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Mantle xenoliths collected from Fuerteventura, one of the easternmost Canary Islands, exhibit a complex evolutionary history comprising events of depletion, serpentinization, dehydration and melt metasomatism. Each of these events left imprints on both the texture and chemistry of the xenoliths. Extensive partial melting is shown by complete lack of primary clinopyroxene, the ultra-refractory trace element composition of orthopyroxene porphyroclasts, and low heavy rare earth element contents as compared with abyssal peridotites sampled along mid-ocean ridges and oceanic fracture zones, in the xenoliths least affected by later metasomatism. In many xenoliths the original orthopyroxene porphyroclasts and some olivines are replaced by fibrous aggregates of orthopyroxene and/or large, deformed olivine porphyroclasts with mottled rims with stringy glass and fluid inclusions. Such features are very rare in ocean island xenoliths. Unusually high H2O and Cl concentrations, together with very high H2O/Ce and Cl/K ratios in interstitial glasses, suggest that the fibrous orthopyroxene formed by local serpentinization by hot seawater. The volume increase accompanying the serpentinization caused extensive fracturing of adjacent olivine porphyroclasts. The most likely scenario for local mantle invasion by hydrous fluids is along deep faults and fractures caused by tectonic movements along the continent–ocean transition during the early phases of the opening of the Atlantic Ocean. The peridotites were later (probably during the Canary Islands magmatism) dehydrated, causing the serpentine minerals to be replaced by porous domains of fibrous orthopyroxene. Hydrous fluids released by the deserpentinization escaped into neighbouring and overlying rocks leaving trails of fluid inclusions along fractures and grain boundaries causing mottled rims and zones in olivine porphyroclasts. During the Canary Islands magmatism the upper mantle beneath Fuerteventura was also infiltrated by enriched silicate magmas that caused different degrees of Fe–Ti-metasomatism. A higher degree of melt metasomatism in rocks with fibrous orthopyroxene and mottled olivine than in the massive harzburgites strongly suggests that the sublithospheric Canarian magmas reused serpentinized extensional faults during their rise to the surface. The strongest degree of melt metasomatism appears to have resulted in the formation of lherzolites, wehrlites, and dunites. [ABSTRACT FROM AUTHOR]

The intrusions of Adamello and Valmasino Bregaglia are related to the Alpine continental collision and contain cumulus amphibole-rich gabbroic rocks (hornblendites, amphibole-gabbros and olivine-gabbros). Literature Nd-Sr-O data suggest that these rocks were derived from uncontaminated mantle-derived liquids. Brown amphibole and its clinopyroxene inclusions were analysed for a large number of trace elements by laser ablation ICP-MS and ion microprobe. On the basis of a suitable set of [sup S/L]D, the compositions of parental liquids were determined. Primary liquid compositions were calculated assuming variable degrees of early fractional crystallisation on the basis of olivine composition. Computed liquids have a marked enrichment of light, large-ion lithophile elements (LILEs), U and Th over high field strength elements (HFSEs) and rare-earth elements (REEs). The light REEs are slightly enriched relative to heavy REEs, and clear Nb and Ta negative anomalies are lacking. HFSE and HREE compositions can be related to small degrees of batch melting of a spinel facies, MORB-type source. The enrichment of highly incompatible trace elements over HFSEs and HREEs reflect metasomatic processes which could be of Alpine and/or pre-Alpine age. The latter hypothesis implies a subcontinental lithospheric origin for the mantle sources. Nevertheless, the abrupt B enrichment of Valmasino Bregaglia liquids suggests that the partial melting of the mantle sources was triggered by a B-rich fluid of Alpine origin. [ABSTRACT FROM AUTHOR]

Selective enrichment or depletion in either Zr and Hf (HFSE4+) or Nb and Ta (HFSE5+) is a feature commonly observed in many mantle-derived melts and amphiboles occurring as either disseminated minerals in mantle xenoliths and peridotite massifs or in vein assemblages cutting these rocks. The fractionation of Nb from Zr seen in natural mantle amphiboles suggests that their incorporation is governed by different crystal-chemical mechanisms. An extensive set of new partitioning experiments between pargasite–kaersutite and melt under upper-mantle conditions shows that HFSE incorporation and fractionation depends on amphibole major-element composition and the presence or absence of dehydrogenation. Multiple regression analysis shows that Amph/LDNb/Zr is strongly dependent on the mg-number of the amphibole as a result of a combination of amphibole and melt structure effects, so that the following generalizations apply: (1) high-mg-number amphiboles crystallized from unmodified mantle melts more easily incorporate Zr relative to Nb leading to an increase of the Nb/Zr ratio in the residual melt; (2) low-mg-number amphiboles, such as those found in veins cutting peridotites, may strongly deplete the residual melt in Nb and cause very low Nb/Zr in residual melts. Implications and applications to mantle environments are discussed. [ABSTRACT FROM PUBLISHER]

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The conservation law of radiance as a suitable tool for investigation of radiation transfer processes between two systems is treated. Original proofs of this law are given and its deep thermodynamical foundation is pointed out. Finally, applications to general problems of power coupling and particularly to the radiation transfer from incoherent sources (LED) into multimode optical fibres are carried out. [ABSTRACT FROM AUTHOR]

In this paper the geometrical theory of pulse distortion and energy launching into multimode optical fibres is generalized when skew rays are taken into account. To this purpose, within the geometrical theory of skew rays, we firstly obtained a new expression for the numerical aperture. From this expression we derived an extensive analysis of the energy launched and the pulse response of a multimode optical fibre. A better launching efficiency and a different pulse form at the output of the fibre together with a larger broadening are obtained in comparison with the results derived from theories only for meridional rays. The theory is also applied to sources having planar geometry (such as LED) and linear geometry (such as semiconductor lasers), and the response to some rectangular-shaped pulses is investigated. Finally some considerations concerning scattering effects are described. [ABSTRACT FROM AUTHOR]

In this paper the different loss mechanisms of light in multimode fibres are analysed from the point of view of the extinction of leaky skew rays. First, the intrinsic loss mechanism of leaky rays due to optical tunnel effect is fully investigated by means of a quasi-classical approach and a well approximated form of the relative extinction coefficient is derived. Second, the influence of other loss phenomena, due to imperfections or impurities in the fibre such as core and cladding absorption and scattering, on the relative contribution of leaky rays is analysed. Finally some phenomena of failed excitation of leaky rays are also examined. The phenomena are analysed both qualitatively and quantitatively and a comparative analysis of various effects referring to actual fibres is made. [ABSTRACT FROM AUTHOR]

The article discusses various reports published within the issue, including one on the formation of shallow peridotites, and another on the Nikanbetsu plagioclase lherzolite from Hokkaido, Japan.