Crystallization Conditions and Mineral Chemistry in the East of Tafresh, Central Iran, with Insights into Magmatic Processes

<p>Bal&#305;kesir Volcanites (BV) are included into the Bal&#305;kesir Volcanic Province and contain various products of Oligo-Miocene volcanic activity in NW Anatolia. BV are formed from trachyandesite, andesite and dacite lavas with associated pyroclastic rocks. In this study, we report the petrographical investigations, mineral chemistry results and geothermobarometry calculations of the Bal&#305;kesir Volcanites in order to deduce the magma chamber processes and crystallization conditions. Andesites present a mineral composition of plagioclase (An35&#8211;50) + amphibole (edenitic hornblende) +biotite &#177; quartz and opaque minerals. The major phenocryst phases in dacite lavas are plagioclase (An39&#8211;53), quartz, amphibole (magnesio-hornblende), biotite, sanidine and opaque minerals. The mineral composition of the trachyandesites, on the other hand, is represented by plagioclase (An38&#8211;57) + amphibole (pargasitic hornblende) + biotite + clinopyroxene (endiopside- augite) &#177; sanidine &#177; quartz &#177; opaque minerals. Bal&#305;kesir Volcanites present distinct textural properties such as rounded plagioclase phenocrysts with reaction rims, oscillatory zoning, honeycomb and sieve textures in plagioclase, reverse mantled biotite and hornblende crystals. The plagioclase- amphibole geothermobarometry calculations of Bal&#305;kesir volcanites indicate that, andesite and dacite lavas present similar crystallization temperature and pressures conditions of 798- 813&#176;C and 1,98- 2.17 kbar. Oppositely, trachyandesites were crystallized under 857&#176;C and 3,72 kbar temperature and pressure conditions. These results show that the andesite and dacite lavas were originated from the same magma chamber with the depth of 7km whereas trachyandesites were evolved in a deeper magma chamber with 13 km depth. Combined mineral chemistry, petrography and geothermobarometry studies indicate that the open system processes such as magma mixing/mingling and/or assimilation fractional crystallization (AFC) were responsible for the textural and compositional variations of the Bal&#305;kesir Volcanites.</p>

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Mineral chemistry, crystallization conditions and geodynamic implications of the Oligo–Miocene granitoids in the Biga Peninsula, Northwest Turkey

Journal of Asian Earth Sciences ◽

10.1016/j.jseaes.2015.03.026 ◽

2015 ◽

Vol 105 ◽

pp. 68-84 ◽

Cited By ~ 12

Author(s):

Namık Aysal

Keyword(s):

Mineral Chemistry ◽

Biga Peninsula ◽

Crystallization Conditions

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Serpentinization and chloritization of metamorphosed lherzolites in Darreh-Deh (east of Nain Ophiolite, Central Iran): Calcium source for rodingitization and tremolitization

Neues Jahrbuch für Mineralogie - Abhandlungen Journal of Mineralogy and Geochemistry ◽

10.1127/njma/2019/0163 ◽

2020 ◽

Vol 196 (3) ◽

pp. 179-191

Author(s):

Nargess Shirdashtzadeh ◽

Ghodrat Torabi

Keyword(s):

Crystal Lattice ◽

Calcium Content ◽

Mineral Chemistry ◽

Amphibolite Facies ◽

Central Iran ◽

Coarse Grained ◽

Potential Source ◽

Calcium Source ◽

Mantle Olivine ◽

Microprobe Data

The petrography and mineral chemistry of the metamorphosed lherzolite in Darreh-Deh massif (east of Nain Ophiolite, Central Iran) is investigated in order to find the calcium source for rodingitization and tremolitization. In comparison with olivine and orthopyroxene, the clinopyroxene has lower modal content and is more alteration-resistant. The microprobe data and petrography of these lherzolites indicate that Ca2+ cations can be released during serpentinization of orthopyroxene (with ~18 vol% and CaO~2.7 wt%) and clinopyroxene (with ~6 vol% and CaO~ > 20 wt%). In contrast, per- vasive serpentinization of mantle olivine with ~70 vol% and CaO~0.02–0.07 wt% is another expected source for producing Ca2+ rather than metamorphic olivine with CaO~ < 0.02 wt%. The released Ca2+ cannot be completely accommodated in crystal lattice of produced serpentine (with CaO~0.02–0.06 wt%), talc and chlorite (with CaO~0.015 wt%), but it can participate in formation of Ca-bearing tremolite (CaO~13 wt%), as a result of serpentinization of clinopyroxenes or subsequent metamorphism of peridotites at amphibolite facies and in formation of coarse-grained clinopyroxene blades and tremolite during rodingitization. Therefore, the calcium content in clinopyroxene, orthopyroxene and olivine of a plagioclase–free peridotite is a potential source of Ca2+, depending on the degree of serpentinization or chloritization.

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