Based on petrological and geochemical characteristics such as rock assemblage, petrogeochemistry, Sr-Nd isotope, zircon U-Pb age, and Hf isotope, we studied geochronological framework, magma types, source characters, ...Based on petrological and geochemical characteristics such as rock assemblage, petrogeochemistry, Sr-Nd isotope, zircon U-Pb age, and Hf isotope, we studied geochronological framework, magma types, source characters, and petrogenesis of different stages of magmatism of the granitic rocks from the Gangdese batholith in southern Tibet. The magmatic activities of the Gangdese batholith can be divided into three stages. The Mesozoic magmatism, induced by northern subduction of Neotethyan slab, was continuously developed, with two peak periods of Late Jurassic and Early Cretaceous. The Paleocene-Eocene magmatism was the most intensive, and resulted from a complex progress of Neotethyan oceanic slab, including subduction, rollback, and subsequent breakoff. And the Oligocene-Miocene magmatism was attributed to the convective removal of thickened lithosphere in an east-west extension setting after India-Asia collision. Isotopically, zircons from these granitic rocks are characterized by positive εHf(t) values, suggesting that the magmatic source of the Gangdese batholith might be an arc terrane, which was accreted to the southern margin of Asia during Late Paleozoic. Therefore, the chronological framework and Hf isotopic characteristics of the Gangdese batholith are distinct from the granitic rocks in adjacent areas, which can be served as a powerful tracer in studying source-to-sink relation of sediments during the uplift and erosion of Tibetan Plateau.展开更多
We report for the first time the geochemistry of rare earth elements（REE） in the weathered crusts of I-type and calc-alkaline to high-K（shoshonitic） granitic rocks at Mamasa and Palu region, Sulawesi Island, Indon...We report for the first time the geochemistry of rare earth elements（REE） in the weathered crusts of I-type and calc-alkaline to high-K（shoshonitic） granitic rocks at Mamasa and Palu region, Sulawesi Island, Indonesia. The weathered crusts can be divided into horizon A（lateritic profile） and B（weathered horizon）. Quartz, albite, kaolinite, halloysite and montmorrilonite prevail in the weathered crust. Both weathered profiles show that the total REE increased from the parent rocks to the horizon B but significantly decrease toward the upper part（horizon A）. LREE are enriched toward the upper part of the profile as shown by La/YbN value. However, HREE concentrations are high in horizon B1 in Palu profile. The total REE content of the weathered crust are relatively elevated compared to the parent rocks, particularly in the lower part of horizon B in Mamasa profile and in horizon B2 in Palu profile. This suggests that REE-bearing accessory minerals may be resistant against weathering and may remain as residual phase in the weathered crusts. The normalized isocon diagram shows that the mass balance of major and REE components between each horizon in Mamasa and Palu weathering profile are different. The positive Ce anomaly in the horizon A of Mamasa profile indicated that Ce is rapidly precipitated during weathering and retain at the upper soil horizon.展开更多
High-precision data on U and Th contents and Th/U ratios of zircon obtained using secondary ion mass spectrometry analysis have been collected from the literature. Zircon in the granitic rocks has median values of 350...High-precision data on U and Th contents and Th/U ratios of zircon obtained using secondary ion mass spectrometry analysis have been collected from the literature. Zircon in the granitic rocks has median values of 350 ppm U, 140 ppm Th, and Th/U=0.52; the recommended zircon-melt partition coefficients are 81 for Du and 8.2 for DTh. In zircon from mafic and intermediate rocks, the median values are 270 ppm U, 170 ppm Th, and Th/U=0.81, and the recommended zirconmelt partition coefficients are 169 for Du and 59 for DTh. The U and Th contents and Th/U ratios of magmatic zircon are low when zircon crystallizes in equilibrium with the melt. Increasing magma temperature should promote higher Th contents relative to U contents, resulting in higher Th/U ratios for zircon in mafic to intermediate rocks than in granitic rocks. However, when zircon crystallizes in disequilibrium with the melt, U and Th are more easily able to enter the zircon lattice, and their contents and Th/U ratios depend mainly on the degree of disequilibrium. The behavior of U and Th in magmatic zircon can be used as a geochemical indicator to determine the origins and crystallization environments of magmatic zircon.展开更多
Veined gold deposit is product of crustal evolution in special space and special time.It has close relations between the product of veined gold deposit and the formation mechanism (process of mineralization geodynamic...Veined gold deposit is product of crustal evolution in special space and special time.It has close relations between the product of veined gold deposit and the formation mechanism (process of mineralization geodynamics),It has special geological significance in the aspect of source of metallogenic material and metallogenic fluid,migration and precipitation, especially in vein gold deposit of structure boundary.This pater discusses four aspects,i.e. The geodynamic background,source of metallogenic fluid,fluid migration mechanism and structural position of deposits.The concluding remarks are given as follows. 1\ The Pre Cambrian metamorphic complexes emerged extensively in the Wutaishan Hengshan area, more than 60% of those are granitic rock, as the oldest continential crust of crystalline basement they all have the characteristics of deformation and gneiss, and many of them were formed in 2500～2700 Ma, in them some high rank deformed super crust inclusions, or relicts of different rock facies showing 2800～2900 Ma or earlier ages. Through the comphrehensive analysis of large rock chemical data on the relevant diagram about their characteristics, it reflects that not only the granitic rock has two different characteristics of rock series and regionalization but also shows several distinct source tendencies. Itsuggests that the large emergence of granitic rock in Archean era in the area is related to certain collision mechanism, thus resulted in the connection of the landmass, north to Hengshan and the landmass of Bupin,and so completed the cratonization of North China platform. The formation of granitic rock in early Proterozoic era is relevant to rifting which belongs to the genetic series of later orogenic to postorogenic period. 2\ The zonal super crust rock series that stretches in NEE direction on the Archaeozoic crystalline basement in Wutaishan and its vicinity area is called Wutai Group and Hutuo Group. The Wutai Group is mainly consisted of mafic volcanic rock, and uncomformably was under laid the Hutuo展开更多
The paper reports SHRIMP U-Pb zircon data of a dark eclogite and a post-eclogite garnet-bearing gneissic granitic rock from the Bixiling area, Yuexi County, Anhui Province, in the eastern Dabie Mountains. The eclogite...The paper reports SHRIMP U-Pb zircon data of a dark eclogite and a post-eclogite garnet-bearing gneissic granitic rock from the Bixiling area, Yuexi County, Anhui Province, in the eastern Dabie Mountains. The eclogite, which is metamorphosed basic tuff, contains very scarce zircons in omphacite or garnet, but more zircons in quartz. They usually exhibit a double-layered texture, as shown clearly in cathodoluminescence images. Their inner main parts give a 206Pb/238U age of 757±7 Ma, representing the approximate age of the high-pressure (HP)- ultrahigh-pressure (UHP) metamorphic event during which the eclogite was formed. The outer peripheral parts of the zircons, which have been modified by late-stage fluids, give an age of 223±3 Ma. The granitic rock contains more zircons of anatectic origin found mostly in feldspar and quartz and usually also showing a similar composite texture. The inner main parts of the anatectic zircons with oscillatory zoning give a 206Pb/238U age of 727±15 Ma for the approximate age of the emplacement of the granitic rock, and their outer parts, an age of 219±3 Ma for a similar or even the same fluid event. It is thus suggested that the HP-UHP metamorphism of the Bixiling eclogite facies rocks took place during the Neoproterozoic Jinningian, and the Indosinian age values may only represent a late event in the nature of fluid activity.展开更多
The Mesozoic high-K granitic intrusions from the eastern Dabie Mountains, Central China, can be divided into three superunits namely the Yaohe, Penghe and Huangbai superunits. The Yaohe superunit is compositionally do...The Mesozoic high-K granitic intrusions from the eastern Dabie Mountains, Central China, can be divided into three superunits namely the Yaohe, Penghe and Huangbai superunits. The Yaohe superunit is compositionally dominated by quartz monzonite extending as a band in NW direction which is differently foliated, contains numerous dioritic enclaves and has been dated as 174 Ma. The Penghe superunit, widely distributed in the field, varies in composition but is dominated by quartz monzonitic and granitic rocks, which is massive in structure, has well developed with dioritic enclaves and is aged in 125-127 Ma. The Huangbai superunit is mainly composed of granitic composition which is massive in structure, rarely contains dioritic enclaves and is aged in 120-111 Ma. These three superunits of granitic intrusions can also be clearly distinguished in geochemistry. They have recorded an orogenic process of the Dabie Mountains from the end of regional metamorphism to the overprinting of the circum-Pacific tectonic regime.展开更多
In-situ rock failures can result from stress changes due to pure loading and/or unloading. Understanding of the damage evolution behavior in brittle rocks during loading and unloading is imperative for the designs of ...In-situ rock failures can result from stress changes due to pure loading and/or unloading. Understanding of the damage evolution behavior in brittle rocks during loading and unloading is imperative for the designs of rock structures. In this paper, we investigate the damage evolution characteristics of a granitic rock during loading and unloading after a series of triaxial experiments performed at different confining pressures. The axial stress-axial strain variations of the tested specimens revealed that the specimens undergoing unloading fail with a lower axial strain compared to the specimens failed purely by loading. Higher confining pressures were observed to exacerbate the difference. Volumetric strain versus axial strain curves indicated that the curves reverse the trend with the beginning of major damage of specimens. We suggest here a new form of equation to describe the secant modulus variation of brittle rocks against the axial stress for the unloading process. Failure mechanisms of tested specimens showed two distinct patterns, namely, specimens under pure loading failed with a single distinct shear fracture while for the unloading case specimens displayed multiple intersecting fractures. In addition, analysis of the evolution of dissipation and elastic energy during deformation of the specimens under loading and unloading conditions showed differentiable characteristics. Moreover, we evaluated the variations of two damage indices defined based on the energy dissipation and secant modulus evolution during deformation and observed that both of them satisfactorily distinguish key stages of damage evolution.展开更多
From a practical point of view,grain structure heterogeneities are key parameters that control the rock response and still remains a challenge to incorporate in a quantitative manner.One of the less discussed topics i...From a practical point of view,grain structure heterogeneities are key parameters that control the rock response and still remains a challenge to incorporate in a quantitative manner.One of the less discussed topics in the context of the grain-based model(GBM)in the particle flow code(PFC)is the contact heterogeneities and the appropriate contact model to mimic the grain boundary behavior.Generally,the smooth joint(SJ)model and linear parallel bond(LPB)model are used to simulate the grain boundary behavior.However,the literature does not document the suitability of different models for specific problems.Another challenge in implementing GBM in PFC is that only a single bonding parameter is used at the grain boundaries.The aim of this study is to investigate the responses of a laboratory-scale specimen with SJ and LPB models,considering grain boundary heterogeneous and homogeneous contact parameters.Uniaxial and biaxial compression tests are performed to calibrate the response of Creighton granite.The stressestrain curves,volumetric dilation,inter-crack(crack in the grain boundary),and intra-crack(crack within the grain)development,and failure patterns associated with different contact models are examined.It was found that both the SJ and LPB models can reproduce the pre-peak behavior observed for a granitic rock type.However,the LPB model is unable to reproduce the post-peak behavior.Due to the large interlocking effect originating from the balls in contact and the ball size in the LPB model,local dilation is induced at the grain boundaries.This overestimates the volumetric dilation and residual shear strength.The LPB model tends to result in discontinuous inter-cracks and stress localization in the rock specimen,resulting in fine fragments at the rock surface during failure.展开更多
基金Supported by Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. KZCX2-YW-Q09-06)National Natural Science Foundation of China (Grant No. 40721062)
文摘Based on petrological and geochemical characteristics such as rock assemblage, petrogeochemistry, Sr-Nd isotope, zircon U-Pb age, and Hf isotope, we studied geochronological framework, magma types, source characters, and petrogenesis of different stages of magmatism of the granitic rocks from the Gangdese batholith in southern Tibet. The magmatic activities of the Gangdese batholith can be divided into three stages. The Mesozoic magmatism, induced by northern subduction of Neotethyan slab, was continuously developed, with two peak periods of Late Jurassic and Early Cretaceous. The Paleocene-Eocene magmatism was the most intensive, and resulted from a complex progress of Neotethyan oceanic slab, including subduction, rollback, and subsequent breakoff. And the Oligocene-Miocene magmatism was attributed to the convective removal of thickened lithosphere in an east-west extension setting after India-Asia collision. Isotopically, zircons from these granitic rocks are characterized by positive εHf(t) values, suggesting that the magmatic source of the Gangdese batholith might be an arc terrane, which was accreted to the southern margin of Asia during Late Paleozoic. Therefore, the chronological framework and Hf isotopic characteristics of the Gangdese batholith are distinct from the granitic rocks in adjacent areas, which can be served as a powerful tracer in studying source-to-sink relation of sediments during the uplift and erosion of Tibetan Plateau.
基金Financial support assistance from Global-Centre of Excellent (GCOE) program Kyushu University
文摘We report for the first time the geochemistry of rare earth elements（REE） in the weathered crusts of I-type and calc-alkaline to high-K（shoshonitic） granitic rocks at Mamasa and Palu region, Sulawesi Island, Indonesia. The weathered crusts can be divided into horizon A（lateritic profile） and B（weathered horizon）. Quartz, albite, kaolinite, halloysite and montmorrilonite prevail in the weathered crust. Both weathered profiles show that the total REE increased from the parent rocks to the horizon B but significantly decrease toward the upper part（horizon A）. LREE are enriched toward the upper part of the profile as shown by La/YbN value. However, HREE concentrations are high in horizon B1 in Palu profile. The total REE content of the weathered crust are relatively elevated compared to the parent rocks, particularly in the lower part of horizon B in Mamasa profile and in horizon B2 in Palu profile. This suggests that REE-bearing accessory minerals may be resistant against weathering and may remain as residual phase in the weathered crusts. The normalized isocon diagram shows that the mass balance of major and REE components between each horizon in Mamasa and Palu weathering profile are different. The positive Ce anomaly in the horizon A of Mamasa profile indicated that Ce is rapidly precipitated during weathering and retain at the upper soil horizon.
基金supported by the National Natural Science Foundation of China(Grant No. 40972058)the research grants(2008-Ⅰ-02 and 2008-Ⅱ-08)from the State Key Laboratory for Mineral Deposit Research,Nanjing University
文摘High-precision data on U and Th contents and Th/U ratios of zircon obtained using secondary ion mass spectrometry analysis have been collected from the literature. Zircon in the granitic rocks has median values of 350 ppm U, 140 ppm Th, and Th/U=0.52; the recommended zircon-melt partition coefficients are 81 for Du and 8.2 for DTh. In zircon from mafic and intermediate rocks, the median values are 270 ppm U, 170 ppm Th, and Th/U=0.81, and the recommended zirconmelt partition coefficients are 169 for Du and 59 for DTh. The U and Th contents and Th/U ratios of magmatic zircon are low when zircon crystallizes in equilibrium with the melt. Increasing magma temperature should promote higher Th contents relative to U contents, resulting in higher Th/U ratios for zircon in mafic to intermediate rocks than in granitic rocks. However, when zircon crystallizes in disequilibrium with the melt, U and Th are more easily able to enter the zircon lattice, and their contents and Th/U ratios depend mainly on the degree of disequilibrium. The behavior of U and Th in magmatic zircon can be used as a geochemical indicator to determine the origins and crystallization environments of magmatic zircon.
文摘Veined gold deposit is product of crustal evolution in special space and special time.It has close relations between the product of veined gold deposit and the formation mechanism (process of mineralization geodynamics),It has special geological significance in the aspect of source of metallogenic material and metallogenic fluid,migration and precipitation, especially in vein gold deposit of structure boundary.This pater discusses four aspects,i.e. The geodynamic background,source of metallogenic fluid,fluid migration mechanism and structural position of deposits.The concluding remarks are given as follows. 1\ The Pre Cambrian metamorphic complexes emerged extensively in the Wutaishan Hengshan area, more than 60% of those are granitic rock, as the oldest continential crust of crystalline basement they all have the characteristics of deformation and gneiss, and many of them were formed in 2500～2700 Ma, in them some high rank deformed super crust inclusions, or relicts of different rock facies showing 2800～2900 Ma or earlier ages. Through the comphrehensive analysis of large rock chemical data on the relevant diagram about their characteristics, it reflects that not only the granitic rock has two different characteristics of rock series and regionalization but also shows several distinct source tendencies. Itsuggests that the large emergence of granitic rock in Archean era in the area is related to certain collision mechanism, thus resulted in the connection of the landmass, north to Hengshan and the landmass of Bupin,and so completed the cratonization of North China platform. The formation of granitic rock in early Proterozoic era is relevant to rifting which belongs to the genetic series of later orogenic to postorogenic period. 2\ The zonal super crust rock series that stretches in NEE direction on the Archaeozoic crystalline basement in Wutaishan and its vicinity area is called Wutai Group and Hutuo Group. The Wutai Group is mainly consisted of mafic volcanic rock, and uncomformably was under laid the Hutuo
文摘The paper reports SHRIMP U-Pb zircon data of a dark eclogite and a post-eclogite garnet-bearing gneissic granitic rock from the Bixiling area, Yuexi County, Anhui Province, in the eastern Dabie Mountains. The eclogite, which is metamorphosed basic tuff, contains very scarce zircons in omphacite or garnet, but more zircons in quartz. They usually exhibit a double-layered texture, as shown clearly in cathodoluminescence images. Their inner main parts give a 206Pb/238U age of 757±7 Ma, representing the approximate age of the high-pressure (HP)- ultrahigh-pressure (UHP) metamorphic event during which the eclogite was formed. The outer peripheral parts of the zircons, which have been modified by late-stage fluids, give an age of 223±3 Ma. The granitic rock contains more zircons of anatectic origin found mostly in feldspar and quartz and usually also showing a similar composite texture. The inner main parts of the anatectic zircons with oscillatory zoning give a 206Pb/238U age of 727±15 Ma for the approximate age of the emplacement of the granitic rock, and their outer parts, an age of 219±3 Ma for a similar or even the same fluid event. It is thus suggested that the HP-UHP metamorphism of the Bixiling eclogite facies rocks took place during the Neoproterozoic Jinningian, and the Indosinian age values may only represent a late event in the nature of fluid activity.
基金the National Natural Science Foundation of China (Grant No. 49772104) and the Mapping Projects Scaled on 1/50000 from the Ministry of Geology and Mineral Resources of China.
文摘The Mesozoic high-K granitic intrusions from the eastern Dabie Mountains, Central China, can be divided into three superunits namely the Yaohe, Penghe and Huangbai superunits. The Yaohe superunit is compositionally dominated by quartz monzonite extending as a band in NW direction which is differently foliated, contains numerous dioritic enclaves and has been dated as 174 Ma. The Penghe superunit, widely distributed in the field, varies in composition but is dominated by quartz monzonitic and granitic rocks, which is massive in structure, has well developed with dioritic enclaves and is aged in 125-127 Ma. The Huangbai superunit is mainly composed of granitic composition which is massive in structure, rarely contains dioritic enclaves and is aged in 120-111 Ma. These three superunits of granitic intrusions can also be clearly distinguished in geochemistry. They have recorded an orogenic process of the Dabie Mountains from the end of regional metamorphism to the overprinting of the circum-Pacific tectonic regime.
基金Projects(51774187,51324744,51374129)supported by the National Natural Science Foundation of ChinaProject(71380100006)supported by the Innovation Foundation of Doctoral Student in Hunan Province,China+1 种基金Project(2017SK2280)supported by the Key Research and Development Program of Hunan Provincial Science and Technology Department,ChinaProject(17A184)supported by the Key Research Foundation of Education Bureau of Hunan Province,China
文摘In-situ rock failures can result from stress changes due to pure loading and/or unloading. Understanding of the damage evolution behavior in brittle rocks during loading and unloading is imperative for the designs of rock structures. In this paper, we investigate the damage evolution characteristics of a granitic rock during loading and unloading after a series of triaxial experiments performed at different confining pressures. The axial stress-axial strain variations of the tested specimens revealed that the specimens undergoing unloading fail with a lower axial strain compared to the specimens failed purely by loading. Higher confining pressures were observed to exacerbate the difference. Volumetric strain versus axial strain curves indicated that the curves reverse the trend with the beginning of major damage of specimens. We suggest here a new form of equation to describe the secant modulus variation of brittle rocks against the axial stress for the unloading process. Failure mechanisms of tested specimens showed two distinct patterns, namely, specimens under pure loading failed with a single distinct shear fracture while for the unloading case specimens displayed multiple intersecting fractures. In addition, analysis of the evolution of dissipation and elastic energy during deformation of the specimens under loading and unloading conditions showed differentiable characteristics. Moreover, we evaluated the variations of two damage indices defined based on the energy dissipation and secant modulus evolution during deformation and observed that both of them satisfactorily distinguish key stages of damage evolution.
基金Supports from the University Transportation Center for Underground Transportation Infrastructure(UTC-UTI)at the Colorado School of Mines for funding this research under Grant No.69A3551747118 from the US Department of Transportation(DOT)the Fundamental Research Funds for the Central Universities under Grant No.A0920502052401-210 are gratefully acknowledged.
文摘From a practical point of view,grain structure heterogeneities are key parameters that control the rock response and still remains a challenge to incorporate in a quantitative manner.One of the less discussed topics in the context of the grain-based model(GBM)in the particle flow code(PFC)is the contact heterogeneities and the appropriate contact model to mimic the grain boundary behavior.Generally,the smooth joint(SJ)model and linear parallel bond(LPB)model are used to simulate the grain boundary behavior.However,the literature does not document the suitability of different models for specific problems.Another challenge in implementing GBM in PFC is that only a single bonding parameter is used at the grain boundaries.The aim of this study is to investigate the responses of a laboratory-scale specimen with SJ and LPB models,considering grain boundary heterogeneous and homogeneous contact parameters.Uniaxial and biaxial compression tests are performed to calibrate the response of Creighton granite.The stressestrain curves,volumetric dilation,inter-crack(crack in the grain boundary),and intra-crack(crack within the grain)development,and failure patterns associated with different contact models are examined.It was found that both the SJ and LPB models can reproduce the pre-peak behavior observed for a granitic rock type.However,the LPB model is unable to reproduce the post-peak behavior.Due to the large interlocking effect originating from the balls in contact and the ball size in the LPB model,local dilation is induced at the grain boundaries.This overestimates the volumetric dilation and residual shear strength.The LPB model tends to result in discontinuous inter-cracks and stress localization in the rock specimen,resulting in fine fragments at the rock surface during failure.
