GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 1.3 161 CRUSTAL STRUCTURES OF THE ZAGROS MOUNTAINS COLLISION BELT AND THE IRANIAN PLATEAU FROM A COMBINATION OF ISOSTATIC, SEISMIC AND GRAVIMETRIC OBSERVATIONS T. Pivetta, C. Braitenberg, A. Pastorutti, M. Tesauro Dipartimento di Matematica e Geoscienze, Università di Trieste, Italia. The Zagros Mountains belt is the result of the collision between the Arabian and Eurasian plates, after the consumption of the Neotethys ocean during the subduction process. The Zagros orogen is composed by a series of parallel thrusts NE-SW trending which extends for about 2000 km (Tunini et al. , 2014). The collision process has led to a complex crustal configuration with the juxtaposition of different terranes, from old metamorphic crustal rocks, to sedimentary and ophiolitic rocks typical of the marine and oceanic environment. Furthermore, the subduction process caused also the emplacement in the Iranian Plateau of a widespread tertiary volcanic and magmatic complex, the Urumieh Dokhtar Magmatic Arc. Understanding the actual crustal configuration by estimating the Moho depths, the presence of eventual sub-surface magmatic bodies and underplating is a prerequisite for a consistent geological interpretation of the surface structures and topographic evolution in time. In this study we take advantage of the recent satellite global gravity data in combination with topography, crustal velocity profiles (Gvirtzmann et al. , 2016) and seismic tomography (Kaviani et al. , 2020) to constrain the present crustal structure and the isostatic state of the area. In particular, we isolated the crustal root effect from the Bouguer anomalies by employing a statistical analysis (Pivetta e Braitenberg, 2020) between gravity and topographic loads. The crustal root effect is then inverted in terms of crustal undulation and an optimal density contrast at the Moho level is estimated by fitting the sparse seismic observations. The Bouguer signals unrelated to Moho undulations, reflect density variations mostly depending on the surface geologic structures. The crustal model, defined by the Moho thickness and density contrasts, is discussed in terms of a final isostatic equilibrium in response to internal and topographic loading. This information is relevant for understanding the topography evolution. Acknowledgements. Funding for this research was provided by MIUR (Italian Ministry of University and Research) PRIN funds –PRIN2017 project entitled “Intraplate deformation, magmatism and topographic evolution of a diffuse collisional belt: Insights into the geodynamics of the Arabia-Eurasia collisional zones”. References Gvirtzman Z., Faccenna C., and Becker, T. W.; 2016: Isostasy, flexure, and dynamic topography . Tectonophysics, 683 , 255–271, https://doi.org/10.1016/j.tecto.2016.05.041. Kaviani, A., Paul A., Moradi A., Mai P. M., Pilia S., Boschi L., Rümpker G., Lu Y., Tang Z. and Sandvol, E.; 2020: Crustal and uppermost mantle shear wave velocity structure beneath the Middle East from surface wave tomography . Geophys. J. Int., 221 , 1349–1365, https://doi.org/10.1093/gji/ggaa075. Pivetta T. and Braitenberg C.; 2020: Sensitivity of gravity and topography regressions to earth and planetary structures . Tectonophysics, 774 , 228299, https://doi.org/10.1016/j.tecto.2019.228299. Tunini L., Jiménez-Munt I., Fernandez M., Vergés J., and Villaseñor A., 2014: Lithospheric mantle heterogeneities beneath the Zagros Mountains and the Iranian Plateau: a petrological-geophysical study . Geophys. J. Int., 200, 596–614, https://doi.org/10.1093/gji/ggu418.