InSAR measurements of uplift rates of Mount Sedom salt diapir, Dead Sea Rift, with implications to salt-rock properties and emplacement mechanism
Gidon Baer(1) , Ram Weinberger(1)
, Vladimir Lyakhovsky(1)
, and Ze'ev B. Begin(1)
Geological Survey of Israel,
30, Malkhe Yisrael St., ,
Salt flow commonly forms discordant penetrating structures known as diapirs. These structures have attracted considerable attention over the last few decades due to their importance in controlling the location of natural hydrocarbon traps. Salt diapirs also possess physical properties that allow storage of fuel or waste in engineering cavities. Thus, constraining the properties of rock-salt mass and revealing the strain rates associated with their growth are of great interest both academically and economically. In this study, we use topographic and uplift-rate profiles of Mount Sedom salt diapir (Dead Sea Rift, Israel), to construct an analytical model for the growth of a salt diapir in a tectonically active basin. Mount Sedom is a north-south trending ridge about 10km long, 2km wide, and 250m high. The mountain is the surface expression of a salt diapir that has been rising since the Pleistocene and re-emerged at the early Holocene. Because the fined-grained Sedom rock salt deformed at relatively low strain rates we adopted a Newtonian rheology in our model. Based on the present topography of the diapir and its emergence time, we use the model to constrain the effective viscosity of the rock salt to 3x10e18 Pa s. Strain rates at different levels of the diapir are estimated from geological structures and then compared with recent InSAR measurements.
Interferograms were made for periods of 3-89 months between June 1992 and January 2001. Interferograms with higher coherence within the interval 1993-2001 were phase-unwrapped for analysis of the diapir geometry and uplift rate. The uplift rate of Mount Sedom varies from 6 mm/y to 9 mm/y and the current strain rates are 10e12-10e13 1/s. The geometry of the rising diapir is examined by uplift profiles made along 13 W-E sections and one N-S section for the period 10/1997 – 01/2001. The northern W-E profiles show a pronounced asymmetry, with steep gradients on the western flanks and gradual gradients eastwards. The central and southern profiles are relatively more symmetrical. The steep gradients coincide with previously mapped piercement faults of the salt into the overlying country rock, or their along-strike continuations. Gradual uplift gradients are generally associated with zones where bedding plane slippage has been observed or suggested. Similarity between the current topography and uplift patterns indicates a relatively low contribution of surface processes such as erosion, dissolution, or slope deposition. In some exceptional cases the uplift and topographic profiles show an apparent lateral shift indicating that the current uplift is different than the time-averaged uplift. The higher uplift rate in the northern part of the mountain where the current elevation is lower may also indicate temporal changes in uplift styles.
The uplift profiles are generally in good agreement with synthetic profiles generated by the analytical model. However, along the western diapir margins the uplift profiles are significantly steeper than the model profiles. This could imply that power-law rheology is more suitable than Newtonian rheology at the western margins.