3-D thermochemical structure of lithospheric mantle beneath the Iranian plateau and surrounding areas from geophysical–petrological modelling

Abstract

SUMMARY While the crustal structure across the Iranian plateau is fairly well constrained from controlled source and passive seismic data, the lithospheric mantle structure remains relatively poorly known, in particular in terms of lithology. Geodynamics rely on a robust image of the present-day thermochemical structure interpretations of the area. In this study, the 3-D crustal and upper mantle structure of the Iranian plateau is investigated, for the first time, through integrated geophysical–petrological modelling combining elevation, gravity and gravity gradient fields, seismic and petrological data. Our modelling approach allows us to simultaneously match complementary data sets with key mantle physical parameters (density and seismic velocities) being determined within a self-consistent thermodynamic framework. We first elaborate a new 3-D isostatically balanced crustal model constrained by available controlled source and passive seismic data, as well as complementary by gravity data. Next, we follow a progressively complex modelling strategy, starting from a laterally quasi chemically homogeneous model and then including structural, petrological and seismic tomography constraints. Distinct mantle compositions are tested in each of the tectonothermal terranes in our study region based on available local xenolith suites and global petrological data sets. Our preferred model matches the input geophysical observables (gravity field and elevation), includes local xenolith data, and qualitatively matches velocity anomalies from state of the art seismic tomography models. Beneath the Caspian and Oman seas (offshore areas) our model is defined by an average Phanerozoic fertile composition. The Arabian Plate and the Turan platform are characterized by a Proterozoic composition based on xenolith samples from eastern Arabia. In agreement with previous studies, our results also suggest a moderately refractory Proterozoic type composition in Zagros-Makran belt, extending to Alborz, Turan and Kopeh-Dagh terranes. In contrast, the mantle in our preferred model in Central Iran is defined by a fertile composition derived from a xenolith suite in northeast Iran. Our results indicate that the deepest Moho boundary is located beneath the high Zagros Mountains (∼65 km). The thinnest crust is found in the Oman Sea, Central Iran (Lut Block) and Talesh Mountains. A relatively deep Moho boundary is modelled in the Kopeh-Dagh Mountains, where Moho depth reaches to ∼55 km. The lithosphere is ∼280 km thick beneath the Persian Gulf (Arabian–Eurasian Plate boundary) and the Caspian Sea, thinning towards the Turan platform and the high Zagros. Beneath the Oman Sea, the base of the lithosphere is at ∼150 km depth, rising to ∼120 km beneath Central Iran, with the thinnest lithosphere (<100 km) being located beneath the northwest part of the Iranian plateau. We propose that the present-day lithosphere–asthenosphere topography is the result of the superposition of different geodynamic processes: (i) Arabia–Eurasia convergence lasting from mid Jurassic to recent and closure of Neo-Tethys ocean, (ii) reunification of Gondwanian fragments to form the Central Iran block and Iranian microcontinent, (iii) impingement of a small-scale convection and slab break-off beneath Central Iran commencing in the mid Eocene and (iv) refertilization of the lithospheric mantle beneath the Iranian microcontinent.

The shallow and deep crustal structure in Zagros from inversion and forward modeling: insights from the application of Moho-free Bouguer anomaly

“…The crustal thickness in central Iran is approximately 45 km (Mousavi and Ebbing, 2018). In more recent studies, Mousavi and Fullea (2020) suggested a Moho relief using an integrated geophysical-petrological modeling approach.…”

“…In this respect, we can refer to several published papers such as, Werner, 1953;Bott, 1960;Cordell, et al, 1968;Oldenberg, 1974;Parker, 1972;Reid, et al, 1990;Salem, et al, 2007;Martins, et al, 2011, Fedi, et al, 2012Sun, et al, 2015;Feng, et al, 2018;Florio, 2020, Schmidt et al, 2010and Sampietro, 2016 The depth of the Moho beneath the Iranian plateau has been investigated by several researchers through gravity modeling, (Dehghani and Makris, 1983;Snyder and Barazangi, 1986, Dehghan et al, 2021, Ebadi et al, 2019, Heydarizadeh Shali et al, 2020, Eshagh, 2014Ardestani and Mousavi, 2022). A combined gravity and magnetic modeling (Mousavi and Ebbing, 2018), seismic (Tatar, 2001;Javan-Doloei, 2002, Paul et al, 2006, Motaghi et al, 2015, integrated thermal modeling , Motavalli et al, 2011 and integrated geophysical-petrological modeling (Mousavi and Fullea, 2020).…”

Least squares collocation method in Moho depth determination in Iran using gravity gradient data

“…Mousavi and Fullea [ 32 ] investigated the 3-D crustal structure of the Iranian plateau by integrated geophysical–petrological modeling combining elevation, gravity, and gravity gradient fields, seismic and petrological data. They estimated the maximum Moho depth equal to 65 km beneath the Zagros Mountain, while the thinnest crust was reported for the Oman sea and the central part of Iran [ 33 ].…”