Medium pressure crystallization of a monchiquitic magma — evidence from megacrysts of Drever's block, Ubekendt Ejland, West Greenland

Larsen, Jørgen Gutzon

doi:10.1016/0024-4937(81)90053-0

Cited by 21 publications

(25 citation statements)

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“…In the west Greenland Tertiary province (Clarke and Pedersen, 1976) scattered nodules of serpentinite, dunite with harzburgitic affinities, and a solitary Iherzolite, 1-5 cm in diameter, have been obtained from one of the uppermost alkaline lavas on Ubekendt Ejland ( fig. 1) (Larsen, 1977). A single lherzolite inclusion, 3 cm in size, has also been found in one of the late lamprophyre dykes (Larsen, 1981).…”

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Mantle-derived dunite and lherzolite nodules from Ubekendt Ejland, west Greenland Tertiary province

Larsen

1982

Mineral. mag.

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ABSTRACT. Scattered dunite and iherzolite nodules occur in one of the youngest basanitoid lavas on Ubekendt Ejland. They have protogranular to porphyroclastic textures. The dunites are oamposed of olivine (Fo93.2-91.9b), enstatite (En93.4_92.8) lOW in Al2Oa and CaO, and Cr-spinel (61-13% Cr20 3 and 3-55% AI203). A solitary lherzolite module has olivine (Fo94.7_94.1), enstatite (En94.7-94.2), Cr-rich spinel, Ti-phlogopite (11% TiO2), and hyalophane. Petrographic evidence suggests that the two latter minerals have not been introduced by magmatic injection from the host in spite of the refractory nature of the coexisting phases, and metasomatic processes prior to the last deformation are therefore indicated. Partial melting of such mantle material would presumably produce small amounts of alkaline liquids even at very high temperatures. Another lherzolite nodule from a lamprophyre dyke has minerals with lower Mg/(Mg + Fe) ratios which, together with its preserved igneous textures, suggest a high-pressure precipitate. The lowest wellestablished equilibrium temperatures of 700-830~ for both dunites and lherzolites indicate a pressure regime of 12-17 kbar, according to the oceanic geotherm, whereas unrealistically high pressure (20-5 kbar) are suggested using the continental shield geotherm.

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“…1) (Larsen, 1977). A single lherzolite inclusion, 3 cm in size, has also been found in one of the late lamprophyre dykes (Larsen, 1981).…”

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Mantle-derived dunite and lherzolite nodules from Ubekendt Ejland, west Greenland Tertiary province

Larsen

1982

Mineral. mag.

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“…They are predominantly anorthoclase with subordinate sanidine and albitic plagioclase. Sanidine megacrysts are reported only from Prezazzo-Monzoni area, Italy (Lucchini et al, 1969); Ubekendt Ejiand, Greenland (Larsen, 1981); Keluo, NE China (this work), and Scotland (Aspen et al, 1990). The hosts for all the sanidine megacrysts except those from Scotland, whose compositions are not documented, are potassic (K20/Na20 >1.0) mafic rocks.…”

Section: Origins Of Hyalophanes and Their Contrasting Zoning Patternsmentioning

confidence: 71%

The origins of contrasting zoning patterns in hyalophane from olivine leucitites, Northeast China

et al. 1993

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Olivine (ol) leucitite lavas from Northeast China contain hyalophanes with contrasting Ba-zoning patterns. The hyalophanes occur: (1) in a magmatic inclusion (DZ2n), consisting of barian-titanian phlogopite + hyalophane + leucite + sodalite, and (2) as a mantle surrounding a sanidine megacryst (DZ19). Hyalophanes contain 4.6-20.2 mol.% celsian (Cn). The DZ2n hyalophane is normally zoned with respect to Ba (decreasing Ba toward rim), whereas the hyalophane mantle of megacryst DZ19 is reversely zoned. DZ2n probably crystallised from an extensively evolved (>80 wt.% crystallisation) potassic melt derived from a primitive magma chemically similar to the host, at relatively low temperatures and pressures (e.g. T-720 ~ P-2 kbar). Competition with barian-titanian phlogopite for Ba, and limited Ba supply from the residual melt are the main cause for the normal Ba zonation. Sanidine megacryst DZ19 originated as a high P-T product (e.g. T >950 ~ P > 15 kbar) of an evolved leucite (lc) basanite/trachybasalt genetically related to ol-leucitites. Subsequently, it was incorporated into the host ol-leucititic magma at which point it was partially resorbed and then mantled by hyalophane. An increase in KBa affliq values with decreasing temperature and pressure and cocrystallisation of the hyalophane mantle with Ba-free phases may have caused the unusual reverse zonation.

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“…Its presence has been described in low-pressure skarns, low to medium pressure regional metamorphic rocks, medium to high pressure/depth assemblages of amphibolite and granulite facies and even in kimberlites and basalts (Baker and Newton, 1994 and references therein). It is also thought to occur as a primary mineral in alkaline igneous rocks (Larsen, 1981;Goff et al, 1982). Well-known occurrences of scapolite in Greece include the Serifos Island skarn (Mposkos, 1978), the Kerdillion Unit amphibolites of the Serbo-Macedonian Massif (Rentina and Stratoni areas) (Kassoli-Fournaraki, 1981), the Chalkidiki peninsula quartz amphibolites (Sarti area) (Kassoli-Fournaraki, 1991) and the eastern Rhodope amphibolitized eclogites (Organi-Kimi area) (Mposkos and Mpaziotis, 2005).…”

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Marialitic Scapolite Occurences From the Kimmeria-Lefkopetra Metamorphic Contact, Xanthi (N. Greece)

Mouchos¹,

Papadopoulou

Williamson

et al. 2017

geosociety

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Medium pressure crystallization of a monchiquitic magma — evidence from megacrysts of Drever's block, Ubekendt Ejland, West Greenland

Cited by 21 publications

References 63 publications

Mantle-derived dunite and lherzolite nodules from Ubekendt Ejland, west Greenland Tertiary province

Mantle-derived dunite and lherzolite nodules from Ubekendt Ejland, west Greenland Tertiary province

The origins of contrasting zoning patterns in hyalophane from olivine leucitites, Northeast China

Marialitic Scapolite Occurences From the Kimmeria-Lefkopetra Metamorphic Contact, Xanthi (N. Greece)

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