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Document Type |
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Article In Journal |
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Document Title |
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Composition-Volume Changes during Metasomatic Alteration of Pan African Andesitic Volcanic Rocks at Gabal El Dokhan Area, Northeastern Desert, Egypt. التغير الحجمي والتركيبي خلال تغير وتحول صخور الانديزيت البركانية في منطقة جبل الدخان ، شمال الصحراء الشرقية ، مصر |
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Subject |
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Earth Sciences |
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Document Language |
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English |
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Abstract |
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Metasomatic alterations of the Late Proterozoic andesites
at Gabal El Dokhan area display obvious change in mineralogical and
chemical composition, if compared with the least altered andesitic
rock types (assumed protoliths). These altered andesitic rocks have
been metamorphosed to lower-middle greenschist facies typified by
biotite-actinolite-chlorite-albite-epidote-quartz-opaque minerals/sphene
assemblages. Five alteration facies have been recognized: 1) Biotitization-
silicification, 2) Sericitization-silicification, 3) Albitizationsilicification,
4) Epidotization-silicification, and 5) Chloritization.
The biotitized-silicified rock types are enriched in K-Rb-Ba-FTSM
and depleted in LREE relative to the least altered rock. The sericitized-
silicified rock types are significantly enriched in K-Rb-Ba
and depleted in FTSM and LREE. The albitized-silicified rock types
are strongly enriched in Na and depleted in LILE and LREE relative
to the least altered rock types. The epidotized-silicified rock types are
enriched in Ca-Cu-Pb and depleted in LILE and LREE. The chloritized
rock types exhibit relative enrichment in Mg, FTSM, Zn-As-Pb
and depletion in LILE and LREE.
The behavior of the Ti, Al, Fet, P, and most HFS elements during
biotitization, sericitization, albitization, epidotization and chloritization
suggests that they were inert during metasomatic modification
of the andesites. Mass balance calculations suggest that volume
change was restricted between zero and up to + 20% for the altered
upper andesites and ?25 and up to +25% for the altered lower andesites
during the different types of metasomatic facies. Elemental
mobilities are interpreted in terms of the controlling mineral phases
and the possible nature of the various metasomatising fluids. |
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ISSN |
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1012-8832 |
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Journal Name |
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Earth Sciences Journal |
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Volume |
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11 |
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Issue Number |
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1 |
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Publishing Year |
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1420 AH
1999 AD |
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Number Of Pages |
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29 |
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Article Type |
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Article |
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Added Date |
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Sunday, October 11, 2009 |
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Researchers
| عزالدين عبدالحكيم خلف | EZZ-EL-DIN A. KHALAF | Researcher | | |
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