Ultra High Resolution Transmission Electron Microscopy of Matrix Mineral Grains in CM Chondrites: Preaccretionary or Parent Body Aqueous Processing?

CM chondrites are highly hydrated meteorites associated with a parent asteroid that has experienced significant aqueous processing. The meteoritic evidence indicates that these non-differentiated asteroids are formed by fine-grained minerals embedded in a nanometric matrix that preserves chemical clues of the forming environment. So far there are two hypothesis to explain the presence of hydrated minerals in the content of CM chondrites: one is based on textural features in chondrule-rim boundaries [1-3], and the other ‘preaccretionary’ hypothesis proposes the incorporation of hydrated phases from the protoplanetary disk [4-6]. The highly porous structure of these chondrites is inherited from the diverse materials present in the protoplanetary disk environment. These bodies were presumably formed by low relative velocity encounters that led to the accretion of silicate-rich chondrules, refractory Ca- and Al-rich inclusions (CAIs), metal grains, and the fine-grained materials forming the matrix. Owing to the presence of significant terrestrial water in meteorite finds [7], here we have focused on two CM chondrite falls with minimal terrestrial processing: Murchison and Cold Bokkeveld. Anhydrous carbonaceous chondrite matrices are usually represented by highly chemically unequilibrated samples that contain distinguishable stellar grains. Other chondrites have experienced hydration and chemical homogeneization that reveal parent body processes. We have studied CM chondrites because these meteorites have experienced variable hydration levels [8-10]. It is important to study the textural effects of aqueous alteration in the main minerals to decipher which steps and environments promote bulk chemistry changes, and create the distinctive alteration products. It is thought that aqueous alteration has particularly played a key role in modifying primordial bulk chemistry, and homogenizing the isotopic content of fine-grained matrix materials [7, 11, 12]. Fortunately, the mineralogy produced by parent-body and terrestrial aqueous alteration processes is distinctive [5, 11]

Estudio de Parmacella valenciennesii Webb & Van Beneden, 1836, y consideraciones sobre la posición sistemática de la familia Parmacellidae (Mollusca, Pulmonata, Stylommatophora)

Abstract not availabl

Observaciones anatómicas sobre Tudorella ferruginea (Lamarck, 1822) (Mollusca, Prosobranchia, Pomatiasidae)

Abstract not availabl

Actas del III Congreso General de Historia de Navarra (20 al 23 de septiembre de 1994) [Reseña]

Reseña del libro de AA.VV., Actas del III Congreso General de Historia de Navarra (20 al 23 de septiembre de 1994), Gobierno de Navarra, Departamento de educación y cultura, Institución Príncipe de Viana (s.l) 1998, formato CD-ROM

Europa in Messico: per una collaborazione tra le scienze sociali (Reseña)

Reseña del libro de Alicia HERNÁNDEZ CHÁVEz-Marcello CARMAGNANI (coords.), Europa in Messico: per una collaborazione tra le scienze sociali. Centro Interuniversitario di Storia dell'America Latina, Centro de estudios de México en Italia, Torino 1997, 226 pp

Art and faith in tridentine Spain (1545-1690) (Reseña)

Reseña del libro de Alain SAINT-SAÉNS, Art and faith in tridentine Spain (1545-1690), Peter Lang («Ibérica» 14), New York 1995, 223 pp

Los milenarismos en la historia. Actas del VI Simposio de la Iglesia en España y América: siglos XVI-XX (Reseña)

Reseña del libro de Paulino CASTAÑEDA y Manuel J. COCINA (coords.), Los milenarismos en la historia. Actas del VI Simposio de la Iglesia en España y América: siglos XVI-XX, celebrado en Sevilla el 5 de mayo de 1995, CajaSur («Mayor»), Córdoba 1996, 128 pp

Liberales, protestantes y masones, modernidad y tolerancia religiosa. Perú, siglo XIX. [Reseña]

Reseña de: Fernando ARMAS ASÍN, Liberales, protestantes y masones, modernidad y tolerancia religiosa. Perú, siglo XIX, Centro de Estudios Regionales Andinos «Bartolomé de las Casas» - Pontificia Universidad Católica del Perú, Cusco (Perú) 1998, 298 pp