Geochemistry and preliminary assessment of resource potential for postorogenic granites of the southwestern Arabian Shield, Kingdom of Saudi Arabia

Abstract

Geochemical data for samples from 55 postorogenic plutons of the southwestern Arabian Shield show that these granitoids are generally less evolved than similar granitoids of the eastern Arabian Shield. Radioelement contents are low to normal relative to typical granitic rocks and uranium contents are distinctly low relative to rocks of the eastern Arabian Shield. The data indicate low favorability for ore deposits of elements that are typically enriched in granites at the end stages of magmatism such as tin, tungsten, niobium, tantalum, molybdenum, rare-earth elements, and radioactive elements. Regional geochemical patterns are not consistent with the north-south trending microplate boundary that has been proposed by other workers. Correlation coefficients for trace-element data obtained during the current study also argue against sharp compositional breaks in the protolith for the postorogenic granites. Consideration of the data presented here and similar data for granitoids of the eastern Arabian Shield, suggest the existence of a compositionally gradational protolith of continental affinity to the east and oceanic affinity to the west. \J All tables arc at the end of the report. See page 24. Jabal Kor, Jabal Taweel, and Jabal Amoudah) contain peralkaline rocks. In addition, Schmidt (1980a) notes that the central part of Jabal Khashmadheeb and small plug about 20 km southeast of Al Mu'taridah (fig. 1) are also peralkaline, but these areas were not sampled as part of the current study. Only seven samples are truly peralkaline, and thus they were not treated statistically as a separate subset of the data. All of the known peralkaline rocks within the study area, except Jabal An, lie along a north-south trend of peralkaline plutonism which was originally described by Stoeser and Elliott (1980). Samples from all of the postorogenic plutons along this trend are hypersolvus alkaji feldspar granites. Within the eastern part of the study area, Schmidt (1980a and'Vfsuggcsts that all of the alkali feldspar granites are the youngest plutonic rocks. The pluton at Jabal An is spatially separated from the main trend of peralkaline rocks within the Arabian Shield, and its trachytic texture is also unique. Gonzalez (1973) reports a whole-rock K-Ar age for Jabal An of 21.6+3.5 Ma, but the sample locality is not documented, and the technique and sample medium provide data of questionable validity given the proximity to the Tertiary basalt field. Experimental and theoretical studies (Watson and Harrison, 1983) have shown that the saturation limit of zirconium is much higher in peralkaline rocks than in rocks that are saturated or over-saturated with respect to alumina. Peralkaline rocks from the study area show contents of zirconium that are high relative to most of the non-peralkaline samples (table 2), but in contrast to peralkaline rocks outside of the study area (Stuckless and others, 198$ 1985) the peralkaline samples from the study area (except for Jabal An) are not noticeably enriched in uranium, thorium, niobium, or rare-...

Petrography and geochemistry of Palaeozoic quartz-rich sandstones from Saudi Arabia: implications for provenance and chemostratigraphy

“…These are interpreted as relictic signals from the last stages of the amalgamation of Gondwana, which were carried over by glaciogenic sediments. Jackson et al 1984;Stuckless et al 1985Stuckless et al , 1986Jackson and Douche 1986;Leo 1986;Ramsay et al 1986; and own samples), grey area represents Palaeozoic sediments from Tables Table 1. Palaeozoic sampling sites and outcrops with GPS coordinates Table 2. Modal composition and framework mineralogy for Palaeozoic sandstones.…”

“…In Fig. 5b, some typical basement rocks of the Arabian Shield (from Jackson et al 1984;Stuckless et al 1985Stuckless et al , 1986Jackson and Douche 1986;Leo 1986;Ramsay et al 1986;and own samples) (1993), the Zr/Sc ratios of Saudi Arabian Palaeozoic sandstones seem not only to be controlled by sedimentary processes but also have significant dependence on the source rocks as well.…”

Geothermal energy resources of Jizan, SW Saudi Arabia

“…These features became conducive to geothermal system in this region. Besides the heat flow from the mantle due to thinned continental crust, the granites, (Stuckless et al, 1987) containing high content of radioactive elements are also a source, augmenting the heat flow value. Long period of circulation (12-33 kilo years) of infiltrated meteoric waters within the granites substantially heated the waters, facilitating exchange of oxygen isotope between the rock and the fluids resulting in oxygen isotope shift (Fig.…”

“…The Jizan geothermal province lies over a thinned continental crust with spreading ocean ridge crust underplating, represented by sheeted dikes, pillow lavas, gabbro, serpentinized ultramafic rocks that are typical of ocean ridge environment (ophiolite components) as well as granophyres, diorite plutons (McGuire and Coleman, 1986). The calcium rich trondhjemite, tonalite and granodiorite (see Section 2) have also been formed under marine environment due to the melting of the primitive low potassic tholeiitic island arc crust during the initial stages of the shield formation (Harris et al, 1986;Stuckless et al, 1987;Jackson, 1986a).…”

CO2 mitigation strategy through geothermal energy, Saudi Arabia

“…Nearly 37% of the plutonic rocks that are exposed in the shield are granites [23]. These last stage granitic rocks became focus of intense investigation because these rocks are enriched in several elements of economic importance including radioactive elements like uranium, thorium and potassium [24,10,23,25]. The late stage granitic rocks are termed as high heat generating granites because the heat generated by these rocks due to radioactive decay of uranium, thorium and potassium is anomalously high relative to normal granites.…”