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Document Type |
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Article In Journal |
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Document Title |
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Mantle-crustal Source of Mafic-felsic Magmas in the Dubr-Igla Intrusive Complex, Egypt: Inference from Geochemistry and Sr-Nd Isotopic Study دراسة جيوكيميائية ونظائرية للروبيديوم - استرنشيوم والسماريوم - نيودميوم لمعقد دوبر - عجلة المتداخل بمصر : مثال لصهارات قاعدية - حمضية متمازجة |
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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 Dubr-Igla intrusive complex (DIC) is a composite
batholith intruded into the Pan-African terrain of the Egyptian basement
complex. It represents an uplifted tectonic block, comprising a
diverse rock association ranging from gabbro to granite. These rocks
belong to two distinct suites; the gabbroid-diorite (maficintermediate)
and granodiorite-monzogranite (felsic) suites. The gabbroid-
diorite suite has a calc-alkaline affinity and an overall depletion
of Nb, Y, K, and Rb with slightly fractionated REE pattern (La/Ybn =
0.96 -3.72). The granodiorite and monzogranites are late to post orogenic
calc-alkaline rocks with metaluminous to mildly peraluminous
character and are relatively enriched in LIL elements but depleted in
HFS elements. They have fractionated REE patterns (La/Ybn =2.62-
6.97), flat HREE (Gd/Ybn = 0.89-1.10) and well-developed negative
Eu anomalies (Eu/Eu =0.74-3.0). The granitoid rocks of the DIC have
trace element and REE signatures characteristic of I-type granites
formed in subduction-related, arc environments.
The whole-rock Rb-Sr isochron ages of the monzogranites and the
diorite-quartz diorite from DIC are 644 ± 7 Ma and 704 ± 13 Ma, respectively.
The diorite-quartz diorite shows a narrow range of tNd
(+ 6.7 - + 8.5) and initial 87Sr/86Sr ratio (0.7022-0.7025). These isotopic
characteristics and the overall depletion of the LIL elements and
LREE and low Rb/Sr suggest that they had been derived from a depleted
mantle source. The granodiorite and monzogranites have low
initial 87Sr/86Sri ratio (0.7025 - 0.7035) and positive spread tNd (+ 3.4 - + 5.2), which indicate that their protolith was either mantle or
most likely juvenile lower crust that had been separated from the mantle.
Isotopic, REE data and numerical modeling performed on the three
rock types of the DIC (diorite-quartz diorite, granodiorite and monzogranite)
indicate that complex petrogenetic processes generated
them as follows: 1) the diorite-quartz diorite was formed by 10%-15%
partial melting of mantle-derived basaltic source similar in composition
to the associated gabbroid rocks; 2) the monzogranites were derived
through: a dehydration melting (30%) of mafic metaigneous
lower crustal material due to underplating by a mantle-derived magma
which supplies heat budget for melting followed by about 70%-80%
fractional crystallization of a crustal derived- primitive granitic melt
to yield the differentiated monzogranites in the DIC; 3) the granodiorite
shows abundant field and petrographic evidence for variable
extent of mafic-felsic magma interactions (mingling, mixing and heterogeneous
hybridization). Least squares mixing tests, using trace and
major elements support the formation of the granodiorite rocks by a
simple mixing of two end-members, the diorite and the less differentiated
monzogranite. A proportion of the diorite end-member
ranging between 15 and 50% can explain the observed chemical variations
in the granodiorite. |
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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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38 |
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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
| محمد عبدالسميع حسنين | MOHAMED A. HASSANEN | Researcher | | |
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