Petrogenesis of Late Campanian Alkaline Igneous Rocks in Eastern Anatolia: Magmatism related to a subduction transform edge propagator (STEP) fault?

In eastern Anatolia, the Divrigi-Hekimhan Magmatic Province (DHMP) includes similar to 77-69 Ma alkaline rock units which are located to the NW of the Baskil Arc of similar to 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 (Or(2-11)Ab(32-51)An(39-64)) + clinopyroxene (Wo(47-51)En(35-42)Fs(9-16)) + Fe-Ti oxide +/- alkali feldspar (Or(57-98)Ab(2-42)An(1)) +/- biotite +/- olivine. Their Sr-87/Sr-86((I)) ratios and epsilon Nd-(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 (Or(45-61)Ab(38-54)An(0-2)), biotite, and Fe-Ti oxides. The trachytic volcanic rocks are made up of feldspar (Or(38-63)Ab(34-59)An(1-4)) in a fine-grained matrix. Their Sr-87/Sr-86((I)) ratios and epsilon Nd-(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.