To investigate the influence mechanism of geostress on rockburst characteristics,three groups of gneiss rockburst experiments were conducted under different initial geostress conditions.A high-speed photography system...To investigate the influence mechanism of geostress on rockburst characteristics,three groups of gneiss rockburst experiments were conducted under different initial geostress conditions.A high-speed photography system and acoustic emission(AE)monitoring system were used to monitor the entire rockburst process in real time.The experimental results show that when the initial burial depth increases from 928 m to 1320 m,the proportion of large fracture scale in rockburst increases by 154.54%,and the AE energy increases by 565.63%,reflecting that the degree and severity of rockburst increase with the increase of burial depth.And then,two mechanisms are proposed to explain this effect,including(i)the increase of initial geostress improves the energy storage capacity of gneiss,and then,the excess energy which can be converted into kinetic energy of debris ejection increases,consequently,a more pronounced violent ejection phenomenon is observed at rockburst;(ii)the increase of initial geostress causes more sufficient plate cracks of gneiss after unloading ofσh,which provides a basis for more severe ejection of rockburst.What’s more,a precursor with clear physical meaning for rockburst is proposed under the framework of dynamic response process of crack evolution.Finally,potential value in long term rockburst warning of the precursor obtained in this study is shown via the comparison of conventional precursor.展开更多
The Trans-North China Orogen is a major Neoarchean Paleoproterozoic collisional orogenic belt above the North China Craton, formed due to prolonged and complex processes. Even though many NeoarcheanPaleoproterozoic ma...The Trans-North China Orogen is a major Neoarchean Paleoproterozoic collisional orogenic belt above the North China Craton, formed due to prolonged and complex processes. Even though many NeoarcheanPaleoproterozoic magmatic and metamorphic activities have been reported, due to the Huozhou Complex’s small outcropping range, little attention has been paid to the origin of various igneous rocks of the Huozhou Complex in the center of the Trans-North China Orogen. The Huozhou Complex, located south of the Luè liang, Wutai, and Hengshan complexes, is an important window into the Early Precambrian structure and evolution of the North China Craton. Its magma and metamorphism are crucial to understanding the development of the structural evolution of the Trans-North China Orogen. The Huozhou metamorphic complex area exposes a range of Precambrian metamorphic rocks, among which the most extensively dispersed is felsic biotite plagioclase gneiss. In this study comprehensive geological field survey, micropetrology,chronology, geochemistry, and Hf isotope analysis were carried out for the Qinggangping and Anziping gneiss in the north of the Huozhou Complex. The results show that the magmatic zircon age of the Qinggangping gneiss is2196 ± 14 Ma, and its protolith is I-type granite, formed by partial melting of igneous rocks in the absence of weathering. Its source is mainly the juvenile crust from depleted mantle dating 2431–2719 Ma, with a small amount of mantle-derived material. The Anziping gneiss has a metamorphic zircon age of 1931 ± 13 Ma with an S-type granite protolith belonging to peraluminous granite.The Anziping gneiss is formed by recycling pre-existing crustal components at 2613–2848 Ma. A minor quantity of mantle-derived magma is also introduced to the crust simultaneously. The samples of Qinggangping gneiss and Anziping gneiss show the characteristics of obvious negative Nb, Ti, and P elements in the spider diagram of primitive mantle standardization. This implies that the rocks have the characteristics of magmatic rocks in an island arc or subduction environment, which could have formed in the tectonic environment of the continental margin arc.展开更多
In the gneisses from the drillhole ZK2304 of the Donghai area, there have been preserved high- and ultrahigh-pressure metamorphic mineral assemblages, a series of complicated retrogressive textures and relevant metamo...In the gneisses from the drillhole ZK2304 of the Donghai area, there have been preserved high- and ultrahigh-pressure metamorphic mineral assemblages, a series of complicated retrogressive textures and relevant metamorphic reactions. In addition to garnet, jadeititic-clinopyroxene and rutile, other peak stage (M2) minerals in some gneisses include phengite, aragonite and coesite or quartz pseudomorphs after coesite. The typical peak-stage mineral assemblages in gneisses are characterized by garnet + jadeitic-clinopyroxene + rutile + coesite, garnet + jadeitic-clinopyroxene + phengite + rutile ± coesite and garnet + jadeitic-clinopyroxene + aragonite + rutile ± coesite. The grossular content (Gro) in garnet is high and may reach 50. 1 mol%. The SiO2 content of phengite ranges from 54.37% to 54.84% with 3.54-3.57 p.f.u. Quartz pseudomorphs after coesite occur as inclusions in garnet.The gneisses of the Donghai area have been subjected to multistage recrystallization and exhibit a closewise P-T展开更多
The granitic gneisses from the ultrahigh-pressure (UHP) metamorphic terrain of the southeastern Dabie Mountains encompass two types: monzonitic granitic gneiss and alkali-feldspar granitic gneiss, which are characteri...The granitic gneisses from the ultrahigh-pressure (UHP) metamorphic terrain of the southeastern Dabie Mountains encompass two types: monzonitic granitic gneiss and alkali-feldspar granitic gneiss, which are characterized by rich alkalis, poor CaO, high FeO/MgO, particularly high Ba, Rb, Th, Ta, REE (except Eu), Ga, Nb and Zn, and low Sr, Eu, Cr, Co and Ni. The gneisses, particularly the alkali-feldspar granitic gneiss, have typical chemical characteristics of A-type granites. They resulted from partial melting of crustal materials existing in the rift zone along the northern margin of the South China block during the Neoproterozoic. These gneisses might not have undergone UHP metamorphism during the late Triassic, but were involved into UHP rocks by the tectonic mixing process and kept the exhumation message of the UHP rocks from the middle and upper crust.展开更多
The Dabie complex (DC) and the Tongbai complex (TBC) are separately distributed in the middle and eastern parts of the Qinling-Tongbai-Dabie orogenic belt. In this study, the Dabie complex can be divided into two unit...The Dabie complex (DC) and the Tongbai complex (TBC) are separately distributed in the middle and eastern parts of the Qinling-Tongbai-Dabie orogenic belt. In this study, the Dabie complex can be divided into two units: one is the complex with no high pressure and ultrahigh pressure metamorphic rocks (DC1), and the other is the complex containing coesite-bearing eclogite lenses or boudins (DC2). Gneisses are predominant in the TBC, DC1 and DC2. Major and trace element data of gneisses in the TBC, DC1 and DC2 show them to be the orthogneisses. The gneisses in the DC1 have higher incompatible element contents and higher ratios of w(K 2O)/w(Na 2O) and w(La) n/w(Yb) n than those in the DC2. However, no obvious differences arise in other element contents and the ratios of w(La)/ w(Nb), w(Nb)/w(Th), w(Nb)/w(Hf), w(Ba)/w(La), w(Sm)/w(Nd) and w(Th)/w(U) between the gneisses in the DC2 and those in the DC1. These observations suggest that the protoliths of the gneisses in the DC2 have affinities to those in the DC1. The difference between the DC1 and DC2 gneisses in incompatible element contents could reflect the difference in their partial melting extent. The TBC gneisses are geochemically similar to the DC1 gneisses, suggesting that the TBC and DC1 gneisses are the same lithologic unit in the Qinling-Tongbai-Dabie orogenic belt and that they have experienced similar formations and evolution histories. In the Qinling-Tongbai area, the TBC is part of the northern blocks of the Yangtze craton. Given the similarity of geochemical characteristics, the rock assemblage and the ages between the TBC and DC1 gneisses, we can infer that the Dabie complex also belongs to the northern blocks of the Yangtze craton. In terms of the distribution of eclogites and metamorphic facies, we propose that the collisional suture in the Dabie area is distributed along the Xiaotian-Mozitan fault, at the contact with the Shang-Dan-Tongbai fault to the west.展开更多
Using the single-zircon evaporation technique and U-Pb method, the authors have conducted an isotope geochonological study of the Huilanshan granulite and Shima garnet-bearing plagioclase gneiss (' country rocks&#...Using the single-zircon evaporation technique and U-Pb method, the authors have conducted an isotope geochonological study of the Huilanshan granulite and Shima garnet-bearing plagioclase gneiss (' country rocks' of the Shima eclogite) in the Dabie Mountains. The study shows that these rocks have peak metamorphic ages of 443-455 Ma, which are essentially consistent with that of the Caledonian high-ultrahigh pressure eclogites. This indicates the existence of the Caledonian collisional orogeny in the Dabie Mountains.展开更多
Jebba area southwestern Nigeria forms part of the Nigerian basement complex which lies in the Neoproterozoic PanAfrican mobile belt. It is underlain by several lithological units among which is a polydeformed granitic...Jebba area southwestern Nigeria forms part of the Nigerian basement complex which lies in the Neoproterozoic PanAfrican mobile belt. It is underlain by several lithological units among which is a polydeformed granitic gneiss. This rock has been dated by LA-ICP-MS yielding a concordant U-Pb zircon age of 2207 ± 20 Ma indicating the crystallization age of the granite protolith. This early Rhyacian age and its affinity with within-plate granites indicates emplacement during crustal extension and rifting presceding the main phase of the Eburnean orogeny. The strong, early, shear fabric, S1, in the rock is interpreted to be also of Paleoproterozoic age i.e. imprinted during the Eburnean orogeny. The Jebba granitic gneiss is thus correlatable with the widely abundant Paleoproterozoic granitic magmatism now represented by many orthogneisses and documented in other parts of southwestern Nigeria, the West African craton, the Borborema Province, the Gurupi Belt, Sao Luis craton and Sao Francisco craton in Brazil.展开更多
Study of micro-area chemical compositions indicates that phengite in albite gneiss from hole ZK2304 of the Donghai region has evident compositional zoning. SiO2 and tetrahedrally coordinated Si contents decrease, and ...Study of micro-area chemical compositions indicates that phengite in albite gneiss from hole ZK2304 of the Donghai region has evident compositional zoning. SiO2 and tetrahedrally coordinated Si contents decrease, and Al2O3, AlIV and AlVI contents increase gradually from core to rim. However, K2O, MgO and FeO contents basically remain unchanged from core to rim. According to P-T estimates obtained from geothermometers and barometers, combined with previous experimental data, the core belt (micro-area I) of phengite was formed at T=637-672℃ and P=1.55-1.73 GPa, and the transitional belt (micro-area II) of the phengite were formed at r=594-654℃ and P=1.35-1.45 GPa. Towards the rim belt (micro-area III), the temperature decreased slightly, but the pressure decreased rapidly with r=542-630℃ and P=1.12-1.19 GPa. The P-T evolution path recorded by the compositional zoning of phengite is characterized by significant near-isothermal decompression, revealing that the gneiss has. undergone展开更多
The Suichang mine is the largest silicified vein-type silver-gold mineralization system in Southeast China, whose ore bodies are controlled by shear zones developing in Lower Proterozoic gneiss terrene with initial mi...The Suichang mine is the largest silicified vein-type silver-gold mineralization system in Southeast China, whose ore bodies are controlled by shear zones developing in Lower Proterozoic gneiss terrene with initial migmatization, which is covered by Upper Jurassic and Lower Cretaceous volcanic rock system and cut by acidic igneous veins of Jurassic and Cretaceous. The conclusions are as follows: (1) The ore-forming fluid is defined as superhigh tectonic-metamorphic fluid on the base of : 1 (D)-(18O) values 2 fluid inclusions;3 trace elements of pyrite from ores. (2) The shear zone silicified orebod-ies occurred in proterozoic, Jurassic and Cretaceous, which have been transforms in part by ore-bearing comb quartz vein of volcanism.展开更多
The chemical and petrological correlation of metamorphic nappes and klippes overlying the Proterozoic sedimentary units in the Kumaun Himalaya is still debated. The Ramgarh and Almora gneisses, not previously distingu...The chemical and petrological correlation of metamorphic nappes and klippes overlying the Proterozoic sedimentary units in the Kumaun Himalaya is still debated. The Ramgarh and Almora gneisses, not previously distinguished in the Askot Klippe, show distinct field, petrological and chemical signatures markedly similar to the tectonostratigraphic disposition of the Almora Nappe. A negative Eu anomaly in the Ramgarh granitic gneisses indicates lesser plagioclase fractionation while the Eu anomaly in the Almora pelitic gneisses is likely to have been controlled by feldspar crystallization in restites. During the anatexis at > 776°C temperature and >6.6 kbar pressure, the melt moved slightly away to its crystallization sites. The Rb/Sr ratio ?0.54 and Nb ?10 ppm is consistent with the granodioritic composition. The negative Sr anomaly in the underlying Ramgarh granitic gneisses indicates a distinct mantle derived source/plagioclase fractionation with a notable correspondence to other late orogenic granites, particularly the basement Ulleri gneisses from the Nepal Himalaya. Ramgarh gneisses plot in the late-and post-COLG field. The Askot ensemble is likely to be the tectonometamorphically reworked basement, viz. the Ramgarh Group along with its metapelitic cover o f the Almora Group, together comprising southward thrust remnants of the leading edge of the Indian Plate that collided with Tibet during the Tertiary Himalayan orogeny.展开更多
Geology setting and petrological features Qiangtang composite plate is located between Xijinwulan—Jinshajiang and Bangonghu—Nujiang suture zones, with the total area of several ten thousand square kilometers. The ex...Geology setting and petrological features Qiangtang composite plate is located between Xijinwulan—Jinshajiang and Bangonghu—Nujiang suture zones, with the total area of several ten thousand square kilometers. The exposed rocks are mainly Paleozoic, Mesozoic marine sedimentary rocks.. Around Zhabu—Shuanghu area, there exits a post late Triassic uplift, in which middle Devonian low\|intermediate degree metamorphic rocks with solid chronological evidence have been found. However, in central Qiangtang, debate is still there in several aspects, such as there is crystalline basement or not, basement features, and the pre\|Devonian evolution of Qiangtang plate, etc. (Cai Li et al.,1997)Duguer gneiss is the only proved gneiss in Qiangtang region upto now, which is exposed at Duguer mountain (peak, 6208m above sea level), Gaize county, and is confined by faults. An E—W oriented thrust fault zone is its south boundary, which is more than 200m wide and makes the gneiss overthrust on upper Carboniferous strata and Tertiary red beds southwardly. On the east and north sides of the gneiss are upper Carboniferous strata. The gneiss occurs as a triangle form with a long E—W trending bottom line (about 20km) and a height about 10km in S—N direction, which is the main part of Duguer Duguer mountain.Duguer gneiss consists of two rocks types, i.e. granitic gneiss (the dominant component) and amphibole\|plagioclase gneiss. The latter one occurs as a group of nearly E—W trending dikes with clear boundary, which are obviously late basic dikes that intruded into granite. Granitic gneiss is composed of porphyroclast granitic gneiss, banded granitic gneiss, gneissoid granite and granitic mylonite. Both granitic and amphibole\|plagioclase gneisses have been undergone same type and same degree metamorphism and deformation. The typical mineral assemblage of the former gneiss include quartz(30%), microcline(25%),plagioclase(30%), two mica (biotite +muscovite,13%) and the accessory minerals such as zircon, magnetite, and apatite etc. The main oxide contents of the granitic gneiss are (average of three samples) 73 53% SiO\-2, 12 9% Al\-2O\-3, 1 57% FeO, 0 52% MgO, 3 24%Na\-2O and 0 22% K\-2O. The REE distribution pattern shows typical features of granite, i.e. LREE enrichment, HREE depletion and rather strong negative Eu anomaly.展开更多
High in sodium and low in potassium （Na<sub>2</sub>O/ K<sub>2</sub>O】1）, the charnockitic gneiss series in theSantunying- Taipingzhai area, eastern Hebei province, consists of hypersthene- q...High in sodium and low in potassium （Na<sub>2</sub>O/ K<sub>2</sub>O】1）, the charnockitic gneiss series in theSantunying- Taipingzhai area, eastern Hebei province, consists of hypersthene- quartz- diorite,hypersthene-granodiorite and hypersthene-plagioclase-granite. Geological, petrological and large ion lithophileelement（LILE）, high field strength element （HFSE） and REE geochemical studies suggest that themedium-coarse-grained hypersthene-granodiorite is the product of crystallization of anatectic magmas of thesame composition. Under granulite facies conditions, the equilibrium crystallization differentiation of themagmas yielded the early crystallization phase-high-SiO<sub>2</sub>, LILE-depleted, low-∑REE, positive Eu anomalyand REE- saturated hypersthene- plagioclase- granite. The residual phase, coarse- grained to pegmatitichypersthene- granodiorite, is marked by low SiO<sub>2</sub>, LILE-enrichment, high ∑REE and REE-undersaturation.These rocks and hypersthene-quartz-diorite enclaves constitute the sodium-charnockitic gneiss series in easternHebei province. Model calculation for trace elements in the granitoids was applied. On the basis of a systematicgeological study, the equation for calculation was chosen, the source magma was determined and the partitioncoefficients were obtained. The resulting curves are entirely consistent with those observed in the patterns of ac-tual rocks. The study indicates that whole-rock REE patterns can not be used directly in the comparison of thesources and genesis of granitoids.展开更多
The Banded Gneissic Complex(BGC) of the Aravalli Craton is divided into BGC-I and BGC-Ⅱ; the BGC-Ⅱ(central Rajasthan) is comprised of the Sandmata Complex and the Mangalwar Complex. We report elemental and Nd-isotop...The Banded Gneissic Complex(BGC) of the Aravalli Craton is divided into BGC-I and BGC-Ⅱ; the BGC-Ⅱ(central Rajasthan) is comprised of the Sandmata Complex and the Mangalwar Complex. We report elemental and Nd-isotope geochemistry of basement gneisses of the Mangalwar Complex and constrain its origin and evolution. Geochemically, the basement gneisses have been classified as low-SiO_2 gneisses(LSG) and high-SiO_2 gneisses(HSG). Both the LSG and HSG are potassic, calc-alkaline and peraluminous in nature. The LSG are enriched in incompatible(K, Sr, Ba, large ion lithophile elements) and compatible elements(MgO, Cr, and Ni). They display fractionated rare earth element patterns(avg.La_N/Yb_N=12.1)with small Eu-anomaly(δEu=0.9), and exhibit negative anomalies of Nb and Ti in primitive mantlenormalized multi-element diagram. In terms of Nd-isotope geochemistry, the LSG are characterized by_(εNd)(t)=4.2 and depleted mantle model age of 3.3 Ga. To account for these geochemical characteristics we propose a three-stage petrogenetic model for the LSG:(1) fluids released from dehydration of subducting slab metasomatised the mantle-wedge;(2) the subducting slab underwent slab-breakoff causing upwelling and decompression melting of the asthenosphere during waning stage of subduction; and(3)upwelling asthenosphere provided the requisite heat for partial melting of the metasomatised mantlewedge leading to generation of the LSG parental magma. Asthenospheric upwelling also contributed in the LSG petrogenesis which is evident from its high Mg#(avg. 0.53). The LSG formed in this way are contemporary and chemically akin to sanukitoids of the BGC-I and Archean sanukitoids reported elsewhere. This provides a basis to consider the LSG as a part of the BGC-I. Contrary to the LSG, the HSG are depleted in compatible elements(MgO=avg. 1.1 wt.%; Cr=avg. 8 ppm; Ni=avg. 6 ppm) but enriched in incompatible elements(Sr=avg. 239 ppm, Ba=avg. 469 ppm). Its_(εNd)(t) values vary from-9.5 to-5.4.These chemical features of the HSG are akin to potassic granitoids found elsewhere. In this backdrop, we propose that the HSG suite of the Mangalwar Complex was derived from re-melting(partial) of an older crust(TTG?) occurring within the BGC-Ⅱ.展开更多
Grey gneisses are tonalitic intrusive rocks that have Archaean characteristics and tectonic significance. Archaean grey gneisses in North China may be classified into two types: the Zunhua type and the Heagshan type. ...Grey gneisses are tonalitic intrusive rocks that have Archaean characteristics and tectonic significance. Archaean grey gneisses in North China may be classified into two types: the Zunhua type and the Heagshan type. Grey gneisses of the Zunhua type alternate with basic granulites, forming a bimodal migmatitic suite. The rock is characterized by complex mineral composition, highly varied REE patterns and positive Eu anomaly and originated from autochthonous or partly autochthonous deep-level migmatization with a high degree (30%±) of fusion. As the sub-stratum in the root of the early-stage high-grade greenstone belt, they prevented basic rocks from sinking. Grey gneisses of the Hengshan type are characterized by a relatively distinct intrusion form, large-amplitude upward emplacement, rather simple mineral composition, only slight/changes of REE patterns and absence of Eu anomaly. The rock is a product of subduction and underthrusting of the high-grade greenstone belt and then fusion and emplacement展开更多
Phase equilibria modelling coupled with U–Pb zircon and monazite ages of garnet–cordierite gneiss from Vallikodu Kottayam in the Kerala Khondalite Belt,southern India are presented here.The results suggest that the ...Phase equilibria modelling coupled with U–Pb zircon and monazite ages of garnet–cordierite gneiss from Vallikodu Kottayam in the Kerala Khondalite Belt,southern India are presented here.The results suggest that the area attained peak P–T conditions of^900C at 7.5–8 kbar,followed by decompression to 3.5–5 kbar and cooling to 450–480C,preserving signatures of the partial melting event in the field of high to ultra-high temperature metamorphism.Melt reintegration models suggest that up to 35%granitic melt could have been produced during metamorphism at^950C.The U–Pb age data from zircons(~1.0–~0.7 Ga)and chemical ages from monazites(~540 Ma and^941 Ma)reflect a complex tectonometamorphic evolution of the terrain.The^941 Ma age reported from these monazites indicate a Tonian ultra-high temperature event,linked to juvenile magmatism/deformation episodes reported from the Southern Granulite Terrane and associated fragments in Rodinia,which were subsequently overprinted by the Cambrian(~540 Ma)tectonothermal episode.展开更多
Investigating and modeling fluid flow in fractured aquifers is a challenge. This study presents the results of a series of packer tests conducted in a fractured aquifer in Freiberg, Germany, where gneiss is the domina...Investigating and modeling fluid flow in fractured aquifers is a challenge. This study presents the results of a series of packer tests conducted in a fractured aquifer in Freiberg, Germany, where gneiss is the dominant rock type. Two methods were applied to acquire hydraulic properties from the packer tests: analytical and numerical modeling. MLU (Multi-Layer Unsteady state) for Windows is the analytical model that was applied. ANSYS-FLOTRAN was used to build a two-dimensional numerical model of the geometry of the layered aquifer. A reasonable match between experimental data and simulated data was achieved with the 2D numerical model while the solution from the analytical model revealed significant deviations with respect to direction.展开更多
The grey gneisses are composed of early-stage layered TTG and late-stage diapiric tonalite in-trusions.The Dabie complex,northeastern Hubei Province,may be distinguished into supracrustal sequenceand grey gneisses.Dif...The grey gneisses are composed of early-stage layered TTG and late-stage diapiric tonalite in-trusions.The Dabie complex,northeastern Hubei Province,may be distinguished into supracrustal sequenceand grey gneisses.Different distribution patterns of rare earth elements in the early- and late- stage gneisses,i.e.the early-stage gneisses are enriched in LREE and remarkably depleted in HREE;and late-stage isslightly enriched in LREE and unevidently depleted in HREE.Geological evidence and characteristics of el-ement ratio diagrams suggest that the TTG is mainly controlled by portional partial melting and accompa-nied with fractional crystallization.The quantitative modelling of REE pattern indicates that TTG is formedfrom amphibolite transformed from basic rocks with 25%～65% of portional partial melt while thelate-stage tonalite intrusion was also accompanied with fractional crystalization of 22% biotites.展开更多
The sample location in our paper(Sorcar et al.,2020)was incorrectly marked in Fig.1,although the GPS location was reported correctly.The corrected sample location of garnet-cordierite gneiss is shown in Fig.1.The samp...The sample location in our paper(Sorcar et al.,2020)was incorrectly marked in Fig.1,although the GPS location was reported correctly.The corrected sample location of garnet-cordierite gneiss is shown in Fig.1.The sample location falls within the Achankovil Shear Zone(ASZ)and not in the Trivandrum Block as stated in our paper.Thus,the Tonian ultrahigh-temperature(UHT)metamorphic event reported in our paper is applicable to ASZ,and not for the Trivandrum Block.The related discussion on Gondwana correlation in our paper may be viewed and read in that context.展开更多
The Chaihulanzi area in eastern Inner Mongolia is tectonically situated on the northern margin of the North China Craton(NCC). The main Precambrian lithologies of the area have been referred to the Archean Jianping Gr...The Chaihulanzi area in eastern Inner Mongolia is tectonically situated on the northern margin of the North China Craton(NCC). The main Precambrian lithologies of the area have been referred to the Archean Jianping Group metasupracrustal sequences. Based on field observations, petrographic, whole-rock geochemical, and zircon U-Pb geochronological results, a magmatic origin for the units is proposed. Our results show that the Chaihulanzi gneisses are mainly of granitic, dioritic and granodioritic compositions, and show typical magmatic rock textures and mineral assemblages. The dioritic and granodioritic gneisses show Na-rich tonalite–trondhjemite–granodiorite(TTG)-like affinity with zircon U-Pb dates of ca. 2.57–2.59 Ga, representing a juvenile continental growth for the northeastern NCC. The granitic gneiss is indeed potassic granite and yielded a zircon U-Pb date of ~2.50 Ga, which is contemporaneous with the Jining–Jiaoliao microblock collision(2.53–2.49 Ga), implying another crustal growth event. The well-developed gneissosity in 2.57–2.59 Ga dioritic and granodioritic gneisses together with the 2.5 Ga potassic granite, which crosscuts the gneissosity implies a 2.57–2.50 Ga(mainly 2.53–2.51 Ga) collisional orogeny, probably related to the Jining–Jiaoliao microblock collision. Our new geology and chronological results provide new evidence for the early Precambrian tectonic evolution of the NCC.展开更多
The cratonization history of the North China Craton(NCC)and the nature of tectonothermal events are still highly controversial.Tonalite-trondhjemite-granodiorite(TTG)gneisses,as the dominant lithological assemblages i...The cratonization history of the North China Craton(NCC)and the nature of tectonothermal events are still highly controversial.Tonalite-trondhjemite-granodiorite(TTG)gneisses,as the dominant lithological assemblages in Archean metamorphic terranes,can provide significant clues to the magmatic and metamorphic evolution of Precambrian crust.This study presents zircon laser-ablation inductively-coupled-plasma mass spectrometry U–Pb ages,trace-element,and in-situ LA-MC-ICPMS zircon Hf isotope data for the TTG gneisses from the Bengbu-Wuhe area on the southeastern margin of the NCC.Cathodoluminescence images and trace elements indicated that magmatic zircons display the characteristics of euhedral-subhedral crystals with oscillatory growth zoning structures,high RREE contents,marked Ce positive anomalies,and Pr–Eu negative anomalies.The metamorphic zircons display the spherical-oval crystals with distinct core-rim structures,high and homogeneous luminescent intensity,lower RREE,Nb,Ta,Hf contents,relative flat REE patterns,weak Ce positive anomalies,and Pr-Eu negative anomalies.The Ti–in–zircon geothermometer data indicate that the crystallization temperature of the TTG gneiss ranged from 754 to 868℃.Zircon U–Pb ages indicate that the TTG gneisses formed at 2.79–2.77 Ga and 2.50 Ga and underwent metamorphism at 2.57–2.52 Ga.The Hf isotopic data indicate that the magmatic zircons exhibit high,positive eHf(t)values close to those of the coeval depleted mantle,whereas the metamorphic zircons exhibit negative or nil eHf(t)values.This implies that the TTG gneisses were derived from the partial melting of the~2.9–2.6 Ga juvenile crustal sources mixed with~3.0–2.8 Ga ancient crustal materials.Combined with the regional tectonic evolution,we propose that the metamorphic basement at the southeastern margin of the NCC underwent episodic crustal growth at~2.7 and~2.5 Ga and subsequently underwent crustal reworking or re-melting of the ancient crust during the Neoarchean.The Neoarchean TTG gneisses might have been derived from the partial melting of lower crustal materials related to plate subduction.展开更多
基金support from the National Natural Science Foundation of China(No.41941018,No.52074299)the Fundamental Research Funds for the Central Universities(No.2023JCCXSB02)the China Geological Survey Project(DD20221816,DD20211376)are gratefully acknowledged.
文摘To investigate the influence mechanism of geostress on rockburst characteristics,three groups of gneiss rockburst experiments were conducted under different initial geostress conditions.A high-speed photography system and acoustic emission(AE)monitoring system were used to monitor the entire rockburst process in real time.The experimental results show that when the initial burial depth increases from 928 m to 1320 m,the proportion of large fracture scale in rockburst increases by 154.54%,and the AE energy increases by 565.63%,reflecting that the degree and severity of rockburst increase with the increase of burial depth.And then,two mechanisms are proposed to explain this effect,including(i)the increase of initial geostress improves the energy storage capacity of gneiss,and then,the excess energy which can be converted into kinetic energy of debris ejection increases,consequently,a more pronounced violent ejection phenomenon is observed at rockburst;(ii)the increase of initial geostress causes more sufficient plate cracks of gneiss after unloading ofσh,which provides a basis for more severe ejection of rockburst.What’s more,a precursor with clear physical meaning for rockburst is proposed under the framework of dynamic response process of crack evolution.Finally,potential value in long term rockburst warning of the precursor obtained in this study is shown via the comparison of conventional precursor.
基金supported by the open fund from the Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences (Number J1901-16)the project of graduate education and teaching reform in Shanxi Province (Award Number 2021YJJG147)+3 种基金the teaching reform project ‘‘Geographic Modeling,Simulation and Visualization’’ established by Shanxi Normal University (Number 2019JGXM-39)‘‘The Research Start-up Fund of Shanxi Normal University for Dr. Peng Chong in 2016’’(Number0505/02070438)‘‘The Research Start-up Fund of Shanxi Normal University for Dr. Liu Haiyan in 2017’’(Number 0505/02070458)‘‘The Research Fund for Outstanding Doctor in 2017’’(Number0503/02010168)。
文摘The Trans-North China Orogen is a major Neoarchean Paleoproterozoic collisional orogenic belt above the North China Craton, formed due to prolonged and complex processes. Even though many NeoarcheanPaleoproterozoic magmatic and metamorphic activities have been reported, due to the Huozhou Complex’s small outcropping range, little attention has been paid to the origin of various igneous rocks of the Huozhou Complex in the center of the Trans-North China Orogen. The Huozhou Complex, located south of the Luè liang, Wutai, and Hengshan complexes, is an important window into the Early Precambrian structure and evolution of the North China Craton. Its magma and metamorphism are crucial to understanding the development of the structural evolution of the Trans-North China Orogen. The Huozhou metamorphic complex area exposes a range of Precambrian metamorphic rocks, among which the most extensively dispersed is felsic biotite plagioclase gneiss. In this study comprehensive geological field survey, micropetrology,chronology, geochemistry, and Hf isotope analysis were carried out for the Qinggangping and Anziping gneiss in the north of the Huozhou Complex. The results show that the magmatic zircon age of the Qinggangping gneiss is2196 ± 14 Ma, and its protolith is I-type granite, formed by partial melting of igneous rocks in the absence of weathering. Its source is mainly the juvenile crust from depleted mantle dating 2431–2719 Ma, with a small amount of mantle-derived material. The Anziping gneiss has a metamorphic zircon age of 1931 ± 13 Ma with an S-type granite protolith belonging to peraluminous granite.The Anziping gneiss is formed by recycling pre-existing crustal components at 2613–2848 Ma. A minor quantity of mantle-derived magma is also introduced to the crust simultaneously. The samples of Qinggangping gneiss and Anziping gneiss show the characteristics of obvious negative Nb, Ti, and P elements in the spider diagram of primitive mantle standardization. This implies that the rocks have the characteristics of magmatic rocks in an island arc or subduction environment, which could have formed in the tectonic environment of the continental margin arc.
文摘In the gneisses from the drillhole ZK2304 of the Donghai area, there have been preserved high- and ultrahigh-pressure metamorphic mineral assemblages, a series of complicated retrogressive textures and relevant metamorphic reactions. In addition to garnet, jadeititic-clinopyroxene and rutile, other peak stage (M2) minerals in some gneisses include phengite, aragonite and coesite or quartz pseudomorphs after coesite. The typical peak-stage mineral assemblages in gneisses are characterized by garnet + jadeitic-clinopyroxene + rutile + coesite, garnet + jadeitic-clinopyroxene + phengite + rutile ± coesite and garnet + jadeitic-clinopyroxene + aragonite + rutile ± coesite. The grossular content (Gro) in garnet is high and may reach 50. 1 mol%. The SiO2 content of phengite ranges from 54.37% to 54.84% with 3.54-3.57 p.f.u. Quartz pseudomorphs after coesite occur as inclusions in garnet.The gneisses of the Donghai area have been subjected to multistage recrystallization and exhibit a closewise P-T
文摘The granitic gneisses from the ultrahigh-pressure (UHP) metamorphic terrain of the southeastern Dabie Mountains encompass two types: monzonitic granitic gneiss and alkali-feldspar granitic gneiss, which are characterized by rich alkalis, poor CaO, high FeO/MgO, particularly high Ba, Rb, Th, Ta, REE (except Eu), Ga, Nb and Zn, and low Sr, Eu, Cr, Co and Ni. The gneisses, particularly the alkali-feldspar granitic gneiss, have typical chemical characteristics of A-type granites. They resulted from partial melting of crustal materials existing in the rift zone along the northern margin of the South China block during the Neoproterozoic. These gneisses might not have undergone UHP metamorphism during the late Triassic, but were involved into UHP rocks by the tectonic mixing process and kept the exhumation message of the UHP rocks from the middle and upper crust.
文摘The Dabie complex (DC) and the Tongbai complex (TBC) are separately distributed in the middle and eastern parts of the Qinling-Tongbai-Dabie orogenic belt. In this study, the Dabie complex can be divided into two units: one is the complex with no high pressure and ultrahigh pressure metamorphic rocks (DC1), and the other is the complex containing coesite-bearing eclogite lenses or boudins (DC2). Gneisses are predominant in the TBC, DC1 and DC2. Major and trace element data of gneisses in the TBC, DC1 and DC2 show them to be the orthogneisses. The gneisses in the DC1 have higher incompatible element contents and higher ratios of w(K 2O)/w(Na 2O) and w(La) n/w(Yb) n than those in the DC2. However, no obvious differences arise in other element contents and the ratios of w(La)/ w(Nb), w(Nb)/w(Th), w(Nb)/w(Hf), w(Ba)/w(La), w(Sm)/w(Nd) and w(Th)/w(U) between the gneisses in the DC2 and those in the DC1. These observations suggest that the protoliths of the gneisses in the DC2 have affinities to those in the DC1. The difference between the DC1 and DC2 gneisses in incompatible element contents could reflect the difference in their partial melting extent. The TBC gneisses are geochemically similar to the DC1 gneisses, suggesting that the TBC and DC1 gneisses are the same lithologic unit in the Qinling-Tongbai-Dabie orogenic belt and that they have experienced similar formations and evolution histories. In the Qinling-Tongbai area, the TBC is part of the northern blocks of the Yangtze craton. Given the similarity of geochemical characteristics, the rock assemblage and the ages between the TBC and DC1 gneisses, we can infer that the Dabie complex also belongs to the northern blocks of the Yangtze craton. In terms of the distribution of eclogites and metamorphic facies, we propose that the collisional suture in the Dabie area is distributed along the Xiaotian-Mozitan fault, at the contact with the Shang-Dan-Tongbai fault to the west.
基金This study was supported by the National Natural Science Foundation of China grants 49572146 and 49772147 and the Foundation for Development of Science and Technology in Geology grant 9514.
文摘Using the single-zircon evaporation technique and U-Pb method, the authors have conducted an isotope geochonological study of the Huilanshan granulite and Shima garnet-bearing plagioclase gneiss (' country rocks' of the Shima eclogite) in the Dabie Mountains. The study shows that these rocks have peak metamorphic ages of 443-455 Ma, which are essentially consistent with that of the Caledonian high-ultrahigh pressure eclogites. This indicates the existence of the Caledonian collisional orogeny in the Dabie Mountains.
文摘Jebba area southwestern Nigeria forms part of the Nigerian basement complex which lies in the Neoproterozoic PanAfrican mobile belt. It is underlain by several lithological units among which is a polydeformed granitic gneiss. This rock has been dated by LA-ICP-MS yielding a concordant U-Pb zircon age of 2207 ± 20 Ma indicating the crystallization age of the granite protolith. This early Rhyacian age and its affinity with within-plate granites indicates emplacement during crustal extension and rifting presceding the main phase of the Eburnean orogeny. The strong, early, shear fabric, S1, in the rock is interpreted to be also of Paleoproterozoic age i.e. imprinted during the Eburnean orogeny. The Jebba granitic gneiss is thus correlatable with the widely abundant Paleoproterozoic granitic magmatism now represented by many orthogneisses and documented in other parts of southwestern Nigeria, the West African craton, the Borborema Province, the Gurupi Belt, Sao Luis craton and Sao Francisco craton in Brazil.
基金This study was supported by the Ministry of Land and Resources of China Projects“1:250000 Regional Geological Surveyofthe Lianyugang Sheet (150C002004) of P.R.China""Geological Research for Selecting a Drillhole in the Donghai TargetArea of the Chinese Continental Scientific Drilling Programme”.
文摘Study of micro-area chemical compositions indicates that phengite in albite gneiss from hole ZK2304 of the Donghai region has evident compositional zoning. SiO2 and tetrahedrally coordinated Si contents decrease, and Al2O3, AlIV and AlVI contents increase gradually from core to rim. However, K2O, MgO and FeO contents basically remain unchanged from core to rim. According to P-T estimates obtained from geothermometers and barometers, combined with previous experimental data, the core belt (micro-area I) of phengite was formed at T=637-672℃ and P=1.55-1.73 GPa, and the transitional belt (micro-area II) of the phengite were formed at r=594-654℃ and P=1.35-1.45 GPa. Towards the rim belt (micro-area III), the temperature decreased slightly, but the pressure decreased rapidly with r=542-630℃ and P=1.12-1.19 GPa. The P-T evolution path recorded by the compositional zoning of phengite is characterized by significant near-isothermal decompression, revealing that the gneiss has. undergone
基金Chinese Gold Management. Office (No.93-45-33) and Zhejiag Metallurgical (No. 98-27).
文摘The Suichang mine is the largest silicified vein-type silver-gold mineralization system in Southeast China, whose ore bodies are controlled by shear zones developing in Lower Proterozoic gneiss terrene with initial migmatization, which is covered by Upper Jurassic and Lower Cretaceous volcanic rock system and cut by acidic igneous veins of Jurassic and Cretaceous. The conclusions are as follows: (1) The ore-forming fluid is defined as superhigh tectonic-metamorphic fluid on the base of : 1 (D)-(18O) values 2 fluid inclusions;3 trace elements of pyrite from ores. (2) The shear zone silicified orebod-ies occurred in proterozoic, Jurassic and Cretaceous, which have been transforms in part by ore-bearing comb quartz vein of volcanism.
基金the financial support from the UGC CAS-I & II grantDSTs New Delhi for financial assistance to MJ. BPD
文摘The chemical and petrological correlation of metamorphic nappes and klippes overlying the Proterozoic sedimentary units in the Kumaun Himalaya is still debated. The Ramgarh and Almora gneisses, not previously distinguished in the Askot Klippe, show distinct field, petrological and chemical signatures markedly similar to the tectonostratigraphic disposition of the Almora Nappe. A negative Eu anomaly in the Ramgarh granitic gneisses indicates lesser plagioclase fractionation while the Eu anomaly in the Almora pelitic gneisses is likely to have been controlled by feldspar crystallization in restites. During the anatexis at > 776°C temperature and >6.6 kbar pressure, the melt moved slightly away to its crystallization sites. The Rb/Sr ratio ?0.54 and Nb ?10 ppm is consistent with the granodioritic composition. The negative Sr anomaly in the underlying Ramgarh granitic gneisses indicates a distinct mantle derived source/plagioclase fractionation with a notable correspondence to other late orogenic granites, particularly the basement Ulleri gneisses from the Nepal Himalaya. Ramgarh gneisses plot in the late-and post-COLG field. The Askot ensemble is likely to be the tectonometamorphically reworked basement, viz. the Ramgarh Group along with its metapelitic cover o f the Almora Group, together comprising southward thrust remnants of the leading edge of the Indian Plate that collided with Tibet during the Tertiary Himalayan orogeny.
文摘Geology setting and petrological features Qiangtang composite plate is located between Xijinwulan—Jinshajiang and Bangonghu—Nujiang suture zones, with the total area of several ten thousand square kilometers. The exposed rocks are mainly Paleozoic, Mesozoic marine sedimentary rocks.. Around Zhabu—Shuanghu area, there exits a post late Triassic uplift, in which middle Devonian low\|intermediate degree metamorphic rocks with solid chronological evidence have been found. However, in central Qiangtang, debate is still there in several aspects, such as there is crystalline basement or not, basement features, and the pre\|Devonian evolution of Qiangtang plate, etc. (Cai Li et al.,1997)Duguer gneiss is the only proved gneiss in Qiangtang region upto now, which is exposed at Duguer mountain (peak, 6208m above sea level), Gaize county, and is confined by faults. An E—W oriented thrust fault zone is its south boundary, which is more than 200m wide and makes the gneiss overthrust on upper Carboniferous strata and Tertiary red beds southwardly. On the east and north sides of the gneiss are upper Carboniferous strata. The gneiss occurs as a triangle form with a long E—W trending bottom line (about 20km) and a height about 10km in S—N direction, which is the main part of Duguer Duguer mountain.Duguer gneiss consists of two rocks types, i.e. granitic gneiss (the dominant component) and amphibole\|plagioclase gneiss. The latter one occurs as a group of nearly E—W trending dikes with clear boundary, which are obviously late basic dikes that intruded into granite. Granitic gneiss is composed of porphyroclast granitic gneiss, banded granitic gneiss, gneissoid granite and granitic mylonite. Both granitic and amphibole\|plagioclase gneisses have been undergone same type and same degree metamorphism and deformation. The typical mineral assemblage of the former gneiss include quartz(30%), microcline(25%),plagioclase(30%), two mica (biotite +muscovite,13%) and the accessory minerals such as zircon, magnetite, and apatite etc. The main oxide contents of the granitic gneiss are (average of three samples) 73 53% SiO\-2, 12 9% Al\-2O\-3, 1 57% FeO, 0 52% MgO, 3 24%Na\-2O and 0 22% K\-2O. The REE distribution pattern shows typical features of granite, i.e. LREE enrichment, HREE depletion and rather strong negative Eu anomaly.
文摘High in sodium and low in potassium （Na<sub>2</sub>O/ K<sub>2</sub>O】1）, the charnockitic gneiss series in theSantunying- Taipingzhai area, eastern Hebei province, consists of hypersthene- quartz- diorite,hypersthene-granodiorite and hypersthene-plagioclase-granite. Geological, petrological and large ion lithophileelement（LILE）, high field strength element （HFSE） and REE geochemical studies suggest that themedium-coarse-grained hypersthene-granodiorite is the product of crystallization of anatectic magmas of thesame composition. Under granulite facies conditions, the equilibrium crystallization differentiation of themagmas yielded the early crystallization phase-high-SiO<sub>2</sub>, LILE-depleted, low-∑REE, positive Eu anomalyand REE- saturated hypersthene- plagioclase- granite. The residual phase, coarse- grained to pegmatitichypersthene- granodiorite, is marked by low SiO<sub>2</sub>, LILE-enrichment, high ∑REE and REE-undersaturation.These rocks and hypersthene-quartz-diorite enclaves constitute the sodium-charnockitic gneiss series in easternHebei province. Model calculation for trace elements in the granitoids was applied. On the basis of a systematicgeological study, the equation for calculation was chosen, the source magma was determined and the partitioncoefficients were obtained. The resulting curves are entirely consistent with those observed in the patterns of ac-tual rocks. The study indicates that whole-rock REE patterns can not be used directly in the comparison of thesources and genesis of granitoids.
文摘The Banded Gneissic Complex(BGC) of the Aravalli Craton is divided into BGC-I and BGC-Ⅱ; the BGC-Ⅱ(central Rajasthan) is comprised of the Sandmata Complex and the Mangalwar Complex. We report elemental and Nd-isotope geochemistry of basement gneisses of the Mangalwar Complex and constrain its origin and evolution. Geochemically, the basement gneisses have been classified as low-SiO_2 gneisses(LSG) and high-SiO_2 gneisses(HSG). Both the LSG and HSG are potassic, calc-alkaline and peraluminous in nature. The LSG are enriched in incompatible(K, Sr, Ba, large ion lithophile elements) and compatible elements(MgO, Cr, and Ni). They display fractionated rare earth element patterns(avg.La_N/Yb_N=12.1)with small Eu-anomaly(δEu=0.9), and exhibit negative anomalies of Nb and Ti in primitive mantlenormalized multi-element diagram. In terms of Nd-isotope geochemistry, the LSG are characterized by_(εNd)(t)=4.2 and depleted mantle model age of 3.3 Ga. To account for these geochemical characteristics we propose a three-stage petrogenetic model for the LSG:(1) fluids released from dehydration of subducting slab metasomatised the mantle-wedge;(2) the subducting slab underwent slab-breakoff causing upwelling and decompression melting of the asthenosphere during waning stage of subduction; and(3)upwelling asthenosphere provided the requisite heat for partial melting of the metasomatised mantlewedge leading to generation of the LSG parental magma. Asthenospheric upwelling also contributed in the LSG petrogenesis which is evident from its high Mg#(avg. 0.53). The LSG formed in this way are contemporary and chemically akin to sanukitoids of the BGC-I and Archean sanukitoids reported elsewhere. This provides a basis to consider the LSG as a part of the BGC-I. Contrary to the LSG, the HSG are depleted in compatible elements(MgO=avg. 1.1 wt.%; Cr=avg. 8 ppm; Ni=avg. 6 ppm) but enriched in incompatible elements(Sr=avg. 239 ppm, Ba=avg. 469 ppm). Its_(εNd)(t) values vary from-9.5 to-5.4.These chemical features of the HSG are akin to potassic granitoids found elsewhere. In this backdrop, we propose that the HSG suite of the Mangalwar Complex was derived from re-melting(partial) of an older crust(TTG?) occurring within the BGC-Ⅱ.
基金This study is a project (Nos.38970134 and 49070136)supported by the National Natural Science Foundation of China
文摘Grey gneisses are tonalitic intrusive rocks that have Archaean characteristics and tectonic significance. Archaean grey gneisses in North China may be classified into two types: the Zunhua type and the Heagshan type. Grey gneisses of the Zunhua type alternate with basic granulites, forming a bimodal migmatitic suite. The rock is characterized by complex mineral composition, highly varied REE patterns and positive Eu anomaly and originated from autochthonous or partly autochthonous deep-level migmatization with a high degree (30%±) of fusion. As the sub-stratum in the root of the early-stage high-grade greenstone belt, they prevented basic rocks from sinking. Grey gneisses of the Hengshan type are characterized by a relatively distinct intrusion form, large-amplitude upward emplacement, rather simple mineral composition, only slight/changes of REE patterns and absence of Eu anomaly. The rock is a product of subduction and underthrusting of the high-grade greenstone belt and then fusion and emplacement
基金funding from the Department of Science and Technology, Government of India(India) under the DST INSPIRE Faculty Scheme (Grant:DST/INSPIRE/04/2014/000221)
文摘Phase equilibria modelling coupled with U–Pb zircon and monazite ages of garnet–cordierite gneiss from Vallikodu Kottayam in the Kerala Khondalite Belt,southern India are presented here.The results suggest that the area attained peak P–T conditions of^900C at 7.5–8 kbar,followed by decompression to 3.5–5 kbar and cooling to 450–480C,preserving signatures of the partial melting event in the field of high to ultra-high temperature metamorphism.Melt reintegration models suggest that up to 35%granitic melt could have been produced during metamorphism at^950C.The U–Pb age data from zircons(~1.0–~0.7 Ga)and chemical ages from monazites(~540 Ma and^941 Ma)reflect a complex tectonometamorphic evolution of the terrain.The^941 Ma age reported from these monazites indicate a Tonian ultra-high temperature event,linked to juvenile magmatism/deformation episodes reported from the Southern Granulite Terrane and associated fragments in Rodinia,which were subsequently overprinted by the Cambrian(~540 Ma)tectonothermal episode.
基金supported by the Department of Hydrogeology at TU Freiberg.
文摘Investigating and modeling fluid flow in fractured aquifers is a challenge. This study presents the results of a series of packer tests conducted in a fractured aquifer in Freiberg, Germany, where gneiss is the dominant rock type. Two methods were applied to acquire hydraulic properties from the packer tests: analytical and numerical modeling. MLU (Multi-Layer Unsteady state) for Windows is the analytical model that was applied. ANSYS-FLOTRAN was used to build a two-dimensional numerical model of the geometry of the layered aquifer. A reasonable match between experimental data and simulated data was achieved with the 2D numerical model while the solution from the analytical model revealed significant deviations with respect to direction.
基金The project supported by the National Natural Science Foundation of China
文摘The grey gneisses are composed of early-stage layered TTG and late-stage diapiric tonalite in-trusions.The Dabie complex,northeastern Hubei Province,may be distinguished into supracrustal sequenceand grey gneisses.Different distribution patterns of rare earth elements in the early- and late- stage gneisses,i.e.the early-stage gneisses are enriched in LREE and remarkably depleted in HREE;and late-stage isslightly enriched in LREE and unevidently depleted in HREE.Geological evidence and characteristics of el-ement ratio diagrams suggest that the TTG is mainly controlled by portional partial melting and accompa-nied with fractional crystallization.The quantitative modelling of REE pattern indicates that TTG is formedfrom amphibolite transformed from basic rocks with 25%～65% of portional partial melt while thelate-stage tonalite intrusion was also accompanied with fractional crystalization of 22% biotites.
文摘The sample location in our paper(Sorcar et al.,2020)was incorrectly marked in Fig.1,although the GPS location was reported correctly.The corrected sample location of garnet-cordierite gneiss is shown in Fig.1.The sample location falls within the Achankovil Shear Zone(ASZ)and not in the Trivandrum Block as stated in our paper.Thus,the Tonian ultrahigh-temperature(UHT)metamorphic event reported in our paper is applicable to ASZ,and not for the Trivandrum Block.The related discussion on Gondwana correlation in our paper may be viewed and read in that context.
基金financially supported by the Ministry of Science and Technology of China(State Key Research Project No.2017YFC0601302)the Chifeng Chaihulanzi Gold Mining Co.Ltd.(Shandong Gold Group)。
文摘The Chaihulanzi area in eastern Inner Mongolia is tectonically situated on the northern margin of the North China Craton(NCC). The main Precambrian lithologies of the area have been referred to the Archean Jianping Group metasupracrustal sequences. Based on field observations, petrographic, whole-rock geochemical, and zircon U-Pb geochronological results, a magmatic origin for the units is proposed. Our results show that the Chaihulanzi gneisses are mainly of granitic, dioritic and granodioritic compositions, and show typical magmatic rock textures and mineral assemblages. The dioritic and granodioritic gneisses show Na-rich tonalite–trondhjemite–granodiorite(TTG)-like affinity with zircon U-Pb dates of ca. 2.57–2.59 Ga, representing a juvenile continental growth for the northeastern NCC. The granitic gneiss is indeed potassic granite and yielded a zircon U-Pb date of ~2.50 Ga, which is contemporaneous with the Jining–Jiaoliao microblock collision(2.53–2.49 Ga), implying another crustal growth event. The well-developed gneissosity in 2.57–2.59 Ga dioritic and granodioritic gneisses together with the 2.5 Ga potassic granite, which crosscuts the gneissosity implies a 2.57–2.50 Ga(mainly 2.53–2.51 Ga) collisional orogeny, probably related to the Jining–Jiaoliao microblock collision. Our new geology and chronological results provide new evidence for the early Precambrian tectonic evolution of the NCC.
基金supported by the National Natural Science Foundation of China(Nos.41303041 and41763005)Open Fund(Nos.Z1909,Z1912,RGET1804,15LCD08)of the State Key Laboratory of Nuclear Resources and Environment+1 种基金Fundamental Science on Radioactive Geology and Exploration Technology LaboratoryState Key Laboratory of Continental Dynamics。
文摘The cratonization history of the North China Craton(NCC)and the nature of tectonothermal events are still highly controversial.Tonalite-trondhjemite-granodiorite(TTG)gneisses,as the dominant lithological assemblages in Archean metamorphic terranes,can provide significant clues to the magmatic and metamorphic evolution of Precambrian crust.This study presents zircon laser-ablation inductively-coupled-plasma mass spectrometry U–Pb ages,trace-element,and in-situ LA-MC-ICPMS zircon Hf isotope data for the TTG gneisses from the Bengbu-Wuhe area on the southeastern margin of the NCC.Cathodoluminescence images and trace elements indicated that magmatic zircons display the characteristics of euhedral-subhedral crystals with oscillatory growth zoning structures,high RREE contents,marked Ce positive anomalies,and Pr–Eu negative anomalies.The metamorphic zircons display the spherical-oval crystals with distinct core-rim structures,high and homogeneous luminescent intensity,lower RREE,Nb,Ta,Hf contents,relative flat REE patterns,weak Ce positive anomalies,and Pr-Eu negative anomalies.The Ti–in–zircon geothermometer data indicate that the crystallization temperature of the TTG gneiss ranged from 754 to 868℃.Zircon U–Pb ages indicate that the TTG gneisses formed at 2.79–2.77 Ga and 2.50 Ga and underwent metamorphism at 2.57–2.52 Ga.The Hf isotopic data indicate that the magmatic zircons exhibit high,positive eHf(t)values close to those of the coeval depleted mantle,whereas the metamorphic zircons exhibit negative or nil eHf(t)values.This implies that the TTG gneisses were derived from the partial melting of the~2.9–2.6 Ga juvenile crustal sources mixed with~3.0–2.8 Ga ancient crustal materials.Combined with the regional tectonic evolution,we propose that the metamorphic basement at the southeastern margin of the NCC underwent episodic crustal growth at~2.7 and~2.5 Ga and subsequently underwent crustal reworking or re-melting of the ancient crust during the Neoarchean.The Neoarchean TTG gneisses might have been derived from the partial melting of lower crustal materials related to plate subduction.
