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 Copernicus Publications
Résumé : International audience
During Ocean Drilling Program Leg 134, a mixed sequence of volcaniclastic and carbonate sediments was cored together with basaltic breccias and a single basalt sill in Hole 833B. In this study, data from Schlumberger's Geochemical Logging Tool, together with physical property logs, characterise part of the section and establish a complete log-derived lithostratigraphy. The major transition between the sedimentary rocks and a basaltic sill at 830 mbsf (metres below sea floor) is clearly seen as well as the distinction between the silicate-rich sediments and the carbonate-rich part of the section. The transition between the volcanic sandstone interbedded with basaltic and sed-lithic breccia of Unit III, and the volcanic sandstone of Unit IV is clearly marked by the physical property logs. The accuracy of the logging data was evaluated and discussed with an improved log versus core correlation. The cluster analysis of the complete data set shows a correlation with the data provided by the mechanical caliper device, which in turn indicates the quality of the borehole.
ISSN: 1816-8957

hal-00642165
http://hal.upmc.fr/hal-00642165
http://hal.upmc.fr/hal-00642165/document
http://hal.upmc.fr/hal-00642165/file/Rabaute_et_al-SciDrilling-1997.pdf