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The causes of U-Pb isotopic discordance documented by Paquette et al. (2004) in monazite grains from the ultra-high temperature (UHT) granulite of the Andriamena unit of Madagascar are re-evaluated in the light of nanoscale crystal-chemical characterization utilising Atom Probe Tomography (APT) and state-of-the-art Scanning Transmission Electron Microscopy (STEM). APT provides isotopic (208Pb/232Th) dating and information on the chemical segregation of trace elements (e.g., Pb) in monazite at nanoscale. Latest generation of STEM allows complementary high-resolution chemical and structural characterization at nanoscale. In situ isotopic U–Pb dating with Secondary Ion Mass Spectrometry (SIMS) on 25 monazite grains and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) on zircon have been employed to refine the age spectra. Monazite and zircon grains located in quartz and garnet formed with the peak UHT metamorphic assemblage, which is partially overprinted by retrograde coronitic textures. Zircon grains hosted in garnet and in quartz yield concordant U–Pb ages at 2758 ± 28 Ma and 2609 ± 51 Ma, respectively whereas monazite grains hosted in quartz and garnet show a discordant Pb* loss trend on the Concordia diagram recording disturbance at 1053 ± 246 Ma that is not seen by the zircon, underlining the importance of combining the use of monazite and zircon to understand the history of polymetamorphic rocks. The Pb*-loss trend of monazite is related to petrographic position, with less Pb* lost from monazite hosted in quartz and garnet than monazite hosted in the coronitic reaction texture domains. STEM shows that the garnet- and quartz-hosted monazite grains contain more Pb-bearing nanophases than monazite grains located in the coronitic textures. An inverse correlation between the number of Pb-bearing nanophases and the percentage of Pb*-loss in monazite grains demonstrates that Pb* is retained in the grain in the form of nanophases. The formation of Pb-bearing nanophases limits Pb*-loss at the grain scale and therefore allows the preservation of early events. 208Pb/232Th ratios obtained with APT in monazite located in quartz and garnet and excluding Pb*-bearing nanophases indicate a mean age of 1059 ± 129 Ma corresponding to a disturbance event hitherto undetected in the geochronological record of the Andriamena unit. Thus, geochronology with APT allows access to information and the definition of events that may be blurred or obscured when examined at lower spatial resolution.

The isolation of human bronchial epithelial (HBEC) and fibroblastic cells (HBFC) from biopsies of asthmatic and non-asthmatic volunteers provided unique cellular materials to be used for the production of bioengineered bronchial equivalents (BE) in vitro. The HBEC are grown on a mesenchymal layer seeded with HBFC and the BE can be maintained for at least 15 days in culture. Under the BE culture conditions established previously, HBEC undergo differentiation into ciliated and goblet cells, within a pseudostratified organization comparable to human bronchi. We published previously the results from histologic and functional analyses of such BE produced exclusively using non-asthmatic HBEC and HBFC. We report here the comparative analyses of BE produced with non-asthmatic and asthmatic living HBEC and HBFC (naBE and aBE, respectively). Our data indicated that all asthmatic HBEC populations grown on a mesenchymal layer, containing non-asthmatic HBFC, slowly reached a confluent state but then detached from the matrix upon culture time. These BE appear to be very good models to study the mechanisms involved in asthma in vitro.

New geochemical data and radiometric ages of the protoliths of variably reworked metamafic (granulites and gabbros) and felsic rocks (orthogneisses) from the Cabo Ortegal allochthonous Complex are presented. Their igneous precursors were emplaced in ensialic environments and exhibit geochemical signatures transitional to tholeiitic character, probably originating in arc settings (with continental and oceanic components and minor crustal recycling). The new geochronological results (encompassing the Miaolingian and Furongian epochs of the Cambrian) link the aforementioned scenarios to a Cadomian magmatic arc. The 505Ma protoliths of calc-alkaline orthogneisses and mafic granulites would be the oldest in the sequence of intrusion events. The latter and the 498–486Ma protoliths of gabbros (emplaced in sedimentary host sequences later transformed into Variscan high-pressure and intermediate-pressure gneisses) can be considered as snapshots of the ongoing continental arc evolution. The 498–486Ma gabbro intrusives of these gneisses, together with the 505–503Ma orthogneisses, are ascribable to palaeo-geographically separate scenarios before the Variscan amalgamation of their country rocks. They would expand the initiation of rifting of the Gondwana continental margin to the Miaolingian Cambrian epoch. It is inferred that the Cadomian continental-arc (active at least since 750Ma) experienced in the 510–460Ma interval the consequences of a vanishing active subduction. Certain domains flanking the arc underwent forearc sedimentation and deformation, whereas others were affected by an increasing extension (rifting) and/or back-arc basin formation. The latter marked the initiation of the beginning of a Wilson Cycle, which ended in the late Palaeozoicwith the formation of the Variscan interior orogenic belt. [ABSTRACT FROM AUTHOR]

Monazite is extensively used to date crustal processes and is usually considered to be resistant to diffusive Pb loss. Nevertheless, fluid-assisted recrystallisation is known to be capable of resetting the monazite chronometer. This study focuses on chemical and isotopic disturbances in monazite grains from two microgranite intrusions in the French Central Massif (Charron and Montasset). Petrologic data and oxygen isotopes suggest that both intrusions have interacted with alkali-bearing hydrothermal-magmatic fluids. In the Charron intrusion, regardless of their textural location, monazite grains are sub-euhedral and cover a large domain of compositions. U-Pb chronometers yield a lower intercept age of 297 [+ or -] 4 Ma. An inherited component at 320 Ma is responsible for the scattering of the U-Th-Pb ages. The Montasset intrusion was later affected by an additional F-rich crustal fluid with crystallisation of Ca-REE-fluorocarbonates, fluorite, calcite and chloritisation. Pristine monazite is chemically homogeneous and displays [sup.208]Pb/[sup.232]Th and [sup.206]Pb/[sup.238]U concordant ages at 307 ± 2 Ma. By contrast, groundmass monazite shows dissolution-recrystallisation features associated with apatite and thorite precipitation (Th-silicate) and strong chemical reequilibration. [sup.208]Pb/[sup.232]Th ages are disturbed and range between 270 and 690 Ma showing that the Th/Pb ratio is highly fractionated during the interaction with fluids. Apparent U-Pb ages are older due to common Pb incorporation yielding a lower intercept age at 312 ± 10 Ma, the age of the pristine monazite. These results show that F-rich fluids are responsible for Th mobility and incorporation of excess Pb, which thus strongly disturbed the U-Th-Pb chronometers in the monazite. Keywords Monazite * U-Th-Pb dating * Fluid * LA-ICP-MS * Velay, Introduction Monazite [(Ce, La, Nd, Th)PO4] has been extensively used for dating crustal processes in magmatic and metamorphic rocks (Overstreet 1964; Parrish 1990). For around 10 years, monazite, a so-called [...]