The volcanism in the western Arabian plate extends from the Red Sea through the Harrat Ash Shaam system to western Syria, as far north as the Bitlis suture in the Taurides. The Harrat Ash Shaam volcanic system in Jordan consists of northwest-trending dikes and a volcanic field that together encompass a width of 220 km. In terms of width, direction, and age of the main volcanic phases, the system is similar to the Red Sea dike belt. About 130 new K-Ar age determinations show that the ages of the Harrat Ash Shaam system (dikes and flows) range from Oligocene to Quaternary. However, there is a distinct gap in the ages between ∼22 and 13 Ma. This gap coincides with an apparent decrease in volcanism in the Red Sea region from around 20 to 12 Ma. We interpret this 9 m.y. gap as a quiescent period interrupting the volcanic activity in the region and suggest that from ∼22 to 13 Ma, tectonic activity in the Arabian plate was mainly restricted to the Red Sea region. A renewal of volcanism along the western margins of the Arabian plate at 13 Ma was very likely associated with the sinistral movement along the north-trending Dead Sea transform. This renewal of volcanism and tectonic activity may reflect the emergence of upper-mantle upwelling beneath the western Arabian plate at that time.