QE152 : Petrogenesis of Neogene Igneous Rocks in the North Anbarabad (Mashkan)
Thesis > Central Library of Shahrood University > Geosciences > MSc > 2009
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Abstarct: Cenozoic calc-alkaline volcanic belt of south of Quchan is located in north of Sabzevar ophiolitic belt in south side of Binaloud zone.This belt has been composed of Eocene basic-intermediate rocks and Neogene basic and intermediate-acid rocks. In this arc, magmatic activities has been started since Eocene (about 40 Ma ago) and continued to Plio-pleistocene (about 2 Ma ago). The ages of volcanic rocks range from Eocene to Plio-pleistocene from south (in adjacent to the ophiolitic and mextamorphic belt) to north (in south of Quchan) respectively. Neogene northern part of this arc composed of pyroclastic units and several domes contain trachyandesites, trachytes, dacites and rhyodacites(2-12 Ma ago) Existence of Eocene volcanic enclaves and gneissic, siltstonic, marlly and pellitic enclaves, appearance and disappearance of some mineral phases, corrosions and chemical disequilibriums of some phenocrysts and sieve textures are some evidences of magmatic contamination.
A clear positive anomaly in LREE and LILE and a negative anomaly in HREE found in the rocks of Neogene domes. Negative anomalies in HFSE(e.g. P, Nb, Ti) which is the indicator of arc settings, also found in the rocks. Calc-alkaline nature, the role of fractional crystallization, assimilation and magmatic contamination in the genesis and evolution of magma, continental arc subduction setting, presence of an eclogitic or garnet-amphibolitic source rock resulted from mextamorphism of subducted oceanic crust in the area indicated by geochemical evidences. geochemical characteristics studies indicate rocks the area have adakitic nature and are from type high silicic adakite. This adakitic magma was the latest melts resulted from partial melting of Sabzevar Neotethyan subducted oceanic crust and its overlaying mantle wedge in a young arc subduction zone with northward dip that subducted beneath the south side of Binalood zone.
Keywords:
#Petrology #Geochemistry #Continental arc #Adakite #Quchan Link
Keeping place: Central Library of Shahrood University
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Keeping place: Central Library of Shahrood University
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