Mineral chemistry and petrology of magmatic rocks from NW Takestan (NW Iran)

In northwest of the Takestan area (NW Iran), as a part of the western Alborz mountain belt, various plutonic (monzodiorite, quartz monzonite, granite, and alkali granite), volcanic (andesite, basalt, basaltic andesite, rhyolite, and dacite) and pyroclastic rocks (tuff, agglomerate, and ignimbrite) are hosted of Eocene age. Electron probe micro analyzing (EPMA) on clinopyroxene, orthopyroxene, biotite, and amphibole show that they are diopside to augite (Mg# = 0.6-0.8), enstatite (Mg# = 0.63-0.68), annite to phlogopite (Fe# = 0.15 -0.3) and pargasite (Mg# = 0.6 -0.8), respectively. The plagioclases have different compositions with normal chemical zoning from labradorite (in the basalts, An% = 40 -60) to andesine (in the monzodiorite, An% = 27 -50) to oligoclase (in the other rocks, An% = 13 -38). All minerals are primary magmatic except for the alkali granite biotites that have low Ti contents which indicate that they formed by re-equilibrium with a hydrothermal fluid. Chemical compositions of the clinopyroxene, biotite, and amphibole reveal that they crystallized from calc-alkaline magmas formed by subduction of Neo-Tethys oceanic crust beneath the Iran micro-plate. Geothermometry calculations based on the mineral compositions indicate ca. 880 to 980 degrees C for the basalts, 800 to 850 degrees C for the andesite and the dacite, 750 to 820 degrees C for the monzodiorites and the quartz monzonite, and 520 to 670 degrees C for the alkali granite. High Al contents of the plagioclases from the quartz monzonite and monzodiorite as well as Fe+3 contents of the biotites from the alkali granite show that they formed from oxidized magmas that were suitable for Cu porphyry systems. Propylitic and argillic alteration zones in the area confirm it.