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991.
Abdelilah Dekayir Marc Amouric Juan Olives Claude Parron Abdelilah Nadiri Abdelkader Chergui M.Abdeljalil El Hajraoui 《Comptes Rendus Geoscience》2004,336(12):1061-1070
In Volubilis, Roman mosaics are very beautiful and reveal, from the bottom to the surface, three layers: (i) ‘hedgehog’ layer, (ii) coarse grain mortar layer (rudus + nucleus) and (iii) tesselatum. Mineralogical analysis of coarse grain mortar sampled in Flavius Germanus mosaic shows that it consisted of quartz and calcite, with some feldspar and probably mica and dolomite. Fine-grained mortar in tesselatum is made from a mixture of calcite and quartz only. Limestone tesserae (white, pink and brown) show petrographic facies that change from micritic to oolithic limestone. Conversely, black and brick red tesserae are respectively made of marble, red sandstone and from fire clay. Other colours as yellow, blue, green and grey are obtained from artificial glass with different chemical compositions. To cite this article: A. Dekayir et al., C. R. Geoscience 336 (2004). 相似文献
992.
Zaineb?HajjarEmail author Amina?Wafik Marc?Constantin Mohamed?Bhilisse 《Arabian Journal of Geosciences》2016,9(6):471
The Beni Bousera massif forms part of the Sebtide units in the internal Rif Mountain (Morocco). It is mainly composed of mantle peridotites surrounded by crustal metamorphic rocks (kinzigites, micaschists, and schists). The serpentinization affects all of peridotite massif to various degrees. Serpentinization is concentrated at the top of the peridotites, along the mylonitized zone, and in the NE part of the massif. It is manifested by the formation of mesh and hourglass textures along the tectonic foliation in the highly serpentinized peridotites; and brecciated texture in the least serpentinized peridotites. Pyroxene minerals are still intact hosting few serpentine veins. These petrographic features are consistent with the geochemical data, marked by the increasing of LOI and decreasing of MgO and FeO toward the top of the massif and Aaraben fault. The Raman characterization of serpentine with the brecciated mesh and hourglass textures correspond to lizardite type whereas the serpentine with the vein texture is formed by lizardite + chrysotile. 相似文献
993.
Few global syntheses of oxygen and carbon isotope composition of pedogenic carbonates have been attempted,unlike marine carbonates.Pedogenic carbonates represent in-situ indicators of the climate conditions prevailing on land.The δ~(18)O and δ~(13)C values of pedogenic carbonates are controlled by local and global factors,many of them not affecting the marine carbonates largely used to probe global climate changes.We compile pedogenic oxygen and carbon isotopic data(N= 12,167) from Cretaceous to Quaternary-aged paleosols to identify potential trends through time and tie them to possible controlling factors.While discrete events such as the PaleoceneEocene Thermal Maximum are clearly evidenced,our analysis reveals an increasing complexity in the distribution of the δ~(18)O vs δ~(13)C values through the Cenozoic.As could be expected,the rise of C_4 plants induces a shift towards higher δ~(13)C values during the Neogene and Quaternary.We also show that the increase in global hypsometry during the Neogene plays a major role in controlling the δ~(18)O and δ~(13)C values of pedogenic carbonates by increasing aridity downwind of orographic barriers.Finally,during the Quaternary,an increase of 3‰ inδ~(18)O values is recorded both by the pedogenic carbonates and the marine foraminifera suggesting that both indicators may be used to track global climate signal. 相似文献
994.
Martin Simon Pavel Pitra Philippe Yamato Marc Poujol 《Journal of Metamorphic Geology》2023,41(1):181-203
In the Western Gneiss Region in Norway, mafic eclogites form lenses within granitoid orthogneiss and contain the best record of the pressure and temperature evolution of this ultrahigh-pressure (UHP) terrane. Their exhumation from the UHP conditions has been extensively studied, but their prograde evolution has been rarely quantified although it represents a key constraint for the tectonic history of this area. This study focused on a well-preserved phengite-bearing eclogite sample from the Nordfjord region. The sample was investigated using phase-equilibrium modelling, trace-element analyses of garnet, trace- and major-element thermobarometry and quartz-in-garnet barometry by Raman spectroscopy. Inclusions in garnet core point to crystallization conditions in the amphibolite facies at 510–600°C and 11–16 kbar, whereas chemical zoning in garnet suggests growth during isothermal compression up to the peak pressure of 28 kbar at 600°C, followed by near-isobaric heating to 660–680°C. Near-isothermal decompression to 10–14 kbar is recorded in fine-grained clinopyroxene–amphibole–plagioclase symplectites. The absence of a temperature increase during compression seems incompatible with the classic view of crystallization along a geothermal gradient in a subduction zone and may question the tectonic significance of eclogite facies metamorphism. Two end-member tectonic scenarios are proposed to explain such an isothermal compression: Either (1) the mafic rocks were originally at depth within the lower crust and were consecutively buried along the isothermal portion of the subducting slab or (2) the mafic rocks recorded up to 14 kbar of tectonic overpressure at constant depth and temperature during the collisional stage of the orogeny. 相似文献