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zircon

zircon的相关文献在1993年到2022年内共计48篇,主要集中在地质学、冶金工业、原子能技术 等领域,其中期刊论文48篇、相关期刊22种,包括地球学报、地学前缘、中国铅锌锡锑等; zircon的相关文献由161位作者贡献,包括LI、CHEN、Chunmei等。

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zircon

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    • Ademuyiwa Adetunji; Valentin YGanev
    • 摘要: The Neoproterozoic quartz potassic syenite of the Iwo area,Southwestern Nigeria has been investigated for its magmatic history and zircon saturation temperature.The zircon morphology showed irregular shapes with sectoral and oscillatory micro zoning.The majority of the zircon grains have embayment,which corresponds to magmatic resorption.The syenite crystallized from probably multiple recharge of less evolved magma.Both the magma injection and subsequent crystallization of the rock occurred over a length of time giving the rock some degree of protracted thermal history and slight fluctuation in chemistry,which are manifested as zonation in the analyzed zircon grains.The initial stage of zircon crystallization was marked by a lower cerium anomaly than the final stage,which indicates changes from lower oxidizing to higher oxidizing conditions.The protracted history does not affect the europium anomalies at any stage of crystallization.An average zircon saturation temperature of 865°Cestimated from titanium in zircon(T_(Tiz)°C)thermometer using titanium activity of 0.7(^(a)TiO_(2)~0.7)is taken as reasonable crystallization temperature of the rock.This is fairly consistent with 877°Cdeduced from the zircon solubility model.The titanium in zircon temperature of 910°Cat aTiO_(2)~1 is rather too high to be a useful estimate.Both the temperatures 865 and 877°Care however consistent with those of intermediate rocks.The size of the syenite and protracted crystallization history would have made the temperature to have impacted the metamorphic envelope around the syenite.
    • Tarmo Kiipli
    • 摘要: The present study deals with the possibilities of applying the zircon saturation thermometry, which is based on the equilibrium between the zircon crystals and the melt, to strongly altered volcanic ashes—bentonites. It proposes an alternative to a widely used method of calculating magma temperature from Zr content and major component composition(Boehnke in Chem Geol351:324–333, 2013), that is not suitable for bentonites, as most of the major components have been largely altered in these rocks. For calculating source magma temperatures in strongly altered volcanic ashes, the exponential function from the Zr(ppm)/Al_(2)O_(3)(%) ratio with compositional corrections from the TiO_(2)/Al_(2)O_(3) ratio was found applicable. The idea to use the ratios of these elements is based on the low mobility of these elements in the earth’s surface conditions. Temperatures of magma, forming in the partial melting process, are assessed from the bulk rock composition. Pre-eruption temperatures were estimated from the composition of fine fractions of bentonites. The accuracy of the new method was established from comparison with the method by Boehnke et al.(Chem Geol 351:324–333,2013). The difference between the two methods was mostly less than ± 30° to ± 50°. The comparison with the magma temperature, estimated from the sanidine composition,revealed 13° lower values on average. Although the proposed method for estimating the source magma temperatures is less precise than the method of accounting for detailed rock compositions, it can be used in strongly altered rocks, where other methods are not usable. The new method still enables differentiation between felsic source magmas originating at low or high temperatures. Early Palaeozoic bentonites in the Baltic Basin can be divided,according to the source magma temperatures, into two types:(1) Low temperature(650–790 °C), containing potassium-rich sanidine and abundant biotite(S type),(2)high temperature(770–850 °C) with sodium-rich sanidine and scarce biotite(I type).
    • Dongyu Zheng; Sixuan Wu; Chao Ma; Lu Xiang; Li Hou; Anqing Chen; Mingcai Hou
    • 摘要: Zircon is a widely-used heavy mineral in geochronological and geochemical research because it can extract important information to understand the history and genesis of rocks. Zircon has various types,and an accurate examination of zircon type is a prerequisite procedure before further analysis.Cathodoluminescence(CL) imaging is one of the most reliable ways to classify zircons. However, current CL image examination is conducted by manual work, which is time-consuming, bias-prone, and requires expertise. An automated and bias-free method for zircon classification is absent but necessary. To this end, deep convolutional neural networks(DCNNs) and transfer learning are applied in this study to classify the common types of zircons, i.e., igneous, metamorphic, and hydrothermal zircons. An atlas with over 4000 CL images of these three types of zircons is created, and three DCNNs are trained using these images. The results of this study indicate that the DCNNs can distinguish hydrothermal zircons from other zircons, as indicated by the highest accuracy of 100%. Although similar textures in igneous and metamorphic zircons pose great challenges for zircon classification, the DCNNs successfully classify 95% igneous and 92% metamorphic zircons. This study demonstrates the high accuracy of DCNNs in zircon classification and presents the great potentiality of deep learning techniques in numerous geoscientific disciplines.
    • Kirill Svjatoslavich Ivanov; Nikolay Pavlovich Kostrov; Yuriy Viktorovich Erokhin; Vladimir Sergeevich Ponomarev
    • 摘要: An additional comprehensive study of the west Siberia Karabash zone basement has been conducted. Core samples from more than 300 wells that opened the rocks of the basement were analyzed by different methods. A new map of the pre-Jurassic basement of Karabash zone of the west part of the Khanty-Mansi Autonomous Okrug (KhMAO) has been made. For the first time for the West Siberia megabasin U-Pb dating was made for samples from Shaim-Kuznetsovsk meganticlinorium and late to middle Devonian ages were obtained. The Devonian ages was obtained for metamorphic complexes of the region and, in general, for the basement of West Siberia. The complexes considered as Precambrian before that. The obtained results enable significantly to clarify more exact history of pre-Jurassic rock forming for the basement of the west part of West Siberia craton and its structure in the limits of Karabash zone. Thus, obtained data testify that in pre-Jurassic basement of the west part of the West Siberia (Karabash zone), filling grabens basalt effusion began during Permian time (probably at the end of early Permian) at sublatitudinal compression, that is, at collision, possibly immediately after or subsynchronously with the origin of the granite. On the edge of Permian and Triassic (or in early Triassic), sublatitudinal compression changed into stretching, and submeridional grabens came to existence and basalt effusion came up to the maximum.
    • HE Sheng; LI Ziying; GUO Dongfa; WANG Yongjian; ZHANG Chuang; GUO Jian; FAN Zengwei
    • 摘要: Objective The Hengjian uranium deposit is a typical hydrothermal deposit in the Xiangshan uranium ore field.The uranium mineralization ages of the Xiangshan deposits are poorly constrained,and only a few mineralization ages using the pitchblende U–Pb method have been published.These ages are commonly discordant and dispersed for abundant inclusions and an open U–Pb system.Zircon grains after strong hydrothermal alteration are usually characterized by high common Pb contents,and their U–Pb isochron ages recorded the hydrothermal alteration event without interference of common Pb components.The Hengjian gray/grayish-green granite porphyry experienced strong alteration by hydrothermal fluids during the pervasive uranium mineralization in the Xiangshan uranium ore field.Uranium mineralization in the Hengjian deposit may had different stages,and strong hydromicatization alteration occurred at a relatively early stage.Their altered zircon U–Pb isochron ages possibly represent relatively early mineralization age of the Xiangshan uranium deposits.Altered zircon grains from the Hengjian granite porphyry were analyzed using the secondary ion mass spectrometry(SIMS)U-Pb method in this study,and U–Pb isochron ages were measured to constrain the relatively early mineralization age of the Hengjian uranium deposit.
    • MA Xu; CHEN Bin; CHEN Jiafu
    • 摘要: Objective Though the Central Asian Orogenic Belt (CAOB) is characterized by widespread Phanerozoic crustal growth,there is little juvenile crust documented in its southeastern segment,northern margin of the North China Craton(NCC)(Zhang et al,2007,2009).Late Carboniferous Dongwanzi ultramafic-mafic cumulate complex occurs in northern margin of the NCC and is intruded by a syenite with depleted Sr-Nd isotopes (Ma et al.,2014).However,the age and petrogenesis of this syenite is poorly constrained.In this study,we present new petrological,zircon U-Pb and Hf isotopic data of the Dongwanzi syenite,in order to put insights on its formation age and petrogenetic relationship with cumulates.
    • JIA Wenbin; LI Yongsheng; MI Kuifeng; YU Xiaofei
    • 摘要: 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.
    • O.A.Ebyan; H.A.Khamis; A.R.Baghdady; M.G.El-Feky; N.S.Abed
    • 摘要: The stream sediments of Wadi El Reddah(North Eastern Desert,Egypt)are geochemically and mineralogically investigated.Their content of radioactive and other heavy minerals is mainly represented by thorite,uranothorite,zircon,monazite,xenotime,columbite,fergusonite,and unknown rare earth elements(REEs)bearing minerals as well as cassiterite.Special emphasis on REE content of thorite,uranothorite,zircon and xenotime has been done to correlate them with the increase of uranium contents in these sediments.The key evidence for the presence lowtemperature alteration processes includes the presence of some zircon crystals as remnants after complete dissolution of the overgrowth zircon in severe acidic environment,the sulphur content,biogenic minerals,occurrence of unusual minerals as cassiterite pore filling in zircon,variation in the REEs content from the surrounding granites to the stream sediments and the abundance of monazite in the surrounding granites.Most minerals are partially and/or completely altered,which indicated by the pseudomorphism of zircon by xenotime,thorite,and uranothorite.
    • GE Rongfeng; ZHU Wenbin; Simon AWILDE; WU Hailin
    • 摘要: Eoarchean(3.6–4.0 Ga)tonalite–trondhjemite–granodiorite(TTG)are the major component of Earth’s oldest persevered continental crust,thereby holding the key to understanding how continental crust originated and when plate tectonics started in the early Earth.TTGs are mostly generated by partial melting of hydrated mafic rocks at different depths(e.g.,Moyen and Martin,2012),but whether this requires subduction remains enigmatic(e.g.,Palin et al.,2016).Recent studies show that most early Archean TTGs formed at relatively low pressures(≤1.5 GPa)and do not require subduction(e.g.,Johnson et al.,2017).We have identified a suite of Eoarchean tonalitic gneisses dated at^3.7 Ga from the Tarim Craton,northwestern China(Ge et al.,2018).These rocks are probably the oldest high-pressure TTGs so far documented worldwide.Thermodynamic and trace element modelling demonstrates that the parent magma may have been generated by water-fluxed partial melting of moderately enriched arc-like basalts at 1.8–1.9 GPa and 800–830°C,indicating an apparent geothermal gradient(400–450°CGPa-1)typical for hot subduction zones.They also locally record geochemical evidence for magma interaction with a mantle wedge.Accordingly,we propose that these highpressure TTGs were generated by partial melting of a subducted proto-arc during arc accretion.Our model implies that modernstyle plate tectonics was operative,at least locally,at^3.7 Ga and was responsible for generating some of the oldest continental nuclei.
    • LIU Siqi; ZHENG Yuanchuan; SHEN Yang; HOU Zengqian; WANG Lu; WANG Zixuan
    • 摘要: Objective The Beiya super-large Au-rich porphyry deposit(304 t Au,2.4 g/t Au)is located within the western Yangtze craton,to the southeast of the Sanjiang Tethyan Orogen(Fig.1).The ore-forming porphyry is adakitic,characterized by high Sr/Y and La/Yb ratios coupled with low Y and Yb contents,and is generally thought to be derived from partial melting of thickened mafic lower crust.The lower crust underneath the western Yangtze craton is mainly composed of ancient crust with Archean ages,juvenile crust resulting from the Neoproterozoic subduction(740–1000 Ma),and late Permian juvenile crust related to the Emeishan mantle plume.Which lower crustal end-member has played a critical role in genesis of the Beiya ore-forming porphyry can be constrained by zircon U-Pb ages of amphibolite xenoliths hosted in the ore-forming porphyry,because these xenoliths represent direct samples of the source.In this study,we present new zircon U-Pb ages of these amphibolite xenoliths to have insight into the nature of the Beiya adakitic porphyry source.
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