Abstract As part of the NE-trending Mourizidie Shear Zone in south-central Libya (south of Mourizidie pass), four units representing Preccambrian basement rocks (metasediments) were mapped during field work: phyllites (metaclaystone); metapelites (metasiltstone); pasmmites (metasandstone) and Quartzites. Granitic bodies of various sizes (few meters to hundreds of meters) are found throughout the study area. The metasediments and granites are both intruded by veins and dikes having an overall NE trend. Four Palaeozoic sedimentary units were mapped within the study area. The concidence of the S1 foliation with the S0 of the original bedding of the protolith is a proof that the S1 foliation is caused by deep burial. The petrographic description of the minerals in thin section shows an assemblage of sericite, muscovite and biotite, all representing a sub-greenschist facies to greenshcist facies. This low grade metamorphism helped in preseving the original sedimentary structures of the protolith, thus helping in identifying the original bedding plane S0. Faults observed in the field or traced on aerial photograhs belong to three major trend: NE, NNE, and ENE. Folds are extremely diverse in shape, attiude and tightness, thus their classification is equally diverse. This diversity is observed in the field even within a distance of no more than few meters. The isostatic rebound of the basement could have caused this great difference in the attitude of the folds, especially at considerable depths characterised by a kinematically ductile, restricted and contained settingAt least two phases of deformation are present in the area. D1 is marked by the generation of S1, while D2 is marked by the first folding F1 caused by the isostatic rebound he generation of S2 foliation as fan cleavage is directly related to the F1 folding. Some folds underwent refolding, which lead to an F2 phase of folding.Sequential schematic structural model is proposed to explain the structural history of the study area. This model should be tested through intensive detailed field work large scale map in nearby areas.
مسعودة محمد حنبولة (2015)

Abstract The Sarir Sandstone in Messla Oil Field are of Lower Cretaceous ageAptian Alpian and occur in the subsurface of the eastern part of the Messla high in the southeast Sirt Basin. The Sarir Sandstone interpret as fluvial and alluvial fan deposits whereas the Lower Sarir Sandstone were deposited in a braided system as inter-channel bars. The Upper Sarir Sandstone were deposited in the meandering belt of the fluvial system. The Sarir Sandstone is on-lapping Formation and wedge out against Rakb Group. The Sarir Sandstone is unconformable overlies the Pre-Cambrian Basement and unconformable overlain by the Upper-Cretaceous Rakb Group where it is pinching (wedging) out against the Bald Basement; Messla High)). Lithostratigraphic correlations of borehole logs ((well logs)) in concession 65 suggests that deposits gradually downed a fault controlled topographic surface increased in thickness on the down-thrown side of a fault controlled the topographic surface of Pre-Upper Cretaceous Unconformity. IV M. Sc. Hassin Haweel “Sedimentological Aspects of the Sarir Sandstone in Messla Oil Field”, 2015 Core Samples record mainly sandstone units interbedded with sandstone and shale and minor streaks and the Red Shale Unit. Estimation of depositional environment has thus been made from grain size analyses using thin sections. Petrographic studies show that the Sarir Sandstone in composition from (subarkose to arkosic arenite). The Sandstones range from texturally immature to submature, however, much of the clay content is diagenetic in origin and not a function of the depositional regime. Diagenetic studies reveal a gnite complex paragenesis. During early diagenesis, the Sarir Sandstones were modified by Calcite, dolomite, and locally pyrite, diagenesis process; replacements of corroded silica by carbonates. Cementation fluvial sandstones Intrastratal dissolution and precipitation of kaolinite in the resulting pore space. Deformation of micas between more resistant grainy pre-dates one phase of quartz overgrowth, probably the carbonates.The purpose of this study was to investigate in detail the characteristics of the Sarir Sandstone in Messla Oil Field. Another aim was to find out the relation to the adjacent area. The method of this study was conducted with the review of the previousworks in Messla Oil Field; published papers, the open file of the Arabian Gulf Oil Company (AGOCO), well files for the data to be used in constructing maps, cross sections and profiles. Four cored wells (418 feet) V M. Sc. Hassin Haweel “Sedimentological Aspects of the Sarir Sandstone in Messla Oil Field”, 2015 were used for the core descriptions and cut samples that represent the Sarir Sandstone and (130) thin sections were used for the Petrographic analysis with polarized and scanning electron microscopes (SEM). On the other hand, XRD and XRF were not available. The results of the study were: Subsurface investigations including cores (conventional and side walls), petrographic analysis, and wire-line logs suggested that this formation (Sarir Sandstone) can be divided in to three main units in Messla Oil Field; these units are: The Lower Sarir Sandstone, the Red Shale, and the Upper Sarir Sandstone. In the adjacent area Sarir Formation was divided in to five members; Pre-Upper Cretaceous Member-1 unconformably overlying Pre-Cambrian Basement, and upwards; Member 2, Member 3, Member 4, and Member 5 unconformably overlain by Rakb Group. The Lower Sarir Sandstone in Messla Oil Field is characterized by the presence of gravely sandstone, gradually changes in to the Red Shale. Also, from the core descriptions plotted sheets, and the well logs it is finning upwards. The quarzitic sandstones of (the Lower and the Upper Sarir Sandstones) are considered to be the main producing horizons where quartz grains have undergone a complex diagenetic history, including: Authigenesis, quartz and feldspar overgrowths, dissolution, carbonates cementation, and replacement. The principal conclusion was that: the gravelly sandstone unit at the Lower part of the Lower Sarir Sandstone was deposited, most likely in a braided system as inter-channel bars. The sandstone unit of the Upper Sarir VI M. Sc. Hassin Haweel “Sedimentological Aspects of the Sarir Sandstone in Messla Oil Field”, 2015 Sandstone was deposited in the meandering belt of the fluvial system. The shale facies of the Red Shale unit represents a well-developed break between the Lower Sarir Sandstone and Upper Sarir Sandstone units; it also provides a good seal for the underlying sandstone of the Lower Sarir Sandstone. The nature of the shale facies, (i.e. lack of organic content, and presence of oxidizing conditions indicated by iron oxides color, indicate that they are not a significant source of hydrocarbons. On the other hand, the Rakb Shale isthe only source rock in the studied and adjacent areas.
حسين محمد علي حويل (2015)

Abstract The basaltic Intrusions of the Central Jabal Nafūsah Foothills which extend from NW Wādi Zāret to NE Wādi Ghān Dām are part of the latest stage of Gharyān Volcanic Province (GVP). These intrusions are classified on basis of their shape and mechanism of emplacement into four kinds of volcanic bodies. These are; sheets (dykes and a sill), dykes associated with volcaniclasts, volcanic cone and lava mounds. Generally, the dyke emplacements are restricted only to the area between Wādi Zāret to Abū Ghaylān, while the other forms extend from Rās al Mazūl Dome to Wādi Ghān Dam. The more differentiated rocks are restricted to the area between Rās al Mazūl Dome and Wādi Ghān. Farther west towards Wādi Zāret, ultramafic xenoliths and magnesium-number increase, suggesting closer proximity to the source. The rocks are essentially alkaline with within Intraplate signatures. They straddle the composition from picrites, basanites, alkali basalts through hawaiites, mugearite to benmoreites with a compositional gap between the last two types. Generally, the phenocrysts are represented by foresteritic olivine, Cadiopsidic pyroxene, magnesiotaramitic amphibole, plagioclase, K-feldspar and titanomagnetite. The chemical composition of the mafic minerals indicates that they are high pressure phenocryst phases. The most primitive picrites satisfied the criteria of primary mantle melts. The rocks are generally, enriched in LILE suggesting an enriched mantle source. The studied rocks were grouped into five groups based on incompatible trace element ratios; Group-A includes picrite, basanites and hawaiites, and Group-B includes picrite (Z-3), basanites , alkali basalts, and hawaiites, while Group-C is formed of hawaiites, Group-D is composed of mugearite and Group-E is made up of benmoreites. Picrites and basanites of these rock have high Mg-number (>0.64), high Cr and Ni contents and strong light rare earth element enrichment, but systematic depletion in Rb, K and Ba relative to trace elements of similar compatibility in anhydrous mantle. Alkali basalts and more differentiated magmatic rocks have lower Mg-number and lower abundances of Ni and Cr, and have undergone fractionation of mainly olivine, clinopyroxene, Fe–Ti oxide, amphibole and plagioclase. The variation in the concentrations of major, trace, rare earth elements, and incompatible element ratios in the rock samples demonstrate the heterogeneous character of their source region. Such heterogeneity can be interpreted by the involvement of a heterogeneous mantle reservoir to different degrees of partial melting. The REE data require residual spinel stability peridotite field in the source and constrain the melting process of Group-C and Group-D to 2% to 3.5% degrees of melting respectively, Group-A and Group-B both to 5% degree of partial melting while Group-E to 10% degree of partial melting of spinel lherzolite xenoliths of Al Ourban area. Mass balance modelling of the major suggests two possible FC scenarios; Derivation of basanites and hawaiites of group-A from G-3 picritic parental magma. Derivation of Group-D and Group-E was also possible from these basanites. Derivation of basanites of Group-B from Z-3 picrite parental magma and simultaneous derivation of G-4 and QJ-1 alkali basalts from Z-3 picrite parental magma. V Simple mass-balance calculations suggest that the melting assemblages of picrites and basanites consisted of forsteritic olivine, diopsidic clinopyroxene, Ti-magnetite. While the alkali basalts and more differentiated magmatic rocks, mass-balance calculations suggest that the melting assemblages consisted of sodic plagioclase, magnesiotaramitic amphibole, diopsidic pyroxene, Ti-magnetite, K-feldspar with sub amounts of apatite and sphene.
سمية عون (2015)