Economic Geology
Morteza Delavari; Amir Ali Tabakh Shabani; Samaneh Ghanbari
Abstract
The Oligocene dacitic volcanic rocks display widespread exposures in south of Julfa (eastern Azerbaijan). They generally show porphyritic to hyalo-porphyritic textures with major minerals of plagioclase, amphibole, quartz and biotite. Electron probe micro analyzer (EPMA) data indicates oscillatory zoning ...
Read More
The Oligocene dacitic volcanic rocks display widespread exposures in south of Julfa (eastern Azerbaijan). They generally show porphyritic to hyalo-porphyritic textures with major minerals of plagioclase, amphibole, quartz and biotite. Electron probe micro analyzer (EPMA) data indicates oscillatory zoning and chemical variation of amphiboles (pargasite and edenite). The plagioclase crystals are, chemically, andesine (An= 29-51%) which mostly display oscillatory zoning. Based on geobarometric calculations, plagioclase displays pressures of 5 to 8 kb and amphiboles demonstrate different pressure ranges of 1.5 to 3 and 5 to 9 kb. Moreover, geothermometric calculations of plagioclase and amphibole provide temperatures of 1020-1050 and 850-900 °C, respectively. On the basis of geobarometric results, crystallization and growth of the minerals took place in magmatic chambers of different levels. Some of the amphiboles nucleated in lower continental crust and subsequently grown during magma ascent in middle crust whereas some others crystallized in the upper continental crust. Therefore, existence of minerals of different levels inside the studied rocks could be related to magma mixing in shallow magma chambers.
F. Rostami; M. Delavari; S. Amini; A. Dolati
Abstract
The Permian volcanic rocks of Central Alborz (northeast of Baladeh- Siahbisheh) crop out between Ruteh and Nesen Formations. The volcanic rocks are predominantly basaltic and plagioclase- phyric. Ferromagnesian minerals such as clinopyroxene and olivine are not modally abundant and sometimes are totally ...
Read More
The Permian volcanic rocks of Central Alborz (northeast of Baladeh- Siahbisheh) crop out between Ruteh and Nesen Formations. The volcanic rocks are predominantly basaltic and plagioclase- phyric. Ferromagnesian minerals such as clinopyroxene and olivine are not modally abundant and sometimes are totally altered. Based on microprobe data, clinopyroxene and plagioclase are diopside (En34.2-36.4 Wo43.1-47.2 Fs14.9-18.1) and labradorite (50<An%<55), respectively. Clinopyroxene and plagioclase geothermobarometric calculations shows the temperature and pressure ranges of 1050 to 1200 °C and 2 contents (4.94- 7.24 wt. %). Clinopyroxene chemical data display that the parent melt was alkaline basalt, generated in a within plate setting. On the basis of our findings it can be stated that, Central Alborz was a continental passive margin in middle- late Permian at south of Paleo-Tethys and its magmatism was likely triggered by late Paleozoic extensional tectonism of northern margin of Gondwana during the early stages of Neo-Tethyan development.
