Mg-Al sapphirine- and Ca-Al hibonite-bearing granulite xenoliths from the Chyulu Hills Volcanic Field, Kenya

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Serval ID
serval:BIB_2EF763202FE9
Type
Article: article from journal or magazin.
Collection
Publications
Title
Mg-Al sapphirine- and Ca-Al hibonite-bearing granulite xenoliths from the Chyulu Hills Volcanic Field, Kenya
Journal
Journal of Petrology
Author(s)
Ulianov A., Kalt A.
ISSN-L
0022-3530
Publication state
Published
Issued date
2006
Peer-reviewed
Oui
Volume
47
Pages
901-927
Language
english
Notes
ISI:000236432600003
Abstract
Basanites of the Chyulu Hills (Kenya Rift) contain mafic Mg-Al and Ca-Al
granulite xenoliths. Their protoliths are interpreted as troctolitic
cumulates; however, the original mineral assemblages were almost
completely transformed by subsolidus reactions. Mg-Al granulites contain
the minerals spinel, sapphirine, sillimanite, plagioclase, corundum,
clinopyroxene, orthopyroxene and garnet, whereas Ca-Al granulites are
characterized by hibonite, spinel, sapphirine, mullite, sillimanite,
plagioclase, quartz, clinopyroxene, corundum, and garnet. In the Mg-Al
granulites, the first generation of orthopyroxene and some spinel may be
of igneous origin. In the Ca-Al granulites, hibonite (and possibly some
spinel) are the earliest, possibly igneous, minerals in the
crystallization sequence. Most pyroxene, spinel and corundum in Mg-Al
and Ca-Al granulites formed by subsolidus reactions. The qualitative P-T
path derived from metamorphic reactions corresponds to subsolidus
cooling, probably accompanied, or followed by, compression. Final
equilibration was achieved at T approximate to 600-740 degrees C and P <
8 kbar, in the stability field of sillimanite. The early coexistence of
corundum and pyroxenes (+/- spinel), as well as the association of
sillimanite and sapphirine with clinopyroxene and the presence of
hibonite, makes both types of granulite rare. The Ca-Al hibonite-bearing
granulites are unique. Both types enlarge the spectrum of known
Ca-Al-Mg-rich granulites worldwide.
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Yes
Create date
24/09/2012 19:35
Last modification date
24/09/2019 7:49
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