Transition From Low‐K to High‐K Calc‐Alkaline Magmatism at Approximately 84 Ma in the Eastern Pontides (NE Turkey): Magmatic Response to Slab Rollback of the Black Sea

Abstract

Compositional changes of magma in space and time can be used to infer mantle dynamics and crust‐mantle interaction that are responsible for the generation of magma and evolution. This study reveals, for the first time, the presence of magma compositional transition at approximately 84 Ma in the eastern Pontides arc (NE Turkey), providing important insights into the mantle dynamics responsible for the generation of the extensive Late Cretaceous arc magmatism. The Late Cretaceous granitoids can be divided geochemically into two groups. Group I samples were emplaced at 91–86 Ma and are characterized by low K2O/Na2O, whereas Group II samples were emplaced at 83–78 Ma and display high K2O/Na2O. Group I samples have positive zircon εHf (t), whole‐rock ɛNd (t), and mantle‐like zircon δ18O, which significantly differs from the Group II samples with negative to positive εHf (t), negative whole‐rock ɛNd (t), and enhanced zircon δ18O. The Nd‐Hf‐O isotopic compositions of the Group I and II samples can be quantitatively interpreted as being derived from partial melting of the low‐K amphibolite source within the juvenile lower arc crust that incorporated 5–30% and 50–60% enriched components from the basement rocks into the magmatic systems, respectively. Considering the occurrences of regional thermal subsidence and extensional structure during the Late Cretaceous, the compositional transition from Group I to II and the coeval magmatic flare‐up represented by Group II samples can be linked with the slab rollback of the southward subducting Black Sea (Paleotethys) oceanic lithosphere.

Major Late Cretaceous Mass Flows in Central Turkey Recording the Disruption of the Mesozoic Continental Margin

“…(b) The arc magmatism in the western Sakarya Zone starts in the Campanian (approximately 78 Ma; e.g., Aysal et al, ). In contrast, there is ample evidence for earlier arc magmatism in the eastern Sakarya Zone (Eastern Pontides, 91–72 Ma; e.g., Aydınçakır, ; Eyuboglu, ; Kaygusuz et al, ; Liu et al, ; Özdamar, ). We suggest that the eastern margin of the western Sakarya Zone formed a transform fault (Figure ), which linked the subduction under the Eastern Pontides to an intraoceanic subduction zone, which was initiated in the Turonian (approximately 93 Ma; Plunder et al, ).…”

Jurassic to Cenozoic Magmatic and Geodynamic Evolution of the Eastern Pontides and Caucasus Belts, and Their Relationship With the Eastern Black Sea Basin Opening

“…In this model, the BS opened in an intra-arc to back-arc setting. The second features a south dipping subduction of Paleotethys throughout the Mesozoic to early Cenozoic times below the northern margin of the Pontides (Bektaş, 1986;Eyüboğlu, 2010Eyüboğlu, , 2015Eyüboğlu et al, 2007Eyüboğlu et al, , 2013Eyüboğlu et al, , 2017Eyüboğlu et al, , 2018Liu et al, 2018). Recent modifications of this model also feature two subduction zones, a south and north dipping subductions along the northern and southern margins of the Pontides, respectively, during latest Cretaceous to early Cenozoic times (Eyüboğlu et al, 2019).…”

“…An alternative model considers the Black Sea as a relic of the Paleotethys realm, which mostly disappeared due to a south dipping subduction just north of the EP and LC throughout the Mesozoic and the early Cenozoic (Bektaş, 1986;Eyüboğlu, 2010Eyüboğlu, , 2015Eyüboğlu et al, 2013Eyüboğlu et al, , 2017Eyüboğlu et al, , 2019Liu et al, 2018). In this alternative setup, the Northern Neotethyan realm opened in a back-arc configuration of this south • Early Jurassic-early Cenozoic subduction/collision-related magmatic arc emplacement is due to a single north dipping subduction • Early Cretaceous roll-back and Eastern Black Sea opening caused gradual separation of a remnant arc from the active supra-subduction zone • Jurassic arc-related magmatic of the Greater Caucasus belong to the arc of the north dipping subduction below the Southern Eurasian margin…”

“…An alternative model considers the Black Sea as a relic of the Paleotethys realm, which mostly disappeared due to a south dipping subduction just north of the EP and LC throughout the Mesozoic and the early Cenozoic (Bektaş, 1986; Eyüboğlu, 2010, 2015; Eyüboğlu et al, 2013, 2017, 2018, 2019; Liu et al, 2018). In this alternative setup, the Northern Neotethyan realm opened in a back‐arc configuration of this south dipping Paleotethyan subduction just south of the EP and SK arcs (Eyüboğlu et al, 2019; Galoyan et al, 2018).…”

Review of Late Cretaceous volcanogenic massive sulfide mineralization in the Eastern Pontides, NE Turkey

“…The plutonic rocks of the belt have different ages and compositions. They range in age from Carboniferous to Neogene (Delaloye et al, 1972;Taner, 1977;Kamitani and Akıncı, 1979;Moore et al, 1980;Şen, 1987;Okay and Şahintürk, 1997;Yılmaz et al, 1997;Kaygusuz, 2000;Arslan et al, 2004;Aydınçakır and Şen, 2013;Delibas et al, 2016;Eyuboglu et al, 2017Eyuboglu et al, , 2019Liu et al, 2018). The plutonic rocks exhibit a broad compositional range and are dominated by tholeiitic and calc-alkaline granitoids and alkaline syenite/monzonites (Yılmaz and Boztuğ, 1996).…”