78 research outputs found
Intrusion of Oceanic-type Basaltic Melts Precedes Continental Break up in the Red Sea Rift
The role of magmatism in continental rifting and break up and in the birth of a new ocean are not well understood.
Continental break up can take place with intense and voluminous volcanism, as in the Southern Red Sea/Afar Rift,
or in a relatively amagmatic mode, as in the Mesozoic Iberian Atlantic rift. Studies of gabbros from the Brothers
and Zabargad islands suggest that continental break up in the northern Red Sea, a relatively non-volcanic rift, is
preceded by intrusion of oceanic-type basaltic melts that crystallize at progressively shallower crustal depths as
rifting progresses towards continental break-up. A seismic reflection profile running across the central part of the
southern Thetis basin, shows a âŒ5 km wide reflector âŒ1.25 s below the axial neovolcanic zone. We interpret it
as marking the roof of a magma chamber or melt lens, similar to those identified below several mid-ocean ridges.
Assuming a 4.5 km/s acoustic velocity for the upper oceanic crust at Thetis, this reflector is âŒ3.5 km below
the seafloor. The presence of a few kilometers deep subrift magma chamber soon after the initiation of oceanic
spreading implies the crystallization of lower oceanic crust intrusives as a last step in a sequence of basaltic melt
intrusion from pre-oceanic continental rifting to oceanic spreading. Thus, oceanic crust accretion in the Red Sea rift
starts at depth before continental break up, emplacement of oceanic basalt at the sea floor, and development of Vine-
Matthews magnetic anomalies, pointing to a rift model, where the lower continental lithosphere has been replaced
by upwelling asthenosphere before continental rupturing. This model would imply depth-dependent extension due
to decoupling between the upper and lower lithosphere with mantle-lithosphere-necking breakup before crustalnecking
breakup. This mode of initial oceanic crust accretion may have been common in Mesozoic Atlantic-type
rifts, in addition to wider, amagmatic, Iberian-type continent-ocean zones of transition
Clinopyroxene microtextures reveal incompletely extracted melts in abyssal peridotites.
ABSTRACT Textural evidence is interpreted to suggest that in regions where upwelling rates of the mantle are slow to very slow, a small amount (Ïł2%) of melt was present when plagioclasefree abyssal peridotites entered the conductive regime at the base of the oceanic lithosphere. Upon crystallization, this melt appears to have been undersaturated in orthopyroxene, but precipitated clinopyroxene, Al-rich and Ti-poor spinel, and sulfides. Furthermore, the primary clinopyroxene grains have rare earth element patterns typical of residues of fractional melting, suggesting that the interstitial liquids were incremental partial melts rather than having mid-oceanic-ridge basalt compositions
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A 19 to 17 Ma amagmatic extension event at the Mid-Atlantic Ridge: Ultramafic mylonites from the Vema Lithospheric Section
A >300 km long lithospheric section (Vema Lithospheric Section or VLS) is exposed south of the Vema transform at 11°N in the Atlantic. It is oriented along a seafloor spreading flow line and represents âŒ26 Ma of accretion at a single 80 km long segment (EMAR) of the Mid-Atlantic Ridge. The basal part of the VLS exposes a mantle unit made mostly of relatively undeformed coarse-grained/porphyroclastic peridotites that were sampled at close intervals. Strongly deformed mylonitic peridotites were found at 14 contiguous sites within a âŒ80 km stretch (âŒ4.7 Ma interval); they are dominant in a time interval of 1.4 Ma, from crustal ages of 16.8 to 18.2 Ma (mylonitic stretch). Some of the mylonites are "dry," showing anhydrous high-T deformation, but most contain amphibole. The mylonitic peridotites tend to be less depleted than the porphyroclastic peridotites on the basis of mineral major and trace elements composition, suggesting that the mylonites parent was a subridge mantle that underwent a relatively low degree of melting. The Sr, Nd, and O isotopic composition of the amphiboles is MORB-like and suggests either that seawater did not contribute to their isotopic signature or that their isotopic ratios re-equilibrated during fluid circulation in the upper mantle. Four 40Ar/39Ar ages, on three amphiboles separated from the peridotites, are close to crustal ages predicted from magnetic anomalies, confirming that the amphiboles formed close to ridge axis. We propose that crustal accretion at the EMAR segment has been mostly symmetrical for the 26 Ma of its recorded history, except for the âŒ1.4 Ma interval of prevalent ultramafic mylonites (mylonitic stretch) that may record a period of quasi-amagmatic asymmetric accretion of oceanic lithosphere close to the ridgeâVema transform intersection, possibly with development of detachment faults. This interval may correspond to a thermal minimum of the subridge upwelling mantle, marking the transition from a period of decreasing to one of increasing mantle melting below the EMAR segment
Pervasive melt percolation reactions in ultra-depleted refractory harzburgites at the Mid-Atlantic Ridge, 15° 20âČN : ODP Hole 1274A
Author Posting. © The Authors, 2006. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Contributions to Mineralogy and Petrology 153 (2007): 303-319, doi:10.1007/s00410-006-0148-6.ODP Leg 209 Site 1274 mantle peridotites are highly refractory in terms of lack of residual
clinopyroxene, olivine Mg# (up to 0.92) and spinel Cr# (~0.5), suggesting high degree of partial
melting (>20%). Detailed studies of their microstructures show that they have extensively
reacted with a pervading intergranular melt prior to cooling in the lithosphere, leading to
crystallization of olivine, clinopyroxene and spinel at the expense of orthopyroxene. The least
reacted harzburgites are too rich in orthopyroxene to be simple residues of low-pressure (spinel
field) partial melting. Cu-rich sulfides that precipitated with the clinopyroxenes indicate that
the intergranular melt was generated by no more than 12% melting of a MORB mantle or by
more extensive melting of a clinopyroxene-rich lithology. Rare olivine-rich lherzolitic domains,
characterized by relics of coarse clinopyroxenes intergrown with magmatic sulfides, support
the second interpretation. Further, coarse and intergranular clinopyroxenes are highly depleted
in REE, Zr and Ti. A two-stage partial melting/melt-rock reaction history is proposed, in which
initial mantle underwent depletion and refertilization after an earlier high pressure (garnet field)
melting event before upwelling and remelting beneath the present-day ridge. The ultra-depleted
compositions were acquired through melt re-equilibration with residual harzburgites.Funding for this
research was provided by Centre National de la Recherche Scientifique-Institut National des
Sciences de lâUnivers (Programme Dynamique et Evolution de la Terre Interne)
Magmatologie des sĂ©ries volcaniques mĂ©tamorphiques. Lâexemple des mĂ©tavolcanites cambro-ordoviciennes, en particulier alcalines, du socle provençal (France)
Seyler Monique. Magmatologie des sĂ©ries volcaniques mĂ©tamorphiques. Lâexemple des mĂ©tavolcanites cambro-ordoviciennes, en particulier alcalines, du socle provençal (France). In: Documents des Laboratoires de GĂ©ologie, Lyon, n°96, 1986. Magmatologie des sĂ©ries volcaniques mĂ©tamorphiques. Lâexemple des mĂ©tavolcanites cambro-ordoviciennes, en particulier alcalines, du socle provençal (France) pp. 3-376
De la prison semi-privée à la prison vraiment publique. La fin du systÚme de l'entreprise générale sous la IIIe République
Das neue durch die AssemblĂ©e Constituante in 1791 gegrĂŒndete GefĂ€ngnis verursachte dem Staat das Problem der tĂ glichen Versorgung, welche die Arbeitsbeschaffung der Gefangenen einschloss. Ohne Erfahrung, ohne Geld liess er Privatpersonen diese Aufgabe erfullen. Dieses System nannte man «l'Entreprise GĂ©nĂ©rale». Das Unternehmen ĂŒbernahm ailes. Es handelte den lagessatz und die Erlaubnis, die Gefangenen lohnabhangig zu beschĂ ftigen, aus, allerdings zu einem 20 % geringeren Lohn als die freien Arbeiter... Auch der Kantinenbetrieb wurde von ihm verwaltet. Allerdings wurden die LĂŽhne und GehĂ€lter des GefĂ€ngnispersonals und grosse Reparaturarbeiten am GebĂąude nient vom Unternehmer ubernommen. Die Mangel dieses Systems, welches die Gefangenen in totale AbhĂ€ngigkeit vom Unternehmer brachte, der vor allem ans Geldverdienen dachte, wurden sehr schnell Objekt heftiger Kritik, vor allem von seiten der Reformatoren der Julimonarchie. Aber man musste das Ende des Jahrhunderts abwarten, bis die III. Republik, vorangetrieben durch den Gesinnungswandel und die internationalen Ănderungen der Aufassung vom Strafvollzug, selbst die Funning der Gevangnisse ĂŒbernahm.As a result of the creation of the new prison by the Constituent Assembly in 1791, the State was immediately faced with the problem of assuming the day- to-day management of custodial establishments, which included providing work for prisoners. Without either experience or money, the State shifted that responsibility on to private persons: the system was called the general enterprise. In return for a day price, the canteen market and the authorization to use the penal manpower paid at a 20% lower tariff than that of free labour, the enterprise took everything in hand except the wages of staff and major repairs to buildings. The defects of that system which left prisoners to the mercy of entrepreneurs whose only aim was to make a profit was soon criticized severely, in particular by the reformers of the July Monarchy. However, it was not until the end of the- century that the Third Republic, pressed by the state of mentalities in France and international penitentiary opinion, eventually took the necessary measures to be able to assume the management of its prisons.La nouvelle prison crĂ©Ă©e par l'assemblĂ©e constituante en 1971 posa de suite Ă l'Etat le problĂšme d'assumer sa quotidiennetĂ© matĂ©rielle qui incluait la fourniture de travail aux prisonniers. Sans expĂ©rience, sans argent, il se dĂ©chargea de ce soin sur des personnes privĂ©es: c'est ce systĂšme que l'on appelle l'entreprise gĂ©nĂ©rale.
Moeynnant un prix de journĂ©e, l'autorisation d'utiliser la main-d'Ćuvre pĂ©nale payĂ©e Ă un tarif infĂ©rieur de 20% Ă celui du «travail libre» et le marchĂ© de la cantine, l'entreprise se chargeait de tout Ă l'exclusion des salaires des personnels et des grosses rĂ©parations des bĂątiments.
Les vices de ce systĂšme qui mettait les dĂ©tenus Ă la totale discrĂ©tion des entrepreneurs dont l'unique affaire Ă©tait de gagner de l'argent fit trĂšs tĂŽt l'objet de violentes critiques notamment de la part des rĂ©formateurs de la Monarchie de Juillet, mais il fallut attendre la fin du siĂšcle pour que, pressĂ©e par l'Ă©tat des mentalitĂ©s en France et l'opinion pĂ©nitentiaire internationale, la IIIe RĂ©publique se donne enfin les moyens d'assumer elle-mĂȘme la gestion de ses prisons.De nieuwe gevangenis, opgericht door de grondwetgevende vergadering van 1791, stelde onmiddelijk aan de Staat het probleem van haar dagelijk materiĂ«le organisatie, met inbegrip van het tewerkstellen van de gevangenen. Zonder ervaring en zonder geld, laat ze die zorg over aan privĂ© personen. Dit systeem heet de algemene onderneming. Mits een prijs per dag, de toelating om de strafarbeiders te gebruiken tegen tarief 20% lager dan van de «vrij arbeid» en de markt van de cantine, nam de onderneming ailes op zich, met uitsluiting van het loon van het personeel en de grote herstellingen van de gebouwen.
De gebreken van dit systeem, die de gevangenen totaal afhankelijk maakten van de ondernemers wiens enig doel was geld te verdienen, werd zeer snel zwaar bekritiseerd onder andere door de Herformers van de juli Monarchie. Maar men moest het einde van de eeuw afwachten vooraleer, onder druk van de evolutie van de geestgestekdheid in Frankrijk, de Hide Republiek zich eindelijk de middelen toekent om zelf het beheer van haar gevangenissen in handen te nemen.Seyler Monique. De la prison semi-privée à la prison vraiment publique. La fin du systÚme de l'entreprise générale sous la IIIe République. In: Déviance et société. 1989 - Vol. 13 - N°2. pp. 125-140
Vivre avec son temps : les cantines des prisons
Im französischen GefĂ€ngnis des 19. Jahrhunderts waren « la cantine » in erster Linie die Lebensmittel, die die Gefangenen kaufen konnten, um sich zu ernĂ€hren. Nur dank dieser « cantine » die sir erwerben konnten, waren die Gefangenen in der Lage physisch zu ĂŒberleben. Dieses System wurde von denjenigen Unternehmern gestĂŒtzt, die diesen Market belief erten. Heute werden die Gefangenen ausreichend ernĂ€hrt; die «cantine » nimmt deshalb eine andere Rolle im Gefangnissystem ein. Sie dient heute in erster Linie dazu, die Situation, die Strenge der Einschliessung dadurch zu erleichtern, dass die Gefangenen sich die verschiedesten Konsumguter kaufen können. In der Ver gangheit bestand der Preis, den das GefĂ€ngnis fur ein störungsfreies Funktionnieren zu zahlen hatte, in der Aufgabe der Idee, die Gefangenen moralisch zu verbessern. Heute besteht das Problem darin, dass durch die «cantine» sich das VerhĂ€ltnis zwischen Gefangenen und GefĂ ngnispersonal kompliziert, sich quasi ein «Konsumkonkurrenz entwickelt.The canteen is, in french prison, the diverses consumer goods the prisoners are allowed to buy with their own money. During the XIX-century, only the provisions, sold by the entrepreneur, who had the market of the canteen, allow the prisoners to survive. Today, prisoners are eating one's file ans the role of the canteen is another one. Well provided with all kinds of goods, it is improving the every day life of the prisoners and let them accept the hardness of the confinement. For the prison, the price to be paid for the smooth functionning of the system was formerly the renunciation to the project of moral reformation of the prisoners. It is, to-day, the necessity, for the penal administration, to manage more complex relations than in the olden days, between prisoners and guards.La cantine est dans les prisons le «suplus» que les dĂ©tenus peuvent se procurer sur leur argent propre. Tout au long du XIXe siĂšcle, c'est Ă l'existence de ce surplus, favorisĂ© par les entrepreneurs qui en avaient le marchĂ©, que la population pĂ©nale a dĂ» simplement sa survie. Aujourd'hui, les dĂ©tenus mangent Ă leur faim et le rĂŽle dĂ©volu Ă la cantine a changĂ©. Bien pourvue en biens de toutes sortes, elle amĂ©liore la quotidiennetĂ© carcĂ©rale et fait accepter la rigueur de l'enfermement. Pour l'institution pĂ©nitentiaire, le prix Ă payer pour l'aide ainsi apportĂ©e Ă son fonctionnement sans trop de heurts, ce fut jadis l'abandon de son projet de rĂ©forme morale des populations carcĂ©rales. C'est aujourd'hui la nĂ©cessitĂ© de gĂ©rer des rapports devenus plus complexes entre surveillants et dĂ©tenus.In de gevangenissen betekent de kantine het «suplus» dat de gedetineerden zich op eigen kosten kunnen verschaffen. Dank zij het bestaan van dit suplus, in de hand gewerkt door ondernemers die de markt in handen hadden, kon gedurende de ganse XIX ° eeuw de gevangenisbevolking overleven. Hedenten- dage hebben de gedetineerden voldoende te eten en is de roi van de kantine veranderd. Goed voorzien van aller hande goederen, leidt zij tot verbetering van het dagelijks gevangenisleven en helpt de strenge opsluiting aanvaarden. Voor de hulp die op die wijze werd verleend om zonder al te veel moeilijkheden te functioneren, moest de gevangenisinstelling destijds haar plan ter morele verbetering van de gevangenen opgeven. Nu krijgt de kantine de noodzakelijke functie de meer ingewikkeld geworden verhoudingen tussen bewaarders en gedetineerden te regelen.Seyler Monique. Vivre avec son temps : les cantines des prisons. In: DĂ©viance et sociĂ©tĂ©. 1988 - Vol. 12 - N°2. pp. 127-145
La banalisation pénitentiaire ou le voeu d'une réforme impossible
Diese Studie verfolgt den Zweck, die RationalitĂąt der Hindernisse und Oppositionen aufzudecken, aufdie die Inkraftsetzung der Strafvoll- zugsreform von 1975 in den GefĂ ngnissen stösst. Um dies zu erreichen, haben wir vorerst versucht, einen dem Weberschen Idealtypus verwandten Funktionsmodus zu entdecken. Wir glauben, ihn in der auf diese Institution bisher anwendbaren Reform von 1944 gefunden zu haben. Mit diesem konzeptuellen Werkzeug versehen zogen wir darauf einen Vergleich mit der Reform von 1975 und analysierten, inwiefern diese vom "Gefangmodell" â wie wir es nennen â abweicht, oder mit ihm ĂŒbereinstimmt. Dabei ergibt sich, dass die "Aussenwelt" und das GefĂ€ngnis von entgegengesetzten Werten bestimmt sind, die jeweils erst ihr Funktionieren ermöglichen.The objet of this study is to uncover the rationality that governs the obstacles and refusals which in prison confront the application of the penitentiary reform of 1975. In a first step, we tried to define a mode of functioning similar to the weberian ideal type. We recognized it in the reform of 1944, which had governed this institution prece- dently. Our second step was to confront it with the 1975 reform and to analyze how far the latter approached, or differed from, what we will name the "penitentiary model". Two antagonistic sets of values could be perceived in this manner, one belonging to the prison, the other to the "exterior" world, both worlds needing them in order to function.Cette Ă©tude a pour objet de mettre Ă jour la rationalitĂ© qui gouverne les blocages et les refus auxquels se heurte, dans les prisons, l'application de la rĂ©forme pĂ©nitentiaire de 1975. Pour tenter d'y parvenir, nous avons, dans un premier temps, essayĂ© de trouver un mode de fonctionnement qui s'apparente au type idĂ©al weberien. Nous avons pensĂ© le trouver dans la rĂ©forme de 1944, qui gouvernait prĂ©cĂ©demment l'institution. Nous avons, dans un second temps, confrontĂ© cet outil conceptuel avec la rĂ©forme de 1975 et analysĂ© dans quelle mesure cette derniĂšre s'Ă©carte ou s'approche de ce que nous appellerons le "modĂšle pĂ©nitentiaire". On s'aperçoit que le monde "extĂ©rieur" et la prison sont rĂ©gis par des valeurs antagonistes, nĂ©cessaires, chacune, Ă leur fonctionnement respectif.Het doel van dit onderzoek is de rationaliteit te onthullen, die het remmen en het weigeren van de toepassing der pĂ©nitentiaire hervorming van 1975 in de franse gevangenissen beheerst. Zo werd in een eerste fase getracht een wijze van funktioneren terug te vinden, die vermant is met het weberiaanse ideaaltype. Wij dachten die te vinden in de hervorming van 1944, die voordien het gevangeniswezen beheerste. Aan de hand van dit beripp en-instrument hebben wij in een tweede fase de hervorming van 1975 ontleed en nagegaan in welke mate zij zich verwijdert van of benadert wat wij zullen noemen "het penitentiair model". Men stelt vast dat de "externe" wereld en de gevangenis worden beheerst door tegengestelde waarden, die elk op zichzelf nodig zijn om iedervan die werelden te doen funktioneren.Seyler Monique. La banalisation pĂ©nitentiaire ou le voeu d'une rĂ©forme impossible. In: DĂ©viance et sociĂ©tĂ©. 1980 - Vol. 4 - N°2. pp. 131-147
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