Reconnaissance geology of the Jibal Matalli Quadrangle, sheet 27/40 D, Kingdom of Saudi Arabia

Open-File Report 84-378




The Jibal Matalli quadrangle lies along the northern boundary of the Arabian Shield about 90 km west-southwest of Ha'il. The quadrangle consists of about 45 percent Precambrian bedrock, 50 percent Quaternary deposits, and 5 percent sedimentary cover rocks. The Precambrian rocks include volcaniclastic and volcanic rocks that are slightly metamorphosed and various granitic plutons. The volcaniclastic and volcanic rocks are correlated with the Hulayfah group and the Hadn formation. The older Hulayfah is principally basalt of probably submarine origin that has locally been metamorphosed to greenschist facies. The Hadn is composed of submarine and subaerial deposits. These consist of volcanic-derived sandstone and siltstone and lesser amounts of chiefly rhyolite volcanic rocks. In most areas, the Hadn shows little in the way of metamorphic effects, but locally it too has been metamorphosed to greenschist facies. The volcanic rocks of the Hadn include ash-flow tuffs; some appear to be water-laid, but others are subaerial. The oldest pluton is diorite, those of intermediate age are monzogranite and syenogranite, and the youngest are alkali feldspar granites. The largest pluton, a metaluminous, low-calcium, biotite monzogranite, occupies much of the southern part of the quadrangle. The alkali feldspar granites are mostly peralkaline; the two youngest are particularly so. The latter two are located in the southwest and southeast corners of the quadrangle, and both contain arfvedsonite and kataphorite. The pluton in the southeast grades outward from a peraluminous core to a peralkaline, comenditic peripheral zone and is inferred to be genetically related to a spectacular, west-trending comendite dike swarm in the southern half of the quadrangle.

Two northeast-trending buried right-lateral faults are inferred in the quadrangle; one in the southeast and one in the northwest. The one in the northwest probably offsets the comendite dike swarm about 3 km. This fault appears to be part of a broad right-lateral fault and flexure zone that juxtaposes the Hadn formation on the west against the Hulayfah group on the east.

Study Area

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USGS Numbered Series
Reconnaissance geology of the Jibal Matalli Quadrangle, sheet 27/40 D, Kingdom of Saudi Arabia
Series title:
Open-File Report
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U.S. Geological Survey
Publisher location:
Reston, VA
ii, 38 p. . :ill., maps ;28 cm.
Saudi Arabia
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