P’yŏngyang — ancient and modern —the capital of North Koreangyang — ancient and modern —the capital of North Korea

The capital of the Democratic People’s Republic of Korea (North Korea) is both the oldest and the newest settlement in Korea. The basic concepts in its early urban development made it the model for Korean cities of later ages. In the 6th and 7th century AD P’yôngyang was one of the largest cities in Asia, second only to the imperial capital of China, but it later declined. It partly recovered its former position when it became the capital of North Korea after World War II. Its reconstruction since the Korean War has made it one of the most striking examples of socialist city planning.     

Fractal and Multifractal Propertiesof the Spatial Distribution of Natural Fractures——Analyses and Applications

The Cantor's dust theory is applied to investigate the scaling properties of the spatial distribution of natural fractures obtained from detailed scanline surveys of 27 field sites in the Appalachian Plateau of western New York, USA. The results obtained in this study indicate: 1) fracture spacing is characterized by fractal and multifractal properties. On small scales analyses yield an average fractal dimension of 0.15, which suggests a very high degree of clustering. In contrast, on large scales, fractures tend to be more regular and evenly distributed with an average fracture dimension of 0.52; 2) fractal dimension varies with different sets in different orientations, which can be attributed to interactions between pre-existing fractures and younger ones, as well as variations of the intensity of the stresses under which the fractures were formed; 3) a time sequence of fracture set formation can be proposed based on fractal and multifractal analyses, which consists of (from old to young): N-S, NW, EN     

Age and composition of dykes emplaced before and during the opening of the Tasman Sea—source implications

Abstract

Dykes are common in the wave-cut platforms along the coast from Newcastle to Sydney. According to some authors, they may be related to the opening of the Tasman Sea that commenced ca 84?Ma ago. However, there are few detailed radiogenic dating and geochemical studies to evaluate this. We attempt to resolve this by K–Ar dating of plagioclase in and geochemical studies of, basaltic dykes intruding Permo-Triassic sequences on the wave-cut platforms and Carboniferous and Permo-Triassic sequences inland. The plagioclase separated from the dykes give K–Ar ages ranging from 266 to 53?Ma with the majority older than 84?Ma indicating that most dykes were emplaced before the Tasman Seafloor formation. The dykes are generally mildly alkaline, high-Ti basalts; fewer are tholeiitic and calc-alkaline, low-Ti basalts. Strongly light rare earth element (LREE)-enriched patterns typify the former and flat, LREE-depleted or slightly to moderately enriched LREE patterns, the latter. High-Ti basalts have ocean-island-basalt-like and low-Ti basalts, calc-alkaline or mid-ocean ridge basalt (MORB)-like patterns. Most high-Ti and some low-Ti basalts show plume-like characteristics, others N-type MORB and arc-like characteristics. Dykes intruding the Carboniferous sequences show a distinct contamination signature that could be crustal or due to subduction-related metasomatism of the subcontinental lithospheric mantle. The sources of the basaltic magmas vary substantially and in places changes with time. All alkali basalts are derived from enriched asthenospheric sources at varying depths (90–147?km) and most tholeiitic, low-Ti basalts have been extracted from asthenospheric and depleted asthenospheric–lithospheric sources indicating substantial compositional heterogeneity of the mantle. Further, Nd model ages varying from Neoproterozoic (940–580?Ma) to Paleozoic (460–370?Ma) suggest variation in the age of mantle sources for the basalts.     

Lead orthophosphates—IV Formation and stability in the environment

Experimental and predicted thermochemical constants are used to assess the formation and stability of lead phosphates in soil and sedimentary environments. For the chemical conditions likely to be encountered in oxidizing environments, the stability fields of pyromorphites [Pb₅(PO₄)₃X, X = OH^?, Cl^?, Br^? and F^?] and plumbogummite [PbAl₃(PO₄)₂(OH)₅-H₂O] predominate strongly over those of the other secondary lead minerals. The theoretical phase relationships together with several field observations are used as the basis for suggesting that the interaction of lead and phosphorus (to form pyromorphites and plumbogummite in particular) is an important buffer mechanism controlling the migration and fixation of lead in the environment. Calculations using the concentrations of lead and phosphate ions in serum indicate that the solubility of lead phosphates may be the limiting factor with regard to lead ion concentration in human body. The removal of lead from wastewater by precipitation as lead chloropyromorphite is considered a spin-off of possible industrial interest.     

Determination and Significance of the Bluemull Blastomylonite Zone in the Northeast——East of Yell,Shetland

There is a zone of blastomylonites containing hornblende gneisses of Lewisian Inliertype in the northeast-east of Yell,Shetland.This zone with a north—northwesterlytrend consists of blastomylonised hornblende-banded gneiss,hornblende-feldspar gneissand mica-felsie-gneiss with lenses of hornblende gneiss.It is indicated that theblastomylonite zone is actually a ductile shear zone and the sense of shear is dextral.This contributes to understanding the details of tectonic evolution in this area,and thiszone is probably a part of tectonic system of the British Caledonides.     

Geochemistry of the Baishitouquan Amazonite—and Topaz—bearing Granite in the Mid—Tianshan Belt,Xinjiang,China

The Baishitouquan amazonite and topaz-bearing granite is one of the typical high-rubidium and high-fluorine granites in the eastern part of the Mid-Tianshan belt. This intrusion is in sharp contact with Mid-Proterozoic schists, gneisses and marbles, and is composed of four zones transitional from the bottom upwards: leucogranite, amazonite granite, topaz-bearing amazonite granite and topaz quartz albitite. The Baishitouquan granite contains highly ordered K-feldspar, Li-rich mica, Mn-rich garnet, α-quartz and low temperature zircon and is chemically high in Si, K, Na, Al, Li, Rb, Cs and F, and low in Ti, Fe, Ca, Mg, P, Co, Ni, Cr, V, Sr and Ba, with Na₂O<K₂O. Amazonite from the amazonite granite zone contains 1867 ppm Rb. The F contents of bulk rocks are 3040 and 4597 for the amazonite granite and topaz-bearing amazonite granite zones, respectively. These two zones have δ¹⁸O values of 8.97–9.85‰ (SMOW) and show flat REE distribution patterns with strong Eu depletion. K-Ar and Rb-Sr ages of this intrusion are 226. 6 Ma and 209. 6 Ma respectively, with an initial⁸⁷Sr/⁸⁶Sr ratio of 0.987±0.213. The Baishitouquan granite is the product of crystallization of a low temperature, and water, rubidium and fluorine-rich magma, which may have been derived from partial melting of muscovite-rich crustal rocks. Consolidation of this granite involved two contrasting and successive stages: melt crystallization and hydrothermal metasomatism and precipitation. Various geological features of this granite were formed during the transition from the magmatic to the hydrothermal stage.     

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 Hydrothermal Na-Ca Alteration at the Marginal Part 0f the Florina Granite and the Associated Magnetite-Hematite Bands With Thorium and Uranium Mineralization

The Oxia mineralized granite is the product of differentiation in the external parts of the Florina magmatic mass. Acidic hydrothermal solutions either of magmatic or of meteoric origin reacted with the upper tectonically fractured parts of the Florina granite and became enriched in iron, thorium, uranium, zircon and rare-earth elements. The most abundant alteration minerals are sericite and quartz, while the minerals of the mineralization bands include magnetite, hematite, thorite, monazite and zircon. The outer parts of the Oxia granite made it easy the percolation of hydrothermal solutions from the deeper heater to the upper cooler parts of the granite which acted as a hot spot.     

北淮阳新开岭地区花岗岩锆石U-Pb年龄和氧同位素组成

对大别造山带北麓的北淮阳新开岭地区岩浆岩进行了锆石阴极发光显微结构观察和SHRIMP法锆石微区UPb定年.在锆石阴极发光图像中, 一个花岗岩样品中的大部分锆石颗粒具有明显的初始岩浆振荡环带, 为典型的岩浆锆石, 少有蚀变的颗粒和/或区域; 而另一个花岗岩样品中的锆石虽然同样具有振荡环带, 但是大部分颗粒中心的初始岩浆环带被扰动, 指示这些锆石为岩浆锆石, 受到了较强的后期热液蚀变的改造.对锆石具有初始岩浆环带和溶蚀结构的区域分别进行SHRIMP法UPb微区定年结果表明, 这些岩浆岩的形成年龄为(820±4) Ma, 热液蚀变作用发生的时间为(780±4) Ma.新开岭地区新元古代花岗质岩石的形成和后期超固相热液蚀变作用分别对应于超大陆裂解之前的约830~795Ma岩浆活动和裂解过程中约780~745Ma的岩浆作用.单矿物激光氟化氧同位素分析结果表明, 这些岩浆岩具有非常低的δ18O值, 其中锆石为1.90‰~5.78‰, 石英为-2.88‰~-7.67‰, 斜长石为-4.01‰~-11.40‰.锆石和其他矿物之间表现出强烈的氧同位素不平衡, 而其他矿物之间则达到了氧同位素的再平衡.结合不同δ18O值锆石的内部结构特征, 认为该地区的热液蚀变作用为超固相条件下的高温热液蚀变.这一过程不但改变了石英等矿物的氧同位素组成, 同时也不同程度地改变了锆石的氧同位素组成, 所以这些样品中低δ18O值锆石可能是超固相条件下热液蚀变的结果.石英中具有异常低的δ18O值表明蚀变流体来源应为寒冷气候大气降水.所以, 新开岭地区亏损18O蚀变岩石的形成与裂谷岩浆作用和雪球地球事件相耦合的高温大气降水热液蚀变有关.      

Geochronology and S–Pb–O–H isotopic constraints on the generation of the Luoyang Fe deposit in southwest Fujian Province,SE China

The Luoyang Fe polymetallic deposit is a well‐known Makeng‐type ore deposit in a late Paleozoic basin in southwest Fujian, southeast China. To investigate the generation of Makeng‐type Fe deposits, we conducted an integrated study of geochronology and S–Pb–O–H isotope compositions of the Luoyang Fe deposit. The LA–ICP–MS zircon U–Pb ages of the granite and Re–Os ages of the molybdenite suggest that the emplacement of the granite was coeval with the mineralization of the Luoyang deposit at 133–131 Ma. The H–O and S–Pb isotope compositions indicate that the metallogenic material of the Luoyang deposit had a magmatic hydrothermal source, and was derived mainly from the upper crust with a low degree of contamination of mantle material. The Pb isotope analyses of the ore minerals show that the Luoyang Fe deposit formed in an orogenic setting.     

东昆仑格尔木东部金水口片麻状富铝花岗岩锆石微区Raman光谱研究

通过对金水口片麻状富铝花岗岩中锆石的宏观形态特征和微区Raman光谱特征的研究发现，该套片麻状花岗岩中的锆石主要有2种类型：颗粒较小的简单锆石和颗粒较大的复杂锆石。复杂锆石由3部分组成：细小的残留核、浅色部分和褐色部分。简单锆石和复杂锆石核部残留锆石均为变质成因；复杂锆石的浅色部分和褐色部分均为岩浆锆石。结合锆石Raman谱线研究结果，对金水口片麻状富铝花岗岩已有的锆石U-Pb年龄进行进一步的解释，认为390-414Ma可能代表了复杂锆石的浅色部分或褐色部分的岩浆锆石的形成时代，而1600-1800MaW能记录了复杂锆石核部变质事件的时代。     

Magmatic-to-hydrothermal crystallization in the W–Sn mineralized Mole Granite (NSW, Australia): Part II: Evolving zircon and thorite trace element chemistry

The Sn–W mineralized Mole Granite in Eastern Australia hosts zircon populations that crystallized at several stages during a protracted magmatic to hydrothermal evolution. Thirty-four elements have been quantified by laser-ablation inductively-coupled-plasma mass-spectrometric microanalysis with the aim of relating the chemistry of zircon to its growth environment. Trace element contents are highly variable for all textural occurrences. Zircon inclusions in earliest quartz phenocryst suggest that zircon was a liquidus phase that crystallized probably deep in the crust. Trace element contents are conspicuously high, showing only a slight positive Ce anomaly but a pronounced negative Eu-anomaly. Successive crystallization stages of magmatic zircon are characterized by progressive depletion in trace element contents, notably the rare earth elements, with an increasingly important positive Ce-anomaly. This evolution reflects saturation of REE accepting minerals such as monazite, thorite, xenotime and possibly apatite and is affected little by the exsolution of a magmatic–hydrothermal fluid. Zircon that is interpreted to have precipitated from aqueous fluids in Sn–W-bearing quartz veins shows REE patterns indistinguishable from those of late magmatic zircon. When combined with experimental evidence on the fluid–melt partitioning of REE, it indicates that the REE distribution coefficients for zircon/melt and zircon/fluid are largely comparable.

The second example of hydrothermal zircon crystallized some 2 My after the host granite. These crystals reveal an intragranular zonation of increasing trace element concentrations from core to rim. Therefore, REE abundances and patterns alone are not conclusive indicators of the geological environment in which zircon crystallized. Nevertheless, variations in trace element contents of zircon that relate to the chemistry of the melt or fluid from which zircon crystallized, as measured in cogenetic melt and fluid inclusions, are promising for future petrogenetic modeling.

Lead and Cs are strongly incompatible in hydrothermal zircon, with estimated zircon–fluid distribution coefficients D ≤ 0.001, while Sn and Li are moderately incompatible, D_Sn  0.6 and D_Li  0.1, and Ce is compatible, D_Ce  14. Moreover, hydrothermal zircon has a more pronounced negative Eu-anomaly and higher Ta/Nb and U/Th ratios than the magmatic zircons of the Mole Granite.     

Geochemistry of magmatic and hydrothermal zircon from the highly evolved Baerzhe alkaline granite: implications for Zr–REE–Nb mineralization

The Baerzhe alkaline granite pluton hosts one of the largest rare metal (Zr, rare earth elements, and Nb) deposits in Asia. It contains a geological resource of about 100 Mt at 1.84 % ZrO₂, 0.30 % Ce₂O₃, and 0.26 % Nb₂O₅. Zirconium, rare earth elements (REE), and Nb are primarily hosted by zircon, yttroceberysite, fergusonite, ferrocolumbite, and pyrochlore. Three types of zircon can be identified in the deposit: magmatic, metamict, and hydrothermal. Primary magmatic zircon grains occur in the barren hypersolvus granite and are commonly prismatic, with oscillatory zones and abundant melt and mineral inclusions. The occurrence of aegirine and fluorite in the recrystallized melt inclusions hosted in the magmatic zircon indicates that the parental magma of the Baerzhe pluton is alkali- and F-rich. Metamict zircon grains occur in the mineralized subsolvus granite and are commonly prismatic and murky with cracks, pores, and mineral inclusions. They commonly show dissolution textures, indicating a magmatic origin with later metamictization due to deuteric hydrothermal alteration. Hydrothermal zircon grains occur in mineralized subsolvus granite and are dipyramidal with quartz inclusions, with murky CL images. They have 608 to 2,502 ppm light REE and 787 to 2,521 ppm Nb, much higher than magmatic zircon. The texture and composition of the three types of zircon indicate that they experienced remobilization and recrystallization during the transition from a magmatic to a hydrothermal system. Large amounts of Zr, REE, and Nb were enriched and precipitated during the transitional period to form the giant low-grade Baerzhe Zr–REE–Nb deposit.     

Trace-element composition of hydrothermal zircon and the alteration of Hadean zircon from the Jack Hills,Australia

Hydrothermal zircon can be used to date fluid-infiltration events and water/rock interaction. At the Boggy Plain zoned pluton (BPZP), eastern Australia, hydrothermal zircon occurs with hydrothermal scheelite, molybdenite, thorite and rutile in incipiently altered aplite and monzogranite. The hydrothermal zircon is texturally distinct from magmatic zircon in the same rocks, occurring as murky-brown translucent 20–50 μm-thick mantles on magmatic cores and less commonly as individual crystals. The hydrothermal mantles are internally textureless in back-scatter electron and cathodoluminescence images whereas magmatic zircon is oscillatory zoned. The age of the hydrothermal zircon is indistinguishable from magmatic zircon, indicating precipitation from a fluid evolved from the magma during the final stages of crystallization. Despite indistinguishable U-Pb isotopic compositions, the trace-element compositions of the hydrothermal and magmatic zircon are distinct. Hydrothermal zircon is enriched in all measured trace-elements relative to magmatic zircon in the same rock, including V, Ti, Nb, Hf, Sc, Mn, U, Y, Th and the rare-earth elements (REE). Chondrite-normalized REE abundances form two distinct pattern groupings: type-1 (magmatic) patterns increase steeply from La to Lu and have Ce and Eu anomalies—these are patterns typical for unaltered magmatic zircon in continental crust rock types; type-2 (hydrothermal) patterns generally have higher abundances of the REE, flatter light-REE patterns [(Sm/La)_N = 1.5–4.4 vs. 22–110 for magmatic zircon] and smaller Ce anomalies (Ce/Ce* = 1.8–3.5 vs. 32–49 for magmatic zircon). Type-2 patterns have also been described for hydrothermally-altered zircon from the Gabel Hamradom granite, Egypt, and a granitic dyke from the Acasta Gneiss Complex, Canada.Hadean (∼4.5–4.0 Ga) zircon from the Jack Hills, Western Australia, have variable normalized REE patterns. In particular, the oldest piece of Earth—zircon crystal W74/2-36 (dated at 4.4 Ga)—contains both type-1 and type-2 patterns on a 50 μm scale, a phenomenon not yet reported for unaltered magmatic zircon. In the context of documented magmatic and hydrothermal zircon compositions from constrained samples from the BPZP and the literature, the type-2 patterns in crystal W74/2-36 and other Jack Hills Hadean (JHH) zircon are interpreted as hydrothermally-altered magmatic compositions. An alteration scenario, constrained by isotope and trace-element data, as well as α-decay event calculations, involving fluid/zircon cation and oxygen isotope exchange within partially metamict zones and minor dissolution/reprecipitation, may have occurred episodically for some JHH zircon and at ∼4.27 Ga for zircon W74/2-36. Type-2 compositions in JHH zircon are interpreted to represent localized exchange with a light-REE-bearing, high δ¹⁸O (∼6–10‰ or higher) fluid. Thus, a complex explanation involving “permanent” liquid water oceans, large-scale water/rock interaction and plate tectonics in the very early Archean is not necessary as the zircon textures and compositions are simply explained by exchange between partially metamict zircon and a low volume ephemeral fluid.     

诸广南部产铀花岗岩长江岩体中的绿泥石和铀源矿物研究

长江岩体是诸广南部地区重要的产铀花岗岩体之一,此次研究运用电子探针和扫描电镜对长江岩体新鲜花岗岩和 蚀变花岗岩中的绿泥石和有关含铀矿物进行了精细对比,揭示花岗岩中铀的活化与成矿前期或早期致使花岗岩发生绿泥 石化的还原性热液蚀变作用关系密切,黑云母等的绿泥石化蚀变,使其中包裹的一些含铀副矿物也发生蚀变,导致原来 以类质同象形式存在于副矿物中的惰性铀转变成活性铀,并在绿泥石附近沉淀成铀石等铀含量高且在成矿期低度氧化性 热液作用下容易释放铀的矿物。长江岩体中的副矿物有锆石、磷灰石、褐帘石、铀石-钍石、晶质铀矿、独居石等,其 中,晶质铀矿、铀石、铀钍石中铀含量高且铀容易释放,是长江岩体的主要铀源矿物;独居石中铀含量较高,当其周围 矿物绿泥石化时,独居石蚀变形成直氟碳钙铈矿并释放铀,因而也是长江岩体的潜在铀源矿物;锆石中铀含量虽高,但 因其结构稳定,铀难以释放,因此它不是长江岩体中重要的铀源矿物;磷灰石、褐帘石中铀含量均低于检测限,作为铀 源矿物的可能性很小。     

福建闽江和九龙江现代沉积物重矿物特征及其物源意义*

通过对闽江和九龙江沿岸沉积物中重矿物的分析,发现重矿物组合与源区岩石具有极好的相关性。两条河流流域重矿物组合为不透明铁矿类—绿帘石—锆石—电气石—角闪石,特征矿物为绿帘石,含量高达原生透明重矿物比重的70%,其成因除与高级变质岩有关外,还与中酸性岩浆岩及其与围岩接触蚀变发生的绿帘石化有关。从重矿物组合、重矿物特征指数以及与锆石年龄谱系的比对分析发现,闽江流域重矿物源自闽西北武夷山前寒武纪的变质岩、闽东广泛出露的燕山期岩浆岩和接触变质岩,而九龙江流域重矿物源自闽西南的印支—燕山期花岗岩。闽江上游沉积物重矿物以源自高级变质岩的重矿物为特征,中下游由上游来源的重矿物和下游酸性岩浆岩及接触变质岩形成的重矿物共同构成;九龙江以印支—燕山期花岗岩中的副矿物组合为特征。研究结果显示,对于中小流域面积的河流,由于搬运距离有限,重矿物组合保存的源岩信息量大,可作为研究流域内构造演化和源汇对比的重要手段。     

The Genesis of the Cornubian Batholith (South-West England): the example of the Carnmenellis Pluton

The origin of the Carnmenellis granite is discussed in the lightof new petrographic and chemical data which suggest that thepresent mineral assemblage comprises refractory, magmatic, subsolidusand hydrothermal phases. The present homogeneity of the plutonresults from subsolidus to pervasive hydrothermal reworkinginvolving selective leaching of alkalis and Fe-Mg and an increasein Li, F, B, and Rb, which were introduced, or redistributed,through high temperature hydrothermal circulation. The compositionsof the primary minerals were re-equilibrated with respect tothese water-rock interactions. Rb-Sr systematics demonstratethat whole rock samples show lower ages than the minerals (260and 285 Ma, respectively). The perturbation in the former isotopedistribution is in agreement with the chemical re-equilibrationof the mica with external Rb-rich and Sr-depleted solutions.The distribution of rare-earths reveal that most reside in afew accessory phases, viz. monazite, zircon, and apatite; theirnear-liquidus fractionation is responsible for the loweringof the bulk REE content compared to pelitic source materialand for the present REE pattern of the pluton. Conditions of magma generation by partial melting of cordierite-sillimanite-spinelpelitic gneisses were estimated to be around 800?C and 5 kbwith water content in the magma of about 4 wt. per cent. H₂Osaturation was reached late during the ascent of the magma,making possible the crystallization of muscovite from the residualmelt. The highly evolved peraluminous composition of the plutonis not explained by a simple magmatic differentiation. Comparedto the Carnmenellis pluton, the Land's End massif of similarmineralogy appears less evolved, either because of less subsolidusreworking or deeper structural emplacement.