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Geological View of the Carbonatitic
Rocks at Dibba Area, UAE
Sulaiman A. S. A. Alkaabi & Bahaa Eddin Mahmoud
Department of Geology, College of Science, United Arab Emirates University
P.O. Box: 15551, AlAin UAE, Email: [email protected]
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Content
• Identify Carbonatite
• UAE Carbonatitic Rocks
• Field occurrence
• Petrography
• Major Elements
• Trace Elements signature
• REEs signature
• O & C Isotope
•3/23/2015
Conclusion
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What is Carbonatite?
 Igneous Carbonate (not sedimentary) rock
 Unusual & uncommon intrusive or extrusive
 Formed probably by unusual processes and/or
from unusual source rocks.
 About 450 sites are so far designated.
 Most along interpolate-rifting zones.
 Associated with Alkali magmatic activities.
 Main mineral composition is Carbonate minerals.
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Ol Doinyo Lengia, Tanzania
* The only active
cabonatitic volcano
recorded in the Earth
history.
* Still until nowadays.
Natrocabonatite
= alkali rich
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Carbonatites
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Why it is Important?
 Igneous Carbonate (vs silicate) rocks
 Unusual, uncommon & Rare rock
 Many record high REE concentration
REE: Rare Earth Elements
A group of seventeen chemical elements
consists of yttrium, scandium and the 15
lanthanide elements (lanthanum, cerium,
praseodymium, neodymium, promethium,
samarium, europium, gadolinium, terbium,
dysprosium, holmium, erbium, thulium,
ytterbium, and lutetium).
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UAE Carbonatitic Rocks
•
They are reported in in two main places:
1.
Dibba “Uyaynah” Area
2.
Hatta Area
•
Little, but geochemically significant.
•
Relatively more in Dibba than Hatta
•
Occur within the metamorphic sole of the Semail
ophiolite.
•
Extrusive (Globally few, only 9%)
•
Associate woth alkaline meta volcanics.
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Dibba Carbonatitic Rocks
Location
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Field Occurrence
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Field Occurrence
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Field Occurrence
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Field Occurrence
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Petrography
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Major Elements &
CaO vs. SiO2
Dibba carbonatitic rocks cab
be grouped into three
groups:
1. Calsio
2. Ferro
3. Silico
CaO vs. SiO2 plot show:
• All plot within the
Extrusive boundary
• Calsio and ferro are
clustering close to each
other
• Silico are away from them
and within the fort Portal
Pyroclastics range
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Trace Elements
Two Populations:
1. Depleted
2. Enriched
Same
General
trend
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REE Elements
Two
Populations:
1. Depleted
2. Enriched
Same general
trend
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C & O Isotopes
δ13C and δ18O diagram show
That:
• the samples vary from
primitive mantle
carbonatite (Deines, 1989)
to higher isotopic value.
• Many samples show a high
enrichment of the heavier
C-O isotopes.
• This enrichment is unusual
in pure (unaltered)
carbonatites, and may
signify an fertile source in
the origin of emplacement
history of these rocks.
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Conclusion
• The UAE carbonatites are found associated with the
metamorphic sole of the Semail ophiolite.
• Geochemically appear to be two connected groups.
1. One with a significant enrichment in the REE and trace
elements, close to but little above the unaltered
carbonatite composition.
2. The other reveals a considerable depletion in trace and
REE elements.
• δ18O and δ13C analysis shows an increase in the isotopic
composition of the studied rocks in array from the primary
igneous carbonatite, indicating a heavier isotopic source
affected these carbonatites.
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Conclusion
• From petrographic study, geochemical and isotopic
signatures, the UAE carbonatites might have formed in
association with alkaline volcanic activities at the
oceanic environment of the Semail ophiolite prior its
obduction and final emplacement.
• They had been probably affected by hydrothermal hot
fluid metasomatism that lead to reduce significantly
the characteristic elements of some UAE carbonatites
and probably increase the heavier isotopic composition
• If the enriched Carbonatitic (2nd) rocks found
widespread, mining may be workable.
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