Browsing by Author "Karaoglu, Ozgur"

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Glass Geochemistry and Tephrostratigraphy of Key Tephra Layers in and Around Lake Van, Eastern Anatolian Volcanic Province (Eavp)
(Pergamon-elsevier Science Ltd, 2025) Kearney, Rebecca J.; Goff, Jeremy; Smith, Victoria; Ozdemir, Yavuz; Schwab, Markus J.; Karaoglu, Ozgur; Brauer, Achim
The volcanoes of Nemrut and Suphan in the Eastern Anatolian Volcanic Province (EAVP) are significant sources of volcanic ash (tephra), which are found in palaeoclimatic and archaeological records in the eastern Mediterranean region. However, there is sparse glass geochemistry and little known about the eruption history of these volcanoes, limiting their full tephrochronological potential. Here, we present detailed, comprehensive singleshard major, minor and trace elem geochemistry of tephra deposits sampled at new and previously studied proximal outcrops around Lake Van and fourteen visible tephra layers (V-layers) from the ICDP Ahlat Ridge (AR) core of Lake Van spanning 130 to 30 ka. The volcanic glass from the following proximal eruption units: Lower Trachytic Pumice (LT-P), Lower Trachytic Ignimbrite (LT-I), Middle Pumices, Upper Rhyolitic Pumice and Ignimbrite (UR-PI), Upper Trachytic Ignimbrite (UT-I), and the chosen V-layers were geochemically characterised. This new glass data allows new and revised previous chrono-stratigraphic correlations between the proximal units and several V-layers. Mixed rhyolitic and trachytic glasses of V-18a correlate to the UR-P and UR-I proximal tephra units, and to previously published data from the Middle Nemrut (M-NF)-O, M-NF-I, Tatvan Ignimbrite and AP-8 units. These are all from the same caldera forming eruption of Nemrut at similar to 33 ka. Glasses of the older V-30 layer correlate to a Middle Pumice Unit and M-NF-R, and V-45 represents the 'Cekmece Formation'. The trachytic glasses of V-51 correlate to LT-P, LT-I and the M-NF-Agglutinate unit erupted from Nemrut. The distinctive basaltic glasses from V-60 correlate to an eruption of.Incekaya and V-64 is a newly identified eruption from the Suphan volcano. The older V-layers identified and analysed are from Nemrut based on comparing the new glass compositions to previously published whole-rock and glass data. This comparison indicates the V-75 pantelleritic tephra correlates to the dated AP-4 proximal unit. Each of these large eruptions are easily chemically differentiated using SiO2, FeOt, CaO and Al2O3. The integration of the proximal outcrops with the continuous, well-constrained Lake Van sedimentary medial record provides a detailed tephrostratigraphic record in a volcanic region where the proximal outcrop record is fragmented and confusing.
Isotopic Evidence for a Transition From Subduction To Slab-Tear Related Volcanism in Western Anatolia, Turkey
(Elsevier, 2014) Karaoglu, Ozgur; Helvaci, Cahit
Volcanic rocks in western Turkey show age progressive magmatism migrating from northeast to southwest that reflects a southward shift of the Aegean subduction zone during the Miocene. Slab segmentation during this period of trench-roll back is thought to have imposed source region heterogeneity trending northwest to southeast. In this study, we present new Sr, Nd, Pb and 0 isotopic analyses from the Miocene volcanic rocks of the Usak-Gure basin and compare these to previously published data. The data demonstrate a change from subduction-related sources around the Menderes Core Complex to more asthenospheric sources in the Afyon region. Isotopic compositions (Sr-Nd-Pb) of volcanic rocks from the Demirci and Selendi basins to the west and the Afyon volcanic area to the east indicate minimal upper crustal contamination. The most primitive lavas also reveal increasing K contents from west (the NE-SW-trending basins) to east (Afyon region). It is suggested that the composition of the western Anatolian volcanic rocks change from orogenic (with lithospheric mantle sources) associated to denudation of the Menderes Massif Core Complex (MMCC) to anorogenic (with asthenospheric mantle sources) in the vicinity of the Kirka-Afyon-Isparta (KAI) volcanic province with time, from Early Miocene to Quaternary. There is no asthenospheric contribution during the late Miocene onwards in the eastern margin of the MMCC, while the asthenospheric upwelling occurred only in a small area beneath the exhuming core complex. We interpret the U Usak-Gure basin to reflect a structural boundary showing a transition from a subduction-influenced metasomatized mantle source to asthenospheric mantle source volcanism driven by slab-tearing between the Hellenic and Cyprus slab segments. The Usak-Mugla Transfer Zone (UMTZ) most likely corresponds to slab-tear related westernmost faults that were induced by initiation of slab segmentation processes following the late Miocene (circa 11 Ma), and possibly since the Early Miocene. (C) 2014 Elsevier B.V. All rights reserved.
Tectonic Controls on the Karliova Triple Junction (Turkey): Implications for Tectonic Inversion and the Initiation of Volcanism
(Elsevier, 2017) Karaoglu, Ozgur; Selcuk, Azad Saglam; Gudmundsson, Agust
Few places on Earth are tectonically as active as the Karhova region of eastern Turkey which comprises a triple junction (KTJ). Triple junctions result in complex kinematic and mechanical interactions within -the lithosphere generating tectonic inversions and uplift, extensive seismicity and volcanism. Here we present new data, and summarize existing data, on the tectonic evolution of the KTJ in eastern Turkey over the past 6 Ma. In particular, we present a kinematic model for the ICI) and the surrounding area as well as new structural maps. The deformation or strain rate has varied over this 6 million year period. The maximum strain rate occurred between 6 Ma and 3 Ma, a period that coincides with the initiation of activity in Varto Volcano.We suggest that increased strain rate and the initiation of activity at the Varto Volcano may be tectonically related. Subsequent to its formation, the Varto Volcano was dissected by active faults associated with the Varto Fault Zone, including reverse, normal and strike -slip faults. During thepast 3 Ma, however, the KTJ area was deformed, dominantly through dextral crustal movements associated to right -lateral faults. This deformation resulted in the development of a NE SW -trending extensional/transtensional regime, together with a complementary NW -SE -trending contractional regime. In the past 6 Ma the east end of the KTJ has been subjected to incremental deformation. This deformation has resulted in many episodes of faulting during (i) ongoing shortening phases driven by a regional -scale thrust tectonic regime, and (ii) local -scale transtensional phases caused by westward extrusion. (C) 2016 Elsevier B.V. All rights reserved.
Tectonic Controls on the Yamanlar Volcano and Yuntdagi Volcanic Region, Western Turkey: Implications for an Incremental Deformation
(Elsevier, 2014) Karaoglu, Ozgur
Over the past ten years, it has been proposed that the western part of the Menderes Massif was strongly structurally-controlled by the Izmir-Balikesir transfer zone (IBTZ). Yamanlar volcano is a key area for understanding the deformation of Miocene volcanoes in western Turkey because of its progressive extensional tectonics. Structural analysis provides that this volcano has undergone the incremental tectonic controls in western Turkey since Early Miocene. The volcano experienced deformation and erosional processes associated with activity of intense tectonic regime that resulted in the dissection of the southern flank of the volcano mostly by NE-SW-striking oblique and strike-slip faults together with cross-cutting faults during and after Miocene period. The orientation of volcanic domes, dykes and intrusive bodies indicates successive and reactive tectonic phases that caused incremental complex movements of numerous fault blocks during the destruction area of the Yamanlar volcano. Structural data documents that the region around Izmir Bay and Yuntdagi volcanic complex is prevailed by far more than three deformation phases. Cross-faults do not reflect to the NE-SW-trending transtensional deformation thereafter Early-Middle Miocene for just the area of the Yuntdagi volcanic system. The nearly E-W-oriented faults are inferred to be the most likely cause of the destruction of both the Yamanlar and Dumanlidag volcanoes coincident with the last stage of the deformation phases the region experienced. This study proposed that the western part of the MMCC was affected by different deformational phases instead of IBTZ resulting in different stage magma ascents: (i) early-Miocene transtensional tectonic; (ii) middle Miocene extensional tectonic related to slab-retreat and (iii) late Miocene tectonic block rotation. (C) 2014 Elsevier B.V. All rights reserved. Over the past ten years, it has been proposed that the western part of the Menderes Massif was strongly structurally-controlled by the Izmir-Balikesir transfer zone (IBTZ). Yamanlar volcano is a key area for understanding the deformation of Miocene volcanoes in western Turkey because of its progressive extensional tectonics. Structural analysis provides that this volcano has undergone the incremental tectonic controls in western Turkey since Early Miocene. The volcano experienced deformation and erosional processes associated with activity of intense tectonic regime that resulted in the dissection of the southern flank of the volcano mostly by NE-SW-striking oblique and strike-slip faults together with cross-cutting faults during and after Miocene period. The orientation of volcanic domes, dykes and intrusive bodies indicates successive and reactive tectonic phases that caused incremental complex movements of numerous fault blocks during the destruction area of the Yamanlar volcano. Structural data documents that the region around Izmir Bay and Yuntdagi volcanic complex is prevailed by far more than three deformation phases. Cross-faults do not reflect to the NE-SW-trending transtensional deformation thereafter Early-Middle Miocene for just the area of the Yuntdagi volcanic system. The nearly E-W-oriented faults are inferred to be the most likely cause of the destruction of both the Yamanlar and Dumanlidag volcanoes coincident with the last stage of the deformation phases the region experienced. This study proposed that the western part of the MMCC was affected by different deformational phases instead of IBTZ resulting in different stage magma ascents: (i) early-Miocene transtensional tectonic; (ii) middle Miocene extensional tectonic related to slab-retreat and (iii) late Miocene tectonic block rotation. (C) 2014 Elsevier B.V. All rights reserved. Over the past ten years, it has been proposed that the western part of the Menderes Massif was strongly structurally-controlled by the Izmir-Balikesir transfer zone (IBTZ). Yamanlar volcano is a key area for understanding the deformation of Miocene volcanoes in western Turkey because of its progressive extensional tectonics. Structural analysis provides that this volcano has undergone the incremental tectonic controls in western Turkey since Early Miocene. The volcano experienced deformation and erosional processes associated with activity of intense tectonic regime that resulted in the dissection of the southern flank of the volcano mostly by NE-SW-striking oblique and strike-slip faults together with cross-cutting faults during and after Miocene period. The orientation of volcanic domes, dykes and intrusive bodies indicates successive and reactive tectonic phases that caused incremental complex movements of numerous fault blocks during the destruction area of the Yamanlar volcano. Structural data documents that the region around Izmir Bay and Yuntdagi volcanic complex is prevailed by far more than three deformation phases. Cross-faults do not reflect to the NE-SW-trending transtensional deformation thereafter Early-Middle Miocene for just the area of the Yuntdagi volcanic system. The nearly E-W-oriented faults are inferred to be the most likely cause of the destruction of both the Yamanlar and Dumanlidag volcanoes coincident with the last stage of the deformation phases the region experienced. This study proposed that the western part of the MMCC was affected by different deformational phases instead of IBTZ resulting in different stage magma ascents: (i) early-Miocene transtensional tectonic; (ii) middle Miocene extensional tectonic related to slab-retreat and (iii) late Miocene tectonic block rotation. (C) 2014 Elsevier B.V. All rights reserved.