The Zoned Plagioclase of the Skaergaard Intrusion, East Greenland

Maaløe, Sven

doi:10.1093/petrology/17.3.398

Cited by 76 publications

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“…A exploratory drill hole into the unexposed part of the intrusion unfortunately did not reveal the thickness of the HZ or the nature of the very first cumulates as it only extended about 150 m into the HZ (Humphreys 2009;Maaløe 1976), but it has been argued that the bottom of the drill hole is close to the intrusion base (Holness et al 2007;Humphreys 2009). However, Nielsen (2004) models the HZ with an increasing thickness toward the south and the compositions of HZ gabbros or troctolites under the central and southern parts of the intrusion are not constrained.…”

Section: Discussionmentioning

confidence: 99%

“…The lowest part of the LS is unexposed and is traditionally referred to as the Hidden Zone (HZ), its relative size is unknown but various estimates for HZ range from 15 to 70% of the entire intrusion (Blank and Gettings 1973;Maaløe 1976;Norton et al 1984;Wager 1960). The lowermost part of LS denoted Lower Zone a (LZa) and the drilled part of HZ have essentially the same mineralogy (Maaløe 1976) and consist of cumulus plagioclase and olivine with poikilitic augite.…”

Section: Geological Settingmentioning

confidence: 99%

“…The lowermost part of LS denoted Lower Zone a (LZa) and the drilled part of HZ have essentially the same mineralogy (Maaløe 1976) and consist of cumulus plagioclase and olivine with poikilitic augite. Inverted pigeonite and interstitial oxides occur in small amounts.…”

Section: Geological Settingmentioning

confidence: 99%

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Parental magma of the Skaergaard intrusion: constraints from melt inclusions in primitive troctolite blocks and FG-1 dykes

Jakobsen

Tegner

Brooks

et al. 2009

Contrib Mineral Petrol

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Troctolite blocks with compositions akin to the Hidden Zone are exposed in a tholeiitic dyke cutting across the Skaergaard intrusion, East Greenland. Plagioclase in these blocks contains finely crystallised melt inclusions that we have homogenised to constrain the parental magma to 47.4-49.0 wt.% SiO 2 , 13.4-14.9 wt.% Al 2 O 3 and 10.7-14.1 wt.% FeO T . These compositions are lower in FeO T and higher in SiO 2 than previous estimates and have distinct La/Sm N and Dy/Yb N ratios that link them to the lowermost volcanic succession (Milne Land Formation) of the regional East Greenland flood basalt province. New major-and trace element compositions for the FG-1 dyke swarm, previously taken to represent Skaergaard magmas, overlap with the entire range of the regional flood basalt succession and do not form a coherent suite of Skaergaard like melts. These dykes are therefore re-interpreted as feeder dykes throughout the main phase of flood basalt volcanism.

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Section: Discussionmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

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Parental magma of the Skaergaard intrusion: constraints from melt inclusions in primitive troctolite blocks and FG-1 dykes

Jakobsen

Tegner

Brooks

et al. 2009

Contrib Mineral Petrol

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“…Although the cumulus mineral assemblage (cumulus olivine and intercumulus plagioclase) is at variance with the earliest formed Skaergaard cumulates (cumulus plagioclase and interstitial olivine, Maaløe 1976;Hoover 1989a), it is fair to say that our knowledge of the MBS at the base of the intrusion is limited. The chilled margin is variable in texture and composition (Hoover 1989a), and it is likely that heterogeneity could lead to local variations in the cumulus mineral assemblages.…”

Section: Relationship To the Skaergaard Intrusionmentioning

confidence: 99%

Platinum-group mineralization at the margin of the Skaergaard intrusion, East Greenland

et al. 2017

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Two occurrences of platinum-group elements (PGEs) along the northern margin of the Skaergaard intrusion include a sulfide-bearing gabbro with slightly less than 1 ppm PGE + Au and a clinopyroxene-actinolite-plagioclase-biotiteilmenite schist with 16 vol% sulfide and 1.8 ppm PGE + Au. Both have assemblages of pyrrhotite, pentlandite, and chalcopyrite typical for orthomagmatic sulfides. Matching platinumgroup mineral assemblages with sperrylite (PtAs 2 ), kotulskite (Pd(Bi,Te) 1-2 ), froodite (PdBi 2 ), michenerite (PdBiTe), and electrum (Au,Ag) suggest a common origin. Petrological and geochemical similarities suggest that the occurrences are related to the Skaergaard intrusion. The Marginal Border Series locally displays Ni depletion consistent with sulfide fractionation, and the PGE fractionation trends of the occurrences are systematically enriched by 10-50 times over the chilled margin. The PGE can be explained by sulfide-silicate immiscibility in the Skaergaard magma with R factors of 110-220. Nickel depletion in olivine suggests that the process occurred within the host cumulate, and the low R factors require little sulfide mobility. The sulfide assemblages are different to the chalcopyrite-bornite-digenite assemblage found in the Skaergaard Layered Series and Platinova Reef. These differences can be explained by the early formation of sulfide melt, while magmatic differentiation or sulfur loss caused the unusual sulfide assemblage within the Layered Series. The PGEs indicate that the sulfides formed from the Skaergaard magma. The sulfides and PGEs could not have formed from the nearby Watkins Fjord wehrlite intrusion, which is nearly barren in sulfide. We suggest that silicate-sulfide immiscibility led to PGE concentration where the Skaergaard magma became contaminated with material from the Archean basement.

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“…Several natural occurrences of reversely zoned plagioclases have been described from maficultramafic plutonic rocks (e.g. Maaloe 1976;Berg 1980;Mathison 1987), and have been interpreted in terms of supercooling through heat loss to country rocks or abrupt loss of volatile from the magma. It is unlikely the zoning results from metamorphic or magmatic reaction between pyroxenes and plagioclase (or a plagioclase liquid), or a secondary effect of K-metasomatism, because coexisting metamorphic pyroxenes would be Ca-rich diopsides and not the Ca-poor orthopyroxenes observed.…”

Section: Plagioclasementioning

confidence: 99%

Genesis of the Precambrian copper-rich Caraiba hypersthenite-norite complex, Brazil

Oliveira¹,

Tarney

1995

Mineral. Deposita

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Abstract. Caraiba, the largest Brazilian copper deposit under exploitation, consists mostly of disseminated and remobilised bornite and chalcopyrite hosted in early Proterozoic norite and hypersthenite. The mafic igneous complex comprises multiple intrusions of dykes, veins and breccias of norites and hypersthenites, with minor proportions of amphibolised gabbronorite and peridotite xenoliths transported by the magma from deeper levels in the lithosphere. The country rocks are high-grade gneisses, granulites and metasediments. Compositions of plagioclase (An6o-40) and orthopyroxene (EnTo-6o) fall in a narrow range similar to the Koperberg Suite from the Okiep copper district, South Africa, and to that in many massif-type anorthosites. Whole-rock major and trace element geochemistry indicate a parental magma enriched in Fe, LREE, P, K, and Cu. Negative Nb anomalies on multi-element plots and fractionated REE patterns, along with sulphide sulphur isotopes in the range 634S = -1.495 to + 0.643%o, suggest a primary mantle lithosphere source, although a lower crustal source for the gabbronorite and peridotite xenoliths cannot be excluded. Geochronological and field evidence indicate that both norite and hypersthenite are likely to have been emplaced during a major sinistral transcurrent (partly transpressional) shearing event associated with the waning stage of evolution of the early Proterozoic Salvador-Curag~ orogen.

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The Zoned Plagioclase of the Skaergaard Intrusion, East Greenland

Cited by 76 publications

References 0 publications

Parental magma of the Skaergaard intrusion: constraints from melt inclusions in primitive troctolite blocks and FG-1 dykes

Parental magma of the Skaergaard intrusion: constraints from melt inclusions in primitive troctolite blocks and FG-1 dykes

Platinum-group mineralization at the margin of the Skaergaard intrusion, East Greenland

Genesis of the Precambrian copper-rich Caraiba hypersthenite-norite complex, Brazil

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