Granites play a crucial role in the Earth's thermal regime and its evolution.Radiogenic heat production(RHP)by the decay of radioactive elements(U,Th,K)in granites is a significant parameter in estimating the ther...Granites play a crucial role in the Earth's thermal regime and its evolution.Radiogenic heat production(RHP)by the decay of radioactive elements(U,Th,K)in granites is a significant parameter in estimating the thermal structure of the lithosphere.RHP variability of granites with their emplacement ages could provide insights for thermal modeling in different geological epochs.An aggregated RHP from 2877 globally-distributed granitic samples of continental crust are analyzed for this study;these sample cover the entire geological history.The average bulk RHP in all types of granitic rocks of all ages is 2.92±1.86μW/m^(3).The RHP tends to increase gradually with progressively younger geologic emplacement age,based on a statistical analysis of the data.However,the youngest granites do not necessarily have the highest RHP.The mean RHP in 181 representative Cenozoic Himalayan leucogranitesdwhich are the youngest granites found on Earth,is as low as 1.84μW/m^(3).This is probably related to the initial conditions of magma formation,magmatic source material,and differentiation processes in the HimalayaneTibetan plateau.By correcting the decay factor,variations of the RHP in the emplaced granitic rocks are obtained,indicating the changing levels of heat production and different thermal regimes on Earth in various geological epochs.The highest RHP in granitic rocks emplaced in the Archean and Early Proterozoic corresponds to two global-scale collisional events during supercontinent cycles,at 2.7 and 1.9 Ga respectively.RHPs of granites can be an important indicator in the study of Earth's thermal regime and its evolution.展开更多
It is generally considered that granitic plutons are forcefully emplaced in acompressional setting and permissively emplaced in an extensional setting. This paper, however,shows that syn-kinematic (extensional) ellipt...It is generally considered that granitic plutons are forcefully emplaced in acompressional setting and permissively emplaced in an extensional setting. This paper, however,shows that syn-kinematic (extensional) elliptic granitic plutons in the Yagan-Onch Hayrhanmetamorphic core complex (MCC) have relatively strong forceful emplacement, which are indicated by(1) concentric distribution of the rock units, (2) a strain pattern with strong strains on themargins and low strains at the centre of a pluton, and particularly (3) syn-emplacement shorteningof the host rocks within the aureole. The strain analysis for the host rocks shows that thehost-rock ductile shortening, i.e. forceful emplacement, provides about 16-24 percent of theemplacement space for the present plutons. All these suggest that forceful emplacement occurs notonly in a compressional tectonic setting, but also in an extensional setting. This study furtherdemonstrates the significance of the multiple emplacement of granitic plutons and provides newinformation about the causality between granitic magmatism and the formation of the MCC and itsdynamics.展开更多
Late Carboniferous to Early Permian A-type granites are extensively distributed throughout the West Junggar region, NW China, and the Akebasitao pluton is extremely distinguished among these plutons. In this paper, we...Late Carboniferous to Early Permian A-type granites are extensively distributed throughout the West Junggar region, NW China, and the Akebasitao pluton is extremely distinguished among these plutons. In this paper, we reported new anisotropy of magnetic susceptible (AMS) data combine with detailed field study and audio magnetotelluric (AMT) sounding to assess the three-dimensional shape and magmatic emplacement mechanism of the Akebasitao pluton. The geological features and the AMT sounding indicate that the pluton had a slightly oblique movement of magma from northwest to southeast, which was most likely to correspond to an asymmetrical torch with a laccolith-shaped upper part, and a lower part formed by sub-vertical "root" that was located within its northwestern part, probably controlled by the NE-trending Anqi fault. The AMS fabrics of all the specimens reveal a low Pj value (mean of 1.02) and a low T value (mean of -0.024), suggesting that the deformation of the AMS ellipsoid is relatively weak. The specimens exhibit both oblate and prolate shapes of the AMS ellipsoid. Magnetic lineations and foliations are randomly distributed throughout the pluton without any preferred orientation. These AMS patterns indicate that the pluton formed in a relatively stable structural environment with no regional extrusion. Therefore, we propose a complex emplacement process in which the magmas reached the shallower crust levels via deep-faults and subsequently occupied the room created by doming, accompanied by stoping near the pluton roof. Additionally, the regional tectonic setting was relatively stable during the emplacement of the Akebasitao pluton, indicating the termination of compressional orogeny during the late Late Carboniferous in the West Junggar region. This conclusion perfectly coincides with the regional tectonic paleogeography, magmatic system, and paleostress field.展开更多
Emplacement ages, geochemical characteristics and analysis of continental dynamics on gabbroic intrusions in Luodian County, Guizhou Province, have been discussed based on studies of isotopic chronology (the whole-ro...Emplacement ages, geochemical characteristics and analysis of continental dynamics on gabbroic intrusions in Luodian County, Guizhou Province, have been discussed based on studies of isotopic chronology (the whole-rock Sm-Nd and Rb-Sr isochron methods), major elements, trace elements and PGE. Intrusive activities of the gabbroic intrusions in the study area took place during the Late Yanshanian Orogenic Movement (the Cretaceous Period), as indicated by the Sm-Nd isochron ages (t)=(99.6±4.5) (2σ) Ma and by the Rb-Sr isochron ages t=(97±1.6) (2σ) Ma. The gabbroic intrusions are attached to mafic rocks in cal-alkaline basaltic series. They occurred as dikes and might be formed under an extensional background of the continent. Differentiation of their magmatic crystallization resulted in obvious zonation of petrography. In the gabbroic intrusions of this study, large ion lithophile elements and LREE are enriched, and the chondrite-normalized REE distribution pattern is leftward inclined without anomalies of JCe or JEu, and there are high concentrations of PGE and ratios of Pd/Ir (averaging 4.21). All of these imply that their source areas may be basaltic magma in the upper mantle with high-level partial melting, derived from EMl-type enriched mantle. It is different from Emeishan basalt, which may be related to the upper mantle at low-grade partial melting. Emplacement mechanism of the gabbroic intrusions in this study may suppose to be asthenosphere upheaving as an isolated hot wave in the presence of mantle fluid, resulting in basaltic magma intruded into the continental crust as a diapiric intrusion. Therefore, uplifting of faulting-block and extensional deformation could take place in the shallow part of the continental crust while vertical amassing and accretion of magmatic materials in the deep part of the continental crust. These special processes could supposed to be a special background of continental dynamics for this large-scale epithermal metallogenic domain, such as Au, As, Sb and Hg deposits, and vertical uplifting of the Yunnan-Guizhou Plateau in the Cretaceous Period.展开更多
The Fenghuangshan Pluton is located in the Tongling polymineral-cluster district in the middle-lower section of the Yangtze metallogenic belt. In tectonic terms, it is in the middle of the Guichi-Fanchang faulted fold...The Fenghuangshan Pluton is located in the Tongling polymineral-cluster district in the middle-lower section of the Yangtze metallogenic belt. In tectonic terms, it is in the middle of the Guichi-Fanchang faulted fold bundle of the lower Yangtze Platform fold belt between the Dabie Orogenic Belt and the Jiangnan Massif. Analyses of the structural deformation characteristics of both the contact zone and the interior of the pluton are used to explain its emplacement mechanism. The foliation and lineation of the pluton, consisting of the oriented distribution of dark minerals and xenoliths, mainly concentrate along the margin of the pluton. Toward the center of the pluton, the foliation structure becomes weak, showing intense compression formation at the margin, and reflecting the conformable intrusion of the pluton. The relatively gentle lineation is evidence of a rotatory emplacement mechanism. Relatively steep marginal foliation reflects compression expanding. Affected by the thermal power of the pluton, the metamorphism of the contact zone has zonation. Both the strike of the axial plane of fold at the contact zone and that of the flow cleavage of the ductile shear zone are consistent with the boundary of the pluton, which reflects the speciality of conformable intrusion. The hinges of the folds are mostly inclined and erect, reflecting both the rotation of the pluton and its upward spiraling emplacement mechanism. Boudins developed in both the contact zone and the steep strata indicate the emplacement characteristic of the ballon expanding. The surrounding rock of the contact zone shortens horizontally. The average percentage of shortening is 39.7%, which further proves the mechanism of the pluton expanding, and the space occupied by the active expanding intrusion was provided by the shortening of the surrounding rock. The left-lateral shear shown by the ductile shear zone and the rheomorphic fold reveals that the pluton emplacement and the deformation of surrounding rock are controlled by a NNE-striking left-lateral shear stress field. These characteristics of pluton structures provide a mechanism of emplacement. In the deep, the pluton apirally rose left lateral, and in the shallow, the one forcefully emplaced balloningly.展开更多
About 300 mafic dykes are intruded Eocene volcanic and pyroclastic rocks,north east of Meshkinshahr city in the NW of Iran.Most of dyke swarms display NNE-SSE trend.Their composition varies from basalt to tephrite and
The Zhoukoudian stock in Beijing is a concentric zoned complex intrusive body formed by two successive intrusions. Quartz-diorite formed by the first intrusion is scattered sparsely on the margins of the body, while g...The Zhoukoudian stock in Beijing is a concentric zoned complex intrusive body formed by two successive intrusions. Quartz-diorite formed by the first intrusion is scattered sparsely on the margins of the body, while granodiorite resulting from the second intrusion constitutes the main part of the intrusion. It exhibits three distinct petrographic zones macroscopically, and is chemically characterized by enrichment of high-temperature components, such as Mg, Ca, Sc, Ti, Cr, Mn. Fe and Co, on its border and merely slight enrichment of some low-temperature components, such as Na and Si, in its central part. A series of structural features indicate that the deformation of the intrusion and thermo-metamorphic rocks becomes weaker with an increase of distance from the contact, and that the intrusive body is a product of ballooning or inflating diapiric emplacement. Based on calculations of the density, viscosity and yield strength of magma and the reasonable diffusion constants and oxygen isotopic data, the mechanism of the compositional zonation of the major part of the stock is discussed. It is considered that the Soret effect, combined with double-diffusive convection, can explain the compositional zonation of the intrusion. Calculation of the ascent rates of magma shows that successive upwelling of magma got faster and faster with the progress of time.展开更多
Remote sensing has played a pivotal role in our understanding of the geometry of dykes and dyke swarms on Earth,Venus and Mars(West and Ernst,1991;Mege and Masson,1995;Ernst et al.,2005).Since the 1970’s
Dayishan granite, a significant metallogenic-rock body located in Shaoyang-Chenxian tectonomagmatic belt of Hunan Province, was controlled by 'Dayishan-type' fault pattern. Based on the study of tectonic setti...Dayishan granite, a significant metallogenic-rock body located in Shaoyang-Chenxian tectonomagmatic belt of Hunan Province, was controlled by 'Dayishan-type' fault pattern. Based on the study of tectonic setting and geological features of the grantie, it is concluded that the tectonic system controlling magmatic emplacement is a shear folded-fauted zone which resulted from NW-trending convergent strike-slip faulting. The close relationship between the temporal-spatial distribution, emplacement mechanism of Dayishan granite and the strike-slip faulting is detailed.展开更多
The new micro-structural and magnetic fabric data on Cuizhao plutou and their emplacement implications are demonstrated in this peper. The magnetic foliations develop better and the degree of magnetic susceptibility a...The new micro-structural and magnetic fabric data on Cuizhao plutou and their emplacement implications are demonstrated in this peper. The magnetic foliations develop better and the degree of magnetic susceptibility anlsotropy is larger in the margin of the pluton than that in the center,which reveals mainly horizontal compression or magma during emplacement- The mapnetic lineations are not very well developed. The magnetic fabrics in the Cuizhao pluton reveal horizontal compression like the bollooning model during emplacement near the Earth surrace. This feature was fixed in later tectonic events.展开更多
Ophiolites represent on-land fragments of paleooceanic crust and have been recognized as one of the key markers of suture zones.Here,we provide new insights into the emplacement of ophiolitic mélanges based on de...Ophiolites represent on-land fragments of paleooceanic crust and have been recognized as one of the key markers of suture zones.Here,we provide new insights into the emplacement of ophiolitic mélanges based on detailed geological mapping and structural analysis in the West Junggar and Songpan-Ganzi-Bayan Har orogens(Fig.1 and Fig.2).The results show that some ophiolitic mélange belts cannot be regarded as suture zones.The distribution of these ophiolitic mélange belts are usually associated with the structural processes during the closure of remnant oceanic basins.After the remnant-oceanic basin is filled with thick clastic deposit,the oceanic lithosphere material as the base of the remnant basin can be injected into the overlying sedimentary strata through various faultings under the regional compressive stress,forming the remnant oceanic basintype ophiolitic mélange system with dispersive distribution characteristics.Combining with previous researches,the emplacement mechanism of ophiolitic mélanges can be divided into four categories:subduction type which oceanic lithosphere subducted beneath active continental margin,obduction type which oceanic lithosphere obducted over passive continental margin,collision type between two continental lithospheres,and closure type of remnant-oceanic basin(Fig.3).These different types of ophiolitic mélange belts will be superimposed and even re-emplacement by the tectonic processes of post-plate convergence,complicating their distribution.Therefore,identifying the emplacement mechanism type of ophiolitic mélange belts formed in different tectonic processes and backgrounds is of importance for understanding the process of ocean-continental transition and the evolution of orogenic belts.展开更多
Prolonged extensional regime in peninsular India resulted in formation of rift and grabens,elongated basins and Gondwana sedimentation along them.Downward progression of rift related faults caused decompression
1 Introduction The North China Craton(NCC)has experienced lithospheric destruction in Mesozoic accompanied with crustal exhumation.Fission track or(U-Th)/He dating of zircon and apatite for the Mesozoic granitoids in the
The Moyar-Bhavani Shear Zone(MBSZ)of the South Indian Granulite Terrain(SIGT),a complex continental block formed by the accretion of various crustal units during the Archaean to Neoproterozoic,bear evidences of
The Molopo Farms Complex(MFC)is a 13000 km2layered,mafic-ultramafic intrusion straddling the southern border of Botswana with South Africa.It does not outcrop due to Cenozoic cover,but is believed to intrude the
We illustrate intricate genetic relationship between prolonged extensional tectonics,formation of several sedimentary basins,enormous Cretaceous volcanism and emplacement of great dyke swarms as well assequential
Excellent outcrops in Matale Sri Lanka provide unique insight into the emplacement and evolution history of hydrothermal and pegmatitic rocks in the central highlands of Sri Lanka. Field, structural, petrological, the...Excellent outcrops in Matale Sri Lanka provide unique insight into the emplacement and evolution history of hydrothermal and pegmatitic rocks in the central highlands of Sri Lanka. Field, structural, petrological, thermo-barometric studies in the metamorphic basement rocks in the central highlands and related hydrothermal deposits are presented in this study. Detailed petrographic and mineralogical data reveal peak metamorphic conditions for the crustal unit in the study area as 854 ± 44oC at 10.83 ± 0.86 kbar. Hydrothermal veins consisting of quartz and mica are closely related to cross-cutting pegmatites, which significantly post-date the peak metamorphic conditions of the crustal unit. Field relations indicate that the veins originated as ductile-brittle fractures have subsequently sealed by pegmatites and hydrothermal crystallization. Geological, textural and mineralogical data suggest that most enriched hydrothermal veins have evolved from a fractionated granitic melt progressively enriched in H2O, F, etc. Quartz, K-feldspar, mica, tourmaline, fluorite and topaz bear evidence of multistage crystallization that alternated with episodes of resorption. It was suggested that the level of emplacement of pegmatites of the Matale District was middle crust, near the crustal scale brittle-ductile transition zone at a temperature of about 600oC. For this crustal level and temperature range, it is considered very unlikely that intruding pegmatitic melts followed pre-existing cracks. As such the emplacement temperatures of the pegmatites could be well below the peak metamorphic estimates in the mafic granulites. The metamorphic P-T strategy and position of formation of hydrothermal deposits and pegmatites is summarized in the modified P-T-t-D diagrams.展开更多
South Nam Xe carbonatites are located in northwest Vietnam and include calcio-and ferro-carbonatite dikes.This investigation on their petrography,mineralogy and whole rock chemistry aims to constrain temporal emplacem...South Nam Xe carbonatites are located in northwest Vietnam and include calcio-and ferro-carbonatite dikes.This investigation on their petrography,mineralogy and whole rock chemistry aims to constrain temporal emplacement sequence of the carbonatites during their evolution.The calciocarbonatites are supposed to be formed in the first or second stage due to massive coarse-grained texture with an assemblage of calcite,typical magmatic alkaline silicates(aegirine,arfvedsonite),biotite,fluorapatite and magnetite.Their calcites show a high CaO/(MgO+Fe_(2)O_(3)+MnO)ratio and a predominance of SrO over MnO(SrO=3.81-3.98 wt.%;MnO=0.66-0.78 wt.%).Rare earth elements(REE)tend to participate in rock-forming minerals rather than in isolated REE minerals.The ferrocarbonatites are composed of magmatic and hydrothermal varieties and assumed to be formed in the third and/or fourth stage.Major minerals of the former include zoned ankerite,Sr-rich calcite,subhedral feldspar crystals,phlogopite and magnetite;fluorapatite,monazite and REE carbonates are minor resulting in a moderate REE concentration of 43,200 ppm.Meanwhile,the latter is predominant by syntax-texture REE fluorcarbonates and(Ba,Sr)sulphates.Further,the highest REE concentration(163,900 ppm)of the rock coupled with abundance of volatile minerals(fluorite,fluorcarbonates,sulphides)and ^(18)O enrichment in the calcites(δ^(18)O_(V-SMOW)=12.01-13.26‰)is probably attributed to hydrothermal subjection in the last stage.展开更多
基金This study was financially supported by National Key Research and Development projects(No.2019YFC0604903,No.2021YFA0716004)by Joint Funds of the National Natural Science Foundation of China(Grant No.U20B6001).
文摘Granites play a crucial role in the Earth's thermal regime and its evolution.Radiogenic heat production(RHP)by the decay of radioactive elements(U,Th,K)in granites is a significant parameter in estimating the thermal structure of the lithosphere.RHP variability of granites with their emplacement ages could provide insights for thermal modeling in different geological epochs.An aggregated RHP from 2877 globally-distributed granitic samples of continental crust are analyzed for this study;these sample cover the entire geological history.The average bulk RHP in all types of granitic rocks of all ages is 2.92±1.86μW/m^(3).The RHP tends to increase gradually with progressively younger geologic emplacement age,based on a statistical analysis of the data.However,the youngest granites do not necessarily have the highest RHP.The mean RHP in 181 representative Cenozoic Himalayan leucogranitesdwhich are the youngest granites found on Earth,is as low as 1.84μW/m^(3).This is probably related to the initial conditions of magma formation,magmatic source material,and differentiation processes in the HimalayaneTibetan plateau.By correcting the decay factor,variations of the RHP in the emplaced granitic rocks are obtained,indicating the changing levels of heat production and different thermal regimes on Earth in various geological epochs.The highest RHP in granitic rocks emplaced in the Archean and Early Proterozoic corresponds to two global-scale collisional events during supercontinent cycles,at 2.7 and 1.9 Ga respectively.RHPs of granites can be an important indicator in the study of Earth's thermal regime and its evolution.
基金the National Natural Science Foundation of China(grant 49872072) the Postdoctoral Foundation of China.
文摘It is generally considered that granitic plutons are forcefully emplaced in acompressional setting and permissively emplaced in an extensional setting. This paper, however,shows that syn-kinematic (extensional) elliptic granitic plutons in the Yagan-Onch Hayrhanmetamorphic core complex (MCC) have relatively strong forceful emplacement, which are indicated by(1) concentric distribution of the rock units, (2) a strain pattern with strong strains on themargins and low strains at the centre of a pluton, and particularly (3) syn-emplacement shorteningof the host rocks within the aureole. The strain analysis for the host rocks shows that thehost-rock ductile shortening, i.e. forceful emplacement, provides about 16-24 percent of theemplacement space for the present plutons. All these suggest that forceful emplacement occurs notonly in a compressional tectonic setting, but also in an extensional setting. This study furtherdemonstrates the significance of the multiple emplacement of granitic plutons and provides newinformation about the causality between granitic magmatism and the formation of the MCC and itsdynamics.
基金funded by the China Geological Survey (Grant Nos.1212011120502,1212011220245)
文摘Late Carboniferous to Early Permian A-type granites are extensively distributed throughout the West Junggar region, NW China, and the Akebasitao pluton is extremely distinguished among these plutons. In this paper, we reported new anisotropy of magnetic susceptible (AMS) data combine with detailed field study and audio magnetotelluric (AMT) sounding to assess the three-dimensional shape and magmatic emplacement mechanism of the Akebasitao pluton. The geological features and the AMT sounding indicate that the pluton had a slightly oblique movement of magma from northwest to southeast, which was most likely to correspond to an asymmetrical torch with a laccolith-shaped upper part, and a lower part formed by sub-vertical "root" that was located within its northwestern part, probably controlled by the NE-trending Anqi fault. The AMS fabrics of all the specimens reveal a low Pj value (mean of 1.02) and a low T value (mean of -0.024), suggesting that the deformation of the AMS ellipsoid is relatively weak. The specimens exhibit both oblate and prolate shapes of the AMS ellipsoid. Magnetic lineations and foliations are randomly distributed throughout the pluton without any preferred orientation. These AMS patterns indicate that the pluton formed in a relatively stable structural environment with no regional extrusion. Therefore, we propose a complex emplacement process in which the magmas reached the shallower crust levels via deep-faults and subsequently occupied the room created by doming, accompanied by stoping near the pluton roof. Additionally, the regional tectonic setting was relatively stable during the emplacement of the Akebasitao pluton, indicating the termination of compressional orogeny during the late Late Carboniferous in the West Junggar region. This conclusion perfectly coincides with the regional tectonic paleogeography, magmatic system, and paleostress field.
文摘Emplacement ages, geochemical characteristics and analysis of continental dynamics on gabbroic intrusions in Luodian County, Guizhou Province, have been discussed based on studies of isotopic chronology (the whole-rock Sm-Nd and Rb-Sr isochron methods), major elements, trace elements and PGE. Intrusive activities of the gabbroic intrusions in the study area took place during the Late Yanshanian Orogenic Movement (the Cretaceous Period), as indicated by the Sm-Nd isochron ages (t)=(99.6±4.5) (2σ) Ma and by the Rb-Sr isochron ages t=(97±1.6) (2σ) Ma. The gabbroic intrusions are attached to mafic rocks in cal-alkaline basaltic series. They occurred as dikes and might be formed under an extensional background of the continent. Differentiation of their magmatic crystallization resulted in obvious zonation of petrography. In the gabbroic intrusions of this study, large ion lithophile elements and LREE are enriched, and the chondrite-normalized REE distribution pattern is leftward inclined without anomalies of JCe or JEu, and there are high concentrations of PGE and ratios of Pd/Ir (averaging 4.21). All of these imply that their source areas may be basaltic magma in the upper mantle with high-level partial melting, derived from EMl-type enriched mantle. It is different from Emeishan basalt, which may be related to the upper mantle at low-grade partial melting. Emplacement mechanism of the gabbroic intrusions in this study may suppose to be asthenosphere upheaving as an isolated hot wave in the presence of mantle fluid, resulting in basaltic magma intruded into the continental crust as a diapiric intrusion. Therefore, uplifting of faulting-block and extensional deformation could take place in the shallow part of the continental crust while vertical amassing and accretion of magmatic materials in the deep part of the continental crust. These special processes could supposed to be a special background of continental dynamics for this large-scale epithermal metallogenic domain, such as Au, As, Sb and Hg deposits, and vertical uplifting of the Yunnan-Guizhou Plateau in the Cretaceous Period.
基金the Major State Basic Research Program(No.G1999043206)the Project of National Natrual Science Foundation of China(No.40372050) the Project of Resources Assessment of the China Geological Survey(No.200310200064).
文摘The Fenghuangshan Pluton is located in the Tongling polymineral-cluster district in the middle-lower section of the Yangtze metallogenic belt. In tectonic terms, it is in the middle of the Guichi-Fanchang faulted fold bundle of the lower Yangtze Platform fold belt between the Dabie Orogenic Belt and the Jiangnan Massif. Analyses of the structural deformation characteristics of both the contact zone and the interior of the pluton are used to explain its emplacement mechanism. The foliation and lineation of the pluton, consisting of the oriented distribution of dark minerals and xenoliths, mainly concentrate along the margin of the pluton. Toward the center of the pluton, the foliation structure becomes weak, showing intense compression formation at the margin, and reflecting the conformable intrusion of the pluton. The relatively gentle lineation is evidence of a rotatory emplacement mechanism. Relatively steep marginal foliation reflects compression expanding. Affected by the thermal power of the pluton, the metamorphism of the contact zone has zonation. Both the strike of the axial plane of fold at the contact zone and that of the flow cleavage of the ductile shear zone are consistent with the boundary of the pluton, which reflects the speciality of conformable intrusion. The hinges of the folds are mostly inclined and erect, reflecting both the rotation of the pluton and its upward spiraling emplacement mechanism. Boudins developed in both the contact zone and the steep strata indicate the emplacement characteristic of the ballon expanding. The surrounding rock of the contact zone shortens horizontally. The average percentage of shortening is 39.7%, which further proves the mechanism of the pluton expanding, and the space occupied by the active expanding intrusion was provided by the shortening of the surrounding rock. The left-lateral shear shown by the ductile shear zone and the rheomorphic fold reveals that the pluton emplacement and the deformation of surrounding rock are controlled by a NNE-striking left-lateral shear stress field. These characteristics of pluton structures provide a mechanism of emplacement. In the deep, the pluton apirally rose left lateral, and in the shallow, the one forcefully emplaced balloningly.
文摘About 300 mafic dykes are intruded Eocene volcanic and pyroclastic rocks,north east of Meshkinshahr city in the NW of Iran.Most of dyke swarms display NNE-SSE trend.Their composition varies from basalt to tephrite and
文摘The Zhoukoudian stock in Beijing is a concentric zoned complex intrusive body formed by two successive intrusions. Quartz-diorite formed by the first intrusion is scattered sparsely on the margins of the body, while granodiorite resulting from the second intrusion constitutes the main part of the intrusion. It exhibits three distinct petrographic zones macroscopically, and is chemically characterized by enrichment of high-temperature components, such as Mg, Ca, Sc, Ti, Cr, Mn. Fe and Co, on its border and merely slight enrichment of some low-temperature components, such as Na and Si, in its central part. A series of structural features indicate that the deformation of the intrusion and thermo-metamorphic rocks becomes weaker with an increase of distance from the contact, and that the intrusive body is a product of ballooning or inflating diapiric emplacement. Based on calculations of the density, viscosity and yield strength of magma and the reasonable diffusion constants and oxygen isotopic data, the mechanism of the compositional zonation of the major part of the stock is discussed. It is considered that the Soret effect, combined with double-diffusive convection, can explain the compositional zonation of the intrusion. Calculation of the ascent rates of magma shows that successive upwelling of magma got faster and faster with the progress of time.
文摘Remote sensing has played a pivotal role in our understanding of the geometry of dykes and dyke swarms on Earth,Venus and Mars(West and Ernst,1991;Mege and Masson,1995;Ernst et al.,2005).Since the 1970’s
文摘Dayishan granite, a significant metallogenic-rock body located in Shaoyang-Chenxian tectonomagmatic belt of Hunan Province, was controlled by 'Dayishan-type' fault pattern. Based on the study of tectonic setting and geological features of the grantie, it is concluded that the tectonic system controlling magmatic emplacement is a shear folded-fauted zone which resulted from NW-trending convergent strike-slip faulting. The close relationship between the temporal-spatial distribution, emplacement mechanism of Dayishan granite and the strike-slip faulting is detailed.
文摘The new micro-structural and magnetic fabric data on Cuizhao plutou and their emplacement implications are demonstrated in this peper. The magnetic foliations develop better and the degree of magnetic susceptibility anlsotropy is larger in the margin of the pluton than that in the center,which reveals mainly horizontal compression or magma during emplacement- The mapnetic lineations are not very well developed. The magnetic fabrics in the Cuizhao pluton reveal horizontal compression like the bollooning model during emplacement near the Earth surrace. This feature was fixed in later tectonic events.
基金granted by the China Geological Survey(Grand No.1212011220245,DD20179607,DD20160060)
文摘Ophiolites represent on-land fragments of paleooceanic crust and have been recognized as one of the key markers of suture zones.Here,we provide new insights into the emplacement of ophiolitic mélanges based on detailed geological mapping and structural analysis in the West Junggar and Songpan-Ganzi-Bayan Har orogens(Fig.1 and Fig.2).The results show that some ophiolitic mélange belts cannot be regarded as suture zones.The distribution of these ophiolitic mélange belts are usually associated with the structural processes during the closure of remnant oceanic basins.After the remnant-oceanic basin is filled with thick clastic deposit,the oceanic lithosphere material as the base of the remnant basin can be injected into the overlying sedimentary strata through various faultings under the regional compressive stress,forming the remnant oceanic basintype ophiolitic mélange system with dispersive distribution characteristics.Combining with previous researches,the emplacement mechanism of ophiolitic mélanges can be divided into four categories:subduction type which oceanic lithosphere subducted beneath active continental margin,obduction type which oceanic lithosphere obducted over passive continental margin,collision type between two continental lithospheres,and closure type of remnant-oceanic basin(Fig.3).These different types of ophiolitic mélange belts will be superimposed and even re-emplacement by the tectonic processes of post-plate convergence,complicating their distribution.Therefore,identifying the emplacement mechanism type of ophiolitic mélange belts formed in different tectonic processes and backgrounds is of importance for understanding the process of ocean-continental transition and the evolution of orogenic belts.
文摘Prolonged extensional regime in peninsular India resulted in formation of rift and grabens,elongated basins and Gondwana sedimentation along them.Downward progression of rift related faults caused decompression
基金supported by the National Natural Science Foundation of China (Grant No. 41230311)National Key Research and Development Program of China (Grant No. 2016YFC0600106)
文摘1 Introduction The North China Craton(NCC)has experienced lithospheric destruction in Mesozoic accompanied with crustal exhumation.Fission track or(U-Th)/He dating of zircon and apatite for the Mesozoic granitoids in the
文摘The Moyar-Bhavani Shear Zone(MBSZ)of the South Indian Granulite Terrain(SIGT),a complex continental block formed by the accretion of various crustal units during the Archaean to Neoproterozoic,bear evidences of
文摘The Molopo Farms Complex(MFC)is a 13000 km2layered,mafic-ultramafic intrusion straddling the southern border of Botswana with South Africa.It does not outcrop due to Cenozoic cover,but is believed to intrude the
文摘We illustrate intricate genetic relationship between prolonged extensional tectonics,formation of several sedimentary basins,enormous Cretaceous volcanism and emplacement of great dyke swarms as well assequential
文摘Excellent outcrops in Matale Sri Lanka provide unique insight into the emplacement and evolution history of hydrothermal and pegmatitic rocks in the central highlands of Sri Lanka. Field, structural, petrological, thermo-barometric studies in the metamorphic basement rocks in the central highlands and related hydrothermal deposits are presented in this study. Detailed petrographic and mineralogical data reveal peak metamorphic conditions for the crustal unit in the study area as 854 ± 44oC at 10.83 ± 0.86 kbar. Hydrothermal veins consisting of quartz and mica are closely related to cross-cutting pegmatites, which significantly post-date the peak metamorphic conditions of the crustal unit. Field relations indicate that the veins originated as ductile-brittle fractures have subsequently sealed by pegmatites and hydrothermal crystallization. Geological, textural and mineralogical data suggest that most enriched hydrothermal veins have evolved from a fractionated granitic melt progressively enriched in H2O, F, etc. Quartz, K-feldspar, mica, tourmaline, fluorite and topaz bear evidence of multistage crystallization that alternated with episodes of resorption. It was suggested that the level of emplacement of pegmatites of the Matale District was middle crust, near the crustal scale brittle-ductile transition zone at a temperature of about 600oC. For this crustal level and temperature range, it is considered very unlikely that intruding pegmatitic melts followed pre-existing cracks. As such the emplacement temperatures of the pegmatites could be well below the peak metamorphic estimates in the mafic granulites. The metamorphic P-T strategy and position of formation of hydrothermal deposits and pegmatites is summarized in the modified P-T-t-D diagrams.
文摘South Nam Xe carbonatites are located in northwest Vietnam and include calcio-and ferro-carbonatite dikes.This investigation on their petrography,mineralogy and whole rock chemistry aims to constrain temporal emplacement sequence of the carbonatites during their evolution.The calciocarbonatites are supposed to be formed in the first or second stage due to massive coarse-grained texture with an assemblage of calcite,typical magmatic alkaline silicates(aegirine,arfvedsonite),biotite,fluorapatite and magnetite.Their calcites show a high CaO/(MgO+Fe_(2)O_(3)+MnO)ratio and a predominance of SrO over MnO(SrO=3.81-3.98 wt.%;MnO=0.66-0.78 wt.%).Rare earth elements(REE)tend to participate in rock-forming minerals rather than in isolated REE minerals.The ferrocarbonatites are composed of magmatic and hydrothermal varieties and assumed to be formed in the third and/or fourth stage.Major minerals of the former include zoned ankerite,Sr-rich calcite,subhedral feldspar crystals,phlogopite and magnetite;fluorapatite,monazite and REE carbonates are minor resulting in a moderate REE concentration of 43,200 ppm.Meanwhile,the latter is predominant by syntax-texture REE fluorcarbonates and(Ba,Sr)sulphates.Further,the highest REE concentration(163,900 ppm)of the rock coupled with abundance of volatile minerals(fluorite,fluorcarbonates,sulphides)and ^(18)O enrichment in the calcites(δ^(18)O_(V-SMOW)=12.01-13.26‰)is probably attributed to hydrothermal subjection in the last stage.