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Tourmaline-rich rocks (up to 60% tourmaline) associated with low–medium grade metamorphic assemblages occur in the Sierra Nevada area (Betic Cordillera, southeastern Spain). Tourmaline appears in a variety of forms: (1) stratiform tourmalinites; (2) quartz–tourmaline nodules; (3) porphyroclasts in felsic orthogneisses; and (4) disseminations in psammopelitic metasediments and gneisses. Tourmaline within these lithologic groups exhibits textural and chemical variations that reflect complex premetamorphic growth under open-system conditions, and subsequent changes due to Alpine regional metamorphism. Microprobe analyses of the tourmalines reveal a wide compositional variation between schorl and dravite end members with variable contents of X-site vacancies (av. 0.084–0.225 apfu), Ca (av. 0.095–0.269 apfu), and excess of Al (up to 6.588 apfu) compared with the theoretical value of 6 in ideal schorl and dravite. The amount of Ca may be significant in porphyroclasts from the gneisses. Fe/(Fe+Mg) ratios for tourmalines in tourmalinites, metasediments, and gneisses range from 0.34 to 0.95, 0.16 to 0.92, and 0.28 to 0.97, respectively. Na/(Na+Ca) ratios are also variable, mostly ranging from 0.5 to 0.9. Many of the tourmalines have complex chemical and colour zoning patterns, including significant fluctuations in Al, Fe, Mg, Na, Ca, Ti, and F. Based on petrographic and chemical data, three generations of tourmaline have been established. The first generation corresponds to magmatic–postmagmatic tourmaline that is represented by tourmaline porphyroclasts within the orthogneisses. The second generation of tourmaline formed during tourmalinization of psammopelitic rocks giving rise to tourmalinites. The third generation of tourmaline is represented by cellular textures, pale reaction rims and overgrowths developed during the Alpine regional metamorphic overprint. D 2002 Elsevier Science B.V. All rights reserved.

¶Rocks containing braunite from the Ossa-Morena central belt (Iberian Massif, SW Spain) have been studied; these include nodules and layers of braunite (association I), Mn-slates (association II) and Mn-metatuffs (associations III and IV). Geochemical features of braunite nodules such as Mn/Fe ratios around 2, positive Ce-anomalies and good correlations among Mn, Fe, Co, Cu and REE contents indicate that the protolith of the braunite-nodules was precipitated from oxidising sea water. Greenschist facies Hercynian metamorphism reduced initial Mn4+ to Mn3+ and Mn2+. High initial fO2 of oxide beds (association I) limited reduction to the formation of braunite. Reduction continued until the formation of garnet + piemontite (associations II and III), and pyroxmangite + pyrophanite (association IV). Ti-rich braunites (up to 6.8% of TiO2) occur in slates and metatuffs in which the (Mn + Fe)/Ti ratio of the whole rock is lower than 30, while braunites have lower Ti contents in slates and metatuffs with (Mn + Fe)/Ti ratios around 90. Fe-rich braunite crystallized in rocks with Mn2+ oxide and silicate where low Mn3+/Mn2+ in the whole rock facilitated substitution of Fe3+ for Mn3+.

11 páginas, 9 figuras, 3 tablas., Experimental illitization of smectite was studied by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Experiments were performed on the, Financial support was supplied by Research Project nº BTE 2000-0582 of the Spanish Ministry of Science and Technology, Research Group RNM-0179 of the Junta de Andalucia and the REN2001-3868 and REN 2000-0798 projects.

Principal component analysis (PCA) and correspondence analysis (CA) have been used to identify several critical mineral crystallization factors during metamorphism of Mn-rich lithologies from the Iberian Massif, Spain. Three types of variables have been considered in the system: mineralogical variables, bulk composition variables and one physical variable (oxygen fugacity). PCA was applied to the compositional variables to obtain four components, which were used as new compositional variables. These, together with the mineralogical and physical variables, were treated in the CA. The plot of the variables on the factor 1-factor 2 plane reveals that tephroite crystallization is controlled by a compositional variable representing low values of ratio Si/(Mn+Fe) in the rocks. Moreover, it is possible to deduce from this plot the importance of high oxygen fugacity conditions for the crystallization of piemontite. The third factor shows that the crystallization of spessartine does not require very restrictive physical-chemical conditions.

A 30-year-old man presented at the emergency department with a 2 h onset of intense left upper quadrant pain irradiating to his back. Physical examination showed tenderness in the left hypochondrium. Initial laboratory results were unremarkable. Abdominal computed tomography was performed …

13 páginas, In order to obtain an indication of metamorphic conditions we have studied the mineralogy of the clastic rocks, in particular the phyllosilicates, from three Precambrian series in the Central-Iberian and Ossa-Morena zones of the Southern Hesperian Massif: the Esquisto Grauváquico Complex; the so-called Serie Negra; and the Azuaga Formation. For this purpose we have used the crystal-chemical parameters obtained via X-ray diffraction (d001, b0, ratios of the basal intensity of the white micas and chlorites, and the crystallinity index of the mica) together with electron microprobe data from selected areas, obtained via backscattered electron images. The mineral assemblages, commonly quartz+muscovite +albite +chlorite ±biotite, and the values obtained for the illite crystallinity index (between 0.18° and 0.20° 2Θ) in rocks with non-diagnostic mineral assemblages point to at least greenschist-facies metamorphic conditons. The phengite content of the mica indicates an overall pressure regime near the limits between low and intermediate pressure, but some significant differences exist between the series studied. The Azuaga Formation shows the lowest pressure (about 4 kbar), while the Serie Negra indicates a pressure of at least 1 kbar more. In the Esquisto Grauváquico Complex, when the samples are considered overall, the results are similar to those of the Serie Negra, but there is inhomogeneity in the rocks from the two sections studied. The various types of chlorite, both textural and optical, are homogeneous in composition in each rock specimen and their chemical composition depends primarily on the composition of the host-rock.

Paleokarstic deposits have been found in certain zones in the lead-(zinc)-fluorite Triassic deposits of the Alpujarride Complex. The karstic cavities appear to be developed in peritidal sequences shallowing upwards, which, in turn, are included in megasequences corresponding to transgressive-regressive sedimentary subcycles within a cycle tending to be regressive overall. The erosion and/or karstification surfaces, from which the cavities have developed, are found at the top of the sequences.