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  • 1
    Electronic Resource
    Electronic Resource
    Petrographic and trace element analysis of uranium-rich tufa calcite, middle Miocene Barstow Formation, California, USA (2004)
    Oxford, UK : Blackwell Science Ltd
    Sedimentology 51 (2004), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: An integrated petrographic and spectroscopic (X-ray diffraction, phosphor imaging and synchrotron X-ray absorption spectroscopy) study of tufas from the Miocene Barstow Formation, California, relates sample morphology, mineralogy and geochemical composition. The tufas, composed mainly of calcite that formed at the interface between an ancient alkaline lake and ground or spring waters, have textures similar to those of microbially mediated terrestrial stromatolites and travertines. The tufas have elevated concentrations of a number of trace elements including Mn, Fe, Sr and U. Synchrotron X-ray fluorescence analyses show that U concentrations can exceed 500 p.p.m. X-ray absorption spectroscopy indicates that the U in these samples is incorporated as U(IV). It is suggested here that alkaline lake waters had a high U/Ca ratio and tufa calcite formed where groundwater or (possibly epithermal) springs brought in Ca and trace elements such as Sr. The rapid, and possibly microbially mediated, precipitation of calcite allowed for incorporation of high concentrations of trace metals as either structural substitutes or extremely fine-scale inclusions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.2004.00631.x
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  • 2
    Electronic Resource
    Electronic Resource
    Dolomitization of the Devonian Swan Hills Formation, Rosevear Field, Alberta, Canada (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 38 (1991), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The Swan Hills Formation (Middle-Upper Devonian) of the Western Canada Basin is host to several NW-SE-trending gas fields developed in massive replacement dolostone. One of these, the Rosevear Field, contains two major dolostone trends along opposing margins of a marine channel that penetrates into a platform-reef complex. Dolostones consist predominantly of branching and bulbous strdmatoporoid floatstones and rudstones with well-developed moldic and vuggy porosity. Replacement dolomite is coarsely crystalline (100-600 μm), inclusion-rich, composed of euhedral through anhedral crystals and has a blotchy to homogeneous red cathodoluminescence. Geochemically, replacement dolomite is characterized by (i) nearly stoichiometric composition (50.1-51.1 mol% CaCO3), (ii) negative δ18O values (mean=-7.5‰, PDB) and (iii) variable 87Sr/86Sr ratios ranging from values similar to Late Devonian-Early Mississippian seawater (∼0.7082) to radiogenic compositions comparable to saddle dolomite cements (〉0.7100).Dolomitization began after widespread precipitation of early, equant calcite spar and after the onset of pressure solution, implying that replacement dolomite formed in a burial environment. Oxygen isotope data suggest that dolomite formed at 35-75°C, temperatures reached during burial in Late Devonian through Jurassic time, at minimum depths of 450 m. The linear NW-SE orientation of most dolomite fields in the Swan Hills Formation is suggestive of fault control on fluid circulation. Two models are proposed for fault-controlled circulation of dolomitizing fluids at the Rosevear Field. In the first, compaction-driven, updip fluid migration occurred in response to basin tilting commencing in the Late Palaeozoic. Deep basinal fluids migrating updip were focused into channel-margin sediments along fault conduits. The second model calls upon fault-controlled convective circulation of (i) warm Devonian-Mississippian seawater or (ii) Middle Devonian residual evaporitic brines.The overlap in 87Sr/86Sr and δ18O compositions, and similar cathodoluminescence properties between replacement and saddle dolomites provide evidence for neomorphism of some replacement dolomite. Quantitative modelling of Sr and O isotopes and Sr abundances suggests partial equilibration of some replacement dolomite with hot radiogenic brines derived during deep burial of the Swan Hills Formation in the Late Cretaceous-Palaeocene. Interaction of replacement dolomite with deep brines led to enrichment in 87Sr while leaving δ18O similar to pre-neomorphism values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1991.tb01854.x
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  • 3
    Electronic Resource
    Electronic Resource
    Rare earth element mobility in the Roffna Gneiss, Switzerland (1987)
    Springer
    Contributions to mineralogy and petrology 95 (1987), S. 145-154 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Roffna Gneiss, a deformed Hercynian granite porphyry within the Penninic nappes of eastern Switzerland, underwent extreme cataclasis with the progressive development of phengite towards the margins of the nappe under conditions of the glaucophane schist to greenschist facies. This resulted in the selective mobilization of major and trace elements over distances of 10's to 100's of meters and the resetting of the Rb — Sr whole rock isotopic systems some 100 my ago. The component ratios and compositionvolume relationships of progressively deformed gneiss samples studied here suggest that this process was essentially isovolumetric. The mineralogy of the deformation sequence appears to have been controlled by a reaction involving the breakdown of microcline, albite and biotite and the formation of phengite and quartz. The fluids introduced Mg and H2O, promoting the development of phengite, and removed the Na being released by the breakdown of albite. The fluids were most probably derived from the surrounding Triassic carbonates and quartzites. These relatively high fO2 and carbonate rich fluids also introduced rare earth elements (REE) into the gneiss. The gneiss was progressively enriched in Eu up to 60%, Y up to 40%, and Yb up to 100%. These enrichments are associated with the development of epitaxial xenotime around zircon in the most phengite-rich sample. While the REE were mobile, uranium and thorium were essentially immobile. The formation of xenotime was suggested to explain the observed heavy REE enrichment when large differences in the REE contents were found for replicate analyses using HF and then lithium metaborate for dissolution. These differences arose because xenotime, like monazite, can be difficult (if not impossible) to dissolve in hydrofluoric acid. Due to the possibility of incomplete sample dissolution, we now recommend fusion with lithium metaborate for all REE, Lu — Hf or Sm — Nd studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00381264
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  • 4
    Electronic Resource
    Electronic Resource
    Evidence for a higher pH in the glacial ocean from boron isotopes in foraminifera (1995)
    [s.l.] : Nature Publishing Group
    Nature 373 (1995), S. 234-236 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The basis for the boron-isotope palaeoacidity indicator is that the uncharged species B(OH)3 is enriched6 in UB by ~20%o over the charged borate species, B(OH)4 . As the fraction of the boron present as these species changes with pH, so also must their respective isotopic compositions. It is ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/373234a0
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  • 5
    Electronic Resource
    Electronic Resource
    Mantle-derived Archaean monozodiorites and trachyandesites (1984)
    [s.l.] : Nature Publishing Group
    Nature 310 (1984), S. 222-224 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Rocks occurring as monzodiorites and andsites through trachyandesites in the Rainy Lake region form a suite of cogenetic rocks. They occur as volcanic units in the Keewatin Series, as intrusive and volcanic units in the Rocky Islet Bay complex and as the major component of the Coutchiching ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/310222a0
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of fluids on the interaction of granites with limestones: The Notch Peak stock, Utah (1988)
    Springer
    Contributions to mineralogy and petrology 99 (1988), S. 49-61 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract In this paper we consider the mechanisms by which the mineralogy and composition of the margins of the Notch Peak granitic stock, Utah, were affected by calcareous argillite country rocks. The contact zone of the granite relative to the unaffected granite is enriched in: K2O from about 4 to 10 wt.%, Rb from 250 to 510 ppm, Sr from 150 to 790 ppm and Ba from 250 to 2160 ppm. Locally, some of the intrusive rocks at the contact are nearly devoid of quartz and can be classified as syenites. The initial 87Sr/86Sr ratios range from 0.7069 in the unaffected rocks to 0.7100 in the potassium-enriched samples, approaching the values of the calc-silicate country rocks of about 0.7110. Calculations show that the characteristics of the contact zone near the top of the stock are the result of a number of sequential processes. CO2-rich fluids derived from the heated calcareous argillites apparently caused a shift in the phase boundaries in the magma, enhancing accumulation of K-feldspar and high-Ca augite at the expense of other phases. The accumulation resulted in the high Ba and Sr concentrations in some samples. However, the high K2O and Rb concentrations and magmatic δ18O values indicate infiltration of magmatic fluid emanating from the solidifying lower portions of the pluton subsequent to solidification of the cap. The minimum fluid-rock ratios of 4.6 by mass, calculated on the basis of K2O and Rb concentration shifts, indicate that a substantial amount of the fluid was channeled through this contact zone. The desilication of the rocks forming the syenitic samples at the contact apparently occurred when a chemical potential gradient of silica between the granite and wall-rocks was established as quartz was consumed in the wall-rocks during calc-silicate reactions. The infiltrating magmatic fluid probably acted as a medium for transport of silica across the contact and perhaps exchange of Sr between the country rocks and the intrusion where up to 30% of strontium in the granitic and syenitic samples from the contact zone was derived from the calc-silicates. The syenitic rocks cannot be explained by desilication reactions involving assimilation of the calc-silicates by the granite magma. The results of this study show that fluids interacting with the country rocks need to be considered to explain the effects of country rocks on the composition of the margins of granitic intrusions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00399365
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  • 7
    Electronic Resource
    Electronic Resource
    Trace element constraints on pegmatite genesis: Tin Mountain pegmatite, Black Hills, South Dakota (1989)
    Springer
    Contributions to mineralogy and petrology 101 (1989), S. 290-300 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Tin Mountain pegmatite is a small, zoned granitic body that is extremely enriched in Rb and Li, but has moderate concentrations of Sr and Ba. These trace elements are modelled using granitic distribution coefficients in order to test the potentials of partial melting of metasedimentary rocks and fractionation of a less-evolved granitic melt to have produced the parental liquid to the Tin Mountain pegmatite. Batch melting of any reasonable metasedimentary source rock would likely have yielded melts that were either insufficiently enriched in Rb and Li to be the parental liquid, or that had Sr and Ba concentrations that were much higher than those estimated for the parental liquid. The modelling of simple fractional crystallization and equilibrium crystallization of a granitic melt within the compositional range of the spatially associated Harney Peak Granite gives calculated melt compositions with either lower Sr and Ba concentrations or inadequate Rb and Li enrichments, to be the parent liquid of the pegmatite. At least two variants from simple crystal-liquid fractionation models can, however, successfully account for the derivation of the parent liquid: 1) generation of a Rb-, Li-, Ba- and Sr-rich granitic melt (outside of the compositional range of the sampled portions of the Harney Peak Granite complex) by low degrees of partial melting of metasedimentary rocks found in the Black Hills, followed by moderate extents of fractional or equilibrium crystallization, 2) derivation from Harney Peak granite via a complex, multi-stage crystal-liquid fractionation process, such as progressive equilibrium crystallization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00375314
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  • 8
    Electronic Resource
    Electronic Resource
    Petrogenesis and source characteristics of metatholeiites from the Archean Ramagiri schist belt, eastern part of Dharwar craton, India (1997)
    Springer
    Contributions to mineralogy and petrology 129 (1997), S. 87-104 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The N–S trending, 2–4 km wide Ramagiri schist belt is made up of three blocks dominated by metavolcanic rocks, separated and surrounded by granitic rocks of distinct characteristics. The metavolcanic rocks are tholeiitic in composition and are very similar in their major element composition as well as in their abundances of some trace elements. However, the rare earth elements (REE) require distinct sources. The rocks of the amphibolite facies eastern block have LREE depleted REE patterns ([Ce/Yb] = 0.7–0.9), requiring derivation from depleted mantle-like sources. The greenschist facies metatholeiitic rocks of the central block have LREE enriched REE patterns ([Ce/Yb] = 3–6), reflecting the nature of their source(s). The Nd isotopic data require that the LREE enriched nature could not have been attained significantly prior to its melting. The fine-grained, upper greenschist facies metatholeiites of the western block have flat to slightly LREE depleted patterns ([Ce/Yb] = 0.8–0.95). Minor fractional crystallization of rock forming minerals may relate a few samples to each other among samples from each of the three blocks. Different extents of partial melting of distinct mantle sources have played a dominant role in the generation of the parent magmas to the central versus eastern and western block metatholeiites. The geochemical data suggest that the mantle sources were non-lherzolitic, and that these sources may have seen previous episodes of melt addition and extraction prior to melting that gave rise to the parent melts to the rocks ∼2750 Ma ago. The REE data indicate that while the sources of the eastern and western block rocks were similar to depleted mantle (ɛNd( i ) about +2), the source of the central block rocks (ɛNd( i ) about +3.5) were enriched in large ion lithophile element (LILE)-rich fluids/melts probably derived from subducting oceanic crust. This and other trace element signatures point to magma extraction in tectonic settings similar to modern island arcs. Subsequent to magma emplacement and crystallization, all the three suites of rocks were affected by interaction with low-temperature, crustal derived fluids (ɛNd 2750Ma of about −8 to −12), probably during the accretion of the three blocks of the belt in the present form. The inferred source characteristics, tectonic setting of magma generation and the crustal fluid processes seem to suggest that Phanerozoic-style tectonic processes may have been important in the generation of Archean crust in the Dharwar craton.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100050325
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  • 9
    Electronic Resource
    Electronic Resource
    An assessment of the utility of staurolite in U-Pb dating of metamorphism (1997)
    Springer
    Contributions to mineralogy and petrology 129 (1997), S. 352-365 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Pb isotope data, major and trace element compositions, fission track and synchrotron X-ray fluorescence analyses are presented for staurolites from nine pelitic schists in the continental United States to evaluate their potential use in U-Pb geochronology. Seven U-Pb analyses from Lanzirotti and Hanson (1995) are reexamined with respect to this additional data which was not available at the time. These data are then compared to 21 new U-Pb analyses of staurolite of varying composition from a variety of localities. The primary goals of this study are to: (1) evaluate the variability in U and Pb abundance and U/Pb ratio in staurolites of varying composition; (2) constrain how much of the measured U and Pb is derived from radiogenic solid inclusions such as monazite and zircon; (3) constrain how much of the measured U and Pb is derived from staurolite itself and evaluate any possible correlation of U and Pb abundance and U/Pb ratio to major element composition; (4) place preliminary constraints on closure temperature to Pb diffusion in staurolite; (5) evaluate how meaningful U-Pb ages can better be calculated for the low U/Pb ratio minerals. In the staurolite fractions analyzed U abundances range from 0.2 to 24.9 ppm, Pb from 0.13 to 2.41 ppm, the 238U/204Pb ratios vary from 135 to 9447, and the 206Pb/204Pb ratios from 23 to 623. For many of the fractions analyzed precise U-Pb ages can be calculated (±10 Ma or better) that appear to be consistent with available age constraints on the time of peak metamorphism. Mass balance calculations, fission track analysis, and synchrotron X-ray fluorescence trace element mapping show that although radiogenic inclusions are almost always present in large staurolite porphyroblasts, it is difficult for inclusions to account for the measured Pb isotopic compositions. It is also demonstrated that the U-Pb ages calculated for staurolites from Connecticut are at least 20 Ma older than nearby Rb-Sr muscovite and 40Ar-39Ar hornblende ages. This is consistent with staurolite having a closure temperature to U and Pb diffusion significantly higher than 500 °C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100050342
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  • 10
    Electronic Resource
    Electronic Resource
    Geochemistry and origin of massif-type anorthosites (1978)
    Springer
    Contributions to mineralogy and petrology 66 (1978), S. 119-135 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Samples of Proterozoic anorthosite complexes from the Adirondack Mountains of New York, Burwash Area of Ontario, and the Nain Complex of Labrador, ranging in composition from anorthosite to anorthositic gabbro, have been analyzed for major elements, Rb, Sr, Ba and nine rare-earth elements (REE), in order to set limits on the compositions and origins of their parent magmas. Similar rock types from the different areas have similar major and trace element compositions. The anorthosites have high Sr/Ba ratios, low REE abundances (Ce about 10, Yb about 0.5–1.5 times chondrites) and large positive Eu anomalies. The associated anorthositic gabbros have lower Sr/Ba ratios, REE abundances nearly an order of magnitude higher than the anorthosites, and small to negligible positive Eu anomalies. Model calculations using the adcumulate rocks with the lowest REE abundances and published distribution coefficients yield parent liquids having REE abundances and patterns similar to those of the associated anorthositic gabbros with the highest REE abundances. Rocks with intermediate REE abundances are the result of incorporation of a liquid component by a plagioclase-rich cumulate similar to the adcumulate samples. The analytical data and model calculations both suggest parent liquids having compositions of 50–54% SiO2, greater than 20% Al2O3, about 1% K2O, atomic Mg/(Mg+Fe2+) ratios (Mg No.'s) of less than 0.4, 15–30 ppm Rb, 400–600 ppm Sr and 400–600 ppm Ba, 40–50 times chondrites for Ce and 8–10 times chondrites for Yb. The low atomic Mg/(Mg+Fe2+) values for these rocks combined with geophysical evidence suggesting there are not large quantities of ferromagnesian material at depth, indicate that the anorthositic masses are not products of fractional crystallization of mafic melt derived from melting of the mantle. Rather, it is suggested that they are a result of partial melting of tholeiitic compositions at depths shallower than the basalt-eclogite transformation, leaving a pyroxene-dominated residue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00372151
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