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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Mineralium deposita 12 (1977), S. 263-279 
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Stratiform Cu-Pb-Zn (-Au-Ag) mineralization associated with black carbonaceous schists and acid metatuffs is restricted to distinct horizons within the Cretaceous sequence of the Diahot region. The sulphides occur in sharply bounded lenses which show varying degrees of compositional banding conformable with the foliation of the country schists. The deposits are sedimentary-exhalative of the Rio Tinto-type and have been modified by mid-Tertiary high-pressure metamorphism (lawsonite-albite and glaucophanitic greenschist facies). The ores are not strongly deformed by the metamorphism and sedimentary structures, pyrite framboids and atoll structures are preserved in some deposits. With increasing metamorphic grade sphalerite becomes more iron-rich, pyrrhotite becomes more abundant, and the sulphides show a general increase in grain-size which parallels that of the silicates in the enclosing rocks. In the more highly metamorphosed deposits the sulphide associations are retrograde assemblages. There is no evidence of large-scale metamorphic remobilization of sulphides. No differences were observed in either the sulphide assemblages or in the composition of the sulphides to indicate that the metamorphism was of the high pressure rather than the low pressure type.
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 211 (1966), S. 725-726 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The field evidence for the age of these intrusions has not been conclusive. The Paritu Tonalite1 intrudes a basement sedimentary sequence which may have begun in the Permian1 and extended through to possible Jurassic2. Fossil control is poor. These rocks are overlain by terrestrial volcanics which ...
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  • 3
    ISSN: 1523-9829
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Technology , Medicine
    Notes: Abstract The goal of the Image Guided Therapy Program, as the name implies, is to develop the use of imaging to guide minimally invasive therapy. The program combines interventional and intraoperative magnetic resonance imaging (MRI) with high-performance computing and novel therapeutic devices. In clinical practice the multidisciplinary program provides for the investigation of a wide range of interventional and surgical procedures. The Signa SP 0.5 T superconducting MRI system (GE Medical Systems, Milwaukee, WI) has a 56-cm-wide vertical gap, allowing access to the patient and permitting the execution of interactive MRI-guided procedures. This system is integrated with an optical tracking system and utilizes flexible surface coils and MRI-compatible displays to facilitate procedures. Images are obtained with routine pulse sequences. Nearly real-time imaging, with fast gradient-recalled echo sequences, may be acquired at a rate of one image every 1.5 s with interactive image plane selection. Since 1994, more than 800 of these procedures, including various percutaneous procedures and open surgeries, have been successfully performed at Brigham and Women's Hospital (Boston, MA).
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  • 4
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract Mg–Fe carpholite is widespread in the Diahot region of New Caledonia in highly aluminous schists and as veins in what was originally a clay-rich hydrothermal alteration envelope about massive suphide deposits. These carpholites have Fe/(Fe + Mg) ratios of 0.03–0.65 and no significant Mn component. Mg-carpholite + quartz occur in assemblages with chlorite or pyrophyllite, pyrophyllite + kaolinite and pyrophyllite + diaspore. Temperatures of 230–320° C and minimum pressures of 7 kbar are indicated for the Mg–Fe carpholite-bearing rocks. The regional distribution of aragonite and Mg–Fe carpholite parallel to a major zone of dominantly transcurrent movement and oblique to the trend of the subduction complex indicates the high-P/low-T schists owe their rapid uplift and preservation to the vertical component of the transcurrent faulting.
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  • 5
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract The Mesozoic Murihiku and Waipapa terranes are two accretionary wedges of linked forearc and trench sediments, respectively, that were juxtaposed in the early Cretaceous.Late Triassic to late Jurassic Murihiku terrane volcaniclastic sediments are folded into a regional syncline and have been diagenetically altered. There is a general relationship between zeolite occurrence, clay mineralogy, vitrinite reflectance and stratigraphic position. Youngest Jurassic sediments contain heulandite, analcime and stilbite, whereas late Triassic to mid-Jurassic sediments have laumontite and heulandite (in detail the zeolite distribution is complicated). Tuffaceous horizons on the eastern limb of the syncline are calcitized rather than zeolitized. Post-diagenetic fractures associated with uplift are laumontite-filled. The inferred geothermal gradient is c. 15° C km−1.The Waipapa terrane is an accretionary complex dominated by imbricated terrigenous sediments of Triassic and Jurassic age with enclosed Permian to Jurassic pelagic sediments and basalts. Late Jurassic sediments are massive volaniclastic sandstones. The sediments are non-foliated, and metamorphic minerals in the massive sandstones have crystallized in specific domains. The observed metamorphic succession of prehnite-pumpellyite and pumpellyite-actinolite facies assemblages was overprinted in the imbricated rocks during a thermal event that was late in the deformation sequence and broadly coincident with hydraulic fracturing and veining.The metamorphic successions in the two terranes and their relationships to structural features are in excellent accord with accretionary complex models.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 5 (1987), S. 0 
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract Chloritoid-bearing metasedimentary rocks occur in close proximity to blueschists and eclogites in the Tertiary high-pressure metamorphic belt of northern New Caledonia. The typical assemblage of chloritoid-bearing rocks in the epidote zone is quartzchlorite-muscovite-garnet-chloritoid. In the omphacite zone, epidote is an additional member of the chloritoid-bearing assemblage. Paragonite is rare, plagioclase was not detected, and rutile and ilmenite are the Fe-Ti oxide phases. Chloritoid-glaucophane is not a common assemblage. Chloritoid-bearing rocks have relatively low (Ca+K+Na)/Al ratios and the chloritoids are relatively Mg-rich with Mg/ (Mg+Fe) up to about 0.4. A comparison of the mineral assemblages and mineral chemistry with experimental and computed phase equilibria suggest an upper temperature limit near 560° C in the omphacite zone and a minimum temperature limit near 450° C at 10 kbar. An empirical garnet-chlorite Fe-Mg exchange thermometer does not yield consistent results for the higher-grade rocks, suggesting Ts ranging from 390 to 535° C in the omphacite zone and 420–465° C in the epidote zone. The distribution coefficient KD= (Fe/Mg)ctd/(Fe/Mg)chl for chloritoid and chlorite ranges from 3.9 to 6.4, values which are lower than those (=10) from lower greenschist facies rocks, but are near those of upper greenschist facies and albite-epidote amphibolite facies.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 68 (1978), S. 63-78 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The northern portion of the Tertiary high-pressure schist belt in New Caledonia contains, from west to east, a metamorphic progression from lawsonite-albite facies through glaucophanitic greenschists to eclogitic albite-epidote amphibolites. This belt is flanked to the west by Upper Cretaceous-Eocene metasediments, of prehnite-pumpellyite grade. Paraschists throughout this whole sequence contain abundant carbonaceous material which shows a progressive metamorphism from coal to graphite. Structural analysis of lithostatic load and oxygen isotope data have provided a PT profile for the carbon metamorphism. In the prehnite-pumpellyite metasediments, phytoclasts were progressively coalified to anthracite rank under PT conditions which extended up to 3 kb/255 ° C at the lawsonite isograd where graphite first appears. On the high grade side of the lawsonite isograd a transitional mixed zone of continued coalification and graphitization occurred within the PT range 3 kb/255 ° C to 5.5 kb/335 ° C which included the ferroglaucophane isograd. Immediately beyond this zone all phytoclasts were completely graphitized before the epidote isograd was reached at 6.3 kb/ 390 ° C. The prevailing metamorphic environment retarded coalification, but accelerated graphitization, under conditions of high pressure and a low temperature gradient (7 ° C/km) that had been generated within the sedimentary pile by rapid tectonic thickening and consequent deep burial.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 65 (1977), S. 69-78 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A regional melange zone, 150 km long and 30 km wide, forms the southern boundary and structural capping to a high-pressure blueschist belt in northern New Caledonia. The disrupted country rocks in the melange zone are Mesozoic metagrey-wackes and Eocene chert-limestone sequences which have been penetrated from below by tectonically-injected ophiolite slivers containing metamorphosed serpentinite, gabbro, dolerite, basalt, tuff, chert and shale. An ocean crust origin for these rocks is indicated by chemical, mineralogical and radiometric data from coastal outcrops at Anse Ponandou on the northeast coast. The age (41 m.y.), metamorphic environment (350 ° C at 7 kb), and mineral association (acmitic jadeite-riebeckite-pyropic spessartine-pistacitic epidote-lawsonite-high Si phengite) are significantly different from those of the adjacent regional high-pressure schist belt, indicating a separate structural site for blueschist metamorphism of buried ophiolitic ocean crust during early Tertiary orogenesis.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 91 (1985), S. 151-162 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract In the New Caledonia high-pressure schists pyrite, pyrrhotite, chalcopyrite, rutile and sphene are common phases while hematite and ilmenite are rare and magnetite is absent. The parageneses of these minerals were clarified from their occurrence as inclusions in garnet, from phase relations in the Cu-Fe-S and Fe-Ti-O-S systems, and from phase rule considerations for the multi-component system. The sulfur fugacity estimated for pelites and basites containing pyrrhotite, pyrite and rutile increased with increasing metamorphic grade; the oxygen fugacity in these schists was less than 10−27.6 bars at 400° C, 10 kb and 10−22.3 bars at 500° C, 11 kb. Among the other components of the metamorphic fluid in pelites, H2O was major, CH4, CO2 and H2S minor, and H2, CO, COS and SO2 rare. The fluid composition altered with advancing metamorphic grade, such that H2O decreased while CO2, CH4 and H2S increased, and this change was linked to concurrent massive decarbonization in the rock matrices.
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  • 10
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