Al-spinels in primitive arc volcanics

Dellapasqua, FN, Kamenetsky, VS, Gasparon, M, Crawford, AJ and Varne, R (1995) Al-spinels in primitive arc volcanics. Mineralogy and Petrology, 53 1-3: 1-26. doi:10.1007/BF01171944

Author Dellapasqua, FN
Kamenetsky, VS
Gasparon, M
Crawford, AJ
Varne, R
Title Al-spinels in primitive arc volcanics
Journal name Mineralogy and Petrology   Check publisher's open access policy
ISSN 0930-0708
Publication date 1995
Sub-type Article (original research)
DOI 10.1007/BF01171944
Volume 53
Issue 1-3
Start page 1
End page 26
Total pages 26
Publisher Springer-Verlag
Language eng
Subject 1908 Geophysics
1906 Geochemistry and Petrology
Abstract Al-rich spinels (100Cr/(Cr + Al) < 5, Al2O3 > 50 wt%) are common in alpine peridotites, both terrestrial and lunar mafic and ultramafic cumulates, and in certain metamorphic rocks, but they are apparently rare in terrestrial volcanic rocks. Here we describe the occurrence of Al-rich spinel inclusions in olivine phenocrysts in island arc volcanic rocks from five new localities: Bukit Mapas (Sumatra) and eastern Bali in the Sunda arc, and Epi, Merelava, and Ambrym islands in the Vanuatu arc. More commonly, relatively Cr-rich spinels also occur as inclusions in the saine olivine phenocrysts, and it appears that the Cr-poor aluminous spinels must be in disequilibrium with the host basaltic melts. In the rocks studied, Al-rich spinels also coexist with trapped silicate glasses and highly aluminous clinopyroxene in melt inclusions in olivine. This paragenesis suggests an origin involving contamination by localized Al-rich melt pockets as opposed to a xenocrystic origin. Two mechanisms to produce this high-Al melt in basaltic magma chambers are suggested: (1) localized high-Al melt production by complete breakdown of assimilated lower crustal gabbroic rocks. In this model the high-Al melt may crystallise Al-rich spinels which are subsequently trapped as solid inclusions by phenocryst phases of the host basaltic melt or may be trapped as melt inclusions in which Al-rich spinels and Al-rich clinopyroxene crystallise as daughter phases, and (2) in congruent breakdown of amphibole in amphibole-rich cumulates in sub-arc, or sub-OIB volcano magma chambers. The latter reaction produces a melt with ∼ 20-22% of Al2O3, aluminous clinopyroxene, Al-rich spinel and olivine. Mixing between these amphibole breakdown products and host basaltic melt may occur throughout the evolution of a magmatic system, but particularly during recharge with hot magnesian basalt batches. Aluminous spinels and aluminous clinopyroxene produced during amphibole breakdown, or perhaps crystallised from aluminous melt produced in the saine reaction, are incorporated into the magma during recharge, and subsequently trapped, together with the coexisting Cr-spinels, by crystallising olivine and clinopyroxene.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collection: Scopus Import
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Citation counts: TR Web of Science Citation Count  Cited 21 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 23 times in Scopus Article | Citations
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Created: Tue, 02 Feb 2016, 16:15:11 EST by Associate Professor Massimo Gasparon