Oligocene crustal xenolith‐bearing alkaline basalt from Jandaq area (Central Iran): implications for magma genesis and crustal nature

Abstract

The Oligocene alkaline basalts of Toveireh area (southwest of Jandaq, Central Iran) exhibit northwest-southeast to west-east exposure in northwest of the central-east Iranian microcontinent (CEIM). These basalts are composed of olivine (Fo 70-90 ), clinopyroxene (diopside, augite), plagioclase (labradorite), spinel, and titanomagnetite as primary minerals and serpentine and zeolite as secondary ones. They are enriched in alkalis, TiO 2 and light rare earth elements (La/Yb = 9.64-12.68) and are characterized by enrichment in large ion lithophile elements (Cs, Rb, Ba) and high field strength elements (Nb, Ta). The geochemical features of the rocks suggest that the Toveireh alkaline basalts are derived from a moderate degree partial melting (10-20%) of a previously enriched garnet lherzolite of asthenospheric mantle. Subduction of the CEIM confining oceanic crust from the Triassic to Eocene is the reason of mantle enrichment. The studied basalts contain mafic-ultramafic and aluminous granulitic xenoliths. The rock-forming minerals of the mafic-ultramafic xenoliths are Cr-free/poor spinel, olivine, Al-rich pyroxene, and feldspar. The aluminous granulitic xenoliths consist of an assemblage of hercynitic spinel + plagioclase (andesine-labradorite) ± corundum ± sillimanite. They show interstitial texture, which is consistent with granulite facies. They are enriched in high field strength elements (Ti, Nb and Ta), light rare earth elements (La/Yb = 37-193) and exhibit a positive Eu anomaly. These granulitic xenoliths may be Al-saturated but Siundersaturated feldspar bearing restitic materials of the lower crust. The Oligocene Toveireh basaltic magma passed and entrained these xenoliths from the lower crust to the surface.

Transport of Volatile-rich Melt from the Mantle Transition Zone via Compaction Pockets: Implications for Mantle Metasomatism and the Origin of Alkaline Lavas in the Turkish–Iranian Plateau

“…A few younger alkali basaltic outcrops occur along the Great Kavir and Naiband faults (e.g. Saadat et al, 2010;Rajabi et al, 2014;Kheirkhah et al, 2015).…”

“…The mineral assemblages of cumulate xenoliths derived from depths equivalent to < ~2 GPa pressure below the TIP may in fact be consistent with such seismic velocities (see Fig. 13b for their location), and therefore, we used the modal mineral proportions evaluated by Rajabi et al (2014) and Su et al (2014) for cumulate and pyroxenite mantle xenoliths, respectively, and incorporated them in Hacker & Abers (2004) Excel worksheet. The estimated Vs reaches 3.9 km/s for cumulates originating from the base of a thick crust (~1.5 GPa equivalent pressure) at 600°C, and 4.3 km/s for mantle xenoliths at ~2.2 GPa and 1000°C.…”

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

“…The surrounding rocks of the Toveireh pluton mainly include Eocene and Oligocene volcanic rocks and Eocene to Oligocene sandstone and conglomerate ( Figure 2b). The Toveireh pluton cuts the Eocene basaltic and andesitic volcanic rocks (48-53 Ma, K-Ar by Aistov et al, 1984) and is overlain by Early Oligocene alkaline basalts (33 Ma, K-Ar by Aistov et al, 1984;Rajabi et al, 2014) ( Figure 3a). The alkaline basalts form a linear northwestsoutheast trend and overlie the Upper Eocene-Oligocene sandstone and conglomerate (Rajabi et al, 2014;Sargazi and Torabi, 2019).…”

“…The Toveireh pluton cuts the Eocene basaltic and andesitic volcanic rocks (48-53 Ma, K-Ar by Aistov et al, 1984) and is overlain by Early Oligocene alkaline basalts (33 Ma, K-Ar by Aistov et al, 1984;Rajabi et al, 2014) ( Figure 3a). The alkaline basalts form a linear northwestsoutheast trend and overlie the Upper Eocene-Oligocene sandstone and conglomerate (Rajabi et al, 2014;Sargazi and Torabi, 2019). In the eastern part of the study area, several parallel lamprophyre dikes with a dominant northsouth direction intrude into the Pis-Kuh formation and Eocene volcanic rocks (Torabi, 2010).…”

Whole rock and mineral chemistry of hornblenditic xenoliths in volcanic alkaline rocks from the northern part of Uromieh Dokhatar magmatic belt (NW Iran)

“…Hornblende-rich xenoliths have been reported from several locations worldwide; e.g., northeast of Iran [Yousefzadeh and Sabzehei, 2012], central Mexico [Blatter and Carmichael, 1998], Iberian Peninsula [Capedri et al, 1989], western and central Europe [Downes et al, 2001, Carraro and Visonà, 2003, and central Spain [Orejana et al, 2006]. The majority of the hornblendite xenoliths are related to the host volcanic rocks [Witt-Eickschen and Kramm, 1998] while some others are witnesses of a metasomatized mantle or cumulates from older magmatic events [e.g., Frey and Prinz, 1978, Irving, 1980, Capedri et al, 1989, Saadat and Stern, 2012, Rajabi et al, 2014, Su et al, 2014, Kheirkhah et al, 2015.…”