Ice-rich terrain in Gusev Crater, Mars?     

Tracy K.P. Gregg  Jason P. Briner  Kristen N. Paris   《Icarus》2007,192(2):348-360

The morphology of materials on the floor of Gusev Crater (14° S, 175° W), Mars, imply a history of volcanism and subsequent removal of an ice-rich deposit. Fluid lava flows observed in the western portion of Gusev Crater paradoxically terminate in a steep, thick (<60 m) flow front adjacent to hummocky terrain. The hummocky terrain is morphologically similar to deglaciated terrain on Earth, generated when glacial debris are left behind after the glacier has retreated. We propose the following scenario for the floor of Gusev Crater. First, ice-rich material was deposited adjacent to Thira Crater. Second, fluid lavas were emplaced and ponded against the ice-rich deposits. At some later time, the ice within the deposit sublimated, leaving hummocky terrain. Current age estimates for the Gusev flows are Hesperian, suggesting that the ice removal occurred in the upper Hesperian or more recently. If this hypothesis is correct, quench features (glassy rinds, columnar jointing) should be observed at the lava flow margin; the hummocky deposit should be poorly sorted, angular debris.  相似文献   

Boron isotope ratios of surface waters in Guadeloupe,Lesser Antilles     

Pascale Louvat  Jérôme Gaillardet  Guillaume Paris  Céline Dessert 《Applied Geochemistry》2011

Large variations are reported in the B concentrations and isotopic ratios of river and thermal spring waters in Guadeloupe, Lesser Antilles. Rivers have δ¹¹B values around 40‰ and B concentrations lower than 30 μg/L, while thermal springs have δ¹¹B of 8–15‰ and B concentrations of 250–1000 μg/L. River samples strongly impacted by hydrothermal inputs have intermediate δ¹¹B and B contents. None of these surface water samples have δ¹¹B comparable to the local unweathered volcanic rocks (around 0‰), implying that a huge isotopic fractionation of 40‰ takes place during rock weathering, which could be explained by preferential incorporation of ¹⁰B during secondary mineral formation and adsorption on clays, during rock weathering or in the soils. The soil-vegetation B cycle could also be a cause for such a fractionation. Atmospheric B with δ¹¹B of 45‰ represents 25–95% of the river B content. The variety of the thermal spring chemical composition renders the understanding of B behavior in Guadeloupe hydrothermal system quite difficult. Complementary geochemical tracers would be helpful.  相似文献   

Coupling eruption and tsunami records: the Krakatau 1883 case study,Indonesia     

Raphaël Paris  Patrick Wassmer  Franck Lavigne  Alexander Belousov  Marina Belousova  Yan Iskandarsyah  Mhammed Benbakkar  Budianto Ontowirjo  Nelly Mazzoni 《Bulletin of Volcanology》2014,76(4):1-23

The well-documented 1883 eruption of Krakatau volcano (Indonesia) offers an opportunity to couple the eruption’s history with the tsunami record. The aim of this paper is not to re-analyse the scenario for the 1883 eruption but to demonstrate that the study of tsunami deposits provides information for reconstructing past eruptions. Indeed, though the characteristics of volcanogenic tsunami deposits are similar to those of other tsunami deposits, they may include juvenile material (e.g. fresh pumice) or be interbedded with distal pyroclastic deposits (ash fall, surges), due to their simultaneity with the eruption. Five kinds of sedimentary and volcanic facies related to the 1883 events were identified along the coasts of Java and Sumatra: (1) bioclastic tsunami sands and (2) pumiceous tsunami sands, deposited respectively before and during the Plinian phase (26–27 August); (3) rounded pumice lapilli reworked by tsunami; (4) pumiceous ash fall deposits and (5) pyroclastic surge deposits (only in Sumatra). The stratigraphic record on the coasts of Java and Sumatra, which agrees particularly well with observations of the 1883 events, is tentatively linked to the proximal stratigraphy of the eruption.  相似文献   

Distinction between six- and fourfold coordinated silicon in SiO2 polymorphs via electron loss near edge structure (ELNES) spectroscopy     

T. Sharp  Z. Wu  F. Seifert  B. Poe  M. Doerr  E. Paris 《Physics and Chemistry of Minerals》1996,23(1):17-24

Si K-, L- and O K-edge ELNES spectra of natural α-quartz and synthetic coesite on one side and synthetic stishovite on the other show characteristic differences that can be related, by comparison with multiple-scattering (MS) calculations, to the fourfold vs. sixfold coordination of Si in these polymorphs of SiO₂. It is shown by MS calculations on large clusters that the outer shells contribute relatively little to the overall topologies of the spectra. Therefore, distinction between fourfold- and sixfold-coordinated Si is possible even on a nm scale and probably also in amorphous substances.  相似文献   

The local structure of Ca-Na pyroxenes. II. XANES studies at the Mg and Al K edges     

A. Mottana  T. Murata  A. Marcelli  Z. Y. Wu  G. Cibin  E. Paris  G. Giuli 《Physics and Chemistry of Minerals》1999,27(1):20-33

X-ray absorption spectra at the Mg and Al K edges have been recorded using synchrotron radiation on synthetic end member diopside (Di) and jadeite (Jd) and on a series of natural Fe-poor Ca-Na clinopyroxenes compositionally straddling the Jd-Di join. The spectra of C2/c end members and intermediate members of the solid solution series (C-omphacites) are different from those of the intermediate members having P2/n symmetry (P-omphacites). Differences can be interpreted and explained by comparing the experimental spectra with theoretical spectra calculated via the full multiple-scattering formalism, starting from the atomic positional parameters determined by single-crystal X-ray diffraction structure refinement on the same samples. Atomic clusters with at least 89 atoms, extending to more than 0.60 nm away from the Mg or Al absorbers, are needed to reproduce the experimental spectra. This shows that in the clinopyroxene systems XANES detects medium- rather than short-range order-disorder relationships. Theoretical spectra match the experimental ones well for all features in the regions from 16 to 60 eV above threshold. Experimental near-edge features in the first 16 eV are also reproduced, albeit less accurately. Certain near-edge features of C-omphacites reflect the octahedral arrangement of the back-scattering six O atoms nearest neighbours of the probed atom (Mg or Al) located at site M1 of the crystal structure, thus being indicators of short-range order. Others arise again from medium-range order. P-omphacites show more complicated spectra than C-omphacites. Their additional features reflect the increased complexity of the structure and the greater local disorder around the probed atom induced by the two alternative M1, M11 configurations of the six O atoms forming the first coordination shells. Mg and Al are confirmed to be preferentially partitioned in the M1 and M11 site of the P-omphacite crystal structure, however with a certain degree of local disorder. The relative heights of certain prominent features are directly related to sample composition in terms of Di:Jd ratio in the Al K-edge spectra, whereas they show abrupt variations in the Mg K-edge spectra. They demonstrate that XANES is directly related to composition and may be used to distinguish C- from P-omphacites. Received: 24 November 1998 / Revised, accepted: 10 June 1999  相似文献   

Some major concepts of metallogeny     

Laboratoire de Géologie Appliquée  Université de Paris 《Mineralium Deposita》1973,8(3):237-258

These notes, which summarize part of over ten years of laboratory work, aim to clarify and inter-relate three fundamental concepts of current Metallogeny: consanguinity, heritage, province. — 1. The concept of consanguinity: its criteria, limits and graduations, are first presented; 2. They are illustrated by the analysis of a complex example: the lead-zinc mineralisations in Trias around the Cévennes (South of the French Massif Central); 3. The likelihood of consanguinity for various strata-bound mineralisations, particularly misappreciated and misinterpreted, is then shown: — tungsten in the Cévennes — gold at Passagem (Brazil), about which microstructural and geochemical arguments are especially employed — cobalt at Bou Azzer (Marocco); 4. From consanguinity in a sedimentary environment, the authors turn to the crustal phenomena cycle, during which the heritages of the cations succeed one another. Examples of heritages, linked with sedimentation-volcanism: Sierra de Carthagena (Spain) — metamorphism — granitisation, are rapidly examined or referred to in literature. Particular attention has been paid to heritage by secretion, illustrated by the antimony lodes of the French Massif Central. Consequently, it may be understood how the successive heritages involve geochemical permanences and determine the geochemical provinces going back to ancient times in which the mineral provinces were built up. 5. In a last section the transformist guide line is compared with other concepts and tools of Metallogeny: lineaments and isotopic ratios. — In conclusion, the intra-crustal heritages still remain under-estimated and badly deciphered and are not sufficiently taken into consideration in mineral exploration.

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Zusammenfassung Diese Veröffentlichung, die einen Teil der während eines Jahrzehnts in einem Laboratorium ausgeführten Arbeiten kurz behandelt, hat die Aufgabe, drei Grundbegriffe der gegenwärtigen Metallogenese klarzustellen und miteinander zu verknüpfen: Familiarität (Verwandtschaft), Vererbung und Provinz. — 1. Der Begriff der Verwandtschaft sowie seine Kriterien, Grenzen und Nuancen werden zuerst auseinandergesetzt. 2. Dann wird dieser Begriff anhand der Analyse eines komplizierten Beispiels veranschaulicht, und zwar der Blei-Zink-Mineralisationen in der Trias am Rand der Cevennen, im Süden des französischen Zentralmassivs gelegen; 3. Anschließend wird die Wahrscheinlichkeit der Verwandtschaft für verschiedene schichtgebundene, besonders verkannte und falsch interpretierte Mineralisationen aufgezeigt. Es handelt sich einerseits um das Wolfram der Cevennen sowie das Kobalt von Bou Azzer (Marokko) und andererseits um das Gold von Passagem (Brasilien), zu dessen Erklärung insbesonders mikrostrukturelle und geochemische Argumente herangezogen werden; 4. So gelangt man in den Kreislauf der Krustalerscheinungen, währenddessen Vererbungen von Kationen aufeinanderfolgen. Beispiele von Vererbungen, die an Sedimentation, Vulkanismus (Sierra von Cartagena, Spanien), Metamorphose und Granitisierung gebunden sind, werden kurz untersucht oder anhand von Literaturangaben erwähnt. Besondere Erwähnung verdient die Sekretionsvererbung, die am Beispiel der Antimonerzgänge des französischen Zentralmassivs veranschaulicht wird. Somit wird verständlich, wie die aufeinanderfolgenden Vererbungen geochemische Beständigkeiten bedingen. Sie bestimmen ebenfalls geochemische, auf das hohe Altertum zurückgehende Provinzen, auf denen sich die Mineralprovinzen aufbauen; 5. Zum Schluss wird diese transformistische Leitrichtung mit anderen Konzepten und Arbeitsmitteln der Metallogenese verglichen: den Lineamenten und Isotopenverhältnissen. — Es wird der Schluß gefolgert, daß die intrakrustalen Vererbungen immer noch unterschätzt, schlecht entziffert und bei der Lagerstättenforschung ungenügend in Betracht gezogen werden.

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Illustrated by Examples

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Laboratory associated with the C.N.R.S. (n^o 65). Contributors to this paper: P. Routhier (former Director of the Laboratory at present Director in the B.R.G.M.) and P. Brouder, R. Fleischer, (at present in the Penarroya C⁰), J. C. Macquar, Melle M. J. Pavillon, G. Roger and H. Rouvier.  相似文献   

塔里木板块西南缘晚侏罗世古地磁研究   总被引：1，自引：0，他引：1       下载免费PDF全文

李永安  陈岩  Cogne Jean PASCAL  Gilder STUART  孙东江 《地质学报》2003,77(2):151-157

塔里木板块西南缘托云、奥依塔格晚侏罗世古地磁研究,获得了托云地区特征磁化方向:Ds=1.5°,Is=50.8°;古地磁极:λ=81.0°,ψ=247.0°,古纬度31.5°N。奥依塔格地区特征磁化方向:Ds=118.4°,Is=55.9°;古地磁极:λ=4.9°,ψ=120.6°,古纬度=36.4°N。从古地磁结果认为:①托云和奥依塔格相对托云地区产生顺时针旋转;②这两个地区古纬度为31°～36°左右,与塔里木平均古纬度30°N是基本一致的,但与现在纬度差达8°～10°左右,造成纬度差主要原因是构造运动造成的;③塔里木晚侏罗世古地磁亦与华北、华南基本一致,说明晚侏罗世塔里木、华北、华南三板块已联合成一个整体,拼合成统一的中国大陆,其位于热带—亚热带古气候环境。  相似文献   

阿尔金断裂带东段地表破裂分段研究   总被引：6，自引：10，他引：6       下载免费PDF全文

王峰  徐锡伟  郑荣章  陈文彬  Tapponnier Paul 《地震地质》2002,24(2):145-158

对活动断层进行正确的分段有助于我们对地震造成断层的发生、发展过程有一个正确的认识。阿尔金断裂带是青藏高原北部的巨型左旋走滑断裂带 ,将青藏高原和塔里木盆地两大构造单元截然分开。通过对阿尔金断裂带东部青崖子—宽滩山的Spot数字化卫星影像资料进行详细的分析 ,结合研究区内的断错地貌和前人的古地震研究成果 ,对阿尔金断裂带东段进行了地表破裂性分段。将阿尔金断裂带东段青崖子—宽滩山分为 3段 :青崖子—芦草湾为阿克塞破裂段 ;芦草湾—北祁连山逆断裂为疏勒河破裂段 ;北祁连山逆断裂—宽滩山为宽滩山破裂段。其中阿克塞破裂段的最后破裂时间晚于 (5 2 4± 0 4 0 )kaB .P .,疏勒河破裂段最后破裂时间早于 (6 97± 0 5 3)kaB .P .,而宽滩山段的最后破裂时间估计晚于 5kaB  相似文献   

Iron local structure in tektites and impact glasses by extended X-ray absorption fine structure and high-resolution X-ray absorption near-edge structure spectroscopy     

Gabriele Giuli  Giovanni Pratesi  Curzio CiprianiEleonora Paris 《Geochimica et cosmochimica acta》2002,66(24):4347-4353

The local structure of iron in three tektites has been studied by means of Fe K-edge extended X-ray absorption fine structure (EXAFS) and high-resolution X-ray absorption near-edge structure (XANES) spectroscopy in order to provide quantitative data on <Fe-O> distance and Fe coordination number. The samples studied are a moldavite and two australasian tektites. Fe model compounds with known Fe oxidation state and coordination number were used as standards in order to extract structural information from the XANES pre-edge peak. EXAFS-derived grand mean <Fe-O> distances and Fe coordination numbers for the three tektite samples are constant within the estimated error (<Fe-O > =2.00 Å ± 0.02 Å, CN = 4.0 ± 0.4). In contrast to other data from the literature on Fe-bearing silicate glasses, the tektites spectra could not be fitted with a single Fe-O distance, but rather were fit with two independent distances (2 × 1.92 Å and 2 × 2.08 Å). High-resolution XANES spectra of the three tektites display a pre-edge peak whose intensity is intermediate between those of staurolite and grandidierite, thus suggesting a mean coordination number intermediate between 4 and 5. Combining the EXAFS and XANES data for Fe, we infer the mean coordination number to be close to 4.5.Comparison of the tektites XANES spectra with those of a suite of different impact glasses clearly shows that tektites display a relatively narrow range of Fe oxidation state and coordination numbers, whereas impact glasses data span a much wider range of Fe oxidation states (from divalent to trivalent) and coordination numbers (from tetra-coordinated to esa-coordinated). These data suggest that the tektite production process is very similar for all the known strewn fields, whereas impact glasses can experience a wide variety of different temperature-pressure-oxygen fugacity conditions, leading to different Fe local structure in the resulting glasses. These data could be of aid in discriminating between tektite-like impact glasses and impact glasses sensu strictu.  相似文献   

超高压变质作用不同阶段的流体变化：碧溪岭榴辉岩的氢、硼同位素分析   总被引：2，自引：3，他引：2  

夏群科  盛英明Etienne DELOULE 《岩石学报》2004,20(3):677-684

大别山碧溪岭榴辉岩中有三种含水矿物:多硅白云母、角闪石和黑云母,它们分别是超高压(UHP)阶段(即柯石英榴辉岩相阶段)或者石英榴辉岩相阶段、退变质后成合晶阶段和角闪岩相退变质阶段的产物,本文利用离子探针技术对它们进行了氢同位素和硼同位素的分析。三种矿物内部的同位素组成都是均一的,多硅白云母的δD为-105‰±9‰,δ~(11)B为-25.9‰±2.0‰;角闪石的δD为-100‰±9‰,δ~(11)B为-24.4‰±0.9‰;黑云母的δD为-65‰±4‰,δ~(11)B为-19.3‰±1.3‰。多硅白云母和角闪石的氢-硼同位素组成在误差范围内是相同的,而和黑云母则有明显的差别,这表明,从UHP阶段或者石英榴辉岩相阶段到随后的后成合晶阶段,变质流体是内部缓冲的,而在角闪岩相变质阶段,则有了外来流体的加入,这个流体是相对富集D和~(11)B的。碧溪岭榴辉岩矿物相对于其地壳原岩表现出低δ~(11)B的特征,说明俯冲过程中板块经历了强烈的脱硼。  相似文献