Lithospheric structure and the isostatic state of Eastern Anatolia: Insight from gravity data modelling

Abstract

Eastern Anatolia, Turkey, is a part of the Alpine-Himalayan collisional belt where continental crust is relatively thin for a collisional belt. The region contains part of the Zagros suture zone, which formed during collision of the Arabian and Anatolian plates in the Miocene. It is underlain by a low-velocity zone associated with asthenospheric flow in the uppermost mantle.We constructed gravity models of the crust and upper-mantle structures to assess the driving mechanism of asthenospheric flow and the isostatic state of Eastern Anatolia. Our density models are based on terrestrial and satellite-derived gravity data, and they are constrained by receiver function and seismic tomography. The gravity models show significant lithospheric thickness variations across the Anatolian and Arabian plates. The lithospheric mantle in Eastern Anatolia is thinner (~62-74 km) than the Arabian plate (~84-95 km), indicating that part of the Anatolian mantle lithosphere might have been removed by delamination. The lithospheric removal process might have occurred following the detachment of the Arabian slab in the Miocene. Widespread Holocene volcanism and high heat flow in Eastern Anatolia can be considered as evidence of lithospheric delamination and slab break-off. The upward asthenospheric flow and subsequent asthenospheric underplating beneath Eastern Anatolia might have been induced by both delamination and slab break-off. These two processes may account for the rapid uplift of the Anatolian Plateau. There is a residual topography of ~1.7 km that cannot be explained by crustal roots. Based on our gravity models, we suggest that part of the eastern Anatolian Plateau is dynamically supported by asthenospheric flow in the upper mantle.

Geodynamics of Anatolia: Lithosphere Thermal Structure and Thickness

“…However, in the East Anatolian Plateau we also observe strong short‐wavelength variations, with the smallest values of lithosphere thickness determined for the region of the Neogene volcanism (Figure ). These values are similar to the LAB depth estimates by RFs (Angus et al, ; Ozacar et al, ), while the largest values (~125 km in case of DT = 0.5 and ~140 km for DT = 1.0 km; Figures b and c) are similar to the LAB depth estimate of 110–130 km based on gravity modeling, seismic tomography, and RF (Mahatsente et al, ).…”

“…The smallest values tend to be associated with the Neogene volcanoes (Figure ) and are similar to the lithosphere thickness (60–80 km) determined by RFs (Angus et al, ; Ozacar et al, ). Lithosphere thermal thickness is close to the estimate of 62–74 km thickness of the LM (the latter yields thickness of ~110 to 130 km for the entire lithosphere, including the crust), based on gravity modeling constrained by seismic tomography and RF (Mahatsente et al, ). The patchy pattern of lithosphere thickness suggests the presence of slab windows associated with slab tearing, fragmentation, and a possible interplay of multiple paleosubduction systems. The lithosphere beneath the Eastern Pontides orogenic belt and the Lesser Caucasus is 150–200 km thick and is probably also associated with the presence of the Neo‐Tethys slabs (Eyuboglu et al, ).…”

“…While some seismic tomography models suggest that the Tethyan lithosphere may be trapped in the lower part of the mantle transition zone (Biryol et al, ), other tomography models image a complex mosaic pattern of seismic velocity anomalies in the upper mantle of Anatolia (see section ). A broad range of regional geodynamic models has been proposed based on seismic models for the crustal and upper mantle structure (Bartol & Govers, ; Göğüş & Pysklywec, ; Hafkenscheid et al, ; Jolivet et al, ; Keskin, ; Mahatsente et al, ; Sengör et al, ; Zor, ). In most cases, low seismic velocities are interpreted in terms of high mantle temperatures and without considering the hydration effect on seismic velocities.…”

Lithospheric Structure of Eastern Tibetan Plateau from Terrestrial and Satellite Gravity Data Modeling: Implication for Asthenospheric Underplating

“…Gravity disturbance values from the topographic model were calculated using isGrafLab [89]. The EIGEN-6C4 model is suitable for modeling of lithospheric blocks and can be used to analyze geologic structures whose lateral dimensions lie above the resolution of the geopotential models [90,91].…”

“…The presence of asthenospheric material at shallow depths below the Tibetan plateau is reminiscent of the Anatolian plateau, where crustal thinning is much more pronounced comparatively. But, similar to the Tibetan plateau, lithospheric delamination and slab break-off are major drivers for asthenospheric flow in the upper-most mantle [91]. Even though the Anatolian plateau is part of the Himalayan-Alpine collisional belt, the Early Miocene Arabian-Eurasian collision is much younger, and the aftermath presents a very different picture as compared to the Tibetan plateau.…”