海岸沙丘表面现代风成沙地球化学元素分异的典型研究--以河北昌黎黄金海岸横向沙脊为例

在我国海岸沙丘主要分布地区河北昌黎黄金海岸选取代表性的海岸横向沙脊为研究对象,对其典型断面上沙丘表面不同部位的21种地球化学元素的含量进行了比较分析。结果表明,Co、Zr和Mg三种元素在海岸沙脊表面不同部位的含量差异明显且与海滩沙相比含量差异较大,Cr、Pb、Ti、Nb、As、Mn、Zn和Ba等8种元素的含量差异程度中等,但Y、Ca、Fe、Na、Al、Sr、P、K、Rb和Si等10种元素的差异并不明显,而11种差异程度中等以上元素在海岸横向沙脊迎风坡脚、迎风坡、脊顶、背风坡、背风坡脚等部位的含量变化特征并不一致,呈现出不同的分异模式,其主要原因是受沉积环境、化学元素性质、粒度特征及营力的影响等。     

元素比值研究玄武岩源区成分的若干问题讨论

本文讨论了以元素比值研究玄武岩成分的限制条件及岩浆结晶分异作用对熔体元素比值的影响，笔者认为采用元素比值研究源岩成分时，除了要考虑两元素分配系数及部分熔融程度的差异外，还应考虑部分熔融方式的影响，另外，由于结晶分异作用对元素比值的影响很小，因此该方法很适合于研究玄武岩源岩的不相容元素，最后，本文提出了一种较为实用的逼近玄武岩源岩元素比值的方法。     

与钨矿有关的两类花岗岩的元素演化趋势

通过对英安流纹岩(同熔型)和二长花岗斑岩(改造型)的全岩与基质元素含量差异的比较,以及元素的斑晶—基质分配系数的计算,得出了两种在岩浆结晶分异过程中的元素演化趋势。它们分别与和钨矿有关的同熔型和改造型复式岩体的元素演化趋势相吻合。这说明岩浆自身的分异演化是形成两类复式钨矿成矿岩体的可能方式之一。文中强调了上述两种元素的演化趋势在REE、K和Na、W演化上的差异。     

枇杷的不同器官中元素地球化学特征

枇杷是药用价值很高的一种经济水果。研究不同母岩类型产区的枇杷中元素的地球化学特征,发现同一品种枇杷中元素的富集部位各不相同;而不同品种的枇杷所富集的元素种类大致相同,只是富集程度有差异。有益、营养元素在叶片中的含量大多高于其他部位;有害元素不超标。与枇杷果关系较为密切的营养元素主要为N、P、K、Ca、Mg;微量营养元素为B、Zn、Cu。     

人发根中梢部微量元素含量的对比

用电感耦合等离子发射光谱法测定人发根部,中部,梢部３３种微量元素的含量,并进行对比。结果表明大多数元素三部分含量分布不均匀,部分元素存在显著性差异。     

中心差异向量法及其应用——地球化学找矿新方法初探

矿床所处的地球化学背景不同,其标志性伴生元素的特征异常值也不同。但元素的原子结构、矿物结构及其能量特征是基本不变的,在成矿过程中发生活化、迁移所表现出的相对活动性也基本不变。通过研究矿区中相关元素的富集中心差异关系,可预测另一些元素隐伏的富集中心,这就是本文提出的中心差异向量法。该方法对四川拉拉铜矿12个元素中心差异向量计算结果,已为钻探工作证实。表明该方法是一具有实际意义的地球化学找矿方法。     

分量化探法在砂岩型铀矿区域预测评价中的研究与应用

1 元素分量和分量化探 元素分量是相对采样介质中元素总量而言的.元素总量是指元素在每一种采样介质(如土壤、水、底沉积、岩石、矿石、生物等)中各种存在形式含量的总和.而采样介质中每一种存在形式的含量就称为该元素的一种分量.     

亦论韧性剪切变形与金的成矿作用：与邵世才《试论韧性剪切变形与 …

剪切带型金矿是一种重要的金矿类型。韧性－超韧性深层次剪切变形是促使Ａｕ元素活化分异、形成动力变质含金热液的过程,中浅层次的韧脆性、脆性剪切变形区是Ａｕ元素聚集成矿部位。韧脆性剪切带的不同变形层次及其构造岩类型决定了剪切带型金矿床的矿化类型。剪切带型金矿床往往具有成矿时代滞后、空间规模差异、物源指示差异、韧性变形强度与Ａｕ元素含量反相关等异常特征。长期演化的造山带附近及边缘是寻找大型剪切带型金矿床的     

真菌-玄武岩相互作用过程中真菌属种差异对元素释放行为的影响

真菌在矿物、岩石风化和元素溶解过程中发挥着重要作用。土壤中分布和生长着多种真菌,这些不同真菌在矿物和岩石风化,以及元素溶解过程中发挥的作用可能存在显著差异。为限定此差异,本研究从玄武岩风化土壤中分离获取了4种真菌(Aspergillus pesudofelis、Aspergillus viridinutans、Aspergillus undagawae和Aspergillus clavatus),设计批式溶解实验,探究了实验室条件下(28℃、30天内)4种真菌对玄武岩的风化作用,主要通过分析元素(包括Mg、Al、Si、Ca、Ti、Mn、Fe、Ni和Sr)的溶解速率和机制揭示不同属种真菌造成的玄武岩风化差异,并选取其中两种典型真菌所在的体系进行分析。实验结果显示不同属种真菌对玄武岩的风化和元素溶解的作用确实存在显著差异:1)与无机对照组相比,真菌A.pseudofelis的生长使得溶液pH值发生显著变化,元素的线性释放速率(Ril)显著升高;2)不同种真菌对体系pH值和Ril的影响差别巨大,且并非所有真菌均能加快玄武岩风化,如经过30天反应,含真菌A.pseudofelis体系溶液pH值上升了2.1,元素Mg的线性释放速率是无机对照组的22.5倍;而含真菌A.viridinutans体系溶液pH值仅上升了0.1,Mg的线性释放速率与无机对照组近似相等;3)Mg、Al、Ca、Ti元素的线性释放速率Ril最大值均出现在溶液最低pH值条件下,表明这4种元素的释放行为很大程度上受控于质子交换作用,而Fe和Ni的释放则由真菌代谢的草酸主导。由此可知,不同种真菌对有机酸代谢水平的差异影响了玄武岩中元素的释放行为。这也可能表明,在岩石早期风化过程中,具有较强有机酸(如草酸)代谢能力的真菌在Fe和Mg等生命必需元素的释放过程中起着重要作用。     

韧性剪切带型金矿成矿模式

剪切带型金矿是一种重要的金矿床类型,深层次韧性剪切变形是金元素活化迁移过程之一,导致含金动力变质热液形成,中浅层次的韧脆性剪变形区是金元素聚集成矿部位;韧性剪切带的不同变形层次及其人断层岩类型制约着金矿化类型,剪切带型金矿床具有成矿滞后,空间规模差异,物源指示差异,韧性变形强度与金元素含量呈反相关等特征,长期演化的韧性剪切带是剪切带金矿床形成并导致多种金矿化类型叠加,形成大型金矿床的有利条件,也是     

冀东太平寨紫苏花岗岩类深熔成因的矿物标志

冀东太平寨地区紫苏花岗岩的矿物学研究结果表明,该类岩石中的主要组成矿物具有残晶相和结晶相矿物共存特点。残晶相和结晶相矿物与围岩中同类矿物对比研究表明,该区的紫苏花岗岩类是由其围岩—石英闪长质-英云闪长质紫苏斜长片麻岩深熔而成。     

冀东迁安地区太古代片麻杂岩的地球化学和演化

曹庄片麻杂岩包括35亿年的表壳岩及三个不同时期的复期正片麻岩。水厂片麻杂岩包括水厂表壳岩及侵入其中的淡花岗岩和紫苏花岗岩,后者年龄为26.5亿年。     

New Insights into the Origin of Kabbaldurga Charnockites, Karnataka, South India

A detailed study of the structure and petrology of the rocks bordering the Kabbaldurga-type charnockites provides important constraints on the origin of these charnockites. The structural elements register three phases of deformation and show a uniform pattern in the larger area, a pattern consistent with the regional structure of the Precambrian of Southern Karnataka. In the Kabbaldurga area, however, some of the earlier structures are poorly preserved. Yet there are vestiges of early folds described by banded/layered charnockites as in the neighbouring Kodamballi area, and a consistent development of dilatant structures which can be related to the kinematics of deformation in the larger terrain. At Kabbaldurga the pegmatitic charnockites occur as veins of diverse orientation; but they rarely follow the shear - generated structures.

The metamorphic reactions invoked by previous workers to explain in situ transformation of gneiss to charnockite were based on chemical similarity of some close pairs. But the petrographic and chemical variations in the pegmatitic charnockites and the Peninsular gneisses at Kabbaldurga quarry are compelling features which cannot be explained by the hypothesis of in situ transformation. We have argued, on the basis of rock and mineral chemistry, that derivation of the pegmatitic charnockites by dehydration melting in metabasites offers a better explanation. Pressure-temperature values (at least 850° to 900° C, 7 kbar) obtained by us for the granulites of this area, viewed against the results of experimental dehydration melting in basic rocks with hornblende and/or biotite, provide strong support for this model. In the field leucosomes within the basic granulites of Kabbaldurga are not uncommon. The compositions of the pegmatitic charnockites (tonalitic and granitic) match those of the melts produced in experiments. Further, the pattern of variation in the composition of hornblende and plagioclase in the basic granulites of the Kabbaldurga area is compatible with extraction of melts. This alternative model for the origin of the Kabbaldurga charnockites is petrologically feasible and does not require either in situ transformation or structurally controlled growth, which, incidentally, are not ubiquitous at Kabbaldurga     

High radiogenic heat production in the Kerala Khondalite Block,Southern Granulite Province,India

In situ radioelemental (K, U and Th) analysis and heat production estimates have been made at 59 sites in the Kerala Khondalite Block (KKB) of the Southern Granulite Province (SGP) of India. Together with the in situ analyses on granulites and gneisses previously reported from 28 sites, and heat production estimated from the published geochemical analyses on granites and syenites of the KKB, the new data set allows good characterization of heat production for the major granulite facies rocks and granitoids of the KKB. Garnet biotite gneisses are characterized by high levels of Th and U, with mean values of 60 and 3 ppm, respectively. Khondalites, leptynites and charnockites have slightly lower levels of Th (23, 20 and 22 ppm, respectively) and U (2.9, 2.4 and 0.9 ppm, respectively). The mean K, U, Th abundances for the granites, leucogranites and granitic gneisses ranges from 3.9 to 4.3%, 2.6 to 4.3 ppm, 22 to 50 ppm respectively, and for the syenites 4.8%, 2 ppm and 5.7 ppm. Mean radiogenic heat production values for garnet–biotite gneiss, khondalite, leptynite and charnockite are 5.5, 2.7, 2.4 and 2.2 μW m⁻³, respectively. For the granites, leucogranites, granitic gneisses and syenites it is 2.6, 3.4, 4.6 and 1.4 μW m⁻³, respectively. Heat production of granulite facies rocks, which are the most abundant rocks in KKB, correlate well with Th, but less with U, suggesting that variation is caused by Th and U bearing accessory minerals such as monazite and zircon. The high heat production of the KKB granulites are in contrast to the low heat production of the Late Archaean granulites of the Northern Block (NB) of the SGP which are highly depleted in radioelements and also the granulites of Madurai Block (MB) that have higher radioelemental abundances than in the granulites of the NB. The high heat production of the KKB granulites could be due to the nature of protoliths and/or metasomatism associated with Neoproteroic- to- Pan African alkaline magmatic activity represented by alkali granite and syenite–carbonatite emplacements and emplacement of pegmatites.     

Orthopyroxene-Bearing Rocks of Charnockitic Affinities in the South Savanna--Kanuku Complex of British Guiana

Orthopyroxene-bearing rocks of the South Savanna—Kanukucomplex of British Guiana vary in composition from basic toacid types. They include basic granulites; acid, orthopyroxene-bearingbiotite gneisses; orthopyroxene-bearing acid granulites; orthopyroxene-bearinggranites, and orthopyroxene-bearing xenoliths contained in theSouth Savanna Granite. The field, petrographic, and chemicalcharacters of the rocks bear strong resemblances to charnockitesdescribed from other parts of the world, but the origins formany charnockites are inconsistent with evidence advanced forthe evolution of the South Savanna—Kanuku rocks. Fieldand petrographic criteria indicate that the basic granuliteswere originally intrusive basic rocks and have suffered regionalmetamorphism of Granulite Facies grade, which induced the conversionof clinopyroxene to orthopyroxene. The orthopyroxene-bearing,acid biotite gneisses and acid granulites have resulted fromcontamination by enclosed basic granulites which occur as boudins,bands, and lenses. The orthopyroxene-bearing granites and xenolithsare related to the assimilation of intruded orthopyroxene-bearingcountry rocks by the South Savanna Granite and its apophyses. The chemistry of the rocks appears to support the conclusionsreached from field and petrographic studies by indicating consistentenrichment of Ca, Mg, Fe, and Na in the orthopyroxene-bearingrocks compared with their non-orthopyroxene-bearing equivalents.Variation diagrams also indicate slightly anomalous plots forthe orthopyroxene-bearing rocks of the complex.     

Rare-earth element geochemistry of Madras granulites

Archaean granulites from the type charnockite locality of Pallavaram, Madras City, Tamil Nadu, southern India consist of a bimodal suite of basic and silicic orthogneisses, associated with metasedimentary gneisses (khondalites). Charnockite is the dominant rock type. Basic granulites display a tholeiitic trend of strong iron enrichment accompanied by an increase in the concentration of the rare earth elements (REE), and the development of appreciable negative europium anomalies. These trends are considered to reflect low pressure fractional crystallisation of pyroxene-plagioclase assemblages under conditions of lowf _{O 2}. Ultramafic granulites may represent the cumulus material of such a process. The silicic granulites (charnockites) are generally K₂O rich and in marked contrast to the low K₂O (tonalitic) silicic gneisses which dominate most granulite facies terrains. Their REE abundances, however, embrace the complete range of patterns observed in both K-rich and K-poor Archaean gneisses. The presence of a large number of pre-granulite facies potassic pegmatites in the area suggests metasomatism of an originally less potassic suite of rocks. Trace element considerations lead to a model whereby metasomatism and partial fusion of silicic gneisses in the terrain preceded the granulite facies metamorphic event. This sequence of events is best related to fluctuations in the composition of metamorphic fluids in the lower crust.     

A review of the In Ouzzal granulitic terrane (Tuareg shield, Algeria): its significance within the Pan-African Trans-Saharan belt

The In Ouzzal terrane (IOT) or In Ouzzal granulite unit (IOGU) is an elongated Palaeoproterozoic block within the Neoproterozoic Pan-African belt of north-west Africa. The granulites derive from Archaean protoliths that include a large volume of metasediments which were deposited on a 3.2-Ga gneissic basement. Near-peak granulite facies conditions between 2.17 and 2 Ga were estimated at P=10 kbar and T rising from 800 to 1000°C. Premetamorphic orthogneisses were intruded at 2.5 Ga, and followed by the emplacement of syn- to late-kinematic charnockites, syenites and carbonatites at around 2 Ga. Cooling of the granulites occurred till 1800 Ma. Shortly after its exhumation coeval with crustal extension and related alkaline magmatism in adjacent areas, the IOT was buried beneath late Palaeoproterozoic and Neoproterozoic cover sequences, and then behaved as a rigid block. Both margins are lithospheric faults, as evidenced by the occurrence of shear-zone-related mafic and felsic plutons. Pan-African tectonothermal events were negligible in the north, but granulites in the south were significantly reworked under lower greenschist facies conditions during the northern motion of the block with respect to both the western and the eastern Pan-African terranes. The Cambrian molasse, associated with widespread alkaline volcanism and subvolcanic granites, is horizontal in the north. The IOT, which was part of a larger continental mass including its counterpart in northern Mali, is interpreted as an exotic terrane which may have docked during Pan-African plate convergence and lateral collision. The unchanged pediplain since c. 1.7 Ga in the north suggests that the IOT is underlain by thick Palaeoproterozoic lithospheric mantle, whereas its southern part is probably allochthonous and overlies Pan-African structural units.     

Mantle to lower-crust fluid/melt transfer through granulite metamorphism

The “unexpected” (the word is from H.G.F. Winkler, 1974) discovery of CO₂-rich inclusions in granulites has initiated a debate which, after more than 35 years, is still an important issue in metamorphic petrology. Experimental and stable isotope data have led to the conception of a “fluid-absent” model, opposed to the “fluid-assisted” hypothesis, derived from fluid inclusion evidence. Besides CO₂, other fluids have been found to be of importance in these rocks, notably concentrated aqueous solutions (brines), also able to coexist with granulite mineral assemblages at high P and T. Brines also occur in inclusions or, more impressively, have left their trace in large scale metasomatic effects, typical of a number of high-grade areas: e.g., intergranular K-feldspar veining and quartz exsolution (myrmekites), carbonate metasomatism along km-scale shear zones (Norway, India), “incipient charnockites” (India, Sri Lanka, Scandinavia), highly oxidized Archean granulites. All together, this impressive amount of evidence suggests that the amount of fluids in the lower crust, under peak metamorphic conditions, was very large indeed, far too important to be only locally derived. Then, except for remnants contained in inclusions, these fluids have left the rock system during postmetamorphic uplift.Fluid remnants identical to those occurring in deep crustal granulites are also found in mantle minerals, including diamonds. Major mantle fluid source is related to the final stages of melting processes: late magmatic emanations from alkalic basaltic melts, carbonate-metasomatizing aqueous fluids issued from igneous carbonatites. Even if a local derivation of some fluids by crustal melting cannot be excluded, most lower-crustal granulite fluids have the same origin. They are transferred from the mantle into the crust by synmetamorphic intrusives, also responsible for the high thermal gradient typical of granulites, notably HT- or UHT-types. These are mostly found in Precambrian times, generated during a small number of time intervals: e.g., around 500, 1000, 1800, 2500 Ma. HT-granulites forming events occur at world-scale in supercontinents or supercratons, either at the end of amalgamation, or shortly before breaking-off. They provide a mechanism for a vertical accretion of the continental slab, which complement the more classical way of lateral accretion above subduction zones at convergent boundaries.     

Dehydration melting, fluid buffering and decompressional P–T path in a granulite complex from the Eastern Ghats, India

A suite of metapelites, charnockites, calc-silicate rocks, quartzo-feldspathic gneisses and mafic granulites is exposed at Garbham, a part of the Eastern Ghats granulite belt of India. Reaction textures and mineral compositional data have been used to determine the P–T–X evolutionary history of the granulites. In metapelites and charnockites, dehydration melting reactions involving biotite produced quartzofeldspathic segregations during peak metamorphism. However, migration of melt from the site of generation was limited. Subsequent to peak metamorphism at c . 860° C and 8 kbar, the complex evolved through nearly isothermal decompression to 530–650° C and 4–5 kbar. During this phase, coronal garnet grew in the calc-silicates, while garnet in the presence of quartz broke down in charnockite and mafic granulite. Fluid activities during metamorphism were internally buffered in different lithologies in the presence of a melt phase. The P–T path of the granulites at Garbham contrasts sharply with the other parts of the Eastern Ghats granulite belt where the rocks show dominantly near-isobaric cooling subsequent to peak metamorphism.     

冀东-辽西太古宙火成岩岩石组合和动力学意义

冀东-辽西地区是华北克拉通北部出露面积最大的太古宙变质基底区.经过岩石组合填图和综合研究,将其太古宙变质火成岩分为2.64~2.60 Ga MORB型拉斑玄武质火山岩、2.61~2.52 Ga拉斑玄武质-钙碱性变质火山岩、2.52~2.50 Ga浅变质钙碱性火山岩组合和2.54~2.50 Ga英云闪长质-奥长花岗质-花岗闪长质片麻岩、2.54~2.51 Ga闪长质-石英闪长质-英云闪长质-奥长花岗质-花岗闪长质片麻岩、2.54~2.51 Ga紫苏花岗闪长质-紫苏花岗质岩石、2.57~2.52 Ga闪长质-石英二长闪长质-花岗闪长质-二长花岗质片麻岩和2.53~2.51 Ga弱片麻状到块状二长花岗质-正长花岗质深成侵入体岩石组合.这些岩石组合从东北部的辽西阜新到西南部的遵化马兰峪地区呈现出条带状时-空分布特征.变质作用研究揭示了青龙-上营-洒河桥-马兰峪为高压麻粒岩带,记录了ITD型PTt轨迹,与NNW-NW向SSE-SE方向逆冲推覆构造相伴生;而三屯营-太平寨高温麻粒岩带,记录了IBC型PTt轨迹,与锦州-兴城-安子岭-界岭口-太平寨-三屯营伸展-底劈构造带相伴生.综合分析表明冀东-辽西太古宙晚期的构造-岩浆活动形成于热造山带型俯冲-弧后伸展到碰撞隆升的侧向增生动力学过程.