Document Details
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Document Type |
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Thesis |
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Document Title |
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PETROLOGY AND MINERALIZATION OF MAFIC-ULTRAMAFIC ROCKS IN SELECTED OPHIOLITE AND LAYERED INTRUSION COMPLEXES IN SAUDI ARABIA : A COMPARATIVE STUDY بتروغرافي وتمعدنات الصخور المافية والفوق مافية في بعض تداخلات الأفيولايت والتداخلات الطبقية في المملكة العربية السعودية: دراسة مقارنة |
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Subject |
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Faculty of Earth Sciences |
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Document Language |
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Arabic |
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Abstract |
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Mafic-ultramafic rocks in the Arabian Shield of Saudi Arabia have three genetically sources with which several ore deposit types are located: (1) ophiolitic upper mantle rocks including dunites, harzburgites, gabbros and norite, where podiformchromitite deposits and associated platinum group elements (PGE) are linked; (2) Layered mafic-ultramafic intrusions, where characteristic Fe-Ti-V- Ni-Co PGE deposits are located; and (3) concentrically-zoned (Alaskan type) mafic–ultramafic intrusions,where also characteristic Fe-Ti-V-Ni-Co PGEs deposits and chromites are located. For these reasons, some localities in the Arabian Shield which contains different types of mafic-ultramafic rocks were selected to be investigated for their petrology,geochemistry and mineralization types.
Gabal Taftafan mafic–ultramafic complex which lies within the central part of the Makkah quadrangleis one of the selected mafic-ultramafic areas in the west central Arabian Shield. It is a part of the Jeddah terrane in the Precambrian basement, Western Arabian Shield of Saudi Arabia. Bir Tuluha mafic-ultramafic complex is another selected locality in the northern Arabian Shield of Saudi Arabia to be compared with the first, Gabal Taftafan complex. BirT uluhaophiolite represents a part of Nabitah belt in North Arabian Shield, Saudi Arabia. This study was focused on the petrology, geochemistry (bulk-rock and mineral chemistry) and mineralization of the rock assemblage in these two areas. The Gabal Taftafan mafic–ultramafic complex is a well-differentiated rock association, which comprises of dunite core, hornblende and plagioclase-bearing peridotites, troctolite, clinopyroxenite and marginal gabbro, in a distinctive zonal structure.
The bulk-rock geochemistry of the Gabal Taftafan mafic–ultramafic rocks is characterized by a tholeiitic/sub-alkaline affinity with high Mg# in the ultramafic core (0.84) and is systematically decreased towards the marginal gabbro (0.60). The patterns of trace elements show enrichment in the fluid-mobile elements (Sr, Ba) and a pronounced negative Nb anomaly which reflect a hydrous parental magma generated in a subduction tectonic setting. The mafic–ultramafic rocks of theGabal Taftafan complex have low total rare earth elements (REE) displaying sub-parallel patterns leading to the assumption that these rocks are comagmatic and are formed by fractional crystallization from a common magma type. The platinum-group elements (PGE) content of all rock types in the Taftafan complex is very low, with ΣPPGE >ΣIPGE; displaying slightly positive slopes of the PGE distribution patterns. The chemistry of ferromagnesian minerals is characterized by a high forsterite (Fo) olivine with wide range (Fo91–67), from ultramafic core to the marginal gabbro, Ca-rich diopsidic clinopyroxene, and calcic hornblende. Orthopyroxene is almost absent from all rock types, or very rare when present. Hornblende and Ca-plagioclase possess the longest crystallization history since they are present in almost all rock types of the complex. Spinels in the dunite and hornblende-bearing peridotite core show homogeneous composition with intermediate Cr# (0.53–0.67). Plagioclase-bearing peridotite and troctolite have two exsolved types of spinel; Al-rich and Fe-rich varieties. All spinel varieties in the mafic–ultramafic rocks have high Fe3+ and TiO2 contents. The estimated melt composition in equilibrium with Gabal Taftafan complex is mostly similar to that of the supra-subduction zone (SSZ) boninitic magmas.
The Gabal Taftafan mafic–ultramafic rocks show many similarities with the Alaskan-type mafic–ultramafic complexes, including the internal zonal lithology, bulk rock geochemistry, and mineral chemistry. Thus, it is neither related to a fragment of ophiolite sequence nor to the stratiform mafic–ultramafic intrusion. The location of the Gabal Taftafan complex along a major fracture zone parallel to the suture between Jeddah and Asir terranes in addition to the aforementioned striking similarities to the Alaskan-type complexes, suggests a formation in subduction-related setting from a common hydrous mafic magma.
The Bir Tuluha mafic-ultramafic complex consists mainly of serpentinized harzburgites, dunites, chromitite pods, and locally layered meta-gabbros. Podiform chromitites are widely distributed as lensoidal pods of variable sizes that are occasionally enveloped by dunite envelopes, and both of them are enclosed within harzburgite. Chromian spinels in all the studied chromitite pods are of high-Cr variety; Cr# show restricted range between 0.73 and 0.81. Chromian spinels of the dunite envelopes also show high Cr#, but slightly lower than those in the chromitite pods (0.73-0.78). Chromians pinels in the harzburgite host show fairly lower Cr# (0.49-0.57) than those in dunites and chromitites. Platinum-group elements in chromitite pods display general steep negative slopes of PGE distribution patterns. Chromitite pods have typical ophiolitic chromitite PGE patterns; being show enrichment in IPGE (Os, Ir andRu), over PPGE (Rh, Pt and Pd). The Bir Tuluha complexis a unimodal type in terms of the presence of Ru-rich laurite as the sole primary platinum-group minerals (PGM) in chromitite pods. These petrological features are indicating that the Bir Tuluha complex is a typical ophiolite slice that was initially generated from a mid-ocean ridge environment and then invaded later by a widespread homogeneous boninitic melt produced above supra-subduction zone setting. The Bir Tuluha ophiolite belt is mostly similar to the mantle section of the Proterozoic and phanerozoic ophiolites, but it is a"unimodal" type in terms of high-Cr chromitites and PGE-PGM distribution. There are so many chromite pods in the Bir Tuluha ophiolite, which can be mined economically, since they are of metallurigical chromite type.
The obtained data shows distinctive features in petrology, geochemistry, mineral chemistry and mineralization types between Gabal Taftafan mafic-ultramafic complex and those in the Bir Tuluha ophiolite complex. Further field studies are urgently needed to estimate the presence and frequent distribution of Cr-Fe-Ti-V-Ni-Co-PGEs depositsin the Gabal Taftafan mafic-ultramafic complexes. |
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Supervisor |
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Prof. Ahmed Hassan Ahmed |
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Thesis Type |
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Doctorate Thesis |
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Publishing Year |
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1439 AH
2018 AD |
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Added Date |
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Monday, July 23, 2018 |
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Researchers
| عبدالمنعم مرصاص حبتور | Habtoor, Abdelmonem Marsas | Researcher | Doctorate | |
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