Dear Inal,
Taking in consideration all the information you provided, you should suspect that some of your age numbers are not geologically meaningful. You've observed that rutile is partially resorbed by titanite, however your rutile age number is younger than that obtained for titanite.
Although it is very tempting to construct complex and innovative geological models with analytical data, first you should evaluate if the data are accurate (not only precise). In other words, numbers should match logical observations. If they do not, the simplest reasoning and probably the right one is that your numbers are wrong or have a different interpretation.
Best wishes,
Javier Rodríguez, PhD.
Servicio de Geocronología y Geoquímica Isotópica
SGIker – Facultad de Ciencia y Tecnología
Universidad del País Vasco (UPV/EHU)
Barrio Sarriena s/n
E48940 Leioa
Spain
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http://www.ehu.eus/en/web/sgiker/geokronologia-eta-geokimika-isotopikoa
http://www.linkedin.com/in/javi-rodriguez-032a5360
-----Mensaje original-----
De: Metamorphic Studies Group <[log in to unmask]> En nombre de Inal Demirkaya
Enviado el: miércoles, 1 de junio de 2022 22:21
Para: [log in to unmask]
Asunto: Re: Metamorphic areas with very slow cooling
Dear Soucy, Sumit, Jesse, Yong-Fei, Daniela, Matt, Juergen and Denis,
Thank you for your very detailed and helpful comments.
Actually, this metamorphic area is located close to the Neo-Tethyan suture in northwest Turkey. Therefore it was surprising to determine that the exhumation of the metamorphic rocks close to the suture took so long (from Middle Permian (ca. 255 Ma) to Late Jurassic (ca. 155 Ma)).
The chronometers used are U-Pb zircon (255-260 Ma), U-Pb titanite (ca. 230 Ma), Ar-Ar hornblende (ca. 205 Ma), U-Pb rutile (ca. 180 Ma), and Rb-Sr biotite (ca. 155 Ma). The metamorphic domain consists mainly of amphibolite (hornblende, plagioclase, epidote, titanite, rutile, and biotite). The rocks are well-recrystallized and are devoid of any obvious reaction texture. The only reaction texture is the resorption of rutile by titanite. Therefore we are not able to deduce a P-T-t path.
Metamorphic temperatures are ca. 700 °C as calculated by Zr in rutile and Zr in titanite thermometers. We were in indecision whether U-Pb zircon ages represent the peak metamorphism or protolith ages. Th/U ratios are significantly higher than 0.1 (mostly in the range of 0.15-0.50). As the amphibolites display locally stromatic migmatitic structures in the field and this leucocratic (trondhjemitic) domains in composition, produced probably by water present melting) yielded identical U-Pb zircon ages we tend to interpret U-Pb zircon ages as the age of the peak metamorphism. Even if I regard the zircon ages as the protolith age, it is still a very long process ca. 230-155 Ma (75 Ma).
Once again thanks a lot for your comments. They helped me a lot.
İnal
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