Jabal Arkeno Ring Complex is a Tertiary cone sheet structure in southeast Libya consisting mainly of syenites and equivalent rocks. It is distinguished from the other three major complexes around it and many others in Sudan and Egypt by comprising multi-intrusion centers as well as several cauldron subsidence foci and a syenite rock series spanning the spectrum of the silica continuum.

The map to the right covers about two-thirds of the complex, which is oval in shape and extending about 16 km in an east-west direction. The map is based on detailed ground mapping and sampling. Green and red and related shades and hues denote undersaturated syenites (and their equivalent aphanites), whereas brown and blue colors and their different shades and hues denote saturated and over-saturated syenites (and their equivalent aphanites), respectively.

Fifty-nine rock units were mapped based on identifiable mineralogy and/or texture. Some units were partially weathered.

As shown on the map, cross-cutting relationships indicate an initial migration of magmatic centers from east to west followed by a migratory, broad shift of igneous activity eastward. This was accompanied by cauldron collapse, the largest of which assumes a central position in the lower third of the complex. The strong alkaline affinity of the arkenoan rocks is shown on the alkali-silica diagram to the left. Most rock units are peralkaline. Furthermore, the suite includes both agpaiitic and miskitic types of syenites and aphanitic equivalents such as tiguaite and nepheline-bearing trachyte.

As several nepheline syenite sheets were emplaced as droplets rising from their magmatic source and began crystallizing, they were intruded into older units. Part of the latter appear as xenoliths that suffered little alteration indicating that the time span of emplacement was relatively short. Phonolite dikes and sheets appear to have been emplaced after the syenite rock units were largely solidified, but some were sunk into their own magma at depth.