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摘要
The Mamakan gabbroic intrusions in the northwest of Iran were intruded into Paleozoic platform rocks at 303-298 Ma in the northern part of the Sanandaj-Sirjan shear zone (SSSZ) of central Iran. These intrusions are divided into the layered and massive gabbros. Layered gabbros are interspersed with lenticular bodies of anorthosite and homblendites that have either gradational or sharp boundaries with the gabbros. There is no obvious deformation in the Mamakan gabbroic intrusions. Hence, the changes in mineral compositions are interpreted as the result of crystallization processes, such as fractionation in the magma chamber. The Mamakan intrusions are a bimodal Hercynian appinitic suite. Hornblende-bearing pegmatitic gabbros, hornblende-bearing gabbros (massive and layered types), ultramafic rocks such as wehrlite, homblendites, and hornblende peridotites are coeval with peraluminous granitoid rocks in the study area. The abundance of hornblende relative to plagioclase, olivine and pyroxene in rocks of mafic composition, the widespread development of mafic pegmatites (homblendites) and hornblende-bearing massive and layered gabbros are taken to indicate that the Mamakan appinitic mafic magmas are unusually enriched in H2O. Geochemical data show that the intrusions were formed from an Al-, Sr-, Mg-, Fe-enriched and K-, Nb-, Ta-, and P- depleted tholeiitic basaltic magma. The rocks show marked negative High Field Strength Elements (HFSE: P, Zr, Hf, Nb, and Ta) and positive Ba and K anomalies that are typical of subduction-related magmas. The magma resulted from the partial melting of a metasomatized spinel peridotite wedge as a result of the beginning of Paleotethys subduction beneath the Mamakan island arc. This island arc was developed over supra-subduction oceanic crust between Gondwanaland and the Paleozoic platform of central Iran (south part of Eurasia).
- 出版日期2013-9
