Moho depth and lithospheric thickness of the Arabian and Eurasian collision zone from potential field data

Authors

1 Assistant Professor, Department of Earth Physics, Institute of Geophysics, University of Tehran, Iran

2 Professor, Department of Earth Physics, Institute of Geophysics, University of Tehran, Iran

3 Professor, Faculty of Earth Sciences, Paris University, France

Abstract

The targeted area of this research includes E Anatoly, NW Zagros, and Caucasus. These structures are known as a complex and active area and in the early stage of continent-continent collision, which give us unique possibility to monitor such collision in real time. Therefore, it is very important to study this active area to have a better knowledge about its tectonic behavior and lithospheric structure. Key parameters that we are looking for in this research are Moho depth, lithosphere-asthenosphere boundary (LAB) and average crustal density.
There are methods, which can give us some information about lithospheric structure such as the seismological method, seismic (controlled source) method, magnetotelluric, volcanology etc. The method used here is a direct, linearized, iterative inversion procedure in order to determine lateral variations in crustal thickness, average crustal density and lithospheric thickness via potential field data. The area of interest is subdivided into rectangular columns of constant size in E-W (X) and N-S (Y) directions. In depth (Z), each column is subdivided into four layers: seawater if present (with known thickness, i.e. bathymetry, and a density of 1030 kg/m3), crust, lithospheric mantle, and asthenosphere. For our research, the definition of the LAB is an isotherm and we try to calculate the temperature distribution in the lithosphere. During the inversion process, a cost function has to be minimized defined as C=Ed+lEp+mEs. The factor l allows controlling the overall importance of parameter variability (Ep) with respect to data adjustment (Ed), whereas m is a factor controlling the importance of smoothing, which can be different for each parameter set.
The method uses potential field data (free air gravity, geoid, and topography) which are globally available by satellite measurement and are freely accessible on the internet. The potential field data are sensitive to the lateral density variations, which happen across these two boundaries but at different depth. Free air gravity data are 2.5×2.5 arc-minute grid, which was taken from the database of Bureau Gravimétrique International (BGI). Geoid height variations correspond to the EGM2008 model. In order to avoid the effects of sublithospheric density variations on the geoid, we have removed the long-wavelength geoid signature corresponding to spherical harmonics until degree and order 10, tapered between 8 and 12. Topography data are taken from the 1-minute TOPEX global data sets. All data were interpolated on a regular 10x10 km grid.
Inverting potential field and topography data suffers from non-uniqueness since these data are not sensitive to vertical density variations, which may produce instabilities of the solution. Stabilization of the inversion process may be obtained through parameter damping and smoothing as well as the use of a priori information like crustal thicknesses from seismic profiles.
The 3D results show an important crustal root under Caucasus and relatively thick Moho for the eastern part of Anatolia and NW Zagros and a thin crust under the southern part of the Black Sea, which is thickening northward. Regarding LAB, the 3D results show thin lithosphere under the E-Anatolia, NW Zagros and the western part of Caucasus. The LAB thickens northward towards the Eurasia and in the western part of Anatolia.
 

Keywords

Main Subjects

References

  1. 1.        

-          Angus D. A., Wilson D. C., Sandvol E. and Ni J. F., Lithospheric structure of the Arabian and Eurasian collision zone in eastern Turkey from S-wave receiver functions, Geophys. J. Int. (2006) 166, 1335–1346.

-          Cakir, O. & Erduran, M., 2004. Constraining crustal and uppermost mantle structure beneath station TBZ (Trabzon, Turkey) by receiver function and dispersion analyses, Geophys. J. Int., 158, 955–971.

-          Cakir, O., Erduran,M.,C¸ inar,H. & Yilmaztu¨rk,A., 2000. Forwardmodelling receiver functions for crustal structure beneath station TBZ (Trabzon, Turkey), Geophys. J. Int., 140, 341–356.

-          Chase, C. G., J. C. Libarkin, and A. J. Sussman (2002), Colorado Plateau: Geoid and means of isostatic support, Int. Geol. Rev., 44, 575-587.

-          Coblentz, D., C. G. Chase, K. E. Karlstrom, and J. van Wijk (2011), Topography, the geoid, and compensation mechanisms for the southern Rocky Mountains, Geochem. Geophys. Geosyst., 12(4), Q04002.

-          Fullea, J., M. Fernàndez, and H. Zeyen (2005), Lithospheric structure in the Atlantic-Mediterranean transition zone: joint inversion of elevation and geoid anomalies, C. R. Geosciences, 338(1-2), 140-151.

-          Fullea, J., J. C. Afonso, J. A. D. Connolly, M. Fernàndez, D. García-Castellanos, and H. Zeyen (2009), LitMod3D: An interactive 3-D software to model the thermal, compositional, density, seismological, and rheological structure of the lithosphere and sublithospheric upper mantle, Geochem. Geophys. Geosyst., 10, Q08019.

-          Gallardo-Delgado, L. A., M. A. Pérez-Flores, and E. Gómez-Treviño (2003), A versatile algorithm for joint 3D inversion of gravity and magnetic data, Geophysics, 68(3), 949-959.

-          McKenzie, D. (1994), The relationship between topography and gravity on Earth and Venus, Icarus, 112(1), 55-88.

-          McKenzie, D., and D. Fairhead (1997), Estimates of the effective elastic thickness of the continental lithosphere from Bouguer and free air gravity anomalies, J. Geophys. Res., 102, 27523-27552.

-          Menke, W., 1984. Geophysical data analysis: Discrete inverse theory. Academic Press, London, 260 pp.

-          Motavalli-Anbaran, S.-H., Zeyen, H. and Ardestani, V. E., (2013) 3D Joint inversion modeling of the lithospheric density structure based on gravity, geoid and topography data – application to the Alborz Mountains (Iran) and south Caspian Basin region, Tectonophysics, Volume 586, Pages 192–205.

-          Mutlu, A. K. and Karabulut H., 2011, Anisotropic Pn tomography of Turkey and adjacent area. Geophysical Journal International, Volume 187, Issue 3, pages 1743-1758.

-          Pavlis, N. K., S. A. Holmes, S. C. Kenyon, and J. K. Factor (2008), An Earth gravitational model to degree 2160: EGM2008, in General Assembly of the European Geosciences Union, edited, Vienna, Austria, April 13-18, 2008.

-          Reilinger, R.E. et al., 1997a. Global positioning system measurements of present-day crustal movements in the Arabia-Africa-Eurasia plate collision zone, J. geophys. Res., 102(B5), 9983–9999.

-          Sandwell, D. T., and W. H. F. Smith (1997), Marine gravity anomalies from GEOSAT and ERS-1 satellite altimetry, J. Geophys. Res., 102(B5), 10039-10054.

-          Sandwell, D. T., and W. H. F. Smith (2009), Global marine gravity from retracked Geosat and ERS-1 altimetry: Ridge segmentation versus spreading rate, J. Geophys. Res., 114, B01411.

-          Zeyen, H., and M. Fernàndez (1994), Integrated lithospheric modeling combining thermal, gravity and local isostasy analysis: application to the NE Spanish Geotransect, J. Geophys. Res., 99, 18089-18102.

-          Zor, E., Sandvol, E., Gurbuz, C., Turkelli, N., Seber, D. & Barazangi, M., 2003. The crustal structure of the East Anatolian plateau (Turkey) from receiver functions, Geophys. Res. Lett., 30(24), 8044, doi:10.1029/2003GL018192.

Journal of the Earth and Space Physics
Volume 41, Issue 2 - Serial Number 2
August 2015
Pages 249-256

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