Sm Nd isotopic compositions of eight lamprophyre samples, which come from the Gezhen gold bearing shear zone on western Hainan Island, are measured. The Sm Nd isochron age is 495.98±13.14 Ma, (143Nd/144Nd)0=0.512...Sm Nd isotopic compositions of eight lamprophyre samples, which come from the Gezhen gold bearing shear zone on western Hainan Island, are measured. The Sm Nd isochron age is 495.98±13.14 Ma, (143Nd/144Nd)0=0.512094, εNd(t) ranges from +1.80 to +2.00 and TDM from 982 Ma to 1196 Ma (average: 1060 Ma). The authors point out that the whole rock Sm Nd isochron age (495.98±13.14 Ma) really represents the petrogenetic age of lamprophyre and the time of magmatism during subsequent subduction.展开更多
As the principal ore mineral in various tungsten(-gold)deposits,scheelite(CaWO_(4))plays an important role in directly dating the timing of ore formation,and in tracing associated material sources through the study of...As the principal ore mineral in various tungsten(-gold)deposits,scheelite(CaWO_(4))plays an important role in directly dating the timing of ore formation,and in tracing associated material sources through the study of its Sm-Nd geochronology and Nd isotopic characteristics.Since the retention of Sm-Nd systematics within scheelite is presently unconstrained,equivocal interpretations for isotopic data resulting from this method have occurred quite often in previous studies that apply these isotopic data.In order to better elucidate the closure of Sm-Nd in scheelite,the kinetics of Sm and Nd within this mineral lattice were investigated through calculation of diffusion constants presented herein.The following Arrhenius relations were obtained:D_(Nd)=4.00exp(-438 kJ·mol^(–1)/RT)cm^(2)/s D_(Sm)=1.85exp(-427 kJ·mol^(–1)/RT)cm^(2)/s showing diffusion rate of Nd is near identical to Sm in scheelite when at the same temperature.However,compared to other rare earth elements(REEs),which have markedly different atomic radii to either Nd or Sm,these are shown to exhibit a great variation in diffusivities.The observed trends in our data are in excellent agreement with the diffusion characteristics of REEs in other tetragonal ABO4 minerals,indicating that ionic radius is a key constraint to the diffusivity of REEs in the various crystal lattices.With this in mind,the same substitution mechanism and a very slight discrepancy in radii will allow us to infer that significant Sm/Nd diffusional fractionation in scheelite is unlikely to occur during most geological processes.Based upon the diffusion data determined herein,Sm and Nd closure temperatures and retention times in scheelite are discussed in terms of diffusion dynamics.Those results suggest that closure temperatures for Sm-Nd within this mineral are relatively high in contrast to the temperature ranges of ore-formation responsible for scheelite-related deposits,and any later thermal environments.It is likely,therefore,that relevant isotopic information could be easily retained under most geological conditions,since initial crystallization of the scheelite.In addition,comparison of this mineral-element pair over a range of temperatures with some other common minerals used as geochronometers(e.g.,zircon and apatite)indicates that Sm-Nd system has a slower diffusive rate in scheelite than for Sr in apatite or Ar in quartz,and only a little faster than for Pb in zircon.It should be noted,within most hydrothermal deposits where zircon has crystallized,its size is typically no more than 100μm,whereas scheelite commonly occurs as macroscopic grains.For this reason,the larger dimensions of scheelite would provide a robust Sm-Nd system more able to resist perturbations,relating to any later thermal process.As such Sm-Nd investigations of scheelite are akin to U-Pb within zircon samples used in isotopic dating.These observations indicate that Sm-Nd age and isotopic information can provide reliable data in all but the most extreme case,especially when data are extracted from macroscopic grains of scheelite that are chosen to be“pristine”(i.e.,free of surface alteration and/or fractures).展开更多
Sm-Nd isotopic ages for C-type eclogite (243.9±5.6 Ma) and mafic and ultramafic rocks(230.6±30.7 Ma and 402.6±17.4 Ma) from the Qinling-Dabieshan orogenic belt are reported.These ages suggest that at th...Sm-Nd isotopic ages for C-type eclogite (243.9±5.6 Ma) and mafic and ultramafic rocks(230.6±30.7 Ma and 402.6±17.4 Ma) from the Qinling-Dabieshan orogenic belt are reported.These ages suggest that at the early Triassic, the North and South China Blocks have beenunited along the Qinling-Dabieshan collision zone, and before the final collision, a se-ries of ophiolite obductions took place successively away from the continental marginduring the Paleozoic.展开更多
A large eclogite belt developed along the Dabie Mountains and Subei-Jiaonan Rise in central China is a result of collision between the North China and Yangtze blocks. Recently, coesite and coesite pseudomorphs are rec...A large eclogite belt developed along the Dabie Mountains and Subei-Jiaonan Rise in central China is a result of collision between the North China and Yangtze blocks. Recently, coesite and coesite pseudomorphs are recognized as an inclusion in both garnet展开更多
Qinling-Dabieshan orogenic belt is generally believed to be a collision zone between the North China Block (NCB) and the Yangtze Block (YB). Various high P/T metamorphic rocks, such as blueschist, C-type eclogite, are...Qinling-Dabieshan orogenic belt is generally believed to be a collision zone between the North China Block (NCB) and the Yangtze Block (YB). Various high P/T metamorphic rocks, such as blueschist, C-type eclogite, are well developed along the suture in this belt.Precise dating of the eclogite has very important significance for understanding of the collision time between the NCB and the YB and the evolutionary history of the orogenic belt.展开更多
GEOLOGICAL scientists have paid much attention to the suture zones formed by collision between the Sino-Korean and Yangtze blocks because of the discovery of the ultrahigh pressue metamorphic (UHPM) rocksfrom northern...GEOLOGICAL scientists have paid much attention to the suture zones formed by collision between the Sino-Korean and Yangtze blocks because of the discovery of the ultrahigh pressue metamorphic (UHPM) rocksfrom northern Jiangsu Province (Su), southern Shandong Province (Lu) and the Dabie Mountains.Although the age of 200-240 Ma is probably the best estimation for UHPM metamorphism in the DabieMountains, the primary intrusive and metamorphic ages of the complex from northern Jiangsu Provincehave not been determined before. Using the Sm-Nd isotopic dating method, our study is aimed at datingthe UHPM metanorphic event of northern Jiangsu Province and researching a probable relation between theUHPM rocks from the Dabie Mountains and the UHPM rocks from northern Jiangsu Province.展开更多
We report geochemical data, SHRIMP zircon ages and Hf-in-zircon isotopic compositions for Cenozoic granitoids from major fault systems in the Tethyan belt in western Yunnan Province, southwestern China.Four magmatic p...We report geochemical data, SHRIMP zircon ages and Hf-in-zircon isotopic compositions for Cenozoic granitoids from major fault systems in the Tethyan belt in western Yunnan Province, southwestern China.Four magmatic pulses occurred in the Paleogene, namely at ca.57 Ma, ca.50 Ma, 45–40 Ma, and 38–34 Ma.Early magmatism of this episode(57–50 Ma) produced S-type granites whose zircons yielded εHf(t) values of-5.0 to-0.3.In contrast, late magmatism of this episode reflects heterogeneous sources.Zircons from a granite porphyry along the Ailaoshan-Red River fault system have slightly positive εHf(t) values suggesting derivation from relatively young crust and/or a juvenile source.However, zircons from a granite along the Gaoligong fault system have strongly negative εHf(t) values and suggest derivation from a Paleoproterozoic crustal source.The composition of the granitoids varies with age(from ca.57 Ma to ca.34 Ma) from peraluminous to metaluminous and also suggests a change from syn-collisional to late-orogenic tectonic setting.A new tectonic model, impacting lithospheric wedge(ILW) is shown for the origin of Paleogene granitoids in this paper.展开更多
The Dehe granitic pluton intruded the Xiahe Group which is in the core complex of the North Qinling Orogenic Belt(NQOB).It shows gneissic bedding and possesses typical S-type granite minerals such as muscovite and gar...The Dehe granitic pluton intruded the Xiahe Group which is in the core complex of the North Qinling Orogenic Belt(NQOB).It shows gneissic bedding and possesses typical S-type granite minerals such as muscovite and garnet.LA-ICP-MS U-Pb isotopic dating of the Dehe granite yielded a weighted average age of 925±23 Ma which represents the emplacement age of the pluton.Most of the εHf(t) values are negative,and the two-stage model ages are consistent with the age of the Qinling Group.The isotope data show that the Dehe granite was formed in the following geological setting:in the syn-collision setting of the NQOB in the Neoproterozoic,crustal thickening induced partial melting of materials derived from the Qinling complex,and then the maga upwelled and intruded into the Xiahe Group.The formation of the Dehe S-type granite implied the occurrence of a convergent event in the QOB during the Neoproterozoic.展开更多
Keban magmatics consist of plutonic rocks of acidic and intermediate compositions with diffe rent phases. They are the equivalent of surface rocks. In the current study on plutonic rocks, general petrographic features...Keban magmatics consist of plutonic rocks of acidic and intermediate compositions with diffe rent phases. They are the equivalent of surface rocks. In the current study on plutonic rocks, general petrographic features, disequilibrium textures such as skeletal formation in minerals, poikilitic texture, oscillatory zoning, and mineral fragmentation, and growth states are observed. Besides these microscopic properties, the existence of rounded mafic enclaves of various sizes, petrographic synplutonic dykes, and field data support the idea that mafic and felsic magmas are mixed. Keban magmatics have I-type, metaluminous-peraluminous characteristics. Diorites and quartz diorites have low-K tholeiitic features, whereas tonalites have low-K calcalkaline features. Compared with diorites, tonalites are richer in terms of LREE (Rock/ Chondrite);Rb, Sr, and Ba (LILE);and Hf, Zr, Th, and U (HFSE) elements. LILE enrichment, which signals the crustal contamination of mantle- originated magmas, is particularly observable in tonalites. In both rock groups, the negative anomaly of Nb is a sign of similarity of pluton to the subduction zone magma series. Based on the K-Ar geochronology dating of amphibole minerals, the ages of these rocks are found to be 75.65 ± 1.5 and 59.77 ± 1.2 Ma in tonalites and 84.76 ± 1.8 and 84.35 ± 1.7 Ma in diorite and quartz diorites. The 87Sr/86Sr isotope ratios in tonalites are 0.705405 and 0.706053, whereas these ratios are 0.704828 and 0.704754 in dioritic rocks. Pb isotope ratios are similar in both rock types.展开更多
The Zhalaxiageyong lead-zinc-copper polymetallic deposit is a typical porphyry deposit of the Tuotuohe area. Whole-rock geochemical analyses,Zircon U-Pb dating and Hf isotope analysis are undertaken for the ore host t...The Zhalaxiageyong lead-zinc-copper polymetallic deposit is a typical porphyry deposit of the Tuotuohe area. Whole-rock geochemical analyses,Zircon U-Pb dating and Hf isotope analysis are undertaken for the ore host trachydacite with the aim of constraining its petrogenesis,magma source and regional tectonic setting.LA-ICP-MS zircon U-Pb dating indicates that the trachydacite was formed in 32. 68 ± 0. 50 Ma( MSWD =1. 6),i. e.,Oligocene. The trachydacite is rich in potassium and poor in Mg#( 5. 10-9. 70),belonging to the peraluminous shoshonite series. The rocks are enriched in LILE( large ion lithophile elements) Rb,Ba,K and LREE,depleted in HFSE( high field strength elements) Nb,Ta,P,Ti,with high Sr and low Y and Yb,having the characteristics of the C type adakite. It is calculated that the initial εHf( t) of the zircons range from-0. 92 to 2. 07 and their two-stage Hf model ages T_(DM2) range from 978 Ma to 1 169 Ma. The magma source should be mainly the partially melt mafic rocks of the thickened Middle Neoproterozoic lower crust of the Northern Qiangtang massif with the addition of ancient aluminosilica material in the melting process. The rocks formed in the tectonic setting of delamination of lithosphere and extension of the thickened crust. During the period of 40-32 Ma,large-scale potassium rich alkaline magmatism occurred in this area. The porphyry metallogenesis is related to the magmatic activities in this period.展开更多
Objective The Geza arc in Yunnan Province,located in the southern Yidun arc,is an important part of the Sanjiang tectonic-magmatic belts in southwestern China and is a newly discovered copper polymetallic ore-concentr...Objective The Geza arc in Yunnan Province,located in the southern Yidun arc,is an important part of the Sanjiang tectonic-magmatic belts in southwestern China and is a newly discovered copper polymetallic ore-concentrating district.Recent studies show that the newly discovered Yanshanian porphyry Cu-Mo polymetallic mineralization superimposed in the Indosinian porphyry copper belt in this area.展开更多
The combined petrographic,petrological,geochemical and geochronological study of the Neoproterozoic gneisses of the Sarychabyn and Baskan complexes of the Junggar Alataw of South Kazakhstan elucidate the Precambrian t...The combined petrographic,petrological,geochemical and geochronological study of the Neoproterozoic gneisses of the Sarychabyn and Baskan complexes of the Junggar Alataw of South Kazakhstan elucidate the Precambrian tectonic evolution of the Aktau–Yili terrane.It is one of the largest Precambrian crustal blocks in the western Central Asian orogenic belt.The U-Pb single-grain zircon ages indicate that granite-gneisses formed from the same source and crystallised in the early Neoproterozoic ca.930–920 Ma.The chemical composition of gneisses corresponds to A2-type granites.The whole-rock Nd isotopic characteristics(εNd(t)=−4.9 to−1.0 and TNd(DM-2st)=1.9 to 1.7 Ga)indicate the involvement of Paleoproterozoic crustal rocks in magma generation.Early Neoproterozoic ca.930–920 Ma A-type granitoids in the Aktau–Yili terrane of South and Central Kazakhstan might reflect within-plate magmatism adjacent to the collisional belt or a local extension setting in back-arc areas of the continental arc.展开更多
Iron formations are valuable archives of sedimentary conditions and post-depositional events.However,geochemical proxies commonly used to determine genetic characteristics can be variably modified during metamorphism ...Iron formations are valuable archives of sedimentary conditions and post-depositional events.However,geochemical proxies commonly used to determine genetic characteristics can be variably modified during metamorphism and deformation,hampering their use as records of regional geological events.This work focuses on strongly reworked magnetite-quartz-rich rocks from the São Josédo Campestre Massif,one of the oldest fragments of preserved crust in South America.The genetic classification of these magnetite-quartz-rich rocks is not straightforward because primary assemblages and textures were variably modified by granulite facies metamorphism during a regional Paleoproterozoic migmatization event.To address genetic ambiguities,we analyzed their magnetite and pyroxene chemistry,wholerock geochemistry,and Sm-Nd isotopes.Magnetite chemistry indicates that pyroxene-poor iron formations(Type B)are low in trace elements such as Ti,Al,V,and Mn,suggesting a chemical similarity to iron formations elsewhere.In contrast,magnetites from pyroxene-enriched Type A iron formations are rich in trace elements and more akin to magnetite crystallized from higher temperature systems,such as skarn and IOCG.The^(147)Sm/^(144)Nd of these rocks show substantial variation even at the outcrop scale,indicating a locally-controlled,highly heterogeneous mixture of Archean,Paleoproterozoic,and Neoproterozoic sources.Therefore,our geochemical tools point out to heterogenous signatures of these magnetitequartz rocks and proxies compatible with both low and high-temperature conditions and age of deposition spanning sources from the Archean to the Neoproterozoic.We interpret that the studied São Josédo Campestre magnetite-quartz rocks represent Archean iron formations with original magnetite chemistry and isotopic signatures variably modified by metamorphism and by at least one deformation-related hydrothermal event.These results contrast with similar examples from China and Greenland where iron formations either preserved the magnetite chemistry or the primary isotopic signatures.Our study indicates that metamorphism can selectively affect chemical proxies used to study iron formations and undermine the genetic classification of iron ores.Thus,these proxies should be carefully applied in the interpretation of syn-depositional environments of polydeformed belts.展开更多
A large area of Late Paleozoic intrusions occursalong the Kalamaili fault in North Xinjiang,which is divided into I-type and A-type granite(Liu et al.,2013),and are the ideal objects for revealing the geological evolu...A large area of Late Paleozoic intrusions occursalong the Kalamaili fault in North Xinjiang,which is divided into I-type and A-type granite(Liu et al.,2013),and are the ideal objects for revealing the geological evolution of this region.However,the study of the granodioritic pluton in East Junggar is particularly weak.展开更多
The provenance of sandstones derived from theLower Voltaian Kwahu-Morago Group and the Middle Voltaian Oti-Pendjari Group of the Neoproterozoic Voltaian basin are discriminated by their Sm-Nd Isotopic compositions. Pl...The provenance of sandstones derived from theLower Voltaian Kwahu-Morago Group and the Middle Voltaian Oti-Pendjari Group of the Neoproterozoic Voltaian basin are discriminated by their Sm-Nd Isotopic compositions. Plots from the Sm-Nd data suggested provenance of the Kwahu-Morago Group to be from the Birimian metasediments and associated “basin type”granitoids. The Sm-Nd studies have further revealed an average TDM model age of whole rock samples in the Kwahu-Morago Group to be 2.2 Ga which shows that this portion of the Voltaian Supergroup represents eroded remnants of “basin type” granitoids. Sm-Nd data from the Oti-Pendjari Group suggested provenance from the Birimian volcanic rocks and probably with contribution from the Pan African rocks. Its average TDM model age of whole rock samples was 2.0 Ga, which generally falls in the range of the model ages for the basement Birimian volcanic rocks as well as the model ages for the granitoid rocks and thus suggests the major source rock of the Oti-Pendjari Group as coming from the volcanic belts. The model ages for both groups seem to indicate clastic supply from an early Proterozoic crustal provenance. This study shows that whole rock isotopic analyses can also be complementary in providing an insight into the origin and development of sedimentary successions.展开更多
Objective The Late Paleozoic Southern Tianshan Ocean is usually considered to be the last-closed ocean in the Tianshan Orogeny. However, there is still no consensus if this is indeed the case. Blueschist, eclogite an...Objective The Late Paleozoic Southern Tianshan Ocean is usually considered to be the last-closed ocean in the Tianshan Orogeny. However, there is still no consensus if this is indeed the case. Blueschist, eclogite and ophiolite are present in the Atbashi Range, Kyrgyzstan, which are believed to be the relics of the Southern Tianshan Ocean. New data obtained through Ar-Ar isotopic analysis in this research provide reliable chronological restrictions for this problem.展开更多
Whole-rock Rb-Sr, zircon U-Pb and hornblende, biotite and K-feldspar K-Ar ages areused to reconstruct the cooling history of the Huangmeijian intrusion in the Anqing-Lujiangquartz-syenite belt in Anhui. Oxygen isotope...Whole-rock Rb-Sr, zircon U-Pb and hornblende, biotite and K-feldspar K-Ar ages areused to reconstruct the cooling history of the Huangmeijian intrusion in the Anqing-Lujiangquartz-syenite belt in Anhui. Oxygen isotope geothermometry of mineral pairs demonstrates thatdiffusion is a dominant factor controlling the closure of isotopic systems. Assuming the coolingof the intrusion is synchronous with a dicrease in local geothermal gradients, an emplacementdepth of about 8 km and the magma crystallization temperature of 800±50℃ are estimated. TheHuangmeijian intrusion experienced a rapid cooling process and uplifted after its emplacementand crystallization at 133 Ma B.P. with a cooling rate of 34.5℃/Ma and an uplifting rate of 0.35mm/a. The intrusion was rising until it rested at a depth of 3km at a temperature of 300±50℃about 14 Ma later. Then the intrusion was in slow cooling and uplifting with a cooling rate of4.4℃/Ma and an uplifting rate of 0.04 mm/a. U-Pb dating of pitchblende is done for the hydrothermal uranium deposit formed in thecontact zone of the Huangmeijian intrusion. The result shows that the mineralization age is closeto the closing time of the K-Ar system in biotite. The fluid inclusion thermometry indicates thatthe mineralization temperature is in agreement with the closure temperature of the biotite K-Arsystem. This suggests a close relationship between the slow cooling of the intrusion and thehydrothermal uranium mineralization process.展开更多
Located in the middle segment of the Trans-North China Orogen, the Fuping Complex is considered as a critical area in understanding the evolution history of the North China Craton (NCC). The complex is composed of v...Located in the middle segment of the Trans-North China Orogen, the Fuping Complex is considered as a critical area in understanding the evolution history of the North China Craton (NCC). The complex is composed of various high-grade and multiply deformed rocks, including gray gneiss, basic granulite, amphibolite, fine-grained gneiss and marble, metamorphosed to upper amphibolite or granulite facies. It can be divided into four rock units: the Fuping TTG gneisses, Longquanguan augen gneisses, Wanzi supracrustals, and Nanying granitic gneisses. U-Pb age and Hf isotope compositions of about 200 detrital zircons from the Wanzi supracrustals of the Fuping Complex have been analyzed. The data on metamorphic zircon rims give ages of 1.82-1.84 Ga, corresponding to the final amalgamation event of the NCC, whereas the data for igneous zircon cores yield two age populations at -2.10 and -2.51 Ga, with some inherited ages scattering between 2.5 and 2.9 Ga. These results suggest that the Wanzi supracrustals were derived from the Fuping TTG gneisses (-2.5 Ga) and the Nanying granitic gneisses (2.0-2.1 Ga) and deposited between 2.10 and 1.84 Ga. All zircons with -2.51 Ga age have positive initial εHf values from +1.4 to +10.9, suggesting an important crustal growth event at -2.5 Ga through the addition of juvenile materials from the mantle. The Hf isotope data for the detrital zircons further imply that the 2.8 Ga rocks are important components in the lower crust, which is consistent with a suggestion from Nd isotope data for the Eastern Block. The zircons of 2.10 Ga population have initial εHf values of-4.9 to +6.1, interpreted as mixing of crustal re-melt with minor juvenile material contribution at 2.1 Ga. These results are distinct from that for the Western Block, supporting that the Fuping Complex was emplaced in a tectonic active environment at the western margin of the Eastern Block.展开更多
We report here U-Pb age and in situ Hf isotopic results for detrital and magmatic zircons from one conglomerate and four tuffite samples from the Late Triassic Nadigangri Formation across the North Qiangtang depressio...We report here U-Pb age and in situ Hf isotopic results for detrital and magmatic zircons from one conglomerate and four tuffite samples from the Late Triassic Nadigangri Formation across the North Qiangtang depression, Tibet. Coupled with previously published data in the region, this paper proposes new insights into the geochronological framework for the Nadigangri Formation. The deposition ages of tuffite from top to bottom in the Woruo Mountain, Quem Co and Dongqu River, are 203 Ma, 226 Ma, 221.5 Ma and 221.1 Ma, respectively. The detrital zircons yield a younger cluster of ages of 201.5-225 Ma from the conglomerate of the Quem Co Formation. The Late Triassic Nadigangri Formation defines a temporal range approximately between 201 and 225 Ma (Norian-Rhaetian), including three predominant groups of 220-225 Ma, 210-217 Ma and 201-205 Ma, which correspond with the three main rifting episodes of initial rifting, further rifting and final rifting. Positive ~Hf(t) value and low model ages in younger detrital zircons suggests a juvenile character. However, the Hf isotopes of magmatic zircons display the presence of reworked ancient crust with 1.1-1.8 Ga. These results provide strong constraints not only on the temporal range of the Late Triassic Nadigangri Formation, but also on the onset of the Qiangtang Mesozoic rift basin.展开更多
Late Mesozoic volcanic-subvolcanic rocks and related iron deposits, known as porphyry iron deposits in China, are widespread in the Ningwu ore district (Cretaceous basin) of the middle-lower Yangtze River polymetall...Late Mesozoic volcanic-subvolcanic rocks and related iron deposits, known as porphyry iron deposits in China, are widespread in the Ningwu ore district (Cretaceous basin) of the middle-lower Yangtze River polymetallic ore belt, East China. Two types of Late Mesozoic magmatic rocks are exposed: one is dioritic rocks closely related to iron mineralization as the hosted rock, and the other one is granodioritic (-granitic) rocks that cut the ore bodies. To understand the age of the iron mineralization and the ore-forming event, detailed zircon U-Pb dating and Hf isotope measurement were performed on granodioritic stocks in the Washan, Gaocun-Nanshan, Dongshan and Heshangqiao iron deposits in the basin. Four emplacement and crystallization (typically for zircons) ages of granodioritic rocks were measured as 126.1±0.5 Ma, 126.8±0.5 Ma, 127.3±0.5 Ma and 126.3±0.4 Ma, respectively in these four deposits, with the LA-MC-ICP-MS zircon U-Pb method. Based on the above results combined with previous dating, it is inferred that the iron deposits in the Ningwu Cretaceous basin occurred in a very short period of 131-127 Ma. In situ zircon Hf compositions of εHf(t) of the granodiorite are mainly from -3 to -8 and their corresponding 176Hf/177Hf ratio are from 0.28245 to 0.28265, indicating similar characteristics of dioritic rocks in the basin. We infer that granodioritic rocks occurring in the Ningwu ore district have an original relationship with dioritic rocks. These new results provide significant evidence for further study of this ore district so as to understand the ore-forming event in the study area.展开更多
文摘Sm Nd isotopic compositions of eight lamprophyre samples, which come from the Gezhen gold bearing shear zone on western Hainan Island, are measured. The Sm Nd isochron age is 495.98±13.14 Ma, (143Nd/144Nd)0=0.512094, εNd(t) ranges from +1.80 to +2.00 and TDM from 982 Ma to 1196 Ma (average: 1060 Ma). The authors point out that the whole rock Sm Nd isochron age (495.98±13.14 Ma) really represents the petrogenetic age of lamprophyre and the time of magmatism during subsequent subduction.
基金financially supported by the National Natural Science Foundation of China(Grant No.41403035)the National Basic Research Program of China(Grant No.2014CB440901)。
文摘As the principal ore mineral in various tungsten(-gold)deposits,scheelite(CaWO_(4))plays an important role in directly dating the timing of ore formation,and in tracing associated material sources through the study of its Sm-Nd geochronology and Nd isotopic characteristics.Since the retention of Sm-Nd systematics within scheelite is presently unconstrained,equivocal interpretations for isotopic data resulting from this method have occurred quite often in previous studies that apply these isotopic data.In order to better elucidate the closure of Sm-Nd in scheelite,the kinetics of Sm and Nd within this mineral lattice were investigated through calculation of diffusion constants presented herein.The following Arrhenius relations were obtained:D_(Nd)=4.00exp(-438 kJ·mol^(–1)/RT)cm^(2)/s D_(Sm)=1.85exp(-427 kJ·mol^(–1)/RT)cm^(2)/s showing diffusion rate of Nd is near identical to Sm in scheelite when at the same temperature.However,compared to other rare earth elements(REEs),which have markedly different atomic radii to either Nd or Sm,these are shown to exhibit a great variation in diffusivities.The observed trends in our data are in excellent agreement with the diffusion characteristics of REEs in other tetragonal ABO4 minerals,indicating that ionic radius is a key constraint to the diffusivity of REEs in the various crystal lattices.With this in mind,the same substitution mechanism and a very slight discrepancy in radii will allow us to infer that significant Sm/Nd diffusional fractionation in scheelite is unlikely to occur during most geological processes.Based upon the diffusion data determined herein,Sm and Nd closure temperatures and retention times in scheelite are discussed in terms of diffusion dynamics.Those results suggest that closure temperatures for Sm-Nd within this mineral are relatively high in contrast to the temperature ranges of ore-formation responsible for scheelite-related deposits,and any later thermal environments.It is likely,therefore,that relevant isotopic information could be easily retained under most geological conditions,since initial crystallization of the scheelite.In addition,comparison of this mineral-element pair over a range of temperatures with some other common minerals used as geochronometers(e.g.,zircon and apatite)indicates that Sm-Nd system has a slower diffusive rate in scheelite than for Sr in apatite or Ar in quartz,and only a little faster than for Pb in zircon.It should be noted,within most hydrothermal deposits where zircon has crystallized,its size is typically no more than 100μm,whereas scheelite commonly occurs as macroscopic grains.For this reason,the larger dimensions of scheelite would provide a robust Sm-Nd system more able to resist perturbations,relating to any later thermal process.As such Sm-Nd investigations of scheelite are akin to U-Pb within zircon samples used in isotopic dating.These observations indicate that Sm-Nd age and isotopic information can provide reliable data in all but the most extreme case,especially when data are extracted from macroscopic grains of scheelite that are chosen to be“pristine”(i.e.,free of surface alteration and/or fractures).
文摘Sm-Nd isotopic ages for C-type eclogite (243.9±5.6 Ma) and mafic and ultramafic rocks(230.6±30.7 Ma and 402.6±17.4 Ma) from the Qinling-Dabieshan orogenic belt are reported.These ages suggest that at the early Triassic, the North and South China Blocks have beenunited along the Qinling-Dabieshan collision zone, and before the final collision, a se-ries of ophiolite obductions took place successively away from the continental marginduring the Paleozoic.
基金Project supported by the National Natural Science Foundation of China
文摘A large eclogite belt developed along the Dabie Mountains and Subei-Jiaonan Rise in central China is a result of collision between the North China and Yangtze blocks. Recently, coesite and coesite pseudomorphs are recognized as an inclusion in both garnet
基金Project supported by the National Natural Science Foundation of China
文摘Qinling-Dabieshan orogenic belt is generally believed to be a collision zone between the North China Block (NCB) and the Yangtze Block (YB). Various high P/T metamorphic rocks, such as blueschist, C-type eclogite, are well developed along the suture in this belt.Precise dating of the eclogite has very important significance for understanding of the collision time between the NCB and the YB and the evolutionary history of the orogenic belt.
文摘GEOLOGICAL scientists have paid much attention to the suture zones formed by collision between the Sino-Korean and Yangtze blocks because of the discovery of the ultrahigh pressue metamorphic (UHPM) rocksfrom northern Jiangsu Province (Su), southern Shandong Province (Lu) and the Dabie Mountains.Although the age of 200-240 Ma is probably the best estimation for UHPM metamorphism in the DabieMountains, the primary intrusive and metamorphic ages of the complex from northern Jiangsu Provincehave not been determined before. Using the Sm-Nd isotopic dating method, our study is aimed at datingthe UHPM metanorphic event of northern Jiangsu Province and researching a probable relation between theUHPM rocks from the Dabie Mountains and the UHPM rocks from northern Jiangsu Province.
基金financially supported by Geological Survey of China Projects(Nos.1212010814054,1212010911049)Ministry of land and resources of public welfare scientific research(No.201311116)
文摘We report geochemical data, SHRIMP zircon ages and Hf-in-zircon isotopic compositions for Cenozoic granitoids from major fault systems in the Tethyan belt in western Yunnan Province, southwestern China.Four magmatic pulses occurred in the Paleogene, namely at ca.57 Ma, ca.50 Ma, 45–40 Ma, and 38–34 Ma.Early magmatism of this episode(57–50 Ma) produced S-type granites whose zircons yielded εHf(t) values of-5.0 to-0.3.In contrast, late magmatism of this episode reflects heterogeneous sources.Zircons from a granite porphyry along the Ailaoshan-Red River fault system have slightly positive εHf(t) values suggesting derivation from relatively young crust and/or a juvenile source.However, zircons from a granite along the Gaoligong fault system have strongly negative εHf(t) values and suggest derivation from a Paleoproterozoic crustal source.The composition of the granitoids varies with age(from ca.57 Ma to ca.34 Ma) from peraluminous to metaluminous and also suggests a change from syn-collisional to late-orogenic tectonic setting.A new tectonic model, impacting lithospheric wedge(ILW) is shown for the origin of Paleogene granitoids in this paper.
基金supported jointly by the National Natural Science Foundation of China (Grant Nos. 41030423,41072068 and 40872071)National Basic Research Program of China (Grant No. 2006CB403502)+2 种基金MOST Special Fund from the State Key Laboratory of Continental Dynamics, Northwest University (Grant No. BJ091349)National Found for Fostering Talents of Basic Sciences (Grant No. J0830519)Graduate Innovation and Creativity Funds of Northwest University,China (Grant No. 10YZZ24)
文摘The Dehe granitic pluton intruded the Xiahe Group which is in the core complex of the North Qinling Orogenic Belt(NQOB).It shows gneissic bedding and possesses typical S-type granite minerals such as muscovite and garnet.LA-ICP-MS U-Pb isotopic dating of the Dehe granite yielded a weighted average age of 925±23 Ma which represents the emplacement age of the pluton.Most of the εHf(t) values are negative,and the two-stage model ages are consistent with the age of the Qinling Group.The isotope data show that the Dehe granite was formed in the following geological setting:in the syn-collision setting of the NQOB in the Neoproterozoic,crustal thickening induced partial melting of materials derived from the Qinling complex,and then the maga upwelled and intruded into the Xiahe Group.The formation of the Dehe S-type granite implied the occurrence of a convergent event in the QOB during the Neoproterozoic.
文摘Keban magmatics consist of plutonic rocks of acidic and intermediate compositions with diffe rent phases. They are the equivalent of surface rocks. In the current study on plutonic rocks, general petrographic features, disequilibrium textures such as skeletal formation in minerals, poikilitic texture, oscillatory zoning, and mineral fragmentation, and growth states are observed. Besides these microscopic properties, the existence of rounded mafic enclaves of various sizes, petrographic synplutonic dykes, and field data support the idea that mafic and felsic magmas are mixed. Keban magmatics have I-type, metaluminous-peraluminous characteristics. Diorites and quartz diorites have low-K tholeiitic features, whereas tonalites have low-K calcalkaline features. Compared with diorites, tonalites are richer in terms of LREE (Rock/ Chondrite);Rb, Sr, and Ba (LILE);and Hf, Zr, Th, and U (HFSE) elements. LILE enrichment, which signals the crustal contamination of mantle- originated magmas, is particularly observable in tonalites. In both rock groups, the negative anomaly of Nb is a sign of similarity of pluton to the subduction zone magma series. Based on the K-Ar geochronology dating of amphibole minerals, the ages of these rocks are found to be 75.65 ± 1.5 and 59.77 ± 1.2 Ma in tonalites and 84.76 ± 1.8 and 84.35 ± 1.7 Ma in diorite and quartz diorites. The 87Sr/86Sr isotope ratios in tonalites are 0.705405 and 0.706053, whereas these ratios are 0.704828 and 0.704754 in dioritic rocks. Pb isotope ratios are similar in both rock types.
基金Supported by Project of China Geological Survey(No.12120114080901)
文摘The Zhalaxiageyong lead-zinc-copper polymetallic deposit is a typical porphyry deposit of the Tuotuohe area. Whole-rock geochemical analyses,Zircon U-Pb dating and Hf isotope analysis are undertaken for the ore host trachydacite with the aim of constraining its petrogenesis,magma source and regional tectonic setting.LA-ICP-MS zircon U-Pb dating indicates that the trachydacite was formed in 32. 68 ± 0. 50 Ma( MSWD =1. 6),i. e.,Oligocene. The trachydacite is rich in potassium and poor in Mg#( 5. 10-9. 70),belonging to the peraluminous shoshonite series. The rocks are enriched in LILE( large ion lithophile elements) Rb,Ba,K and LREE,depleted in HFSE( high field strength elements) Nb,Ta,P,Ti,with high Sr and low Y and Yb,having the characteristics of the C type adakite. It is calculated that the initial εHf( t) of the zircons range from-0. 92 to 2. 07 and their two-stage Hf model ages T_(DM2) range from 978 Ma to 1 169 Ma. The magma source should be mainly the partially melt mafic rocks of the thickened Middle Neoproterozoic lower crust of the Northern Qiangtang massif with the addition of ancient aluminosilica material in the melting process. The rocks formed in the tectonic setting of delamination of lithosphere and extension of the thickened crust. During the period of 40-32 Ma,large-scale potassium rich alkaline magmatism occurred in this area. The porphyry metallogenesis is related to the magmatic activities in this period.
基金financially supported by the National Natural Science Foundation of China (grant No.41502076)the Leading Talents Plan Project of Science and Technology of Yunnan Province (grant No.2013HA001)the Science Research Fund of Yunnan Provincial Education Department (grant No.2015Y066)
文摘Objective The Geza arc in Yunnan Province,located in the southern Yidun arc,is an important part of the Sanjiang tectonic-magmatic belts in southwestern China and is a newly discovered copper polymetallic ore-concentrating district.Recent studies show that the newly discovered Yanshanian porphyry Cu-Mo polymetallic mineralization superimposed in the Indosinian porphyry copper belt in this area.
基金financially supported by the Russian Science Foundation (RSF) (Grant No. 22-77-00082)financially supported of grant 075-15-2021-680 of the Ministry of Science and Higher Education of the Russian Federation
文摘The combined petrographic,petrological,geochemical and geochronological study of the Neoproterozoic gneisses of the Sarychabyn and Baskan complexes of the Junggar Alataw of South Kazakhstan elucidate the Precambrian tectonic evolution of the Aktau–Yili terrane.It is one of the largest Precambrian crustal blocks in the western Central Asian orogenic belt.The U-Pb single-grain zircon ages indicate that granite-gneisses formed from the same source and crystallised in the early Neoproterozoic ca.930–920 Ma.The chemical composition of gneisses corresponds to A2-type granites.The whole-rock Nd isotopic characteristics(εNd(t)=−4.9 to−1.0 and TNd(DM-2st)=1.9 to 1.7 Ga)indicate the involvement of Paleoproterozoic crustal rocks in magma generation.Early Neoproterozoic ca.930–920 Ma A-type granitoids in the Aktau–Yili terrane of South and Central Kazakhstan might reflect within-plate magmatism adjacent to the collisional belt or a local extension setting in back-arc areas of the continental arc.
基金supported by the National Council for the Improvement of Higher Education(CAPES)the Brazilian Council for Research and Technological Development(CNPQ)。
文摘Iron formations are valuable archives of sedimentary conditions and post-depositional events.However,geochemical proxies commonly used to determine genetic characteristics can be variably modified during metamorphism and deformation,hampering their use as records of regional geological events.This work focuses on strongly reworked magnetite-quartz-rich rocks from the São Josédo Campestre Massif,one of the oldest fragments of preserved crust in South America.The genetic classification of these magnetite-quartz-rich rocks is not straightforward because primary assemblages and textures were variably modified by granulite facies metamorphism during a regional Paleoproterozoic migmatization event.To address genetic ambiguities,we analyzed their magnetite and pyroxene chemistry,wholerock geochemistry,and Sm-Nd isotopes.Magnetite chemistry indicates that pyroxene-poor iron formations(Type B)are low in trace elements such as Ti,Al,V,and Mn,suggesting a chemical similarity to iron formations elsewhere.In contrast,magnetites from pyroxene-enriched Type A iron formations are rich in trace elements and more akin to magnetite crystallized from higher temperature systems,such as skarn and IOCG.The^(147)Sm/^(144)Nd of these rocks show substantial variation even at the outcrop scale,indicating a locally-controlled,highly heterogeneous mixture of Archean,Paleoproterozoic,and Neoproterozoic sources.Therefore,our geochemical tools point out to heterogenous signatures of these magnetitequartz rocks and proxies compatible with both low and high-temperature conditions and age of deposition spanning sources from the Archean to the Neoproterozoic.We interpret that the studied São Josédo Campestre magnetite-quartz rocks represent Archean iron formations with original magnetite chemistry and isotopic signatures variably modified by metamorphism and by at least one deformation-related hydrothermal event.These results contrast with similar examples from China and Greenland where iron formations either preserved the magnetite chemistry or the primary isotopic signatures.Our study indicates that metamorphism can selectively affect chemical proxies used to study iron formations and undermine the genetic classification of iron ores.Thus,these proxies should be carefully applied in the interpretation of syn-depositional environments of polydeformed belts.
基金supported financially by the NSFC projects(Grant Nos.U1403291,41830216,and 41802074)projects of the China Geological Survey(Grant Nos.DD20160024,DD20160123,and DD20160345)IGCP 662.
文摘A large area of Late Paleozoic intrusions occursalong the Kalamaili fault in North Xinjiang,which is divided into I-type and A-type granite(Liu et al.,2013),and are the ideal objects for revealing the geological evolution of this region.However,the study of the granodioritic pluton in East Junggar is particularly weak.
文摘The provenance of sandstones derived from theLower Voltaian Kwahu-Morago Group and the Middle Voltaian Oti-Pendjari Group of the Neoproterozoic Voltaian basin are discriminated by their Sm-Nd Isotopic compositions. Plots from the Sm-Nd data suggested provenance of the Kwahu-Morago Group to be from the Birimian metasediments and associated “basin type”granitoids. The Sm-Nd studies have further revealed an average TDM model age of whole rock samples in the Kwahu-Morago Group to be 2.2 Ga which shows that this portion of the Voltaian Supergroup represents eroded remnants of “basin type” granitoids. Sm-Nd data from the Oti-Pendjari Group suggested provenance from the Birimian volcanic rocks and probably with contribution from the Pan African rocks. Its average TDM model age of whole rock samples was 2.0 Ga, which generally falls in the range of the model ages for the basement Birimian volcanic rocks as well as the model ages for the granitoid rocks and thus suggests the major source rock of the Oti-Pendjari Group as coming from the volcanic belts. The model ages for both groups seem to indicate clastic supply from an early Proterozoic crustal provenance. This study shows that whole rock isotopic analyses can also be complementary in providing an insight into the origin and development of sedimentary successions.
基金sponsored by the China Geological Survey(grants No.1212011120335 and 12120114006201)
文摘Objective The Late Paleozoic Southern Tianshan Ocean is usually considered to be the last-closed ocean in the Tianshan Orogeny. However, there is still no consensus if this is indeed the case. Blueschist, eclogite and ophiolite are present in the Atbashi Range, Kyrgyzstan, which are believed to be the relics of the Southern Tianshan Ocean. New data obtained through Ar-Ar isotopic analysis in this research provide reliable chronological restrictions for this problem.
文摘Whole-rock Rb-Sr, zircon U-Pb and hornblende, biotite and K-feldspar K-Ar ages areused to reconstruct the cooling history of the Huangmeijian intrusion in the Anqing-Lujiangquartz-syenite belt in Anhui. Oxygen isotope geothermometry of mineral pairs demonstrates thatdiffusion is a dominant factor controlling the closure of isotopic systems. Assuming the coolingof the intrusion is synchronous with a dicrease in local geothermal gradients, an emplacementdepth of about 8 km and the magma crystallization temperature of 800±50℃ are estimated. TheHuangmeijian intrusion experienced a rapid cooling process and uplifted after its emplacementand crystallization at 133 Ma B.P. with a cooling rate of 34.5℃/Ma and an uplifting rate of 0.35mm/a. The intrusion was rising until it rested at a depth of 3km at a temperature of 300±50℃about 14 Ma later. Then the intrusion was in slow cooling and uplifting with a cooling rate of4.4℃/Ma and an uplifting rate of 0.04 mm/a. U-Pb dating of pitchblende is done for the hydrothermal uranium deposit formed in thecontact zone of the Huangmeijian intrusion. The result shows that the mineralization age is closeto the closing time of the K-Ar system in biotite. The fluid inclusion thermometry indicates thatthe mineralization temperature is in agreement with the closure temperature of the biotite K-Arsystem. This suggests a close relationship between the slow cooling of the intrusion and thehydrothermal uranium mineralization process.
文摘Located in the middle segment of the Trans-North China Orogen, the Fuping Complex is considered as a critical area in understanding the evolution history of the North China Craton (NCC). The complex is composed of various high-grade and multiply deformed rocks, including gray gneiss, basic granulite, amphibolite, fine-grained gneiss and marble, metamorphosed to upper amphibolite or granulite facies. It can be divided into four rock units: the Fuping TTG gneisses, Longquanguan augen gneisses, Wanzi supracrustals, and Nanying granitic gneisses. U-Pb age and Hf isotope compositions of about 200 detrital zircons from the Wanzi supracrustals of the Fuping Complex have been analyzed. The data on metamorphic zircon rims give ages of 1.82-1.84 Ga, corresponding to the final amalgamation event of the NCC, whereas the data for igneous zircon cores yield two age populations at -2.10 and -2.51 Ga, with some inherited ages scattering between 2.5 and 2.9 Ga. These results suggest that the Wanzi supracrustals were derived from the Fuping TTG gneisses (-2.5 Ga) and the Nanying granitic gneisses (2.0-2.1 Ga) and deposited between 2.10 and 1.84 Ga. All zircons with -2.51 Ga age have positive initial εHf values from +1.4 to +10.9, suggesting an important crustal growth event at -2.5 Ga through the addition of juvenile materials from the mantle. The Hf isotope data for the detrital zircons further imply that the 2.8 Ga rocks are important components in the lower crust, which is consistent with a suggestion from Nd isotope data for the Eastern Block. The zircons of 2.10 Ga population have initial εHf values of-4.9 to +6.1, interpreted as mixing of crustal re-melt with minor juvenile material contribution at 2.1 Ga. These results are distinct from that for the Western Block, supporting that the Fuping Complex was emplaced in a tectonic active environment at the western margin of the Eastern Block.
基金funded by the National Natural Science Foundation of China(Grant No.41502112 and 41702119)a project program under China Geological Survey(No.DD20160159)
文摘We report here U-Pb age and in situ Hf isotopic results for detrital and magmatic zircons from one conglomerate and four tuffite samples from the Late Triassic Nadigangri Formation across the North Qiangtang depression, Tibet. Coupled with previously published data in the region, this paper proposes new insights into the geochronological framework for the Nadigangri Formation. The deposition ages of tuffite from top to bottom in the Woruo Mountain, Quem Co and Dongqu River, are 203 Ma, 226 Ma, 221.5 Ma and 221.1 Ma, respectively. The detrital zircons yield a younger cluster of ages of 201.5-225 Ma from the conglomerate of the Quem Co Formation. The Late Triassic Nadigangri Formation defines a temporal range approximately between 201 and 225 Ma (Norian-Rhaetian), including three predominant groups of 220-225 Ma, 210-217 Ma and 201-205 Ma, which correspond with the three main rifting episodes of initial rifting, further rifting and final rifting. Positive ~Hf(t) value and low model ages in younger detrital zircons suggests a juvenile character. However, the Hf isotopes of magmatic zircons display the presence of reworked ancient crust with 1.1-1.8 Ga. These results provide strong constraints not only on the temporal range of the Late Triassic Nadigangri Formation, but also on the onset of the Qiangtang Mesozoic rift basin.
基金supported by the National Natural Science Foundation of China (Grant No. 40930419)the National Special Research Programs for Non-Profit Trades (Sponsored by MLR, Grant Nos. 200911007 and 200811114)Open Foundation of State Key laboratory of Geological Processes and Mineral Resources, School of the Earth Sciences and Resources, China University of Geosciences, Beijing (Grant No. GPMR201029)
文摘Late Mesozoic volcanic-subvolcanic rocks and related iron deposits, known as porphyry iron deposits in China, are widespread in the Ningwu ore district (Cretaceous basin) of the middle-lower Yangtze River polymetallic ore belt, East China. Two types of Late Mesozoic magmatic rocks are exposed: one is dioritic rocks closely related to iron mineralization as the hosted rock, and the other one is granodioritic (-granitic) rocks that cut the ore bodies. To understand the age of the iron mineralization and the ore-forming event, detailed zircon U-Pb dating and Hf isotope measurement were performed on granodioritic stocks in the Washan, Gaocun-Nanshan, Dongshan and Heshangqiao iron deposits in the basin. Four emplacement and crystallization (typically for zircons) ages of granodioritic rocks were measured as 126.1±0.5 Ma, 126.8±0.5 Ma, 127.3±0.5 Ma and 126.3±0.4 Ma, respectively in these four deposits, with the LA-MC-ICP-MS zircon U-Pb method. Based on the above results combined with previous dating, it is inferred that the iron deposits in the Ningwu Cretaceous basin occurred in a very short period of 131-127 Ma. In situ zircon Hf compositions of εHf(t) of the granodiorite are mainly from -3 to -8 and their corresponding 176Hf/177Hf ratio are from 0.28245 to 0.28265, indicating similar characteristics of dioritic rocks in the basin. We infer that granodioritic rocks occurring in the Ningwu ore district have an original relationship with dioritic rocks. These new results provide significant evidence for further study of this ore district so as to understand the ore-forming event in the study area.