More than 200 piercement salt plugs are present in southern Iran and in the Persian Gulf region. Recent investigations have shown the salt, the Hormuz Series, to be largely of Precambrian (late Proterozoic) age. The diapirs are famous for their tonguelike projections, known as “salt glaciers,” and for their associated igneous, metamorphic, and sedimentary exotic blocks. In many places the salt plugs form spectacular mountains, rising up to 4,000 ft above the adjacent valley floor. The diapirs generally are associated with anticlines, and in many areas pierce the structure at the plunging end or on the flanks. Diapirs in synclines also are present.
Four stages in the evolution of the Hormuz diapirs have been recognized. These stages are represented by bulging folds, pierced and collapsed structures, and large solution cauldrons.
There have been at least two periods of salt mobilization and intrusion: a pre-Zagros (pre-Alpine) phase, possibly dating back to the Triassic; and a late Tertiary syn- to post-orogenic phase. The rate of intrusion is a highly fluctuating quantity, amounting to about 2 mm per year in the most actively rising diapirs.
The regional pattern of salt structures is related to north-south-trending regional fractures in the underlying Precambrian basement.