Medium pressure crystallization of a monchiquitic magma — evidence from megacrysts of Drever's block, Ubekendt Ejland, West Greenland期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

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

Authors:	Jrgen Gutzon Larsen

Institution:	^a Geologisk Centralinstitut, Øster Voldgade 10, 1350, København K, Denmark

Abstract:	Megacrysts and polymineralic fragments of extraordinary diversity from a Tertiary monchiquitic dyke of Ubekendt Ejland comprise three groups: (1) Cr-diopside-fassaitic diopside + olivine, Fo_90.5?81.5 + CrAl spinels. (II) Fassaitic salite-ferrisalite + KTi-pargasite-ferropargasite + apatite + AlTi-magnetite, (III) Scapolite + hyalophane + potassium feldspar + nepheline + analcime. By comparison with mineralogy and phase relations in the host rock and experimental data from alkaline rocks the megacrysts are related to a sequence of crystallization from primitive monchiquitic to potassic phonolitic magmas rich in H₂O and CO₂ at 5–11 kb. Group I megacrysts formed at temperatures of 1300-1150°C and group II between ? $1150–?800° C and f_{o_{2}} < 10^{?9}$ bar at the latter temperature. High P_co₂ may have stabilized the scapolite in the more evolved liquid and K-feldspar and nepheline began to crystallize at ca. 800°C possibly together with the ferrisalite.

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