Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : International audience
Upper Triassic volcanic and sedimentary rocks of the Mamonia Complex in southwestern Cyprus are exposed in erosional windows through the post-Cretaceous cover, where the Mamonia Complex is tectonically imbricated with the Troodos and Akamas ophiolitic suites. Most of these Upper Triassic volcanic rocks have been considered to represent remnants of Triassic oceanic crust and its associated seamounts. New Nd and Pb isotopic data show that the whole Mamonia volcanic suite exhibits features of oceanic island basalts (OIB). Four rock types have been distinguished on the basis of the petrology and chemistry of the rocks. Volcanism began with the eruption of depleted olivine tholeiites (Type 1) and oceanic island tholeiites (Type 2) associated with deep basin siliceous and/or calcareous sediments. The tholeiites were followed by highly phyric alkali basalts (Type 3) interbedded with pelagic Halobia-bearing limestones or white reefal limestones. Strongly LREE-enriched trachytes (Type 4) were emplaced during the final stage of volcanic activity. Nd and Pb isotopic ratios suggest that tholeiites and mildly alkali basalts derived from partial melting of heterogeneous enriched mantle sources. Fractional crystallization alone cannot account for the derivation of trachytes from alkaline basalts. The trachytes could have been derived from the partial melting at depth of mafic material which shares with the alkali basalts similar trace element and isotopic compositions. This is corroborated by the rather similar isotopic compositions of the alkali basalts and trachytes. The correlations observed between incompatible elements (Nb, Th) and {varepsilon}Nd and Pb isotopic initial ratios suggest that the Mamonia suite was derived from the mixing of a depleted mantle (DMM) and an enriched component of High µ (µ = 238U/204Pb, HIMU) type. Models using both Nd and Pb isotopic initial ratios suggest that the depleted tholeiites (Type 1) derived from a DMM source contaminated by an Enriched Mantle Type 2 component (EM2), and that the oceanic tholeiites (Type 2), alkali basalts (Type 3) and trachytes (Type 4) were derived from the mixing of the enriched mantle source of the depleted tholeiites with a HIMU component. None of the Mamonia volcanic rocks show evidence of crustal contamination. The Upper Triassic within-plate volcanism likely erupted in a small southerly Neotethyan basin, located north of the Eratosthenes seamount and likely floored by oceanic crust.
ISSN: 0016-7568

insu-00353657
https://hal-insu.archives-ouvertes.fr/insu-00353657
DOI : 10.1017/S0016756806002937

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The paleostorm history of coastal lagoon environments (Pierre Blanche Lagoon, central part of the Gulf of Lions) has been established by integrating clay mineralogy and geochemical analysis. Clay mineralogy combined with bulk major and trace elements concentrations allow for the definition of four different end members: the Mosson drainage basin, the sandy barrier, the biogenic and the anthropic components. The two main sedimentary sources of the lagoonal system are the Mosson drainage basin which has a high concentration of smectite and Al2O3, and the sandy barrier characterized by high contents of illite, chlorite, SiO2 and Zr. Smectite/(illite + chlorite), SiO2/Al2O3 and Zr/Al2O3 ratios can be used to reconstruct the past storm history of the Pierre Blanche Lagoon. Our results indicate that the sensitivities of the clay mineralogy and geochemistry proxies are different. These sensitivities could be related: 1) first, to the comparison between different grain size for geochemistry and for clay mineralogy: 2) second, to the complexity of the mix (four end-members for the geochemistry and two end-members for the clay minerals): and 3) third, by the storm's ability to transport sediment of different sizes. (C) 2010 Elsevier B.V. All rights reserved.
ISSN: 0037-0738

hal-00512614
https://hal.archives-ouvertes.fr/hal-00512614
DOI : 10.1016/j.sedgeo.2010.04.012

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Isotopes have been widely used for source identification since the early twentieth century. Recent advances in analytical techniques have increased the precision and the accuracy of isotope analysis. As a result, the use of isotopes has spread to several fields (e.g., ecology, food chemistry, archaeology, environmental health and pollution, and forensic sciences). This review examines the principal uses of stable-isotope analyses for tracing origins or sources, along with statistical methods employed for data interpretation, in recent papers (2007―09) dealing essentially with food authentication, ecology, environmental pollution and other applications, including geology, police forensics, hydrology and archaeometry. The main elements analyzed were H, C, N, O, S, Sr and Pb. For isotope-data interpretation, statistical methods appear to depend essentially on the field, the objectives of the study and the number of parameters. They were not often stated explicitly because the studies were exploratory and aimed primarily at assessing the relevance of the analytical techniques used to identify sources. We critically discuss the adequacy of these methods.
ISSN: 0165-9936

hal-00687383
https://hal.archives-ouvertes.fr/hal-00687383

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
For the first time, an albite orthogneiss has been recognised and dated within the HP-LT blueschist facies metabasites and metapelites of the Ile de Groix. It is characterised by a peraluminous composition, high LILE, Th and U contents, MORB-like HREE abundances and moderate Nb and Y values. A U-Pb age of 480.8 ± 4.8 Ma was obtained by LA-ICP-MS dating of zircon and titanite. It is interpreted as the age of the magmatic emplacement during the Early Ordovician. Morphologically different zircon grains yield late Neoproterozoic ages of 546.6-647.4 Ma. Zircon and titanite U-Pb ages indicate that the felsic magmatism from the Ile de Groix is contemporaneous with the acid, pre-orogenic magmatism widely recognised in the internal zones of the Variscan belt, related to the Cambro-Ordovician continental rifting. The magmatic protolith probably inherited a specific chemical composition from a combination of orogenic, back-arc and anorogenic signatures because of partial melting of the Cadomian basement during magma emplacement. Besides, the late Devonian U-Pb age of 366 ± 33 Ma obtained for titanite from a blueschist facies metapelite corresponds to the age of the HP-LT peak metamorphism.
ISSN: 1437-3254

insu-00714570
https://hal-insu.archives-ouvertes.fr/insu-00714570
DOI : 10.1007/s00531-011-0732-5

Éditeur(s) : HAL CCSD Universidad de Barcelona
Résumé : Tens of Surtseyan tuff cones are exposed in the Rio Coichel valley, between Nireguao and Estancia Bano Nuevo (Southern Chilean Andes). The Early Cretaceous products of the submarine eruptions rest on, or are interbedded with, shallow marine sandstones of the Hauterivian-early Aptian Apeleg Formation. The Early Cretaceous rocks typically contain large amphibole phenocrysts, clinopyroxene and plagioclase, and have compositions that range from relatively primitive basalts to andesites. The basalts are slightly enriched in LREE and incompatible trace elements. They have low Ti-contents and negative anomalies in Nb and Ta, characteristic of subduction-related magmas. Centimetre-sized amphibole megacrysts and an amphibole-bearing clinopyroxenite xenolith have been found in one of the tuff cones located near Estancia Bano Nuevo. The amphibole megacrysts are pargasite (low Si and Ti, high Mg). The xenolith has diopsidic clinopyroxene with abundant inclusions, and pargasite veins enclosing smaller clinopyroxene neoblasts. Geochemical data show that the megacrysts and the xenolith have the same origin and correspond to underplated igneous bodies crystallized at high pressure.
ISSN: 1695-6133

hal-00512829
https://hal.archives-ouvertes.fr/hal-00512829
DOI : 10.1344/105.000001530

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : Ten international laboratories participated in an inter-laboratory comparison of a fossil bone composite with the objective of producing a matrix and structure-matched reference material for studies of the bio-mineralization of ancient fossil bone. We report the major and trace element compositions of the fossil bone composite, using in-situ method as well as various wet chemical digestion techniques. For major element concentrations, the intra-laboratory analytical precision (%RSDr) ranges from 7 to 18%, with higher percentages for Ti and K. The %RSDr are smaller than the inter-laboratory analytical precision (%RSDR; <15-30%). Trace element concentrations vary by similar to 5 orders of magnitude (0.1 mg kg(-1) for Th to 10,000 mg kg(-1) for Ba). The intra-laboratory analytical precision %RSDr varies between 8 and 45%. The reproducibility values (%RSDR) range from 13 to <50%, although extreme value >100% was found for the high field strength elements (Hf, Th, Zr, Nb). The rare earth element (REE) concentrations, which vary over 3 orders of magnitude, have %RSDr and %RSDR values at 8-15% and 20-32%, respectively. However, the REE patterns (which are very important for paleo-environmental, taphonomic and paleo-oceanographic analyses) are much more consistent. These data suggest that the complex and unpredictable nature of the mineralogical and chemical composition of fossil bone makes it difficult to set-up and calibrate analytical instruments using conventional standards, and may result in non-spectral matrix effects. We propose an analytical protocol that can be employed in future inter-laboratory studies to produce a certified fossil bone geochemical standard. (C) 2007 Elsevier B.V. All rights reserved.
ISSN: 0003-2670

hal-00407629
https://hal.archives-ouvertes.fr/hal-00407629
DOI : 10.1016/j.aca.2007.08.015

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Spinel (± plagioclase) peridotite xenoliths from the Tallante and Los Perez volcanic centres in the eastern Betics (SE Spain) range from depleted (clinopyroxene-poor) harzburgites to fertile (clinopyroxene-rich) lherzolites and orthopyroxene-free wehrlites. Significantly, only one harzburgite, which is depleted in heavy rare earth elements (HREE), retains the imprint of ca. 20% ancient melting of an original garnet lherzolite source. In contrast, REE abundances of other harzburgites and lherzolites from the eastern Betics have been increased by melt-rock reaction. The whole-rock and mineral compositions of these mantle rocks are largely controlled by three types of modal metasomatism: 1) common clinopyroxene-orthopyroxene addition and olivine consumption which increased FeOt, SiO2 and Al2O3, and decreased MgO compared to the refractory melting products; 2) subordinate orthopyroxene dissolution and precipitation of clinopyroxene and olivine, which led to higher FeOt and MgO and lower SiO2 than in common (orthopyroxene-rich) lherzolites; and 3) rare orthopyroxene consumption and olivine addition that caused higher FeOt and lower SiO2 compared to the original melting residues. These mineral modal and major element variations have been produced mostly by interactions with relatively FeOt-rich/SiO2-poor melts, likely derived from a peridotite-pyroxenite lithospheric mantle with a highly heterogeneous isotopic composition. Melting of the lithospheric mantle in the western Mediterranean was triggered by upwelling of the asthenosphere induced by back-arc extension in the Late Oligocene-Early Miocene. Trapping of small fractions of exotic melts in whole-rocks — likely the parental magmas of Miocene back-arc dykes that intruded the Betic crust — caused local disequilibrium between the trace element signatures and Pb isotopic compositions of clinopyroxene and whole-rock. Subsequent interaction with SiO2-undersaturated magmas, similar to the parental melts of the Pliocene alkali basalts that host the xenoliths, promoted orthopyroxene consumption and clinopyroxene-olivine enrichment at locations close to magma conduits, and finally generated orthopyroxene-free wehrlites. This event constitutes the last episode of the Cenozoic magmatic evolution of the westernmost Mediterranean which is recorded in the mantle xenoliths from the eastern Betics.
ISSN: 0024-4937

hal-01553092
https://hal.archives-ouvertes.fr/hal-01553092
DOI : 10.1016/j.lithos.2016.12.011