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International Journal of Earth Sciences

, Volume 102, Issue 6, pp 1603–1625 | Cite as

The magmatic record in the Arghash region (northeast Iran) and tectonic implications

  • Zahra Alaminia
  • Mohammad Hassan Karimpour
  • Seyed Massoud Homam
  • Fritz Finger
Original Paper

Abstract

The area of Arghash in northeast Iran, prominent for its gold mineralization, was newly mapped on a scale of 1:20,000 with particular attention to the occurring generations of igneous rocks. In addition, geochronological and geochemical investigations were carried out. The oldest geological unit is a late Precambrian, hornblende-bearing diorite pluton with low-K composition and primitive isotope signatures. This diorite (U–Pb zircon age 554 ± 6 Ma) is most likely a remnant from a Peri-Gondwana island-arc or back-arc basin. About one-third of the map area is interpreted as an Upper Cretaceous magmatic arc consisting of a volcanic and a plutonic part. The plutonic part is represented by a suite of hornblende-bearing medium-K, I-type granitoids (minor diorite, mainly quartz–monzodiorite and granodiorite) dated at 92.8 ± 1.3 Ma (U–Pb zircon age). The volcanic part comprises medium-K andesite, dacite and tuffitic rocks and must be at least slightly older, because it is locally affected by contact metamorphism through the hornblende–granitoids. The Upper Cretaceous arc magmatism in the Arghash Massif is probably related to the northward subduction of the Sabzevar oceanic basin, which holds a back-arc position behind the main Neotethys subduction front. Small occurrences of pillow basalts and sediments (sandstone, conglomerate, limestone) tectonically intercalated in the older volcanic series may be relics of earlier Cretaceous or even pre-Cretaceous rocks. In the early Cenozoic, the Cretaceous magmatic arc was intruded by bodies of felsic, weakly peraluminous granite (U–Pb zircon age 55.4 ± 2.3 Ma). Another strong pulse of magmatism followed slightly later in the Eocene, producing large masses of andesitic to dacitic volcanic rocks. The geochemistry of this prominent Eocene volcanism is very distinct, with a high-K signature and trace element contents similar to shoshonitic series (high P, Zr, Cr, Sr and Ba). High Sr/Y ratios feature affinities to adakite magmas. The Eocene magmatism in the Arghash Massif is interpreted as related to thermal anomalies in crust and mantle that developed when the Sabzevar subduction system collapsed. The youngest magmatic activities in the Arghash Massif are lamprophyres and small intrusions of quartz–monzodiorite porphyries, which cut through all other rocks including an Oligocene–Miocene conglomerate cover series.

Keywords

Arghash Massif NE Iran Magmatism Granitoids U–Pb dating Geochemistry 

Notes

Acknowledgments

This paper is part of the PhD thesis of the first author. Zahra Alaminia would like to thank the Ministry of Sciences Research and Technology of Iran for financing a sabbatical period at Salzburg University and the staff of the Mineralogical Division at Salzburg University for kind support during her stay. George Gehrels and Victor Valencia from the Department of Geosciences, University of Arizona, Tucson, Arizona, carried out the U–Th–Pb zircon age dating. We are thankful for two careful reviews by J. Von Raumer and S. Bagheri.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  • Zahra Alaminia
    • 1
  • Mohammad Hassan Karimpour
    • 1
    • 2
  • Seyed Massoud Homam
    • 1
  • Fritz Finger
    • 3
  1. 1.Department of GeologyFerdowsi University of MashhadMashhadIran
  2. 2.Research Center for Ore Deposits of Eastern IranFerdowsi University of MashhadMashhadIran
  3. 3.Fachbereich Materialforschung und PhysikUniversität SalzburgSalzburgAustria

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