Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harşit Pluton, Eastern Turkey

Abstract

We present elemental and Sr-Nd-Pb isotopic data for the magmatic suite (*79 Ma) of the Harşit pluton, from the Eastern Pontides (NE Turkey), with the aim of determining its magma source and geodynamic evolution. The pluton comprises granite, granodiorite, tonalite and minor diorite (SiO 2 = 59.43-76.95 wt%), with only minor gabbroic diorite mafic microgranular enclaves in composition (SiO 2 = 54.95-56.32 wt%), and exhibits low Mg# (\46). All samples show a high-K calc-alkaline differentiation trend and I-type features. The chondrite-normalized REE patterns are fractionated [(La/Yb) 83. These geochemical data rule out pure crustalderived magma genesis in a post-collision extensional stage and suggest mixed-origin magma generation in a subduction setting. The melting that generated these high-K granitoidic rocks may have resulted from the upper Cretaceous subduction of the Izmir-Ankara-Erzincan oceanic slab beneath the Eurasian block in the region. The back-arc extensional events would have caused melting of the enriched subcontinental lithospheric mantle and formed mafic magma. The underplating of the lower crust by mafic magmas would have played a significant role in the generation of high-K magma. Thus, a thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower part of the crust. In this scenario, the lithospheric mantle-derived basaltic melt first mixed with granitic magma of crustal origin at depth. Then, the melts, which subsequently underwent a fractional crystallization and crustal assimilation processes, could ascend to shallower crustal levels to generate a variety of rock types ranging from diorite to granite. Sr-Nd isotope modeling shows that the generation of these magmas involved *65-75% of the lower crustal-derived melt and *25-35% of subcontinental lithospheric mantle. Further, geochemical data and the Ar-Ar plateau age on hornblende, combined with regional studies, imply that the Communicated by G. Moore. Electronic supplementary material 123Contrib Mineral Petrol (2010) 160:467-487 DOI 10.1007 Harşit pluton formed in a subduction setting and that the back-arc extensional period started by least *79 Ma in the Eastern Pontides.

Upper Campanian calciclastic turbidite sequences from the Hacımehmet area (eastern Pontides, NE Turkey): integrated biostratigraphy and microfacies analysis

“…The Upper Cretaceous sequences of the northern Eastern Pontides are composed mainly of back-arc volcaniclastics (Şengör and Yılmaz 1981;Okay and Şahintürk 1997;Okay and Tüysüz 1999;Dokuz and Tanyolu 2006;Topuz et al 2007;Karslı et al 2010) (Text-figs 1 and 2). These are deposits related to the closure of the northern branch of the Neotethys Ocean and northward subduction of its oceanic crust (Şengör and Yılmaz 1981;Okay and Şahintürk 1997;Yılmaz et al 1997;Okay and Tüysüz 1999;Şengör et al 2003;Çinku et al 2010;Karslı et al 2010).…”

“…These are deposits related to the closure of the northern branch of the Neotethys Ocean and northward subduction of its oceanic crust (Şengör and Yılmaz 1981;Okay and Şahintürk 1997;Yılmaz et al 1997;Okay and Tüysüz 1999;Şengör et al 2003;Çinku et al 2010;Karslı et al 2010). The volcaniclastics are followed by a calciclastics-dominated sedimentary sequence (Text- fig.…”

Subduction-related Late Cretaceous high-K volcanism in the Central Pontides orogenic belt: constraints on geodynamic implications

“…Several researchers suggested that the eastern Pontides was a magmatic arc that occurred as a result of northward subduction of the Neotethys along the southern border of the Sakarya Zone Karsli et al, 2010;Şengör & Yılmaz, 1981;Şengör et al, 2003;Ustaomer & Robertson, 2010;Yilmaz et al, 1997). Conversely, Dewey et al (1973), Bektaş et al (1999), Eyuboglu, Chung, et al (2011), and Eyuboglu, Santosh, et al (2011)proposed a southward subduction that continued uninterruptedly from the Paleozoic period until the end of the Eocene period.…”

“…Previous studies provided certain geochronological and geochemical constraints on the origin and evolution of Late Cretaceous magmatism. The geochemical nature of the great majority of Late Cretaceous magmatism is of calc-alkaline (Aydin, 2014;Ercan & Gedik, 1983;Karsli et al, 2010;Kaygusuz & Aydınçakır, 2009, 2011Tokel, 1983). However, rare volcanic and plutonic bodies, such as those in this study, attained high-K to shoshonitic composition Asan, Kurt, Francis, & Morgan, 2014;Bektas & Gedik, 1988;Eyüboğlu, 2010;Genç et al, 2014;Gülmez & Genc, 2015;Karsli et al, 2012;Varol, 2013).…”

Middle Jurassic MORB-type gabbro, high-Mg diorite, calc-alkaline diorite and granodiorite in the Ando area, central Tibet: Evidence for a slab roll-back of the Bangong-Nujiang Ocean

“…The growth and reworking of continental crust is commonly triggered by the underplating of mantle magmas (Chen and Arakawa, 2005;Jahn et al, 2004). In subdution zones, the mantle rocks and the coeval granites have therefore recorded abundant information regarding the crustal growth and differentiation of continental crust (Kamei et al, 2004;Karsli et al, 2010). However, the production of the subdution-related magmatic rocks was always attributed to distinct dynamic mechanisms, including slab break-off (Davies and von Blanckenburg, 1995), ridge subduction (Abratis and Worner, 2001;Guivel et al, 1999), slab tearing (Guivel et al, 2006;Pallares et al, 2007), or slab roll-back (Kay and Mpodozis, 2001;Ramos and Folguera, 2009).…”