Neogene Uplift and Magmatism of Anatolia: Insights From Drainage Analysis and Basaltic Geochemistry

Abstract

It is agreed that mantle dynamics have played a role in generating and maintaining the elevated topography of Anatolia during Neogene times. However, there is debate about the relative importance of subduction zone and asthenospheric processes. Key issues concern onset and cause of regional uplift, thickness of the lithospheric plate, and the presence/absence of temperature and/or compositional anomalies within the convecting mantle. Here, we tackle these interlinked issues by analyzing and modeling two disparate suites of observations. First, a drainage inventory of 1,844 longitudinal river profiles is assembled. This database is inverted to calculate the variation of Neogene regional uplift through time and space by minimizing the misfit between observed and calculated river profiles subject to independent calibration. Our results suggest that regional uplift commenced at 20 Ma in the east and propagated westward. Second, we have assembled a database of geochemical analyses of basaltic rocks. Two different approaches have been used to quantitatively model this database with a view to determining the depth and degree of asthenospheric melting across Anatolia. Our results suggest that melting occurs at depths as shallow as 60 km in the presence of mantle potential temperatures as high as 1400°C. There is evidence that temperatures are higher in the east, consistent with the pattern of subplate shear wave velocity anomalies. Our combined results are consistent with isostatic and admittance analyses and suggest that elevated asthenospheric temperatures beneath thinned Anatolian lithosphere have played a first‐order role in generating and maintaining regional dynamic topography and basaltic magmatism.

Reply to “Geochemical Characteristics of Anatolian Basalts: Comment on ‘Neogene Uplift and Magmatism of Anatolia: Insights from Drainage Analysis and Basaltic Geochemistry’ by McNab et al.”

“…Revised version of our original Figure 11 (McNab et al, ). Geochemical analyses of mafic volcanism from Western (a–e), Central (f–j), and Eastern (k–o) Anatolia as function of age.…”

“…Geochemical analyses of mafic volcanism from Western (a–e), Central (f–j), and Eastern (k–o) Anatolia as function of age. Open circles with horizontal bars = radiometrically dated samples ±1 σ ; closed circles with horizontal bars = chronostratigraphically dated samples ±1 σ ; black = samples from original compilation of McNab et al (); red = additional samples; gray boxes with dashed lines = mean and standard deviation of ocean island basalts from GEOROC database ( http://www.georoc.edu).…”

“…Fourth, we did consider and test a more detailed geographic subdivision of Anatolian magmatism, along the lines of that proposed by Uslular and Gençalioğlu‐Kuşcu (), during preparation of McNab et al (). This detailed subdivision does not affect the results and conclusions presented by McNab et al (), notably an increase in asthenospheric temperature from west to east that accords with regional topography and with fluvial landscape analysis. Fifth, we reject the assertion that generalization of an OIB‐like affinity within the last 10 Ma is misleading.…”

“…First, we have revised the data compilation shown in our original Figure 11 by including analyses from the publications referred to by Uslular and Gençalioglu-Kuşcu (2018), and 190 additional analyses to which they do not refer. We have included a suite of publications that postdate the original submission of McNab et al (2018). Note that we deliberately excluded the analyses of Parlak et al (2001) since these authors state that the relevant samples are crustally contaminated.…”

“…Third, we acknowledge that we have used the chronologic term "Neogene" rather loosely and that we mislocated the Erciyes and Hasandag stratovolcanoes. These minor errors do not affect the results and conclusions of McNab et al (2018). Fourth, we did consider and test a more detailed geographic subdivision of Anatolian magmatism, along the lines of that proposed by Uslular…”