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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 22 (2004), S. 0 
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A combined metamorphic and isotopic study of lit-par-lit migmatites exposed in the hanging wall of the Main Central Thrust (MCT) from Sikkim has provided a unique insight into the pressure–temperature–time path of the High Himalayan Crystalline Series of the eastern Himalaya. The petrology and geochemistry of one such migmatite indicates that the leucosome comprises a crystallized peraluminous granite coexisting with sillimanite and alkali feldspar. Large garnet crystals (2–3 mm across) are strongly zoned and grew initially within the kyanite stability field. The melanosome is a biotite–garnet pelitic gneiss, with fibrolitic sillimanite resulting from polymorphic inversion of kyanite. By combining garnet zoning profiles with the NaCaMnKFMASHTO pseudosection appropriate to the bulk composition of a migmatite retrieved from c. 1 km above the thrust zone, it has been established that early garnet formed at pressures of 10–12 kbar, and that subsequent decompression caused the rock to enter the melt field at c. 8 kbar and c. 750 °C, generating peritectic sillimanite and alkali feldspar by the incongruent melting of muscovite. Continuing exhumation resulted in resorption of garnet. Sm–Nd growth ages of garnet cores and rim, indicate pre-decompression garnet growth at 23 ± 3 Ma and near-peak temperatures during melting at 16 ± 2 Ma. This provides a decompression rate of 2 ± 1 mm yr−1 that is consistent with exhumation rates inferred from mineral cooling ages from the eastern Himalaya. Simple 1D thermal modelling confirms that exhumation at this rate would result in a near-isothermal decompression path, a result that is supported by the phase relations in both the melanosome and leucosome components of the migmatite. Results from this study suggest that anatexis of Miocene granite protoliths from the Himalaya was a consequence of rapid decompression, probably in response to movement on the MCT and on the South Tibetan detachment to the north.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Mineralogy and petrology 70 (2000), S. 165-198 
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Die wichtigsten Seltene-Element-Pegmatite von Ontario liegen im Gebiet des Separation Lake. Sie umfassen die Petalit-Pegmatit-Systeme von Big Whopper und Big Mack, potentiell die weltweit zweitgrößte Lithiumlagerstätte dieses Typs. Die Pegmatite treten in zwei Gangsystemen in der Nähe des Separation Rapids Plutons auf, der die Quelle der seltenen Elemente sein dürfte. Am weitesten verbreitet sind Beryll-Pegmatite, sowie komplexe Pegmatite des Petalit-Subtyps und, untergeordnet, Pegmatite die Ähnlichkeiten mit dem Lepidolith-Subtyp zeigen. Columbite-Tantalite zeigen ein weites Spektrum von Zusammensetzungen, von primitivem Ferrocolumbit fast bis zu dem Endglied, Manganotantalit. Die Evolution der Schmelzen führte zu erhöhter Fluor-Aktivität (erkennbar an den Zusammensetzungen des Mikroliths). An seltenen Elementen angereicherte Nester mit Lithium-Glimmer, Fluorapatit und Cleavelandit gehen auf in-situ Fraktionierung von Magma in einzelnen Pegmatiten zurück. BSE-Bilder zeigen Zonierungs-Muster mit primären Zusammensetzungen von Columbit-Tantalit, die durch sekundäre Prozesse verändert wurden. Letztere stehen mit extremer Fraktionierung in Zusammenhang und mit der späten Entstehung albitischer Bereiche in einzelnen Pegmatiten. Diese Umwandlung führte zur Rekristallisation von Columbit-Tantalit und zu niedrigeren Ta-Gehalten, bei gleichbleibendem Mn.
    Notes: Summary The Separation Lake area is host to the most important rare-element pegmatites in Ontario, Canada. They include the Big Whopper and Big Mack petalite pegmatite systems which potentially represent the world's second largest lithium deposit of this type. The pegmatites occur in two distinct clusters adjacent to the Separation Rapids pluton which is thought to be the source of the rare-elements. Beryl-type and complex-, petalite-subtype pegmatites are the most common and a few pegmatites have characteristics similar to the lepidolite-subtype. This study reveals that columbite-tantalite in the pegmatites has an extremely wide range of composition from primitive ferrocolumbite to evolved, almost end-member manganotantalite. Evidence is provided that melt evolution resulted in increased fluorine activity (as seen in microlite compositions) and that in situ fractionation of magma within individual pegmatites often led to the crystallization of rare-element-enriched, Li mica-fluorapatite-cleavelandite pods. Zonation patterns seen in backscattered electron images show primary compositions of columbite-tantalite were modified by secondary processes related to extreme fractionation and involving the late stage development of albitic units in individual pegmatites. This alteration led to recrystallization of columbite-tantalite and produced compositions with lower Ta contents, but with little change in Mn content.
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  • 3
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The 1983 hawaiite of Mount Etna was sampled and analyzed for groundmass and mineral compositions, rare-earth-element concentrations and Sr-Nd isotope ratios. Microprobe data for coexisting mineral phases and glass show crystallization temperatures of around 1100° C from a rather differentiated hawaiite magma at rather highfO2 (10−8 at 1100° C), well above the QFM buffer. The hawaiites are characterized by a marked enrichment in the light REE similar to other alkaline magmas: the (Ce)N/(Yb)N is greater than 10, a feature these hawaiites have in common with alkaline magmas erupted earlier on Mount Etna. Since the Ce/Yb ratio cannot be affected by fractionation of clinopyroxene and plagioclase, it is taken as an accurate reflection of the LREE-enriched nature of the hawaiites. From this point of view, the Etnean hawaiites are identical to within-plate alkaline magmas erupted on the Hawaiian islands. This similarity extends to the Nd-Sr isotope features. Two hawaiites have87Sr/86Sr=0.70346 and 0.70352 and143Nd/144Nd=0.51286 and 0.51284. These data indicate a source similar to oceanic-island basalts, a source depleted in Rb/Sr and Nd/Sm for some period of time. The Sr isotope data are identical to that previously reported for Mount Etna. Extraction of hawaiites from depleted source regions requires either recent enrichment events, mixing of asthenospheric and lithospheric melts, or variable degrees of melting. At present, the data do not allow a clear decision. The peculiar tectonic setting of Mount Etna, between the relatively undeformed African foreland and the active Aeolian volcanic islands, may suggest contributions to the source region from subduction and within-plate processes. Etnean lavas have a geochemical imprint of subduction-related enrichment processes, and they also share petrological and chemical features identical to oceanic-island basalts whose source region has been affected by within-palte enrichment processes.
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  • 4
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    Unknown
    PANGAEA
    In:  Supplement to: Pearce, Julian A; Rogers, Nick; Tindle, A J; Watson, J S (1986): Geochemistry and petrogenesis of basalts from Deep Sea Drilling Project Leg 92, eastern Pacific. In: Leinen, M; Rea DK; et al. (eds.), Initial Reports of the Deep Sea Drilling Project, Washington (U.S. Govt. Printing Office), 92, 435-457, https://doi.org/10.2973/dsdp.proc.92.126.1986
    Publication Date: 2023-05-12
    Description: Basalts recovered on DSDP Leg 92 include all the major basalt types so far recovered from the ocean crust of the eastern Pacific. Basalts from Holes 597, 597A, 597B, 597C, and 599B are tholeiites exhibiting all the mineralogical and geochemical characteristics of N-type mid-ocean ridge basalts (MORB). Fragments of ferrobasalts and alkali basalts were also obtained, however, from Holes 60IB and 602B, respectively. Hole 597C, which penetrated 91 m into basement and is the deepest hole so far drilled in fast-spreading crust, yielded basalts that can be divided into three major lithologic units. The lowest unit, Unit III, contains modal olivine and comprises basalts which, at about 8 to 10% MgO, are as basic as any sampled from fast-spreading crust. The middle unit, Unit II, is the most evolved; its basalts are olivine free and contain between 6 and 7.5% MgO. The upper unit, Unit I, is intermediate in composition between Units II and III; it is characterized by both modal olivine and glomerocrysts made up of plagioclase and rare olivine. Unit I is probably a massive flow, whereas Units II and III may be massive flows or sills. The basalts appear to have undergone three stages of alteration ("deuteric," "relatively reducing," and "oxidizing"), the intensity of alteration decreasing markedly downcore. Hole 597B, at 26.4 m of basement penetration the only other "deep" hole, contains just one lithologic unit, which closely resembles Unit I of Hole 597C. Petrogenetic modeling reveals that the three lithologic units in Hole 597C are cogenetic and that they were derived from a depleted mantle source similar to the source of the tholeiites and ferrobasalts sampled in other holes; the alkali basalts are the only rocks derived from enriched mantle. Lavas of Unit III probably lay on the olivine-plagioclase cotectic, whereas the other lavas lay on an olivine-plagioclase-clinopyroxene peritectic. Some 60% of closed-system crystallization is needed to generate the most-evolved from the last-fractionated tholeiite, and a further 50% crystallization (80% overall) is needed to generate the ferrobasalts. Xenocrysts of calcic plagioclase and pseudomorphosed olivine in tholeiites from Hole 597B and Unit I of Hole 597C, and in the ferrobasalts from Hole 601B, provide evidence, however, that some magma mixing may have taken place.
    Keywords: Deep Sea Drilling Project; DSDP
    Type: Dataset
    Format: application/zip, 7 datasets
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  • 5
    Publication Date: 2023-06-27
    Keywords: 92-597B; 92-597C; Aluminium oxide; Anorthite; Calcium oxide; Deep Sea Drilling Project; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Electron microprobe (EMP); Elevation of event; Event label; Glomar Challenger; Iron oxide, FeO; Latitude of event; Leg92; Location type; Longitude of event; Potassium oxide; Sample code/label; Silicon dioxide; Sodium oxide; South Pacific; Total
    Type: Dataset
    Format: text/tab-separated-values, 120 data points
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  • 6
    Publication Date: 2023-06-27
    Keywords: 92-597B; 92-597C; 92-599B; 92-601B; 92-602B; Aluminium oxide; Calcium; Calcium oxide; Chromium(III) oxide; Deep Sea Drilling Project; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Electron microprobe (EMP); Elevation of event; Event label; Glomar Challenger; Iron; Iron oxide, FeO; Latitude of event; Leg92; Longitude of event; Magnesium; Magnesium oxide; Manganese oxide; Pyroxene; Sample code/label; Sample position; Silicon dioxide; Sodium oxide; South Pacific; South Pacific/CONT RISE; South Pacific/PLATEAU; South Pacific/TROUGH; Subsampling; Titanium dioxide; Total
    Type: Dataset
    Format: text/tab-separated-values, 1728 data points
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  • 7
    Publication Date: 2023-06-27
    Keywords: 92-597C; 92-602B; Aluminium oxide; Calcium oxide; Deep Sea Drilling Project; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Electron microprobe (EMP); Event label; Forsterite; Glomar Challenger; Iron oxide, FeO; Leg92; Magnesium oxide; Manganese oxide; Medium; Potassium oxide; Sample code/label; Silicon dioxide; Sodium oxide; South Pacific; South Pacific/TROUGH; Titanium dioxide; Total
    Type: Dataset
    Format: text/tab-separated-values, 83 data points
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  • 8
    Publication Date: 2023-06-27
    Keywords: 92-597B; 92-597C; Aluminium oxide; Calcium oxide; Deep Sea Drilling Project; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Electron microprobe (EMP); Event label; Glomar Challenger; Iron oxide, FeO; Leg92; Magnesium oxide; Manganese oxide; Sample code/label; Sample position; Silicon dioxide; South Pacific; Subsampling; Titanium dioxide; Total
    Type: Dataset
    Format: text/tab-separated-values, 540 data points
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  • 9
    Publication Date: 2023-06-27
    Keywords: 92-597B; 92-597C; 92-599B; 92-601B; 92-602B; Aluminium oxide; Anorthite; Calcium oxide; Deep Sea Drilling Project; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Electron microprobe (EMP); Elevation of event; Event label; Glomar Challenger; Iron oxide, FeO; Latitude of event; Leg92; Longitude of event; Potassium oxide; Pyroxene; Sample code/label; Sample position; Silicon dioxide; Sodium oxide; South Pacific; South Pacific/CONT RISE; South Pacific/PLATEAU; South Pacific/TROUGH; Subsampling; Total
    Type: Dataset
    Format: text/tab-separated-values, 1100 data points
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  • 10
    Publication Date: 2023-06-27
    Keywords: 92-597; 92-597B; 92-597C; 92-599B; 92-601B; 92-602B; Albite; Aluminium oxide; Anorthite; Apatite; Calcium oxide; Chromium; CIPW Norm; Copper; Deep Sea Drilling Project; Diopside; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Elevation of event; Event label; Glomar Challenger; Hypersthene; Ilmenite; Iron oxide, Fe2O3; Latitude of event; Leg92; Longitude of event; Loss on ignition; Magnesium oxide; Magnetite; Manganese oxide; Nepheline; Nickel; Niobium; Olivine; Orthoclase; Phosphorus pentoxide; Potassium oxide; Quartz; Rubidium; Sample code/label; Sample position; Silicon dioxide; Sodium oxide; South Pacific; South Pacific/CONT RISE; South Pacific/PLATEAU; South Pacific/TROUGH; Strontium; Subsampling; Titanium dioxide; Total; Vanadium; X-ray fluorescence (XRF); Yttrium; Zinc; Zirconium
    Type: Dataset
    Format: text/tab-separated-values, 3604 data points
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