Experimental investigation of reactions between two-mica granite and boron-rich fluids: Implications for the formation of tourmaline granite

The genetic relationship between different types of granite is critical for understanding the formation and evolution of granitic magma. Fluid-rock interaction experiments between two-mica leucogranite and boron-rich fluids were carried out at 600–700°C and 200 MPa to investigate the effects of boron content in fluid and temperature on the reaction products. Our experimental results show that tourmaline granite can be produced by reactions between boron-rich fluid and two-mica granite.At 700°C, the addition of boron-rich fluid resulted in partial melting of two-mica granite and crystallization of tourmaline from the boron-rich partial melt. Increasing boron concentration in fluid promotes the melting of two-mica granite and the growth of tourmaline. No melt was produced in experiments at 600°C, in which Fe, Mg and Al released from biotite decomposition combined with boron from the fluid to form tourmaline under subsolidus conditions. The Na required for tourmaline crystallization derived from Na/K exchange between feldspar and the K released by biotite decomposition. The produced tourmaline generally has core-rim structures, indicating that the composition of melt or fluid evolved during tourmaline crystallization.Based on the experimental results, we propose that tourmaline granite veins or dikes can be formed by the reactions between boron-rich fluids, presumably produced by devolatilization of boron-bearing granitic magma, and incompletely crystallized granite at the top of the magma chamber. This "self-metasomatism" involving boron-rich fluid in the late stage of magma crystallization could be an important mechanism for the formation of tourmaline granite.     

Marcel Bertrand et „l'orogenèse programmée“

Résumé Marcel Bertrand (1847–1907) est surtout connu pour avoir été le promoteur de la tectonique des grandes nappes alpines. Le présent article entend attirer l'attention sur un aspect moins souvent abordé de son oeuvre. En passant en revue et comparant, de façon à la fois méthodique et empirique, les données alors disponibles, il découvre une homologie frappante entre les suites d'évènements qui ont abouti à la formation des grandes chaînes de montagnes successives de l'Europe. Chacune a ses gneiss, son «Flysch fin» précoce, son «Flysch grossier» tardif externe et enfin ses grès rouges (molasses); de même, pour l'histoire magmatique et même métallogénique (roches vertes précoces, puis granite, «porphyres» et enfin laves basiques post-tectoniques). Il est donc clair que Marcel Bertrand a été le véritable initiateur (se gardant de tout dogmatisme), du modèle «programmé» de l'orogenèse, en général attribué à Hans Stille et ses é mules. D'un point de vue historique, on peut voir dans sa conception de l'orogenèse une synthèse réconciliant plusieurs théories jusque là antagonistes: l'étagement des grandes formations universelles de Werner devient le produit régionalement hétérochrone des cycles de transformation de Hutton; et les soulèvements successifs catastrophiques d'Elie de Beaumont sont retraduits en termes lyelliens, processus lents et graduels, néanmoins récurrents et ordonnés.

---

Marcel Bertrand (1847–1907) is best known for his trail-blazing recognition of the great nappes. The present paper draws attention to a lesser known side of his work: through a methodical, empirical review of the available data, Marcel Bertrand brought to light a striking similarity in the sequence of events which led to the formation of each of the successive mountain chains of Europe. Each has its own gneisses, early fine Flysch, later coarse external Flysch, and late red sandstone; and also the same magmatic (and even metallogenic) suite (early greenstones, then granite, porphyries, and finally post-tectonic basic lavas). Thus it appears that Marcel Bertrand was the real originator (avoiding any dogmatization) of the programmed model of orogeny commonly ascribed to Hans Stille and his followers. From a historical point of view, one may see in this conception of mountain building a conciliatory synthesis between some major antagonistic theories: the Wernerian universal formations become heterochronous products of the Huttonian cycle; and the catastrophic successive orogenies of Elie de Beaumont actually amount to slow, gradual, Lyellian processes, nonetheless orderly and recurrent.

---

Zusammenfassung Marcel Bertrand ist besonders als der Entdecker der großen Alpinen Überschiebungen bekannt. Hier wird eine weniger bekannte Seite seines Werkes erwähnt: er hat klargemacht, daß die verschiedenen europäischen Gebirgsketten eine parallele und strukturierte Geschichte haben (sedimentär, magamatisch, metallogenisch). Eine objektive Zusammenstellung der tatsächlichen Kenntnisse zeigt, daß jedes Orogen seine Gneise, seinen feinen Flysch in dem zentralen Trog, seinen groben Flysch am Rand und sein Rotliegendes als Späterscheinung hat. In jedem Fall erkennt man die Anwesenheit von basischen Gesteinen als Früherscheinungen, von Graniten, dann von Porphyren und am Ende von posttektonischen, basischen Gesteinen. Hier kann man das von H. Stille und seinen Nachfolgern entwickelte Schema erkennen, das aber hier bei M. Bertrand rein empirisch bleibt. Vom historischen Standpunkt her ist es möglich, das Werk von M. Bertrand als die Synthese, die Zusammenfassung verschiedener, bis dahin antagonistisch gestellter Strömungen zu betrachten: der Wernersche, stufenartige, theoretische Bau wird zur heterochronen Folge des Huttonschen Zyklus; die nacheinander sich entwikkelnden katastrophalen Orogenesen von Elie de Beaumont werden, wie bei Lyell, langsam aber dennoch strukturiert und wiederkehrend.

---

Marcel Bertrand . : , (, , ). , , , . , , , , . , , M. Bertrand'OM, . Bertrand'a , - , : , Elie de Beaumont — .

     

Technetium-99 content in some marine organisms collected near La Hague,France

Analyses for ⁹⁹Tc in some marine biological samples taken near the outlet of the low level radioactive effluent pipeline of the nuclear reprocessing plant of La Hague, France, gave positive results. From 500 to 3500 pCi kg^?1 wet weight of ⁹⁹Tc were observed in brown algae; Fucus sp. appeared to be a good indicator of this long-lived radionuclide in a marine environment.     

The formation of SiO<Subscript>2</Subscript>-rich melts within the deep oceanic crust by hydrous partial melting of gabbros

Small amounts of felsic, evolved plutonic rocks, often called oceanic plagiogranites, always occur as veins or small stocks within the gabbroic section of the oceanic crust. Four major models are under debate to explain the formation of these rocks: (1) late-stage differentiation of a parental MORB melt, (2) partial melting of gabbroic rocks, (3) immiscibility in an evolved tholeiitic liquid, and (4) assimilation and partial melting of previously altered dikes. Recent experimental data in hydrous MORB-type systems are used to evaluate the petrogenesis of oceanic plagiogranites within the deep oceanic crust. Experiments show that TiO₂ is a key parameter for the discrimination between different processes: TiO₂ is relatively low in melts generated by anatexis of gabbros which is a consequence of the low TiO₂ contents of the protolith, due to the depleted nature of typical cumulate gabbros formed in the oceanic crust. On the other hand, TiO₂ is relatively high in those melts generated by MORB differentiation or liquid immiscibility. Since the TiO₂ content of many oceanic plagiogranites is far below that expected in case of a generation by simple MORB differentiation or immiscibility, these rocks may be regarded as products of anatexis. This may indicate that partial melting processes triggered by water-rich fluids are more common in the deep oceanic crust than believed up to now. At slow-spreading ridges, seawater may be transported via high-temperature shear zones deeply into the crust and thus made available for melting processes.     

利用陆面岩石中生成的宇生同位素重建冰川漂砾运动历史的尝试

冰川漂砾的形成年代通常难以直接测定，并且漂砾形成以后是否被再次搬运或者移动过，更是无法知道。本文研究发现，通过测试砾石不同部位的宇生同位素，不仅可以测定砾石形成的时代，而且可以确定砾石再次被搬运或者被翻转的年代，从而恢复砾石运动的历史。本文以石英中生成的宇生同位素^10Be，对青藏高原东南部海子山的冰川漂砾进行了探讨，结果表明该砾石形成于倒数第二次冰期(186～128ka BP之间)，在末次冰期中再次被冰川搬运，使之反转。该方法不局限于^10Be和冰川漂砾，也适用于其他陆面岩石中生成的宇生同位素以及其他成因的石块或者砾石。因此为探讨冰川作用、泥石流活动、重力崩塌等过程提供了一种重要的方法和技术途径。     

Subarctic Pacific evidence for a glacial deepening of the oceanic respired carbon pool

Measurements of benthic foraminiferal cadmium:calcium (Cd/Ca) have indicated that the glacial–interglacial change in deep North Pacific phosphate (PO₄) concentration was minimal, which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean. Here we present sedimentary redox-sensitive trace metal records from Ocean Drilling Program (ODP) Site 882 (NW subarctic Pacific, water depth 3244 m) to make inferences about changes in deep North Pacific oxygenation – and thus respired carbon storage – over the past 150,000 yr. These observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep-water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment. Our results suggest that the deep subarctic Pacific water mass was depleted in oxygen during glacial maxima, though it was not anoxic. We reconcile our results with the existing benthic foraminiferal Cd/Ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed, rather than remineralized. This change would have corresponded to an increase in the deep Pacific storage of respired carbon, which would have lowered atmospheric carbon dioxide (CO₂) by sequestering CO₂ away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea. The magnitude of change in preformed nutrients suggested by the North Pacific data would have accounted for a majority of the observed decrease in glacial atmospheric pCO₂.     

Orbital identification of clays and carbonates in Gusev crater

Gusev crater was selected as the landing site of one of the two NASA Mars Exploration Rovers because water once could have ponded within the crater and partly filled it with sediments as suggested by the presence of a feeder channel and the fluvial-lacustrine morphology of the in-filling. However, the paucity of mineralogical evidence for fluvial-lacustrine activity revealed by the Spirit rover has remained a puzzle for years. Using orbital, near-infrared imaging spectroscopy, we report the detection of phyllosilicates and carbonates within and around the landing site of Spirit on the floor of Gusev crater. Placed in their geomorphological context, these minerals shed new light on the aqueous history of this crater, and offer a framework for the Spirit in situ measurements.     

Ferric/ferrous ratio in silicate melts: a new model for 1 atm data with special emphasis on the effects of melt composition

The effect of MgO and total FeO on ferric/ferrous ratio in model multicomponent silicate melts was investigated experimentally in the temperature range 1300–1500 °C at 1 atm total pressure in air. We demonstrate that the addition of these weak network modifier cations results in an increase of Fe³⁺/Fe²⁺ ratio in both mafic and silicic melts. Based on present and published experimental data, a new empirical equation is proposed to predict the ferric/ferrous ratio as a function of oxygen fugacity, temperature and melt composition. In contrast to previous equations, the compositional effect of melts on the Fe³⁺/Fe²⁺ ratio is not only modeled by the sum of the molar fraction of the individual oxide components. Additional interactions terms have also been incorporated. The main advantage of the proposed model is its applicability for a wide compositional range. However, its application to felsic melts (>?68 wt% SiO₂) is not recommended. Other advantages of this equation and differences when compared with previous models are discussed.