Inversion of geoid, topography and gravity data to determine the thickness of the crust and lithosphere in the northeastern region of the Iranian Plateau

Document Type : Research Article


Department of Earth Physics, Institute of Geophysics, University of Tehran, Tehran, Iran.


The main purpose of this research is to determine the thickness of the crust and lithosphere in the northeastern regions of the Iranian plateau. There are different methods to determine these two parameters. According to the definitions and how to determine this thickness, each of the methods has advantages and disadvantages. In this research, large-scale satellite data is used, so we do not need data acquisition that makes it a great advantage, and inversion in this way will give us the final model of the crustal and lithospheric structure in the shortest time.
For this purpose, a joint inversion of geoid topography and gravity data is used. First, we obtain a 1D model that is close to reality using the simultaneous modeling of geoid data, topography, basic concepts of physics and mathematics and local isostasy, for the thickness of the Moho and lithosphere. Then we use a 3D inversion method to reduce the difference between the measured and calculated data. The initial model that is given to the program in 3D inversion is the output of 1D modeling.
The studied area, the northeastern region of the Iranian plateau (including Kopeh-dagh) is an area with great potential in natural resources (mainly oil and gas). The highlands of northeastern Iran are formed in the Alpine-Himalayan folds and are similar to the Zagros mountains from a geological point of view. The Kopeh-dagh mountain range starts from the east of the Caspian Sea and enters Afghanistan after passing through Turkmenistan. The Kopeh-dagh mountain range separates the Turan plate from the central Iranian plate (a part of the Eurasian shield) and reaches a maximum height of 3000 meters. Most geologists consider Kupe-dagh to be the southern edge of the Turan shield and a part of the Eurasian plate. The main fault of Kopeh-dagh (Eshgabad) along the N130 direction forms the southern border of the Turan plate with the Kopedagh mountain range. A very small anomaly, the free-air gradient in the northeast of the Ashgabat fault, indicates the subduction of the southwest-trending Turkmenistan plate beneath Kupeh-dagh. In this way, less displacement is observed between the Turkmenistan plate and the southeastern Caspian lowlands compared to the displacement between the Turkmenistan and Iran plates that can be proved from the value of the gravity anomaly in the west.
There are large gas fields shared by the three countries of Iran, Turkmenistan and Afghanistan in the Kopeh-dagh region and its surrounding areas. Huge gas fields in Iran, Daulatabad-Donmez, Ghazli, Shatlik, Mehri and Bayran Ali in Turkmenistan and Gogar in Afghanistan have been discovered in this area. Geographically, Kopeh-dagh is part of the eastern continuation of the Alborz Mountains, but its geological and structural features are different from the surrounding areas. One of the main goals in the exploration of oil resources is to describe the structure of the sedimentary cover and underground topography. Furthermore, oil production is very sensitive to heat storage by the source rock and thus to the tectonic evolution of the entire lithosphere.
Results show that the thickening of the Moho is observed under the Kopeh-dagh mountain range and the thickness decreases gradually when moving towards the northeast and southwest of the Kopeh-dagh mountain range. The depth of the Moho in the studied area varies from 40 to 60 km. According to the modeling results, the lithosphere-asthenosphere boundary in the southwestern part of the studied area (Central Iran) is approximately 100 km, and it reaches approximately 200 km towards the northeast of the this area.


Main Subjects

Dehghani, G. A., & Makris, J. (1984). The gravity field and crustal structure of Iran. N. Jb. Geol. Palaeont. Abh, 168, 215-229.
Entezar-Saadat, V., Motavalli-Anbaran, S. H., & Zeyen, H. (2017). Lithospheric structure of the Eastern Iranian plateau from integrated geophysical modeling: a transect from Makran to the Turan platform. Journal of Asian Earth Sciences, 138, 357-366.
Fullea, J., Fernàndez, M., & Zeyen, H. (2006). Lithospheric structure in the Atlantic–Mediterranean transition zone (southern Spain, northern Morocco): a simple approach from regional elevation and geoid data. Comptes Rendus Geoscience, 338(1-2), 140-151.
Fullea, J., Fernandez, M., Zeyen, H., & Vergés, J. (2007). A rapid method to map the crustal and lithospheric thickness using elevation, geoid anomaly and thermal analysis. Application to the Gibraltar Arc System, Atlas Mountains and adjacent zones. Tectonophysics, 430(1-4), 97-117.
Fullea, J., Fernàndez, M., Afonso, J. C., Vergés, J., & Zeyen, H. (2010). The structure and evolution of the lithosphere–asthenosphere boundary beneath the Atlantic–Mediterranean Transition Region. Lithos, 120(1-2), 74-95.
Gallardo-Delgado, L. A., Pérez-Flores, M. A., & Gómez-Treviño, E. (2003). A versatile algorithm for joint 3D inversion of gravity and magnetic data. Geophysics, 68(3), 949-959.
Hafkenscheid, E., Wortel, M. J. R., & Spakman, W. (2006). Subduction history of the Tethyan region derived from seismic tomography and tectonic reconstructions. Journal of Geophysical Research: Solid Earth, 111(B8).
Hollingsworth, J., Fattahi, M., Walker, R., Talebian, M., Bahroudi, A., Bolourchi, M. J., Jackson, j., & Copley, A. (2010). Oroclinal bending, distributed thrust and strike-slip faulting, and the accommodation of Arabia–Eurasia convergence in NE Iran since the Oligocene. Geophysical Journal International, 181(3), 1214-1246.
Jackson, J., Priestley, K., Allen, M., & Berberian, M. (2002). Active tectonics of the south Caspian basin. Geophysical Journal International, 148(2), 214-245.
Jimenez-Munt, I., Fernandez, M., Saura, E., Vergés, J., & García-Castellanos, D. (2012). 3-D lithospheric structure and regional/residual Bouguer anomalies in the Arabia—Eurasia collision (Iran). Geophysical Journal International, 190(3), 1311-1324.
Kaviani, A., Paul, A., Bourova, E., Hatzfeld, D., Pedersen, H., & Mokhtari, M. (2007). A strong seismic velocity contrast in the shallow mantle across the Zagros collision zone (Iran). Geophysical Journal International, 171(1), 399-410.
Lachenbruch, A. H., & Morgan, P. (1990). Continental extension, magmatism and elevation; formal relations and rules of thumb. Tectonophysics, 174(1-2), 39-62.
Lü, Y., Liu, B., Pei, S., Sun, Y., Toksöz, M. N., & Zeng, X. (2012). Pn tomographic velocity and anisotropy beneath the Iran region. Bulletin of the Seismological Society of America, 102(1), 426-435.
Maggi, A., Jackson, J. A., Priestley, K., & Baker, C. (2000). A reā€assessment of focal depth distributions in southern Iran, the Tien Shan and northern India: Do earthquakes really occur in the continental mantle?. Geophysical Journal International, 143(3), 629-661.
Manaman, N. S., & Shomali, H. (2010). Upper mantle S-velocity structure and Moho depth variations across Zagros belt, Arabian–Eurasian plate boundary. Physics of the Earth and Planetary Interiors, 180(1-2), 92-103.
Menke, W. (1984) Geophysical data analysis: Discrete inverse theory. Academic Press, London.
Molinaro, M., P. Leturmy, J.-C. Guézou, and D. Frizon de Lamotte (2005), The structure and kinematics of the south-eastern Zagros fold-thrust belt, Iran: from thin-skinned to thick-skinned tectonics. Tectonics, 24, TC3007.
Motaghi, K., Tatar, M., & Priestley, K. (2012a). Crustal thickness variation across the northeast Iran continental collision zone from teleseismic converted waves. Journal of Seismology, 16(2), 253-260.
Motaghi, K., Tatar, M., Shomali, Z. H., Kaviani, A., & Priestley, K. (2012b). High resolution image of uppermost mantle beneath NE Iran continental collision zone. Physics of the Earth and Planetary Interiors, 208, 38-49.
Motavalliā€Anbaran, S. H., Zeyen, H., Brunet, M. F., & Ardestani, V. E. (2011). Crustal and lithospheric structure of the Alborz Mountains, Iran, and surrounding areas from integrated geophysical modeling. Tectonics, 30(5), 5012. doi:10.1029/2011TC002934.
Nowrouzi, G., Priestley, K. F., Ghafory-Ashtiany, M., Javan Doloei, G., & Rham, D. J. (2007). Crustal velocity structure in Iranian Kopeh-Dagh, from analysis of P-waveform receiver functions. Journal of Seismology and Earthquake Engineering, 8(4), 187-194.
Paul, A., Hatzfeld, D., Kaviani, A., Tatar, M., & Péquegnat, C. (2010). Seismic imaging of the lithospheric structure of the Zagros mountain belt (Iran). Geological Society, London, Special Publications, 330(1), 5-18.
Pavlis, N. K. (2008). An earth gravitational model to degree 2160: EGM2008. the 2008 General Assembly of the European Geosciences Union, Vienna, Austria, April 13-18.
Sandwell, D. T., Müller, R. D., Smith, W. H. F., Garcia, E., & Francis, R. (2014). On-shore Bouguer anomaly based of Gtopo30 DEM using density 2.67 g/cc. Original gravity data from New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure. Science, 346(6205), 65-67.
Shad Manaman, N., Shomali, H., & Koyi, H. (2011). New constraints on upper-mantle S-velocity structure and crustal thickness of the Iranian plateau using partitioned waveform inversion. Geophysical Journal International, 184(1), 247-267.
Sodoudi, F., Yuan, X., Kind, R., Heit, B., & Sadidkhouy, A. (2009). Evidence for a missing crustal root and a thin lithosphere beneath the Central Alborz by receiver function studies. Geophysical Journal International, 177(2), 733-742.
Taghizadeh-Farahmand, F., Sodoudi, F., Afsari, N., & Mohammadi, N. (2013). A detailed receiver function image of the lithosphere beneath the Kopeh-Dagh (Northeast Iran). Journal of seismology, 17(4), 1207-1221.
Taghizadeh-Farahmand, F., Afsari, N., & Sodoudi, F. (2015). Crustal thickness of Iran inferred from converted waves. Pure and Applied Geophysics, 172(2), 309-331.
Tozer, B., Sandwell, D. T., Smith, W. H., Olson, C., Beale, J. R., & Wessel, P. (2019). Global bathymetry and topography at 15 arc sec: SRTM15+. Earth and Space Science, 6(10), 1847-1864.
Turcotte, D. L., & Schubert, G. (1982). and G. Schubert, Geodynamics, 450 pp.
Zeyen, H., & Fernàndez, M. (1994). Integrated lithospheric modeling combining thermal, gravity, and local isostasy analysis: Application to the NE Spanish Geotransect. Journal of Geophysical Research: Solid Earth, 99(B9), 18089-18102.