associated with apatite, and is commonly armoured within silicate minerals. During the low\|pressure metamorphic event, the armouring protected the older monazites, and a lack of excess apatite in this sample prevented new growth. Textural relationships suggest that apatite is one of the necessary monazite\|producing reactants, and spots within monazite that are rich in Ca, Fe, Al and Si suggest that allanite acted as a preexisting rare earth element host. We propose a simplified reaction for monazite crystallization based on this evidence.展开更多
In the gneisses from the drillhole ZK2304 of the Donghai area, there have been preserved high- and ultrahigh-pressure metamorphic mineral assemblages, a series of complicated retrogressive textures and relevant metamo...In the gneisses from the drillhole ZK2304 of the Donghai area, there have been preserved high- and ultrahigh-pressure metamorphic mineral assemblages, a series of complicated retrogressive textures and relevant metamorphic reactions. In addition to garnet, jadeititic-clinopyroxene and rutile, other peak stage (M2) minerals in some gneisses include phengite, aragonite and coesite or quartz pseudomorphs after coesite. The typical peak-stage mineral assemblages in gneisses are characterized by garnet + jadeitic-clinopyroxene + rutile + coesite, garnet + jadeitic-clinopyroxene + phengite + rutile ± coesite and garnet + jadeitic-clinopyroxene + aragonite + rutile ± coesite. The grossular content (Gro) in garnet is high and may reach 50. 1 mol%. The SiO2 content of phengite ranges from 54.37% to 54.84% with 3.54-3.57 p.f.u. Quartz pseudomorphs after coesite occur as inclusions in garnet.The gneisses of the Donghai area have been subjected to multistage recrystallization and exhibit a closewise P-T evolutional path characterized by the near-isothermal decompression. The inclusion assemblage (Hb+Ep+Bi+Pl+Qz) within garnet and other minerals has recorded a pre-peak stage (Mi) epidote amphibole fades metamorphic event. High- and ultrahigh-pressure peak metamorphism (M2) took place at T=750-860℃ and P>2.7 GPa. The symplectitic assemblages after garnet, jadeitic-clinopyroxene and rutile imply a near-isothermal decompression metamorphism (M3, M4) during the rapid exhumation. Several lines of evidence of petrography and metamorphic reactions indicate that both gneisses and eclogites have experienced ultrahigh-pressure metamorphism in the Donghai area. This research may be of great significance for an in-depth study of the metamorphism and tectonic evolution in the Su-Lu ultrahigh-pressure metamorphic belt.展开更多
Lithosphere extension and upwelling of asthenosphere at post-collisional stage of an orogenic cycle generally induce diverse magmatism and/or associated high-temperature metamorphism. Nevertheless, the intimate coexis...Lithosphere extension and upwelling of asthenosphere at post-collisional stage of an orogenic cycle generally induce diverse magmatism and/or associated high-temperature metamorphism. Nevertheless, the intimate coexistence of post-collisional magmatic activity and high-temperature metamorphism is rare.In this contribution, a lithological assemblage composing of diverse magmatic rocks deriving from distinct magma sources and coeval high-temperature metamorphism was identified in eastern Kunlun.Petrography, ages, mineral chemistry and whole-rock geochemistry demonstrated that those intimately coexistent diverse rocks were genetically related to post-collisional extension. The garnet-bearing mafic granulites in Jinshuikou area interior of the East Kunlun Orogenic Belt are mainly composed of garnet,orthopyroxene, and plagioclase, with peak metamorphic P–T conditions of ~ 701–756 ℃and 5.6–7.0 kbar,representing a granulite-facies metamorphism at 409.7 ± 1.7 Ma. The diverse contemporaneous magmatic rocks including hornblendites, gabbros and granites yield zircon U–Pb ages of 408.6 ± 2.5 Ma,413.4 ± 4.6 Ma, and 387–407 Ma, respectively. The hornblendites show N-MORB-like REE patterns with(La/Sm)Nvalues of 0.85–0.94. They have positive zircon εHf(t) values of 0.1–4.9 and whole-rock εNd(t) values of 3.9–4.7 but relatively high(^(87)Sr/^(86)Sr)_(i)values of 0.7081 to 0.7088. These features demonstrate that the hornblendites derived from a depleted asthenospheric mantle source with minor continental crustal materials in source. As for the gabbros, they exhibit arc-like elemental signatures, low zircon εHf(t) values(-4.3 to 2.5) and variable whole-rock εNd(t) values(-4.9 to 1.2) as well as high(^(87)Sr/86 Sr)ivalues(0.7068 to 0.7126), arguing for that they were originated from partial melting of heterogeneous lithospheric mantle anteriorly metasomatized by subducted-sediment released melts. Geochemistry of the granites defines their strongly peraluminous S-type signatures. Zircons from the granites yield a large range of εHf(t) values ranging from -30.8 to -5.1, while the whole-rock samples yield consistent(^(87)Sr/86 Sr)ivalues(0.7301 to 0.7342) and negative εNd(t) values(-10.1 to -12.4). These features indicate that the S-type granites could be generated by reworking of an ancient crust. Taken together, the penecontemporaneous magmatism and metamorphic event, demonstrated the early-middle Devonian transition from crustal thickening to extensional collapse. The post-collisional mantle-derived magmas serve as an essential driving force for the high-temperature granulite-facies metamorphism and anataxis of the crust associated with formation of S-type granite. This study not only constructs a more detail Proto-Tethys evolution process of the eastern Kunlun, but also sheds new light on better understanding the intimate relationship between magmatism and metamorphism during post-collisional extensional collapse.展开更多
The Himalayan Orogen, resulting from the Tertiary collision of Indian and Asian continents, is a natural laboratory for studying metamorphism, partial melting and granite formation of collisional orogens. However, met...The Himalayan Orogen, resulting from the Tertiary collision of Indian and Asian continents, is a natural laboratory for studying metamorphism, partial melting and granite formation of collisional orogens. However, metamorphic and anatectic conditions and timescales of meta-mafic rocks in the Greater Himalayan Sequences （GHS） in the east-central Himalaya remain controversial, in this paper, we conduct a study of petrology and geochronology of mafic granulite from the Eastern Himalayan Syntaxis （EHS）. The mafic granulite with abundant leucosome bands occurs as layers within felsic granulites and is well deformed. The granulite consists of garnet, plagioclase, amphibole and quartz with minor clinopyroxene, orthopyroxene, biotite, rutile, titanite and ilmenite. The garnet has growth compositional zoning and contains abundant mineral inclusions in its core. Peak metamorphic mineral assemblage of the granulite is garnet, amphibole, plagioclase, quartz, clinopyroxene and futile, recording a high-pressure （HP） and high-temperature （HT） peak-metamorphism under conditions of 14-15.5 kbar and 780-790 ℃ in the presence of melt. The reconstructed clockwise P-T path is characterized by an early heating and burial prograde metamorphism, and late isothermal and cooling decompression retrogression. The granulite witnessed a long lasting HT metamorphism, partial melting and melt crystallization process which began at ca. 39 Ma and lasted to ca. 11 Ma. The present study shows that various high-grade rocks of the GHS in the EHS core experienced similar metamorphic conditions and P-T-t paths, indicating that they occurred as a coherent slab during the subduction and exhumation of Indian lithosphere. The significant melts generated during the prograde metamorphism of the GHS rocks not only contributed to the formation of the Himalayan leucogranite, but also resulted in the rheological weakening and ductile flow of the thickened lower crust of the Himalayan Orogen.展开更多
We used illite and chlorite crystaHinities, index minerals, mineral assemblages, polytype and domain size of white mica, electron microprobe analysis （EMPA）, b0 geobarometer and chlorite geothermometer to quantify t...We used illite and chlorite crystaHinities, index minerals, mineral assemblages, polytype and domain size of white mica, electron microprobe analysis （EMPA）, b0 geobarometer and chlorite geothermometer to quantify the diagenetic and metamorphic overprint on the Triassic flysch formations in the Songpan-Garze orogen along profile Zoige-Lushan, northwest Sichuan. Two anchizones, two epizones, one diagenetic zone and a transition belt in-between them are defined on the basis of the obtained data. lllite crystallinity correlates strongly with the best mean domain size of mica and moderately with chlorite crystallinity. 2M1 white mica polytype are observed within the epizone whilst 2M1 and 1M polytypes occur in the anchizone and diagenetic zone. Epizonal metamorphism reached maximum temperatures of 370℃±21℃ at low-to intermediate pressure conditions. Clay minerals underwent Ostwald ripening during metamorphism. Rocks from both sides of the Longmenshan fault reveal contrasting degrees of metamorphic overprint： on the northwest side of the Longmenshan fault, epimetamorphic conditions contrast with diagenetic rocks on the southeast side.展开更多
The east sector of the southern Qinling belt is, lithologically, composed mainly of metapelites, ***qüartzites, marbles and small amount of metabasites and gneisses, whose protoliths are the Silurian, Devonian an...The east sector of the southern Qinling belt is, lithologically, composed mainly of metapelites, ***qüartzites, marbles and small amount of metabasites and gneisses, whose protoliths are the Silurian, Devonian and less commonly the Sinian and Upper Palaeozoic. They have been subjected at least to two epochs of metamorphism. The early epoch belongs to progressive metamorphism which is centered on high amphibolite-granulite fades in the Fuping area and changed outwards into low amphibolite facies (staurolite-kyanite zone), epidote amphibolite facies (garnet zone) and greenschist facies (chlorite and biotite zones), the metamorphic age of which is about 220–260 Ma. This early-epoch metamorphism belongs to different pressure types: the rocks from greenschist to low amphibolite facies belong to the typical medium-pressure type which shows geothermal gradients of about 17–20 ***C/km and was probably produced by a crustal thickening process related to continental collision, and the high amphibolite-granulite facies belongs to the low-pressure type which shows geothermal gradients of about 25–38 ***C/km and was probably affected by some magmatic heats. Based on the basic characteristics of the P-T paths of the different facies calculated from the garnet zonations, it can be deduced that the metamorphism of medium-pressure facies series took place during an imbricated thickening process, rather than during the uplifting process after thickening. The late-epoch metamorphism belongs to dynamic metamorphism of greenschist facies which is overprinted on the early-epoch metamorphic rocks and is Yanshanian or Himalayan in age, probably related to intracontinental orogeny.展开更多
The nature and evolution of the Proto-Tethys Ocean originated from the breakup of the supercontinent Rodinia remain controversial. Early Paleozoic magmatism and metamorphism can pro- vide important constraints on the ...The nature and evolution of the Proto-Tethys Ocean originated from the breakup of the supercontinent Rodinia remain controversial. Early Paleozoic magmatism and metamorphism can pro- vide important constraints on the closure of the Proto-Tethys Ocean. This paper reports on a set of geological, petrographical, geochronological, mineralogical and geochemical data for Early Paleozoic granite, gabbro, granulite and granitic leucosome in the northern Wulan terrane of the Quanji Massif. Zircon LA-ICP-MS U-Pb dating reveals two episodes of magmatism, with the emplacement of a gran- itic pluton at 476.7±2.8 Ma and a gabbroic dike at 423±2 Ma. Whole-rock geochemistry suggests an arc affinity for the magma of the granitic pluton but a post-collisional extension setting for the gabbroic dike. Zircon LA-ICP-MS U-Pb dating also shows that the peak granulite-facies metamorphism and anatexis occurred at --475 Ma, coeval with the formation of the granitic pluton in the Quanji Massif as well as the early lawsonite-bearing eclogites in the North Qaidam high-pressure and ultrahigh-pressure (HP-UHP) metamorphic belt to the south. The granulite-facies metamorphism with peak P-T condi- tions at 718-729 ℃ and 0.46-0.53 GPa is characterized by an anticlockwise P-T path. Our data provide compelling evidence for Early Paleozoic paired metamorphic belts with HP-UHP metamorphism in the North Qaidam to the south and low PIT metamorphism in the Quanji Massif as a continental arc to the north, hence suggesting a northward subduction polarity for the Proto-Tethys oceanic plate. The intrusion of the post-collisional gabbroic dike supports for the closure of the Proto-Tethys Ocean in north- western China before 423 Ma.展开更多
In order to constrain temperature during subduction and subsequent exhumation of fel- sic continental crust, we carried out a Ti-in-zircon thermometer coupled with zircon internal structure and U-Pb age on migmatitic ...In order to constrain temperature during subduction and subsequent exhumation of fel- sic continental crust, we carried out a Ti-in-zircon thermometer coupled with zircon internal structure and U-Pb age on migmatitic gneisses from the Weihai region in the Sulu ultra-high pres- sure （UHP） metamorphic terrane, eastern China. The Weihai migmatitic gneisses are composed of in- tercalated compositional layers of melanosome and plagioclase （Pl）-rich lencosome and K-feldspar （Kfs）-rich pegmatite veins. Four stages of zircon growth were recognized in the Weihai migmatitic gneisses. They successively recorded informations of protolith, prograde metamorphism, decompres- sional partial melting during early stage exhumation and subsequent fractional crystallization of pri- mary melt during later stage cooling exhumation. The inherited cores in zircon from the melanosome and the Pl-rich leucosome suggest that the pro- tolith of the migmatitic gneiss is Mid- Neoproterozoic （-780 Ma） magmatic rock. Metamorphic zircons with concordant ages ranging from 243 to 256 Ma occur as over- growth mantles on the protolith magmatic zir- con cores. The estimated growth temperatures （625-717 ＂C） of the metamorphic zircons have a negative correlation with their ages, indicating a progressive metamorphism in HP eciogite-facies condition during subduction. Zircon recrystal- lized rims （228-2 Ma） in the PI-rich ieucosome layers provide the lower limit of the decompress-sional partial melting time during exhumation. The ages from 228^-2 to 219~2 Ma recorded in the Pl-rich leucosome and the Kfs-rich pegmatite vein, respectively, suggest the duration of the fractional crystallization of primary melt during exhumation. The calculated growth temperatures of the zircon rims from the Pl-rich leucosome range from 858 to 739 , and the temperatures of new growth zircon grains （219±2 Ma） in Kfs-rich vein are between 769 and 529 . The estimated temperatures have a positive correlation with ages from the Pl-rich leucosome to the Kfs-rich pegmatite vein, strongly indi- cating that a process of fractional crystallization of the partial melt during exhumation.展开更多
Yushugou granulite-peridotite complex,located at the east part of the northern margin of South Tianshan,may represent an ophiolitic slice subducted to 40–50 km depth with high-pressure granulite facies metamorphism.A...Yushugou granulite-peridotite complex,located at the east part of the northern margin of South Tianshan,may represent an ophiolitic slice subducted to 40–50 km depth with high-pressure granulite facies metamorphism.Although a lot of studies have been conducted on rocks in this belt,the rock association and tectonic background of the ophiolitic slice are still in dispute.A detailed study on petrology,phase equilibrium modeling and U-Pb zircon ages have been performed on the metagabbro vein in peridotite unit to constrain the tectonic evolution of the Yushugou granulite-peridotite complex.Three stages of mineral assemblage in the metagabbro were defined as stage I:Cpx^A+Opx^A+Pl^A,which represents the original minerals of the metagabbro vein;stage II:Cpx^B+Opx^B+Pl^B+Spl,which represents the mineral assemblage of granulite facies metamorphism with peak P-T conditions of 4.2–6.9 kbar and 940–1070℃;stage III is characterized by the existence of prehnite,thomsonite and amphibole in the matrix,indicating that the metagabbro vein may be influenced by fluids during retrograde metamorphism.Combined with the crosscut relationship,it can be deduced that the metagabbro vein,together with the peridotite in Yushugou granulite-peridotite complex has experienced similar high-temperature granulite facies metamorphism.The zircon chronological data shows that the protolith age of the metagabbro vein is 400.5±6.2 Ma,reflecting Devonian magmatism event and the granulite facies metamorphism occurred at^270 Ma which may be related to the post-collisional magmatism.展开更多
The origin, age and evolution of the Precambrian metamorphic basement of southern China provide useful insights into early crustal development. Here, we present new laser ablation-inductively coupled plasma-mass spect...The origin, age and evolution of the Precambrian metamorphic basement of southern China provide useful insights into early crustal development. Here, we present new laser ablation-inductively coupled plasma-mass spectrometry （LA-ICP-MS） U-Pb age data for detrital zircons from five samples of the Precambrian metamorphic basement of the Xiangshan uranium orefield. Two of these samples, from the northern Xiangshan volcanic basin, yielded a total of 140 U-Pb ages that cluster within the Neoproterozoic （773-963 Ma; 79.3% of data points）, with the rest being scattered through the Paleoproterozoic and Mesoproterozoic, along with a single Archean age. These ages indicate that this basement material is associated with the Cathaysia Block. In comparison, the 172 concordant ages from the other three samples from the southern part of the Xiangshan volcanic basin cluster within the Neoproterozoic （767-944 Ma; 59.8%） as well as the Proterozoic （37.8%） and the Archean （2502-2712 Ma; 14.5%）. These samples are also free of zircons with Grenvillian ages, indicating that these units are associated with the southeastern Yangtze Block. Combining these data with the geochemistry of these units, which suggests that the metamorphosed sedimentary rocks within the northern and southern parts of the Xiangshan basin have a common component from a magmatic island arc that formed during the early Neoproterozoic, we infer that the basin was located along the boundary between the Cathaysian and Yangtze blocks. In addition, the zircons within the samples from the southern and northern parts of the Xiangshan basin show different pre-Neoproterozoic （963 Ma） age populations but similar post- Neoproterozoic zircon populations, indicating that the amalgamation of the Cathaysian and Yangtze blocks occurred after the Neoproterozoic （960 Ma）, with magmatism peaking at 830 Ma and rifting starting at -770 Ma, leading to the subsequent deposition （from bottom to top） of the Shenshan, Kuli, and Shangshi formations.展开更多
In this study, we carried out petrography, zircon U-Pb geochronology and Hf isotopic analyses on a granitic pegmatite dyke in the Xiaoqinling area in southern margin of the North China Craton（NCC）. Our study suggest...In this study, we carried out petrography, zircon U-Pb geochronology and Hf isotopic analyses on a granitic pegmatite dyke in the Xiaoqinling area in southern margin of the North China Craton（NCC）. Our study suggests that the pegmatite dyke likely crystallized from a volatile-rich pegmatitic magma. Different from most other pegmatite elsewhere, zircon from this pegmatite dyke does not contain unusually high U and Th concentrations and suffered no evident radioactive damage, therefore we successfully obtained a zircon U-Pb dating using laser ablation-inductively coupled plasma-mass spectrometry（LA-ICP-MS）, which yields an average 207Pb/206 Pb age of 1 814±6 Ma, representing the intrusive age of the granitic pegmatite dyke. Zircon εHf（t） values are between-8.3 and-3.0, corresponding to Hf depleted mantle model ages from 2 649 to 2 991 Ma with an average of 2 881 Ma. These data indicate that this granitic pegmatite dyke may have been derived from partial melting of Meso-Neoarchean metamorphic rocks from the Xiaoqinling basement. Granitic pegmatite magma may have emplaced within the Taihua Group wall rocks during the last stage of the middle to high grade metamorphism. Furthermore, according to the petrographic observation, the 1.81 Ga pegmatite dyke and the 1 800–1 750 Ma Xiong’er Group rocks were not undergone middle to high grade metamorphism, indicating 1.81 Ga as the termination of the latest regional metamorphism in the southern margin of the NCC.展开更多
Based upon fluid effects, retrograde metamorphism of eclogites in the Dabieregion can be divided into the fluid-poor, fluid-bearing and fluid-rich stages. The fluid-poor stageis marked by polymorphic inversion, recrys...Based upon fluid effects, retrograde metamorphism of eclogites in the Dabieregion can be divided into the fluid-poor, fluid-bearing and fluid-rich stages. The fluid-poor stageis marked by polymorphic inversion, recrystallization and exsolution of solid solutions, and isthought to represent eclogite-facies retrograde environments. The fluid-bearing stage is likely tohave occurred at the late stage of ecologite-facies diaphthorosis and is represented by kyaniteporphyroblasts, rutile, and sodic pyroxene in association with high-pressure hydrous minerals suchas phengite and zoisite (clinozoisite) without significant amount of hydrous minerals such asamphibole, epidote and biotite. The fluid-rich stage might have commenced concomitantly with loweramphibolite-facies diaphthoresis and persisted all the way towards the near-surface environment. Theproduct of this stage is characterized by plentiful hydrous and volatile-bearing phases.The dissemination-type rutile mineralizations in eclogites might have formed by preferentialshearing-induced pressure solution of gangue minerals at the fluid-bearing stage. The accompanyingvein rutile was precipitated from fluids of this stage after local transport and concentration, andmay hence represent proximal mobilization of titanium from the eclogite. Therefore, rutile veins canbe used as an exploration indicator for dissemination-type rutile deposits.展开更多
Ultrahigh-temperature （UHT） metamorphism represents extreme crustal metamorphism with peak metamorphic temperatures exceeding 900 ℃ and pressures ranging from 7 to 13 kbar with or without partial melting of crusts,...Ultrahigh-temperature （UHT） metamorphism represents extreme crustal metamorphism with peak metamorphic temperatures exceeding 900 ℃ and pressures ranging from 7 to 13 kbar with or without partial melting of crusts, which is usually identified in the granulite-facies rocks. UHT rocks are recognized in all major continents related to both extensional and compressive tectonic environments. UHT metamorphism spans different geological ages from Archean to Phanerozoic, providing information of the nature, petrofabric and thermal evolution of crusts. UHT metamorphism is traditionally identified by the presence of a diagnostic mineral assemblage with an appropriate bulk composition and oxidation state in Mg-Al-rich metapelite rocks. Unconventional geothermobarometers including Ti-in-zircon （TIZ） and Zr-in-rutile （ZIR） thermometers and phase equilibria modeling are increasingly being used to estimate UHT metamorphism. Concentrated on the issues about UHT metamorphism, this review presents the research history about UHT metamorphism, the global distribution of UHT rocks, the current methods for constraints on the UHT metamorphism, and the heat sources and tectonic settings of UHT meta- morphism. Some key issues and prospects about the study of UHT metamorphism are discussed, e.g., identification of UHT metamorphism for non-supracrustal rocks, robustness of the unconventional geothermometers, tectonic affinity of UHT metamorphic rocks, and methods for the constraints of age and duration of UHT metamorphism. It is concluded that UHT metamorphism is of great importance to the understanding of thermal evolution of the lithosphere.展开更多
The Chertovo Koryto gold deposit（80 t Au at 1.84 g/t） in the Lena world-class province,Siberia,is hosted in a metamorphosed sequence of the Paleoproterozoic Mikhailovsk Formation that comprises the oldest black shal...The Chertovo Koryto gold deposit（80 t Au at 1.84 g/t） in the Lena world-class province,Siberia,is hosted in a metamorphosed sequence of the Paleoproterozoic Mikhailovsk Formation that comprises the oldest black shale strata of the Baikal-Patom region.The mineralisation is confined to the thrust zone complicated with a conjugate anticline fold,zones of shearing and dislocation.The struaural position of the mineralisation is similar to that at the giant Sukhoi Log deposit in the neighbouring Mama-Bodaibo zone.In the latter,the isotope age data suggest that Khomolkho black shales,hosts to Sukhoi Log mineralisation,are of Ediacaran age and underwent prograde metamorphism during early Paleozoic.The geochemical composition of the terrigenous rocks that host Sukhoi Log,Chertovo Koryto,and a number of other deposits at the various stratigraphic levels throughout the Proterozoic sequence have much in common.They do not show elevated metal contents above the common black shale abundances,except for Au and As,which is at variance with the accepted view on diagenetic enrichment of black shales in the Lena province.The occurrence of sagenitic rutile in quartz and chlorite pseudomorphs after biotite and other petrographic observations provide evidence on a retrograde nature of the metamorphic mineral assemblages in the Mikhailovsk rocks.The sulphides are pyrrhotite and arsenopyrite with very minor pyrite at Chertovo Koryto,whereas pyrite is the predominant sulphide in the Sukhoi Log ore.Fluid inclusion data on both deposits emphasise a high-temperature nature of the mineralisation albeit revealing great contrast in the fluid composition.Sukhoi Log mineralisation was formed at mixing between low-salinity aqueous solutions and dense gaseous carbonic fluids,which facilitated effective gold scavenging and precipitation,as demonstrated by thermodynamic simulation.The precursory devolatilisation of the Mikhailovsk sediments at the prograde stage results in the paucity of gaseous carbonic fluid during retrograde metamorphism and mineralisation.The similarity in the styles and chemical parameters of mineralisation,and the predominant structural control of ore localisation within the same Precambrian regional tectonic unit support an idea that orogenic gold mineralisation in the Lena province was produced during a single early Paleozoic event.展开更多
文摘New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase metamorphic history, with peak Barrovian metamorphism at (32 2±0 4)Ma and a later high\|temperature, low\|pressure event (620℃, 400MPa) at (22 7±0 2)Ma.. Emplacement and crystallization of the Everest granite subsequently occurred at 20 5～21 3Ma. The monazite crystallization ages that differ by 10Ma are recorded in two structurally adjacent rocks of different lithology, which have the same post collisional p—T history.. Scanning electron microscopy reveals that the younger monazite is elaborately shaped and grew in close association with apatite at grain boundaries and triple junctions, suggesting that growth was stimulated by a change in the fluid regime. The older monazite is euhedral, is not associated with apatite, and is commonly armoured within silicate minerals. During the low\|pressure metamorphic event, the armouring protected the older monazites, and a lack of excess apatite in this sample prevented new growth. Textural relationships suggest that apatite is one of the necessary monazite\|producing reactants, and spots within monazite that are rich in Ca, Fe, Al and Si suggest that allanite acted as a preexisting rare earth element host. We propose a simplified reaction for monazite crystallization based on this evidence.
文摘In the gneisses from the drillhole ZK2304 of the Donghai area, there have been preserved high- and ultrahigh-pressure metamorphic mineral assemblages, a series of complicated retrogressive textures and relevant metamorphic reactions. In addition to garnet, jadeititic-clinopyroxene and rutile, other peak stage (M2) minerals in some gneisses include phengite, aragonite and coesite or quartz pseudomorphs after coesite. The typical peak-stage mineral assemblages in gneisses are characterized by garnet + jadeitic-clinopyroxene + rutile + coesite, garnet + jadeitic-clinopyroxene + phengite + rutile ± coesite and garnet + jadeitic-clinopyroxene + aragonite + rutile ± coesite. The grossular content (Gro) in garnet is high and may reach 50. 1 mol%. The SiO2 content of phengite ranges from 54.37% to 54.84% with 3.54-3.57 p.f.u. Quartz pseudomorphs after coesite occur as inclusions in garnet.The gneisses of the Donghai area have been subjected to multistage recrystallization and exhibit a closewise P-T evolutional path characterized by the near-isothermal decompression. The inclusion assemblage (Hb+Ep+Bi+Pl+Qz) within garnet and other minerals has recorded a pre-peak stage (Mi) epidote amphibole fades metamorphic event. High- and ultrahigh-pressure peak metamorphism (M2) took place at T=750-860℃ and P>2.7 GPa. The symplectitic assemblages after garnet, jadeitic-clinopyroxene and rutile imply a near-isothermal decompression metamorphism (M3, M4) during the rapid exhumation. Several lines of evidence of petrography and metamorphic reactions indicate that both gneisses and eclogites have experienced ultrahigh-pressure metamorphism in the Donghai area. This research may be of great significance for an in-depth study of the metamorphism and tectonic evolution in the Su-Lu ultrahigh-pressure metamorphic belt.
基金supported by the Fundamental Research Funds for the Central Universities(No.2019B00414)Open Fund of the Key Laboratory of Marine Geology and Environment Chinese Academy of Sciences(No.MGE2020KG03)the PHD early development program of East China University of Technology(No.DHBK2018035)。
文摘Lithosphere extension and upwelling of asthenosphere at post-collisional stage of an orogenic cycle generally induce diverse magmatism and/or associated high-temperature metamorphism. Nevertheless, the intimate coexistence of post-collisional magmatic activity and high-temperature metamorphism is rare.In this contribution, a lithological assemblage composing of diverse magmatic rocks deriving from distinct magma sources and coeval high-temperature metamorphism was identified in eastern Kunlun.Petrography, ages, mineral chemistry and whole-rock geochemistry demonstrated that those intimately coexistent diverse rocks were genetically related to post-collisional extension. The garnet-bearing mafic granulites in Jinshuikou area interior of the East Kunlun Orogenic Belt are mainly composed of garnet,orthopyroxene, and plagioclase, with peak metamorphic P–T conditions of ~ 701–756 ℃and 5.6–7.0 kbar,representing a granulite-facies metamorphism at 409.7 ± 1.7 Ma. The diverse contemporaneous magmatic rocks including hornblendites, gabbros and granites yield zircon U–Pb ages of 408.6 ± 2.5 Ma,413.4 ± 4.6 Ma, and 387–407 Ma, respectively. The hornblendites show N-MORB-like REE patterns with(La/Sm)Nvalues of 0.85–0.94. They have positive zircon εHf(t) values of 0.1–4.9 and whole-rock εNd(t) values of 3.9–4.7 but relatively high(^(87)Sr/^(86)Sr)_(i)values of 0.7081 to 0.7088. These features demonstrate that the hornblendites derived from a depleted asthenospheric mantle source with minor continental crustal materials in source. As for the gabbros, they exhibit arc-like elemental signatures, low zircon εHf(t) values(-4.3 to 2.5) and variable whole-rock εNd(t) values(-4.9 to 1.2) as well as high(^(87)Sr/86 Sr)ivalues(0.7068 to 0.7126), arguing for that they were originated from partial melting of heterogeneous lithospheric mantle anteriorly metasomatized by subducted-sediment released melts. Geochemistry of the granites defines their strongly peraluminous S-type signatures. Zircons from the granites yield a large range of εHf(t) values ranging from -30.8 to -5.1, while the whole-rock samples yield consistent(^(87)Sr/86 Sr)ivalues(0.7301 to 0.7342) and negative εNd(t) values(-10.1 to -12.4). These features indicate that the S-type granites could be generated by reworking of an ancient crust. Taken together, the penecontemporaneous magmatism and metamorphic event, demonstrated the early-middle Devonian transition from crustal thickening to extensional collapse. The post-collisional mantle-derived magmas serve as an essential driving force for the high-temperature granulite-facies metamorphism and anataxis of the crust associated with formation of S-type granite. This study not only constructs a more detail Proto-Tethys evolution process of the eastern Kunlun, but also sheds new light on better understanding the intimate relationship between magmatism and metamorphism during post-collisional extensional collapse.
基金co-supported by the National Key Research and Development Project of China (No. 2016YFC0600310)the National Natural Science Foundation of China (Nos. 41230205 and 41602062)the China Geological Survey (No. DD20160122)
文摘The Himalayan Orogen, resulting from the Tertiary collision of Indian and Asian continents, is a natural laboratory for studying metamorphism, partial melting and granite formation of collisional orogens. However, metamorphic and anatectic conditions and timescales of meta-mafic rocks in the Greater Himalayan Sequences （GHS） in the east-central Himalaya remain controversial, in this paper, we conduct a study of petrology and geochronology of mafic granulite from the Eastern Himalayan Syntaxis （EHS）. The mafic granulite with abundant leucosome bands occurs as layers within felsic granulites and is well deformed. The granulite consists of garnet, plagioclase, amphibole and quartz with minor clinopyroxene, orthopyroxene, biotite, rutile, titanite and ilmenite. The garnet has growth compositional zoning and contains abundant mineral inclusions in its core. Peak metamorphic mineral assemblage of the granulite is garnet, amphibole, plagioclase, quartz, clinopyroxene and futile, recording a high-pressure （HP） and high-temperature （HT） peak-metamorphism under conditions of 14-15.5 kbar and 780-790 ℃ in the presence of melt. The reconstructed clockwise P-T path is characterized by an early heating and burial prograde metamorphism, and late isothermal and cooling decompression retrogression. The granulite witnessed a long lasting HT metamorphism, partial melting and melt crystallization process which began at ca. 39 Ma and lasted to ca. 11 Ma. The present study shows that various high-grade rocks of the GHS in the EHS core experienced similar metamorphic conditions and P-T-t paths, indicating that they occurred as a coherent slab during the subduction and exhumation of Indian lithosphere. The significant melts generated during the prograde metamorphism of the GHS rocks not only contributed to the formation of the Himalayan leucogranite, but also resulted in the rheological weakening and ductile flow of the thickened lower crust of the Himalayan Orogen.
基金This study was supported by the National Natural Science Foundation of China （Grant No. 40572032）；the open fund of the central laboratory of Peking University （No. 14 and 15）.
文摘We used illite and chlorite crystaHinities, index minerals, mineral assemblages, polytype and domain size of white mica, electron microprobe analysis （EMPA）, b0 geobarometer and chlorite geothermometer to quantify the diagenetic and metamorphic overprint on the Triassic flysch formations in the Songpan-Garze orogen along profile Zoige-Lushan, northwest Sichuan. Two anchizones, two epizones, one diagenetic zone and a transition belt in-between them are defined on the basis of the obtained data. lllite crystallinity correlates strongly with the best mean domain size of mica and moderately with chlorite crystallinity. 2M1 white mica polytype are observed within the epizone whilst 2M1 and 1M polytypes occur in the anchizone and diagenetic zone. Epizonal metamorphism reached maximum temperatures of 370℃±21℃ at low-to intermediate pressure conditions. Clay minerals underwent Ostwald ripening during metamorphism. Rocks from both sides of the Longmenshan fault reveal contrasting degrees of metamorphic overprint： on the northwest side of the Longmenshan fault, epimetamorphic conditions contrast with diagenetic rocks on the southeast side.
文摘The east sector of the southern Qinling belt is, lithologically, composed mainly of metapelites, ***qüartzites, marbles and small amount of metabasites and gneisses, whose protoliths are the Silurian, Devonian and less commonly the Sinian and Upper Palaeozoic. They have been subjected at least to two epochs of metamorphism. The early epoch belongs to progressive metamorphism which is centered on high amphibolite-granulite fades in the Fuping area and changed outwards into low amphibolite facies (staurolite-kyanite zone), epidote amphibolite facies (garnet zone) and greenschist facies (chlorite and biotite zones), the metamorphic age of which is about 220–260 Ma. This early-epoch metamorphism belongs to different pressure types: the rocks from greenschist to low amphibolite facies belong to the typical medium-pressure type which shows geothermal gradients of about 17–20 ***C/km and was probably produced by a crustal thickening process related to continental collision, and the high amphibolite-granulite facies belongs to the low-pressure type which shows geothermal gradients of about 25–38 ***C/km and was probably affected by some magmatic heats. Based on the basic characteristics of the P-T paths of the different facies calculated from the garnet zonations, it can be deduced that the metamorphism of medium-pressure facies series took place during an imbricated thickening process, rather than during the uplifting process after thickening. The late-epoch metamorphism belongs to dynamic metamorphism of greenschist facies which is overprinted on the early-epoch metamorphic rocks and is Yanshanian or Himalayan in age, probably related to intracontinental orogeny.
基金supported by the National Natural Science Foundation of China(Nos.41072044,41130315 and 41530319)
文摘The nature and evolution of the Proto-Tethys Ocean originated from the breakup of the supercontinent Rodinia remain controversial. Early Paleozoic magmatism and metamorphism can pro- vide important constraints on the closure of the Proto-Tethys Ocean. This paper reports on a set of geological, petrographical, geochronological, mineralogical and geochemical data for Early Paleozoic granite, gabbro, granulite and granitic leucosome in the northern Wulan terrane of the Quanji Massif. Zircon LA-ICP-MS U-Pb dating reveals two episodes of magmatism, with the emplacement of a gran- itic pluton at 476.7±2.8 Ma and a gabbroic dike at 423±2 Ma. Whole-rock geochemistry suggests an arc affinity for the magma of the granitic pluton but a post-collisional extension setting for the gabbroic dike. Zircon LA-ICP-MS U-Pb dating also shows that the peak granulite-facies metamorphism and anatexis occurred at --475 Ma, coeval with the formation of the granitic pluton in the Quanji Massif as well as the early lawsonite-bearing eclogites in the North Qaidam high-pressure and ultrahigh-pressure (HP-UHP) metamorphic belt to the south. The granulite-facies metamorphism with peak P-T condi- tions at 718-729 ℃ and 0.46-0.53 GPa is characterized by an anticlockwise P-T path. Our data provide compelling evidence for Early Paleozoic paired metamorphic belts with HP-UHP metamorphism in the North Qaidam to the south and low PIT metamorphism in the Quanji Massif as a continental arc to the north, hence suggesting a northward subduction polarity for the Proto-Tethys oceanic plate. The intrusion of the post-collisional gabbroic dike supports for the closure of the Proto-Tethys Ocean in north- western China before 423 Ma.
基金supported by the National Key Basic Research Program of China (No.2009CB825001)the National Natural Science Foundation of China (Nos.40603002,41072046,and 41090371)the Fundamental Research Funds for the Central Universities,China University of Geosciences,Wuhan (No.CUG120121)
文摘In order to constrain temperature during subduction and subsequent exhumation of fel- sic continental crust, we carried out a Ti-in-zircon thermometer coupled with zircon internal structure and U-Pb age on migmatitic gneisses from the Weihai region in the Sulu ultra-high pres- sure （UHP） metamorphic terrane, eastern China. The Weihai migmatitic gneisses are composed of in- tercalated compositional layers of melanosome and plagioclase （Pl）-rich lencosome and K-feldspar （Kfs）-rich pegmatite veins. Four stages of zircon growth were recognized in the Weihai migmatitic gneisses. They successively recorded informations of protolith, prograde metamorphism, decompres- sional partial melting during early stage exhumation and subsequent fractional crystallization of pri- mary melt during later stage cooling exhumation. The inherited cores in zircon from the melanosome and the Pl-rich leucosome suggest that the pro- tolith of the migmatitic gneiss is Mid- Neoproterozoic （-780 Ma） magmatic rock. Metamorphic zircons with concordant ages ranging from 243 to 256 Ma occur as over- growth mantles on the protolith magmatic zir- con cores. The estimated growth temperatures （625-717 ＂C） of the metamorphic zircons have a negative correlation with their ages, indicating a progressive metamorphism in HP eciogite-facies condition during subduction. Zircon recrystal- lized rims （228-2 Ma） in the PI-rich ieucosome layers provide the lower limit of the decompress-sional partial melting time during exhumation. The ages from 228^-2 to 219~2 Ma recorded in the Pl-rich leucosome and the Kfs-rich pegmatite vein, respectively, suggest the duration of the fractional crystallization of primary melt during exhumation. The calculated growth temperatures of the zircon rims from the Pl-rich leucosome range from 858 to 739 , and the temperatures of new growth zircon grains （219±2 Ma） in Kfs-rich vein are between 769 and 529 . The estimated temperatures have a positive correlation with ages from the Pl-rich leucosome to the Kfs-rich pegmatite vein, strongly indi- cating that a process of fractional crystallization of the partial melt during exhumation.
基金financially supported by the National Natural Science Foundation of China (Nos. 41802070,41572051)the China Postdoctoral Science Foundation (No. 2018M631319)the Fund from the Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources
文摘Yushugou granulite-peridotite complex,located at the east part of the northern margin of South Tianshan,may represent an ophiolitic slice subducted to 40–50 km depth with high-pressure granulite facies metamorphism.Although a lot of studies have been conducted on rocks in this belt,the rock association and tectonic background of the ophiolitic slice are still in dispute.A detailed study on petrology,phase equilibrium modeling and U-Pb zircon ages have been performed on the metagabbro vein in peridotite unit to constrain the tectonic evolution of the Yushugou granulite-peridotite complex.Three stages of mineral assemblage in the metagabbro were defined as stage I:Cpx^A+Opx^A+Pl^A,which represents the original minerals of the metagabbro vein;stage II:Cpx^B+Opx^B+Pl^B+Spl,which represents the mineral assemblage of granulite facies metamorphism with peak P-T conditions of 4.2–6.9 kbar and 940–1070℃;stage III is characterized by the existence of prehnite,thomsonite and amphibole in the matrix,indicating that the metagabbro vein may be influenced by fluids during retrograde metamorphism.Combined with the crosscut relationship,it can be deduced that the metagabbro vein,together with the peridotite in Yushugou granulite-peridotite complex has experienced similar high-temperature granulite facies metamorphism.The zircon chronological data shows that the protolith age of the metagabbro vein is 400.5±6.2 Ma,reflecting Devonian magmatism event and the granulite facies metamorphism occurred at^270 Ma which may be related to the post-collisional magmatism.
基金financially supported by the National Natural Science Foundation of China(Grant No.41602069 and 41572185)the Fundamental Science on Radioactive Geology and Exploration Technology Laboratory(Grant No.RGET1402)+1 种基金the Natural Science Foundation of Jiangxi Province(Grant No.20171BAB213026)Science and technology research projectfrom the Education Department of Jiangxi Province(Grant No.GJJ150554)
文摘The origin, age and evolution of the Precambrian metamorphic basement of southern China provide useful insights into early crustal development. Here, we present new laser ablation-inductively coupled plasma-mass spectrometry （LA-ICP-MS） U-Pb age data for detrital zircons from five samples of the Precambrian metamorphic basement of the Xiangshan uranium orefield. Two of these samples, from the northern Xiangshan volcanic basin, yielded a total of 140 U-Pb ages that cluster within the Neoproterozoic （773-963 Ma; 79.3% of data points）, with the rest being scattered through the Paleoproterozoic and Mesoproterozoic, along with a single Archean age. These ages indicate that this basement material is associated with the Cathaysia Block. In comparison, the 172 concordant ages from the other three samples from the southern part of the Xiangshan volcanic basin cluster within the Neoproterozoic （767-944 Ma; 59.8%） as well as the Proterozoic （37.8%） and the Archean （2502-2712 Ma; 14.5%）. These samples are also free of zircons with Grenvillian ages, indicating that these units are associated with the southeastern Yangtze Block. Combining these data with the geochemistry of these units, which suggests that the metamorphosed sedimentary rocks within the northern and southern parts of the Xiangshan basin have a common component from a magmatic island arc that formed during the early Neoproterozoic, we infer that the basin was located along the boundary between the Cathaysian and Yangtze blocks. In addition, the zircons within the samples from the southern and northern parts of the Xiangshan basin show different pre-Neoproterozoic （963 Ma） age populations but similar post- Neoproterozoic zircon populations, indicating that the amalgamation of the Cathaysian and Yangtze blocks occurred after the Neoproterozoic （960 Ma）, with magmatism peaking at 830 Ma and rifting starting at -770 Ma, leading to the subsequent deposition （from bottom to top） of the Shenshan, Kuli, and Shangshi formations.
基金financially supported by the National Key Basic Research Program of China (No. 2006CB403506)the National Natural Science Foundation of China (No. 41203011)the Fundamental Research Funds for the Central Universities (No. 2013B03014)
文摘In this study, we carried out petrography, zircon U-Pb geochronology and Hf isotopic analyses on a granitic pegmatite dyke in the Xiaoqinling area in southern margin of the North China Craton（NCC）. Our study suggests that the pegmatite dyke likely crystallized from a volatile-rich pegmatitic magma. Different from most other pegmatite elsewhere, zircon from this pegmatite dyke does not contain unusually high U and Th concentrations and suffered no evident radioactive damage, therefore we successfully obtained a zircon U-Pb dating using laser ablation-inductively coupled plasma-mass spectrometry（LA-ICP-MS）, which yields an average 207Pb/206 Pb age of 1 814±6 Ma, representing the intrusive age of the granitic pegmatite dyke. Zircon εHf（t） values are between-8.3 and-3.0, corresponding to Hf depleted mantle model ages from 2 649 to 2 991 Ma with an average of 2 881 Ma. These data indicate that this granitic pegmatite dyke may have been derived from partial melting of Meso-Neoarchean metamorphic rocks from the Xiaoqinling basement. Granitic pegmatite magma may have emplaced within the Taihua Group wall rocks during the last stage of the middle to high grade metamorphism. Furthermore, according to the petrographic observation, the 1.81 Ga pegmatite dyke and the 1 800–1 750 Ma Xiong’er Group rocks were not undergone middle to high grade metamorphism, indicating 1.81 Ga as the termination of the latest regional metamorphism in the southern margin of the NCC.
文摘Based upon fluid effects, retrograde metamorphism of eclogites in the Dabieregion can be divided into the fluid-poor, fluid-bearing and fluid-rich stages. The fluid-poor stageis marked by polymorphic inversion, recrystallization and exsolution of solid solutions, and isthought to represent eclogite-facies retrograde environments. The fluid-bearing stage is likely tohave occurred at the late stage of ecologite-facies diaphthorosis and is represented by kyaniteporphyroblasts, rutile, and sodic pyroxene in association with high-pressure hydrous minerals suchas phengite and zoisite (clinozoisite) without significant amount of hydrous minerals such asamphibole, epidote and biotite. The fluid-rich stage might have commenced concomitantly with loweramphibolite-facies diaphthoresis and persisted all the way towards the near-surface environment. Theproduct of this stage is characterized by plentiful hydrous and volatile-bearing phases.The dissemination-type rutile mineralizations in eclogites might have formed by preferentialshearing-induced pressure solution of gangue minerals at the fluid-bearing stage. The accompanyingvein rutile was precipitated from fluids of this stage after local transport and concentration, andmay hence represent proximal mobilization of titanium from the eclogite. Therefore, rutile veins canbe used as an exploration indicator for dissemination-type rutile deposits.
基金supported by the National Natural Science Foundation of China (Nos. 41772054, 41572039 and 41372076)the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (No. CUGQYZX1704)
文摘Ultrahigh-temperature （UHT） metamorphism represents extreme crustal metamorphism with peak metamorphic temperatures exceeding 900 ℃ and pressures ranging from 7 to 13 kbar with or without partial melting of crusts, which is usually identified in the granulite-facies rocks. UHT rocks are recognized in all major continents related to both extensional and compressive tectonic environments. UHT metamorphism spans different geological ages from Archean to Phanerozoic, providing information of the nature, petrofabric and thermal evolution of crusts. UHT metamorphism is traditionally identified by the presence of a diagnostic mineral assemblage with an appropriate bulk composition and oxidation state in Mg-Al-rich metapelite rocks. Unconventional geothermobarometers including Ti-in-zircon （TIZ） and Zr-in-rutile （ZIR） thermometers and phase equilibria modeling are increasingly being used to estimate UHT metamorphism. Concentrated on the issues about UHT metamorphism, this review presents the research history about UHT metamorphism, the global distribution of UHT rocks, the current methods for constraints on the UHT metamorphism, and the heat sources and tectonic settings of UHT meta- morphism. Some key issues and prospects about the study of UHT metamorphism are discussed, e.g., identification of UHT metamorphism for non-supracrustal rocks, robustness of the unconventional geothermometers, tectonic affinity of UHT metamorphic rocks, and methods for the constraints of age and duration of UHT metamorphism. It is concluded that UHT metamorphism is of great importance to the understanding of thermal evolution of the lithosphere.
基金partly supported by the Russian Scientific Foundation(Grant 14-17-00693)
文摘The Chertovo Koryto gold deposit（80 t Au at 1.84 g/t） in the Lena world-class province,Siberia,is hosted in a metamorphosed sequence of the Paleoproterozoic Mikhailovsk Formation that comprises the oldest black shale strata of the Baikal-Patom region.The mineralisation is confined to the thrust zone complicated with a conjugate anticline fold,zones of shearing and dislocation.The struaural position of the mineralisation is similar to that at the giant Sukhoi Log deposit in the neighbouring Mama-Bodaibo zone.In the latter,the isotope age data suggest that Khomolkho black shales,hosts to Sukhoi Log mineralisation,are of Ediacaran age and underwent prograde metamorphism during early Paleozoic.The geochemical composition of the terrigenous rocks that host Sukhoi Log,Chertovo Koryto,and a number of other deposits at the various stratigraphic levels throughout the Proterozoic sequence have much in common.They do not show elevated metal contents above the common black shale abundances,except for Au and As,which is at variance with the accepted view on diagenetic enrichment of black shales in the Lena province.The occurrence of sagenitic rutile in quartz and chlorite pseudomorphs after biotite and other petrographic observations provide evidence on a retrograde nature of the metamorphic mineral assemblages in the Mikhailovsk rocks.The sulphides are pyrrhotite and arsenopyrite with very minor pyrite at Chertovo Koryto,whereas pyrite is the predominant sulphide in the Sukhoi Log ore.Fluid inclusion data on both deposits emphasise a high-temperature nature of the mineralisation albeit revealing great contrast in the fluid composition.Sukhoi Log mineralisation was formed at mixing between low-salinity aqueous solutions and dense gaseous carbonic fluids,which facilitated effective gold scavenging and precipitation,as demonstrated by thermodynamic simulation.The precursory devolatilisation of the Mikhailovsk sediments at the prograde stage results in the paucity of gaseous carbonic fluid during retrograde metamorphism and mineralisation.The similarity in the styles and chemical parameters of mineralisation,and the predominant structural control of ore localisation within the same Precambrian regional tectonic unit support an idea that orogenic gold mineralisation in the Lena province was produced during a single early Paleozoic event.
