Ghazi Saffarini

A late Proterozoic bimodal volcanic/subvolcanic suite from Wadi Araba, southwest Jordan

Abstract Geotectonic setting, age relationships, petrography and geochemistry of a Pan-African bimodal volcanic/subvolcanic suite have been examined. The volcanic phase terminated the Pan-African molasse evolution and spans the time interval 550-540 Ma. The volcanics, forming a 70 km NNE-SSW trending belt, are distributed predominantly as rhyolitic lava flows and subordinately as trachybasalts and trachyandesites. The composition of the numerous dikes varies from basalt to trachyandesite and rhyolite. The rhyolites are typified as alkali-rhyolites and comendites. Geochemical criteria characterize a bimodal suite, which is not of cogenetic origin. The basalts are mantle-derived, fractionation -controlled products, whereas the alkali-rhyolites and comendites were generated by partial melting of continental crustal rocks. The investigated magmatic suite has been compared with equivalent suites from the Arabian-Nubian Shield.

Large tectonic and lithospheric structures of the Red Sea region

Abstract Using new tectonic data regarding the timing and mechanical development of large fracture structures and a review of deep seismic data especially in relation to crustal thickness, a geodynamic evolutionary model for the Nubo-Arabian region is described. Combination of the data sets results in a 3-D picture of the crustal structure of the region and definition of problems regarding the geodynamic evolution of the Red Sea structure. Evidence from northwest Saudi Arabia, bordering the northern end of the Red Sea, suggests that rifting began around 32–30 Ma. During the Miocene, rifting intensified probably including significant lithospheric thinning. This first stage of development ended in the Middle Miocene, about 14 Ma, when the complete rift structure was about as wide as the present day Gulf of Suez. Between the Middle Miocene and the Upper Miocene/Pliocene boundary, about 10 ± 2 Ma, the Aqaba-Levant structure became active and thus the Gulf of Suez became essentially stagnant. Since this time about 70% of the total opening of the Red Sea has occurred, again probably including significant lithospheric thinning. This opening has been taken up totally by the movement along the Aqaba-Levant fault. Finally, about 5 Ma seafloor spreading began in the central axial trough of the Red Sea south of 21°N. A better knowledge of the thickness and nature of the present day Red Sea crust is still required so that the amount of opening of the Red Sea can be more accurately estimated.

Spatial distribution of uranium and vanadium in the upper phosphorite member in Eshidiyya basin, southern Jordan

Geostatistical analysis of geochemical exploration data can provide useful information for evaluating the mineralization potential of geologic bodies. The main objective of this study was to evaluate the spatial distribution of U and V over an area in the upper phosphorite member, the A0 unit, in Eshidiyya basin in southern Jordan. Drill-hole samples were analyzed. The geochemistry of the analyzed elements was assessed. The spatial variability of U and V was also assessed using semivariance analysis. Both U and V were found to exhibit a normal distribution as indicated by the constructed histograms and the calculated skewness and kurtosis coefficients. Exponential models with nugget effects were fitted to the experimental semivariograms. Ordinary kriging was performed to generate geochemical maps. The applied interpolation technique proved to be the best in producing geochemical exploration maps for both U and V in Eshidiyya phosphorites. The constructed geochemical maps helped visualize a WNW–ESE U mineralization trend in the studied phosphorites. This trend should be taken into consideration in any future exploration programs for U in south Jordan.

Quantifying the chemical variability of a Precambrian diabase from south Jordan using stochastic techniques: a proposal

Abstract A late Precambrian diabase from south Jordan is used as an introductory case study to examine the possibility of stochastically quantifying the chemical variability of given volcanic rock constituents based on their total alkali (TA) and silica (S) contents. The primary aim has been to quantify the chemical behavior of the rock constituents studied in order to evaluate whether their sample constituents are chemically interdependent, i.e., if knowing one tells us anything about the other, and if so over what range this occurred. The application of the autocorrelogram analysis revealed that most of the rock constituents exhibit specific chemical dependence between 0.40 and 0.80 wt.% along the silica direction and between 0.10 and 0.30 wt.% along the total alkali direction. The deduced autocorrelation functions were found to be correlated over certain chemical ranges with patterns of three basic types: typical; having a large zone of influence; and cyclic with nested structures. The application of semivariogram analyses, on the other hand, indicates that the rock constituents are chemically interdependent over a larger scale, that their interdependence is greater than that encountered when applying autocorrelation techniques (2–5% for major oxides and from 0.87 to 5.30% for Sr and Ni), and that many variables exhibit inherited random variability. The determined ranges of chemical dependence could be used to characterize differentiation trends which prevailed during rock formation, and to develop more precise predictive models regarding petrogenesis.

Distinguishing depositional environments of the Lower Cambrian–Lower Cretaceous siliciclastic sequence of Jordan using geostatistical techniques: A proposal

Applying geostatistical techniques, semivariogram function, and kriging interpolation on the Lower Cambrian–Lower Cretaceous siliciclastic sequence of Jordan yielded a discriminatory diagram that can be utilized to discriminate between the fluvial channel, fluvial floodplain, and shallow marine depositional environments. The mean-sorting index contour values equal to 2.5 or below were found to be indicative of a fluvial channel depositional environment, mean-sorting index contour values above 4.5 may indicate a shallow marine depositional environment, whereas mean-sorting index contour values ranging between 2.5 and 4.5 could indicate a fluvial floodplain depositional environment. The validity of the suggested technique stems from its ability to discriminate between the studied samples of already proven sedimentary environments. Similar studies on other clastic sedimentary rocks would indicate whether this conclusion is valid only for the case study or for all other clastic deposits of different ages, at different locations and of other depositional environments.