Petrology, geochemistry and mineral chemistry of Parachan intrusive body (North of Karaj)

Keshtkar, E.; Ghorbani, M.; Omrani, J.

doi:10.22071/gsj.2018.63804

Document Type : Original Research Paper

Authors

¹ Ph.D. Student, Department of Geology, Faculty of Geosciences, Shahid Beheshti University, Tehran, Iran

² Associate Professor, Department of Geology, Faculty of Geosciences, Shahid Beheshti University, Tehran, Iran

³ Ph.D., Geological Survey of Iran, Tehran, Iran

https://doi.org/10.22071/gsj.2018.63804

Abstract

A gabbro to monzonite sill is injected into the Karaj tuffs at the north of Parachan village, North of Karaj.. The main minerals of these rocks are plagioclase, pyroxene, K feldspar, olivine and biotite. Clinopyroxene mineral chemistry studies carried out on the intrusive bodies, indicate two types of diopside and augite clinopyroxene composition. The chemical composition of the pyroxenes shows that these rocks have been crystallized in a subduction geological setting. The average crystallization temperature of clinopyroxenes is about 1120 to 1170 °C, and it seems that clinopyroxenes crystallized at lower temperature than orthopyroxenes. Plagioclase composition in these rocks is variable, changing from andesine to labradorite. K feldspars are in the orthoclase range and olivine are hyalosiderite. Biotite is one of the most prominent ferromagnesian minerals in the studied bodies. Compositionally, it is plotted between the fields of annite and siderophyllite. Most of these biotites are primary magmatic and some are plotted in the re-equilibrated filed. Petrological evidence represent that fractional crystallization from gabbro to monzonite had main role in genesis of these rocks. Enrichment in LILE) Ba, Rb and Th(and also depletion in HFSE (Nb and Ti) in Rare Earth Elements distribution pattern in spider diagrams, indicate features of subduction-related rocks. Also they are enriched in LREE rather than HREE, the characteristic which is usually observed in the rocks from subduction environments and active continental margins. Chemical and petrological studies, indicate role of fractional crystallization in the evolution of magma, although, minor amounts of assimilation and contamination of magma by crustal rocks occurred. This alkaline magma has been formed by low degree of partial melting of an enriched sub-continental lithospheric garnet-lherzolite mantle source.

Keywords

20.1001.1.10237429.1397.27.107.15.6

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Scientific Quarterly Journal of Geosciences

Petrology, geochemistry and mineral chemistry of Parachan intrusive body (North of Karaj)

References

References

Volume 27, Issue 107
Volume 26, Issue 107, spring 2018
June 2018
Pages 151-164

Petrology, geochemistry and mineral chemistry of Parachan intrusive body (North of Karaj)

References

References

Volume 27, Issue 107Volume 26, Issue 107, spring 2018June 2018Pages 151-164

Volume 27, Issue 107
Volume 26, Issue 107, spring 2018
June 2018
Pages 151-164