Evolution of K-rich magmas derived from a net veined lithospheric mantle in an ongoing extensional setting: Geochronology and geochemistry of Eocene and Miocene volcanic rocks from Eastern Pontides (Turkey)

Abstract

International audienceThe Eocene and Miocene volcanic rocks between the cities of Trabzon and Giresun in the Eastern Pontides (NE Turkey) erupted as mildly and moderately alkaline magmas ranging from silica-saturated to silica-undersaturated types. 40Ar-39Ar dating and petrochemical data reveal that the studied volcanic rocks are discriminated in two: Lutetian (Middle Eocene) mildly alkaline, (basaltic rocks: 45.31 ± 0.18 to 43.86 ± 0.19 Ma; trachytic rocks: 44.87 ± 0.22 to 41.32 ± 0.12 Ma), and Messinian (Late Miocene) moderately alkaline volcanic rocks (tephrytic rocks: 6.05 ± 0.06 and 5.65 ± 0.06 Ma). The trace and the rare earth element systematic, characterised by moderate light earth element (LREE)/heavy rare earth element (HREE) ratios in the Eocene basaltic and trachytic rocks, high LREE/HREE ratios in the Miocene tephrytic rocks, and different degrees of depletion in Nb, Ta, Ti coupled with high Th/Yb ratios, show that the parental magmas of the volcanic rocks were derived from mantle sources previously enriched by slab-derived fluids and subducted sediments. The Sr, Nd and Pb isotopic composition of the Eocene and Miocene volcanic rocks support the presence of subduction-modified subcontinental lithospheric mantle. During the magma ascent in the crust, parental magmas of both the Eocene and Miocene volcanic rocks were mostly affected by fractional crystallisation rather than assimilation coupled with fractional crystallisation and mixing. The silica-undersaturated character of the Miocene tephrytic rocks could be attributed to assimilation of carbonate rocks within shallow-level magma chambers. The parental magmas of the Eocene volcanic rocks resulted from a relatively high melting degree of a net veined mantle and surrounding peridotites in the spinel stability field due to an increase in temperature, resulting from asthenospheric upwelling related to the extension of lithosphere subsequent to delamination. The parental magmas for the Miocene volcanic rocks resulted from a relatively low melting degree of a net veined mantle domain previously modified by metasomatic melts derived from a garnet peridotite source after decompression due to extensional tectonics, combined with strike-slip movement at a regional scale related to ongoing delamination

40Ar-39Ar geochronology and petrogenesis of postcollisional trachytic volcanism along the İzmir-Ankara-Erzincan Suture Zone (NE, Turkey)*

“…For that reason, the character of the mantle source area of the postcollisional magmatic units along the IAESZ was possibly dictated by highly metasomatized and subduction-related signatures even without any influence of an actively subducting slab, which has also been suggested by recent studies (Yücel et al, 2017).…”

“…Thus, we suggest that the trace element ratios/plots used for understanding of the evolution of the arc magmatism can also be reliable tools to investigate the presence and behavior of sedimentary melts/fluids, subduction components in mantle source areas of postcollisional magmatics. (Gülmez et al, 2013;Kasapoğlu et al, 2016) and middle Eocene volcanics from the Eastern Pontides (Kaygusuz et al, 2011;Temizel et al, 2012Temizel et al, , 2016Arslan et al, 2013;Aslan et al, 2014;Yücel et al, 2017) are also plotted. Data for lithospheric mantle array and MORB from Wilson (1989) and Gill (1981).…”

“…Petrological evolution of some portion of these rocks is explained by postcollisional delamination-governed tectonomagmatic processes together with assimilation-related modifications (Temizel et al, 2016;Yücel et al, 2017). However, the generation of coevally developed trachytic units along the other parts of the IAESZ is poorly documented and the petrogenesis of these units needs to be clarified.…”

Mineral Chemistry, Whole-Rock Geochemistry and Petrology of Eocene I-Type Shoshonitic Plutons in the Gölköy Area (Ordu, Ne Turkey)

“…The formation of the early Eocene adakitic rocks in the Eastern Pontides (54-48 Ma) (Topuz et al, 2005;Karslı et al, 2010bKarslı et al, , 2011Eyüboğlu et al, 2011a, b, c;Topuz et al, 2011;Eyüboğlu et al, 2013a, b;Karslı et al, 2013), corresponds to the last stage of the arc to continent collision, and they are associated with syn-and post-collisional origins. As for the Middle Eocene, the post collisional calc-alkaline volcanic rocks and high-K, calc-alkaline, shoshonitic granitoid plutons developed (Yılmaz and Boztuğ, 1996;Arslan et al, 1997;Şen et al, 1998;Aliyazıcıoğlu, 1999;Arslan and Aliyazıcıoğlu, 2001;Arslan et al, 2002;Boztuğ et al, 2004;Topuz et al, 2005;Arslan and Aslan, 2006;Karslı et al, 2007, Boztuğ andHarvalan, 2008;Temizel andArslan, 2008, 2009;Aslan, 2010;Eyüboğlu et al, 2012;Karslı et al, 2012b;Temizel et al, 2012a, b;Yücel et al, 2012;Arslan et al, 2013a, b;Temizel, 2014;Yücel, 2013;Aslan et al, 2014;Temizel et al, 2014;Temizel et al, 2016;Yücel et al, 2017). The clastic rocks are widespread in the region in the post-Eocene (Okay and Şahintürk, 1997) and are generally accompanied by Neogene alkaline volcanic rocks (Aydın et al, 2008(Aydın et al, , 2009Arslan et al, 2013b;Yücel, 2013…”

“…As for the Middle Eocene, the post collisional calc-alkaline volcanic rocks and high-K, calc-alkaline, shoshonitic granitoid plutons developed (Yılmaz and Boztuğ, 1996;Arslan et al, 1997;Şen et al, 1998;Aliyazıcıoğlu, 1999;Arslan and Aliyazıcıoğlu, 2001;Arslan et al, 2002;Boztuğ et al, 2004;Topuz et al, 2005;Arslan and Aslan, 2006;Karslı et al, 2007, Boztuğ andHarvalan, 2008;Temizel andArslan, 2008, 2009;Aslan, 2010;Eyüboğlu et al, 2012;Karslı et al, 2012b;Temizel et al, 2012a, b;Yücel et al, 2012;Arslan et al, 2013a, b;Temizel, 2014;Yücel, 2013;Aslan et al, 2014;Temizel et al, 2014;Temizel et al, 2016;Yücel et al, 2017). The clastic rocks are widespread in the region in the post-Eocene (Okay and Şahintürk, 1997) and are generally accompanied by Neogene alkaline volcanic rocks (Aydın et al, 2008(Aydın et al, , 2009Arslan et al, 2013b;Yücel, 2013, Yücel et al, 2012, 2014, 2017. The Quaternary deposits are represented by travertine and alluvial deposits.…”