Browsing by Author "Leybourne, Matthew"

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Citation - WoS: 5
Citation - Scopus: 3
Ar-Ar Geochronology and Sr-Nd Isotopic Systematics of the Post-Collisional Volcanic Rocks From the Karapinar-Karacadag Area (central Anatolia, Turkey): an Alternative Model for Orogenic Geochemical Signature in Sodic Alkali Basalts
(Ceska Geologicka Spolecnost, 2022) Gençoğlu Korkmaz, Gülin; Kurt, Hüseyin; Asan, Kürşad; Leybourne, Matthew
The Plio???Quaternary post-collisional volcanism in the Karap??nar area is represented by two occurrences: (1) Karacada?? Volcanic Complex (KCVC) and (2) Karap??nar Volcanic Field (KPVF). The investigated volcanic units are the southwes-tern part of the Neogene to Quaternary Cappadocia Volcanic Province (CVP) in Central Anatolia. The CVP generally displays calc???alkaline affinity in the Late Miocene to Pliocene rocks, but both calc-alkaline and sodic alkaline affinity in the Plio???Quaternary rocks, all of which have an orogenic geochemical signature. Such a volcanic activity contradicts the Western and Eastern Anatolian volcanism characterized by anorogenic OIB-like sodic alkaline volcanic rocks postdating early orogenic calc???alkaline ones. We hypothesize that such temporal and geochemical variations in the investigated rocks result from crustal contamination and present major and trace element chemistry and Sr???Nd???Pb???O isotope geochemistry, coupled with 40Ar/39Ar geochronology data to restrict the genesis and evolution of the rocks. The Neogene Karacada?? volcanic rocks are represented by lava flows, domes and their pyroclastic equivalents constituting a stratovolcano, and dated by new 40Ar/39Ar ages of 5.65 to 5.43 Ma. They are mainly composed of andesitic, rarely basaltic, dacitic and trachytic rocks and have a calc???alkaline character. Constituting a monogenetic volcanic field, the Quaternary Karap??nar volcanic rocks are typically formed by cinder cones, maars and associated lavas, including xenoliths and xenocrysts plucked from the Karacada?? rocks. They comprise basaltic to andesitic rocks with a transitional affinity, from sodic alkaline to calc???alkaline. Both the Karacada?? and Karap??nar volcanic rocks display incompatible trace element patterns rather characteristic for orogenic volcanic rocks. The Sr, Nd and Pb isotopic systematics of both units show a relatively narrow range, but their ??18O values are markedly different. The Karacadag volcanic rocks have ??18O values ranging from 7.5 to 8.9 ???, resembling those of subduction-related basalts, but the Karap??nar volcanics have ??18O ratios between 5.7 and 6.5 ??? corresponding to OIB-like rocks. Additionally, ??18O values and 87Sr/86Sr ratios correlate positively with SiO2 in the rocks, indicating that contamination played an important role during differentiation processes. All the data obtained suggest that the Karacada?? basaltic rocks stemmed from a subduction-modified lithospheric mantle source. On the other hand, the origin of the Karap??nar basaltic rocks can be explained in terms of OIB-like melts contaminated with the Karacada?? volcanic rocks to gain orogenic geochemical signature, which may be an alternative model for the origin of the CVP sodic alkali basalts.
Citation - WoS: 1
Citation - Scopus: 2
The Role of Peridotite and Pyroxenite Melts in the Origin of the Karapinar Basalts, Cappadocia Volcanic Province, Central Anatolia
(Ceska Geologicka Spolecnost, 2022) Gençoğlu Korkmaz, Gülin; Kurt, Hüseyin; Asan, Kurşad; Petrelli, Maurizio; Leybourne, Matthew
This study investigates the mantle source characteristics of the Quaternary Karapinar Basalts from the southwestern part of the Cappadocia Volcanic Province (CVP) in Central Anatolia using a combination of whole-rock and olivine major- and trace-element geochemistry as well as olivine oxygen isotope composition. Petrographic features and trace element distributions demonstrate that the Karapinar basalts can be classified into two sub-groups as basalt-1 (KB1/alkaline-calc-alkaline) and basalt-2 (KB2/calc-alkaline). Although these two types of basalts are petrographically, texturally and geochemically different, they exhibit similar orogenic type incompatible trace element patterns in MORB-normalized diagrams. KB1 basalts are relatively primitive (e.g., up to 12 wt. % MgO) and calc-alkaline to mildly alkaline (Ne-normative content up to 5 %) in character, whereas KB2 basalts are enclave-bearing, calc-alkaline (hypersthene-normative plus quartz or olivine) ones with the more evolved composition. The most primitive olivine from the KB1 exhibits normal zoning, from core compositions of Fo(89) to rim compositions of Fo(86), with a concomitant decreasing in Ni and increasing MnO and CaO contents. On the contrary, the KB2 olivines show both inverse and normal zoning in terms of CaO and MnO contents. Moreover, the studied olivine phenocrysts have enriched rims and/or growth zones in Li, Zn, Cr, Ti, Sc, and V contents, which indicates a source containing recycled continental crust and/or magma recharging processes. The olivine from the most primitive samples (KB1; MgO > 10 wt. %) has high Zn/Fe, Fe/Mn, Co, Zn, Ni, Ca, and low Mn/Zn, Co/Fe values indicating melt addition from a pyroxenitic source. Calculations based on the olivine chemistry indicate that the most primitive nepheline normative KB1 rocks originated from the melting of mixed pyroxenitic-peridotitic source that shows the average proportion of similar to 70 % and similar to 30 %, respectively. The mean delta O-18 values of olivine phenocrysts (+ 6.4 %; n = 8) from the Karapinar basaltic rocks are higher than typical mantle olivine (+ 5.1-5.4 %) but overlap known OIB-EMII sources (+ 5.4-6.1 %). Collected data indicate that the Karapinar basalts are the mixing products of partial melts from mantle peridotite and metasomatic pyroxenite generated by the reaction of the subducted oceanic slab-derived melts with the surrounding peridotite, related to the convergence system of the Eurasian and Afro-Arabian plates.
Spatial Mineral Chemistry of Volcanic Rocks from the Karacadağ Volcanic Complex and Karapinar Volcanic Field (Central Anatolia): Evidence for a Trans-Crustal Magmatic System
(Springer Wien, 2025) Korkmaz, Gulin Gencoglu; Kurt, Huseyin; Asan, Kursad; Petrelli, Maurizio; Leybourne, Matthew
This research investigates the trans-crustal magmatic evolution of the Karacada & gbreve; Volcanic Complex (KCVC)-Karap & imath;nar Volcanic Field (KPVF) in Central Anatolia, with a particular focus on the major and trace element compositions of clinopyroxene and amphibole minerals from basaltic and andesitic lavas. Pliocene-aged Karacada & gbreve; andesites and Quaternary-aged Karap & imath;nar basalts contain various crystal cargoes, including crystal clots, several types of enclaves, xenocrysts, autocrysts, and antecrysts, suggesting microscale heterogeneity and potentially reflecting distinct petrogenetic histories. The EPMA results reveal that clinopyroxenes are compositionally diopside to augite, while amphiboles range from magnesio-hornblende, tschermakite, sadanagaite to pargasite. The LA-ICP-MS analyses allow for the classification of four pyroxene (Px-I to Px-IV) and six amphibole types (Amp-I to Amp-VI). Among these, Px-I, Amp-I, Amp-II, and Amp-IV exhibit relatively primitive geochemical signatures compared to their host rocks. These characteristics are consistent with crystallization from earlier, less evolved magmatic pulses, supporting their interpretation as antecrysts, whereas the others are considered as autocrysts. Thermobarometric calculations reveal that amphiboles in the KKVC suite crystallized at pressures ranging from 0.8 to 5.4 kbar, indicating magma storage across both shallow and deep crustal levels. However, those of clinopyroxenes yield 4-9 kbar and 1025-1116 degrees C, suggesting derivation from deeper reservoirs. Clinopyroxene P-T calculations for the KPVF basalts indicate high-pressure crystallization (12-14 kbar) at temperatures up to 1266 degrees C, reflecting deep crustal magma storage. All obtained data reveal open-system magma reservoirs with repeated mixing and recharge, triggering Quaternary eruptions and highlighting the role of trans-crustal magmatic system in Central Anatolia.