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We present new radiometric (Ar-Ar) age data from the volcanic rocks occurring in the Eocene strata in the Hekimhan and Gürün-Darende (Malaya) regions. The Eocene units in these regions are represented separately by the Tohma and Darende formations, respectively. The two basaltic volcanic interlayers in the Tohma Formation, occurring in the lower and upper parts of the succession, yielded Ar-Ar isochron ages of 51.75 ± 0.76 and 42.66 ± 0.43 Ma, respectively, indicating a deposition age of Ypresian-Lutetian interval for the unit. The andesitic volcanic rocks in the basal parts of the Darende Formation yielded an Ar-Ar isochron age of 37.35 ± 0.72 Ma, revealing that the unit was deposited at least in the Bartonian-Priabonian interval, much younger than the nummilites-bearing sedimentary units seen in the Hekimhan area. Based on these data, we present a revised stratigraphy of these units. Based on the age data from these units, it can be suggested that two distinct sectors of the Anatolide-Tauride Block, the Akdere and Munzur sectors, which were separated originally by a transform fault, were tectonically juxtaposed and eroded in the Paleocene times, representing the initial stage of the Gürün Curl, the most prominent structural feature of eastern Taurides in the region. [ABSTRACT FROM AUTHOR]

The east-west trending Taurides form a curved area in central eastern Anatolia known as the Gürün Curl. In order to understand the origin of the Gürün Curl and Tauride evolution in general, the results of a new field study of this region have been synthesized together with previously published data. We suggest that the geodynamic evolution of the area began with the likely presence of a Tethys Ocean transform fault. This fault separated the Taurides into the Akdere Sector in the west and the Munzur Sector in the east in the Late Cretaceous. During the late Santonian–early Campanian, ophiolites obducted onto the Munzur Sector, while platform sediments continued to accumulate in the Akdere Sector. This was followed by the development of an Andean-type arc-type magmatism (the Baskil Arc) during the early–middle Campanian in the Munzur Sector. Continued closure of the Tethys led to the collision of the Bitlis Massif in the south of the Munzur Sector in the Campanian. This, in turn, resulted in continental subduction and slab roll-back that was controlled by a Subduction Transform Edge Propagator (STEP) Fault that lay on the original transform fault between the Akdere and Munzur sectors. Because the subducted slab was free at its western corner, the western edge rolled back faster than in the east, leading to an asymmetrical extensional regime on the upper plate that created the late Campanian Hekimhan Basin. While these geodynamic events were taking place in the Munzur Sector, the Akdere Sector was in a platform setting. During the Palaeocene, the Late Mesozoic units of the Akdere Sector began to overthrust on the Hekimhan Basin and the ophiolites. Following the Palaeocene, all these tectonostratigraphic units were covered by Eocene sediments around the Gürün Curl of which the modern appearance was completed by the Miocene to Recent movements along the strike-slip faults. [ABSTRACT FROM AUTHOR]

In eastern Anatolia, the Divriği-Hekimhan Magmatic Province (DHMP) includes ~77–69 Ma alkaline rock units which are located to the NW of the Baskil Arc of ~85–74 Ma. The magmatic rocks are composed of nepheline (Ne)–to quartz (Q)–normative alkaline basaltic to trachytic/syenitic units. Among them, the basaltic rocks are composed of plagioclase (Or2–11Ab32–51An39–64) + clinopyroxene (Wo47–51En35–42Fs9–16) + Fe-Ti oxide ± alkali feldspar (Or57–98Ab2–42An1) ± biotite ± olivine. Their 87Sr/86Sr(I) ratios and ɛNd(I) values vary in the ranges of 0.70591–0.70871 and−3.2–1.6, respectively. The subvolcanic trachytic rocks are composed of perthitic alkali feldspar phenocryst in a matrix of feldspar (Or45–61Ab38–54An0–2), biotite, and Fe-Ti oxides. The trachytic volcanic rocks are made up of feldspar (Or38–63Ab34–59An1–4) in a fine-grained matrix. Their 87Sr/86Sr(I) ratios and ɛNd(I) values vary in the ranges of 0.70532–0.70952 and−3.2–0.7, respectively. The syenitic rocks in the region contain both quartz- and nepheline-sodalite-bearing syenites. Geochemical features reveal that the Ne-normative basaltic magmas have undergone mafic mineral fractionation coupled with crustal contamination to produce the Q-normative derivatives. Enhanced differentiation of the Ne- and Q-normative fractionated magmas via feldspar-dominated fractionation created the silica-undersaturated and -oversaturated trachytic magmas, respectively. During the feldspar-dominated differentiation, the re-melting of accumulated alkali feldspars in the magma chamber likely gave rise to the formation of trachytic rocks with alkali feldspar-like whole rock compositions. The final products of the Ne-normative magmas are represented by the phonolites and foid-syenites with silica-undersaturated eutectic compositions. A geochemical evaluation of the basaltic rocks revealed that the alkaline magmatism mainly originated from a shallow asthenospheric mantle source which had previously been metasomatized by oceanic to continental subduction. We suggest that the DHMP was formed in response to STEP fault-controlled rolling back of the northward subducting slab of the Baskil Arc, which created a localized gap for asthenospheric upwelling. [ABSTRACT FROM AUTHOR]