The analysis of temperature conditions for eclogites in the northeastern part of North Dabie Terrane

The precise temperature estimation for eclogits across the North Dabie Terrane(NDT) is the most critical to determine the characteristics of the North Dabie metamorphic units correctly.The many uncertainties on the peak temperature estimates and the classification of eclogites across the NDT had arose,as the different thermometers and methods of Fe2+correction of omphacite had been employed to evaluate the P-T values,and the different scenarios for the classification of eclogites had existed.To investigate this issue,5 thermometers and 4 methods for ferric correction of omphacites have been used to calculate the temperature conditions for eclogites in the northeastern part of the NDT in this study.When the Krogh(2000) Grt-Cpx Fe-Mg thermometer has been employed and the ferric in omphacite has been assumed as Fe3+/Fe2+=11,the temperature estimated ought to approach to the real values.The results indicate:Pcalibration=3.5GPa,the temperature is in the range of 600~740℃;Pcalibration=5.0GPa,the temperature is in the range of 670~810℃.Refer to the classification of eclogites from Carswell(1990),the eclogites across the NDT can be considered as the medium temperature eclogites.However,the eclogites from the NDT display different characters from those in the Central Dabie and South Dabie terranes,based on the investigations of geological characteristics,petrographic studies,the analysis of mineral compositions and the results of previous studies for eclogits from the NDT,we conjectured that the eclogites across the NDT underwent higher temperature metamorphism.