The bulk crustal structure of the Anatolian plate: evidence from H-K stacking of receiver functions

Abstract:

The Anatolian Plate captures a broad range of tectonic processes from Aegean extension in the west to Arabian plate continental collision and in the east. The causes of Anatolia’s uplift are debated, with dynamic support from a buoyant mantle, and crustal shortening both likely playing a role. Volcanism associated with subduction and lithospheric delamination/dripping has also affected Anatolia, but its impact on bulk crustal composition is poorly understood.

H-κ stacking is a widely used technique to glean crustal thickness (H) and bulk crustal Vp/Vs ratio (κ) from teleseismic earthquakes and has been employed by several studies on the Anatolian plate. When the crust is a simple layer above a half-space approximation with a sharp Moho, H-κ stacking works well. However, Anatolia’s complex tectonic and magmatic history likely renders this assumption invalid, at least in places, and this may explain why large discrepancies (up to 20km in Moho depth; up to 0.29 inκ) exist between studies with commonly analysed stations.

To address these issues, we use the modified H-κ stacking approach of Ogden et al. (2019) to estimate crustal thickness and Vp/Vs ratio across Anatolia. Rather than using a single set of H-κ stacking parameters (Vp, stacking weights etc), the Ogden et al., (2019) strategy explores the parameter space rigorously, including varying receiver function frequency content, as a means of understanding whether the Moho is an abrupt or gradational feature. We find that crustal thickness increases from 25km in western Anatolia to 47km in eastern Anatolia. In western Anatolia, H-κ stacking is reliable for many stations situated on the metamorphic Anatolide tectonic units, where the crust is ~30km thick. However, H-κ results are unreliable in the Eastern Anatolian Plateau where thick near-surface sedimentary and igneous strata disrupt the simple layer above a half-space assumption on which successful H-κ analysis hinges. Our frequency analysis reveals a gradational Moho is likely present across parts of central and eastern Anatolia, including the Taurides and Pontides, perhaps as a relic of subduction processes. Vp/Vs ratios indicate a generally felsic crust, without evidence for widespread melt or mafic intrusion. We find that dynamic mantle support is required to explain Anatolia’s high elevation.