Reconnaissance geology of the Al Abanat Quadrangle, sheet 25/42 B, Kingdom of Saudi Arabia

Abstract

The Al Abanat quadrangle, located approximately midway between An Nuqrah and Buraydah, contains layered and intrusive rocks that represent the major phases of Proterozoic geology in the northeastern Arabian Shield. Lowpotassium metavolcanic rocks of the Dhiran meta-andesite were intruded 690 Ma to about 670 Ma ago by (possibly cogenetic) low-potassium mafic and intermediate rocks of the Suwaj suite. Both units were probably formed by partial melting of oceanic lithosphere above a southwest-dipping subduction zone. The Dhiran-Suwaj terrane was deformed and metamorphosed during a regional orogenic event that may have coincided with the termination of subduction. The orogenic uplift shed abundant fine-grained sandstone (Murdama group) into fault-bounded, subsiding marine basins. The Ata fault, which forms one of the Murdama basin boundaries, is well exposed in this area and its features suggest it was a major left-slip structure prior to Murdama time, but was reactivated as a dip-slip fault during sedimentation. The unlithified Murdama deposits were penecontemporaneously deformed during basin-subsidence and then regionally folded along north-south trends. This period of regional folding appears to pre-date and overlap with intrusion of batholithic granitic rocks of the Khishaybi suite, probably at about 650 Ma. Regional north-south extension and calc-alkaline volcanic activity began at about 640 Ma and produced voluminous andesitic volcanic and volcaniclastic deposits of the Jurdhawiyah group. Primary volcanic materials and their rapidly eroded detritus were deposited in elongate, fault-bounded basins that were partly shallow-water marine and partly terrestrial. The Lughfiyah-Shuhban reverse fault system was active during a brief interval in late Jurdhawiyah time. This deformation was closely followed by intrusion of elliptical bodies of Idah suite granodiorite porphyry, 620 Ma to 615 Ma ago, that may have been cogenetic with the Jurdhawiyah volcanic rocks. The succeeding 30-Ma interval was characterized by uplift, erosion, and probable planation. During a subsequent period of regional cratonic extension from about 585 to 570 Ma, high-silica, evolved granites of the Abanat suite were intruded in ring dikes and composite plutons of the Asmar complex (dominantly peraluminous) and the Ahmar complex (peralkaline). The Asmar complex partially intruded its coeval rhyolitic volcanic cover (Samra rhyolite).

Results of a geochemical survey, Aban Al Ahmar Quadrangle, Sheet 25F, Kingdom of Saudi Arabia

“…The U.S. Geological Survey (USGS) has recently produced l:100,000-scale geologic maps for the following quadrangles: Uqlat as Suqur, sheet 25/42A (Cole, 1985a) (Cole, 1981); F. As Shubaykiyah 25/43C (Bohannon, 1984); G. Aban al Ahmar 25 F (Cole, 1986); H. Jabal Habashi 26 F (Alien and others, 1984); I. Wadi ar Rimah (Bramkamp and others, 1963). sheet 25/42B (Cole, 1985b), Wadi al Jarir, sheet 25/42C, (Young, 1982), Al Jurdhawiyah, sheet 25/42D (Cole, 1981), An Nabhaniyah, sheet 25/43A (Cole and Bohannon, 1985), and Ash Shubaykiyah, sheet 25/43C (Bohannon, 1984). These l:100,000-scale geologic maps were compiled into a l:250,000-scale geologic map of the Aban Al Ahmar quadrangle by Cole (1986).…”

“…Leucocratic biotite granitic rocks of the Khishaybi suite (fig. 3) intruded rocks of the eastern and southwestern parts of the quadrangle during or following the folding associated with the end of Murdama deposition (Cole, 1985b). Rocks of the Khishaybi suite range in composition from monzogranite to orthoclase granite and contain associated felsic and rare mafic dikes.…”

“…The Asmar complex consists of nested, arcuate intrusions surrounding the central block of Samra rhyolite. The granites range from metaluminous to peraluminous in composition (Stuckless and others, 1982a;Cole, 1985b;Cole and Bohannon, 1985). Samples of wadi concentrates collected during the regional survey contained anomalous concentrations of tin (700 to >1000 ppm) and lead (50 to 200 ppm).…”