Early Oligocene alkaline lamprophyric dykes from the Jandaq area (Isfahan Province, Central Iran): Evidence of Central–East Iranian microcontinent confining oceanic crust subduction

Abstract

The Jandaq lamprophyres occur as eight mostly parallel dykes, which cross-cut Eocene volcanic and sedimentary rocks of the Pis-Kuh Formation in dominant north to south direction. These lamprophyres are mainly composed of kaersutite, clinopyroxene, olivine, feldspar, ilmenite, and spinel as primary minerals. The rocks studied here are enriched in alkalis, TiO 2 , large ion lithophile elements, and light rare-earth elements (LREE), with SiO 2 content between 41.7 and 46.2 wt%, and are classified as camptonite and alkaline lamprophyre according to the mineralogical and chemical characteristics. These rocks exhibit positive Eu anomalies (Eu/Eu* = 1.08-1.39) and are characterized by strong enrichment in LREE relative to heavy REEs, and also by varied Zr/Hf ratios. The geochemical features of the rocks suggest that the lamprophyre magmas were derived from low-degree melting of an amphibole garnet lherzolite that experienced strong metasomatism by carbonate-rich fluids in response to dehydration melting from the subducted slab. The Jandaq lamprophyric magmatism has been attributed to the former subduction of the Central-East Iranian microcontinent confining oceanic crust from the Triassic to Eocene, and decompression melting induced by the extensional basin of the Jandaq area in the early Oligocene.

Late Permian post‐ophiolitic trondhjemites from Central Iran: a mark of subduction role in growth of Paleozoic continental crust

“…In the Late Permian or Triassic, a major rifting event is manifested along the present day Zagros Thrust Zone (Fig. ) (Hassanzadeh ; Bagheri & Stampfli ) which broke away the Arabia–Zagros continental mass from the rest of Iranian plate (Torabi , ; Shirdashtzadeh et al . ).…”

“…The left‐lateral Great Kavir (Doruneh) fault, which is one of the long and prominent faults of Iran, is very close to the study area (Figs ). It plays an important role in the regional tectonics of Central Iran (Torabi , ). Drastic direction change of this fault in the Anarak area marks the western border of the CEIM.…”

Petrological characteristics of the Middle Eocene Toveireh pluton (southwest of Jandaq, central Iran): implications for the eastern branch of the Neo-Tethys subduction

“…The Middle Eocene Pis-Kuh flysch formation, exposed to the northeast side of the Toveireh pluton, is composed of sandstone, conglomerate, and marl. This syn-tectonic formation is thought to display evidence of the subduction of the Neo-Tethyan oceanic crust beneath the central Iranian crustal block (Torabi, 2010). The surrounding rocks of the Toveireh pluton mainly include Eocene and Oligocene volcanic rocks and Eocene to Oligocene sandstone and conglomerate ( Figure 2b).…”

“…The CEIM is bordered by the Great Kavir Fault (GKF) (dextral fault) to the north and northwest, the Bashagard Fault (thrust and reverse fault) to the south, the Dehshir-Baft Fault (strike-slip fault) to the west and southwest, and the Nehbandan Fault (strike-slip fault) to the east (Figure 1). The CEIM is composed of 3 nearly north-south oriented major crustal zones, including the Lut block, the Tabas (Kerman) block, and the Yazd (Naein) block, which were separated from each other by a complex system of north-south trending dextral faults (Torabi, 2010) ( Figure 1). The left-lateral GKF is a prominent feature in Iran, which separates the CEIM from its several adjacent tectonic zones (Figure 1) and has played a significant role in the deformation events and tectonic history of central Iran since the Neogene (Walke and Jackson, 2004).…”

“…The Iranian region is a tectonically active plateau and most parts of its evolution were dominated by the opening and closure of the Paleo-Tethys and Neo-Tethys oceans (Bagheri and Stampfli, 2008). The Mesozoic subduction of the Neo-Tethyan oceanic crust beneath the Central-East Iranian Microcontinent (CEIM) caused extensive magmatism during the Cretaceous to Oligocene (Torabi, 2010). The Toveireh pluton, which is situated in the northwestern margin of the CEIM (southwest of Jandaq, Isfahan Province), formed during the peak activity of this Eocene magmatism.…”