Heating experiments on glass inclusions in Allende (CV3) olivines: Clues to the formation conditions of chondrules?

Several pieces of the Allende CV3 chondrite were heated up to different final temperatures (1100, 1250, 1450 °C) with the aim to study glassy and glass-bearing inclusions in olivines as well as the glass mesostasis of chondrules and aggregates. The experiments were performed in a Pt-Pt90Rh10 heating stage at 1 bar pressure. The oxygen fugacity is estimated to have been between 10-9 and 10-10 atm at 1200 °C. The variation of the chemical composition of the heated glasses gives information concerning the behavior of the incompatible elements (with respect to the host) Al, Ca and Na. The chemical variation in the heated mesostasis glass shows that Ca exchange between the gas and condensed phases at sub-solidus temperatures can occur in a short time. Laboratory heating experiments show that glass inclusions will behave as closed systems and therefore preserved the alkalis they acquired. On the other hand, the mesostasis glass can loose them when heated to temperatures higher than 1100 °C. Evidently, the presence of Na-rich glasses, in chondrules and aggregates available to us, indicate that if there was a thermal process that did affect them, it must have been a low temperature one.Fil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; Argentin

Glasses in meteorites and the Primary Liquid Condensation Model

Meteoritic glasses are quenched samples of the silicate liquid that was involved in the formation of chondritic constituents and achondritic rocks. Conventional genetic models see them as residual liquids from which the associated minerals crystallized – as demonstrated by terrestrial igneous rocks – or as locally produced impact melts. These models are all closely related to our experiences with terrestrial geology and petrology and, consequently,make planetary processes, such asmixing andmelting of solid precursors and planetary differentiation primarily responsible for the formation of the large variety of meteoritic rocks. However, different types of glasses (e.g., glass inclusions in minerals, mesostasis glasses, glass pockets, glass veins) in a variety of meteorites (chondrites and achondrites) have particular chemical features that cannot be reconciled with these models: 1)Glasses do not showthe chemical signature of crystallization of theminerals they are associated with – a geochemical impossibility; 2) All types of glasses in all types of meteorites reported here show very similar trace element abundance pattern with the refractory lithophile element abundances at ~ 10–20 x CI chondrite abundances. 3) All refractory element abundance patterns in primitive glasses have unfractionated solar relative abundances (they are flat) and medium refractory and volatile elements are depleted relative to the refractory elements. 4) Medium volatile and volatile elements, when present, display chaotic abundance patterns. The ubiquitous pattern for refractory elements signals vapor fractionation rather than geochemical (“igneous”) fractionation or stochasticmixing of precursorminerals (as in shockmelts). It indicates that the same process must have been involved in the origin of all glasses in chondritic constituents aswell as achondritic rocks and, consequently, in the formation of allmeteorite types investigated. The chaotic abundances of volatile elements signal that chaotic processes were involved during condensation. 279 Herewe present a newmodel - the Primary Liquid Condensation (PLC)model – as an alternative to the currently acceptedmodels for the formation ofmeteoritic rocks. The PLCmodel is capable of accommodating all observational and chemical data accumulated so far on meteorites – with the exception of enstatite and SNC meteorites, which record physico-chemical conditions that were different fromthose of themajority ofmeteoritic rocks (the processes, however, could have been the same). The new model identifies a new role for silicate liquids in cosmochemistry as being an essential phase for the formation of early crystalline condensates from the hot solar nebula. Liquids are identified to have been the first major phase to condense from the solar nebula. In order to be capable to produce early liquid condensates, the nebula must have been either enriched in condensable elements over solar abundances (> 500 times) or was at total pressuresmuch higher than the canonically predicted ones (> 500 times, > 0.5 bar ). Our data require that this liquid – we named it “universal liquid” (UL) - had a refractory composition (Ca-Mg-Al-silicate or CMAS) and facilitated condensation of the major minerals for chondritic constituents as well as for achondritic rocks. The process possibly was a variant of the vapor-liquid-solid (VLS) condensation process, which is utilized in industrial crystal growth. Thereby, the liquid condenses first, then nucleates a crystal of the species that is oversaturated in the vapor – in the case of the solar nebula usually olivine. As this olivine grows from the liquid, it depletes the liquid in Mg and Si. The liquid tries to maintain equilibrium with the solar nebula. Thereby, Mg and Si are replenished by condensation from the gas phase and all incompatible elements are kept at an equilibrium concentration by condensation-evaporation equilibrium. Thus, the contents of incompatible refractory elements are kept at an approximately constant level throughout crystallization of the major minerals olivine and pyroxene. This way not only the abundances of incompatible refractory elements are kept at a constant level but also their relative abundances remain unfractionated solar. The UL also represents the long sought for refractory component of chondritic constituents and appears also to be the source of achondritic “igneous” rocks. Variations in the amount of liquid available, the liquid condensation and crystal nucleation rates, as well as different crystal-liquid mixing proportion will allow the formation of objects of highly variable composition. The final composition (chemical and isotopic) of any chondritic object or achondrite, as well as that of the associated glasses, will be determined by different degrees of post-formational metasomatic elemental exchange processes taking place between solids and the cooling nebular gas. These processes add medium volatile and volatile elements to the products of high temperature condensation. As these processes usually don’t run to completion, an infinite number of chaotic compositional variations are produced – and this is exactly what we observe in meteorites.Fil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Kurat, G.. Vienna University of Technology; Austri

Glasses in coarse-grained micrometeorites

Micrometeorites (MMs, interplanetary dust particles with 25 - 500 μm diameters) carry the main mass of extraterrestrial matter that is captured by Earth. The coarse-grained MMs mainly consist of olivine aggregates, which - as their counterparts in CC chondrites - also contain pyroxenes and glass. We studied clear glasses in four coarse-grained crystalline MMs (10M12, M92-6b, AM9, and Mc7-10), which were collected from the ice at Cap Prudhomme, Antarctica. Previous studies of glasses (e.g., glass inclusions trapped in olivine and clear mesostasis glass) in carbonaceous and ordinary chondrites showed that these phases could keep memory of the physical-chemical conditions to which extraterrestrial matter was exposed. Here we compare the chemical compositions of MM glasses and glasses from CM chondrites with that in experimentally heated objects from the Allende CV chondrite and with glasses from cometary particles. Our results show that MMs were heated to variable degrees (during entry through the terrestrial atmosphere), which caused a range from very little chemical modification of the glass to total melting of the precursor object. Such modifications include dissolution of minerals in the melted glass precursor and some loss of volatile alkali elements. The chemical composition of all precursor glasses in the MMs investigated is not primitive such as glasses in CM and CR chondrite objects. It shows signs of pre-terrestrial chemical modification, e.g., metasomatic enrichments in Na and Fe2+ presumably in the solar nebula. Glasses of MMs heated to very low degree have a chemical composition indistinguishable from that of glasses in comet Wild 2 particles; giving additional evidence that interplanetary dust (e.g., Antarctic MMs) possibly represents samples from comets. © 2009 Elsevier B.V. All rights reserved.Fil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Kurat, G.. Universidad de Viena; Austri

A química do cosmo

Antes de colidirem com a superfície terrestre, os meteoritos perambularam por vastas regiões do espaço, carregando consigo inumeráveis segredos sobre a formação do sistema solar. Muitas dessas rochas primitivas, com idades que chegam a bilhões de anos, retêm em sua estrutura a "memória" química de tempos em que o Sol, os planetas e todos os outros corpos celestes ainda se formavam a partir de um aglomerado de gás e poeira. Extrair desses mensageiros do cosmo a informação para entender a evolução da galáxia é o papel da chamada cosmoquímica, uma área multidisciplinar que interage com a astrofísica, física, astrobiologia e geologia, para desvendar os principais momentos de uma história que começou muitas vezes a ser delineada nos primórdios do universo, quando as estrelas começavam a nascer.Fil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; Argentin

The primary liquid condensation model and the origin of Barred Olivine Chondrules.

Barred olivine (BO) chondrules are some of the most striking objects in chondrites. Their ubiquitous presence and peculiar texture caught the attention of researchers and, as a consequence, considerable effort has been expenced on unraveling their origin(s). Here we report on a detailed study of two types of chondrules: the Classic and the Multiple-Plate Type of BO chondrules from the Essebi (CM2) , Bishunpur (LL3.1), Acfer 214 (CH3) and DAG 055 (C3-UNGR) chondrites, and discuss the petrographic and chemical data of their major mineral phases and glasses. Glasses occur as mesostasis or as glass inclusions, the latter either enclosed inside the olivine bars (plates) or still connected to the mesostasis. The chemical composition of all glasses, characterized by being Si-Al-Ca-rich and free of alkali elements, is similar to those of the constituents , such as chondrules, aggregates, inclusions, mineral fragments, etc.) of CR and CV3 chondrites. They all have high trace element contents (~ 10 x CI) with unfractionated CI-normalized abundances of refractory trace elements and depletions in moderately volatile and volatile elements with respect to the refractory trace elements. The presence of alkali elements (Na+K+Rb) is coupled with a low Ca content and is only observed in those glasses that have behaved as open systems. This result supports the previous finding that Ca was replaced by alkalis (e.g., Na-Ca exchange), presumably through a vapor-solid reaction. The glasses apparently are the quenched liquid from which the olivine plates crystallized. However, they do not show any chemical fractionation that could have resulted from the crystallization of the olivines, but rather have a constant chemical compositions throughout the formation of the chondrule. In a previous contribution we were able to demonstrate the role of these liquids in supporting crystal growth directly from the vapor. Here we extend application of the primary liquid condensation model to formulate a new model for the origin of BO chondrules. based on the ability of dust-enriched solar-nebula gas to directly condense into a liquid, provided the gas/dust ratio is sufficiently low. Thus, propose that chondrules can be formed by condensation of a liquid droplet directly from the solar nebula. The extensive variability in chemical composition of BO chondrules, which ranges from alkali-poor to alkali-rich, can be explained by elemental exchange reactions with the cooling nebula. We calculate the chemical composition of the initial liquid droplet from which BO chondrules could have formed and speculate about the physical and chemical conditions that prevail  in the specific regions of the solar nebula that can promote creation of these objects.Fil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Kurat, Gero. Universidad de Viena; AustriaFil: Zinner, Ernst. University of Washington; Estados Unido

A liquid-supported condensation of major minerals in the solar nebula: Evidence from glasses in the Kaba (CV3) chondrite

Glasses, in the Kaba CV3 chondrite, occur as mesostasis in chondrules and aggregates and as inclusions in olivines, both confined or open and connected to the mesostasis. The inclusions in olivine and the glassy mesostasis of aggregates seem to have formed contemporaneously. The confined glass inclusions and open inclusions in olivine were formed during olivine growth and the mesostasis glass during olivine aggregation. All glasses have high trace element contents (10 - 20 × CI) with unfractionated CI-normalized abundances of refractory trace elements. In contrast, V, Mn, Li, and Cr are depleted in all glasses with respect to the refractory trace elements, as is Rb in the glass inclusions in olivine but not in the mesostasis glass. This abundance pattern indicates vapor fractionation and a common condensation origin for both glasses. Glasses of confined glass inclusions in olivine have a Si Al Ca-rich composition with a chondritic Ca/Al ratio. Glasses of open glass inclusions and mesostasis are poor in Ca and enriched in alkalis. However, Ca contents of olivines indicate crystallization from a Ca-rich melt of a composition similar to that of the glass inclusions. In addition, trace element abundances indicate that these glasses (liquids) probably had an original composition similar to that of the inclusion glass. They apparently lost Ca in exchange for alkalis in a metasomatic exchange reaction, presumably with the vapor. There is now growing evidence that liquids can indeed condense from a solar nebula gas, provided the gas/dust ratio is sufficiently low. In these regions with enhanced oxygen fugacity as compared to that of a nebula of solar composition, liquids (the glass precursor) probably played an important role in growing crystals from the vapor by liquid-phase epitaxy. The glasses appear to be the remnants of this thin liquid layer interface that supported the growth of olivine from the vapor following the Vapor-Liquid-Solid process. This liquid will have a refractory composition and will have trace element contents which are in equilibrium with the vapor, and, therefore, will not change much during the time of olivine growth. The composition of the liquid seems to be unconstrained by the phases it is in contact with. Samples of this liquid will be retained as glass inclusions in olivine. The glassy mesostasis could also be a sample of this liquid that got trapped in inter-crystal spaces. The mesostasis glass subsequently behaved as an open system and its Ca was exchanged-presumably with the vapor-for the alkali elements Na, K, and Rb. In contrast, glass inclusions in olivine were protected by the host, could not react, and thus preserved the original composition of this liquid.Fil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Kurat, Gero. Universidad de Viena; AustriaFil: Zinner, Ernst. Washington University in St. Louis; Estados Unido

The origin of non-porphyritic pyroxene chondrules in UOCs: Liquid solar nebula condensates?

A total of 56 non-porphyritic pyroxene and pyroxene/olivine micro-objects from different unequilibrated ordinary chondrites were selected for detailed studies to test the existing formation models. Our studies imply that the non-porphyritic objects represent quickly quenched liquids with each object reflecting a very complex and unique evolutionary history. Bulk major element analyses, obtained with EMPA and ASEM, as well as bulk lithophile trace element analyses, determined by LA-ICP-MS, resulted in unfractionated (solar-like) ratios of CaO/Al2O3, Yb/Ce as well as Sc/Yb in many of the studied objects and mostly unfractionated refractory lithophile trace element (RLTE) abundance patterns. These features support an origin by direct condensation from a gas of solar nebula composition. Full equilibrium condensation calculations show that it is theoretically possible that pyroxene-dominated non-porphyritic chondrules with flat REE patterns could have been formed as droplet liquid condensates directly from a nebular gas strongly depleted in olivine. Thus, it is possible to have enstatite as the stable liquidus phase in a 800 × Cl dust-enriched nebular gas at a ptot of 10-3 atm, if about 72% of the original Mg is removed (as forsterite?) from the system. Condensation of liquids from vapor (primary liquid condensation) could be considered as a possible formation process of the pyroxene-dominated non-porphyritic objects. This process can produce a large spectrum of chemical compositions, which always have unfractionated RLTE abundances. Late stage and subsolidus metasomatic events appear to have furthered the compositional diversity of chondrules and related objects by addition of moderately volatile and volatile elements to these objects by exchange reactions with the chondritic reservoir (e.g., V, Cr, Mn, FeO as well as K and Na). The strong fractionation displayed by the volatile lithophile elements could be indicative of a variable efficiency of metasomatic processes occurring during and/or after chondrule formation. Histories of individual objects differ in detail from each other and clearly indicate individual formation and subsequent processing. © 2007 Elsevier Inc. All rights reserved.Fil: Engler, Almut. University of Graz; AustriaFil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Kurat, Gero. Universidad de Viena; AustriaFil: Ebel, Denton. American Museum of Natural History; Estados UnidosFil: Sylvester, Paul. Memorial University Of Newfoundland; Canad

DETERMINING THE WINTERING RANGE OF BROAD-WINGED HAWK (BUTEO PLATYPTERUS) IN SOUTH AMERICA USING CITIZEN-SCIENCE DATABASE

Abstract ∙ Several species of raptors that breed in North America migrate to the southern hemisphere during the non-breeding period. The Broad-winged Hawk (Buteo platypterus) is one of them, and its wintering distribution reaches the north and central part of South America, although there are published records for the species in Argentina and southern Brazil. We did an exhaustive search of records of the Broad-winged Hawk for South America, using bibliography, citizen-science initiatives, personal communications, and own records. We obtained 4025 georeferenced records for the 1879–2017 period. Both the numbers of records per year and the geographical range of the species have apparently increased in recent years. We also obtained the first record for Misiones province in Argentina and for Espírito Santo state, in Brazil. The wintering range of this species is estimated to cover 12.5 million km2 of the north central part of South America, including southern Brazil and northern Argentina. While it is possible that the range has expanded 700 km southwards recently, with the data available it is not possible to disentangle this possibility from changes in the distribution of bird observers. Resumen ∙ Determinando el rango invernal del Aguilucho Alas Anchas (Buteo platypterus) en Sudamérica involucrando datos de ciencia ciudadana Varias especies de aves rapaces se reproducen en América del Norte y migran durante los meses de invierno al hemisferio sur. Uno de ellos, el Aguilucho Alas Anchas (Buteo platypterus), alcanza normalmente el norte y centro de Sudamérica, aunque se han publicado registros en Argentina y en el sur de Brasil. Realizamos una búsqueda exhaustiva de registros del Aguilucho Alas Anchas para Sudamérica, en la literatura científica, en proyectos de ciencia ciudadana, comunicaciones personales y registros propios, obteniendo un total de 4025 registros georreferenciados para el período 1879–2017. Tanto el número de registros por año como el rango geográfico de la especie han aumentado en los últimos años. También reportamos el primer registro para la provincia de Misiones en Argentina y para el estado de Espírito Santo en Brasil. La zona de invernada actual de esta especie cubriría aproximadamente 12,5 millones de km2 de la porción central-norte de Sudamérica, incluyendo el sur de Brasil y el norte de Argentina. Si bien es posible que la especie se haya expandido unos 700 km hacia el sur en tiempos recientes, no es posible diferenciar esta posibilidad de cambios en la distribución de observadores de aves

Fe2+-Mg order-disorder study in orthopyroxenes from São João Nepomuceno (IVA) iron meteorite

São João Nepomuceno (SJN) is an iron meteorite belonging to IVA chemical group. It consists of Fe-Ni metal matrix and silicate inclusions made of a coarse-grained mixture of tridymite, orthopyroxene and clinopyroxene. In spite of the extensive work performed on the IVA group there is still no consensus about their origin and its thermal history is subject of ongoing debates. In this work, we report preliminary results on Fe2 + distribution in the non-equivalent octahedral sites in orthopyroxene crystals extracted from São João Nepomuceno in order to infer on the thermal history of this meteorite and therefore acquire more information related to the origin of the IVA iron meteorite group.Fil: Dos Santos, Eder Paulo. Centro Brasileiro de Pesquisas Fisicas; Brasil;Fil: Scorzelli, R. B.. Centro Brasileiro de Pesquisas Fisicas; Brasil;Fil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Cientifico Tecnológico - Conicet - San Juan. Instituto de Ciencias Astronómicas de la Tierra y del Espacio; ArgentinaFil: Munayco, P.. Centro Brasileiro de Pesquisas Fisicas; Brasil

Synthesis, Secondary Structure, and Anion Binding of Acyclic Carbohydrate-Derived Oligo(amide-triazole)s

A family of linear, carbohydrate-derived oligo(amide-triazole)s has been designed and synthesized. These molecules possess a regular distribution of triazole rings (from one to four) linking the carbohydrate units to give dimer to pentamer derivatives. Their binding to halide anions was qualitatively analyzed by means of NMR spectroscopy and mass spectrometry. All the compounds were able to bind chloride anions, with a stoichiometry that depended on the chain length. The dimer and trimer gave 2:1 host/chloride ratio, while the tetramer and pentamer gave 1:1 complexes. The secondary structure of the oligo(amide-triazole)s was studied using NMR spectroscopy and circular dichroism. These studies showed that the larger host molecules (tetramer and pentamer) adopted a stabilized U-turn and were able to bind just one chloride anion. Only the pentamer displayed a helical conformation, which was slightly distorted in the presence of chloride salts. Interestingly, chloride binding involves not only the triazole-CH but also H atoms from the carbohydrate moieties. These compounds could be applied for chloride sensing by ESI-MS.Fil: Fidalgo, Daniela Marina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; ArgentinaFil: Monge, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Bionanociencias "Elizabeth Jares Erijman"; ArgentinaFil: Varela, Oscar Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; ArgentinaFil: Kolender, Adriana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; Argentin