Petrography and Geochemistry of post-collisional adakites and Nb-enriched basalts association in the Sang-e-Rahuzg area (south of Birjand)

Abstract

The studied rocks consist of Paleogene units with andesite and dacite composition and basaltic lavas belong to the Neogene time. Acid and intermediate lavas have medium to high-K calc alkaline nature and basalt is alkaline. Geochemical evidences show enrichment of LILEs relative to HFSEs in all volcanic rocks of Sang-e-Rahuzg area. Lack of negative Eu anomaly, low HREE (e.g. Yb= 0.67 - 1.62 ppm and Y=7.4 - 17.3 ppm), high Sr content (347.1 - 1010 ppm) and high Sr/Y ratio (31.84-99.99) indicate that the acid and intermediate rocks of Sang-e-Rahuzg area have adakitic nature. Moreover, high SiO2 content (56.65-68.48 wt.%), CaO+ Na2O (7.57-10.47 wt.%) and Sr show that the rocks studied are classified as high-SiO2 adakites. Also, high K2O content (1.22-3.14wt.%), and high K2O/Na2O ratio (0.4-0.8) in compare with high-SiO2 adakites document that these rocks belong to post-collisional adakite type. Low HREE content (YbN2 (1.52 wt.%), Nb (14.9 ppm), Nb/La (0.43) as well as high HFSE content of the basaltic samples of Sang-e-Rahuzg are characteristics of Nb-enriched basalts. Partial melting of metasomatised mantle by adakitic melts, caused suitable conditions for generation of Nb-enriched basalt. All lavas of Sang-e-Rahuzg area were generated, as the result of collision of Lut and Afghan blocks during the Paleogene to the Neogene time, in post-collisional tectonic environment, result of collision of Lut and Afghan blocks in Paleogene to Neogene.

Keywords

• adakite
• Nb-enriched basalt
• post collision
• Sang-e-Rahuzg
• Lut block