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| Titel |
New petrological insights from the Tavşanli zone (Izmir-Ankara suture, Western Anatolia) |
| VerfasserIn |
A. Plunder, P. Agard, C. Chopin, A. I. Okay |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065253
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| Zusammenfassung |
| Our understanding of subduction zone processes is crucial in terms of rheology and coupling
between plates as well as in terms of risk assessment and fluid budget. The present
work focuses on P–T–Tmax estimates as a way to understand the processes acting
along deep portions of the subduction channel (~40-80 km). For this, we study
the Ä°zmir-Ankara suture zone, Western Anatolia, which separates the Pontides
and the Anatolide-Tauride Block. We focus more specifically on the blueschists of
the Tavşanli zone, that represents the northern continental passive margin of the
Anatolide-Tauride block subducted below an oceanic plate (whose remains are found as
ubiquitous, non-metamorphic klippen on top of the blueschists; eg. the Burhan
ophiolite) during the late Cretaceous. The Tavşanli zone is an ideal target to study a
large exposure of the plate interface and one of the best-preserved fossil subduction
channels. It has also been described as one of the lowest geotherms (~5 °C.km-1) ever
recorded (with P–T conditions ~430 ± 30 °C – 22 ± 2 kbar; Okay & Kelley, 1994;
Okay, 2002). Samples were collected in the three units identified on the basis of
previous works, in order to evaluate the P–T–Tmax conditions. These are, from
bottom to top: (1) the greyschist (meta-greywackes and meta-shales) and marbles
of the Orhaneli region (blueschist to eclogite facies conditions); (2) the Devlez
formation, made of metabasites and metacherts (essentially blueschist facies); (3) an
accretionary complex, sandwiched between continental units 1 and 2 below and the
ophiolite on top, which comprises slices of metabasalt and metacherts with different
metamorphic grades. The latter unit reveals P–T conditions ranging from incipient
metamorphism to blueschist facies, with some samples containing high-pressure overprints
after amphibolite relics. Raman spectroscopy on carbonaceous material (RSCM
geothermometer; Beyssac et al., 2002) yield to Tmax between 500–570°C for the greyschists
of the continental lawsonite-glaucophane-jadeite-chloritoid-phengite bearing unit.
Those Tmax are significantly higher than previous P–T estimates, which could be
accounted for by an underestimation of maximum P–T conditions so far or by the
transformation of a markedly different organic precursor (thus leading to a bias in RSCM
temperatures). Pseudosections in the system NaCaKFMASH using Perple_X are in progress
in order to explain the difference between the two sets of estimates and to shed
light on the tectonometamorphic evolution of the plate interface in the Tavşanli
zone.
References:
Beyssac, O., Goffé, B., Chopin, C., & Rouzaud, J. N. 2002. Raman spectra of carbonaceous
material in metasediments: a new geothermometer. Journal of Metamorphic Geology,
20:859–871.
Okay, A.I., 2002, Jadeite-chloritoid-glaucophane-lawsonite schists from northwest Turkey:
unusually high P/T ratios in continental crust. Journal of Metamorphic Geology,
20:757-768.
Okay A.I. & Kelley, S.P, 1994, Tectonic setting, petrology and geochronology of jadeite +
glaucophane and chloritoid + glaucophane schists from northwest Turkey. Journal of
Metamorphic Geology, 12:455-466. |
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