: Using the single—zircon evaporation technique and U—Pb method, the authors have conducted an isotope geochonological study of the Huilanshan granulite and Shima garnet-bearing plagioclase gneiss (“country rocks”...: Using the single—zircon evaporation technique and U—Pb method, the authors have conducted an isotope geochonological study of the Huilanshan granulite and Shima garnet-bearing plagioclase gneiss (“country rocks” of the Shima eclogite) in the Dabie Mountains. The study shows that these rocks have peak metamorphic ages of 443–455 Ma, which are essentially consistent with that of the Caledonian high—ultrahigh pressure eclogites. This indicates the existence of the Caledonian collisional orogeny in the Dabie Mountains.展开更多
A high pressure basic granulite ultramafics belt is found in the late Archaean gneisses of Laixi Laiyang Qixia district, east Shandong. This belt has previously been considered as another eclogite belt in Sulu ultra h...A high pressure basic granulite ultramafics belt is found in the late Archaean gneisses of Laixi Laiyang Qixia district, east Shandong. This belt has previously been considered as another eclogite belt in Sulu ultra high pressure(UHP) terrain. The typical high P granulite is characterized by mineral assemblages of three generations formed in different metamorphic episode respectively. The mineral assemblage of first episode is Grt(core)+Cpx+Pl, that of the second episode is Grt(rim)+Cpx+Opx+Pl+Amp+Q+Mt and that of the third episode is Cpx+Pl+Amp+Q+Mt. In first assemblage, the garnet porphyroblast is rich in grossular and pyrope component, and the coexisting Cpx is Al rich. Using mineral thermobarometer and Berman’s (1991) TWQ program, the P T conditions of three episodes are established, i.e. T=840℃～860℃, P>1.4GPa for first episode; T=720℃～780℃,P=0.8～1.2GPa for second episode and T=600℃～800℃,P=0.5～0.7GPa for the third episode.Considering the reaction texture, mineral Chemistry and PT estmations, a clockwise PTt path can be constructed, which shows post peak isothermal decompression at first and followed by a process of pressure and temperature decreasing. The mineral wholerock Sm Nd isochron age of the granulite is 1752Ma, which indicates its last thermal event during early middle Proterozoic stage. Therefore, it is concluded that the high pressure granulite and ultramafics of this belt represents the lower continental curst of the North China Craton during early Precambrian without any relationship to tectonic process of the Sulu UHP terrain.展开更多
Mafic granulites have been found as structural lenses within the huge thrust system outcropping about 10 km west of Nam Co of the northern Lhasa Terrane, Tibetan Plateau. Petrological evidence from these rocks indicat...Mafic granulites have been found as structural lenses within the huge thrust system outcropping about 10 km west of Nam Co of the northern Lhasa Terrane, Tibetan Plateau. Petrological evidence from these rocks indicates four distinct metamorphic assemblages. The early metamorphic assemblage (M1) is preserved only in the granulites and represented by plagioclase+hornblende inclusions within the cores of garnet porphyroblasts. The peak assemblage (M2) consists of garnet+clinopyroxene+hornblende+plagioclase in the mafic granulites. The peak metamorphism was followed by near-isothermal decompression (M3), which resulted in the development of hornblende+plagioclase symplectites surrounding embayed garnet porphyroblasts, and decompression-cooling (M4) is represented by minerals of hornblende+plagioclase recrystallized during mylonization. The peak (M2) P-T conditions of garnet+ clinopyroxene+plagioclase+hornblende were estimated at 769-905℃ and 0.86-1.02 GPa based on the geothermometers and geobarometers. The P-T conditions of plagioclase+hornblende symplectites (M3) were estimated at 720-800℃ and 0.55-0.68 GPa, and recrystallized hornblende+plagioclase (M4) at 594-708℃ and 0.26-0.47 GPa. It is impossible to estimate the P-T conditions of the early metamorphic assemblage (M1) because of the absence of modal minerals. The combination of petrographic textures, metamorphic reaction history, thermobarometric data and corresponding isotopic ages defines a clockwise near-isothermal decompression metamorphic path, suggesting that the mafic granulites had undergone initial crustal thickening, subsequent exhumation, and cooling and retrogression. This tectonothermal path is considered to record two major phases of collision which resulted in both the assemblage of Gondwanaland during the Pan-African orogeny at 531 Ma and the collision of the Qiangtang and Lhasa Terranes at 174 Ma, respectively.展开更多
The Yushugou HP granulite-peridotite complex is located at east of northern margin of southern Tianshan mountains,China,which consists of granulite unit and peridotite unit mainly.Because of the rare association of
This paper presents the primary results of petrologic, mineralogical and petrochemical studies of garnet-bearing granulite facies rock xenoliths from Xinyang, Henan Province. These xenoliths, which are found in a pipe...This paper presents the primary results of petrologic, mineralogical and petrochemical studies of garnet-bearing granulite facies rock xenoliths from Xinyang, Henan Province. These xenoliths, which are found in a pipe of late Mesozoic volcaniclastic breccia, are of high density (3.13–3.30 g/cm3) and high seismic velocity (Vp = 7.04–7.31 km/s), being products of underplating of basaltic magmas and had experienced granulite facies metamorphism. The underplating and metamorphism took place before the eruption of the host rock. Petrographical studies and equilibrium T-P calculations show that these xenoliths were captured at a 49 km depth and experienced at least a 16 km uplift before they were captured. The dynamics of the uplift could be related to the continent-continent collision between the North China plate and the Yangtze plate during the Triassic.展开更多
High-pressure basic granulite terrain of 2.65 Ga from Jiouhuai’an in the junction of the Hebei and Shanxi provinces was discovered and reported recently. The three metamorphic mineral assemblages and their mineral re...High-pressure basic granulite terrain of 2.65 Ga from Jiouhuai’an in the junction of the Hebei and Shanxi provinces was discovered and reported recently. The three metamorphic mineral assemblages and their mineral reaction texture of the basic granulites have been identified, which represent three main metamorphic episodes of 1.4—1.5 Gpa, 800℃; 0.7—0.9 Gpa, 820℃ and 0.5—0.6 Gpa, 700℃. Their steep decompressional clockwise P-T path implies that a late Archaean continental collision and sole thrusting event perhaps occurred in North China Craton. This is important to study petrogenesis of high-pressure granulites, composition and texture of deep crust in North China Craton, and early Precambrian collision tectonism.展开更多
There is a typical assemblage of garnet + kyanite + microperthite + quartz + rutile in high-pressure (HP) felsic granulite of Qinling complex in Songshugou area. East Qinling. The HP granulite was formed at 800 -900℃...There is a typical assemblage of garnet + kyanite + microperthite + quartz + rutile in high-pressure (HP) felsic granulite of Qinling complex in Songshugou area. East Qinling. The HP granulite was formed at 800 -900℃ and 1.3 -1.6GPa and has experienced two stages of retrograde metamorphism at 600- 650 ℃, 0.8-1.0GPa and 500-600℃, 0.3-0.6GPa, forming two retrograde metamorphic assemblages of margarite + plagiodase (PlI)+quartz and sillimanite + biotite + plagioclase(PlII) + microdine+quartz, respectively. They construct a two-stage clockwise P-T path which shows down-pressure cooling in both early and late stage.展开更多
1 Geological occurrence The ultramafic rocks in the Songshugou area of the North Qinling are structurally emplaced in middle-late Proterozoic amphibolites (fig. 1) which are regarded as an external rootless ophiolite ...1 Geological occurrence The ultramafic rocks in the Songshugou area of the North Qinling are structurally emplaced in middle-late Proterozoic amphibolites (fig. 1) which are regarded as an external rootless ophiolite sheet with emplacement age of (983±140) Ma. The lenticular diopsidegarnet-amphibolites, named garnet-amphibolte by others, are exposed in the amphibolits. The high-pressure basic granulites discussed in this note were found in the lenticular garnet-展开更多
High-pressure mafic granulites occurring as lenticular bodies within garnet-amphibolites in Kangxiwar Fault have been first reported in this paper. The P-T conditions of two metamorphic stages were obtained using cali...High-pressure mafic granulites occurring as lenticular bodies within garnet-amphibolites in Kangxiwar Fault have been first reported in this paper. The P-T conditions of two metamorphic stages were obtained using calibrated geothermal barometers and ThermoCalc Program. The peak metamorphic condition of these high-pressure granulites is about 760–820°C, 1.0–1.2 GPa and the retrograde metamorphic condition is about 620–720°C, 0.7–0.8 GPa. The petrological studies show that they have a near-isobaric cooling P-T path which suggests that the Western Kunlun underwent initial crustal thickening, subsequent exhumation and cooling. The SHRIMP zircon U-Pb dating gives two groups of ages for high-pressure granulites. One is 177±6 Ma which is obtained from the rim of the zircon. We consider this age should be the metamorphic age. And the other is 456±30 Ma which is obtained from the core of the zircon and should be the protolith age. The formation of these high-pressure granulites in western Kunlun is closely correlated with the evolution of the Paleo-Tethys and has important implications for the research on Tethys and Paleo-Asian tectonic zone.展开更多
Recently, a series of basic granulite enclosures are found in the granulite gneisses along the right side of the Yarlung Zangbo River, lying west of the Namjagbarwa Mountain. Es-pecially, some high-pressure granulite ...Recently, a series of basic granulite enclosures are found in the granulite gneisses along the right side of the Yarlung Zangbo River, lying west of the Namjagbarwa Mountain. Es-pecially, some high-pressure granulite enclosures have been discovered in eastern gully of the Zhibei village. To the northwest of the high-pressure granulite belt there occur Yarlung Zangbo ophiolite zone. Southeastward the granulites change into amphibolite and green-schist facies rocks, which constitute a complete lower crust section.展开更多
Hyalophane-rich pegmatites are identified from the Manjinggou high-pressure granulite terrain in the Central Zone of North China Craton. Based on field investigation, mineral assemblage and mineral geochemistry, two t...Hyalophane-rich pegmatites are identified from the Manjinggou high-pressure granulite terrain in the Central Zone of North China Craton. Based on field investigation, mineral assemblage and mineral geochemistry, two types of pegmatites can be defined, i.e., hyalophane pegmatite and hyalophane-rich pegmatite. The hyalophane pegmatite is composed of pure hyalophane with 18.7 mol%-19.4 mol% celsian, whereas the hyalophane-rich pegmatite consists of clinopyroxene + titanite + epidote + hyalophane with 11.9 mol%-12.5 mol% celsian. Hyalophane-rich pegmatite has typical magmatic zircons with oscillatory zoning and high Th/U ratios, implying that this type of pegmatite crystallized from special melt similar to magma. SIMS (Cameca 1280) zircon U-Pb dating shows that the crystallization age of the hyalophane-rich pegmatite is 1812±5 Ma, younger than the regional metamorphic age (peak of ca. 1.85 Ga). Zircon δ18O (8.0 ‰-9.3 ‰) and ?Hf (-7.0 to-2.7) values measured by SIMS suggest that the high-pressure granulite terrain was the source of these veins. Therefore, the hyalophane-rich pegmatite veins were likely to be generated by melting of the high-pressure granulite terrain during post collisional uplift. A quick tectonic uplifting process with a velocity of 0.4 to 0.6 mm/a has been estimated for the high-pressure granulite terrane from the Central Zone of North China Craton.展开更多
Petrological analysis and LA-ICP-MS zircon U-Pb dating were conducted on high- pressure marie granulites, which occured as xenolith within TTG gneisses, from the Nanshankou Village of the Jiaobei terrane, Shandong Pen...Petrological analysis and LA-ICP-MS zircon U-Pb dating were conducted on high- pressure marie granulites, which occured as xenolith within TTG gneisses, from the Nanshankou Village of the Jiaobei terrane, Shandong Peninsula in the north-eastern part of the North China Craton （NCC）. The mafic HP grannlite is composed of garnet, clinopyroxene, orthopyroxene, amphibole and symplectitic clinopyroxene, orthopyroxene, plagioclase, ilmente and magnetite which were formed after the decomposition of porphyroblastic garnet and clinopyroxene. Four stages of metamorphic mineral assemblages for the mafic HP granulites were constrained by detail petrological and mineralogical in- vestigations. The early prograde assemblage is represented by the mineral inclusions within garnet and clinopyroxene porphyroblasts （Opx1＋Pl1＋Qtz1）, recording the metamorphic conditions at -754-757 ℃, 0.63-0.71 GPa; peak metamorphic conditions were determined at -874-891 ℃, 1.32-1.35 GPa with the mineral assemblage of Grt2＋Cpx2＋Amp2＋Pl2＋Qtz2. Retrograde minerals derived from symplectitic assemblage Opx3＋Cpx3＋Amp3＋Pl3＋Qtz3＋Ilm3±Mag3 were formed at 693-796℃, 0.60-0.84 GPa. A final greensehist to sub-greenschist facies event was recorded by the exsolution of actinolite and albite within a retrograded clinopyroxene, as well as the occurrence of prehnite, chlorite and calcite minerals. Accordingly, a clockwise P-T path was concluded on the basis of the different stages of mineral asseblage. Cathodoluminescence imaging, trace element and U-Pb dating of zircons from the mafic HP granulites recorded similar charactistics for three episodes of Paleo-Meso Proterozoic metamorphic events. These are the metamorphic events preserved in mafic and pelitic granulites in the Jiao-Liao-Ji belt （JLJB） with 207 pb/206pb ages of 2.0-1.9 Ga for peak metamorphism and of 1.86-1.84 Ga for decomposing process, followed by a retrograde amphibolite facies metamorphic event related to the post-orogenic extension at the age of 1.76-1.74 Ga, resulting the exhumation of the granulite to the upper crust level.展开更多
The mafic granulites in Dinggye,as various scale lense-shaped enclaves within the high Himalayan crystalline rock series,occur along mylonitic foliations at the junction between the Southern Tibetan Detachment System(...The mafic granulites in Dinggye,as various scale lense-shaped enclaves within the high Himalayan crystalline rock series,occur along mylonitic foliations at the junction between the Southern Tibetan Detachment System(STDS)and the Xainza-Dinggye normal fault system.The main lithological assemblage comprises garnet plagioclase pyroxenite,garnet two-pyroxene granulite,pyroxene garnet amphibolite and so on.The detailed petrological analyses show that these mafic granulites underwent at least four-stage metamorphic evolution.The first metamor-phic stage,the garnet+clinopyroxene+quart mineral assemblage(M1)was probably formed un-der eclogite facies,the second stage,the plagioclase+clinopyroxene symplectite mineral as-semblage(M2)was produced under high-pressure granulite facies by the early decompressive breakdown of M1 mineral assemblage,the third stage,the plagioclase+clinopyroxene+hypersthene symplectite mineral assemblage(M3)was formed at granulite facies by the late period decompressive breakdown of M1 and M2 mineral assemblages and the final stage,pla-gioclase+hornblende mineral assemblage(M4)was formed by hydrolysis of earlier mineral as-semblages during late uplifting.The detailed mineral composition analyses suggest that garnets and clinopyroxenes within M1 and M2 mineral assemblages display similar compositions to the equivalents in the B and C types of eclogites,whereas the M3 clinopyroxenes are akin to these of the same kind of minerals in the granulite.These mineral chemistry features and P-T estimates calculated by mineral thermometers and barometers indicate that the early stage relic porphyro-blasts(M1)could be formed at the eclogite facies,the early decompressive breakdown(M2)occurred at the high-pressures granulite facies of 1.35―1.48 GPa and 625―675℃,the M3 mineral assemblage recorded the granulite facies of 0.7―0.95 GPa and 775―900℃and M4 plagioglase+hornblende retrograde mineral assemblage was produced under the amphibolite facies metamorphism with pressure of 0.4 to 0.75 GPa and temperature at between 660 and 700℃.These construct P-T paths from crustal subduction overthickening to tectonic uplift tectono-thermal evolution.The mineral chemical characteristics and P-T condition at every metamorphic stage of these granulites indicate that these rocks experienced the eclogite facies metamorphism during the early stage.Subsequently,these mafic granulites underwent the three-stage exhuma-tion of the eclogite facies tectonic uplift,isostatic uplift related to the transformation from ec-logite/high-pressure granulite to granulite facies and extensional uplift.展开更多
The studied mafic granulites are located at Xiwangshan,Xuanhua region in the north of the Trans-North China Orogen(TNCO),occurring as lens within tonalite-trondhjemite-granodiorite(TTG)gneisses in the eastern part of ...The studied mafic granulites are located at Xiwangshan,Xuanhua region in the north of the Trans-North China Orogen(TNCO),occurring as lens within tonalite-trondhjemite-granodiorite(TTG)gneisses in the eastern part of the Xiwangshan area.The rocks contain the representative granulite-facies minerals such as garnet,clinopyroxene,orthopyroxene,plagioclase,amphibolite,rutile and quartz,and also well-developed melt pseudomorph and antiperthite.Although the prograde metamorphic stage(M1)cannot be retrieved due to rare preservation of pre-peak-stage mineral associations,three distinct mineral assemblages that formed in different metamorphic stages can be identified,based on petrography and mineralogy characteristics.The peak stage(M2)is characterized by Grt2+Cpx2+Amp2+Pl2+Rt+melt pseudomorphs,and a post-peak decompression stage(M3)contains a mineral assemblage of Grt3+Opx3+Cpx3+Amp3+Pl3,while a later-retrogression stage(M4)is featured by coronas of Amp4+Pl4 surrounding garnet.By calculating metamorphic P-T conditions using THERMOCALC,stage M2 was constrained to be 13.2–14.8 kbar and 1050–1080℃,and M3 recorded P-T conditions of 5.7–7.3 kbar and 825–875℃,while M4 yielded P of^5 kbar and T of^660℃,consistent with amphibolite facies metamorphism.Taking into account of all these petrological data,we propose that the mafic granulite experienced a high-pressure(HP)and ultra-high temperature(UHT)granulite-facies metamorphism during the peak metamorphism,which was accompanied with a clockwise P-T path.U-Pb dating of metamorphic zircons in the granulites yields two groups of ages at 1853±14 and 1744±44 Ma,respectively.We suggest that the older age corresponded to the HP-UHT metamorphism,while the younger age represented an retrograde metamorphic event during cooling.展开更多
基金This study was supported by the National Natural Science Foundation of China grants 49572146 and 49772147 and the Foundation for Development of Science and Technology in Geology grant 9514.
文摘: Using the single—zircon evaporation technique and U—Pb method, the authors have conducted an isotope geochonological study of the Huilanshan granulite and Shima garnet-bearing plagioclase gneiss (“country rocks” of the Shima eclogite) in the Dabie Mountains. The study shows that these rocks have peak metamorphic ages of 443–455 Ma, which are essentially consistent with that of the Caledonian high—ultrahigh pressure eclogites. This indicates the existence of the Caledonian collisional orogeny in the Dabie Mountains.
文摘A high pressure basic granulite ultramafics belt is found in the late Archaean gneisses of Laixi Laiyang Qixia district, east Shandong. This belt has previously been considered as another eclogite belt in Sulu ultra high pressure(UHP) terrain. The typical high P granulite is characterized by mineral assemblages of three generations formed in different metamorphic episode respectively. The mineral assemblage of first episode is Grt(core)+Cpx+Pl, that of the second episode is Grt(rim)+Cpx+Opx+Pl+Amp+Q+Mt and that of the third episode is Cpx+Pl+Amp+Q+Mt. In first assemblage, the garnet porphyroblast is rich in grossular and pyrope component, and the coexisting Cpx is Al rich. Using mineral thermobarometer and Berman’s (1991) TWQ program, the P T conditions of three episodes are established, i.e. T=840℃～860℃, P>1.4GPa for first episode; T=720℃～780℃,P=0.8～1.2GPa for second episode and T=600℃～800℃,P=0.5～0.7GPa for the third episode.Considering the reaction texture, mineral Chemistry and PT estmations, a clockwise PTt path can be constructed, which shows post peak isothermal decompression at first and followed by a process of pressure and temperature decreasing. The mineral wholerock Sm Nd isochron age of the granulite is 1752Ma, which indicates its last thermal event during early middle Proterozoic stage. Therefore, it is concluded that the high pressure granulite and ultramafics of this belt represents the lower continental curst of the North China Craton during early Precambrian without any relationship to tectonic process of the Sulu UHP terrain.
基金China Geological Survey(Grant No.20013000166) Natural Science Foundation of China(Grant No.49902006).
文摘Mafic granulites have been found as structural lenses within the huge thrust system outcropping about 10 km west of Nam Co of the northern Lhasa Terrane, Tibetan Plateau. Petrological evidence from these rocks indicates four distinct metamorphic assemblages. The early metamorphic assemblage (M1) is preserved only in the granulites and represented by plagioclase+hornblende inclusions within the cores of garnet porphyroblasts. The peak assemblage (M2) consists of garnet+clinopyroxene+hornblende+plagioclase in the mafic granulites. The peak metamorphism was followed by near-isothermal decompression (M3), which resulted in the development of hornblende+plagioclase symplectites surrounding embayed garnet porphyroblasts, and decompression-cooling (M4) is represented by minerals of hornblende+plagioclase recrystallized during mylonization. The peak (M2) P-T conditions of garnet+ clinopyroxene+plagioclase+hornblende were estimated at 769-905℃ and 0.86-1.02 GPa based on the geothermometers and geobarometers. The P-T conditions of plagioclase+hornblende symplectites (M3) were estimated at 720-800℃ and 0.55-0.68 GPa, and recrystallized hornblende+plagioclase (M4) at 594-708℃ and 0.26-0.47 GPa. It is impossible to estimate the P-T conditions of the early metamorphic assemblage (M1) because of the absence of modal minerals. The combination of petrographic textures, metamorphic reaction history, thermobarometric data and corresponding isotopic ages defines a clockwise near-isothermal decompression metamorphic path, suggesting that the mafic granulites had undergone initial crustal thickening, subsequent exhumation, and cooling and retrogression. This tectonothermal path is considered to record two major phases of collision which resulted in both the assemblage of Gondwanaland during the Pan-African orogeny at 531 Ma and the collision of the Qiangtang and Lhasa Terranes at 174 Ma, respectively.
文摘The Yushugou HP granulite-peridotite complex is located at east of northern margin of southern Tianshan mountains,China,which consists of granulite unit and peridotite unit mainly.Because of the rare association of
文摘This paper presents the primary results of petrologic, mineralogical and petrochemical studies of garnet-bearing granulite facies rock xenoliths from Xinyang, Henan Province. These xenoliths, which are found in a pipe of late Mesozoic volcaniclastic breccia, are of high density (3.13–3.30 g/cm3) and high seismic velocity (Vp = 7.04–7.31 km/s), being products of underplating of basaltic magmas and had experienced granulite facies metamorphism. The underplating and metamorphism took place before the eruption of the host rock. Petrographical studies and equilibrium T-P calculations show that these xenoliths were captured at a 49 km depth and experienced at least a 16 km uplift before they were captured. The dynamics of the uplift could be related to the continent-continent collision between the North China plate and the Yangtze plate during the Triassic.
基金Project supported by the National Natural Science Foundation of China.
文摘High-pressure basic granulite terrain of 2.65 Ga from Jiouhuai’an in the junction of the Hebei and Shanxi provinces was discovered and reported recently. The three metamorphic mineral assemblages and their mineral reaction texture of the basic granulites have been identified, which represent three main metamorphic episodes of 1.4—1.5 Gpa, 800℃; 0.7—0.9 Gpa, 820℃ and 0.5—0.6 Gpa, 700℃. Their steep decompressional clockwise P-T path implies that a late Archaean continental collision and sole thrusting event perhaps occurred in North China Craton. This is important to study petrogenesis of high-pressure granulites, composition and texture of deep crust in North China Craton, and early Precambrian collision tectonism.
基金Project supported by the National Natural Science Foundation of China.
文摘There is a typical assemblage of garnet + kyanite + microperthite + quartz + rutile in high-pressure (HP) felsic granulite of Qinling complex in Songshugou area. East Qinling. The HP granulite was formed at 800 -900℃ and 1.3 -1.6GPa and has experienced two stages of retrograde metamorphism at 600- 650 ℃, 0.8-1.0GPa and 500-600℃, 0.3-0.6GPa, forming two retrograde metamorphic assemblages of margarite + plagiodase (PlI)+quartz and sillimanite + biotite + plagioclase(PlII) + microdine+quartz, respectively. They construct a two-stage clockwise P-T path which shows down-pressure cooling in both early and late stage.
基金Project supported by the National Natural Science Foundation of China
文摘1 Geological occurrence The ultramafic rocks in the Songshugou area of the North Qinling are structurally emplaced in middle-late Proterozoic amphibolites (fig. 1) which are regarded as an external rootless ophiolite sheet with emplacement age of (983±140) Ma. The lenticular diopsidegarnet-amphibolites, named garnet-amphibolte by others, are exposed in the amphibolits. The high-pressure basic granulites discussed in this note were found in the lenticular garnet-
基金Supported by Geological Survey of Henan Province and the National Natural Sci-ence Foundation of China (Grant No. 40325005)
文摘High-pressure mafic granulites occurring as lenticular bodies within garnet-amphibolites in Kangxiwar Fault have been first reported in this paper. The P-T conditions of two metamorphic stages were obtained using calibrated geothermal barometers and ThermoCalc Program. The peak metamorphic condition of these high-pressure granulites is about 760–820°C, 1.0–1.2 GPa and the retrograde metamorphic condition is about 620–720°C, 0.7–0.8 GPa. The petrological studies show that they have a near-isobaric cooling P-T path which suggests that the Western Kunlun underwent initial crustal thickening, subsequent exhumation and cooling. The SHRIMP zircon U-Pb dating gives two groups of ages for high-pressure granulites. One is 177±6 Ma which is obtained from the rim of the zircon. We consider this age should be the metamorphic age. And the other is 456±30 Ma which is obtained from the core of the zircon and should be the protolith age. The formation of these high-pressure granulites in western Kunlun is closely correlated with the evolution of the Paleo-Tethys and has important implications for the research on Tethys and Paleo-Asian tectonic zone.
基金Project supported by the National Natural Science Foundation of China and the National Key Project KJ 85-07-01-04.
文摘Recently, a series of basic granulite enclosures are found in the granulite gneisses along the right side of the Yarlung Zangbo River, lying west of the Namjagbarwa Mountain. Es-pecially, some high-pressure granulite enclosures have been discovered in eastern gully of the Zhibei village. To the northwest of the high-pressure granulite belt there occur Yarlung Zangbo ophiolite zone. Southeastward the granulites change into amphibolite and green-schist facies rocks, which constitute a complete lower crust section.
基金supported by National Natural Science Foundation of China (Grant Nos. 40730315 and 41023009)State Key Laboratory of Lithospheric Evolution
文摘Hyalophane-rich pegmatites are identified from the Manjinggou high-pressure granulite terrain in the Central Zone of North China Craton. Based on field investigation, mineral assemblage and mineral geochemistry, two types of pegmatites can be defined, i.e., hyalophane pegmatite and hyalophane-rich pegmatite. The hyalophane pegmatite is composed of pure hyalophane with 18.7 mol%-19.4 mol% celsian, whereas the hyalophane-rich pegmatite consists of clinopyroxene + titanite + epidote + hyalophane with 11.9 mol%-12.5 mol% celsian. Hyalophane-rich pegmatite has typical magmatic zircons with oscillatory zoning and high Th/U ratios, implying that this type of pegmatite crystallized from special melt similar to magma. SIMS (Cameca 1280) zircon U-Pb dating shows that the crystallization age of the hyalophane-rich pegmatite is 1812±5 Ma, younger than the regional metamorphic age (peak of ca. 1.85 Ga). Zircon δ18O (8.0 ‰-9.3 ‰) and ?Hf (-7.0 to-2.7) values measured by SIMS suggest that the high-pressure granulite terrain was the source of these veins. Therefore, the hyalophane-rich pegmatite veins were likely to be generated by melting of the high-pressure granulite terrain during post collisional uplift. A quick tectonic uplifting process with a velocity of 0.4 to 0.6 mm/a has been estimated for the high-pressure granulite terrane from the Central Zone of North China Craton.
基金supported by the National Natural Science Foundation of China (No. 41272072)the NSFC/NRF Research Cooperation Programm (No. 41761144061)the SDUST Research Fund (No. 2015TDJH101)
文摘Petrological analysis and LA-ICP-MS zircon U-Pb dating were conducted on high- pressure marie granulites, which occured as xenolith within TTG gneisses, from the Nanshankou Village of the Jiaobei terrane, Shandong Peninsula in the north-eastern part of the North China Craton （NCC）. The mafic HP grannlite is composed of garnet, clinopyroxene, orthopyroxene, amphibole and symplectitic clinopyroxene, orthopyroxene, plagioclase, ilmente and magnetite which were formed after the decomposition of porphyroblastic garnet and clinopyroxene. Four stages of metamorphic mineral assemblages for the mafic HP granulites were constrained by detail petrological and mineralogical in- vestigations. The early prograde assemblage is represented by the mineral inclusions within garnet and clinopyroxene porphyroblasts （Opx1＋Pl1＋Qtz1）, recording the metamorphic conditions at -754-757 ℃, 0.63-0.71 GPa; peak metamorphic conditions were determined at -874-891 ℃, 1.32-1.35 GPa with the mineral assemblage of Grt2＋Cpx2＋Amp2＋Pl2＋Qtz2. Retrograde minerals derived from symplectitic assemblage Opx3＋Cpx3＋Amp3＋Pl3＋Qtz3＋Ilm3±Mag3 were formed at 693-796℃, 0.60-0.84 GPa. A final greensehist to sub-greenschist facies event was recorded by the exsolution of actinolite and albite within a retrograded clinopyroxene, as well as the occurrence of prehnite, chlorite and calcite minerals. Accordingly, a clockwise P-T path was concluded on the basis of the different stages of mineral asseblage. Cathodoluminescence imaging, trace element and U-Pb dating of zircons from the mafic HP granulites recorded similar charactistics for three episodes of Paleo-Meso Proterozoic metamorphic events. These are the metamorphic events preserved in mafic and pelitic granulites in the Jiao-Liao-Ji belt （JLJB） with 207 pb/206pb ages of 2.0-1.9 Ga for peak metamorphism and of 1.86-1.84 Ga for decomposing process, followed by a retrograde amphibolite facies metamorphic event related to the post-orogenic extension at the age of 1.76-1.74 Ga, resulting the exhumation of the granulite to the upper crust level.
基金This work was suppotted by the Ministry of Saance and Techmology of the People's Republic of China(Gant No 2002CB412608)the Specific Project for the Aunthos of Best Dissertations of Chimese Univarsities and Colleges(Grant No.200022).
文摘The mafic granulites in Dinggye,as various scale lense-shaped enclaves within the high Himalayan crystalline rock series,occur along mylonitic foliations at the junction between the Southern Tibetan Detachment System(STDS)and the Xainza-Dinggye normal fault system.The main lithological assemblage comprises garnet plagioclase pyroxenite,garnet two-pyroxene granulite,pyroxene garnet amphibolite and so on.The detailed petrological analyses show that these mafic granulites underwent at least four-stage metamorphic evolution.The first metamor-phic stage,the garnet+clinopyroxene+quart mineral assemblage(M1)was probably formed un-der eclogite facies,the second stage,the plagioclase+clinopyroxene symplectite mineral as-semblage(M2)was produced under high-pressure granulite facies by the early decompressive breakdown of M1 mineral assemblage,the third stage,the plagioclase+clinopyroxene+hypersthene symplectite mineral assemblage(M3)was formed at granulite facies by the late period decompressive breakdown of M1 and M2 mineral assemblages and the final stage,pla-gioclase+hornblende mineral assemblage(M4)was formed by hydrolysis of earlier mineral as-semblages during late uplifting.The detailed mineral composition analyses suggest that garnets and clinopyroxenes within M1 and M2 mineral assemblages display similar compositions to the equivalents in the B and C types of eclogites,whereas the M3 clinopyroxenes are akin to these of the same kind of minerals in the granulite.These mineral chemistry features and P-T estimates calculated by mineral thermometers and barometers indicate that the early stage relic porphyro-blasts(M1)could be formed at the eclogite facies,the early decompressive breakdown(M2)occurred at the high-pressures granulite facies of 1.35―1.48 GPa and 625―675℃,the M3 mineral assemblage recorded the granulite facies of 0.7―0.95 GPa and 775―900℃and M4 plagioglase+hornblende retrograde mineral assemblage was produced under the amphibolite facies metamorphism with pressure of 0.4 to 0.75 GPa and temperature at between 660 and 700℃.These construct P-T paths from crustal subduction overthickening to tectonic uplift tectono-thermal evolution.The mineral chemical characteristics and P-T condition at every metamorphic stage of these granulites indicate that these rocks experienced the eclogite facies metamorphism during the early stage.Subsequently,these mafic granulites underwent the three-stage exhuma-tion of the eclogite facies tectonic uplift,isostatic uplift related to the transformation from ec-logite/high-pressure granulite to granulite facies and extensional uplift.
基金supported by the National Natural Science Foundation of China (No. 41761144061)the Shandong Provincial Natural Science Foundation (No. ZR2016DM04)the University Students Innovation Program of SDUST (No. 2015TDJH101)
文摘The studied mafic granulites are located at Xiwangshan,Xuanhua region in the north of the Trans-North China Orogen(TNCO),occurring as lens within tonalite-trondhjemite-granodiorite(TTG)gneisses in the eastern part of the Xiwangshan area.The rocks contain the representative granulite-facies minerals such as garnet,clinopyroxene,orthopyroxene,plagioclase,amphibolite,rutile and quartz,and also well-developed melt pseudomorph and antiperthite.Although the prograde metamorphic stage(M1)cannot be retrieved due to rare preservation of pre-peak-stage mineral associations,three distinct mineral assemblages that formed in different metamorphic stages can be identified,based on petrography and mineralogy characteristics.The peak stage(M2)is characterized by Grt2+Cpx2+Amp2+Pl2+Rt+melt pseudomorphs,and a post-peak decompression stage(M3)contains a mineral assemblage of Grt3+Opx3+Cpx3+Amp3+Pl3,while a later-retrogression stage(M4)is featured by coronas of Amp4+Pl4 surrounding garnet.By calculating metamorphic P-T conditions using THERMOCALC,stage M2 was constrained to be 13.2–14.8 kbar and 1050–1080℃,and M3 recorded P-T conditions of 5.7–7.3 kbar and 825–875℃,while M4 yielded P of^5 kbar and T of^660℃,consistent with amphibolite facies metamorphism.Taking into account of all these petrological data,we propose that the mafic granulite experienced a high-pressure(HP)and ultra-high temperature(UHT)granulite-facies metamorphism during the peak metamorphism,which was accompanied with a clockwise P-T path.U-Pb dating of metamorphic zircons in the granulites yields two groups of ages at 1853±14 and 1744±44 Ma,respectively.We suggest that the older age corresponded to the HP-UHT metamorphism,while the younger age represented an retrograde metamorphic event during cooling.
