Composite granitic pluton with distinct units is a potential target for identifying its detailed magma evolution.Here,we present zircon U-Pb ages and Hf isotope,whole-rock major and trace element compositions and Nd-P...Composite granitic pluton with distinct units is a potential target for identifying its detailed magma evolution.Here,we present zircon U-Pb ages and Hf isotope,whole-rock major and trace element compositions and Nd-Pb isotopes of the Wangxiang composite pluton,South China.New ages obtained show that these rocks were generated in Late Jurassic(ca.156–158 Ma).The rocks are divided into low silica(SiO_(2)<67 wt.%,biotite granodiorites and their dioritic enclaves)and high silica ones(SiO_(2)>71 wt.%,two-mica granites,garnet-bearing muscovite granites and muscovite granites).The high silica rocks are enriched in light rare earth elements(LREEs)relative to heavy REEs(HREEs)((La/Yb)_(N)=15.6–41.9,while the low silica rocks are not(0.7–76.6).All rocks show various negative Ti,Sr,Eu and strong positive Pb anomalies.The low silica rocks have less negative values ofε_(Nd)(t)(-8.79 to-6.99),similar values of~((206)Pb/^(204)Pb)_(i)(18.155–18.346)andε_(Hf)(t)(-9.51 to-3.47,except one-12.84),compared to the high silica rocks(ε_(Nd)(t)=-11.14 to-10.26;^((206)Pb/^(204)Pb)_(i)=17.935–19.093;ε_(Hf)(t)=-12.03 to-7.15,except one-2.41).Data suggest that the parental magma of the studied rocks(represented by enclaves)was produced by partial melting of a garnet-free crustal source.Subsequently those crustal magmas formed the more evolved units through assimilation and fractional crystallization processes,and fluid enrichment during the final magmatic activity.Combining our results with previous multidisciplinary studies,we propose that the key factor to control the evolution of Wangxiang composite pluton is discrete emplacement of crustal magmas by dyking.展开更多
The Guanpo pegmatite field in the North Qinling orogenic belt(NQB),China,hosts the most abundant LCT pegmatites.However,their emplacement conditions and structural control remain unexplored.In this contribution,we inv...The Guanpo pegmatite field in the North Qinling orogenic belt(NQB),China,hosts the most abundant LCT pegmatites.However,their emplacement conditions and structural control remain unexplored.In this contribution,we investigated it combining pegmatite orientation measurement with oxygen isotope geothermometry and fluid inclusion study.The orientations of type A1 pegmatites(P_(f)<σ_(2))are predominantly influenced by P-and T-fractures due to simple shearing in Shiziping dextral thrust shear zone during D_(2)deformation,whereas type A2 pegmatites(contemporaneous with D_(4))are governed by hydraulic fractures aligned with S_(0)and S_(0+1)stemming from fluid pressure(P_(f)<σ_(2)).Additionally,type B pegmatites(P_(f)≤σ_(2))exhibit orientations shaped by en echelon extensional fractures in local ductile shear zones(contemporaneous with D_(3)).The albite-quartz oxygen isotope geothermometry and microthermometric analysis of fluid inclusions in elbaites from the latest pegmatites(including types B and A2)suggest that the crystallization P-T for late magmatic and hydrothermal stages are 527.5-559.2℃,320℃,3.1-3.6 kbar and 2.0 kbar,respectively.Our observations along with previous studies suggest that the genesis of the LCT pegmatites was a long-term,multi-stage event during early Paleozoic orogeny(including the collision stage)of the NQB,and was facilitated by various local fractures.展开更多
Quartz vein-type tungsten deposits are a common W deposit type.Their ore vein distribution was previously considered to be controlled by regional horizontal tectonic stress.In this paper,14 tungsten deposits with fan-...Quartz vein-type tungsten deposits are a common W deposit type.Their ore vein distribution was previously considered to be controlled by regional horizontal tectonic stress.In this paper,14 tungsten deposits with fan-shaped mineralization in SE China are summarized,and the relations between their ore veins and granite and the ore-forming structural stress field are analyzed.These deposits have a post-magmatic hydrothermal genesis and involve the formation of two sets of veins with similar strike and opposite dips at the top of the ore-causative granite bodies,forming a vertical fan-shaped profile.Their ore veins were coeval with the underlying granite bodies,and generally extend along the long axis of the granite.In such fan-shaped ore formation,the stress is highly focused at the top of the granite and gradually weakens outward.The maximum principal stress(σ1)is perpendicular to the granite contact surface,and radiates outward from the pluton.Meanwhile,the minimum principal stress(σ3)forms an arc-shaped band parallel to the contact surface.Our findings,together with published numerical modeling indicate that the emplacement dynamics of granitic magma(rather than regional horizontal tectonic stress)are essential controls on the distribution of ore veins in quartz vein-type tungsten deposits.展开更多
The late Palaeozoic tectonic magmatism in the north-ern Qaidam tectonic belt(NQTB)related to the Palaeo-Tethys Ocean has become a critical issue.We performed a detailed geochronological and geochemical study of Lenghu...The late Palaeozoic tectonic magmatism in the north-ern Qaidam tectonic belt(NQTB)related to the Palaeo-Tethys Ocean has become a critical issue.We performed a detailed geochronological and geochemical study of Lenghu(LH)granitic rocks in the western NQTB.LA-ICP-MS U-Pb dating of zircons from LH granitic rocks yields emplacement ages of 253±4 Ma and 264±4 Ma,indicating a two-stage emplacement process.Geochemi-cal analyses show that the LH granitic rocks have low ACNK values and are enriched in LILEs(Rb,Th,Ba)and depleted in HFSEs(Sr,Nd,and Ta).The samples are enriched in LREEs(LREE/HREE=1.5-7.3).Values of(La/Yb)N range between 0.9 and 6.5,and all samples show negative Eu anomalies(δEu=0.2-0.6),with typical characteristics of island arc magmatism.The LH granitic rocks haveεHf(t)values of-3.7 to+8.0 and yield a TCDM age of 1.51-0.78 Ga.The data suggest that the LH granitic rocks were derived from partial melting of Proterozoic crust-related mafic to intermediate rocks with significant crust-mantle interac-tions.The results,combined with regional magmatic informa-tion,indicate that the Late Permian-early Triassic magmatism in western NQTB were controlled by subduction rollback-retraction of South Kunlun Oceanic plate under the Kun-lun-Qaidam Block.展开更多
Gabbroic and poikilitic shergottites are intrusive igneous rocks on Mars,providing significant insights into the igneous processes within the Martian crust.However,questions remain regarding the chemical signatures of...Gabbroic and poikilitic shergottites are intrusive igneous rocks on Mars,providing significant insights into the igneous processes within the Martian crust.However,questions remain regarding the chemical signatures of their source reservoirs and the petrogenetic links among shergottites of different subtypes.In this study,we present petrological and mineralogical analyses of the intermediate shergottite Northwest Africa(NWA)12241.Quantitative textural analysis and pyroxene chemistry indicate that,despite minor differences such as the accumulation of intermediate-sized olivine and smaller pyroxene oikocrysts,NWA 12241 has experienced a similar emplacement history as typical poikilitic and gabbroic shergottites.The estimated parent melt of NWA 12241 is consistent with derivation from an intermediate source reservoir,resulting from the mixing of enriched and depleted mantle end-members at depth,prior to magma ascent.Similar emplacement histories of variable poikilitic and gabbroic shergottites suggest the common presence of multiple staging magma chambers with different compositions at the crust–mantle boundary,coupled with prolonged ponding at this depth.Our study highlights that,in addition to magma mixing and assimilation,magmatic differentiation and cooling conditions at shallow depths are crucial processes leading to textural and compositional variations among shergottites of different subtypes.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
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
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
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
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
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
Jingshan superlarge gold deposit is a typical deposit closely related to the ductile shear zone, developing the economic enrichment during the transition form the ductile deformation to the brittle deformation. The or...Jingshan superlarge gold deposit is a typical deposit closely related to the ductile shear zone, developing the economic enrichment during the transition form the ductile deformation to the brittle deformation. The oreforming process of Jingshan Au deposit can be described as the development of marine volcanicturbidity current Aubearing initial sedimentation→regional metamorphism and the first enrichment→strong transformation of dynamic metamorphism and deformation→orecontrolling and oreholding of ductile shear structure→supperimposed transformation and enrichment of magmahydrothermal solution. This process can be summarized as the “sourcemigrationaccumulation” metallogenicgeochemical process of Au. The proved Au reserve of this deposit has ex ceeded 100 t and its prospect of searching for ore is considerable. So it is called the only superlarge gold deposit in the south of the lower reach of the Yangtze River, China.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
基金provided by the National Natural Science Foundation of China(No.41002022)the National Key R&D Program of China(No.2017YFC0602402)+3 种基金the Provincial Natural Science Foundation of Hunan(No.2019JJ50831)the Opening Foundation of State Key Laboratory of Continental Dynamics,Northwest University(No.20LCD08)the Funded by Open Research Fund Programme of the Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring(Central South University),Ministry of Education(No.2018YSJS07)Bruna B.Carvalho is thankful to MIUR(Ministero dell’Istruzione,dell’Universitàe della Ricerca)for the award of a grant(No.PNRA18_00103)。
文摘Composite granitic pluton with distinct units is a potential target for identifying its detailed magma evolution.Here,we present zircon U-Pb ages and Hf isotope,whole-rock major and trace element compositions and Nd-Pb isotopes of the Wangxiang composite pluton,South China.New ages obtained show that these rocks were generated in Late Jurassic(ca.156–158 Ma).The rocks are divided into low silica(SiO_(2)<67 wt.%,biotite granodiorites and their dioritic enclaves)and high silica ones(SiO_(2)>71 wt.%,two-mica granites,garnet-bearing muscovite granites and muscovite granites).The high silica rocks are enriched in light rare earth elements(LREEs)relative to heavy REEs(HREEs)((La/Yb)_(N)=15.6–41.9,while the low silica rocks are not(0.7–76.6).All rocks show various negative Ti,Sr,Eu and strong positive Pb anomalies.The low silica rocks have less negative values ofε_(Nd)(t)(-8.79 to-6.99),similar values of~((206)Pb/^(204)Pb)_(i)(18.155–18.346)andε_(Hf)(t)(-9.51 to-3.47,except one-12.84),compared to the high silica rocks(ε_(Nd)(t)=-11.14 to-10.26;^((206)Pb/^(204)Pb)_(i)=17.935–19.093;ε_(Hf)(t)=-12.03 to-7.15,except one-2.41).Data suggest that the parental magma of the studied rocks(represented by enclaves)was produced by partial melting of a garnet-free crustal source.Subsequently those crustal magmas formed the more evolved units through assimilation and fractional crystallization processes,and fluid enrichment during the final magmatic activity.Combining our results with previous multidisciplinary studies,we propose that the key factor to control the evolution of Wangxiang composite pluton is discrete emplacement of crustal magmas by dyking.
基金supported by the National Key R&D Program of China(Grant Nos.2021YFC2901902 and 2019YFC0605202)。
文摘The Guanpo pegmatite field in the North Qinling orogenic belt(NQB),China,hosts the most abundant LCT pegmatites.However,their emplacement conditions and structural control remain unexplored.In this contribution,we investigated it combining pegmatite orientation measurement with oxygen isotope geothermometry and fluid inclusion study.The orientations of type A1 pegmatites(P_(f)<σ_(2))are predominantly influenced by P-and T-fractures due to simple shearing in Shiziping dextral thrust shear zone during D_(2)deformation,whereas type A2 pegmatites(contemporaneous with D_(4))are governed by hydraulic fractures aligned with S_(0)and S_(0+1)stemming from fluid pressure(P_(f)<σ_(2)).Additionally,type B pegmatites(P_(f)≤σ_(2))exhibit orientations shaped by en echelon extensional fractures in local ductile shear zones(contemporaneous with D_(3)).The albite-quartz oxygen isotope geothermometry and microthermometric analysis of fluid inclusions in elbaites from the latest pegmatites(including types B and A2)suggest that the crystallization P-T for late magmatic and hydrothermal stages are 527.5-559.2℃,320℃,3.1-3.6 kbar and 2.0 kbar,respectively.Our observations along with previous studies suggest that the genesis of the LCT pegmatites was a long-term,multi-stage event during early Paleozoic orogeny(including the collision stage)of the NQB,and was facilitated by various local fractures.
基金funded by the National Key Research&Development Program of China(No.2021YFC2900100)the Guangxi Natural Science Foundation(No.2022GXNSFFA035025)+3 种基金the Chinese National Natural Science Foundation(No.42372099)the China Geological Survey(No.DD20190379)the Science&Technology Fundamental Resources Investigation Program(No.2022FY101800)the Major Talent Program of Guangxi Zhuang Autonomous Region,and the Innovation Project of Guangxi Graduate Education(No.YCSW2023345)。
文摘Quartz vein-type tungsten deposits are a common W deposit type.Their ore vein distribution was previously considered to be controlled by regional horizontal tectonic stress.In this paper,14 tungsten deposits with fan-shaped mineralization in SE China are summarized,and the relations between their ore veins and granite and the ore-forming structural stress field are analyzed.These deposits have a post-magmatic hydrothermal genesis and involve the formation of two sets of veins with similar strike and opposite dips at the top of the ore-causative granite bodies,forming a vertical fan-shaped profile.Their ore veins were coeval with the underlying granite bodies,and generally extend along the long axis of the granite.In such fan-shaped ore formation,the stress is highly focused at the top of the granite and gradually weakens outward.The maximum principal stress(σ1)is perpendicular to the granite contact surface,and radiates outward from the pluton.Meanwhile,the minimum principal stress(σ3)forms an arc-shaped band parallel to the contact surface.Our findings,together with published numerical modeling indicate that the emplacement dynamics of granitic magma(rather than regional horizontal tectonic stress)are essential controls on the distribution of ore veins in quartz vein-type tungsten deposits.
基金supported by the National Natural Science Foundation of China(No.41702204)the China Geology Survey(grant number DD20189614)the Basic Science Founda-tion of the Institute of Geomechanics(grant DZLXJK202004).
文摘The late Palaeozoic tectonic magmatism in the north-ern Qaidam tectonic belt(NQTB)related to the Palaeo-Tethys Ocean has become a critical issue.We performed a detailed geochronological and geochemical study of Lenghu(LH)granitic rocks in the western NQTB.LA-ICP-MS U-Pb dating of zircons from LH granitic rocks yields emplacement ages of 253±4 Ma and 264±4 Ma,indicating a two-stage emplacement process.Geochemi-cal analyses show that the LH granitic rocks have low ACNK values and are enriched in LILEs(Rb,Th,Ba)and depleted in HFSEs(Sr,Nd,and Ta).The samples are enriched in LREEs(LREE/HREE=1.5-7.3).Values of(La/Yb)N range between 0.9 and 6.5,and all samples show negative Eu anomalies(δEu=0.2-0.6),with typical characteristics of island arc magmatism.The LH granitic rocks haveεHf(t)values of-3.7 to+8.0 and yield a TCDM age of 1.51-0.78 Ga.The data suggest that the LH granitic rocks were derived from partial melting of Proterozoic crust-related mafic to intermediate rocks with significant crust-mantle interac-tions.The results,combined with regional magmatic informa-tion,indicate that the Late Permian-early Triassic magmatism in western NQTB were controlled by subduction rollback-retraction of South Kunlun Oceanic plate under the Kun-lun-Qaidam Block.
基金supported by the National Natural Science Foundation of China(Nos.42473049,42241108,and 42273040)the Guangdong Basic and Applied Basic Research Foundation(No.2024A1515011311)the Open Project for Innovative Platform of Meteoritical Research,Shanghai Science and Technology Museum。
文摘Gabbroic and poikilitic shergottites are intrusive igneous rocks on Mars,providing significant insights into the igneous processes within the Martian crust.However,questions remain regarding the chemical signatures of their source reservoirs and the petrogenetic links among shergottites of different subtypes.In this study,we present petrological and mineralogical analyses of the intermediate shergottite Northwest Africa(NWA)12241.Quantitative textural analysis and pyroxene chemistry indicate that,despite minor differences such as the accumulation of intermediate-sized olivine and smaller pyroxene oikocrysts,NWA 12241 has experienced a similar emplacement history as typical poikilitic and gabbroic shergottites.The estimated parent melt of NWA 12241 is consistent with derivation from an intermediate source reservoir,resulting from the mixing of enriched and depleted mantle end-members at depth,prior to magma ascent.Similar emplacement histories of variable poikilitic and gabbroic shergottites suggest the common presence of multiple staging magma chambers with different compositions at the crust–mantle boundary,coupled with prolonged ponding at this depth.Our study highlights that,in addition to magma mixing and assimilation,magmatic differentiation and cooling conditions at shallow depths are crucial processes leading to textural and compositional variations among shergottites of different subtypes.
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.
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.
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.
基金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.
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.
文摘Jingshan superlarge gold deposit is a typical deposit closely related to the ductile shear zone, developing the economic enrichment during the transition form the ductile deformation to the brittle deformation. The oreforming process of Jingshan Au deposit can be described as the development of marine volcanicturbidity current Aubearing initial sedimentation→regional metamorphism and the first enrichment→strong transformation of dynamic metamorphism and deformation→orecontrolling and oreholding of ductile shear structure→supperimposed transformation and enrichment of magmahydrothermal solution. This process can be summarized as the “sourcemigrationaccumulation” metallogenicgeochemical process of Au. The proved Au reserve of this deposit has ex ceeded 100 t and its prospect of searching for ore is considerable. So it is called the only superlarge gold deposit in the south of the lower reach of the Yangtze River, China.
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
