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Document Type |
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Article In Journal |
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Document Title |
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The Late Cretaceous Turabah Ring Dyke, Central Arabian Shield, Kingdom of Saudi Arabia - Geology, Geochemistry and Tectonic Significance قاطع تربه الحلقي من العصر الكريتاوي المتأخر في وسط الدرع العربي - جيولوجيته وجيوكيميائيته والدلالات التكتونية له |
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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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The Turabah ring dyke, in the central Arabian Shield of
Saudi Arabia, is a Late Cretaceous alkaline A-type granite. It was emplaced
at shallow crustal levels in a Pan-African assemblage of calcalkaline
metavolcano-sedimentary association, syn-tectonic metagabbro-
diorite, granodiorite-granite gneiss, tonalite gneiss and syenite.
The metavolcanics and the metagabbro-diorite exhibit petrological and
geochemical characteristics of mantle-derived island-arc rocks, which
were formed by partial melting of a mantle wedge above subduction
zone. The granodiorite-granite gneisses are calc-alkaline I-type granites.
They and the metagabbro-diorite show continuous major and trace
element trends, suggesting that the two suites are genetically related
through fractional crystallization process. The tonalite gneisses possess
low contents of REE (51-74 ppm), Zr (43-72 ppm), Rb (2-17 ppm),
K2O (0.35-1.14 wt. %), Nb (3-5 ppm) and have trace element patterns
not modified greatly by fractionation. These chemical aspects may
suggest their derivation via partial melting of lower crust.
The rocks of the Turabah ring dyke consist of subsolvus monzo-and
syenogranites. They are geochemically evolved (SiO2 = 68-77%),
metaluminous to mildly peralkaline and display a within plate A-type
geochemical signature with enrichment in Fe2O3 (1-4 wt %), Y (7-35
ppm), Nb (3-19 ppm), Rb (45-101 ppm), Zr (101-446 ppm) and depletion
in CaO (0.5-1.9 wt %), MgO (0.02-0.6 wt %), Ba (14-820
ppm) and Sr (5-213 ppm). A model involving partial melting of a
mafic lower continental crust in an extensional environment, to produce
a granodioritic melt, can explain the origin of these rocks. Direct
contamination of that granodioritic melt with an old continental crust
followed by fractional crystallization played an important role in the
evolution and chemical characterization of the Turabah A-type gran58
ites. The complex evolution history of the area may be reflected in the
formation quasi-oval fractures, along which the fractionated melt was
intruded, giving rise to the ring structure in the area. |
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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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14 |
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Issue Number |
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1 |
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Publishing Year |
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1424-1423 AH
2002 - 2003 AD |
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Number Of Pages |
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33 |
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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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