Constraints on the composition and thermal structure of the upper mantle beneath NW Turkey: Evidence from mantle xenoliths and alkali primary melts

Gourgaud, A
Kaymakcı, Nuretdin
Ultramafic xenoliths entrained in the Late Miocene alkali basalts and basanites from NW Turkey include refractory spinel-harzburgites and dunites accompanied by subordinate amount of spinel-lherzolites. Whole-rock major element and mineral chemical characteristics indicate that the xenoliths are mostly the solid residues of varying degrees of partial melting (similar to 3 to similar to 15%), but some have mineral chemical signatures reflecting processes of melt/rock interaction. The mineral compositions of the undisturbed xenoliths have been used to estimate temperatures and, where possible, pressures of equilibration, and to construct a geothermal framework to interpret the thermal structure of the upper mantle beneath the region at the time of basaltic melt extraction. Most of the peridotite xenoliths have chemically homogeneous mineral phases reflecting ambient equilibrium pressure-temperature conditions. The combination of results from Ca-in-orthopyroxene geothermometer and Ca-in-olivine geobarometer yields pressure-temperature estimates for spinel-peridotites that fall in experimentally determined spinel-lherzolite field in CaO-Fe-M-O-Al2O3-SiO2-Cr2O3 (CFMASCr) system. These pressure-temperature data sets have been used to construct the Late Cenozoic geotherm of NW Turkey, which defines a depth-temperature array from about 1.4 GPa at 810 degrees C to 2.1 GPa at 1180 degrees C. Extrapolation of this array to the adiabatic upwelling curve of normal temperature asthenospheric mantle indicates an apparent lithospheric thickness of similar to 80 km. The geothermal gradient of NW Turkey is only slightly higher than that of the conventional conductive models (similar to 90 MW m(-2)) and may be interpreted as being a consequence of the thermal perturbation by the heat input into the relatively thin mantle lithosphere via the passage and emplacement of magma(s). In contrast, the calculations, based on the melt products of experimental phase equilibria, show that the compositions of the host magmas precipitating the most magnesian olivine (with 88.5 to 91.4% forsterite; Mg2SiO4) phenocrysts of alkaline melts reveal significantly higher anhydrous liquidus temperatures that range from about 1290 to 1410 degrees C. The results are inconsistent with melt generation by either deep-seated thermal anomalies associated with mantle plumes (T-p > 1450 degrees C) or melting of thermally perturbed (wet) mantle lithosphere, but are consistent with the adiabatic upwelling of normal temperature (T-p similar to 1300 degrees C) mantle asthenosphere probably along the lithospheric scale major shear zones.


Zircon ages from the Beypazari granitoid pluton (north central Turkey): tectonic implications
Speciale, Pamela A.; Catlos, Elizabeth J.; Yildiz, G. Okan; Shin, Timothy A.; Black, Karen N. (Informa UK Limited, 2012-09-01)
The Beypazari granitoid is emplaced in a Late Cretaceous volcanic arc in north central Turkey and provides evidence for processes that occurred during the closure of the Neo-Tethys Ocean. Zircons from its northern granodiorite and quartz monzonite exposure are dated in rock thin section and display characteristic igneous zoning in cathodoluminescence (CL). Its oldest Late Cretaceous ages (95.4 +/- 4.2-91.3 +/- 6.5 Ma, U-238/Pb-206, +/- 1 sigma) time early crystallization from rising melts, but inspection of...
Pattern of normal faulting in the Gediz Graben, SW Turkey
Ciftci, N. Bozkurt; Bozkurt, Erdin (Elsevier BV, 2009-07-20)
Hanging-wall deformation of the fault systems controlling the southern margin of the Gediz Graben were investigated separately within the Plio-Quaternary and Neogene (predominantly Miocene) deposits of the graben fill. Fault styles observed in both packages share many similarities in terms of geometry and comprise conjugate fault sets that show clustering of strike orientations predominantly around WNW-ESE but also SW-NE and NW-SE directions. The main difference between the two units is observable in terms ...
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Sahin, Nazif; Altıner, Demir; Ercengiz, M. Bulent (Informa UK Limited, 2012-09-01)
Detailed stratigraphic studies on the Middle-Upper Permian rocks of the Tahtalidag nappe (Antalya Nappes), largely exposed along the Guzelsu Corridor in central Taurides, have revealed the presence of basaltic volcanic rocks intercalated within the shallow-marine fossiliferous carbonate successions. Vitrophyric basaltic extrusions producing distinct pillows in the Kizilbag Formation severely dolomitized the associated carbonate rocks. The coeval Cukurkoy Formation, devoid of volcanic layers, is also exposed...
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Gülyüz, Erhan; Özkaptan, Murat; Kaymakcı, Nuretdin; Persano, Cristina; Stuart, Finlay M. (Elsevier BV, 2019-09-05)
Gondwana (Tauride/kirsehir blocks) and Eurasia (Pontides) derived continental blocks delimit the Haymana basin, central Turkey, to the south and the north, respectively. The boundaries of these blocks define the IzmirAnkara-Erzincan and Intra-Tauride Suture zones which are straddled by a number of Late Cretaceous to Oligocene marine to continental basins. The Haymana Basin is located at the junction of the IAESZ and ITSZ and comprises Upper Cretaceous to Middle Eocene basin infill deposited in response to t...
Folding of the Gediz Graben Fill, SW Turkey: Extensional and/or contractional origin?
Ciftci, N. Bozkurt; Bozkurt, Erdin (Informa UK Limited, 2008-05-01)
Folds constitute a significant pan within the dominantly extension-related deformation pattern of the Gediz Graben and their origin either extensional or contractional has been the subject of debate. Field and subsurface data presented in this paper suggest that folds of contractional and extensional origin coexist in the graben-fill sediments. Contractional folds are predominantly observed within the Alasehir formation. A north vergent, plunging, asymmetrical to overturned geometry characterizes these fold...
Citation Formats
E. ALDANMAZ, A. Gourgaud, and N. Kaymakcı, “Constraints on the composition and thermal structure of the upper mantle beneath NW Turkey: Evidence from mantle xenoliths and alkali primary melts,” JOURNAL OF GEODYNAMICS, pp. 277–316, 2005, Accessed: 00, 2020. [Online]. Available: