U-Pb-Hf-trace element systematics and geochronology of zircon from a granulite-facies metamorphosed mafic-ultramafic layered complex in Central Brazil

Zircon recrystallization is a common process during high-grade metamorphism and promotes partial or complete resetting of the original isotopic and chemical characteristics of the mineral and thus complicates U-Pb geochronological interpretation. In Central Brazil, this complexity may be illustrated by three composite mafic-ultramafic intrusions metamorphosed under amphibolite-to-granulite conditions. Their ages of emplacement and metamorphic ages have been a matter of controversy for the last thirty years. The Serra da Malacacheta and Barro Alto complexes make up the southernmost of these layered bodies and four samples from distinct rock types were investigated in order to verify the consequences of metamorphic alteration of zircon for U-Pb dating. Cathodoluminescent imaging reveals internal features which are typical of concomitant dissolution-reprecipitation processes, such as convolute zoning and inward-moving recrystallization fronts, even in samples in which partially preserved igneous textures are observed. Due to this extensive alteration, LA-ICPMS U-Pb isotopic analysis yielded inconclusive data. However, in situ Hf isotopic and trace-element analyses help to clarify the real meaning of the geochronological data. Low Lu/Hf (<0.004) and homogeneous (176)Hf/(177)Hf(t) values imply that the zircon populations within individual samples have crystallized in a single episode, despite the observed variations in age values. Trace element signatures of zircon grains from garnet-bearing samples reveal that they were unreactive to the development of the peak metamorphism mineral assemblage and, thus, the main chemical feature in such grains is attributed to a coupled dissolution-reprecipitation process. However, in the Cafelandia amphibolite an additional alteration process is identified, probably related to the influx of late-stage fluids. Combined isotopic and geochemical investigation on zircon grains allowed the distinction of two magmatic events. The first corresponds to the crystallization of the Serra da Malacacheta Complex and characterizes a juvenile magmatism at similar to 1.3 Ga. The younger episode, recognized in the Barro Alto Complex, is dated at ca. 800 Ma and is represented by mafic and ultramafic rocks showing intense contamination with continental crust, implying that the emplacement took place, most likely, in a continental back-arc setting. Altered zircon domains as well as titanite grains date the metamorphic event at ca. 760-750 Ma. (C) 2011 Elsevier B.V. All rights reserved.

Systematics and phylogeny of the Neotropical Pachymenes de Saussure and Santamenes Giordani Soika (Hymenoptera, Vespidae, Eumeninae)

The genera Pachymenes de Saussure and Santamenes Giordani Soika arerevised and the phylogenetic relationships among their species, based on external mor-phology and male genitalia, are presented. The cladistics analysis, using 22 terminalspecies (19 ingroup and 3 outgroup species) and 44 characters, produced a single clado-gram under implied weighting. Both genera were recovered as paraphyletic, althoughttwo major clades were formed and were well supported by the re-sampling analysis.We propose the synonymy of Pachymenes with Santamenes, and the description of twonew species: P. saussurei Grandinete n.sp. and P. riograndensis Grandinete n.sp..Newcombinations are: Pachymenes novarae (de Saussure) n.comb., P. olympicus (Zavattari)n.comb., P. peregrinus (Zavattari) n.comb. and P. santanna (de Saussure) revised combi-nation. We state the synonymy of P. obscurus orellanoides under P. obscurus consuetus,reviewing the status of the latter and raising P. consuetus to species level. Pachymenesorellanae vardyi is synonymized under P. orellanae; P. ghilianii olivaceus, P. ghilianiiavissimus and P. peruanus are proposed as synonyms of P. ghilianii; P. picturatusobscuratus is synonymized under P. laeviventris; P. picturatus nigromaculatus andP. picturatus var . intermedia are synonymized under P. picturatus and P. a t ra var . ornatis-sima get its lectotype designated and proposed as synonym of P. ater.

Reinstatement of the genus Colopalpus Pritchard and Baker (1958) and re-description of Colopalpus matthyssei Pritchard and Baker (1958), the type species of the genus (Acari, Tenuipalpidae)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Isotopic, trace element and nutrient characterization of coastal waters from Ubatuba inner shelf area, south-eastern Brazil

Stable isotopes, tritium, radium isotopes, radon, trace elements and nutrients data were collected during two sampling campaigns in the Ubatuba coastal area (south-eastern Brazil) with the aim of investigating submarine groundwater discharge (SGD) in the region. The isotopic composition (delta D, delta(18)O, (3)H) of submarine waters was characterised by significant variability and heavy isotope enrichment. The stable isotopes and tritium data showed good separation of groundwater and seawater groups. The contribution of groundwater in submarine waters varied from a few % to 17%. Spatial distribution of (222)Rn activity concentration in surface seawater revealed changes between 50 and 200 Bq m(-3) which were in opposite relationship with observed salinities. Time series measurements of (222)Rn activity concentration in Flamengo Bay (from 1 to 5 kBq m(-3)), obtained by in situ underwater gamma-spectrometry showed a negative correlation between the (222)Rn activity concentration and tide/salinity. This may be caused by sea level changes as tide effects induce variations of hydraulic gradients, which increase (222)Rn concentration during lower sea level, and opposite, during high tides where the (222)Rn activity concentration is smaller. The estimated SGD fluxes varied during 22-26 November between 8 and 40 cm d(-1), with an average value of 21 cm d(-1) (the unit is cm(3)/cm(2) per day). The radium isotopes and nutrient data showed scattered distributions with offshore distance and salinity. which implies that in a complex coast with many small bays and islands, the area has been influenced by local currents and groundwater-seawater mixing. SGD in the Ubatuba area is fed by coastal contaminated groundwater and re-circulated seawater (with small admixtures of groundwater). which claims for potential environmental concern with implications on the management of freshwater resources in the region. (C) 2007 Elsevier Ltd. All rights reserved.

Systematics, phylogeny and biogeography of Juncaginaceae

I investigated the systematics, phylogeny and biogeographical history of Juncaginaceae, a small family of the early-diverging monocot order Alismatales which comprises about 30 species of annual and perennial herbs. A wide range of methods from classical taxonomy to molecular systematic and biogeographic approaches was used. rnrnIn Chapter 1, a phylogenetic analysis of the family and members of Alismatales was conducted to clarify the circumscription of Juncaginaceae and intrafamilial relationships. For the first time, all accepted genera and those associated with the family in the past were analysed together. Phylogenetic analysis of three molecular markers (rbcL, matK, and atpA) showed that Juncaginaceae are not monophyletic. As a consequence the family is re-circumscribed to exclude Maundia which is pro-posed to belong to a separate family Maundiaceae, reducing Juncaginaceae to include Tetroncium, Cycnogeton and Triglochin. Tetroncium is weakly supported as sister to the rest of the family. The reinstated Cycnogeton (formerly included in Triglochin) is highly supported as sister to Triglochin s.str. Lilaea is nested within Triglochin s. str. and highly supported as sister to the T. bulbosa complex. The results of the molecular analysis are discussed in combination with morphological characters, a key to the genera of the family is given, and several new combinations are made.rnrnIn Chapter 2, phylogenetic relationships in Triglochin were investigated. A species-level phylogeny was constructed based on molecular data obtained from nuclear (ITS, internal transcribed spacer) and chloroplast sequence data (psbA-trnH, matK). Based on the phylogeny of the group, divergence times were estimated and ancestral distribution areas reconstructed. The monophyly of Triglochin is confirmed and relationships between the major lineages of the genus were resolved. A clade comprising the Mediterranean/African T. bulbosa complex and the American T. scilloides (= Lilaea s.) is sister to the rest of the genus which contains two main clades. In the first, the widespread T. striata is sister to a clade comprising annual Triglochin species from Australia. The second clade comprises T. palustris as sister to the T. maritima complex, of which the latter is further divided into a Eurasian and an American subclade. Diversification in Triglochin began in the Miocene or Oligocene, and most disjunctions in Triglochin were dated to the Miocene. Taxonomic diversity in some clades is strongly linked to habitat shifts and can not be observed in old but ecologically invariable lineages such as the non-monophyletic T. maritima.rnrnChapter 3 is a collaborative revision of the Triglochin bulbosa complex, a monophyletic group from the Mediterranean region and Africa. One new species, Triglochin buchenaui, and two new subspecies, T. bulbosa subsp. calcicola and subsp. quarcicola, from South Africa were described. Furthermore, two taxa were elevated to species rank and two reinstated. Altogether, seven species and four subspecies are recognised. An identification key, detailed descriptions and accounts of the ecology and distribution of the taxa are provided. An IUCN conservation status is proposed for each taxon.rnrnChapter 4 deals with the monotypic Tetroncium from southern South America. Tetroncium magellanicum is the only dioecious species in the family. The taxonomic history of the species is described, type material is traced, and a lectotype for the name is designated. Based on an extensive study of herbarium specimens and literature, a detailed description of the species and notes on its ecology and conservation status are provided. A detailed map showing the known distribution area of T. magellanicum is presented. rnrnIn Chapter 5, the flower structure of the rare Australian endemic Maundia triglochinoides (Maundiaceae, see Chapter 1) was studied in a collaborative project. As the morphology of Maundia is poorly known and some characters were described differently in the literature, inflorescences, flowers and fruits were studied using serial mictrotome sections and scanning electron microscopy. The phylogenetic placement, affinities to other taxa, and the evolution of certain characters are discussed. As Maundia exhibits a mosaic of characters of other families of tepaloid core Alismatales, its segregation as a separate family seems plausible.

Mo isotopic composition of the mid-Neoproterozoic ocean: an iron formation perspective

The Neoproterozoic was a major turning point in Earth's surficial history, recording several widespread glaciations, the first appearance of complex metazoan life, and a major increase in atmospheric oxygen. Marine redox proxies have resulted in many different estimates of both the timing and magnitude of the increase in free oxygen, although the consensus has been that it occurred following the Marinoan glaciation, the second globally recorded “snowball Earth” event. A critically understudied rock type of the Neoproterozoic is iron formation associated with the Sturtian (first) glaciation. Samples from the <716 Ma Rapitan iron formation were analysed for their Re concentrations and Mo isotopic composition to refine the redox history of its depositional basin. Rhenium concentrations and Re/Mo ratios are consistently low throughout the bottom and middle of the iron formation, reflecting ferruginous to oxic basinal conditions, but samples from the uppermost jasper layers of the iron formation show significantly higher Re concentrations and Re/Mo ratios, indicating that iron formation deposition was terminated by a shift towards a sulfidic water column. Similarly, the δ98Mo values are close to 0.0‰ throughout most of the iron formation, but rise to ~+0.7‰ near the top of the section. The δ98Mo from samples of ferruginous to oxic basinal conditions are the product of adsorption to hematite, indicating that the Neoproterozoic open ocean may have had a δ98Mo of ~1.8‰. Together with the now well-established lack of a positive Eu anomaly in Neoproterozoic iron formations, these results suggest that the ocean was predominantly oxygenated at 700 Ma.

Palladium Isotopic Evidence for Nucleosynthetic and Cosmogenic Isotope Anomalies in IVB Iron Meteorites

The origin of ubiquitous nucleosynthetic isotope anomalies in meteorites may represent spatial and/or temporal heterogeneity in the sources that supplied material to the nascent solar nebula, or enhancement by chemical processing. For elements beyond the Fe peak, deficits in s-process isotopes have been reported in some (e.g., Mo, Ru, W) but not all refractory elements studied (e.g., Os) that, among the iron meteorites, are most pronounced in IVB iron meteorites. Palladium is a non-refractory element in the same mass region as Mo and Ru. In this study, we report the first precise Pd isotopic abundances from IVB irons to test the mechanisms proposed for the origin of isotope anomalies. First, this study determined the existence of a cosmogenic neutron dosimeter from the reaction 103Rh(n, beta-)104Pd in the form of excess 104Pd, correlated with excess 192Pt, in IVB irons. Second, all IVB irons show a deficit of the s-process only isotope 104Pd (\varepsilon 104Pd = -0.48 ± 0.24), an excess of the r-only isotope 110Pd (\varepsilon 110Pd = +0.46 ± 0.12), and no resolvable anomaly in the p-process 102Pd (\varepsilon 102Pd = +1 ± 1). The magnitude of the Pd isotope anomaly is about half that predicted from a uniform depletion of the s-process yields from the correlated isotope anomalies of refractory Mo and Ru. The discrepancy is best understood as the result of nebular processing of the less refractory Pd, implying that all the observed nucleosynthetic anomalies in meteorites are likely to be isotopic relicts. The Mo-Ru-Pd isotope systematics do not support enhanced rates of the 22Ne(alpha,n)25Mg neutron source for the solar system s-process.

Correlated cosmogenic W and Os isotopic variations in Carbo and implications for Hf-W chronology

An obstacle for establishing the chronology of iron meteorite formation using 182Hf-182W systematics (t1/2 = 8.9 Myr) is to find proper neutron fluence monitors to correct for cosmic ray modification of W isotopic composition. Recent studies showed that siderophile elements such as Pt and Os could serve such a purpose. To test and calibrate these neutron dosimeters, the isotopic compositions of W and Os were measured in a slab of the IID iron meteorite Carbo. This slab has a well-characterized noble gas depth profile reflecting different degrees of shielding to cosmic rays. The results show that W and Os isotopic ratios correlate with distance from the pre-atmospheric center. Negative correlations, barely resolved within error, were found between epsilo190Os-epsilo189Os and epsilo186Os-epsilo189Os with slopes of -0.64 ± 0.45 and -1.8(+1.9/-2.1), respectively. These Os isotope correlations broadly agree with model predictions for capture of secondary neutrons produced by cosmic ray irradiation and results reported previously for other groups of iron meteorites. Correlations were also found between epsilo182W-epsilo189Os (slope = 1.02 ± 0.37) and epsilo182W-epsilo190Os (slope = -1.38 ± 0.58). Intercepts of these two correlations yield pre-exposure epsilo182W values of -3.32 ± 0.51 and -3.62 ± 0.23, respectively (weighted average epsilo182W = -3.57 ± 0.21). This value relies on a large extrapolation leading to a large uncertainty but gives a metal-silicate segregation age of -0.5 ± 2.4 Myr after formation of the solar system. Combining the iron meteorite measurements with simulations of cosmogenic effects in iron meteorites, equations are presented to calculate and correct for cosmogenic effects on 182W using Os isotopes.

Nd, Sr and Pb isotopic composition of eolian dust deposited in the central North Pacific

The silicate fractions of recent pelagic sediments in the central north Pacific Ocean are dominated by eolian dust derived from central Asia. An 11 Myr sedimentary record at ODP Sites 885/886 at 44.7°N, 168.3°W allows the evaluation of how such dust and its sources have changed in response to late Cenozoic climate and tectonics. The extracted eolian fraction contains variable amounts (>70%) of clay minerals with subordinate quartz and plagioclase. Uniform Nd isotopic compositions (epsilon-Nd =38.6 to 310.5) and Sm/Nd ratios (0.170-0.192) for most of the 11 Myr record demonstrate a well-mixed provenance in the basins north of the Tibetan Plateau and the Gobi Desert that was a source of dust long before the oldest preserved Asian loess formed. epsilon-Nd values of up to 36.5 for samples 62.9 Ma indicate <=35 wt% admixture of a young, Kamchatka-like volcanic arc component. The coherence of Pb and Nd in the erosional cycle allows us to constrain the Pb isotopic composition of Asian loess devoid of anthropogenic contamination to 206Pb/204Pb =18.97 +/- 0.06, 207Pb/204Pb =15.67 +/- 0.02, 208Pb/204Pb =39.19 +/- 0.11. 87Sr/86Sr (0.711-0.721) and Rb/Sr ratios (0.39-1.1) vary with dust mineralogy and provide an age indication of ~250 Ma. 40Ar/39Ar ages of six dust samples are uniform around 200 Ma and match the K-Ar ages of modern dust deposited on Hawaii. These data reflect the weighted age average of illite formation. Changes from illite- smectite with significant kaolinite to illite- and chlorite-rich, kaolinite-free assemblages since the late Pliocene document changes in the intensity of chemical weathering in the source region. Such weathering evidently did not disturb the K-Ar systematics, and only induced scatter in the Rb-Sr data. We propose that when smectite forms at the expense of illite, K and Ar are quantitatively lost from what becomes smectite, but are quantitatively retained in adjacent illite layers. 40Ar/39Ar age data, therefore, are insensitive to smectite formation during chemical weathering but date the diagenetic growth of illite, the major K-bearing phase in the dust. Over the past 12 Myr, the dust flux to the north Pacific increased by more than an order of magnitude, documenting a substantial drying of central Asia. This climatic change, however, did not alter the ultimate source of the dust, and neoformational products of chemical weathering always remained subordinate to assemblages reworked by mechanical erosion in dust deposited in eastern Asia and the Pacific Ocean.

Rb-Sr isotope systematics and Sr/Ca-Ba/Ca ratios at DSDP Hole 89-462A

Four samples of Nauru Basin basalts (Cores 94 to 109 of Hole 462A, sub-bottom depth 1077-1209 m) have 87Sr/86Sr ratios in the range 0.7037 to 0.7038, which is distinctly higher than the ratios of N-type MORB. The Rb contents of the samples are depleted in comparison with those of MORB and ocean-island basalts. These chemical and isotopic characteristics are identical to those of the basalts previously drilled during Leg 61 (Cores 75 to 90 of Hole 462A), and are explained in terms of inhomogeneity of the source region in the mantle or later alteration effects. Sr/Ca-Ba/Ca systematics of 15 samples from Cores 462A-94 to 462A-109 and 14 samples from Cores 462A-75 to 462A-90 suggest that the Nauru Basin basalts are derived from a mantle peridotite by 20 to 30% partial melting with subsequent Plagioclase crystallization.

Nd, Sr and Sm isotopic composition and model ages of rocks from the Anginskaya and Talanchanskaya formations, Lake Baikal

The paper presents data on the Nd-Sr systematics of magmatic rocks of the Khaidaiskii Series of the Anginskaya Formation in the Ol'khon region, western Baikal area, and rocks of the Talanchanskaya Formation on the eastern shore of Lake Baikal. Geochemical characteristics of these rocks are identical and testify to their arc provenance. At the same time, the epsilon(t)Nd of rocks of the Khaidaiskii Series in the Ol'khon area has positive values, and the data points of these rocks plot near the mantle succession line in the epsilon(t)Nd-87Sr/86Sr diagram, whereas the epsilon(t)Nd values of rocks of the Talanchanskaya Formation are negative, and the data points of these rocks fall into the fourth quadrant in the epsilon(t)Nd -87Sr/86Sr diagram. This testifies to a mantle genesis of the parental magmas of the Khaidaiskii Series and to the significant involvement of older crustal material in the generation of the melts that produced the orthorocks on the eastern shore of the lake. These conclusions are corroborated by model ages of magmatic rocks in the Ol'khon area (close to 1 Ga) and of rocks of the Talanchanskaya Formation (approximately 2 Ga). The comparison of our data with those obtained by other researchers on the Nd-Sr isotopic age of granulites of the Ol'khon Group and metavolcanics in various structural zones in the northern Baikal area suggests, with regard for the geochemistry of these rocks, the accretion of tectonic nappes that had different isotopic histories: some of them were derived from the mantle wedge and localized in the island arc itself (magmatic rocks of the Anginskaya Formation) or backarc spreading zone (mafic metamagmatic rocks of the Ol'khon Group), while others were partial melts derived, with the participation of crustal material, from sources of various age (metagraywackes in the backarc basin in the Ol'khon Group and the ensialic basement of the island arc in the Talanchanskaya Formation).