Yellow impact glass from the K/T boundary at Beloc (Haiti): XANES determination of the Fe oxidation state and implications for formation conditions     

Gabriele GIULI  Sigrid Griet EECKHOUT  Christian KOEBERL  Giovanni PRATESI  Eleonora PARIS 《Meteoritics & planetary science》2008,43(5):981-986

Abstract— We determined the iron oxidation state and coordination number in five samples of yellow impact glass from the Cretaceous‐Tertiary (K/T) boundary section at Beloc, Haiti, which formed as the result of impact melting during the Chicxulub impact event. The samples were analyzed by Fe K‐edge XANES spectroscopy and the results were compared with published data on eight black impact glasses and one high Si‐K impact spherule from the same impact layer. The pre‐edge peak of our high‐resolution XANES spectra displays evident variations indicative of significant changes in the Fe oxidation state, spanning a wide range from about 75 to 100 mole% Fe³⁺. Yellow K/T glasses have significantly higher Fe³⁺/(Fe²⁺ + Fe³⁺) ratios compared to black K/T impact glasses (from 20 to 75 mole% Fe³⁺) and high Si‐K glass (20 mole% Fe³⁺). In particular, all the pre‐edge peak data on these three types of impact glasses plot between two mixing lines joining a point calculated as the mean of a group of tektites studied so far (consisting of ^[4]Fe²⁺ and ^[5]Fe²⁺) to ^[4]Fe³⁺ and ^[5]Fe³⁺, respectively. Thus, the XANES spectra of the yellow K/T glasses can be interpreted as a mixture of ^[4]Fe^{2+, [5]}Fe^{2+, [4]}Fe³⁺, and ^[5]Fe³⁺. Our observations can be explained by a very large range of oxygen fugacity conditions during melt formation. Furthermore, there is a clear positive relationship between the Fe³⁺/(Fe²⁺ + Fe³⁺) ratio and the Ca content of these glasses, suggesting that the Fe oxidation state was influenced by the relative contribution of Ca‐sulfate‐ and Ca‐carbonate‐bearing sedimentary rocks at the impact site.  相似文献   

Volcanic and structural evolution of Pico do Fogo,Cape Verde          下载免费PDF全文

Juan‐Carlos Carracedo  Francisco J. Perez‐Torrado  Alejandro Rodriguez‐Gonzalez  Raphaël Paris  Valentin R. Troll  Abigail K. Barker 《Geology Today》2015,31(4):146-152

In recent months the media have drawn attention to the Cape Verde archipelago, with particular focus on the island of Fogo, the only island presently active and with an eruption that began on 23 November 2014, finally ceasing on 7 February 2015. The Monte Amarelo conical shield forms most of the 476 km² almost circular island of Fogo. After attaining a critical elevation of about 3500 m, the Monte Amarelo shield volcano was decapitated by a giant landslide that formed a caldera‐like depression (Cha das Caldeiras), which was subsequently partially filled by basaltic nested volcanism. This younger eruptive activity culminated in the construction of the 2829 m‐high Pico do Fogo stratocone, apparently entirely made of layers of basaltic lapilli. Continued growth of the Pico do Fogo summit eruptions was interrupted in 1750, most likely after the stratocone reached a critical height. Since then, at least eight eruptions have taken place inside the landslide depression at the periphery of the Pico do Fogo cone, including the 2014–2015 eruptive event. Strong geological similarities with the Canary Islands, 1400 km to the north, have been frequently noted, probably as a consequence of a common process of origin and evolution associated with a mantle hot‐spot. These similarities are particularly evident when comparing Fogo with the Teide Volcanic Complex on Tenerife, where a lateral collapse of the Las Cañadas stratovolcano also formed a large depression (the Caldera de Las Cañadas), now partially filled with the 3718 m‐high Teide stratocone. However, important geological differences also exist and probably relate to the contrasting evolutionary stages of both islands. The Las Cañadas volcano on Tenerife formed at a late post‐erosional stage, with predominantly evolved (trachyte and phonolite) magmas, while at Fogo basaltic volcanism is still dominant.  相似文献   

MC‐ICP‐MS Isotope Measurements with Direct Injection Nebulisation (d‐DIHEN): Optimisation and Application to Boron in Seawater and Carbonate Samples     

Pascale Louvat  Julien Bouchez  Guillaume Paris 《Geostandards and Geoanalytical Research》2011,35(1):75-88

We report here an optimisation of the demountable direct injection high efficiency nebuliser (d‐DIHEN) for isotopic measurements with a Neptune (ThermoFisher Scientific, Bremen, Germany) multi‐collector inductively coupled plasma‐mass spectrometer (MC‐ICP‐MS) and describe a method for boron isotopic ratio determination. With direct injection nebulisation 100% of the analyte was introduced into the ICP‐MS plasma and wash times were drastically reduced for elements such as boron and thorium. Compared to the classical stable introduction system (SIS: double Scott/cyclonic spray chamber), sensitivity for boron was 2–5 times higher with d‐DIHEN and wash times up to ten times shorter. Repeatability of ¹¹B/¹⁰B sample‐calibrator bracketing measurements reached 0.25‰ (2s) for seawater and coral samples. Method accuracy and reproducibility were tested on mixed reference solutions having δ¹¹B values in the ranges ?90 to +40‰ and ?2 to +2.5‰, demonstrating our ability to distinguish δ¹¹B values with differences of only 0.25‰. The international seawater reference material NRCC NASS‐5 (National Research Council, Ottawa, Canada), analysed in different sessions over a 10‐month period, yielded an average δ¹¹B value of +39.89 ± 0.25‰, in the upper range of previously published seawater values. A comparison between δ¹¹B determined by d‐DIHEN MC‐ICP‐MS and positive‐TIMS (P‐TIMS) for four modern corals showed an excellent agreement (with bias of less than 0.4‰).  相似文献   

Australasian microtektites from Antarctica: XAS determination of the Fe oxidation state     

Gabriele Giuli  Maria Rita Cicconi  Sigrid Griet Eeckhout  Giovanni Pratesi  Eleonora Paris  Luigi Folco 《Meteoritics & planetary science》2014,49(4):696-705

The Fe oxidation state and coordination number of 29 impact glass spherules recently recovered from the Transantarctic Mountains (Antarctica) have been determined by X‐ray absorption near edge structure (XANES) spectroscopy. Based on geochemical, isotopic, and fission track data, these spherules are considered as microtektites from the Australasian tektite/microtektite strewn field. Their find location is the farthest so far discovered from the possible source crater region, and their alkali content is the lowest compared with other published data on Australasian microtektite glasses. The Fe³⁺/(Fe²⁺+Fe³⁺) ratio, determined from the analysis of the pre‐edge peak energy position and integrated intensity, is below 0.1 (±0.04) for all the samples, and is comparable to that of most tektites and microtektites from the Australasian strewn field. Also, the pre‐edge peak integrated intensity, which is sensitive to the average Fe coordination geometry, is comparable to that of other Australasian microtektites reported in the literature. The agreement of the Fe oxidation state and coordination number, between the Transantarctic Mountain microtektites (TAM) and the Australasian tektites and microtektites, further confirms the impact origin of these glass spherules and provides an independent suggestion that they represent a major extension southeastward of the Australasian strewn field. The fact that similar redox conditions are observed in tektites and microtektites within the Australasian strewn field regardless of the distance from the source crater area (up to approximately 11000 km) could be an important constraint for better understanding the different processes affecting microtektite formation and transport. The fact that the Fe oxidation state of microtektites does not increase with distance, as in the case of North American microtektites, means that thermal and redox histories of Australasian and TAM microtektites could differ significantly from those of North American microtektites.  相似文献   

Unraveling the hidden origin and migration of plagioclase phenocrysts by in situ Sr isotopes: the case of final dome activity at Nisyros volcano,Greece     

Eleonora?BraschiEmail author  Lorella?Francalanci  Simone?Tommasini  George?E.?Vougioukalakis 《Contributions to Mineralogy and Petrology》2014,167(3):988

This contribution reports a detailed study on in situ Sr isotope analyses, along with textural and compositional characteristics, of plagioclase phenocrysts occurring in the rhyodacitic dome-lavas and associated mafic enclaves, erupted during the last magmatic activity at Nisyros volcano (Greece). Dome-lavas and enclaves have a paragenesis dominated by plagioclase. We recognize five different types of plagioclase based on their specific textures and composition. Dome-lava plagioclases (Type-1) are mainly large (1–5 mm), subhedral, clear, and poorly zoned crystals with low An content (An_25–35). The plagioclase phenocrysts (Type-4 and Type-5) and groundmass microlites crystallizing in the enclaves, and found in dome-lavas as xenocrysts, have high An content (An_75–95). In both dome-lavas and enclaves, two other types of plagioclase do also occur: (1) plagioclase phenocrysts with size and core composition similar to those of Type-1 having a dusty sieve zone (DSZ) at the rims (Type-2); (2) plagioclases with a DSZ affecting the entire crystal but a thin rim (Type-3). The drilled plagioclases have ⁸⁷Sr/⁸⁶Sr negatively correlated with their An content. Low An cores of Type-1 and Type-2 have quite homogeneous ⁸⁷Sr/⁸⁶Sr (0.7044–0.7046), whose values are more radiogenic than their host magmas (0.70403–0.70408) and similar to those of the previous Upper Pumice (UP) rhyolite magma (0.70438–0.70456). The DSZs of Type-2 and Type-3 show lower and scattered ⁸⁷Sr/⁸⁶Sr (0.70397–0.70426) with intermediate and variable An content. High An cores of Type-4 and Type-5 have the least radiogenic Sr isotope composition (0.70379) in equilibrium with that measured in the enclaves (0.70384–0.70389). We demonstrate that Type-1 plagioclase crystallizes in the previous UP rhyolitic magmas representing the silica-rich magma from which the dome-lava melts derived by open system evolutionary processes (e.g., mixing, mingling, and crystal migration), caused by successive refilling of mafic enclave-forming magma. The Type-2 plagioclase derives from entrainment of Type-1 into the still molten enclave magma. The DSZs originated in response to the interaction between the low An plagioclase and the enclave mafic melt in which dissolution and re-crystallization acted together as function of the interaction time. Type-1 and Type-2 plagioclases record, therefore, a long-lived timescale of events starting from their crystallization in the UP rhyolite. Instead, the different width of DSZs (Type-2 and Type-3) seems to indicate short different interaction timescales between the single crystals and the enclave melt (from few hours to some 40 days). These microanalytical data contribute to the understanding of the origin of the rhyodacitic dome-lavas at Nisyros volcano and to set robust constraints on the dynamics of mingling/mixing processes in terms of crystal exchange pathways and enclave disaggregation.  相似文献   

Iron oxidation state in impact glass from the K/T boundary at Beloc,Haiti, by high‐resolution XANES spectroscopy     

Gabriele Giuli  Sigrid Griet Eeckhout  Eleonora Paris  Christian Koeberl  Giovanni Pratesi 《Meteoritics & planetary science》2005,40(11):1575-1580

Abstract— We examined the local iron environment in nine impact glasses from the Cretaceous‐Tertiary (K/T) boundary section at Beloc, Haiti, which formed as the result of impact melting during the Chicxulub impact event. The samples have been analyzed by Fe K‐edge high‐resolution X‐ray absorption near edge structure (XANES) spectroscopy to obtain data on both the Fe oxidation state and the coordination number. The pre‐edge peak of our high‐resolution XANES spectra display noticeable variations indicative of significant changes in the Fe oxidation state spanning a wide range from about 20 to 75 mol% trivalent Fe. All data plot along the same trend, falling between two mixing lines joining a point calculated as the mean of a group of tektites studied so far (consisting of four‐ and five‐coordinated Fe²⁺) to ^[4]Fe³⁺ and ^[5]Fe³⁺, respectively. Thus, the XANES spectra can be interpreted as a mixture of ^[4]Fe²⁺, ^[5]Fe²⁺, ^[4]Fe³⁺, and ^[5]Fe³⁺. There is no evidence for six‐fold coordinated Fe; however, its presence in small amounts cannot be excluded from XANES data alone. Our observations can be explained by two possible scenarios: either these impact glasses formed under very reducing conditions and, because of their small size, were easily oxidized in air while still molten, or they formed under a variety of different oxygen fugacities resulting in different Fe oxidation states. In the first case, the oxidation state and coordination number would imply similar formation conditions as splash‐form tektites, followed by progressive oxidation.  相似文献   

Identifying key environmental and building features affecting the outcome of a seismic event: a case study of the “921” earthquake     

Chen  Tzu-Ling  Paris  Larry 《Natural Hazards》2022,111(3):2627-2647

Natural Hazards - Major earthquakes in a given location are unpredictable, infrequent, and often fatal. Using data from a previous earthquake disaster, this study explores the relationship between...  相似文献   

Correction to: Impact of climate change on landslides frequency: the Esino river basin case study (Central Italy)     

Lorenzo Sangelantoni  Eleonora Gioia  Fausto Marincioni 《Natural Hazards》2018,92(2):885-905

We refine the 1-D velocity model of the Central India Tectonic Zone (CITZ) using well-selected arrival times of P- and S-phases of 354 local earthquakes of magnitude (M_w) between 2.0 and 5.8, recorded by national seismic network from May 1997 to March 2016. Further, we have determined the source mechanisms of 26 selected local events using moment tensor inversion to characterize the dynamics beneath the CITZ. The best-fit simulation between observed and synthetic waveforms obtained the nodal and auxiliary planes of the each faults associated with the earthquake moment magnitude (M_w) for each event. Depth of the fault plane along the CITZ varies from 5 to 38 km. From this study, we found that the western part along the CITZ shows minimum focal depth and reaches maximum 38 kms at Jabalpur in the eastern part. This complex nature of earthquake dynamics occurrence along the CITZ. We propose that the curviplanar the CITZ dominated with sinistral curvature is subjected to compression along the longer ~E–W segments and transtension along shorter segments with ~NE–SW orientations. The occurrences of normal faulting, intrusion of mafic plutons and CLVD mechanisms for earthquakes are interpreted to be linked to the transtension zones and reverse mechanisms associated with the compressions along ~E–W segments.  相似文献   

哈萨克斯坦努尔卡斯甘大型富金斑岩铜矿地质特征及金赋存状态     

冯浩轩  申萍  潘鸿迪  曹冲  SEITMURATOVA Eleonora 《岩石学报》2018,34(3):763-784

努尔卡斯甘富金斑岩铜矿位于中哈萨克斯坦,是中亚成矿域西段重要的早古生代斑岩型铜金矿床,其形成与早志留世花岗闪长斑岩和石英闪长玢岩有关。矿体由浸染状、(网)脉状和角砾状矿石组成,主要产于花岗闪长斑岩、石英闪长玢岩和石英闪长岩体内以及岩体周围的火山岩地层中。矿床内发育热液磁铁矿、金红石和热液硬石膏。矿区热液蚀变强烈,早期发育青磐岩化和钾钙硅酸盐化(钾长石-阳起石化),随后广泛发育中级泥化,到晚期发育绢云母化。铜矿化与钾钙硅酸盐化和中级泥化蚀变密切相关,矿石矿物主要为黄铜矿,少量斑铜矿和蓝辉铜矿。金矿化主要与中级泥化蚀变关系密切,少量与钾钙硅酸盐化蚀变有关。金矿物主要为细粒自然金和银金矿(多小于10μm)。自然金赋存在蚀变岩中,与硅酸盐矿物关系密切,分布在它们表面、颗粒之间(粒间金)、晶体内(包裹金)和内部裂隙之中(裂隙金,少量)。银金矿主要呈包裹金的形式赋存在于与中级泥化蚀变相关的热液角砾岩的黄铜矿胶结物中。努尔卡斯甘斑岩铜金矿床属于高氧化-高硫岩浆-热液成矿体系,金的大规模沉淀很可能与SO_2歧化反应以及磁铁矿和硬石膏大量结晶而造成的高氧化-高硫成矿热液的SO_4~(2-)/H_2S比值和pH显著降低有关。  相似文献   

Magnetic braking during star formation I     

J. Gillis  L. Mestel  R. B. Paris 《Astrophysics and Space Science》1974,27(1):167-194

We study the transport of angular momentum from a cool massive gas cloud by Alfvén waves travelling along the distorted magnetic field linking the cloud with the hot galactic background. The efficiency of braking is never so great as to keep the cloud even roughly corotating with the back-ground. The mathematical approximations are not quite sharp enough to give a definitive answer to the question: is the braking ever so efficient that the centrifugal forces are kept well below gravity, so that the cloud contracts at the (magnetically-diluted) free-fall rate?; or is the cloud maintained in approximate centrifugal balance, with the rate of contractiondetermined by the loss of angular momentum?  相似文献