Ilmenite as a recorder of kimberlite history from mantle to surface: examples from Indian kimberlites     

Xu  Jingyao  Melgarejo  Joan Carles  Castillo-Oliver  Montgarri 《Mineralogy and Petrology》2018,112(2):569-581

Five compositional-textural types of ilmenite can be distinguished in nine kimberlites from the Eastern Dharwar craton of southern India. These ilmenite generations record different processes in kimberlite history, from mantle to surface. A first generation of Mg-rich ilmenite (type 1) was produced by metasomatic processes in the mantle before the emplacement of the kimberlite. It is found as xenolithic polycrystalline ilmenite aggregates as well as megacrysts and macrocrysts. All of these ilmenite forms may disaggregate within the kimberlite. Due to the interaction with low-viscosity kimberlitic magma replacement of pre-existing type 1 ilmenite by a succeeding generation of geikielite (type 2) along grain boundaries and cracks occurs. Another generation of Mg-rich ilmenite maybe produced by exsolution processes (type 3 ilmenite). Although the identity of the host mineral is unclear due to extensive alteration and possibility includes enstatite. Type 4 Mn-rich ilmenite is produced before the crystallization of groundmass perovskite and ulvöspinel. It usually mantles ilmenite and other Ti-rich minerals. Type 5 Mn-rich ilmenite is produced after the crystallization of the groundmass minerals and replaces them. The contents of Cr and Nb in type 2, 4 and 5 ilmenites are highly dependent on the composition of the replaced minerals, they may not be a good argument in exploration. The highest Mg contents are recorded in metasomatic ilmenite that is produced during kimberlite emplacement, and cannot be associated with diamond formation. The higher Mn contents are linked to magmatic processes and also late processes clearly produced after the crystallization of the kimberlite groundmass, and therefore ilmenite with high Mn contents cannot be considered as a reliable diamond indicator mineral (DIM) and kimberlite indicator mineral (KIM).

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Giant gas bubbles in a rheomorphic vent fill at the Las Cañadas caldera,Tenerife (Canary Islands)     

Carles Soriano  Daniele Giordano  Inés Galindo  Marcel Hürlimann  Paola Ardia 《Bulletin of Volcanology》2009,71(8):919-932

During rheomorphism subsequent to fallout deposition, a portion of the densely welded fallout of the La Grieta Member flowed back into the vent from where it was erupted, while the rest of it flowed down the outer slopes of the Las Cañadas caldera in Tenerife. The welded fallout and conduit-vent structure are physically connected and constitute a rare example of this type of deposits rooted to its feeder conduit and exposed in the caldera wall. The lower part of the vent-filling rheomorphic rocks shows gas bubbles and cavities that increase in size (up to 4 m) down vent. Bubbles are deformed against other bubbles, against the steep vent walls, flattened parallel to the flow foliation planes, and elongated parallel to the flow lineation and flow fold axes. The preservation of such giant bubbles, rather than their formation, seems to be a pretty unique feature of the phonolitic products investigated here and it is likely the result of the combination of factors that acted to preserve, in the surrounding of the glass transition interval, the sealing and the late stage cooling of a pressurized system. In addition, strain drop at the base of the vent-filling rheomorphic flow caused by flow stopping against vertical vent walls may have promoted rapid gas exsolution and the formation of large bubbles.  相似文献   

The Cretaceous sediment-hosted copper deposits of San Marcos (Coahuila,Northeastern Mexico): An approach to ore-forming processes     

Donají García-Alonso  Carles Canet  Eduardo González-Partida  Ruth Esther Villanueva-Estrada  Rosa María Prol-Ledesma  Pura Alfonso  Juan Antonio Caballero-Martínez  Rufino Lozano-Santa Cruz 《Journal of South American Earth Sciences》2011,31(4):432-443

In the San Marcos ranges of Cuatrociénegas, NE Mexico, several sediment-hosted copper deposits occur within the boundary between the Coahuila Block, a basement high mostly granitic in composition and Late Paleozoic to Triassic in age, and the Mesozoic Sabinas rift basin. This boundary is outlined by the regional-scale synsedimentary San Marcos Fault. At the basin scale, the copper mineralization occurs at the top of a ～1000 m thick red-bed succession (San Marcos Formation, Berrisian), a few meters below a conformable, transitional contact with micritic limestones (Cupido Formation, Hauterivian to Aptian). It consists of successive decimeter-thick roughly stratiform copper-rich horizons placed just above the red-beds, in a transitional unit of carbonaceous grey-beds grading to micritic limestones. The host rocks are fine- to medium-grained arkoses, with poorly sorted and subangular to subrounded grains. The detrital grains are cemented by quartz and minor calcite; besides, late iron oxide grain-coating cement occurs at the footwall unmineralized red-beds. The source area of the sediments, indicated by their modal composition, is an uplifted basement. The contents of SiO₂ (40.70–87.50 wt.%), Al₂O₃ (5.91–22.00 wt.%), K₂O (3.68–12.50 wt.%), Na₂O (0.03–2.03 wt.%) and CaO (0.09–3.78 wt.%) are within the ranges expected for arkoses. Major oxide ratios indicate that the sedimentary-tectonic setting was a passive margin.The outcropping copper mineralization essentially consists in a supergene assemblage of chrysocolla, malachite and azurite. All that remains of the primary mineralization are micron-sized chalcocite grains shielded by quartz cement. In addition, pyrite subhedral grains occur scattered throughout the copper-mineralized horizons. In these weathered orebodies copper contents range between 4.24 and 7.72 wt.%, silver between 5 and 92 ppm, and cobalt from 8 to 91 ppm. Microthermometric measurements of fluid inclusions in quartz and calcite crystals from footwall barren veinlets gave temperatures of homogenization between 98 °C and 165 °C, and ice-melting temperatures between ?42.5 °C and ?26.1 °C.The primary copper mineralization formed during the early diagenesis, contemporary with the active life of the Sabinas Basin. The mineralizing fluids were dense, near neutral, moderately oxidized brines that originally formed from seawater that, driven by gravity, infiltrated to the deepest parts of the basin and dissolved evaporites. As a result, they became hydrothermal fluids of moderate temperature capable of leaching high amounts of copper. The source of this metal could be mafic detrital grains and iron oxides of the underlying Jurassic and Lower Cretaceous red-beds. Copper precipitation took place when the brines passed through the redox boundary marked by the transition from red- to grey-beds. The upward movement of the brines was promoted by a high heat flow that allowed their convective circulation and their ascent along the synsedimentary San Marcos Fault.  相似文献   

Kinetic studies at room temperature of the cyanide anion CN with cyanoacetylene (HC₃N) reaction     

S. Carles  J.-C. Guillemin 《Icarus》2011,211(1):901-905

Rate coefficient of the cyanide anion (CN⁻) with cyanoacetylene (HC₃N) reaction, has been studied in gas phase at room temperature using a Flowing Afterglow Langmuir Probe - Mass Spectrometer (FALP-MS) apparatus. The rate constant for the CN⁻ + HC₃N reaction is k = 4.8 × 10⁻⁹ cm³/s with an uncertainty of 30%.  相似文献   

The Ardón L6 ordinary chondrite: A long‐hidden Spanish meteorite fall     

Josep M. Trigo‐Rodríguez  Jordi Llorca  Mona Weyrauch  Addi Bischoff  Carles E. Moyano‐Cambero  Klaus Keil  Matthias Laubenstein  Andreas Pack  José María Madiedo  Jacinto Alonso‐Azcárate  My Riebe  Rainer Wieler  Uli Ott  Mar Tapia  Narcís Mestres 《Meteoritics & planetary science》2014,49(8):1475-1484

We report and describe an L6 ordinary chondrite fall that occurred in Ardón, León province, Spain (longitude 5.5605°W, latitude 42.4364°N) on July 9th, 1931. The 5.5 g single stone was kept hidden for 83 yr by Rosa González Pérez, at the time an 11 yr old who had observed the fall and had recovered the meteorite. According to various newspaper reports, the event was widely observed in Northern Spain. Ardón is a very well‐preserved, fresh, strongly metamorphosed (petrologic type 6), and weakly shocked (S3) ordinary chondrite with well‐equilibrated and recrystallized minerals. The mineral compositions (olivine Fa_23.7±0.3, low‐Ca pyroxene Fs_20.4±0.2Wo_1.5±0.2, plagioclase An_10.3±0.5Ab_84.3±1.2), magnetic susceptibility (log χ = 4.95 ± 0.05 × 10^?9 m³ kg^?1), bulk density (3.49 ± 0.05 g   cm^?3), grain density (3.58 ± 0.05 g   cm^?3), and porosity (2.5 vol%) are typical for L6 chondrites. Short‐lived radionuclides confirm that the meteorite constitutes a recent fall. The ²¹Ne and ³⁸Ar cosmic ray exposure ages are both about 20–30 Ma, similar to values for many other L chondrites. The cosmogenic ²²Ne/²¹Ne ratio indicates that preatmospheric Ardón was a relatively large body. The fact that the meteorite was hidden in private hands for 83 yr makes one wonder if other meteorite falls may have experienced the same fate, thus possibly explaining the anomalously low number of falls reported in continental Spain in the 20th century.  相似文献   

Some aspects of transformations of compositional data and the identification of outliers     

Carles Barceló  Vera Pawlowsky  Eric Grunsky 《Mathematical Geology》1996,28(4):501-518

The statistical analysis of compositional data is based on determining an appropriate transformation from the simplex to real space. Possible transfonnations and outliers strongly interact: parameters of transformations may be influenced particularly by outliers, and the result of goodness-of-fit tests will reflect their presence. Thus, the identification of outliers in compositional datasets and the selection of an appropriate transformation of the same data, are problems that cannot be separated. A robust method for outlier detection together with the likelihood of transformed data is presented as a first approach to solve those problems when the additive-logratio and multivariate Box-Cox transformations are used. Three examples illustrate the proposed methodology.  相似文献   

Synchrotron-based X-ray study of iron oxide transformations in terraces from the Tinto-Odiel river system: Influence on arsenic mobility     

Rafael Pérez-López  Maria P. Asta  Gabriela Román-Ross  José Miguel Nieto  Carles Ayora  Rémi Tucoulou 《Chemical Geology》2011,280(3-4):336-343

Simultaneous analysis of micro-X-ray diffraction (μ-XRD) and micro-X-ray fluorescence (μ-XRF) based on synchrotron light sources, and electron microprobe (EMP) analyses, were performed on iron terrace samples taken from Tinto-Odiel river system from the Iberian Pyrite Belt (IBP, SW Iberian Peninsula). Iron terraces are formed during the oxidation and precipitation of dissolved iron along the riverbeds impacted by acid mine drainage (AMD). This paper includes the study of actively-forming current terraces and fossil terraces isolated from the stream courses due to the river migration over time. The results of the study of current terrace samples from AMD-affected streams of two IPB abandoned mines (Tinto Santa Rosa and Cueva de la Mora) showed that fresh precipitates at the surface are composed primarily of metastable schwertmannite, which is gradually transformed at depth over short-time scales into goethite. Sediments of ancient terraces are composed mainly of goethite, which most likely originated from the re-crystallization of a precursor schwertmannite. However, at century-time scale, goethite partially re-crystallizes to hematite due to diagenetic processes. The transformation rate of goethite into hematite is negatively correlated with grain size and the crystallinity of goethite. Moreover, this transformation is accompanied by an increase in grain size and a decrease in surface area of hematite, and a concomitant decrease in arsenic trapped in the solid. This increase in the arsenic mobility during the diagenetic maturation should be considered in the development of conceptual and analytical models describing long-term fate, transport and bioavailability of arsenic in environmental systems.  相似文献   

A model of boiling for fluid inclusion studies: Application to the Bolaños Ag–Au–Pb–Zn epithermal deposit,Western Mexico     

Carles Canet  Sara I. Franco  Rosa María Prol-Ledesma  Eduardo González-Partida  Ruth Esther Villanueva-Estrada 《Journal of Geochemical Exploration》2011

Boiling can be inferred from fluid inclusion microthermometry studies when a progressive increase in apparent salinity is observed along with a decrease of homogenization temperature (T_H) and depth, thus reflecting the partitioning of non-volatile solutes into the liquid phase during steam loss. We propose a model for fluid evolution during boiling based on mass and heat balance equations, which establishes paths in the T_H-salinity space that can be compared with fluid inclusion data to confirm or discard boiling. Additionally, the model allows calculating paleo-depths, for which the effect of steam bubbles lowering the hydrostatic pressure is taken into account.  相似文献   

Aragonite stromatolitic buildups from Santorini (Aegean Sea,Greece): Geochemical and palaeontological constraints of the caldera palaeoenvironment prior to the Minoan eruption (ca 3600 yr bp)     

Pere Anadón  Carles Canet  Walter L. Friedrich 《Sedimentology》2013,60(5):1128-1155

The pyroclastic deposits of the Minoan eruption (ca 3600 yr bp ) in Santorini contain abundant xenoliths. Most of these deposits are calcareous blocks of laminated‐botryoidal, stromatolite‐like buildups that formed in the shallow waters of the flooded pre‐Minoan caldera; they consist of (i) light laminae, of fibrous aragonite arranged perpendicular to layering, and (ii) dark laminae, with calcified filaments of probable biological origin. These microstructures are absent in the light laminae, suggesting a predominant inorganic precipitation of aragonite on substrates probably colonized by microbes. Internal cavities contain loose skeletal grains (molluscs, ostracods, foraminifera and diatoms) that comprise taxa typical of shallow marine and/or lagoon environments. Most of these forms are typical of warm water environments, although no typical taxa from hydrothermal vents have been observed. Past gasohydrothermal venting is recorded by the occurrence of barite, pyrolusite and pyrite traces. The most striking features of the stable isotopic data set are: (i) an overall wide range in δ¹³C_PDB (0·16 to 12·97‰) with a narrower variation for δ¹⁸O_PDB (?0·23 to 4·33‰); and (ii) a relatively uniform isotopic composition for the fibrous aragonite (δ¹³C = 12·40 ± 0·43‰ and δ¹⁸O = 2·42 ± 0·77‰, n = 21). The δ¹³C and δ¹⁸O values from molluscs and ostracods display a covariant trend, which reflects a mixing between sea water and a fluid influenced by volcano‐hydrothermal activity. Accordingly, ⁸⁷Sr/⁸⁶Sr from the studied carbonates (0·708758 to 0·709011 in fibrous aragonite and 0·708920 to 0·708991 in molluscs) suggests that the aragonite buildups developed in sea water under the influence of a hydrothermal/volcanic source. Significant differences in trace elements have been detected between the fibrous aragonite and modern marine aragonite cements. The caldera water from which the fibrous aragonite crusts formed received an input from a volcano‐hydrothermal system, probably producing diffuse venting of volcanogenic CO₂ gas and of a fluid enriched in Ca, Mn and Ba, and depleted in Mg and probably in Sr.  相似文献   

The 2012 Northern Italy Earthquakes: modelling human behaviour   总被引：1，自引：1，他引：0  

Gabriele Prati  Elisa Saccinto  Luca Pietrantoni  Carles Pérez-Testor 《Natural Hazards》2013,69(1):99-113

The aim of this study was to investigate human behaviour during the 2012 Northern Italy Earthquakes. Furthermore, the current study used Kuligowski and Mileti’s (Fire Saf J 44:487–496, 2009) extended model and the Social Attachment Model as a framework to explain the behavioural responses. The study included 1839 participants who were affected by the earthquake occurred in the Emilia-Romagna region (Italy) on 20 May 2012. The most frequent behavioural responses during the earthquake were moving to another room of the house, escaping from home, and waiting in bed. According to Kuligowski and Mileti’s (Fire Saf J 44:487–496, 2009) extended model, perceived risk was associated with evacuation, and emergency preparedness was related to more efficient and effective responses during the earthquake. In line with the Social Attachment Model, affiliation behaviours were more frequent than flight behaviours, while, contrary to predictions, the social context did not influence emotional responses, evacuation behaviour, and search for protection.  相似文献