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The Vendee eclogites (Armorican Massif, France): assemblages vs. Whole rock composition, a modelling perspective.
No full textWalking on a Palaeo Ocean Floor. The Subducted Tethys in the Western Alps - An Excursion Guide
No full textAbstract
This excursion in the Italian Western Alps presents an overview of the eclogitized ophiolite of the Zermatt-Saas unit, focusing on the relationships between various alpine units and on metamorphic features of different lithologies (serpentinite, metagabbro and metabasalt, Mn-rich quartzite, hydrothermal sulphide deposits and metasediments). These rocks underwent high- to ultrahigh-pressure metamorphism during subduction of the Tethys ocean, and developed peculiar high-pressure peak assemblages according to their composition.
First, in order to acquire a general view of the main Alpines and their lithologies, we cross the Tethys ocean suture (the Zermatt-Saas and Combin units of the ophiolitic Piedmont Zone) from the European passive continental margin (now represented by the Monte Rosa unit) to the Adria (Africa) continental margin (Sesia-Lanzo and Dent Blanche nappes). Then, we visit some of the most typical outcrops of Alpine geology in the NW Alps: (i) the Saint-Marcel Fe-Cu hydrothermal sulphide deposits; (ii) the famous Praborna Mn mine with its unique high-pressure minerals; (iii) the Cignana coesite site and the Crepin metagabbro (Valtournanche). Attention is especially focussed on the eclogitized ophiolite and hydrothermal oceanic deposits. In addition, historical aspects, Alpine views and regional geology are taken in consideration. The field trip is concluded with the breathtaking view from Plateau Rosa, south of Cervino (Matterhorn), where it is possible to summarise the regional relationships of the collisional nappe stack and the ophiolitic suture (remnants of the “lost Tethyan ocean”), and to have the opportunity to enjoy some last eclogite outcrops.
Keyword
The subducted Tethys in the Aosta valley (Italian Western Alps)Field Excursion Guide, Field Trip B02
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Symplectite development in a restitic metapelite from the Catena Costiera, Calabria. P-T constraints from phase equilibrium calculations in the system FeO-MgO-Al2O3-SiO2-H2O.
No full textEvoluzione statica di alta T e bassa P dell’unità ercinica di Mandatoriccio (Sila orientale - Calabria)
No full textBoninite-derived amphibolites from the Lanterman-Mariner suture (northern Victoria Land, Antarctica): New geochemical and petrological data
No full textIn northern Victoria Land (Antarctica) the Lanterman-Mariner suture separates the inboard Wilson Terrane from the outboard Bowers and Robertson Bay terranes. This boundary is characterized by the presence of discontinuous bodies of mafic to ultramafic rocks with a metamorphic grade ranging from medium-P amphibolite facies (Mountaineer Range) to ultrahigh-P eclogite facies (Lanterman Range). The Dessent Ridge is a narrow tectonic slice occurring along the Lanterman-Mariner suture in the Mountaineer Range. The slice mainly consists of amphibolites and amphibole-rich schists with very peculiar mineral assemblages comprising talc + clinoamphibole + orthoamphibole +/- staurolite +/- garnet. Talc shows very unusual compositions with significant Al and Na contents linked to the Si-1 square-1Al+1Na+1 and Si-1Mg-1Al+2 substitutions (i.e. "tschermak talc"). Bulk-rock major, trace-element and REE compositions range from MORB/arc tholeiite to boninite. Along the Lanterman-Mariner suture the presence of metamorphic rocks whose protoliths have a boninitic affinity is here reported for the first time. They attest to the past existence of a subduction zone with an arc-backarc system between the Wilson and the Bowers terranes. Mineral assemblages and the mineral chemistry allow us to document a retrograde P-T-path from a regional medium-P amphibolite (T approximate to 690 degrees C; P approximate to 0.9 GPa) to greenschist facies, with a typical cooling-unloading path. Amphibolite-facies metamorphism was followed by structural reworking and partial recrystallization under strike-slip shear deformation. The rocks most affected by shearing document that this deformation developed under the transition amphibolite-greenschist facies, although local higher temperature conditions can be ascribed to shear heating. Comparison with other mafic-ultramafic rocks from the Lanterman-Mariner suture suggests that, from the regional amphibolite-facies metamorphism onwards, the area extending from the Lanterman Range to the Mountaineer Range, including the Dessent Ridge, underwent a nearly synchronous tectono-metamorphic evolution. The Lanterman-Mariner suture resulted from the accretion of an arc/backarc system to the palaeo-Pacific continental margin of Gondwana during the Ross Orogen (Cambro-Ordovician), a typical subduction-accretion orogen. (C) 2012 Elsevier B.V. All rights reserved
Polyphase metamorphic history revealed from garnet-core composition isopleths: an example from the low-P Hercynian basement in Sila (Calabria, Italy)
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