Petrology
Soghra Razaghi; mohsen nasrabady; Kazem Gholizadeh; Zeinab Davoodi
Abstract
The Gash metamorphic complex is situated at the west of Rasht city. Gasht-e-Rodkhan metamorphic rocks are considered as a part of this metamorphic complex. Metapelites (schist, gneiss and migmatite) are the most important lithological unit of the Gasht-e-Rodkhan area. Index minerals consist of staurolite, ...
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The Gash metamorphic complex is situated at the west of Rasht city. Gasht-e-Rodkhan metamorphic rocks are considered as a part of this metamorphic complex. Metapelites (schist, gneiss and migmatite) are the most important lithological unit of the Gasht-e-Rodkhan area. Index minerals consist of staurolite, garnet, sillimanite and kyanite. The main rock forming minerals of muscovite-free melanosome of migmatites are sillimanite and biotite. There is garnet in some melanosome as well. Quartz, K-feldspar and plagioclase are the rock forming minerals of leucosome. Tourmaline, garnet, muscovite and sillimanite are accessory minerals. Average pressure and temperature calculated by Thermocalc software and conventional thermobarometers for schist, gneiss and migmatite samples are 8.6 Kb, 630°C; 6.7 Kb, 650°C and 6.3 Kb, 720°C respectively. Mineralogical parageneses and geothermal gradient resulted from thermobarometry calculations of the Gasht-e-Rodkhan metapelites are compatible with metamorphic Barrovian gradient or orogenic type. Gash complex probably represents metamorphic rocks of medium crustal depth of a collisional tectonic setting between Alborz block and Turan plate. Partial melting of metapelites and generation of associated leucogranites have taken place as a consequence of muscovite dehydration melting.
M Nasrabady; F Rossetti; H Moin Vaziri; S.M.H R; M M
Abstract
Some syntectonic tonalitic and trondhjemitic intrusion bodies have been injected into the Soltan Abad (NE Sabzevar) metamorphic complex. The geochemical investigations of these intrusion bodies demonstrated their very obvious adakitic characteristics (very high ratio of Sr/Y and very low contents of ...
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Some syntectonic tonalitic and trondhjemitic intrusion bodies have been injected into the Soltan Abad (NE Sabzevar) metamorphic complex. The geochemical investigations of these intrusion bodies demonstrated their very obvious adakitic characteristics (very high ratio of Sr/Y and very low contents of Y and Yb). According to the field and microscopic evidences and the geochemical characteristics of the whole intrusion bodies, the creation of such adakitic properties originates from the influence of both partial melting and magmatic differentiation processes. The probable scenario is the partial melting of subducted oceanic lithosphere in a hot subduction zone and the generation of adakitic intermediate melt, then amphibole fractionation and enhancing of adakitic indicators of final acidic melt. The resultant residual of partial melting is garnet-hornblenditic blocks that observed adjacent to some intrusion bodies. The primary adakitic intermediate melt accurs as amphibole-rich diorite in the study area. The differentiated cumulate phase and final fractionated melt constitute the hornblenditic dykes and hololococratic tonalitic-trondhjemitic bodies, respectively. The creation of hot thermal regime and partial melting of subducting oceanic lithosphere have been affected by the factors such as subduction velocity variations, mid oceanic ridge subduction or the slab break-off of the subducting oceanic plate and upwelling of the hot asthenosphere.
