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  • 1
    Electronic Resource
    Electronic Resource
    Pre-Palaeozoic basement of the Scottish Midland Valley (1976)
    [s.l.] : Nature Publishing Group
    Nature 260 (1976), S. 517-518 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The clasts within and around the veit comprise mainly altered alkali basalt and basaltic tuff, with a wide variety of quartzitic sandstones and scarcer chers, limestones and indurated shales. Some relatively coarse-gained biotite-rich mafic and ultramafic clasts also occur andinclude (altered) ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/260517a0
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    Paper (German National Licenses)
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  • 2
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    The lithospheric mantle and lower crust-mantle relationships under Scotland: a xenolithic perspective (2011)
    Geological Society of London
    Details
    Publication Date: 2011-06-16
    Description: : In the British Isles the majority of volcanic rocks containing upper mantle and lower crustal xenoliths occur in Scotland. Most of the occurrences are of Carboniferous–Permian age. This paper presents new data on the mineral chemistry of spinel lherzolite xenoliths from the five principal Scottish tectonic terranes. Compositional variations among the minerals emphasize the broad lateral heterogeneity of the subcontinental lithospheric mantle across the region. The remarkable range of Al 2 O 3 v. CaO exhibited by the clinopyroxenes compared with data from other ‘xenolith provinces' emphasizes the extremely complex tectonomagmatic history of the Scottish lithosphere. The generalized age increase from southern and central Scotland to the Northern Highland and Hebridean terranes of the north and NW, with concomitant complexity of geological history, is reflected also by trace element and isotopic studies. Reaction relationships in lherzolites from the Hebridean Terrane, owing to pervasive metasomatism, involve secondary growth of sodic feldspar. This, and light REE enrichment of clinopyroxenes, points to involvement of a natro-carbonatitic melt. Most pyroxenitic xenoliths are inferred to form a basal crustal layer with a generally sharp discontinuity above the underlying (dominantly lherzolitic) mantle. A second discontinuity is inferred to separate these ultramafic cumulates from overlying, broadly cognate metagabbroic cumulates.
    Print ISSN: 0016-7649
    Topics: Geosciences
    Published by Geological Society of London
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  • 3
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    Mid-Eocene renewal of magmatism in NW Scotland: the Loch Roag Dyke, Outer Hebrides (2012)
    Geological Society of London
    Details
    Publication Date: 2012-03-08
    Description: A monchquite dyke, in the vicinity of Loch Roag, Lewis, Outer Hebrides has an unusually enriched chemistry, and contains a unique assemblage of megacrysts and xenoliths from the lithosphere of the Hebridean craton. A 40 Ar/ 39 Ar plateau age of 45.2 ± 0.2 Ma (2) of a phlogopite megacryst from the dyke overlaps an earlier reported K–Ar age, and confirms that the British Palaeogene Igneous Province extended into the Eocene. Similar late low-volume melts were erupted in the Eocene and Oligocene in West and East Greenland, suggesting that such late-stage magmatic rejuvenescence is a widespread feature across the North Atlantic Igneous Province.
    Print ISSN: 0016-7649
    Topics: Geosciences
    Published by Geological Society of London
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  • 4
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    Characteristics of djerfisherite from fluid-rich, metasomatized alkaline intrusive environments and anhydrous enstatite chondrites and achondrites (2014)
    Mineralogical Society of America
    Details
    Publication Date: 2014-08-13
    Description: Djerfisherite is a K-Cl-bearing sulfide that is present in both ultra-reduced extraterrestrial enstatite meteorites (enstatite chondrites or achondrites) and reduced terrestrial alkaline intrusions, kimberlites, ore deposits, and skarns. Major element chemistry of two terrestrial occurrences of djerfisherite (from the Ilímaussaq and Khibina alkaline igneous suites) and three extraterrestrial examples of djerfisherite have been determined and combined with petrographic characterization and element mapping to unravel three discrete modes of djerfisherite formation. High Fe/Cu is characteristic of extraterrestrial djerfisherite and low Fe/Cu is typical of terrestrial djerfisherite. Ilímaussaq djerfisherite, which has high-Fe contents (~55 wt%) is the exception. Low Ni contents are typical of terrestrial djerfisherite due to preferential incorporation of Fe and/or Cu over Ni, but Ni contents of up to 2.2 wt% are measured in extraterrestrial djerfisherite. Extensive interchange between K and Na is evident in extraterrestrial samples, though Na is limited (〈0.15 wt%) in terrestrial djerfisherite. We propose three setting-dependent mechanisms of djerfisherite formation: primitive djerfisherite as a product of nebula condensation in the unequilibrated E chondrites; formation by extensive K-metasomatism in Khibina djerfisherite; and as a product of primary "unmixing" due to silicate-sulfide immiscibility for Ilímaussaq djerfisherite. There are several important reasons why a deeper understanding of the petrogenesis of this rare and unusual mineral is valuable: (1) its anomalously high K-contents make it a potential target for Ar-Ar geochronology to constrain the timing of metasomatic alteration; (2) typically high Cl-contents (~1.1 wt%) mean it can be used as a valuable tracer of fluid evolution during metasomatic alteration; and (3) it may be a potential source of K and magmatic Cl in the sub-continental lithospheric mantle (SCLM), which has implications for metal solubility and the generation of ore deposits.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 5
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    CHEVKINITE-GROUP MINERALS IN UK PALAEOGENE GRANITES: UNDERESTIMATED REE-BEARING ACCESSORY PHASES (2013)
    Mineralogical Association of Canada
    Details
    Publication Date: 2013-06-12
    Description: Chevkinite-group minerals were sought in 26 granitic bodies from the Palaeogene sequences of Scotland and Northern Ireland, ranging from biotite ± amphibole granites through fayalite-ferrohedenbergite granites to alkali amphibole granites. Chevkinite-(Ce) was found, and analyzed by electron microprobe, in 20 of the bodies, confirming that it is a ubiquitous accessory phase in these rocks. The abundance of the chevkinite is highest in the latter two granite types, sometimes forming more than 50 crystals per thin section. Textural evidence indicates that they crystallized from early- to late-magmatic stages. Compositional variation within and between crystals in the same rock may have resulted partly from fractional crystallization and/or magma mixing and partly from element mobility during metamictization. In some rocks, subsequent hydrothermal alteration affected the composition of the chevkinite-(Ce), in extreme cases leaving totally pseudomorphed material. Apart from mirroring a small enrichment of the LREE in the peralkaline host rocks, there are no systematic changes in chevkinite composition with different bulk-rock compositions.
    Print ISSN: 0008-4476
    Topics: Geosciences
    Published by Mineralogical Association of Canada
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  • 6
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    Kungnat, revisited. A review of five decades of research into an alkaline complex in South Greenland, with new trace-element and Nd isotopic data (2013)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2013-06-19
    Description: The Kûngnât Complex (1275±1.8 Ma) in the Gardar Alkaline Province, South Greenland, cuts Archaean gneisses and comprises two intersecting syenitic stocks and a gabbroic ring-dyke. The magmas, with increasingly more primitive compositions, were emplaced successively by ring-faulting and roof stoping. The syenites are orthocumulates (cumulus alkali feldspar, olivine, pyroxene, titanomagnetite and apatite; intercumulus phases include alkali amphibole, biotite, quartz and calcite). In the well dissected earlier stock, a 2.2 km-thick layered sequence displays graded modal layering, feldspar lamination and cryptic layering. Modal layering in both stocks is directed mainly inwards at 35°–50°. Heterogeneous nucleation of the cumulus assemblage, close to steep thermal boundary layers, is inferred. The modal layering is ascribed primarily to gravitational sorting aided by the large density differential between a) feldspar and b) Fe-rich silicates and oxides. Episodic collapse of cumulus + melt slurries contributed to inward-dipping crystal pediments on the chamber floors. The Ring-Dyke (up to 100 m wide) is nearly continuous through 360°. Kûngnât exhibits a compositional near-continuum from olivine gabbro through syenite intermediaries to alkali granite, ascribed to protracted assimilation/fractional crystallization processes. The most radiogenic Nd isotope data from Kûngnât (Nd i values between –3.3 and –1.0) point to a lithospheric mantle source, whereas the most unradiogenic values imply enrichment in LREE by crustal contamination of the magmas.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
    Published by Mineralogical Society of Great Britain and Ireland
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  • 7
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    Pre-Palaeozoic basement of the Scottish Midland Valley (1976)
    Springer Nature
    Details
    Publication Date: 1976-04-01
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 8
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    The Mull Palaeogene dyke swarm: insights into the evolution of the Mull igneous centre and dyke-emplacement mechanisms (2010)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2010-08-01
    Description: Geochemical data are presented for five large Palaeogene dykes, members of the Mull swarm in southern Scotland and northern England (the Moneyacres, Hawick-Acklington, Barrmill, Muirkirk- Hartfell and Dalraith-Linburn dykes). The rock types range from basalt through andesite to dacite, although the range in individual intrusions is more restricted. The dykes are divisible into two groups; those where the compositional variation was generated by fractional crystallization of basaltic magmas, and those where it resulted from variable degrees of mixing of basaltic and silicic magmas. Several dykes are composite; the marginal facies can be more or less evolved than the central facies. The dyke magmas are thought to have originated from stratified magma chambers beneath the Mull centre and models are presented to show how the different components were derived from the chambers. Some dykes appear to have been terminated at or near the Southern Upland Fault, perhaps as a result of the chilling of early magma pulses by water in the fault. The Palaeogene dyke swarm is considerably more complex than previously recognized and has a significant input to models of the evolution of the Mull magmatic system.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
    Published by Mineralogical Society of Great Britain and Ireland
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  • 9
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    Emeleusite: a new LiNaFeIII silicate from south Greenland (1978)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 1978-03-01
    Description: SummaryEmeleusite (Li2Na4Fe2IIISi12O30) is an orthorhombic (pseudohexagonal) mineral occurring as euhedra within a facies of a peralkaline trachyte dyke. The composition is: SiO2 70·75; TiO2 0·55; ZrO2 0·10; Al2O3 1·34; Fe2O3 12·13; MgO 0·10; MnO 0·03; Na2O 11·98; Li2O 2·78:99·76. The density is 2·775 g/cm3 (calculated) and 2·76(7) g/cm3 (determined); hardness 5–6. It is colourless, transparent, and has a glassy lustre. Emeleusite is biaxial negative with 2Va, varying from near-zero to c. 30° r » v. The refractive indices are α 1·596; β 1·597; y 1·597; with α ∥ b; β ∥ a; y ∥ c. Emeleusite can occur as interpenetration triplets with {110} as twin planes. The space group is Acam or Aba2 with a = 10·073±0·002 Å; b = 17·350±0·005 Å and c = 14·010±0·005 Å. Z = 4. Prominent powder diffraction lines are 7·001(5) 002, 4·352(10) 220, 040, 3·501(7) 004, 3·209(8) 311, and 3·090(7) 124. While the structure is as yet unknown it is suggested that it is an orthorhombic associate of the milarite group.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
    Published by Mineralogical Society of Great Britain and Ireland
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  • 10
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    Narsarsukite: a new occurrence in peralkaline trachyte, south Greenland (1976)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 1976-09-01
    Description: SummaryA flinty, spherulitic dyke of peralkaiine trachyte in a Precambrian dyke-swarm consists mainly of albite and aegirine. Within this, euhedral crystals of narsarsukite, Na2(Ti,Fe)Si4O10(F), occur as short prisms elongate parallel to c. This distinguishes them from all previously described narsarsukites, which have tabular habits. Minor phases present include micas, apatite, quartz, pectolite, nordite, and a thorium silicate. Probe analyses are presented for narsarsukite, aegirine, aibite, biotite, apatite, pectolite, nordite, and the thorium silicate.On mineralogical and geochemical grounds it is unlikely that the narsarsukite-bearing dyke is a differentiate of supposedly mantle-derived basalt-trachyte-comendite magmas in the region. The dyke is colinear with a comendite dyke exposed at lower altitude and it is suggested that the narsarsukite- bearing dyke developed as a rhcomorphic fenite generated by reaction between quartz diorite basement and fugitive alkaline solutions from the subjacent comendite.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
    Published by Mineralogical Society of Great Britain and Ireland
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