In Yuka-Luofengpo area of the north Qaidam Mountains, eclogitic metapelites are recognized. The metapelites enclosed lenses of eclogites, and locally intercalated with eclogites. Their typical mineral assemblages are ...In Yuka-Luofengpo area of the north Qaidam Mountains, eclogitic metapelites are recognized. The metapelites enclosed lenses of eclogites, and locally intercalated with eclogites. Their typical mineral assemblages are garnet+kyanite+chloritoid+phengite+quartz+rutile. Strong growth zoning is preserved in garnets of metapelites, and phengite contains up to 3.4 Si per formula units. The petrographic observations and textural relations testify to the following sequence of mineral assemblages connected to three metamorphic stage: (1) Grt+ChlI+CldI +PheI ± StI+Qtz; (2) Grt+Ky+PheII±CldII+Qtz; and (3) Grt+CldIII+ChlII+PheIII+StII ± ky+ Qtz. Applying THERMOCALC Program, Grt-Phe thermometer and Grt-Ky-Phe-Qtz barometry, P-T conditions for three metamorphic stages were obtained: P=1.07±0.31GPa, T=564±22? (prograde stage); P=2.3–3.1GPa, T=615–700°C-(peak stage); and P =1.22 ± 0.26GPa, T=581±20°C (retrograde stage). A hairpin shape P-T path similar to that of adjacent eclogite is inferred. In combination with eclogitic mineral relics in marbles and orthogneisses enclosing eclogites, we thought that the relationship between eclogites and country rocks is “in situ” rather than “tectonic emplacement”.展开更多
Al-rich metapelites from the Mashan khondalite series are characterized by the assem- blage Spl＋Grt＋Sil＋Crd＋Bt＋Pi （An72）＋Kfs＋Quartz＋graphite. Large amounts of spinel＋quartz assem- blages occur as inclusions...Al-rich metapelites from the Mashan khondalite series are characterized by the assem- blage Spl＋Grt＋Sil＋Crd＋Bt＋Pi （An72）＋Kfs＋Quartz＋graphite. Large amounts of spinel＋quartz assem- blages occur as inclusions in garnet and prismatic sillimanite in the Ai-rich metapelites of the Mashan complex, NE China. The chemical composition of spinel is characterized by Zn-rich （Xzn=0.33-0.40. Xzn=Zn/Zn＋Mg＋Fe＊） （Fe＊=FeZ＋＋Fe3＋） and Fe3＋ rich （up to 0.31 p.f.u.）. The characteristic chemical composition and the mineral association indicated that the formation of spinel and quartz assemblage may be due to the breakdown of Zn-rich staurolite. The geothermobarometers studies show that the peak temperature of the Mashan complex is around 820 ℃ and the peak pressures is 8.0 kbar. The Mashan complex shows a typical orogen style P-T path.展开更多
The nature and formation time of the Xinghuadukou complex in Northeast China are important for determining the tectonic evolution of the Precambrian geological evolution of the Erguna massif. In this study, we present...The nature and formation time of the Xinghuadukou complex in Northeast China are important for determining the tectonic evolution of the Precambrian geological evolution of the Erguna massif. In this study, we present the results of zircon U-Pb dating of two metapelites from the complex. Detrital and metamorphic zircons from the metapelites yield a depositional age of -601 Ma and a metamorphic age of 496-509 Ma, indicating that the supracrustal rocks formed during the Neoproterozoic and recorded pan-African metamorphic events in the Erguna massif. Garnet porphyroblasts in SiI-Grt-Bt-Ms paragneiss show diffusion zoning, implying a decreasing P-T trend. Based on mineral transformation and P-T estimates using conventional geothermobarometers and phase equilibria modeling, three metamorphic stages were determined, including an early prograde metamorphic stage, a near peak upper amphibolite facies metamorphic stage, and a near-isobaric cooling stage with P-T conditions of 6.1 kb, 645 ℃, 5-6 kb, 710-740 ℃, and 4.4 kb, 625℃, respectively. The metamorphic history of the Xinghuadukou complex is thus defined by a clockwise P-T trajectory, which implies that the metamorphism of the metapelites documented the subduction, subsequent uplift and post collision process.展开更多
Here we report the occurrence of garnet porphyroblasts that have overgrown alternating silica-saturated and silica deficient microdomains via different mineral reactions. The samples were collected from ultrahigh-temp...Here we report the occurrence of garnet porphyroblasts that have overgrown alternating silica-saturated and silica deficient microdomains via different mineral reactions. The samples were collected from ultrahigh-temperature(UHT) metapelites in the Highland Complex, Sri Lanka. In some of the metapelites, garnet crystals have cores formed via a dehydration reaction, which had taken place at silicasaturated microdomains and mantle to rim areas formed via a dehydration reaction at silica-deficient microdomains. In contrast, some other garnets in the same rock cores had formed via a dehydration reaction which occurred at silica-deficient microdomains while mantle to rim areas formed via a dehydration reaction at silica-saturated microdomains. Based on the textural observations, we conclude that the studied garnets have grown across different effective bulk compositional microdomains during the prograde evolution. These microdomains could represent heterogeneous compositional layers(paleobedding/laminations) in the precursor sediments or differentiated crenulation cleavages that existed during prograde metamorphism. UHT metamorphism associated with strong ductile deformation, metamorphic differentiation and crystallization of locally produced melt may have obliterated the evidence for such microdomains in the matrix. The lack of significant compositional zoning in garnet probably due to self-diffusion during UHT metamorphism had left mineral inclusions as the sole evidence for earlier microdomains with contrasting chemistry.展开更多
Metapelites from the Mesoproterozoic Xingxingxia group in the Eastern Segment of the Central Tianshan,Northwestern China,were analyzed for major and trace elements,includ-ing rare earth elements.Compared with post-Arc...Metapelites from the Mesoproterozoic Xingxingxia group in the Eastern Segment of the Central Tianshan,Northwestern China,were analyzed for major and trace elements,includ-ing rare earth elements.Compared with post-Archean shales,the metapelites are enriched in Sr,Hf and Zr.The other elements are similar to the compositions of the Phanerozoic North American Shale Composite and the Post-Archean Australian average Shale(PAAS).The characteristics of Al_(2)O_(3)/TiO_(2),Cr/Zr,Cr/Th,Th/Sc and high Zr concentration suggest that these pelites could be derived from a significant proportion of felsic and a few proportion of participation of mafic mate-rials in nature.These rocks display highly fractionated REE patterns,and average(La/Yb)_(n)=18.6.Several samples have slightly negative Eu anomalies(Eu/Eu^(*)=0.7―0.84)in comparison with PAAS(Eu/Eu^(*)=0.65),indicating contribution from young immature materials.The low K_(2)O/Al_(2)O_(3) values of these metapelites suggest that their source materials could contain minimal alkali feldspar.In the A-CN-K triangular diagram,the sample data array intersects the feldspar join,indicating that the source had a plagioclase:K-feldspar ratio of approximately 5:1,repre-senting weathered products from components that could approximately correspond to granodio-rites and tonalites.The low Chemical Index of Alteration(CIA)and high Index of Compositional Variability(ICV)values suggest low degrees of weathering of the source and low compositional maturity of the sediments,respectively.The geochemical characteristics of the metapelites from the Xingxingxia group also demonstrate that these sediments were deposited in a back-arc background within a continental-arc system.展开更多
The Yardoi gneiss dome is located to the easternmost of the North Himalayan Gneiss Dome (NHGD),southern Tibet. It consists of metapelite,garnet amphibolite,granite and leucogranite,and is a key subject to constrain th...The Yardoi gneiss dome is located to the easternmost of the North Himalayan Gneiss Dome (NHGD),southern Tibet. It consists of metapelite,garnet amphibolite,granite and leucogranite,and is a key subject to constrain the formation and tectonic evolution of NHGD. SHRIMP zircon U/Pb data on the leucogranite yield an age of 35.3±1.1 Ma,which is substantially older than that of the similar leu-cogranites to the west. Sr and Nd isotope systematics indicate that this leucogranite was derived from partial melting of the mixed garnet amphibolite and metapelite. Our data suggest that (1) during the early stage of Himalayan magmatism,amphibolite dehydration melting overwhelmed that of the metapelite; and (2) such a melting at middle-lower crust might be a major factor that initiated the movement along the Southern Tibetan Detachment System (STDS).展开更多
The Altun tectonic zone is an important left-handed strike-slip fault zone on the Asian continent. Recent studies reveal that the left-handed strike slip of this fault zone was developed not only in the Cenozoic, but ...The Altun tectonic zone is an important left-handed strike-slip fault zone on the Asian continent. Recent studies reveal that the left-handed strike slip of this fault zone was developed not only in the Cenozoic, but also during the Late Ordovician. The fault zone is mainly composed of Proterozoic schists, volcanics, quartzites and carbonate rocks bearing stromatolites. The overlying strata are dominated by plateform carbonate rocks and展开更多
高喜马拉雅结晶岩系和北喜马拉雅穹隆都发育高角闪岩相—麻粒岩相变泥质岩,岩石组合以富铝质片麻岩类为主,伴生钾质花岗片麻岩、大理岩及基性麻粒岩等。元素地球化学特征表明,其原岩主要为较富铝的长石质砂岩和石英岩质砂岩及少量粘土岩...高喜马拉雅结晶岩系和北喜马拉雅穹隆都发育高角闪岩相—麻粒岩相变泥质岩,岩石组合以富铝质片麻岩类为主,伴生钾质花岗片麻岩、大理岩及基性麻粒岩等。元素地球化学特征表明,其原岩主要为较富铝的长石质砂岩和石英岩质砂岩及少量粘土岩,形成于大陆边缘浅海相沉积环境。这些变泥质岩具有相似的微量元素和稀土元素地球化学特征,表现为大离子亲石元素相对高场强元素较富集,轻稀土较重稀土富集,稀土总量较高,具有较显著的 Eu 负异常。在变质矿物组合、元素地球化学特征及锆石组成等特征上,它们与青藏高原北缘的康西瓦和阿尔金孔兹岩系相似,可能是来源于冈瓦纳大陆边缘的同一套岩石。展开更多
X-ray diffraction methods for estimating the metamorphic grade of diagenetic, anchizone and epizone in metapelites are reviewed and applied to samples from a 7000 m＋ borehole in western China and surface samples from...X-ray diffraction methods for estimating the metamorphic grade of diagenetic, anchizone and epizone in metapelites are reviewed and applied to samples from a 7000 m＋ borehole in western China and surface samples from the surrounding Zoige area. Kiibler＇s illite crystallinity （IC） measurements provide more consistent results than calculated values of percentage of illite in the I/S mixed layers and percentage of I/S mixed layers. Down-borehole IC values display a typical burial metamorphic relationship between stratigraphic level and IC. A method for preparing very low grade metamorphic maps is described, and isograds plotted on a regional geological map at selected values of IC, delineating a high temperature diagenetic zone, an anchizone, and an epizone. The map shows that IC values are controlled by stratigraphic level in the north of the study area （i.e. burial metamorphism）, and proximity to an igneous intrusive body in the south （i.e. contact metamorphism）.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.40272095)the Key Project of the Ministry of Land and Resources of China(Grant No.20010201)Geological Survey Project of China(Grant No.200313000058).
文摘In Yuka-Luofengpo area of the north Qaidam Mountains, eclogitic metapelites are recognized. The metapelites enclosed lenses of eclogites, and locally intercalated with eclogites. Their typical mineral assemblages are garnet+kyanite+chloritoid+phengite+quartz+rutile. Strong growth zoning is preserved in garnets of metapelites, and phengite contains up to 3.4 Si per formula units. The petrographic observations and textural relations testify to the following sequence of mineral assemblages connected to three metamorphic stage: (1) Grt+ChlI+CldI +PheI ± StI+Qtz; (2) Grt+Ky+PheII±CldII+Qtz; and (3) Grt+CldIII+ChlII+PheIII+StII ± ky+ Qtz. Applying THERMOCALC Program, Grt-Phe thermometer and Grt-Ky-Phe-Qtz barometry, P-T conditions for three metamorphic stages were obtained: P=1.07±0.31GPa, T=564±22? (prograde stage); P=2.3–3.1GPa, T=615–700°C-(peak stage); and P =1.22 ± 0.26GPa, T=581±20°C (retrograde stage). A hairpin shape P-T path similar to that of adjacent eclogite is inferred. In combination with eclogitic mineral relics in marbles and orthogneisses enclosing eclogites, we thought that the relationship between eclogites and country rocks is “in situ” rather than “tectonic emplacement”.
基金supported by a JSPS Grant-in-Aid for Scientific Research (No. 17340149) to Akira Takasuby the NSFS of China (No. 40739905) to Yongjiang Liu+1 种基金by the 973 project of the Ministry of Science and Technology of China (No. 2013CB429802)by the National Natural Science Foundation for the Youth of China (No. 41302175) to Weimin Liu
文摘Al-rich metapelites from the Mashan khondalite series are characterized by the assem- blage Spl＋Grt＋Sil＋Crd＋Bt＋Pi （An72）＋Kfs＋Quartz＋graphite. Large amounts of spinel＋quartz assem- blages occur as inclusions in garnet and prismatic sillimanite in the Ai-rich metapelites of the Mashan complex, NE China. The chemical composition of spinel is characterized by Zn-rich （Xzn=0.33-0.40. Xzn=Zn/Zn＋Mg＋Fe＊） （Fe＊=FeZ＋＋Fe3＋） and Fe3＋ rich （up to 0.31 p.f.u.）. The characteristic chemical composition and the mineral association indicated that the formation of spinel and quartz assemblage may be due to the breakdown of Zn-rich staurolite. The geothermobarometers studies show that the peak temperature of the Mashan complex is around 820 ℃ and the peak pressures is 8.0 kbar. The Mashan complex shows a typical orogen style P-T path.
基金supported by the National Natural Science Foundation of China(No.41472164)the MADE-IN-EARTH ERC starting grant of Switzerland(No.33577)
文摘The nature and formation time of the Xinghuadukou complex in Northeast China are important for determining the tectonic evolution of the Precambrian geological evolution of the Erguna massif. In this study, we present the results of zircon U-Pb dating of two metapelites from the complex. Detrital and metamorphic zircons from the metapelites yield a depositional age of -601 Ma and a metamorphic age of 496-509 Ma, indicating that the supracrustal rocks formed during the Neoproterozoic and recorded pan-African metamorphic events in the Erguna massif. Garnet porphyroblasts in SiI-Grt-Bt-Ms paragneiss show diffusion zoning, implying a decreasing P-T trend. Based on mineral transformation and P-T estimates using conventional geothermobarometers and phase equilibria modeling, three metamorphic stages were determined, including an early prograde metamorphic stage, a near peak upper amphibolite facies metamorphic stage, and a near-isobaric cooling stage with P-T conditions of 6.1 kb, 645 ℃, 5-6 kb, 710-740 ℃, and 4.4 kb, 625℃, respectively. The metamorphic history of the Xinghuadukou complex is thus defined by a clockwise P-T trajectory, which implies that the metamorphism of the metapelites documented the subduction, subsequent uplift and post collision process.
基金the National Research Council(NRC) of Sri Lanka(Grant Nos. 11-180 and 15-089)the Indo-Lanka Joint Grant from the Ministry of Technology and Research,Sri Lanka (MTR/TRD/AGR/3/1/04) for funding this projectsupport by the Stichting Dr Schurmannfonds, Grant Nos. 88/2012, 94/2013 and 101/2014
文摘Here we report the occurrence of garnet porphyroblasts that have overgrown alternating silica-saturated and silica deficient microdomains via different mineral reactions. The samples were collected from ultrahigh-temperature(UHT) metapelites in the Highland Complex, Sri Lanka. In some of the metapelites, garnet crystals have cores formed via a dehydration reaction, which had taken place at silicasaturated microdomains and mantle to rim areas formed via a dehydration reaction at silica-deficient microdomains. In contrast, some other garnets in the same rock cores had formed via a dehydration reaction which occurred at silica-deficient microdomains while mantle to rim areas formed via a dehydration reaction at silica-saturated microdomains. Based on the textural observations, we conclude that the studied garnets have grown across different effective bulk compositional microdomains during the prograde evolution. These microdomains could represent heterogeneous compositional layers(paleobedding/laminations) in the precursor sediments or differentiated crenulation cleavages that existed during prograde metamorphism. UHT metamorphism associated with strong ductile deformation, metamorphic differentiation and crystallization of locally produced melt may have obliterated the evidence for such microdomains in the matrix. The lack of significant compositional zoning in garnet probably due to self-diffusion during UHT metamorphism had left mineral inclusions as the sole evidence for earlier microdomains with contrasting chemistry.
基金supported by the National Natural Science Foundation of China(Grant No.40072065).
文摘Metapelites from the Mesoproterozoic Xingxingxia group in the Eastern Segment of the Central Tianshan,Northwestern China,were analyzed for major and trace elements,includ-ing rare earth elements.Compared with post-Archean shales,the metapelites are enriched in Sr,Hf and Zr.The other elements are similar to the compositions of the Phanerozoic North American Shale Composite and the Post-Archean Australian average Shale(PAAS).The characteristics of Al_(2)O_(3)/TiO_(2),Cr/Zr,Cr/Th,Th/Sc and high Zr concentration suggest that these pelites could be derived from a significant proportion of felsic and a few proportion of participation of mafic mate-rials in nature.These rocks display highly fractionated REE patterns,and average(La/Yb)_(n)=18.6.Several samples have slightly negative Eu anomalies(Eu/Eu^(*)=0.7―0.84)in comparison with PAAS(Eu/Eu^(*)=0.65),indicating contribution from young immature materials.The low K_(2)O/Al_(2)O_(3) values of these metapelites suggest that their source materials could contain minimal alkali feldspar.In the A-CN-K triangular diagram,the sample data array intersects the feldspar join,indicating that the source had a plagioclase:K-feldspar ratio of approximately 5:1,repre-senting weathered products from components that could approximately correspond to granodio-rites and tonalites.The low Chemical Index of Alteration(CIA)and high Index of Compositional Variability(ICV)values suggest low degrees of weathering of the source and low compositional maturity of the sediments,respectively.The geochemical characteristics of the metapelites from the Xingxingxia group also demonstrate that these sediments were deposited in a back-arc background within a continental-arc system.
基金Supported by National Natural Science Foundation of China (Grant No.40673027)the Outlay Research Fund of Chinese Academy of Geological Sciences (Grant No.20071120101125)the Hundred Talent Program of Chinese Academy of Sciences
文摘The Yardoi gneiss dome is located to the easternmost of the North Himalayan Gneiss Dome (NHGD),southern Tibet. It consists of metapelite,garnet amphibolite,granite and leucogranite,and is a key subject to constrain the formation and tectonic evolution of NHGD. SHRIMP zircon U/Pb data on the leucogranite yield an age of 35.3±1.1 Ma,which is substantially older than that of the similar leu-cogranites to the west. Sr and Nd isotope systematics indicate that this leucogranite was derived from partial melting of the mixed garnet amphibolite and metapelite. Our data suggest that (1) during the early stage of Himalayan magmatism,amphibolite dehydration melting overwhelmed that of the metapelite; and (2) such a melting at middle-lower crust might be a major factor that initiated the movement along the Southern Tibetan Detachment System (STDS).
文摘The Altun tectonic zone is an important left-handed strike-slip fault zone on the Asian continent. Recent studies reveal that the left-handed strike slip of this fault zone was developed not only in the Cenozoic, but also during the Late Ordovician. The fault zone is mainly composed of Proterozoic schists, volcanics, quartzites and carbonate rocks bearing stromatolites. The overlying strata are dominated by plateform carbonate rocks and
文摘高喜马拉雅结晶岩系和北喜马拉雅穹隆都发育高角闪岩相—麻粒岩相变泥质岩,岩石组合以富铝质片麻岩类为主,伴生钾质花岗片麻岩、大理岩及基性麻粒岩等。元素地球化学特征表明,其原岩主要为较富铝的长石质砂岩和石英岩质砂岩及少量粘土岩,形成于大陆边缘浅海相沉积环境。这些变泥质岩具有相似的微量元素和稀土元素地球化学特征,表现为大离子亲石元素相对高场强元素较富集,轻稀土较重稀土富集,稀土总量较高,具有较显著的 Eu 负异常。在变质矿物组合、元素地球化学特征及锆石组成等特征上,它们与青藏高原北缘的康西瓦和阿尔金孔兹岩系相似,可能是来源于冈瓦纳大陆边缘的同一套岩石。
基金SINOPEC Exploration Southern Company,part of the National Oil and Gas Special Project XQ-04the Special Fund for Basic Scientific Research of Central Colleges,Chang'an University(CHD2011JC185) for supporting this study
文摘X-ray diffraction methods for estimating the metamorphic grade of diagenetic, anchizone and epizone in metapelites are reviewed and applied to samples from a 7000 m＋ borehole in western China and surface samples from the surrounding Zoige area. Kiibler＇s illite crystallinity （IC） measurements provide more consistent results than calculated values of percentage of illite in the I/S mixed layers and percentage of I/S mixed layers. Down-borehole IC values display a typical burial metamorphic relationship between stratigraphic level and IC. A method for preparing very low grade metamorphic maps is described, and isograds plotted on a regional geological map at selected values of IC, delineating a high temperature diagenetic zone, an anchizone, and an epizone. The map shows that IC values are controlled by stratigraphic level in the north of the study area （i.e. burial metamorphism）, and proximity to an igneous intrusive body in the south （i.e. contact metamorphism）.
