Multi Detachments and Oil Blow Up

Pedram Aftabi
Geological Survey of Iran, Tehran, Iran

All the salt sequences in Central Iran involve the same two (or 3) salt sequences are (URF-LRF-Karaj Fm.) generally, two of them separated by lime stones of the Qum . The Qum Fm., does not surface in the emergent salt at Qum, but founded at Great Kavir (dome 27). Field study show that small volumes of white salt lie beneath the more voluminous multicolored salt extruded at Qum Kuh.

Wells and seismic profiles show that current source of multicolored salt being about 3 km deep and therefore is base of URF, and white salt is from 5.5 km deep (base of LRF). Several weak zones( salt gypsum and soft marl) in this area act as different detachments, called multi detachments. The major detachments terminated in diapirs as concentric, thrusted curtain folds (e.g. Kavir). Measurements with >10cm/y and >50 cm/m suggest that, the lower main salt detachment reactivated before 42000 years ago (with rate more than 82 mm a-1).The upper detachment reactivated after this time. The change in the rate of flow in salt dome suggests change in the rate of reactivation of multi detachment system. In Great Kavir domes seen major detachments in the gypsum of M1a (URF) and also in LRF salt.

The implication is of great significant for petroleum. There may be different traps, and migration-flow of oil and gas during reactivation of multi detachments, according to the history of large volume blow up of oil in 1957.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005