Age,Mechanism and Direction of Eash Qinling—Dabieshan Lithosphere Delamination——Petrological Evidence and Stipulation

Throughy studies of P-T-t paths and decompressive retrograde metamorphic textures of metamorphic rocks in the East Qinling-Dabieshan region,the authors determined the Mesozoic crust rapid uplifting age,and then inferred that in the East Qinling-Dabieshan region lithosphere delamination occurred from T3 to J1.The Yanshanian granites produced by delamination are developed well in the East Qinling-Dabieshan region.But due to the Gondwana plate effect,magmatism in the region caused by delamination lagged until J3 when the northern Tibet terrane and the Eurasian plate completely amalgamated.Additionally,due to western Pacific plate subducting underneath the Eurasian plate,in the East Qinling-Dabieshan region the stress state was transformed from compression to extension.So in the region from J3 to K2 magmatism was most intensive,and liberalization was also relatively strong.Geophysical data reflect that in the East Qinling-Dabieshan region the asthenosphere rose to the shallow level,the Moho is flat with no mountain root,and the crustal thickness is less than 40 km on average. These features agree with those of collisional orogenes in which delamination has occurred.Through contrastin differences in surface and interior depth between east and west Qinling we believe that elamination proceeded from east to west.     

Rb—Sr and U—Pb Dating of the Daguzhai and Luobuli Granitic Massifs in South China

Rb-Sr and U-Pb isotopic studies of the two contrasting granite types of the Daguzhai and Luobuli massifs in South China provide new constraints on the interpretation of isotopic age data for plutonic igneous rocks. A Rb-Sr internal isochron age of 146±7Ma for the Luobuli adamellite is interpreted to represent the age of magma crystallization, whereas the whole rock Rb- Sr isochron yields an older apparent age of 161±10Ma which is regarded as resulting from contamination processes affecting the petrogenesis of this adamellite. In the Daguzhai granite the marked scatter of whole- rock Rb-Sr data in isochron diagram is ascribed to the open system behavior of Rb during postmagmatic autometasomatism. Uniformity of initial⁸⁷Sr /⁸⁶Sr ratio in this granite is indicated in a plot of⁸⁷Sr versus⁸⁶Sr. The autometasomatism has also affected zircon U-Pb system, resulting in a spread of data along the concordia curve between 165 and 125Ma. This spread is regarded as indicating the duration of the autometasomatism.     

The Coupled Re—Os and Pt—Os Systematics：A Theoretical Consideration

The ^190Pt-^186Os system should be a unique tracer for mantle processes be-cause both Pt and Os are concentrated in the mantle.The ^190Pt-^186Os system will also be a good supplement to the ^187Re-^187Os system for dating and tracing mantle pro-cesses because the ^190Pt-^186Os system is not so easily contaminated by crustal materials as the ^187Re-^187Os system.In turn,the application of the ^187Re-^187Os system to Pt-enriched materials uncontaminated by crustal materials will indirectly refine the half life of ^190Pt.The ^190Pt is refined.In the coupled ^187Re-^187Os and ^190Pt-^186Os sys-tematics,an ^186Os*/^190Pt-^187Os*/^187Re Concordia diagram similar to the ^206Pb*/^238U-^208Pb*/^232Th Concordia can be constructed.In such a Concordia diagram,a date will be obtained so long as the ^190Pt-^186Os system remains closed even if the ^187Re-^187Os sys -tem is contaminated by crustal materials.In addition ,for the coupled ^190Pt-^186Os and ^187Re-^187Os systematics,the mantle processes and the interactions between the mantle and the crust will be described by two ratios:^186Os/^188Os and ^187Os/^188Os .The coupled ^187Re-^187Os and ^190Pt-^186Os systematics will be a powerful tool in the investigation of the geodynamic history of the Earth because the ^187Re-^187Os system is sensitive to the interactions between the mantle and the crust,while the ^190Pt-^186Os system is a good tracer for mantle processes.     

High—Resolution Dating of Stalagmites and Reconstruction of Paleo—Environments

The discovery of abrupt paleo-climate change events and the prediction of environmental changes in the future time have raised an urgent request for high-resolution paleo-environmental records.This paper reviews the progress made in hronology and paleo-environment of stalagmites from karst caves in China and presents some of the results of TIMS-U-series dating of stalagmites composed of secondary carbonates,taken from the Dongge,Longquan and Yamen karst caves in Libo County and the Qixing karst cave in Duyun,Guizhou Province,on a MAT-262 mass spectrometer.     

The Microarea Composition of Garnet and Biotite from the Ji‘an Group in Tonghua District and Its Significance as an Indicator of Metamorphic P—T—t Path

The garnet(Grt)and biotite(Bt) from gneisses of the Ji‘an Group are characterized by diffusion zoning at the rim,but equilibrium composition of metamorphic peak is usually remained in extensive interior area.Garnet with growth zoning is also found in the kyanite zone.In the light of microarea compositional variation of Grt and Bt,the temperature and pressure at the progressive,peak and post-peak metamorphic stages are determined by correctly using Grt Bt thermometer and GASP barometer.On this basis,a counterclockwise P-T-t path can be constructed,which reflects the closing process of an ensialic rift belt in this region during the Early Proterozoic.     

Ore Zoning and Dynamics of Ore—Forming Processes of Yinshan Polymetallic Deposit in Dexing,Jiangxi

The Yinshan deposit,one of the large-scale Cu-Pb-Zn-Au-Ag polymetallic deposits,may be named a middle-low temperature subvolcanic hydrothermal deposit and referred to as the “transitional deposit“linking mineralization of the epithermal and porphyry coppertypes.In this paper,the characteristics and structures of ore zoning are briefly described.On the basis of the dynamics of ore-forming processes and applying computer numerical simulation technique,the mechanism of ore zoning is discussed and a concealed igneous body controlling ore deposition at depth of the Yinshan mine is predicted.     

C,Si在CO—CO2—SiO气体与Fe—Si—C合金间迁移平衡与Pco2—Psio…

通过评价和优化有关热力学数据，利用冶金物理化学原理建立了钢铁冶金中最为重的Ｆｅ－Ｓｉ－Ｃ三元体系与ＣＯ－ＣＯ２－ＳｉＯ混合气体间硅，碳迁移的热力学数学模型，计算了相关热力学数据并计算机绘制了该体系的Ｐｃｏ２－Ｐｓｉｏ和ｌｇＰｓｉｏ相平衡图。该模型的可靠性１８７３Ｋ高温条件下的一系列的平衡实验中得到了检验。     

邻羧基苯基重氮氨基—4—苯基—2—噻唑光度法测定微量铜的研究

研究了新试剂邻羧基苯基重氮氨基－４－苯基－２－噻唑与Ｃｕ＾２＋的显色反应,在非离子表面活性剂ＴｎｉｔｏｎＸ－１００存在下,于ＰＨ８．６的Ｎａ２Ｂ４Ｏ７－ＨＣｌ缓冲介质中,Ｃｕ＾２＋与该试剂生成１：１的红色配合物,其配合物的最大吸收波长为５１０ｎｍ,摩尔吸光系数为５．４＊１０＾４Ｌ．ｍｏｌ＾－１．ｃｍ＾－１。     

Refining the timing of eclogite metamorphism: a geochemical,petrological, Sm-Nd and U-Pb case study from the Pohorje Mountains,Slovenia (Eastern Alps)

High-pressure metamorphism in the Pohorje Mountains of Slovenia (Austroalpine unit, Eastern Alps) affected N-MORB type metabasic and metapelitic lithologies. Thermodynamic calculations and equilibrium phase diagrams of kyanite–phengite-bearing eclogites reveal PT conditions of >2.1 GPa at T<750°C, but within the stability field of quartz. Metapelitic eclogite country rocks contain the assemblage garnet + phengite + kyanite + quartz, for which calculated peak pressure conditions are in good agreement with results obtained from eclogite samples. The eclogites contain a single population of spherical zircon with a low Th/U ratio. Combined constraints on the age of metamorphism come from U/Pb zircon as well as garnet–whole rock and mineral–mineral Sm-Nd analyses from eclogites. A coherent cluster of single zircon analyses yields a ²⁰⁶Pb/²³⁸U age of 90.7±1.0 Ma that is in good agreement with results from Sm-Nd garnet–whole rock regression of 90.7±3.9 and 90.1±2.0 Ma (εNd: +8) for two eclogite samples. The agreement between U-Pb and Sm-Nd age data strongly suggests an age of approximately 90 Ma for the pressure peak of the eclogites in the Pohorje Mountains. The presence of garnet, omphacite and quartz inclusions in unfractured zircon indicates high-pressure rather than ultrahigh pressure conditions. The analysed metapelite sample yields a Sm-Nd garnet–whole rock scatterchron age of 97±15 Ma. These data probably support a single P-T loop for mafic and pelitic lithologies of the Pohorje area and a late Cretaceous high-pressure event that affected the entire easternmost Austroalpine basement including the Koralpe and Saualpe eclogite type locality in the course of the complex collision of the Apulian microplate and Europe.     

Geochronology of the Dahongshan Group

The Dahongshan Group is divided into five formations from the bottom to the top: the Laochanghe Formation; the Manganghe Formation; the Hongshan Formation, the Feiweihe Formation and the Potou Formation. As can be seen from the U-Pb concordia plot for zircon fractions collected from the metamorphic sodic lava of the Hongshan Formation, the upper intersect age with the concordia is 1665.55 _-10.86 ^+13.56 Ma. Sm-Nd dating of four whole-rock samples and one hornblende from the Manganghe and Hongshan formations yielded an isochron age of 1657 ± 82 Ma. This result is in good agreement with the zircon U-Pb age and thus can represent the formation age of the Dahongshan Group. The initial¹⁴³Nd/¹⁴⁴Nd ratio is estimated at 0.510646. with ENd (T) = + 3.1 ± 1.8. In addition the Dahongshan Group rocks are characterized by low REE contents, with δEu>1. All this goes to show that the original rocks of the Dahongshan Group were derived from a depleted mantle. The calculated Sm-Nd model ages range from ∼ 1900 to ∼ 2000 Ma. representing the time of crust/ mantle differentiation in the area studied. From the above results, in conjunction with the time-scale scheme for China, the Dahongshan Group should be assigned to the Middle Proterozoic.     

U-Pb zircon and Sm—Nd geochronology of mafic and ultramafic rocks from the central part of the Tauern Window (eastern Alps)

Geochronological and geochemical analyses were carried out in order to identify the pre-Variscan basement of the Tauern Window (eastern Alps). Maficultramafic rocks from the central part of the Tauern window have been studied by REE-analysis and U-Pb and Sm-Nd isotopic analyses on whole rock, zircons, garnets and sphene. U-Pb and Sm—Nd zircon dating define both magmatic Pan-African and Cambro-Ordovician events from 650 Ma to 486 Ma within the Alpine fold belt. This indicates a time span of 150 Ma for magmatic activities in the Tauern Window of the eastern Alps. The ages of 657 Ma (U-Pb zircon) and 644 (Sm—Nd zireon) obtained from an amphibolite are the oldest dates of the Eastern Alps; they may be related to the Pan-African orogeny, and imply an early cycle of magmatic intrusion before major activity started at around 500 Ma. Sm-Nd whole rock analyses of the Precambrian rocks do not define an isochron, reflecting heterogenities within the mantle source. The initial _Nd values (+1.2 to +4.7) are very low, implying an enrichment of the magma source. The second main phase of magmatic activity (539 486 Ma) is characterized by the emplacement of mafic/ultramafic rock sequences. As no ophiolitic relies are observed in these domains, the Early Paleozoic magmatism was likely associated with extensional tectonics. Obtained ages of 301±3 and 314+4/-3 Ma point to a Variscan metamorphism. The first combined U-Pb zircon/Sm—Nd zircon data for an amphibolite from the Basal Amphibolite Formation (BAF) favoured the Sm-Nd zircon isochron age as a magmatic age, whereas the low initial _Nd value point to an enriched magma source as well as to heterogenities within the magma source. The obtained ages suggest that parts of the pre-Variscan basement within the Alpine fold belt were formed during the Pan-Africa cycle. The detection of Pre-Variscan ages within the Alpine basement must reffect a complex history involving significant pre-Variscan activity.     

Sm-Nd and U-Pb dating of Early Proterozoic mafic-felsic volcanism in Northernmost Sweden

A Sm-Nd mineral isochron of 1932 ± 45 Ma on a Kiruna greenstone is defined by greenschist facies metamorphic minerals, apparently older than the regional Svecokarelian metamorphism (< 1880 Ma). However, this age agrees within error with U-Pb zircon ages of 1909 ± ₁₆¹⁷ Ma on quartz-bearing prophyries which overlie but are, in part, intercalated with basic volcanics. If these basic volcanics, following previous studies, are considered to be contemporary with the Kiruna greenstones, the present data suggest that eruption of both basic and acid volcanics and associated hydrothermal metamorphism took place over a short time interval close to 1.9 Ga.The greenstone sample is depleted in light rare-earths and has high initial ¹⁴⁵Nd/¹⁴⁴Nd indicating a source in which such depletion has existed for a long time. In contrast, an albite diabase sample with a somewhat younger mineral age (1.80 ± 0.08 Ga) is light rare earth enriched and has a correspondingly low initial Nd isotopic composition.     

四川攀西红格矿区辉长岩和正长岩的SHRIMP U-Pb和Sm-Nd定年及其地质意义

用SHRIMP U-Pb和Sm-Nd定年技术,对攀西红格矿区含矿层状辉长岩、碱性正长岩进行了年龄测定。获得红格辉长岩中3种不同晶形锆石的U-Pb年龄分别为258.4±4.1Ma、1841±34Ma、2487±12Ma,由辉长岩、辉石和磷灰石所构成的Sm-Nd等时线年龄为253±14Ma;碱性正长岩中锆石的U-Pb年龄为257.2±1.5Ma。结果表明,红格辉长岩中具有典型基性岩锆石特征的锆石U-Pb年龄(258Ma)与同一地质样品的Sm-Nd年龄(全岩+矿物内部等时线年龄),以及同一矿区的正长岩锆石U-Pb年龄在测定误差范围内一致。鉴于层状辉长岩和碱性正长岩在空间上密切共生,在形成时间上一致,可以认为它们都属于晚二叠世末岩浆活动的产物;而1841Ma和2487Ma的锆石,可能是在基性-超基性岩浆的上侵过程中,从基底所捕获的岩浆锆石和继承锆石,其年龄信息,揭示了康滇地轴岩浆岩带的下部或结晶基底存在元古代甚至新太古代末期的岩石或物质。     

Origin and timing of the post-Variscan gabbro–granite complex of Porto (Western Corsica)

The post-Variscan complex of Porto consists of metaluminous to slightly peraluminous A-type biotite granites mingled with gabbro-dioritic rocks, and late dykes with basaltic to trachyandesitic composition. U-Pb zircon dating by LA-ICP-MS on two mafic intrusive samples constrains the time of the gabbro–granite crystallisation at 281 ± 3 Ma and 283 ± 2 Ma. Hornblende ⁴⁰Ar-³⁹Ar ages from a late trachyandesite dyke date the dyking event at 280 ± 2 Ma, which is within error the U-Pb zircon ages of the intrusives. Biotite granites show variable major and trace element compositions and similar initial ε_Nd (−0.3 to +0.9). Whole rock chemistry variations and trace element compositions of plagioclase and allanite indicate that the granites are genetically linked, essentially through fractional crystallisation of feldspars and minor allanite. On the basis of whole-rock chemistry e.g. initial ε_Nd +4.9 to +1.7 and trace element clinopyroxene compositions, we have ascertained that the mafic intrusives and basic dykes formed from isotopically depleted mantle source-derived melts with similar trace element signature. These basic melts experienced slightly different evolutionary histories, controlled by fractional crystallisation and crustal contamination, mainly by the acid magma that gave rise to the associated biotite granites, but also by the enclosing older Variscan granitoids. U-Pb zircon data suggest that the Porto complex was affected by hydrothermal fluid circulation at 259 ± 9 Ma.     

Nd—Sr Isotope Geological Study on the Age of Armantai Ophiolite,Xinjiang,China

Sm-Nd and Rb-Sr whole-rock isochron dating of the samples of cumulated gabbro, diabase and andesitic porphyrite from the Armantai ophiolite, Xinjiang, yielded the ages of 561 ± 41 Ma (ε_Nd(t) = 6.1) and 392 ± 17 Ma [(⁸⁷Sr/⁸⁶Sr)_i = 0.7041], which stand for the ages of creation and later metamorphism of the ophiolites, respectively. The creation environment of the Armantai ophiolites seems to a back-arc basin caused by the southward subduction of the palaeo-Asia Ocean. This project was specially granted by the State under the Key Scientific and Technological Program for the “Eight Five-Year Plan” period.     

Age and sources of the anorthosites of the Neoarchean Kolmozero-Voron’ya greenstone belt (Fennoscandian Shield)

New data are reported on U-Pb (SHRIMP-II) age (2662 ± 7 Ma), isotope (Sm-Nd) and geochemical compositions of the anorthosites of the Patchemvarek Massif and “ovoidal” anorthosite sills of the Neoarchean Kolmozero-Voron’ya greenstone belt. Mesoarchean (2938 ± 8 Ma) zircons found in the Patchemvarek anorthosite have low Th/U ratio, are overgrown by a thin rim, and may be interpreted as xenogenic crystals assimilated by primary melts of the gabbro-anorthosite massifs from host Mesoarchean tonalites during crystallization in a magmatic chamber. The “ovoidal” anorthosite sills are dated at 2730–2740 Ma on the basis of U-Pb local zircon isotope analysis. The sills of the “ovoidal” anorthosites in the Kolmozero-Voron’ya GSB represent the older (2730–2740 Ma) rock group, which differs from the Patchemvarek anorthosites in strongly depleted Nd isotope composition and some geochemical features. In terms of age and Sm-Nd isotope characteristics, the “ovoidal” anorthosites are close to the komatiites of the lower volcanogenic sequence (ε_Nd(Т) + 3.0–3.2), and metaandesites (2778 ± 5.4 Ma, U-Pb TIMS, ε_NdТ + 3.5) and metatholeiites of the upper volcanogenic sequence (ε_Nd(Т) + 3.5–3.7) of the supracrustal complex of the Kolmozero-Voron’ya GSB.     

Duration of the formation and sources of the granitoids of the Litsk-Araguba Complex, Kola Peninsula

Postorogenic granitoids of the Litsk-Araguba Complex compose a chain of intrusive bodies around 850 km² in area, which are confined to the NE-trending deep-seated fault zone. Results of U-Pb zircon dating indicate that the formation of granitoids of the Litsk-Araguba Complex lasted 28 ± 9 Ma. Note that the rocks of the first-fourth phases have similar age within (1774–1762 Ma), while quartz syenites of the fifth phase were formed much later (1746 ± 8 Ma). The study of Sm-Nd isotopic system revealed that the quartz syenites plot in the field of the Nd isotopic evolution of the lower crust represented mainly by the Paleoproterozoic garnet granulites with model ages T_Nd(DM) = 2.4–2.7 Ga and ?_Nd(T) from ?5.6 to ?6.3. It was found that the near-contact syenites of the Litsk Massif contain composite zircons with an age of 1758 ± 9Ma. They differ from zircons in coeval porphyraceous granites in lowered U and Th concentrations, which are close to those in zircons from the lower crustal garnet granulites of this region. These data in combination with internal structure of the crystals determine xenogenic lower-crustal origin of zircons from syenites and confirm geochemical data on the lower crustal input in the formation of granitoid melts.     

Isotope geochemistry and geochronology of the gabbro of the Volkovsky Massif,Urals

⁴⁰Ar-³⁹Ar, Sm-Nd, U-Pb, and Lu-Hf isotope data are reported on the gabbro of the Volkovsky Massif, the only massif of the Uralian Platinum Belt wherein economic copper-iron-vanadium and high-grade gold-palladium mineralization is present. The massif is made up of gabbro blocks with concentrically zoned structure and diorite intrusions in its core. In the northeast and southwest, the gabbro is cut by syenite of the Kushva Massif. Gabbro blocks mainly consist of the olivine-anorthite gabbro, while labradorite two- pyroxene gabbro intersects both olivine-anorthite gabbro and Ti-magnetite and copper-PGE mineralization developed in them. The study of both gabbro types by Sm-Nd isochron and U-Pb (SHRIMP II) zircon methods with subsequent REE and Lu-Hf isotope analysis of zircon made it possible to date reliably (428 ± 7 Ma (SHRIMP) and 436 ± 21 Ma (Sm-Nd)) postore labradorite gabbro and, correspondingly, the upper age limit of the mineralization of the Volkovsky Massif. Ore-bearing olivine-anorthite gabbro contain four different-age zircon populations: 2682 ± 37–972 ± 18 Ma, 655 ± 15 to 565 ± 9 Ma; 450 ± 12 Ma, and 343 ± 8 Ma. Hf-Nd isotope systematics showed that zircon with an age of 450 ± 12 Ma presumably marks the formation age of the rocks, the older zircon was trapped, while zircon with an age of 343 ± 8 Ma was formed during low-temperature transformation of the rock and sometimes contains excess radiogenic Hf. Proterozoic xenogenic zircon was inherited from diverse rocks of ancient crust, while the oldest grain with an age of 2065 Ma was possibly formed in a deep mantle source. Vendian zircon was presumably also entrapped, and its morphology and geochemistry point to the crystallization from a basaltic melt. The abundance of pre-Paleozoic zircon in the olivine-anorthite gabbro suggests significant contribution of ancient material in their petrogenesis. This material could serve as source of ore components (metals and sulfur) for unique copper-sulfide gold-PGE mineralization of the Volkovsky Massif.