Objective The Late Cretaceous Xiuwacu ore-bearing porphyry is located in the Geza area of southern Yidun arc, SW China. In this area, the rock mass is mainly composed of three lithofacies： biotite granite porphyry, ...Objective The Late Cretaceous Xiuwacu ore-bearing porphyry is located in the Geza area of southern Yidun arc, SW China. In this area, the rock mass is mainly composed of three lithofacies： biotite granite porphyry, monzonitic granite and light alkali feldspar granite. As a part of the Yidun arc, the Geza arc has common structure and temporal- spatial evolution with the ~idun arc, which has experienced three stages of oceanic crust subduction, collision orogeny and intracontinent convergence stages. The molybdenite ores in the area are mainly hosted in monzonitic granite-porphyry and structural fracture zone, and the ore bodies are strictly controlled by faults. In recent years, great geological prospecting results have been achieved in Xiuwacu, and the deposit has reached a medium scale. However, there are few researches on the metallogenic porphyry. Based on the previous research, we determined the rock-forming and ore-forming age of the porphyry, and found that there were two stages of magmatism intrusion in Xiuwacu： Indosinian and Yanshanian. We also discussed the geochemical characteristics and source area of the rocks in the area.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
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
Objective The Altyn Tagh marks the northern margin of the Qinghai-Tibet Plateau and lies between the Tarim block to the north and the Qaidam block,Qilian Orogen,and Kunlun orogenic belt to the south.The Altyn Tagh reg...Objective The Altyn Tagh marks the northern margin of the Qinghai-Tibet Plateau and lies between the Tarim block to the north and the Qaidam block,Qilian Orogen,and Kunlun orogenic belt to the south.The Altyn Tagh region contains ophiolite,high-to ultrahigh-pressure metamorphic rocks,and igneous rocks.Previous research has virified the occurrence of continental rifting,subduction,slab roll-back,and collision between the Tarim block and Proto-Tethys oceanic plate.Moreover,Kaladaban volcanic rocks are mainly distributed in the north Altyn region.Studies of the magmatic evolution of this region have proposed that Altyn oceanic plate was subducted during the Ordovician(Han et al.,2012;Wang et al.,2017).However,the specific timing and other aspects of the subduction are debated,and an investigation of granite porphyry in the Kaladaban area would improve our understanding of this subduction event.In this study,we present new U-Pb zircon dating result and Sr-Nd isotope composition data for granite porphyry from the North Altyn region.The objective is to constrain the timing of subduction of the North Altyn oceanic plate and establish the petrogenesis and magma source of the granite porphyry.展开更多
The Neoproterozoic evolution of the Jiangnan Orogen is important for understanding the tectonic history of South China.As a volcanic-sedimentary sequence developed in the Nanhua rift,the Banxi Group preserves the reco...The Neoproterozoic evolution of the Jiangnan Orogen is important for understanding the tectonic history of South China.As a volcanic-sedimentary sequence developed in the Nanhua rift,the Banxi Group preserves the records of important magmatic and tectonic events linked to the assembly and breakup of the Rodinia supercontinent.In this study,we report the results from whole-rock major-and trace-element concentrations,with zircon LA-(MC)-ICP-MS U-Pb ages,trace elements and Lu-Hf isotopic compositions of sandstones from the Banxi Group.The rocks are characterized by high SiO_(2)(65.88%–82.76%,with an average of 75.50%)contents,moderate(Fe_(2)O_(3)^(T)+MgO)(1.81%–7.78%,mean:3.79%)and TiO_(2)(0.39%–0.54%,mean:0.48%),low K_(2)O/Na_(2)O(0.03–0.40,mean:0.10)ratios and low Al_2O_(3)/SiO_(2)(0.11–0.24,mean:0.15)ratios.The sandstones have highΣREE contents(mean:179.1 ppm),with chondrite-normalized REE patterns similar to the upper crust and PAAS,showing enriched LREE((La/Yb)_N mean:14.85),sub-horizontal HREE curves and mild Eu(Eu/Eu^(*):0.75–0.89,mean:0.81)negative anomalies.Their geochemical characteristics resemble those of passive continental margin sandstones.Most of the zircons are magmatic in origin and yield a U-Pb age distribution with three peaks:a major age peak at 805 Ma and two subordinate age peaks at 1990 Ma and 2470 Ma,implying three major magmatic sources.The Neoproterozoic zircons haveε_(Hf)(t)values ranging from-47.4 to 12.4(mostly-20 to 0),suggesting a mixture of some juvenile arc-derived material and middle Paleoproterozoic heterogeneous crustal sources.The Hf model ages of middle Paleoproterozoic zircons(~1990 Ma)with negativeε_(Hf)(t)values(-12.65 to-6.21,Ave.=-9.8)concentrated around the Meso-Paleoarchean(mean T_(DM)^(C)=3.3–3.1 Ga).For late Neoarchean detrital zircons(~2470 Ma),ε_(Hf)(t)values are divided into two groups,one with negative values(-9.16 to-0.6)with model ages of 3.5–2.9 Ga,the other featuring positive values(1.0 to 3.9)with model ages of 2.9–2.7 Ga,recording a crustal growth event at~2.5 Ga.Neoproterozoic zircons show volcanic arc affinities with partly intraplate magmatic features.We propose that the Banxi Group formed in a rift basin within a passive continental margin setting,which derived detritus from felsic to intermediate rocks from the Yangtze Block and a small amount of arc volcanic rocks.The middle Paleoproterozoic detrital zircon data suggest Columbia-aged basement lies beneath the western Jiangnan orogen.展开更多
The Central Asian Orogenic Belt(CAOB) was built up through protracted accretion and collision of a variety of terranes/micro-continents during Neoproterozoice Mesozoic time. To understand potential links among Paleozo...The Central Asian Orogenic Belt(CAOB) was built up through protracted accretion and collision of a variety of terranes/micro-continents during Neoproterozoice Mesozoic time. To understand potential links among Paleozoic subduction and accretionary processes that were operative during the development of the southeastern CAOB, we conducted a combined U-Pb and Hf-isotope analysis of detrital zircons from previously defined Devonian, Carboniferous and Early Permian strata in the Bengbatu area,Inner Mongolia. Detrital zircons from(meta-) sandstones in these strata commonly yield major Paleozoic age populations at ca. 300-261 Ma, 351-300 Ma and 517-419 Ma, and also give several Precambrian ages that range from 2687 Ma to 544 Ma. The youngest ages redefine the deposition of all these strata to be in the Middle Permian(Wordiane Capitanian) or later, much younger than previously considered.These ages, coupled with regional magmatic records, support an interpretation of most surrounding areas as possible detritus sources, including the Mongolian arcs to the north, the Northern Accretionary Orogen to the south, and the intervening Erenhote Hegenshan Ophiolite Belt. Zircons with magmatic ages of ca. 500-350 Ma and ca. 300-261 Ma display a large range of εHf(t) values(-13.97 to +15.31),whereas ca. 350-300 Ma zircons are dominated by positive εHf(t) values(+0.14 to +16.00). These results support the occurrence of two significant shifts of the zircon εHf(t) values, which has tectonic implications for the understanding of the Carboniferouse Permian evolution of the southeastern CAOB. A marked shift from mixed to positive zircon εHf(t) values at 350 -330 Ma likely manifests the incipient opening of the Hegenshan Ocean, due to the slab rollback of the subducting Paleo-Asian Oceanic lithosphere. Another shift from positive to mixed zircon εHf(t) values at ca. 300 Ma likely corresponds to a tectonic switch from syn-orogenic subduction-related to post-orogenic extensional setting, genetically related to the tectonic collapse of a formerly overthickened crust.展开更多
Detrital zircon geochronology and Hf isotope analysis can be used for inferring provenance characteristics,and to evaluate the tectonic evolution of sedimentary basins and their link with regional orogenesis.The Paleo...Detrital zircon geochronology and Hf isotope analysis can be used for inferring provenance characteristics,and to evaluate the tectonic evolution of sedimentary basins and their link with regional orogenesis.The Paleozoic sequences of the Okcheon Belt consist of the Lower Paleozoic Joseon and the Upper Paleozoic Pyeongan supergroups with Middle Paleozoic hiatus locally on top of the Neoproterozoic bimodal volcanic rocks,reflecting an intracontinental rift setting between the two basements(viz.Gyeonggi and Yeongnam massifs)at southern part of the Korean Peninsula.Our detrital zircon U-Pb ages and Lu-Hf isotope results show that all these Paleozoic strata commonly have Paleoproterozoic and Paleozoic zircon ages with rare Meso-to Neoproterozoic ages.The individual zircon populations display following features,allowing estimation of their sedimentary provenances:(i)The Paleoproterozoic zircons(ca.1.85 Ga and 2.50 Ga)with similar ranges ofεHf(t)values are most common in the basement rocks of the Korean Peninsula,and were sourced from both the Gyeonggi and Yeongnam massifs.(ii)The Meso-to Neoproterozoic zircons,preserved only in the Middle to Late Cambrian clastic sedimentary rocks within the carbonate sequences probably reflect proximal provenance.(iii)The youngest Paleozoic zircons of each formation,almost coincident with their deposition ages,suggest presence of syndepositional magmatism,indicating proximal magmatic sources during their deposition.(iv)The Cambrian-Ordovician zircons,from the Lower Paleozoic sequences,but rare in the successive Upper Paleozoic sequences,suggest a provenance change after the hiatus between the two sedimentary successions.(v)The Permian zircons showing differentεHf(t)values indicate that detrital sources were varied at that time.The integrated results in our study suggest provenance variability linked to diverse tectonic environments,reflecting prolonged subduction-related crustal evolution of the proto-Korean Peninsula during the Paleozoic.展开更多
The Wuliangshan Group occurs to the east of the Lancang giant igneous zone in SW Yunnan, and is mainly composed of low-grade metamorphosed sedimentary rocks. The group has been considered as the syn-orogenic product o...The Wuliangshan Group occurs to the east of the Lancang giant igneous zone in SW Yunnan, and is mainly composed of low-grade metamorphosed sedimentary rocks. The group has been considered as the syn-orogenic product of the Baoshan with Simao-Indochina blocks. However, its depositional time and provenance remain to be poorly constrained. This paper presents zircon U-Pb dating and Lu-Hf-isotopic data for five representative sandstone samples from the Wuliangshan Group. The detrital grains yield a major age-peak at ~259 Ma, and four subordinary age-peaks at ~1 859, ~941, ~788, and ~447 Ma, respectively. Our results suggest that the Wuliangshan metasedimentary sequence was deposited after Middle Triassic rather than previously-thought Cambrian. The detrital zircon age spectrum, along with in-situ Lu-Hf isotopic data suggest that the Wuliangshan Group might be a syncollisional sedimentary product related to the collision of Baoshan with Simao-Indochina blocks. It is inferred that the provenance of the Wuliangshan Group is mainly from the Simao/Yangtze blocks to the east rather than the Baoshan Block or Lancang igneous zone to the west.展开更多
Detrital zircon U-Pb geochronology combined with Hf isotopic and trace element data from metasedimentary rocks of the Aracuai Belt in southeastern Brazil provide evidence for break-up of the Congo-Sao Francisco Craton...Detrital zircon U-Pb geochronology combined with Hf isotopic and trace element data from metasedimentary rocks of the Aracuai Belt in southeastern Brazil provide evidence for break-up of the Congo-Sao Francisco Craton. The U-Pb age spectra of detrital zircons from metasediments of the Rio Doce Group(RDG) range from 900-650 Ma and define a maximum depositional age of ca. 650 Ma. Zircon trace element and whole rock data constrain an oceanic island arc as source for the deposition setting of the protoliths to the metasediments. Zircon ε_(Hf)(t) values from these rocks are positive between +1 and +15, supporting previous evidence of a Neoproterozoic extensional phase and oceanic crust formation in a precursor basin to the Aracuai Belt. Recrystallization of detrital zircon at ca. 630 Ma is compatible with a regional metamorphic event associated with terrane accretion to the Paleoproterozoic basement after transition from an extensional to a convergent regime. The juvenile nature, age spectra and trace element composition recorded in detrital zircons of metasediments from the Aracuai Belt correspond with zircons from metasedimentary rocks and oceanic crust remnants of other orogenic belts to its south. This suggests that rifting and oceanic crust formation of the entire orogenic system, the so-called Mantiqueira Province, was contemporaneous, most likely related to the opening of a large ocean. It further indicates that the cratonic blocks involved in the orogenic evolution of the Mantiqueira Province were spatially connected as early as 900 Ma.展开更多
Mesozoic sedimentary units within the Nanzhao and Mashiping basins record the paleogeographic and tectonic evolution of the Qinling Orogen(QO).This study uses new detrital zircon U-Pb ages and Hf isotopic data to cons...Mesozoic sedimentary units within the Nanzhao and Mashiping basins record the paleogeographic and tectonic evolution of the Qinling Orogen(QO).This study uses new detrital zircon U-Pb ages and Hf isotopic data to constrain the timing of deposition and provenance of the Taishanmiao,Taizishan,Nanzhao,and Mashiping formations of the North Qinling Orogen(NQO).The detrital zircons can be split by age peaks into five major groups,including Early Cretaceous,Late Triassic,Early Paleozoic,Neoproterozoic and Paleoproterozoic age peaks.On the basis of the youngest zircon ages and age-diagnostic fossils,we conclude that the Taishanmiao(youngest age of 234 Ma)and Taizishan(216 Ma)formations were deposited during the Late Triassic,whereas the Nanzhao Formation(110 Ma)was deposited during the Early Cretaceous rather than the Late Jurassic as previously thought.The Mashiping Formation(110 Ma)was also deposited during the Early Cretaceous.Combined with zircon Hf isotopic compositions,zircons from Late Triassic units were generally derived from the NQO,South Qinling Orogen(SQO),and North China Craton(NCC),with minor amounts derived from the Xing-Meng Orogenic Belt.The sediments within the Nanzhao Formation were mainly derived from the QO,with a minor contribution from the NCC.The Early Cretaceous conglomerates of the Mashiping Formation were generally derived from recycled earlier detritus.This implies that Late Triassic deposition was related to the final closure of the Mianlue Ocean,whereas Early Cretaceous deposition was correlated to the continued intercontinental subduction of the Yangtze Craton beneath the QO.The change in provenance within these Mesozoic sediments suggests the QO underwent two periods of significant uplift,which was a process generated sediments that were deposited in a series of basins of this area.展开更多
The samples from the hidden Daqiling muscovite monzonite granite, which has recently been recognized within the Limu Sn-polymetallic ore field, have been analyzed for zircon U-Pb ages and whole rock geochemical and Nd...The samples from the hidden Daqiling muscovite monzonite granite, which has recently been recognized within the Limu Sn-polymetallic ore field, have been analyzed for zircon U-Pb ages and whole rock geochemical and Nd-Hf isotopic compositions to discuss its genesis, source, and tectonic setting. LA-ICP-MS zircon U-Pb dating indicates that the granite crystallized in the late Indosinian（224.8±1.6 Ma）. The granite is enriched in SiO2 and K2 O and low in CaO and Na2 O. It is strongly peraluminous with the A/CNK values of 1.09–1.20 and 1.4 vol%–2.7 vol% normal corundum. Chondrite-normalized REE patterns show slightly right-dipping shape with strongly negative Eu anomalies（δEu =0.08–0.17）. All samples show enrichment of LILEs（Cs, Rb and K） and HFSEs（U, Pb, Ce and Hf）, but have relatively low contents of Ba, Sr and Ti. The zircon saturation temperatures（Tzr） are from 711 to 740°C, which are slightly lower than the average value of typical S-type granite（764°C）. The granite has negative εNd（t） and εHf（t） values, which change from ？9.1 to ？10.1 with the peak values of ？9.2 to ？9.0 and from ？3.7 to ？12.6 with the peak values of ？6 to ？5, respectively. The C DMT（Nd） and C DMT（Hf） values are 1.74–1.82 Ga with the peak values of 1.73–1.75 Ga and 1.49–2.04 Ga with the peak values of 1.5–1.6 Ga, respectively. These characteristics reveal that the source region of the granite is dominantly late Paleoproterozoic to early Mesoproterozoic crustal materials. Seven inherited magmatic zircons are dated at the age of 248.6±4.3 Ma, which suggests the existence of the early Indosinian granite in Limu area. These zircons have the εHf（t） values of ？6.7– ？2.3, similar to those of the Daqiling granite, implying the involvement of the early Indosinian granite during the formation of the Daqiling granite. Inherited zircon of 945±11 Ma has the εHf（t） and TDM（Hf） values of 8.7 and 1.14 Ga, respectively, compatible with those of the Neoproterozoic arc magmatic rocks in the eastern Jiangnan orogenic belt. Therefore we inferred that Neoproterozoic arc magma might have been involved in the formation of the Daqiling granite, and that the Neoproterozoic arc magma belt and continent-arc collision belt between the Yangtze and Cathaysia Blocks might have extended westsouthward to Limu region. It is proposed that the underplating of mantle materials triggered by crustal extension and thinning resulted in partial melting of crustal materials to form the Daqiling granite in the late Indosinian under post-collisional tectonic setting.展开更多
ABSTRACT： The widespread Neoproterozoic magmatism along the Yangtze block carries critical in- formation for understanding the Neoproterozoic evolution of the Yangtze block. In the northwestern margin of the Yangtze ...ABSTRACT： The widespread Neoproterozoic magmatism along the Yangtze block carries critical in- formation for understanding the Neoproterozoic evolution of the Yangtze block. In the northwestern margin of the Yangtze block, the Hannan （汉南） intrusive complex includes the Wudumen （五堵门）, Erliba （二里坝） and Zushidian （祖师殿） granitoids. Using LA-ICP-MS U-Pb zircon dating method, the Wudumen and Erliba granitoids yielded magma crystallization ages of 785±4 and 778±3 Ma, respectively. Samples from these three granitoids show variable SiO2 contents ranging from 58.8% to 72.6%. They are characterized by enrichment of Al2O3（14.97%-17.87%）, Na2O（3.80%-5.33%） and Sr （504ppm-741 ppm）, and depletion of Y （〈19 ppm） and HREE （e.g., Yb〈1.6 ppm）, resulting in high Sr/Y （29-161） and （La/Yb）N （7.3-27.8） ratios. The geochemical features of the granitoids are comparable with those of adakite. The granitoids have zircon εHdt） values of ＋3.65 to ＋10.05, whole-rock εNd（t） values of -0.09 to ＋2.98 and whole-rock initial ^87Sr/^86Sr ratios of 0.7034-0.7039, indicating that their magma was derived from a juvenile crustal source. Together with geochemical and Hf-Sr-Nd isotopic compositions, it is suggested that the granitoids formed in island-arc setting and originated from partial melting of a subducted oceanic slab. The results support a model that the Yangtze block was surrounded by ocean and arc magmatism in its northern and northwestern margins in Neoproterozoic.展开更多
In order to determine the provenance and variation characteristics of sandstone-type uranium deposits located in the southwest Ordos Basin,U-Pb geochronology and Hf isotope analyses were conducted on detrital zircons ...In order to determine the provenance and variation characteristics of sandstone-type uranium deposits located in the southwest Ordos Basin,U-Pb geochronology and Hf isotope analyses were conducted on detrital zircons from the Late Mesozoic strata of the SD01 well in the Zhenyuan area.The detrital zircon U-Pb ages of four samples exhibited four main peaks at 250–330,420–500,1720–2000,and 2340–2580 Ma,with a small number of zircons dated at 770–1100 Ma.The detrital zircon age spectrum and further restriction provided by the in-situ Hf isotopic data suggest that the provenance of each stratum was mainly derived from the crystalline basement rock series(Khondalites,intermediate-acidic intrusive rocks,and metamorphic rocks)of the Alxa Block to the northwest and the Yinshan Block to the north,with minor amounts of Caledonian magmatic rocks and Jingning Period rocks from the western part of the northern Qilian orogenic belt to the west and the northern Qinling orogenic belt to the south.The provenance of the sandbody has not changed significantly and is of the Middle Jurassic–Early Cretaceous.The clear variations in the zircon ages of the samples from the Zhiluo and Anding formations were likely influenced by climate change during the Middle–Late Jurassic.The Triassic zircon age(<250 Ma)first appeared in Early Cretaceous strata,suggesting that tectonic activity was relatively strong in the northern Qinling orogenic belt during the Late Jurassic and produced extensive outcrops of Indo-Chinese granite,which were a source of basin sediments.展开更多
Here we report an integrated study of zircon U-Pb age and Hf isotope composition for a gneiss sample from the Kongling terrain in the Yangtze Craton. CL imaging reveals that most zircons are magmatic, and a few of the...Here we report an integrated study of zircon U-Pb age and Hf isotope composition for a gneiss sample from the Kongling terrain in the Yangtze Craton. CL imaging reveals that most zircons are magmatic, and a few of them have thin metamorphic rims. The magmatic zircons gave a weighted mean U-Pb age of 3218±13 Ma, indicating the gneiss is the oldest basement rock in the Yangtze Craton found to date. They have εHf(t) value of -2.33±0.51,and two-stage Hf model age of 3679±49 Ma,indicating that the gneiss was derived from partial melting of >3.6 Ga crustal rock. The metamorphic rims yielded an age of 2732±16 Ma, implying that the metamorphic event occurred in the Neoarchean era, which may be also a major tectono-thermal event in the Yangtze Craton.展开更多
Zircon U-Pb dating, Lu-Hf isotopic and geochemical data for the Silurian rhyolites from the Loei fold belt are presented to constrain their petrogenesis and tectonic settings. The rhyolites give a weighted mean 206Pb/...Zircon U-Pb dating, Lu-Hf isotopic and geochemical data for the Silurian rhyolites from the Loei fold belt are presented to constrain their petrogenesis and tectonic settings. The rhyolites give a weighted mean 206Pb/238 U age of 423.7±2.7 Ma, and are characterized by high SiO2, Al2O3, K2 O and low MnO, MgO and P2O5. All samples are enriched in LILEs（e.g., Ba, K, Pb） and LREEs and depleted in HFSEs（e.g., Nb, Ta, Ti） with obvious negative Eu-anomalies（δEu=0.56–0.63）. The calc-alkaline rhyolites are typical arc-related rocks. The Loei rhyolites have high A/CNK ratios（1.19–1.34） and positive εHf（t）（4.03–5.38）, which can be interpreted as partial melting of juvenile crustal materials followed by multistage melting and differentiation, similar to highly fractional I-type rocks. Combined with regional geological surveys, the Loei rhyolites should be formed in a volcanic arc environment and may be in contact with the Truong Son fold belt during the Early Paleozoic. Moreover, the Simao Block might be in contiguity with the Indochina Block during Silurian.展开更多
The composition of single-grain detrital zircons is an effective provenance indicator of loess,and sheds new light on dust formation and transportation.Here we review the features of detrital zircons and their use as ...The composition of single-grain detrital zircons is an effective provenance indicator of loess,and sheds new light on dust formation and transportation.Here we review the features of detrital zircons and their use as a provenance indicator,including internal structure,trace element,U-Pb age spectrum and Hf isotopic compositions,and present a case study from the Horqin sandy land and its surrounding loess.The loess samples have detrital zircon age peaks in range of 2600-2300,2100-1600,and 600-100 Ma,of which the 2600-2300 Ma zircon grains mainly have positive Hf(t) values(3.4-8.7),the 2100-1600 Ma zircon grains mainly have negative Hf(t) values(10.1-6.8),and the 600-100 Ma zircon grains have a variable Hf(t) values ranging from 21 to 15.9.The detrital zircon signatures of the loess are similar to the Horqin sandy land,but clearly different from the Chinese Loess Plateau and central-western deserts,implying that the loess is transported mainly from the Horqin sandy land in the Last Glacial period.Comparing these with neighboring tectonic units,we found that zircon populations at 2600-2300,2100-1600,and 600-100 Ma with negative Hf(t) values may come from the northeast North China Craton(NCC),and those at 600-100 Ma with positive Hf(t) values may come from the east Central Asian Orogenic Belt(CAOB).It is estimated that the two sources contribute equally to the Horqin sandy land and the surrounding loess.展开更多
基金financially supported by the National Natural Science Foundation of China(grant No.41502076)the Science Research Fund of Yunnan Provincial Education Department(grant No.2015Y066)+1 种基金the Provincial People Training Program of Kunming University of Science and Technology(grant No.KKSY201421042)the Project of China Geological Survey(grant No.12120114013701)
文摘Objective The Late Cretaceous Xiuwacu ore-bearing porphyry is located in the Geza area of southern Yidun arc, SW China. In this area, the rock mass is mainly composed of three lithofacies： biotite granite porphyry, monzonitic granite and light alkali feldspar granite. As a part of the Yidun arc, the Geza arc has common structure and temporal- spatial evolution with the ~idun arc, which has experienced three stages of oceanic crust subduction, collision orogeny and intracontinent convergence stages. The molybdenite ores in the area are mainly hosted in monzonitic granite-porphyry and structural fracture zone, and the ore bodies are strictly controlled by faults. In recent years, great geological prospecting results have been achieved in Xiuwacu, and the deposit has reached a medium scale. However, there are few researches on the metallogenic porphyry. Based on the previous research, we determined the rock-forming and ore-forming age of the porphyry, and found that there were two stages of magmatism intrusion in Xiuwacu： Indosinian and Yanshanian. We also discussed the geochemical characteristics and source area of the rocks in the area.
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.
基金jointly supported by the National Key R&D Program of China(Grant No.2018YFC0603704)a Geological Survey Project of the China Geological Survey(DD20160050).
文摘Objective The Altyn Tagh marks the northern margin of the Qinghai-Tibet Plateau and lies between the Tarim block to the north and the Qaidam block,Qilian Orogen,and Kunlun orogenic belt to the south.The Altyn Tagh region contains ophiolite,high-to ultrahigh-pressure metamorphic rocks,and igneous rocks.Previous research has virified the occurrence of continental rifting,subduction,slab roll-back,and collision between the Tarim block and Proto-Tethys oceanic plate.Moreover,Kaladaban volcanic rocks are mainly distributed in the north Altyn region.Studies of the magmatic evolution of this region have proposed that Altyn oceanic plate was subducted during the Ordovician(Han et al.,2012;Wang et al.,2017).However,the specific timing and other aspects of the subduction are debated,and an investigation of granite porphyry in the Kaladaban area would improve our understanding of this subduction event.In this study,we present new U-Pb zircon dating result and Sr-Nd isotope composition data for granite porphyry from the North Altyn region.The objective is to constrain the timing of subduction of the North Altyn oceanic plate and establish the petrogenesis and magma source of the granite porphyry.
基金financially supported by the Natural Science Foundation of China(Grant No.41972198)the Cooperation Foundation of the Key Laboratory of Mineralogy and Metallogeny,Chinese Academy of Sciences(Grant No.KLMM20180201)the Scientific Research Starting Foundation of Central South University。
文摘The Neoproterozoic evolution of the Jiangnan Orogen is important for understanding the tectonic history of South China.As a volcanic-sedimentary sequence developed in the Nanhua rift,the Banxi Group preserves the records of important magmatic and tectonic events linked to the assembly and breakup of the Rodinia supercontinent.In this study,we report the results from whole-rock major-and trace-element concentrations,with zircon LA-(MC)-ICP-MS U-Pb ages,trace elements and Lu-Hf isotopic compositions of sandstones from the Banxi Group.The rocks are characterized by high SiO_(2)(65.88%–82.76%,with an average of 75.50%)contents,moderate(Fe_(2)O_(3)^(T)+MgO)(1.81%–7.78%,mean:3.79%)and TiO_(2)(0.39%–0.54%,mean:0.48%),low K_(2)O/Na_(2)O(0.03–0.40,mean:0.10)ratios and low Al_2O_(3)/SiO_(2)(0.11–0.24,mean:0.15)ratios.The sandstones have highΣREE contents(mean:179.1 ppm),with chondrite-normalized REE patterns similar to the upper crust and PAAS,showing enriched LREE((La/Yb)_N mean:14.85),sub-horizontal HREE curves and mild Eu(Eu/Eu^(*):0.75–0.89,mean:0.81)negative anomalies.Their geochemical characteristics resemble those of passive continental margin sandstones.Most of the zircons are magmatic in origin and yield a U-Pb age distribution with three peaks:a major age peak at 805 Ma and two subordinate age peaks at 1990 Ma and 2470 Ma,implying three major magmatic sources.The Neoproterozoic zircons haveε_(Hf)(t)values ranging from-47.4 to 12.4(mostly-20 to 0),suggesting a mixture of some juvenile arc-derived material and middle Paleoproterozoic heterogeneous crustal sources.The Hf model ages of middle Paleoproterozoic zircons(~1990 Ma)with negativeε_(Hf)(t)values(-12.65 to-6.21,Ave.=-9.8)concentrated around the Meso-Paleoarchean(mean T_(DM)^(C)=3.3–3.1 Ga).For late Neoarchean detrital zircons(~2470 Ma),ε_(Hf)(t)values are divided into two groups,one with negative values(-9.16 to-0.6)with model ages of 3.5–2.9 Ga,the other featuring positive values(1.0 to 3.9)with model ages of 2.9–2.7 Ga,recording a crustal growth event at~2.5 Ga.Neoproterozoic zircons show volcanic arc affinities with partly intraplate magmatic features.We propose that the Banxi Group formed in a rift basin within a passive continental margin setting,which derived detritus from felsic to intermediate rocks from the Yangtze Block and a small amount of arc volcanic rocks.The middle Paleoproterozoic detrital zircon data suggest Columbia-aged basement lies beneath the western Jiangnan orogen.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 41730213, 41190075, 41190070)the Hong Kong Research Grants Council General Research Fund (17301915)the HKU Seed Funding Programme for Basic Research (201611159210)
文摘The Central Asian Orogenic Belt(CAOB) was built up through protracted accretion and collision of a variety of terranes/micro-continents during Neoproterozoice Mesozoic time. To understand potential links among Paleozoic subduction and accretionary processes that were operative during the development of the southeastern CAOB, we conducted a combined U-Pb and Hf-isotope analysis of detrital zircons from previously defined Devonian, Carboniferous and Early Permian strata in the Bengbatu area,Inner Mongolia. Detrital zircons from(meta-) sandstones in these strata commonly yield major Paleozoic age populations at ca. 300-261 Ma, 351-300 Ma and 517-419 Ma, and also give several Precambrian ages that range from 2687 Ma to 544 Ma. The youngest ages redefine the deposition of all these strata to be in the Middle Permian(Wordiane Capitanian) or later, much younger than previously considered.These ages, coupled with regional magmatic records, support an interpretation of most surrounding areas as possible detritus sources, including the Mongolian arcs to the north, the Northern Accretionary Orogen to the south, and the intervening Erenhote Hegenshan Ophiolite Belt. Zircons with magmatic ages of ca. 500-350 Ma and ca. 300-261 Ma display a large range of εHf(t) values(-13.97 to +15.31),whereas ca. 350-300 Ma zircons are dominated by positive εHf(t) values(+0.14 to +16.00). These results support the occurrence of two significant shifts of the zircon εHf(t) values, which has tectonic implications for the understanding of the Carboniferouse Permian evolution of the southeastern CAOB. A marked shift from mixed to positive zircon εHf(t) values at 350 -330 Ma likely manifests the incipient opening of the Hegenshan Ocean, due to the slab rollback of the subducting Paleo-Asian Oceanic lithosphere. Another shift from positive to mixed zircon εHf(t) values at ca. 300 Ma likely corresponds to a tectonic switch from syn-orogenic subduction-related to post-orogenic extensional setting, genetically related to the tectonic collapse of a formerly overthickened crust.
基金supported by the IiKSNF and KETEP grant funded by the Korean government MOTIE (No.2021040101003B)YJ acknowledged NRF-2021R1C1C101057011 through the National Research Foundation of Korea (NRF)funded by the Ministry of Science and ICT,Korea+2 种基金SK acknowledged the 2017R1A6A1A07015374,2019R1A2C1002211the KBSI R&D program (Project No.C330430)supported by Basic Research Project grant (GP2021-004)from the KIGAM funded by the Ministry of Science,ICT,and Future Planning,Korea.
文摘Detrital zircon geochronology and Hf isotope analysis can be used for inferring provenance characteristics,and to evaluate the tectonic evolution of sedimentary basins and their link with regional orogenesis.The Paleozoic sequences of the Okcheon Belt consist of the Lower Paleozoic Joseon and the Upper Paleozoic Pyeongan supergroups with Middle Paleozoic hiatus locally on top of the Neoproterozoic bimodal volcanic rocks,reflecting an intracontinental rift setting between the two basements(viz.Gyeonggi and Yeongnam massifs)at southern part of the Korean Peninsula.Our detrital zircon U-Pb ages and Lu-Hf isotope results show that all these Paleozoic strata commonly have Paleoproterozoic and Paleozoic zircon ages with rare Meso-to Neoproterozoic ages.The individual zircon populations display following features,allowing estimation of their sedimentary provenances:(i)The Paleoproterozoic zircons(ca.1.85 Ga and 2.50 Ga)with similar ranges ofεHf(t)values are most common in the basement rocks of the Korean Peninsula,and were sourced from both the Gyeonggi and Yeongnam massifs.(ii)The Meso-to Neoproterozoic zircons,preserved only in the Middle to Late Cambrian clastic sedimentary rocks within the carbonate sequences probably reflect proximal provenance.(iii)The youngest Paleozoic zircons of each formation,almost coincident with their deposition ages,suggest presence of syndepositional magmatism,indicating proximal magmatic sources during their deposition.(iv)The Cambrian-Ordovician zircons,from the Lower Paleozoic sequences,but rare in the successive Upper Paleozoic sequences,suggest a provenance change after the hiatus between the two sedimentary successions.(v)The Permian zircons showing differentεHf(t)values indicate that detrital sources were varied at that time.The integrated results in our study suggest provenance variability linked to diverse tectonic environments,reflecting prolonged subduction-related crustal evolution of the proto-Korean Peninsula during the Paleozoic.
基金supported by the National Natural Science Foundationof China(No.41190073)the National Basic Research Program of China(No.2014CB440901)the Fundamental Research Funds for the Central Universities to SYSU
文摘The Wuliangshan Group occurs to the east of the Lancang giant igneous zone in SW Yunnan, and is mainly composed of low-grade metamorphosed sedimentary rocks. The group has been considered as the syn-orogenic product of the Baoshan with Simao-Indochina blocks. However, its depositional time and provenance remain to be poorly constrained. This paper presents zircon U-Pb dating and Lu-Hf-isotopic data for five representative sandstone samples from the Wuliangshan Group. The detrital grains yield a major age-peak at ~259 Ma, and four subordinary age-peaks at ~1 859, ~941, ~788, and ~447 Ma, respectively. Our results suggest that the Wuliangshan metasedimentary sequence was deposited after Middle Triassic rather than previously-thought Cambrian. The detrital zircon age spectrum, along with in-situ Lu-Hf isotopic data suggest that the Wuliangshan Group might be a syncollisional sedimentary product related to the collision of Baoshan with Simao-Indochina blocks. It is inferred that the provenance of the Wuliangshan Group is mainly from the Simao/Yangtze blocks to the east rather than the Baoshan Block or Lancang igneous zone to the west.
基金funding from CNPq(401334/2012-0-302058/2015-0-402852/2012-5)FAPEMIG(APQ03943-RPQ-0067-10-RDP00063-10)grants
文摘Detrital zircon U-Pb geochronology combined with Hf isotopic and trace element data from metasedimentary rocks of the Aracuai Belt in southeastern Brazil provide evidence for break-up of the Congo-Sao Francisco Craton. The U-Pb age spectra of detrital zircons from metasediments of the Rio Doce Group(RDG) range from 900-650 Ma and define a maximum depositional age of ca. 650 Ma. Zircon trace element and whole rock data constrain an oceanic island arc as source for the deposition setting of the protoliths to the metasediments. Zircon ε_(Hf)(t) values from these rocks are positive between +1 and +15, supporting previous evidence of a Neoproterozoic extensional phase and oceanic crust formation in a precursor basin to the Aracuai Belt. Recrystallization of detrital zircon at ca. 630 Ma is compatible with a regional metamorphic event associated with terrane accretion to the Paleoproterozoic basement after transition from an extensional to a convergent regime. The juvenile nature, age spectra and trace element composition recorded in detrital zircons of metasediments from the Aracuai Belt correspond with zircons from metasedimentary rocks and oceanic crust remnants of other orogenic belts to its south. This suggests that rifting and oceanic crust formation of the entire orogenic system, the so-called Mantiqueira Province, was contemporaneous, most likely related to the opening of a large ocean. It further indicates that the cratonic blocks involved in the orogenic evolution of the Mantiqueira Province were spatially connected as early as 900 Ma.
基金financially supported by the Natural Science Foundation of China(41722204,42072063 and 41472052)the National Key Research and Development Program of China(2016YFC0600103)+1 种基金the research grant of State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences(SKLaBIGKF-18-06)Basic Scientific Research Foundation of Central Universities of China(Jilin University)。
文摘Mesozoic sedimentary units within the Nanzhao and Mashiping basins record the paleogeographic and tectonic evolution of the Qinling Orogen(QO).This study uses new detrital zircon U-Pb ages and Hf isotopic data to constrain the timing of deposition and provenance of the Taishanmiao,Taizishan,Nanzhao,and Mashiping formations of the North Qinling Orogen(NQO).The detrital zircons can be split by age peaks into five major groups,including Early Cretaceous,Late Triassic,Early Paleozoic,Neoproterozoic and Paleoproterozoic age peaks.On the basis of the youngest zircon ages and age-diagnostic fossils,we conclude that the Taishanmiao(youngest age of 234 Ma)and Taizishan(216 Ma)formations were deposited during the Late Triassic,whereas the Nanzhao Formation(110 Ma)was deposited during the Early Cretaceous rather than the Late Jurassic as previously thought.The Mashiping Formation(110 Ma)was also deposited during the Early Cretaceous.Combined with zircon Hf isotopic compositions,zircons from Late Triassic units were generally derived from the NQO,South Qinling Orogen(SQO),and North China Craton(NCC),with minor amounts derived from the Xing-Meng Orogenic Belt.The sediments within the Nanzhao Formation were mainly derived from the QO,with a minor contribution from the NCC.The Early Cretaceous conglomerates of the Mashiping Formation were generally derived from recycled earlier detritus.This implies that Late Triassic deposition was related to the final closure of the Mianlue Ocean,whereas Early Cretaceous deposition was correlated to the continued intercontinental subduction of the Yangtze Craton beneath the QO.The change in provenance within these Mesozoic sediments suggests the QO underwent two periods of significant uplift,which was a process generated sediments that were deposited in a series of basins of this area.
基金supported by National Key Basic Research Program of China (Grant No. 2012CB416702)National Natural Science Foundation of China (Grant No. 41230315)China Geological Survey Program (Grant No. 1212011085407)
文摘The samples from the hidden Daqiling muscovite monzonite granite, which has recently been recognized within the Limu Sn-polymetallic ore field, have been analyzed for zircon U-Pb ages and whole rock geochemical and Nd-Hf isotopic compositions to discuss its genesis, source, and tectonic setting. LA-ICP-MS zircon U-Pb dating indicates that the granite crystallized in the late Indosinian（224.8±1.6 Ma）. The granite is enriched in SiO2 and K2 O and low in CaO and Na2 O. It is strongly peraluminous with the A/CNK values of 1.09–1.20 and 1.4 vol%–2.7 vol% normal corundum. Chondrite-normalized REE patterns show slightly right-dipping shape with strongly negative Eu anomalies（δEu =0.08–0.17）. All samples show enrichment of LILEs（Cs, Rb and K） and HFSEs（U, Pb, Ce and Hf）, but have relatively low contents of Ba, Sr and Ti. The zircon saturation temperatures（Tzr） are from 711 to 740°C, which are slightly lower than the average value of typical S-type granite（764°C）. The granite has negative εNd（t） and εHf（t） values, which change from ？9.1 to ？10.1 with the peak values of ？9.2 to ？9.0 and from ？3.7 to ？12.6 with the peak values of ？6 to ？5, respectively. The C DMT（Nd） and C DMT（Hf） values are 1.74–1.82 Ga with the peak values of 1.73–1.75 Ga and 1.49–2.04 Ga with the peak values of 1.5–1.6 Ga, respectively. These characteristics reveal that the source region of the granite is dominantly late Paleoproterozoic to early Mesoproterozoic crustal materials. Seven inherited magmatic zircons are dated at the age of 248.6±4.3 Ma, which suggests the existence of the early Indosinian granite in Limu area. These zircons have the εHf（t） values of ？6.7– ？2.3, similar to those of the Daqiling granite, implying the involvement of the early Indosinian granite during the formation of the Daqiling granite. Inherited zircon of 945±11 Ma has the εHf（t） and TDM（Hf） values of 8.7 and 1.14 Ga, respectively, compatible with those of the Neoproterozoic arc magmatic rocks in the eastern Jiangnan orogenic belt. Therefore we inferred that Neoproterozoic arc magma might have been involved in the formation of the Daqiling granite, and that the Neoproterozoic arc magma belt and continent-arc collision belt between the Yangtze and Cathaysia Blocks might have extended westsouthward to Limu region. It is proposed that the underplating of mantle materials triggered by crustal extension and thinning resulted in partial melting of crustal materials to form the Daqiling granite in the late Indosinian under post-collisional tectonic setting.
基金supported by the National Natural Science Foundation of China (Nos. 40773019 and 40821061)the Ministry of Education of China and the State Administration of Foreign Expert Affairs of China (No. B07039)
文摘ABSTRACT： The widespread Neoproterozoic magmatism along the Yangtze block carries critical in- formation for understanding the Neoproterozoic evolution of the Yangtze block. In the northwestern margin of the Yangtze block, the Hannan （汉南） intrusive complex includes the Wudumen （五堵门）, Erliba （二里坝） and Zushidian （祖师殿） granitoids. Using LA-ICP-MS U-Pb zircon dating method, the Wudumen and Erliba granitoids yielded magma crystallization ages of 785±4 and 778±3 Ma, respectively. Samples from these three granitoids show variable SiO2 contents ranging from 58.8% to 72.6%. They are characterized by enrichment of Al2O3（14.97%-17.87%）, Na2O（3.80%-5.33%） and Sr （504ppm-741 ppm）, and depletion of Y （〈19 ppm） and HREE （e.g., Yb〈1.6 ppm）, resulting in high Sr/Y （29-161） and （La/Yb）N （7.3-27.8） ratios. The geochemical features of the granitoids are comparable with those of adakite. The granitoids have zircon εHdt） values of ＋3.65 to ＋10.05, whole-rock εNd（t） values of -0.09 to ＋2.98 and whole-rock initial ^87Sr/^86Sr ratios of 0.7034-0.7039, indicating that their magma was derived from a juvenile crustal source. Together with geochemical and Hf-Sr-Nd isotopic compositions, it is suggested that the granitoids formed in island-arc setting and originated from partial melting of a subducted oceanic slab. The results support a model that the Yangtze block was surrounded by ocean and arc magmatism in its northern and northwestern margins in Neoproterozoic.
基金supported by the National Key Research and Development Program of China (No.2018YFC604201)the International Geoscience Programme (No.IGCP675)
文摘In order to determine the provenance and variation characteristics of sandstone-type uranium deposits located in the southwest Ordos Basin,U-Pb geochronology and Hf isotope analyses were conducted on detrital zircons from the Late Mesozoic strata of the SD01 well in the Zhenyuan area.The detrital zircon U-Pb ages of four samples exhibited four main peaks at 250–330,420–500,1720–2000,and 2340–2580 Ma,with a small number of zircons dated at 770–1100 Ma.The detrital zircon age spectrum and further restriction provided by the in-situ Hf isotopic data suggest that the provenance of each stratum was mainly derived from the crystalline basement rock series(Khondalites,intermediate-acidic intrusive rocks,and metamorphic rocks)of the Alxa Block to the northwest and the Yinshan Block to the north,with minor amounts of Caledonian magmatic rocks and Jingning Period rocks from the western part of the northern Qilian orogenic belt to the west and the northern Qinling orogenic belt to the south.The provenance of the sandbody has not changed significantly and is of the Middle Jurassic–Early Cretaceous.The clear variations in the zircon ages of the samples from the Zhiluo and Anding formations were likely influenced by climate change during the Middle–Late Jurassic.The Triassic zircon age(<250 Ma)first appeared in Early Cretaceous strata,suggesting that tectonic activity was relatively strong in the northern Qinling orogenic belt during the Late Jurassic and produced extensive outcrops of Indo-Chinese granite,which were a source of basin sediments.
基金Supported by National Natural Science Foundation of China (Grant Nos. 40772042, 90714010, 40873043 and 40821061)the Ministry of Education of China (Grant Nos. IRT0441, B07039 and NCET-06-0659)the Opening Foundation of the State Key Laboratory of Continental Dynamics, Northwest University
文摘Here we report an integrated study of zircon U-Pb age and Hf isotope composition for a gneiss sample from the Kongling terrain in the Yangtze Craton. CL imaging reveals that most zircons are magmatic, and a few of them have thin metamorphic rims. The magmatic zircons gave a weighted mean U-Pb age of 3218±13 Ma, indicating the gneiss is the oldest basement rock in the Yangtze Craton found to date. They have εHf(t) value of -2.33±0.51,and two-stage Hf model age of 3679±49 Ma,indicating that the gneiss was derived from partial melting of >3.6 Ga crustal rock. The metamorphic rims yielded an age of 2732±16 Ma, implying that the metamorphic event occurred in the Neoarchean era, which may be also a major tectono-thermal event in the Yangtze Craton.
基金supported by the NSFC(Nos.41172202 and 41190073)the China Geological Survey(No.1212011121256)+1 种基金the Ministry of Education of China(No.20110145130001)the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences in Wuhan(No.MSFGPMR201402)
文摘Zircon U-Pb dating, Lu-Hf isotopic and geochemical data for the Silurian rhyolites from the Loei fold belt are presented to constrain their petrogenesis and tectonic settings. The rhyolites give a weighted mean 206Pb/238 U age of 423.7±2.7 Ma, and are characterized by high SiO2, Al2O3, K2 O and low MnO, MgO and P2O5. All samples are enriched in LILEs（e.g., Ba, K, Pb） and LREEs and depleted in HFSEs（e.g., Nb, Ta, Ti） with obvious negative Eu-anomalies（δEu=0.56–0.63）. The calc-alkaline rhyolites are typical arc-related rocks. The Loei rhyolites have high A/CNK ratios（1.19–1.34） and positive εHf（t）（4.03–5.38）, which can be interpreted as partial melting of juvenile crustal materials followed by multistage melting and differentiation, similar to highly fractional I-type rocks. Combined with regional geological surveys, the Loei rhyolites should be formed in a volcanic arc environment and may be in contact with the Truong Son fold belt during the Early Paleozoic. Moreover, the Simao Block might be in contiguity with the Indochina Block during Silurian.
基金supported by Young Scholars of the National Natural Science Foundation of China (Grant No.40802037)National Basic Research Program of China (Grant No.2010CB950204)Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. 80972970)
文摘The composition of single-grain detrital zircons is an effective provenance indicator of loess,and sheds new light on dust formation and transportation.Here we review the features of detrital zircons and their use as a provenance indicator,including internal structure,trace element,U-Pb age spectrum and Hf isotopic compositions,and present a case study from the Horqin sandy land and its surrounding loess.The loess samples have detrital zircon age peaks in range of 2600-2300,2100-1600,and 600-100 Ma,of which the 2600-2300 Ma zircon grains mainly have positive Hf(t) values(3.4-8.7),the 2100-1600 Ma zircon grains mainly have negative Hf(t) values(10.1-6.8),and the 600-100 Ma zircon grains have a variable Hf(t) values ranging from 21 to 15.9.The detrital zircon signatures of the loess are similar to the Horqin sandy land,but clearly different from the Chinese Loess Plateau and central-western deserts,implying that the loess is transported mainly from the Horqin sandy land in the Last Glacial period.Comparing these with neighboring tectonic units,we found that zircon populations at 2600-2300,2100-1600,and 600-100 Ma with negative Hf(t) values may come from the northeast North China Craton(NCC),and those at 600-100 Ma with positive Hf(t) values may come from the east Central Asian Orogenic Belt(CAOB).It is estimated that the two sources contribute equally to the Horqin sandy land and the surrounding loess.
