Application of Clinopyroxene Chemistry for Investigation of the physical conditions of ascending magma, a case study of volcanic rocks in the Aliabad area (Northwest of Nain)

Rezvan Mehvari, Mortaza Sharifi
2020 Journal of Economic Geology  
Introduction The Aliabad area is located in the northwest of Nain. Volcanic rocks of the Aliabad area have andesitic to rhyolitic composition. On the basis of petrographic investigations, porphyritic texture is the main texture of these rocks. Thus, they have experienced two crystallization stages. In these rocks, phenocrysts have been crystallized in the first stage, and in the second stage the cooling processes were fast, resulting in a groundmass of glass and fine crystals. The second stage
more » ... . The second stage of crystallization in these rocks took place at (near) the earth surface. The composition of phenocrysts such as amphibole, biotite and pyroxene provide valuable data about magmatic series, pressure, and temperature history of the primary magma during crystallization. In this study, the clinopyroxene of these rocks was analyzed in order to estimate the physicochemical conditions of the parent magma. Material and Methods Field work in the Aliabad area was carried out to identify volcanic units and their relationships. About 65 samples were collected. Thin sections were prepared for petrographic studies to select suitable samples of the volcanic rocks for more detailed mineralogical and geochemical studies. The chemical composition of minerals was determined using a wavelength dispersive EPMA (Cameca-SX 100) at Iran Minerals Research and Processing Center. Analytical conditions for the minerals were accelerating voltage of and a beam current of 15 nA. 15 kV. Also, the Minpet software package was used for processing the relevant data and calculating the structural formula of clinopyroxene minerals based on 6 oxygen atoms. Results The chemical compositions of clinopyroxenes were used to estimate the chemical evolution and P-T conditions of the magmas during crystallization. Microprobe analyses show that clinopyroxenes in the andesitic rocks are augite (En43-45Wo 38-42 Fs14-18). According to the clinopyroxene thrmobarometry calculations done by several methods, it was inferred that the clinopyroxenes are crystallized at temp [...]
doi:10.22067/econg.v11i4.71157 doaj:191f022257b94cb8894572427673b2f0 fatcat:ugg2yzyidzgalk5iurjtaip7rm