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Precambrian Crustal Evolution in the North Atlantic Region (1996)

Geological Society (London, U.K.) ; Brewer, T. S.

London : The Geological Society

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Keywords: Atlantischer Raum Nord ; Präkambrium ; Erdkruste ; Crosta da terra (evolução) ; Crust ; Earth ; Earth - Crust - Congresses ; Geology ; Geology, Stratigraphic ; Géologie - Atlantique Nord (région) ; Lithosphère ; North Atlantic Region ; Precambrian ; Pré-cambriano - Oceano atlântico;região norte ; Précambrien

Description / Table of Contents: D. B. Snyder, S. B. Lucas, and J. H. McBride: Crustal and mantle reflectors from Palaeoproterozoic orogens and their relation to arc-continent collisions / Geological Society, London, Special Publications, 112:1-23, doi:10.1144/GSL.SP.1996.112.01.01 --- H. R. Rollinson: Tonalite-trondhjemite-granodiorite magmatism and the genesis of Lewisian crust during the Archaean / Geological Society, London, Special Publications, 112:25-42, doi:10.1144/GSL.SP.1996.112.01.02 --- A. Vrevsky, R. Krimsky, and S. Svetov: Rare earth and isotopic (Nd, O) heterogeneity of the Archaean mantle, Baltic Shield / Geological Society, London, Special Publications, 112:43-53, doi:10.1144/GSL.SP.1996.112.01.03 --- E. V. Bibikova, T. Skiöld, and S. V. Bogdanova: Age and geodynamic aspects of the oldest rocks in the Precambrian Belomorian Belt of the Baltic (Fennoscandian) Shield / Geological Society, London, Special Publications, 112:55-67, doi:10.1144/GSL.SP.1996.112.01.04 --- S. V. Bogdanova: High-grade metamorphism of 2.45–2.4 Ga age in mafic intrusions of the Belomorian Belt in the northeastern Baltic Shield / Geological Society, London, Special Publications, 112:69-90, doi:10.1144/GSL.SP.1996.112.01.05 --- Martin J. Van Kranendonk and Richard J. Wardle: Burwell domain of the Palaeoproterozoic Torngat Orogen, northeastern Canada: tilted cross-section of a magmatic are caught between a rock and a hard place / Geological Society, London, Special Publications, 112:91-115, doi:10.1144/GSL.SP.1996.112.01.06 --- Toby Rivers, Flemming Mengel, David J. Scott, Lisa M. Campbell, and Normand Goulet: Torngat Orogen — a Palaeoproterozoic example of a narrow doubly vergent collisional orogen / Geological Society, London, Special Publications, 112:117-136, doi:10.1144/GSL.SP.1996.112.01.07 --- R. J. Wardle and M. J. Van Kranendonk: The Palaeoproterozoic Southeastern Churchill Province of Labrador-Quebec, Canada: orogenic development as a consequence of oblique collision and indentation / Geological Society, London, Special Publications, 112:137-153, doi:10.1144/GSL.SP.1996.112.01.08 --- Andrew Kerr, Bruce Ryan, Charles F. Gower, Richard J. Wardle, and Andrew Kerr: The Makkovik Province: extension of the Ketilidian Mobile Belt in mainland North America / Geological Society, London, Special Publications, 112:155-177, doi:10.1144/GSL.SP.1996.112.01.09 --- B. Chadwick and A. A. Garde: Palaeoproterozoic oblique plate convergence in South Greenland: a reappraisal of the Ketilidian Orogen / Geological Society, London, Special Publications, 112:179-196, doi:10.1144/GSL.SP.1996.112.01.10 --- Charles F. Gower: The evolution of the Grenville Province in eastern Labrador, Canada / Geological Society, London, Special Publications, 112:197-218, doi:10.1144/GSL.SP.1996.112.01.11 --- Ian C. Starmer: Accretion, rifting, rotation and collision in the North Atlantic supercontinent, 1700-950 Ma / Geological Society, London, Special Publications, 112:219-248, doi:10.1144/GSL.SP.1996.112.01.12 --- A. Wikström, T. Skiöld, and B. Öhlander: The relationship between 1.88 Ga old magmatism and the Baltic-Bothnian shear zone in northern Sweden / Geological Society, London, Special Publications, 112:249-259, doi:10.1144/GSL.SP.1996.112.01.13 --- J. N. Connelly and K-I. Åhäll: The Mesoproterozoic cratonization of Baltica — new age constraints from SW Sweden / Geological Society, London, Special Publications, 112:261-273, doi:10.1144/GSL.SP.1996.112.01.14 --- J. F. Menuge and T. S. Brewer: Mesoproterozoic anorogenic magmatism in southern Norway / Geological Society, London, Special Publications, 112:275-295, doi:10.1144/GSL.SP.1996.112.01.15 --- J. N. Connelly, J. Berglund, and S. Å. Larson: Thermotectonic evolution of the Eastern Segment of southwestern Sweden: tectonic constraints from U-Pb geochronology / Geological Society, London, Special Publications, 112:297-313, doi:10.1144/GSL.SP.1996.112.01.16 --- Laurence M. Page, Michael B. Stephens, and Carl-Henric Wahlgren: 40Ar/39Ar geochronological constraints on the tectonothermal evolution of the Eastern Segment of the Sveconorwegian Orogen, south-central Sweden / Geological Society, London, Special Publications, 112:315-330, doi:10.1144/GSL.SP.1996.112.01.17 --- S. Mertanen, L. J. Pesonen, and H. Huhma: Palaeomagnetism and Sm-Nd ages of the Neoproterozoic diabase dykes in Laanila and Kautokeino, northern Fennoscandia / Geological Society, London, Special Publications, 112:331-358, doi:10.1144/GSL.SP.1996.112.01.18 --- Trevor F. Emmett: The provenance of pre-Scandian continental flakes within the Caledonide Orogen of south-central Norway / Geological Society, London, Special Publications, 112:359-366, doi:10.1144/GSL.SP.1996.112.01.19 --- W. R. Fitches, N. J. G. Pearce, J. A. Evans, and R. J. Muir: Provenance of late Proterozoic Dalradian tillite clasts, Inner Hebrides, Scotland / Geological Society, London, Special Publications, 112:367-377, doi:10.1144/GSL.SP.1996.112.01.20

Pages: Online-Ressource (VII, 386 Seiten) , Illustrationen, Diagramme, Karten

ISBN: 1897799624

URL: http://sp.lyellcollection.org/content/112/1

Language: English

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Chemistry and distribution of accessory Ni, Co, Fe arsenic minerals in the Pechenga Ni-Cu deposits, Kola Peninsula, Russia (1997)

Abzalov, M. Z. ; Brewer, T. S. ; Polezhaeva, L. I.

Springer

Mineralogy and petrology 61 (1997), S. 145-161

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ISSN: 1438-1168

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Description / Table of Contents: Zusammenfassung Ni-, Co- und Fe-Arsenminerale sind verbreitete akzessorische Phasen, sowohl in den Nickel-Kupfer-Vererzungen, als auch in den Sulfiden der Nebengesteine des PechengaKomplexes. Der Großteil der Arsenminerale ist zur Cobaltit-Gersdorffit-Serie zu stellen. Arsenkies, Nickelin und Maucherit sind in geringeren Mengen vorhanden. Diese Minerale sind zwischen den verschiedenen Vererzungstypen gleichmäßig verteilt. Nickelin, Maucherit und Gersdorffit kommen hauptsächlich in hydrothermal veränderten Ni-Cu-Sulfiderzen vor, besonders in Sulfiden der „Stringer-Zone” und in mineralisierten Talk-Karbonat-Gesteinen. Arsenkies kommt nur in Pentlandit-freien Paragenesen in den schiefrigen Nebengesteinen, vor allem in einer remobilisierten Eisensulfidvererzung, vor. Die Konzentrationen von Ni, Fe und Co in Arsenkies nehmen mit zunehmender Entfernung von den Ni-Cu-führenden Intrusionen ab. Cobaltit ist ein verbreitetes Mineral, wobei nickelreicher Cobaltit jedoch hauptsächlich in den Nickel-Kupfererzen vorkommt. Im allgemeinen wird der übergang von NickelKupfererzen zu Nebengesteinen durch den übergang von Nickelarseniden zu NickelKobalt-Sulpharseniden und schließlich zu Eisensulpharseniden markiert. Sedimentärer Pyrit in den schiefrigen Nebengesteinen enthält bis zu 1,8 Gew% As, wobei die Arsenanreicherung während der Sedimentation und Diagenese erfolgten. Metamorphe Rekristallisation authigener As-führenden Pyrite zu As-freiem Magnetkies führte zu signifikanter Freisetzung von Arsen während der Metamorphose. Das mobilisierte Arsen dürfte durch metamorphe Fluide transportiert worden sein, die an der niedriggradigen Alteration der ultramafischen Gesteine und der assoziierten NickelKupfererze beteiligt waren.

Notes: Summary Ni, Co, Fe arsenic minerals are common accessory phases associated with both the Ni-Cu mineralization and country rock sulphides of the Pechenga complex. The majority of the arsenic minerals fall in the cobaltite-gersdorffite series, with minor arsenopyrite, nickeline and maucherite. These minerals are regularly distributed between different types of mineralization. Nickeline, maucherite and gersdorffite occur mainly in hydrothermally altered Ni-Cu sulphide ores, in particular stringer zone sulphides and mineralized talc-carbonate rocks. Arsenopyrite occurs only in pentlandite-free assemblages of the host shales, mainly in remobilized iron sulphide mineralization. The concentrations of Ni and Co in arsenopyrite decrease with the distance from the Ni-Cu bearing intrusions. Cobaltite is an ubiquitous mineral, but Ni-rich cobaltite occurs mainly in the Ni-Cu ores. In general, the transition from Ni-Cu ores to country rocks is marked by the change from Ni-arsenides to Ni-Co sulpharsenides and, finally, to Fe sulpharsenides. Sedimentary pyrite in sulphidic shales contains up to 1.8 wt.% As and was initially enriched in arsenic during sedimentation and diagenesis. Metamorphic recrystallization of authigenic As-bearing pyrite to As-free pyrrhotite led to significant liberation of arsenic during metamorphism. The mobilized arsenic could have been carried by associated metamorphic fluids and then participated in the low-grade alteration of the ultramafic rocks and associated Ni-Cu sulphide ores.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01172481

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The interpretation of thermal neutron properties in ocean floor volcanics (2007)

Brewer, T. S. ; Harvey, P. K. ; Barr, S. R. ; [et al.]

In: Geological Society Special Publication 240: 219-235.

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Publication Date: 2007-10-08

Description: Using near-complete chemical analyses, computed thermal absorption cross-section values ({sigma}) are calculated for ocean-floor basalts from ODP Holes 896a and 1179D. Comparison with nuclear measurement of {sigma}, demonstrates that this computational method is valid and clarifies the interpretation of {sigma} in ocean-floor basalts. Boron, lithium and the rare-earth elements are important controls on the {sigma}-values, and, of these, the distribution of the rare-earth elements is controlled by primary magmatic processes, whereas the distribution of boron and lithium is strongly influenced by secondary low-temperature alteration processes. Consequently, computed {sigma}-values can be used to discriminate between various basalt types and to identify areas of secondary alteration. Following calibration of the fresh basalt' signature, it is possible to interpret log derived neutron absorption measurements of a sample ({Sigma}-values), which, when integrated with other log responses, allow the distribution of alteration within a drilled section to be mapped. Examples from ODP Hole 801C demonstrate the potential of this technique.

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On the neutron absorption properties of basic and ultrabasic rocks: the significance of minor and trace elements (2007)

Harvey, P. K. ; Brewer, T. S.

In: Geological Society Special Publication 240: 207-217.

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Publication Date: 2007-10-08

Description: The neutron absorption macroscopic cross-section, {Sigma}, is measured routinely by neutron porosity tools and, although rarely presented as a logging curve in its own right, is used indirectly for the estimation of (neutron) porosity. One of the reasons that this primary measurement is not often employed directly in petrophysical analysis is the difficulty of interpretation. In particular, little is known about the range of {Sigma} values for common lithologies, or exactly what information the measurement is providing. In this contribution we demonstrate that excellent estimates of {Sigma} can be calculated, provided that the chemistry of a sample is known in sufficient detail. When applied to a range of geochemical reference materials, it becomes apparent that the minor and trace elements present may have a profound effect on the {Sigma} value of a sample, and, in turn, on the interpretation of neutron porosity measurements. Using this approach we present {Sigma} data for basaltic and ultrabasic rocks, and model the change in {Sigma} with alteration. Alteration is considered in these models as an increase in alteration minerals (which are mainly clays, but also carbonates and zeolites in basic rock alteration) and changes in the trace-element chemistry of the rocks. Of the trace elements, boron and some of the rare-earth elements are of particular importance. Modelling the variation in {Sigma} with these mineralogical and compositional changes indicates that increases in boron are the most important of these factors in increasing {Sigma}; this is enhanced by the alteration, particularly to clay phases, which generally accompanies an increase in boron. These models suggest that a {Sigma} log should be able to act as a proxy for alteration trends in basic and ultrabasic crystalline rocks, and a quantitative model for such alteration is described.

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Integration of electrical and optical images for structural analysis: a case study from ODP Hole 1105A (2007)

Haggas, S. L. ; Brewer, T. S. ; Harvey, P. K. ; [et al.]

In: Geological Society Special Publication 240: 165-177.

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Publication Date: 2007-10-08

Description: A significant problem with basement core data acquired by the Ocean Drilling Program (ODP) is that it is unorientated with respect to grid north and in those cores with < 100% core recovery the data may also be inaccurately located within the borehole. In order for structural data from basement cores to be of any real value, the recovered core must firstly be accurately located and orientated. Here, we develop methods for core reorientation and accurate location within a borehole that integrates wireline borehole electrical images with whole-core digital images. Azimuthal orientation and location of individual core pieces allows for the detailed interpretation of structural data, including fabrics and fractures and reorientation of other spatially anisotropic properties of core, such as palaeomagnetism. ODP Hole 1105A is one of a pair of holes drilled on the Atlantis Bank in the SW Indian Ocean, which penetrate sections of the lower ocean crust. Hole 1105A was drilled to a depth of 158 metres below sea-floor (mbsf), with core recovery of 83% and the vast majority of the recovered material being represented by gabbroic rocks. Zones of crystal-plastic deformation occur throughout the core, but overall their frequency increases downhole. In the deformed zones, the gabbros are transformed into equigranular or porphyroclastic gneissose textured rocks, characterized by very prominent planar fabrics. These localized deformation zones relate to the early exhumation history of the lower crust in an environment similar to core-complex formation in continental regions. Using a combination of digital core and formation microscanner (FMS) images, it is now possible to fully orientate structural features in a borehole and so map the oxide gabbro and crystal-plastic deformation zones in Hole 1105A. From the analysis of the crystal-plastic fabrics, the majority appear to dip southwards, with a few (c.5%) dipping to the north. This would suggest that the major exhumation surfaces in this hole are represented by southward-dipping structures, formed at high temperatures during unroofing of the Atlantis Bank.

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Sources of Metals and Fluids in Orogenic Gold Deposits: Insights from the Otago and Alpine Schists, New Zealand (2006)

Pitcairn, I. K. ; Teagle, D. A. H. ; Craw, D. ; [et al.]

Society of Economic Geologists

In: Economic Geology. 2006; 101(8): 1525-1546. Published 2006 Dec 01. doi: 10.2113/gsecongeo.101.8.1525.

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Publication Date: 2006-12-01

Print ISSN: 0361-0128

Electronic ISSN: 1554-0774

Topics: Geosciences

Published by Society of Economic Geologists

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Lower Permian brachiopods from Oman: their potential as climatic proxies (2007)

Angiolini, L. ; Darbyshire, D. P. F. ; Stephenson, M. H. ; [et al.]

Cambridge University Press

In: Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 2007; 98(3-4): 327-344. Published 2007 Sep 01. doi: 10.1017/s1755691008075634.

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Publication Date: 2007-09-01

Description: The Lower Permian of the Haushi basin, Interior Oman (Al Khlata Formation to Saiwan Formation/lower Gharif member) records climate change from glaciation, through marine sedimentation in the Haushi sea, to subtropical desert. To investigate the palaeoclimatic evolution of the Haushi Sea we used O, C, and Sr isotopes from 31 brachiopod shells of eight species collected bed by bed within the type-section of the Saiwan Formation. We assessed diagenesis by scanning electron microscopy of ultrastructure, cathodoluminescence, and geochemistry, and rejected fifteen shells not meeting specific preservation criteria. Spiriferids and spiriferinids show better preservation of the fibrous secondary layer than do orthotetids and productids and are therefore more suitable for isotopic analysis. δ18O of −3·7 to −3·1℅ from brachiopods at the base of the Saiwan Formation are probably related to glacial meltwater. Above this, an increase in δ18O may indicate ice accumulation elsewhere in Gondwana or more probably that the Haushi sea was an evaporating embayment of the Neotethys Ocean. δ13C varies little and is within the range of published data: its trend towards heavier values is consistent with increasing aridity and oligotrophy. Saiwan Sr isotope signatures are less radiogenic than those of the Sakmarian LOWESS seawater curve, which is based on extrapolation between few data points. In the scenario of evaporation in a restricted Haushi basin, the variation in Sr isotope composition may reflect a fluvial component.

Print ISSN: 1755-6910

Electronic ISSN: 1755-6929

Topics: Geosciences