Shallow melting of MORB‐like mantle under hot continental lithosphere, Central Anatolia

Abstract

Widespread mafic volcanism, elevated crustal temperatures, and plateau‐type topography in Central Anatolia, Turkey, could collectively be the result of lithospheric delamination, mantle upwelling, and tectonic escape. We use results from 40Ar/39Ar geochronology, basalt geochemistry, and a passive‐source broadband seismic experiment obtained in a collaborative international effort (Continental Dynamics‐Central Anatolia Tectonics) to investigate the upper mantle structure and evolution of melting conditions over an ∼2400 km2 area south and west of Hasan volcano. New 40Ar/39Ar dates for the basalts mostly cluster between 0.2 and 0.6 Ma, but some scoria cones are as old as 2.5 Ma. Basalts are dominantly Mg‐rich (Mg# = 62–71), moderately alkaline (normative Ne < 5 wt %), and, based on major and trace element signatures, derived from a peridotitic source. Covariations between radiogenic isotope and trace element signatures reveal contributions from a subduction‐related component and intraplate‐like mantle asthenosphere, as well as from ambient upper mantle. Central Anatolian basalts reflect maximum mantle potential temperatures of <1350°C and an average pressure of melt equilibration of 1.4 GPa, which are cooler and shallower than for basalts from Eastern and Western Anatolia. When considered in light of regionally slow upper mantle shear wave velocities, the mantle lithosphere may be thin and infiltrated by melts, or largely absent. An absence of secular changes in melting conditions suggests little to no lithospheric thinning over the past ∼1 Ma, despite evidence for lithospheric extension. Hasan basalts appear to be generated by decompression melting in response to the rollback of the Cyprean slab.

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

“…Our procedure of fitting melting paths through suites of melt equilibration estimates combined with REE inverse modeling yields much lower estimates of melt fraction for Western Anatolia (i.e., ∼4 and ∼2%, respectively), and thus cooler temperatures. Applying the latent heat correction of Putirka et al () to these lower melt fraction estimates would also result in significantly cooler calculated temperatures, accounting for most of the difference between our results and those of Reid et al (). In summary, we believe that a wealth of disparate evidence supports the presence of a westward decrease in asthenospheric potential temperature across Anatolia.…”

“…Reid et al () also report elevated temperatures across Western and Eastern Anatolia. For Eastern Anatolia, their maximum temperature estimates range from 1380 to 1430°C, in broad agreement with our results.…”

“…Inevitably, these estimates are subject to considerable uncertainty. Reid et al () estimate lithospheric thicknesses of ∼60 km beneath Central Anatolia based on analysis of basaltic geochemistry. Estimates based upon receiver function analyses range between 60 and 90 km (Angus et al, ; Çakir & Erduran, ; Kind et al, ).…”

“…Abundant Neogene magmatism occurs throughout Anatolia and its existence is often linked with geodynamic evolution. A range of processes have been proposed to generate this magmatism that include: subduction of oceanic lithosphere (Aldanmaz et al, 2000;Ersoy et al, 2012); slab break off, fragmentation, or roll back (e.g., Agostini et al, 2007;Innocenti et al, 2005;Keskin, 2003;Reid et al, 2017;S¸eng€ or et al, 2003); extension and delamination of continental lithosphere (e.g., Pearce et al, 1990;S¸eng€ or et al, 2008); and elevated asthenospheric temperatures (e.g., Prelević et al, 2012;S¸eng€ or et al, 2003). Each of these processes could generate different surface expressions and thus modify the evolving landscape in different ways.…”

Mantle Sources of Recent Anatolian Intraplate Magmatism: A Regional Plume or Local Tectonic Origin?

“…The calculated pressures of Çoban () are considerably higher for Kula and Ceyhan‐Osmaniye, which seem to reflect his consistent normalization to rather high MgO content (15 wt%) in these areas. Moreover, Reid et al () inferred melt equilibration conditions for Anatolian basalts. While their inferred mantle melting temperatures are either within (Kula and TOP) or close to our estimated temperature ranges (ÜÇT and Karacadağ), their pressure estimates differ more significantly, which could stem from their indirectly derived primary melt compositions and assumptions on the mantle‐melt equilibrium forsterite content, which we have obtained directly from MI and olivine‐spinel compositions.…”