Jean-Yves Calvez - Academia.edu (original) (raw)

Papers by Jean-Yves Calvez

Geologische Rundschau

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Precambrian Research, 1993

Abstract The Precambrian basement of northern Mozambique is composed mainly of high-grade gneiss,... more Abstract The Precambrian basement of northern Mozambique is composed mainly of high-grade gneiss, granulite, migmatite and orogenic plutonic rocks emplaced and deformed during the Mozambican orogeny between 1100 and 850 Ma. Granulite nappes (Lurio ...

Journal of African Earth Sciences, 1994

The Rei Bouba Group is a sedimentary and volcanic sequence (750-?650 Ma), regarded as a remnant o... more The Rei Bouba Group is a sedimentary and volcanic sequence (750-?650 Ma), regarded as a remnant of a Pan-African (back-arc?) orogenic basin that separated a remobflized Paleoproterozoic crust from an accretionary area (Poli Complex: 800-650 Ma). The latter was subjected to early deformation (D1) and intruded by calc-alkalic plutons (670 Ma). Transpreesive tectonics and major thrusting, with emplacement of synkinematic granite, occun~ at ca 630 }via (D2-3) and a late compression (D4), with emplacement of calc-alkalic granite, occonned at ca 570 Ma. The Tchollir~ Shear Zone is regarded as part of the major boundary between a recently accreted crust and the remobflized ma~ of the Congo Craton. R~sum~-Le Groupe de Rei Bouba eonsiste en une s&luence s&limentaire et volcanique (750-?650 Ma) etest eonsid~n~ comme une relique de hassin oros~que (ha~in d'arri~arc?) pan-africain qui s~arait une cro6te pal~oprotCm~o~que remobilh~ d'une zone d'accr~ion (complexe de Poll: 800-650 Ma); cette derni~ a ~t~ affec~ par une d~formation pr~oce (DI) eta ~ intmd~ par des plutons calco-alcalins (670 Ma). Une tectonique transpressive avec charrlages majeurs et accompagn~e de granites syn-cin~matiques s'est d&uul~e vers 630 Ma (D2/3); des granites calco-alcalins, li~s/h une compression tardive (D4), ont ~q~ dates a 570 Ma. La zone transcurrente de TchoUire est consid~e comme la limite principale entre la cro6te n~.oforn~ et la marge remobilis~ du craton du Congo.

Earth and Planetary Science Letters, 1988

Isotopic (Sr, Nd, Pb) and trace element data are reported for samples dredged along the SouthEast... more Isotopic (Sr, Nd, Pb) and trace element data are reported for samples dredged along the SouthEast Indian Ridge (SEIR). They confirm the existence of a geochemical province under the Indian Ocean which is distinct from the provinces observed under the North Atlantic and Pacific Oceans. This province is characterized by the association of Sr and Nd isotopic enrichment features with a depleted Pb signature and of magmaphile element depletion features (low (La/Sm)N , (Nb/Zr)N, Rb/Sr with high Sm/Nd ratios). On a regional scale, the data emphasize the strong relationship existing between the physical structure of the ridge system and its chemical characteristics. It is suggested that these chemical characteristics are the result of contribution of different mantle sources corresponding to different structures of the ridge system:-" normal ridge" segments,-the ridge segment located on an immediately north of the St. Paul-Amsterdam massif,-off-axis structures located on the structural link between Broken Ridge and Kerguelen. In a model of ocean differentiation from Bulk Earth, it is suggested that SEIR mantle sources are the result of separate episodes of differentiation, all taking place more recently than the differentiation of the Atlantic and Pacific oceans.

Contributions to Mineralogy and Petrology, 1978

... The Lower Brioverian, composed first by a pile detrital, volcanic or volcanosedimentary serie... more ... The Lower Brioverian, composed first by a pile detrital, volcanic or volcanosedimentary series was folded and ... the Mancellian domain to the east, is a very thick Brioverian series with little regional metamorphism (except for local diapiric intrusion of the Saint-Malo anatectic dome ...

Chemical Geology, 1988

21 samples of sulphide liquids txapped either as globules or grains in various minerals (olivine,... more 21 samples of sulphide liquids txapped either as globules or grains in various minerals (olivine, pyroxene, clinopyroxene, ilmenite and garnet) or rocks (basalt glasses, peridotites, eclogites and kimberlitas) of mantle origin, have been analysed for their sulphur isotope, and Cu, Ni, Fe compositions by ion microprobe. The results show a wide range of ~34S values between-4.9+1%~ and +8+1%. Sulphides with high nickel contents (up to 40% pentlandite), corresponding mostly to type I peridotites (Lets, Beni Bousera, Ronda,...), have 834S values ranging from-3.27,w to +3.6°/*0 with a mode of +3-+10/~, compared to low Ni content sulphides, mostly contained in type I~ peridotites, OIB (Hawaii, Tahiti,...) and South-African ldmberlites, ranging from-3.6%0 to +80/~ with a mode of +l_+lg',w. These results show a large heterogeneity of the sulphur isotope compositions of the sulphides originating from the mantle. In spite of the high temperature of melting, a significant sulphur isotope fractionation (+2 + 1%~) between immiscible sulphide melts and sulphur dissolved in the silicate melt is suggested by the present data. The sulphide globules with high Ni-contents and 834S values close to +3%0, are probably produced by 10-20% partial melting of a mantle source containing 300 ppm sulphur as an upper limit and having a ~34S value of +0.5_+0.5%0. The mass balance of sulphur isotopes in the system upper mande+oceanic crust+continental crust+seawater requires a mean 834S value of the depleted upper mantle of +0.50/00, significantly different from the ~34S value of ordinary chondrites (+0.2-+ 0.2%e, Thode et al., 1961) but towards that of lunar basahs (1.2V~, Kaplan et al., 1970). RECYCLED OCFANIC LITHOSPHERE IN THE BENI BOUSERA

Canadian Journal of Earth Sciences, Nov 1, 1988

Galena Pb-isotope ratios of epithermal vein and disseminated sulfide occurrences in the Taconian ... more Galena Pb-isotope ratios of epithermal vein and disseminated sulfide occurrences in the Taconian Orogen and Siluro-Devonian basin cluster around 17.90–18.05 for 206Pb/204Pb and 37.70–38.00 for 208Pb/204Pb. The major source of Pb in most, if not all, occurrences is a fairly common continental crust, a characteristic found in published analyses of Grenville feldspar Pb. A southwest to northeast increase in galena 206Pb/204Pb ratios is ascribed to the supply of several types of detritus from Grenville basement during the Cambro-Ordovician: coarse-grained, K-feldspar-bearing in the southwest, grading into fine-grained phyllitic, and relatively more highly radiogenic in the northeast.Emplacement (i) of Pb–Zn–barite veins and disseminations, commonly of homogeneous crustal Pb-isotopic signature, was late Taconian; (ii) of Pb–Zn–quartz veins, of less homogeneous signature, was post-Taconian; and (iii) of Pb–Zn–carbonate veins, relatively highly radiogenic and commonly homogeneous, was late or post-Acadian. Signatures of the first-mentioned group seem to be most useful in exploration.

Les methodes classiques de la geologie structurale ont pour but de reconstituer l'histoire de... more Les methodes classiques de la geologie structurale ont pour but de reconstituer l'histoire de la croute continentale, et pour un domaine donne; d'etablir d'une part, une chronologie des differents orogenes que l'on y observe et d'autre part, de caracteriser les evenements magmatiques, metamorphiques et structuraux, lies au developpement de chaque orogene. Cependant, la superposition des differents evenements orogeniques successifs peut compliquer l'etablissement d'un schema evolutif de ces orogenes, et ainsi rendre problematiques les correlations entre domaines appartenant a une meme chaine. L'un des buts de la geochronologie est d'etablir des reperes chronologiques absolus a l'interieur d'un meme domaine, afin de relier les differents .evenements lies a l'evolution orogenique.

Petrology and Structural Geology, 1991

A Pb isotope study was carried out on three main types of Cu(Au) hydrothermal mineralization in t... more A Pb isotope study was carried out on three main types of Cu(Au) hydrothermal mineralization in the allochthonous terrains of northern Oman: (1) the Al Ajal sulphide-hematite deposit of Late Permian age; (2) massive sulphide deposits emplaced during a major break in the Late Albian-Early Cenomanian volcanic activity; and (3) minor massive sulphides deposited during breaks in the Cenomanian-Turonian volcanic episode.

Revue numismatique, 1985

Nicolet-Pierre Hélène, Barrandon Jean-Noël, Calvez Jean-Yves. Monnaies archaïques d'Athènes s... more Nicolet-Pierre Hélène, Barrandon Jean-Noël, Calvez Jean-Yves. Monnaies archaïques d'Athènes sous Pisistrate et les Pisistratides (c. 545-c. 510) II. Recherches sur la composition métallique des Wappenmünzen. In: Revue numismatique, 6e série - Tome 27, année 1985 pp. 23-44

Precambrian Research, 1982

Marine Geology, 1994

Three cores from different Red Sea deeps were analysed for Sr-Nd isotopes and REE. Non-metallifer... more Three cores from different Red Sea deeps were analysed for Sr-Nd isotopes and REE. Non-metalliferous biodetrital sediment from the Shaban Deep was used as reference. Its REE-pattern characteristics are similar to those of normal detrital sediment, whereas the Sr and Nd isotope ratios (0.7092 and eNa=-4.7) are consistent with deposition from seawater. Sediment of the most metal-enriched hydrothermal core from the Atlantis II Deep shows HREEodepleted patterns with a large positive Eu anomaly, typical of high-temperature fluids. Sr and Nd isotope compositions are the same throughout the core (0.7075 and end =-0.9) and very different from those of the Shaban Deep. The third core, also from the Atlantis II Deep, consists of biodetrital sediment at the base and of increasingly metalliferous sediment toward the top. The positive Eu anomaly becomes larger as STSrff6Sr decreases upward reaching a maximum Eu/Eu* value at 2.58 and a minimum STSr/a6Sr at 0.7076. Sediment containing fish remains (Oudin and Cocherie, 1988) has a high ~REE (776 ppm), its high end (+4.0) indicating that the fluid interacted with underlying basalt. To construct the curve of Nd-evolution in seawater with time, use of the Nd isotope composition of sediment must be accompanied by REE determinations, in order to select samples without potential hydrothermal fluid interaction, as the latter can increase the isotope ratio of Nd.

Journal of Geochemical Exploration, 1989

The Ariab district is part of a vast Late Proterozoic volcanosedimentary complex that extends for... more The Ariab district is part of a vast Late Proterozoic volcanosedimentary complex that extends for 250 km in the Red Sea Hills Province of northeastern Sudan. It includes numerous polymetallic sulphide bodies of exhalative origin and associated economically important auriferous mineralization with quartzbarite breccias. One hundred Pb-isotope analyses have been made of sulphides, gossans, and quartz-barite breccias essentially from the two main prospects of the district, Hassai and Hadal-Awatib. All the samples are rich in Pb (50-200 ppm average) and poor in U (< 1 ppm). RESULTS AND DISCUSSION Hassai Lead-isotope studies have been made of 12 sulphide samples taken from various mineralized levels in four drill cores. The isotopic compositions fall into three groups according to their 2°~pb/2°4pb ratios: 17.42 + 0.03,17.60 + 0.03, and 17.80 + 0.01. Numerous reports in the literature show that polymetallic bodies of exhalative origin throughout the world are characterized by marked Pb isotopic homogeneity, with a maximum variation of 0.2%. The 2°Spb/2°4pb values grouped around 17.42, therefore, most probably belong to sulphides from a single mineralized body (Type 1) intersected by more than one drill hole. Similarly, the values grouped around 17.80 will be those of sulphides belonging to a second mineralized body (Type 2).