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Triassic warm subduction in northeast T urkey: Evidence from the A ğvanis metamorphic rocks
Author(s) -
Topuz Gültekin,
Okay Aral I.,
Altherr Rainer,
Schwarz Winfried H.,
Sunal Gürsel,
Altınkaynak Lütfi
Publication year - 2014
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/iar.12068
Subject(s) - geology , metamorphic rock , geochemistry , metamorphism , greenschist , phyllite , protolith , metamorphic facies , hornblende , ophiolite , accretionary wedge , volcanic rock , subduction , schist , petrology , geomorphology , paleontology , biotite , facies , quartz , tectonics , volcano , structural basin
Within the T ethyan realm, data for the subduction history of the P ermo– T riassic T ethys in the form of accretionary complexes are scarce, coming mainly from northwest T urkey and T ibet. Herein we present field geological, petrological and geochronological data on a T riassic accretionary complex, the Ağvanis metamorphic rocks, from northeast T urkey. The A ğvanis metamorphic rocks form a SSE–NNW trending lozenge‐shaped horst, ∼20 km long and ∼6 km across, bounded by the strands of the active N orth A natolian F ault close to the collision zone between the E astern P ontides and the M enderes– T aurus B lock. The rocks consist mainly of greenschist‐ to epidote‐amphibolite‐facies metabasite, phyllite, marble and minor metachert and serpentinite, interpreted as a metamorphic accretionary complex based on the oceanic rock types and ocean island basaltic, mid‐ocean ridge basaltic and island‐arc tholeiitic affinities of the metabasites. This rock assemblage was intruded by stocks and dikes of E arly E ocene quartz diorite, leucogranodiorite and dacite porphyry. Metamorphic conditions are estimated to be 470–540° C and ∼0.60–0.90 GPa. S tepwise 40 A r/ 39 A r dating of phengite–muscovite separates sampled outside the contact metamorphic aureoles yielded steadily increasing age spectra with the highest incremental stage corresponding to age values ranging from ∼180 to 209 Ma, suggesting that the metamorphism occurred at ≥ 209 Ma. Thus, the A ğvanis metamorphic rocks represent the vestiges of the L ate T riassic or slightly older subduction in northeast T urkey. Estimated P – T conditions indicate higher temperatures than those predicted by steady state thermal models for average subduction zones, and can best be accounted for by a hot subduction zone, similar to the present‐day C ascadia. Contact metamorphic mineral assemblages around an E arly E ocene quartz diorite stock, on the other hand, suggest that the present‐day erosion level was at depths of ∼14 km during the E arly E ocene, indicative of reburial of the metamorphic rocks. Partial disturbance of white‐mica A r– A r age spectra was probably caused by the reburial coupled with heat input by igneous activity, which is probably related to thrusting due to the continental collision between E astern P ontides and the M enderes– T aurus B lock.