Geochemical evidence used to test alternative plate tectonic models for pre-Upper Jurassic (Palaeotethyan) units in the Central Pontides, N Turkey
✍ Scribed by Timur Ustaömer; Alastair H. F. Robertson
- Book ID
- 102658465
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 666 KB
- Volume
- 34
- Category
- Article
- ISSN
- 0072-1050
No coin nor oath required. For personal study only.
✦ Synopsis
East±west trending, inferred Palaeotethyan subduction±accretion complexes form much of the pre-Upper Jurassic basement of the Central Pontides. A number of speci®c tectonic units are present that include variably metamorphosed basic igneous rocks, as dismembered ophiolites, coherent stratigraphical successions, ordered thrust sheets, and blocks in me lange. About 200 samples from a c. 200 km long N±S traverse were analysed by a high-precision X-ray ¯uorescence technique, supplemented by electron microprobe analysis. The basic igneous rocks have not experienced signi®cant chemical mobility after formation and are thus useful for discrimination of tectonic settings of formation using well known binary and ternary plots and mid-ocean ridge basalt (MORB)-normalized spidergrams'. From N to S the main results are that basalts of the KuÈ re Complex were erupted in a subduction-in¯uenced tectonic setting, favouring interpretation as a dismembered ophiolite formed in a marginal basin along the S Eurasian margin. Thick, mainly volcanic, successions of the C Ë angaldagAE Complex show a subduction-in¯uenced calc-alkaline composition, above a basement varying from MORB/island arc tholeiite type to high-Mg (boninitic) type, with an inferred origin as an oceanic arc above forearc basement. Meta-basites from the adjacent Bayam Me lange indicate a supra-subduction zone origin, possibly as a dismembered forearc ophiolite (possibly related to the C Ë angaldagAE ). A large overriding thrust sheet of mainly ultrama®c rocks, the ElekdagAE , is interpreted as a supra-subduction zone ophiolite, based on depleted chrome spinel composition (analysed by microprobe). Eclogitic blocks in structurally underlying me lange are of mid-ocean ridge (MOR) type. Further south, a northward-dipping, inferred subduction±accretion complex, the DomuzdagAE ± SaraycõkdagAE Complex, includes MOR-type meta-basites in the north, and more enriched' compositions in the south, of within-plate origin. Lastly, the geochemistry of meta-basites in the south, within the Kargõ Complex, suggests a plume-MOR to within-plate type eruptive setting, without continental crustal in¯uence.
The geochemical data mainly support a northward rather than southward subduction model for the Palaeotethyan assembly of the Central Pontides, particularly since the KuÈ re ophiolitic basalts in the north exhibit a subduction-in¯uenced chemical signature, in contrast to all the units in the south which lack any identi®able subduction component. Comparisons with published geochemical data from the Karakaya Complex in the SW Pontides reveal similar units, interpreted as accreted MORB lithosphere and oceanic seamounts, but emphasize that the C Ë angaldagAE arc is presently the only known Palaeotethyan subduction arc-related unit in Turkey.