Ar-40-Ar-39 age, petrography and geochemistry of the Yoncayolu Metamorphic Rocks (NE Turkey): Subduction-related metamorphism under greenschist fades conditions

作者：Gucer Mehmet Ali^*; Aslan Zafer

来源：Neues Jahrbuch für Mineralogie - Abhandlungen, 2014, 191(3): 257-276.

DOI：10.1127/0077-7757/2014/0260

• Yoncayolu Metamorphic Rocks
• NE Turkey
• Ar-40-Ar-39 age
• greenschist facies
• chlorite thermobarometry

The Yoncayolu Metamorphic Rocks (YMR), exposed in the Sakarya zone (Erzincan, NE Turkey), consists mainly of greenschist rocks which are chlorite schists, muscovite-chlorite schists, metabasic rocks and lesser extent of pyhllites and calc-schists. All YMR are fine-grained, weakly foliated and often cut by quartz veins. The common mineral assemblage is chlorite+albite+epidote+quartz+/-clinozoisite+/-actinolite+/-opaques. Geochemically, protoliths of the YMR resemble calc-alkaline volcanic arc rocks. The YMR have high contents of large ion lithophile elements (LILEs) and low contents of high field strength elements (HFSEs) similar to mid-ocean ridge basalt (MORB). (La/Lu)(CN) values are between 0.26 and 6.16. The REE patterns show slight or no Eu anomalies (Eu-CN/Eu* of 0.48 to 1.13), suggesting minor plagioglase fractionation. Ar-40-Ar-39 dating on plagioclases from the metabasic samples of the YMR gave ages of 100.8+/-3.4 Ma (Albian) and 94.1+/-3.3 Ma (Cenomanian), suggesting that metamorphism was related to the closure of the Neo-Tethyan Ocean. Metamorphism took place during subduction of the Neo-Tethyan Ocean between similar to 90-70 Ma. Chlorite geothermometry yielded a temperature of 320-350 degrees C and a pressure around 4 kbar. All these findings lend support for greenschist facies metamorphic conditions during the formation of the YMR.

• 出版日期2014-6