La—Ba同位素计时法

1985年10月,笔者访问日本了解到:从1983年以来,增田等人在发表的La-Ce稀土同位素测年方法的基础上,又进一步采用~(138)La(?)~(138)Ba电子俘获衰变体系,研究了另一个目前认为是最新的放射性同位素地质年代学测定方法——La-Ba计时法。虽然这一新的计时法目前离达到实用阶段尚有许多工作要做,但是它无疑丰富了稀土同位素地球化学和同位素地质年代学的研究内容,意义是深远的。现将增田等人所研究的这一新的计时法简介如下:     

La Schistosité et sa Répartition

Zusammenfassung Diese Arbeit stellt einen Überblick über die Arbeiten und Vorstellungen von Prof. Fourmarier dar. Zuerst werden einige Definitionen der benützten Ausdrücke gegeben sowie eine Übersicht über die Faktoren, welche die Schieferung bedingen; die Schlüsse, welche man aus der räumlichen Begrenzung dieser Erscheinung und der damit verwandten Phänomene ziehen kann, werden etwas eingehender behandelt und zum Schlusse wird ihre Anwendung an den Westalpen gezeigt.

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Herr Prof.Fourmarier war so liebenswürdig, die Niederschrift selbst durchzulesen und einige Anmerkungen vorzuschlagen, wofür ich ihm meinen besten Dank ausdrücke.     

La Notion de Migration en Paléontologie

Zusammenfassung Gemessen mit dem Maßstab der geologischen Zeiten, dauern die Wanderungen, wie sie die Biologen studieren, nur fast einen Augenblick; demgegenüber aber erstrecken sich die Verschiebungen der Fauna und Flora, wie sie die geologischen Studien festlegen, über Millionen von Jahren. Diese Verschiebungen sind statistische Erscheinungen aus dem Gebiet der Biogeographie und stellen das Ergebnis von zahlreichen biologischen Bewegungen dar. Die Verfasser untersuchen die Wanderungen der Säugetiere (stete Entwicklung durch erwachsene Typen), die Wanderungen der Pflanzen (unstete Entwicklung durch Keime), die Wanderungen der wirbellosen Seetiere, die man in die eine oder in die andere der vorhergehenden Abteilungen einreihen kann. Einige neue Ausdrücke werden vorgeschlagen.     

氟碳铈矿-(La)的水热合成实验

氟碳铈矿是稀土矿床最主要的矿石矿物,开展氟碳铈矿的水热合成实验对于揭示稀土元素的热液成矿作用具有重要意义。本文采用La(NO_3)_3·6H_2O、NaF和NaHCO_3/Na_2CO_3作为实验初始物,分别在不同温度、pH、氟离子浓度,碳酸氢钠/碳酸钠条件下,运用水热法合成了氟碳铈矿,并对合成产物进行了XRD和SEM分析。实验结果显示,碳酸氢钠、碳酸钠和低氟离子浓度条件下均可形成氟碳铈矿-(La)纯相,但高氟离子浓度条件下还生成有氟铈矿-(La)杂相。鉴于自然界氟碳铈矿的普遍出现以及氟铈矿的极少产出,稀土矿床中氟碳铈矿结晶沉淀于氟离子浓度不太高的环境。     

La déformation post-Miocène en Provence occidentale

Résumé

Le but de la présente étude est de caractériser la déformation récente subie par la Provence occidentale, située entre la nappe de Digne à l’est et la faille de Nîmes à l’ouest. Dans un premier temps, la déformation subie par un marqueur sédimentaire qui est à la fois le plus récent possible et le plus uniformément représenté dans la zone étudiée est considérée. Ce marqueur sédimentaire est le Miocène. La caractérisation de la déformation passe par l’étude de la localisation de celle-ci et donc par l’identification des structures actives responsables de la déformation du Miocène. Ces caractéristiques permettent d’estimer la quantité de raccourcissement total accumulé lors des derniers 20 millions d’années. Dans un deuxième temps, on distingue la part de la déformation postMiocène de cette déformation totale. Les marqueurs utilisés sont des surfaces et des objets géomorphologiques repères. Dans ce travail, nous montrons que la déformation en Provence a été de faible importance entre le Miocène et factuel et qu’elle est surtout produite au cours du Miocène. En conséquence, la déformation récente à actuelle est très difficile à localiser et à caractériser. 11 n’y a pas eu de déplacements post Miocène importants de part et d’autre de la faille de la Durance, pas plus d’ailleurs que le long de toutes les discontinuités majeures du domaine étudié. © 2000 Éditions scientifiques et médicales Elsevier SAS     

La déformation post-Miocène en Provence occidentale

The structure of western Provence (SE France) is the result of successive deformations connected to the building of the Pyrenees and the Alps. It is a seismically active region still undergoing deformation. The aim of this study is to characterize the recent deformation in western Provence and to integrate the cumulated displacements in a coherent deformation model. In order to do this, we identified the recent structures that concentrate the deformation. We used the Miocene as a sedimentary marker to estimate the discontinuous deformation over the last 20 Ma and geomorphic surfaces to evaluate the amount of the post-Miocene deformation. Miocene terrains are deformed along south-vergent thrusts such as Le Luberon, Les Costes, La Trévaresse or Les Alpilles, and along sinistral strike-slip faults such as the Durance and Nîmes faults. North-vergent Pyrenean thrusts such as L’Étoile-Sainte Baume, Sainte Victoire or the Eguilles thrusts were not reactivated during the Alpine phase. Field evidence shows that in the Luberon, the main folding phase occurred during, or immediately after the Burdigalian (20.5–16 Ma). The shortening measured on a regional N–S cross-section is of a few kilometres, implying a deformation of 0.1–0.2 mm·year^–1 since the beginning of the Miocene. Geomorphic surfaces have been reported on cross-sections of the E–W thrusts. The intensity of the deformation decreases southward and through time during the Miocene. Pliocene surfaces are not deformed near the active structures, except at the front of the Digne thrust. Furthermore, Quaternary geomorphic markers such as alluvial fans are not affected by the Durance strike-slip fault. Our results show that from Miocene to the Present, Provence was not intensively deformed (0.1–0.2 mm·year^–1), and occurred in a short period of time during the Miocene. It is coherent with the southward emplacement of the Alpine Digne thrust being the cause of this deformation. Since the end of the Miocene, there have been no major displacements on any of the active structures.     

Carbonate xenoliths in La Palma: Carbonatite or alteration product?

Carbonate xenoliths containing olivine and rimmed by kaersutitic amphibole were collected in basaltic rocks of the Basal Complex of La Palma. The mineralogical composition and microscopic appearance may suggest a relationship with carbonatites in general, thus a major element, trace element and stable isotope study was conducted to investigate the origin of the carbonate formation. Based on electron microprobe analyses, the carbonate is calcite with up to 6.3 wt% MgO and 7.2 wt% SiO₂. The elevated SiO₂ content may suggest a melt origin for the carbonate. However, the C and O isotope compositions of the carbonate xenoliths (δ¹³C and δ¹⁸O around −1‰ and 13‰, respectively) are similar to those of calcite veins and amygdales in basaltic rocks of the Basal Complexes of La Palma and Fuerteventura and are interpreted as produced by fluid degassing and metasomatism by CO₂-H₂O fluid derived from mobilization of sedimentary material. Trace element contents determined by laser-ablation ICP-MS analyses support the assumed origin, thus, the relationship with carbonatitic melts can be excluded. Based on trace element compositions, the amphibole surrounding the xenoliths is not related genetically to the carbonate. The elevated SiO₂ content of the calcite can be attributed to submicron relics of pyroxene, thus, the use of this feature as an evidence for melt origin is questionable.     

La sédimentation vaseuse dans les estuaires de Bretagne occidentale

Sans résumé     

La3+ 离子掺杂钨酸铅单晶的微结构缺陷

钨酸铅晶体是一种非化学计量化合物,缺陷丰富,蕴含着利用掺杂产生新效应和开发新功能的广泛可能性。探讨了不同浓度La3 掺杂对于钨酸铅晶体发光性能的影响,如热释光、X射线激发发光、光致发光等。La3 掺杂有效地抑制了陷阱中心,使发光受到强烈的抑制,在高浓度掺杂的钨酸铅中,激发机制有所改变,通过XPS测试的结果分析了不同浓度La3 掺杂机制。低浓度掺杂中,La3 取代Pb2 ,形成缺陷复合体[2(La3Pb ).-(VPb)″];高浓度掺杂晶体中,La3 离子不但占据Pb2 位置,而且也会占据W6 位置(La3W ),产生La3 的自补偿机制,形成La3 的自补偿对[(La3W )-(La3Pb ).]-(VO)..或缺陷聚集体[3(LaP3b ).-(La3W )]。     

Precambrian geotectonic units of the Río de La Plata craton

The main Precambrian tectonic units of Uruguay include the Piedra Alta tectonostratigraphic terrane (PATT) and Nico Pérez tectonostratigraphic terrane (NPTT), separated by the Sarandí del Yí high-strain zone. Both terranes are well exposed in the Río de La Plata craton (RPC). Although these tectonic units are geographically small, they record a wide span of geologic time. Therefore improved geological knowledge of this area provides a fuller understanding of the evolution of the core of South America. The PATT is constituted by low- to medium-grade metamorphic belts (ca. 2.1 Ga); its petrotectonic associations such as metavolcanic units, conglomerates, banded iron formations, and turbiditic deposits suggest a back-arc or a trench-basin setting. Also in the PATT, a late to post-orogenic, arc-related layered mafic complex (2.3–1.9 Ga), followed by A-type granites (2.08 Ga), and finally a taphrogenic mafic dike swarm (1.78 Ga) occur. The less thoroughly studied NPTT consists of Palaeoproterozoic high-grade metamorphic sequences (ca. 2.2 Ga), mylonites and postorogenic and rapakivi granites (1.75 Ga). The Brasiliano-Pan African orogeny affected this terrane. Neoproterozoic cover occurs in both tectonostratigraphic terranes, but is more developed in the NPTT. Over the past 15 years, new isotopic studies have improved our recognition of different tectonic events and associated processes, such as reactivation of shear zones and fluids circulation. Transamazonian and Statherian tectonic events were recognized in the RPC. Based on magmatism, deformation, basin development and metamorphism, we propose a scheme for the Precambrian tectonic evolution of Uruguay, which is summarized in the first Palaeoproterozoic tectonic map of the Río de La Plata craton.     

ICP—OES测定地球化学样品中La，Y，Ba

水系沉积物、土壤等试样用HF-HCl-HNO3-HClO4混酸消解后,以8％（v／v）HNO3溶解于渣,建立了测定地球化学样品中La,Y,Ba 3种微量元素的电感耦合等离子体发射光谱（ICP-OES）方法。方法测定限（μg／L,10SD）为：La 6．0,Y 1．0,Ba 1．0。精密度（RSD％,n=11）为：0．20～1．50,经国家一级地球化学标准物质的分析验证,结果与标准值吻合,该方法现已用于区域化探试样的分析。     

四川德昌大陆槽氟碳铈矿中Ce、La赋存状态研究

大陆槽氟碳铈矿No.1号矿体矿物组成复杂,且风化严重,属难选矿。选矿厂现有的选矿工艺存在品位和收率不能同时保证、生产稳定性差等问题,急需进行改善。针对此情况,本研究在No.1矿体上选取10个代表性矿样进行工艺矿物学分析,通过X射线荧光光谱、X射线粉晶衍射、扫描电子显微镜—能谱、矿物表征自动定量分析系统对矿体样品进行表征,得到了矿物的化学组成、物相组成、嵌布特征和粒级分布的研究,对后续选矿工艺改进提供了支撑。研究结果表明：（1）稀土氧化物主要成分为CeO₂,La₂O₃,TREO为5.23%,以赋存于氟碳铈矿中为主,脉石矿物主要为长石、方解石、石英、天青石及萤石。（2）在磨矿至75μm时,稀土矿物氟碳铈矿、氟碳铈镧矿仍与主要脉石矿物方解石、天青石、重晶石、萤石等发生二元嵌布,三元包裹的关系。从矿物的比重、磁性考虑,为保证选矿品位和回收率,本矿样应以浮选及强磁选为主,磨矿细度应在-75μm达到80%左右。     

微量元素La,Nb,Zr在判别大地构造环境方面的应用

La，Nb，Zr是一组耐熔强亲岩浆元素。其相互之间的比值关系恢复深部作用的地球化学过程。玄武岩类特别是原始玄武岩浆形成的岩石的La／Zr及Nb／Zr比值，能较好地反映其源区的La，Nb。Zr之间的分异特征，在一般情况下这一特征与某种确定的大地构造环境有密切关系，可用来判别玄武岩类形成的大地构造环境及其源区分异特征。本文根据世界上典型大地构造环境区玄武岩类的La，Nb，Zr数据。划分玄武岩形成的大地构造位置，提出了La／Zr-Nb／Zr双对数图及判别方法。     

稀土La添加量对预合金铁基胎体性能的影响

通过分析不同稀土La添加量对铁基胎体烧结性能的影响,指出在本试验使用预合金粉末和烧结条件下,当La添加量为0.1%时,胎体材料的综合力学性能最好。此外,适量的稀土La加入铁基胎体粉末后可以改善粉末分布的均匀性,提高金属胎体对金刚石的包镶能力。     

褐钇铌矿中La、Ce、Y、Yb的光谱定量测定

本方法应用GSPI-70型半米光栅摄谱仪,采用固体粉末法,以多种化合物作缓冲剂,钪作内标,上下电极同时装样测定矿石中La、Ce、Y、Yb四个稀土元素。测定范围La 0.01-1％,ce 0.07-1％,Y 0.005-0.2％,Yb 0.0005-0.02％,单次摄谱均方误差La±10％,Yb±8.5％,Y±10.8％,Ce±13.8％工作条件及操作手续摄谱仪:GSPI-70型半米光栅摄谱仪,二级光谱中间波长3100(?),三透镜照明系     

Alteration patterns of chromian spinels from La Cabaña peridotite,south-central Chile

La Cabaña peridotite is part of a dismembered ophiolite complex located within the metamorphic basement of the Coastal Cordillera of south-central Chile, and is the only location in Chile were Cr-spinels have been described so far. The La Cabaña peridotite is part of the Western Series unit, which comprises meta-sedimentary rocks, metabasites, and serpentinized ultramafic rocks. This unit has been affected by greenschist-facies metamorphism with reported peak PT conditions of 7.0–9.3 kbar and 380°–420 °C. Within La Cabaña peridotite Cr-spinels are present in two localities: Lavanderos and Centinela Bajo. In Lavanderos, Cr-spinel occurs in small chromitite pods and as accessory/disseminated grains with a porous or spongy texture in serpentinite, whereas in Centinela Bajo Cr-spinel is present as accessory zoned grains in partly serpentinized dunites, and in chromitite blocks. All Cr-spinels display variable degrees of alteration to Fe²⁺-rich chromite with a variation trend of major elements from chromite to Fe²⁺-rich chromite similar to those observed in other locations, i.e., an increase in Fe₂O₃ and FeO, a decrease in Al₂O₃ and MgO. Cr₂O₃ content increases from chromite to Fe²⁺-rich chromite in chromitite pods from Lavanderos and chromitite blocks from Centinela Bajo, but decreases in ferrian chromite zones in accessory grains from Centinela Bajo. The minor element (Ti, V, Zn, Ni) content is mostly low and does not exceed 0.4 wt.%, with the exception of MnO (<0.9 wt.%), which shows a correspondence with increasing degree of alteration. Cr# (Cr/Cr?+?Al) versus Mg# (Mg/Mg?+?Fe²⁺) and Fe³⁺/Fe³⁺+Fe²⁺ versus Mg# plots are used to illustrate the Cr-spinel alteration process. Overall, the Cr-spinels from Lavanderos (chromitite pods and disseminated grains) exhibit Cr# values ranging from 0.6 to 1.0, Mg# (Mg/Mg?+?Fe²⁺) below 0.5, and (Fe³⁺/Fe³⁺+Fe²⁺) <0.4. Cr-spinels from chromitites in Centinela Bajo have Cr# and Mg# values that range from 0.65 to 1.0, and 0.7-0.3, respectively, and (Fe³⁺/Fe³⁺+Fe²⁺)?3+/Fe³⁺+Fe²⁺) ratio is less than 0.4 in chromite cores and Fe²⁺-rich chromite, and >0.5 in ferrian chromite and Cr-magnetite. Interpretation of the data obtained and Cr-spinel textures indicate that the alteration of Cr-spinel is a progressive process that involves in its initial stages the reaction of chromite with olivine under water-saturated conditions to produce clinochlore and Fe²⁺-rich chromite. During this stage the chromite can also incorporate Ni, Mn, and/or Zn from the serpentinization fluids. As alteration progresses, Fe²⁺-rich chromite loses mass resulting in the development of a spongy texture. In a later stage and under more oxidizing conditions Fe³⁺ is incorporated in chromite/Fe²⁺-rich chromite shifting its composition to an Fe³⁺-rich chromite (i.e., ferrian chromite). Depending on the fluid/rock and Cr-spinel/silicate ratios, Cr-magnetite can also form over Fe²⁺-rich chromite and/or ferrian chromite as a secondary overgrowth. The compositional changes observed in Cr-spinels from La Cabaña reflect the initial stages of alteration under serpentinization conditions. Results from this study show that the alteration of Cr-spinels is dependent on temperature. The degree and extent of alteration (formation of Fe²⁺-rich and/or ferrian chromite) are controlled by the redox nature of the fluids, the Cr-spinel/silicate and the fluid/rock ratios.     

闽西南玮埔岩体和赣南菖蒲混合岩锆石La ICPMS U-Pb年代学

闽西玮埔岩体和赣南菖蒲混合岩位于武夷山构造带南部地区。对NNE向展布的闽西玮埔岩体两个样品进行了锆石LaICPMS U-Pb 测年,获得的年龄为447.1±4.7Ma和440.8±3.4Ma,证明这个岩体不是原来认为的印支期花岗岩,而属于加里东岩体。赣南菖蒲混合岩发育于罗浮岩体的北侧,早期将罗浮岩体归于燕山早期岩体。对混合岩进行的锆石LaICPMS U-Pb 测年,获得的年龄为445.9±3.8Ma,确定这个岩体为加里东期。这些新的高精度年龄学数据为武夷山加里东构造运动时限和性质提供了精确约束。     

Geochemical characteristics of the La Réunion mantle plume source inferred from olivine-hosted melt inclusions from the adventive cones of Piton de la Fournaise volcano (La Réunion Island)

Major and trace element compositions were obtained for bulk rocks and melt inclusions hosted in olivine crystals (Fo > 85) from the adventive cones of the Piton de La Fournaise volcano (La Réunion Island). Ratios of highly incompatible trace elements for these magmas are used to identify the nature of the La Réunion mantle plume source. Although adventive cone lavas display unusual major element compositions compared to the historical lavas of the volcano (e.g., lower CaO/Al₂O₃), trace element data suggest that the magmas emitted by the adventive cones originate from a common chemical source. This source may correspond to either a homogeneous mixed source of different mantle components or a near-primitive less-differentiated mantle source. The melt inclusions display ratios of highly incompatible elements (e.g., Th/La, Nb/La) which are similar to primitive mantle values, and lower Nb/U ratios compared to most oceanic basalts. These results and previous isotopic and trace element data suggest that La Réunion plume samples a source which is intermediate between a primitive-like mantle domain and a slightly depleted one almost unaffected by the recycling processes. This source could have originated from early depletion of the primitive mantle. Assuming a depletion 4.45 Gyr ago, ~10% melting of this slightly depleted source could explain the enriched trace element concentrations of the melt inclusions.