bluuebunny/crossref_metadata_2025_split huggingface dataset:
The topaz-bearing rhyolites from the San Luis Potosi area (Mexico): characteristics of the lava and growth conditions of topaz
Authors: Leroy Jacques L. , Rodriguez-Rios Rodolfo , Dewonck Sarah 
Published: June 2005

Abstract
In Mexico, the topaz-bearing rhyolites occur mainly in the San Luis Potosi area (San Luis Potosi and Guanajuato States). These rhyolites appear as domes related to the Tertiary extensional tectonism. Three domes of the San Luis Potosi volcanic field were selected for study, according to the color, the habits and the size of the topaz they contain, in order to determine the characteristics of the lava and the growth conditions of the topaz. These rhyolites are high-silica, metaluminous to slightly peraluminous and alkali-rich lavas. They are enriched in fluorine and in incompatible lithophile elements such as Rb, Cs, Ta, U and Th and depleted in Ba, Sr, Ca, Mg, Ti and Ni. Therefore, they are very similar to the topaz-bearing rhyolites from western United States. In Cerro El Gato dome, both amber-colored and colorless topazes crystallized in voids and fractures. Comparing these different crystals with respect to their growth environment, habits, chemical compositions and EPR characteristics provides an explanation for the crystallization conditions and color of topaz. Colorless topaz from Cerro El Gato crystallized at a temperature above 500oC (lack of color centers) from fluids enriched in elements leached from the lava, whereas the amber-colored topaz crystallized below 500oC (based on the presence of color centers) and from fluids richer in volatile elements (As). In Cerro El Lobo, the topaz have intermediate characteristics between the colorless and the amber-colored topazes of Cerro El Gato.
The Hercynian collision in the Armorican Massif : evidence of different lithospheric domains inferred from seismic tomography and anisotropy
Authors: Judenherc Sébastien , Granet Michel , Brun Jean-Pierre , Poupinet Georges 
Published: June 2005

Abstract
The Hercynian belt is a continental collision orogen extending from south-west Iberia to the Bohemian Massif in Czech Republic. The successive stages of its formation are dated from 400 to 260 Ma.The Armorican Massif is a preserved segment of this orogen. It presents structures oriented NW-SE, parallel to the general Hercynian trend in this region. The massif is divided into three domains (North, Central, and South-Armorican domains) separated by two main shearzones, the North- and South-Armorican shear zones. As the Armorican Massif escaped from any important tectonic or thermal event since the end of Hercynian times, it is particularly suited for the study of an old collision orogen. Thus, in the framework of the GéoFrance3D-ARMOR2 project, two passive seismological experiments were conducted in 1997 and 1999 in the Armorican Massif. The main goals concerned the characterization of the deep geometry of both shear zones, the understanding of their geodynamic bearing on the long term evolution of the Hercynian belt, the study of the lithospheric deformation, and the 3D imaging of the Champtoceaux nappes.The data allow to model seismic anisotropy and to build a 3D P-wave velocity model beneath the Armorican Massif. Crustal images do not evidence any deep rooting of the Champtoceaux nappes in the lower crust. However, the upper mantle images show a clear signal interpreted as the relic of the northward subduction which lasted until Devonian (≈350 Ma). The results also show that the North-Armorican Shear Zone is limited at depth to the crust and topmost mantle, while the South-Armorican Shear Zone can be traced over the whole lithosphere.The strong velocity contrasts are associated to probable relic thermal anomalies but are also significantly related to chemical anomalies.
Microstructural evolution of metabasalts within a contact metamorphic aureole : a preliminary quantitative bi-dimensional approach
Authors: Hebert Ronan , Guézou Jean-Claude , Souque Christine , Ballevre Michel 
Published: June 2005

Abstract
The emplacement of the Saint-Brieuc diorite (533 ± 12 Ma ; Brittany, France) developed a narrow contact aureole in metabasaltic host-rocks which were previously submitted to a regional-scale deformation and metamorphism at around 590-570 Ma. This study aims to qualify and quantify the microstructural changes of rocks that occur within the contact aureole and that are the result of the static recrystallization due to the thermal effect of the diorite. In order to quantify the textural evolution of rocks, an image analysis has been performed on thin sections. It focused on the measurements of morphological features of hornblende and opaque phases. They are anisotropy shape factors (stretching and elongation) of minerals, the preferred orientation of minerals and the distribution size (areas) of minerals. The quantification of these different parameters shows that the static recrystallization, which increases when approaching the contact with the intrusive, (i) is responsible of a reduction of the anisotropy shape and elongation parameters of grains, (ii) causes coarsening and (iii) is responsible for the disappearance of preferred orientation of minerals. Both together, the qualitative description and quantitative measurements show that the solid-state transformations due to contact metamorphism tend to make the rocks isotropic and equigranular.
Paleogeographic patterns of the Cambrian-Ordovician transition in the southern Montagne Noire (France) : preliminary results
Authors: Álvaro J. Javier , González-Gómez Cristina , Vizcaïno Daniel 
Published: June 2005

Abstract
The Cambrian-Ordovician transition in the southern Montagne Noire records a major siliciclastic regressive trend of prograding shoaling complexes (the La Dentelle Formation), separating two transgressive storm-dominated sedimentary systems of mixed (carbonate-siliciclastic) deposits. The latter comprise the underlying La Gardie and Val d’Homs Formations, and the overlying Mounio Formation, all of them displaying evidence of an important synsedimentary tectonic activity. Isolated settings of carbonate productivity, located on intra-shelf ramps and horsts, contain the richest and diversified faunistic communities comprising trilobites, echinoderms, conodonts, carbonate- and phosphate-shell brachiopods, sponge spicules, etc. Although the Cambrian-Ordovician transition of the southern Montagne Noire did not record volcanic events but a rather distensive regime inducing paleotopographies, the latter may reflect a distinct extensional regime recorded in other earliest Ordovician platforms of the French Massif Central, involving oceanization and a major magmatic activity.
Evolution of carbonated, lacustrine environment, with stromatolites : a paleoecological approach (quarry of Montaigu-le-Blin, Limagne graben, Allier, France)
Authors: Wattinne Aurélia , Vennin Emmanuelle , De Wever Patrick 
Published: June 2005

Abstract
The Aquitanian deposits of the quarry of Montaigu-le-Blin, located in the ≪ Limagne bourbonnaise », are characterized by lacustrine marl and limestone alternations. They display well-developed vegetal and fauna associations. The sedimentary deposits show an environment which allowed settlement of fresh water fauna. The deposits reveal variations of the water level and consequently of the water chemistry. These variations are characterized by alternations of anoxic and oxidizing lacustrine environments, which are due to periodic climatic changes (alternating more or less humid periods). These variations induced changes in freshwater faunal and plant associations : there are thanatocoenosis during the anoxic periods and an increasing of development of encrusting algae, responsible for the formation of algae concretions, during the oxidizing period. These oxidizing periods are also characterised by an increased hydrodynamism and terrigenous deposits from watershed. The stromatolites are numerous in the study area and show various shapes, depending on main algae, bacterial communities, and the faunal associations (caddisfly pupal cases) on the one hand, and their growth environment on the other hand. The stromatolites associations can form plurimetrical complexes which are studied in detail, and situated relatively to a paleoshoreline.
Ordovician radiolarian biodiversity : insights based on new and revised data from Kazakhstan
Authors: Danelian Taniel , Popov Leonid 
Published: June 2005

Abstract
Since the 1970s Ordovician carbonate rocks from Kazakhstan have provided well-preserved radiolarian faunas and this country remains one of the most important areas in the world to learn about Lower Palaeozoic radiolarian taxonomy and biostratigraphy. Here we describe a new lower Arenigian radiolarian assemblage and discuss all currently available Ordovician radiolarian data from Kazakhstan. The newly discovered assemblage is curiously oligospecific, despite its good state of preservation. Four morphospecies are recognised, including a new genus and two new species : Inanihella bakanasensis (Nazarov) and I.(?) akzhala n.sp, which characterise the assemblage, together with Triplococcus acanthicus n.gen n.sp. and Proventocitum sp.cf. P. procerulum. This is the oldest radiolarian assemblage from limestone lithologies of Kazakhstan and one of the very few Lower Ordovician assemblages discovered worldwide. We specify in this study the age range of the succeeding Haplentactinia armillata-Proventocitum procerulum assemblage, defined earlier by Nazarov and Popov [1980], which now covers the middle Arenigian – lower Llanvirnian (lower Abereiddian) interval. The succeeding upper Llanvirnian (Llandeilian) Haplentactinia juncta – Inanigutta unica assemblage reported by Nazarov and Popov [1980] reflects a substantial increase in radiolarian diversity, due largely to the introduction of new members of the family Inaniguttidae.
A new scenario for the Domerian - Toarcian transition
Authors: Morard Alain , Guex Jean , Bartolini Annachiara , Morettini Elena , de Wever Patrick 
Published: June 2005

Abstract
In contrast to the majority of recently published hypotheses, we believe that the main trigger for early Toarcian anoxia is neither increased primary productivity during the Tenuicostatum and Falciferum Zones nor sudden methane hydrate degassing close to the transition between these two zones.
In our opinion, this peculiar paleoceanographic episode is linked to a major, though short-lived, regression at the end of Upper Domerian. Sea-level fall resulted from sudden cooling due to increased volcanic activity. This generated global thermal insulation and subsequent glaciation. The regression is responsible for a major hiatus over NW-European epicontinental seas and is later followed by the well-known Lower Toarcian transgression. The interval corresponding to this hiatus allowed vegetation to colonise vast newly emerged surfaces. The leaching and drowning of the accumulated organohumic matter then triggered the anoxic cycle at the transgressive maximum, concomitant with a global warming.
Dynamics and age of formation of the Seram-Ambon ophiolites (Central Indonesia)
Authors: Monnier Christophe , Girardeau Jacques , Permana Hariady , Rehault Jean-Pierre , Bellon Hervé , Cotten Jo 
Published: June 2005

Abstract
The Seram-Ambon ophiolitic series comprise peridotites, websterites, gabbros and lavas. Petro-geochemical data show that the peridotites are weakly depleted rocks, except for the rare Cpx-free harzburgites. They underwent a sub-solidus metamorphic re-equilibration in the plagioclase field. The associated websterites and gabbros display various chemical features, allowing to define 3 types of websterites and 2 groups of gabbros. They have mostly BAB characteristics (presence of negative anomalies in Nb, Zr, Ti and Y), except the group 2 gabbros which have N-MORB features and the type 3 websterites which bear adakitic affinities. Lavas also display a variety of compositions, including high-Mg IAT and Mg-rich BABB with sub-alkaline affinities. Both IAT and BABB display high Th/Nb ratios which support an origin close to a continental crust environment.
Our 20 to 15 Ma 40K/40Ar ages calculated for the BABB and 15-9 Ma for the IAT show that the basin and arc formed in a very short span of time, before their obduction 9–7 Ma ago [Linthout et al., 1997]. Considering the paleogeographic situation in the Miocene [Haile, 1979 ; Haile, 1981] and our data, we propose that the Seram-Ambon ophiolites formed during the early Miocene in a small, short-lived (10 Ma), transtensive basin bordered on its east by an active margin and on its western part by a passive continental margin over which it was later obducted towards the SW direction.
U-Pb zircon age of 548 Ma for the leptynites (high-grade felsic rocks) of the central part of the Maures Massif. Geodynamic significance of the so-called leptyno-amphibolitic complexes of the Variscan belt of western Europe
Authors: Innocent Christophe , Michard Annie , Guerrot Catherine , Hamelin Bruno 
Published: June 2005

Abstract
U-Pb zircon and Rb-Sr geochronological, and Sm-Nd isotopic studies have been carried out on the so-called leptyno-amphibolitic complex of the central part of the Maures Massif. The emplacement of the protolith of the felsic end-member (« leptynites ») has been dated at 548 Ma, an age much older than those (lower Ordovician) previously obtained on other leptyno-amphibolitic complexes. Rb-Sr data obtained on whole rocks and on mineral separates give an age of 348 Ma for the amphibolite-facies metamorphism. Nd isotopes indicate that the amphibolites display clear-cut mantle-derived signatures, whereas a significant crustal contribution is recorded in the three analyzed felsic facies. One of these acidic terms can be interpreted in terms of a simple mixing between two components, respectively similar to the amphibolites and to the two other felsic samples. These latter involve another mantle source, distinct from that of the amphibolites, and comparable to that of continental alkali basalts. These data indicate that the central part of the Maures Massif and the southern Massif Central were possibly part of the same pre-Variscan structural unit. The lack of evidence for a clear genetic relationship between the respective protoliths of the two end-members of the leptyno-amphibolitic complex raises once again the problem of the geodynamic significance of these formations.
Chronostratigraphy of the key Upper Miocene (Lower Turolian) sequence of la Montagne d’Andance (Ardèche, France). Implications of new 40Ar/39Ar laser fusion and unspiked K-Ar dating of trachytic tephra and basalts
Authors: Pastre Jean-François , Singer Brad S. , Guillou Hervé , Pupin Jean-Pierre , Riou Bernard 
Published: June 2005

Abstract
A trachytic tephra layer deposited in the lower part of the Upper Miocene (Turolian) diatomite sequence at la Montagne d’Andance (Coiron basaltic province, France) contains glass shards (73 % SiO2), plus crystals of sanidine, ilmenite, biotite, amphibole, clinopyroxene, zircon, sphene and apatite. This composition and other volcanological data suggest a correlation to the Cantal stratovolcano, 150 km distant, better than to the nearer (50 km) Mézenc area. The 7.54 ± 0.06 Ma (± 2 σ) isochron defined by eight 40Ar/39Ar laser fusion analyses of sanidine gives a precise age for the beginning of the fossiliferous sequence, known for its rich flora and fauna. Moreover, unspiked K-Ar ages determined from three basaltic lava flows that pre- and post-date the lacustrine sedimentation are 7.37 ± 0.06, 7.17 ± 0.06 and 7.13 ± 0.06 Ma (± 2σ), thereby bracketing the sequence to a 400 kyr period between ca. 7.5 and 7.1 Ma. These are the first radioisotopic constraints for the lower part of the Turolian continental stage. They imply an age about 20 % younger for the fauna than proposed by previous biostratigraphic correlation. This new chronology is consistent with correlation of the lower limit of the Turolian to the Tortonian-Messinian boundary (7.30 ± 0.15 Ma) of the global marine stages.
65 m.y.-long magmatic activity in Sumatra (Indonesia), from Paleocene to Present
Authors: Bellon Hervé , Maury René C. , Sutanto  , Soeria-Atmadja Rubini , Cotten Joseph , Polvé Mireille 
Published: June 2005

Abstract
Sumatra is the largest volcanic island of the Indonesian archipelago. The oblique subduction of the Indian Ocean lithosphere below the Sundaland margin is responsible for the development of a NW-SE trending volcanic arc, the location of which coincides approximately with the Great Sumatran Fault Zone (GSFZ). We present in this paper ca. 80 new 40K-40Ar ages measured on Cenozoic calc-alkaline to shoshonitic magmatic rocks sampled all along this arc from Aceh to Lampung. The results show that magmatic activity started during the Paleocene (ca. 63 Ma) all along the arc, and was more or less permanent until Present. However, its spatial distribution increased at ca. 20 Ma, a feature possibly connected to the development of the Great Sumatran Fault. The position of Plio-Quaternary magmatic rocks is shifted away from the trench by a few tens of kilometres with respect to that of Paleocene to Miocene ones, a feature consistent with a significant tectonic erosion of the Sundaland margin during the Cenozoic.
The studied samples display typical subduction-related geochemical signatures. However, we have been unable to identify clear geochemical trends, either spatial or temporal. We suggest that the lack of such regular variations reflects a complex igneous petrogenesis during which the contribution of the Sundaland continental crust overprinted those of the mantle wedge and the subducted slab.
A sequence analyzed from the basin to the platform : the Middle Oxfordian calcareous succession in southeastern France
Authors: Gaillard Christian , Emmanuel Laurent , Hanzo Micheline , Lathuiliere Bernard , Atrops François , Bodeur Yves , Bouhamdi Abdelkader , Marchand Didier , Enay Raymond , Ruget Christiane , Werner Winfried 
Published: June 2005

Abstract
Middle Oxfordian sedimentation is very homogeneous in southeastern France. It is characterized by a specific alternation of marls and fine-grained limestones (G. transversarium Zone). This work shows that sets of calcareous beds allow accurate stratigraphic correlations in various paleogeographic areas, from the shallow Jura platform to the deep Dauphinois basin. Following a rifting period, this sedimentation illustrates a doming period with decreasing subsidence and water depth. This corresponds to the establishment of a wide marine area more favourable to carbonate sedimentation. Considering sequence stratigraphy, some slight variations occur in the sediment record and lead to interesting comparisons between the platform and the basin. The geochemical evolution, mainly the manganese content, seems to be dependant of the activity of the Ligurian Tethys oceanic ridge. This fact shows that sedimentation in southeastern France could be significantly controlled by tectono-eustasy.
Radiolarian Cretaceous age of Soulabest radiolarites in ophiolite suite of eastern Iran
Authors: Babazadeh Seyed Ahmad , De Wever Patrick 
Published: June 2005

Abstract
The ophiolite-flysch range (accretionary prism) of the Sistan suture zone from eastern Iran includes several intensely deformed tectonic units, some of which consist of volcaniclastic rocks, volcanic rocks, siliceous pelagic sediments (cherts and radiolarites) and calcareous rocks (deep marine, platform), whereas others are represented by terrigenous turbidites. The Soulabest radiolarites are located in the Ratuk complex of the Tirrul’s subdivision [Tirrul et al. , 1983], or in the ophiolite suite of the Gazik province.
The local biostratigraphy of this region is based on two faunal assemblages. Faunal assemblage I is dated early Aptian, faunal assemblage II is attributed to middle-late Albian. The most abundant fauna is found in the middle-late Albian. The timing of the oceanic opening in eastern Iran remained questionable until now. The study of the radiolarites of the Soulabest area provides new data for dating the primary opening between two microcontinents : the Lut and Afghan blocks. It is proposed that the oceanic opening of the two blocks occurred prior to the early Aptian. In previous reports, the age of opening was attributed to Upper Cretaceous.
All reported Radiolaria are found in red radiolarites and green-red argillaceous cherts. This formation is unconformably overlain by Maastrichtian conglomerates. It indicates that the closure of the basin occurred in Maastrichtian age.
Late Hercynian leucogranites modelling as deduced from new gravity data : the example of the Millevaches massif (Massif Central, France)
Authors: Gebelin Aude , Martelet Guillaume , Brunel Maurice , Faure Michel , Rossi Philippe 
Published: June 2005

Abstract
The Millevaches granitic complex, located in the northern part of the French Massif Central, is elongated in a N-S direction, perpendicular to the main E-W trend of the Hercynian belt. It is affected on its limits and in its core by several ductile shear zones that have necessarily played a great role in the emplacement and exhumation of the massif. Based on gravity modelling and recent field observations, this study intends to highlight the massif structure at depth and discuss its mode of emplacement and relations with the surrounding terrains.
The new gravity and density measurements on the north-east part of the Millevaches massif improve the gravity coverage of the northern Limousin. Using these new data we model the deep structure of the Millevaches plateau. The density measurements made on the different types of granites of the massif, and on the surrounding terrains improve the interpretation of the Bouguer anomaly. Analysis and inversion of the residual Bouguer anomaly in the area show that the Millevaches massif is 2 to 4 km-thick, from north to south and from west to east, locally rooting down to about 6 km deep in its eastern and southern terminations. These two zones coincide with porphyritic plutons and, because of the complex composite structure of the massif, cannot be definitively interpreted as feeding zones. In the field, the N-S-oriented Pradines vertical fault affects the core of the massif on 4 to 5 km width. Microstructural observations evidence that the faulting is contemporaneous of the granites emplacement. We suggest that this tectonic lineament could have triggered the migration of the magma, although it is not related to a clear gravity anomaly. AMS measurements in the north-central part of the Millevaches massif suggest that the magnetic foliation and lineation display a general sub-horizontal pattern. Moreover, on the western border of the Millevaches massif, the Argentat deep seismic profile shows sub-horizontal layering of gneisses and micaschists and evidences normal faulting offset of this layering along Argentat fault. This agrees fairly well with the gravity results, suggesting that (i) the Millevaches massif would be at a high structural level in the crust, (ii) the exhumation of the massif would have been favoured along the Argentat normal fault. As a whole, the massif can be described as a laccolith, 2 to 4 km-thick, emplaced as a “magmatic lens” into the sub-horizontally foliated gneisses and micaschists.