The Plio-Quaternary volcanic cones in N-Qorveh have been comprised of three volcanic facies includings: pumiceous pyroclastics, fall-out scoria deposits and lava flows. The scoria clasts form the main volume of the cones. Because of this, we call them as “scoria cones”. More
The Plio-Quaternary volcanic cones in N-Qorveh have been comprised of three volcanic facies includings: pumiceous pyroclastics, fall-out scoria deposits and lava flows. The scoria clasts form the main volume of the cones. Because of this, we call them as “scoria cones”. Two types of enclaves are found in the scoria ejecta that are felsic or crustal xenoliths and mafic enclaves. Based on the type and abundances of the minerals, the latter enclaves are subdivided into three types: mica-apatite-hornblende (MAH), mica-apatite-olivine (MAO), and hornblende-apatite-pyroxene (HAP). Because of the textural and compositional similarities between minerals of the mafic enclaves and lava flows and scoria clasts, it must be stated that the mafic enclaves had been the cumulates that brought up the surface by the Strombolian-type explosive eruptions. Moreover, because of high-Mg contents in the mafic minerals and also the co-existences of volatile-bearing and volatile-free minerals, it can be stated that the forming magma of the scoria cones had been produced by the partial melting of the upper mantle due to the mantle metasomatism.
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Gasht metamorphic complex crops out in the Talesh Mountains (Western Alborz). This complex mainly consists of metapelitic and granitic rocks. Tourmaline is prevalent as an accessory phase within these rocks. In schist samples, dravitic tourmaline is abundant as nucleati More
Gasht metamorphic complex crops out in the Talesh Mountains (Western Alborz). This complex mainly consists of metapelitic and granitic rocks. Tourmaline is prevalent as an accessory phase within these rocks. In schist samples, dravitic tourmaline is abundant as nucleation component and fine size, and displays compositional zoning. Dravitic tourmaline of gneissic samples are coarser and homogenous. Tourmaline of the migmatites are restricted to both leucosome and melanosome parts. Brown tourmalines of garnet-bearing melanosome are magnesiofoitite in composition and similar to the other mafic phases of melanosome, indicate a residuum nature. However, dravitic tourmalines of the garnet – free melanosome are coarse crystalline and have grown over biotite with green pleochroism. The composition of the leucogranite tourmalines are schorlitic and they become dravitic toward rims. Different types of replacement are observed in the tourmaline composition of Gasht complex. According to the compositional signatures, metapelites tourmaline were formed mainly under metamorphic conditions, while the one of the leucogranites have been formed in the magmatic conditions.
Probably B-bearing fluids of Gasht complex in the high grade metamorphism caused lowering of the temperature of water-bearing solidus of granite. This resulted in facilitating of migmatitization process. Furthermore, boron element caused decreasing of leucosome viscosity, mobilization and easier fractionation of melt from melanosome and creation of adjacent leucogranites.
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