Abstract
The Kuh-e-Shah complex includes the Paleogene volcano-plutonic belt of the Lut Block, eastern Iran. The volcanic rocks which outcropped in this complex mainly consist of trachy-andesites, andesites, and basaltic-andesites that mineralogically contain plagioclase, pyroxene, hornblende, and minor biotite and olivine. Geochemically, they have features typical of high-K calc-alkaline to shoshsonitic magmas with enrichment in large ion lithophile elements (LILE), and depletion in high field strength elements (HFSE) and heavy rare earth elements (HREE). Chondrite-normalized REE plots show enrichment in light REE (4.9 < LaN/YbN < 11.6), Nb depletion and the slight negative Eu anomalies (Eu/Eu* = 0.80–0.99). Tectonic discrimination diagrams are used to infer a volcanic arc setting related to a continental subduction zone. It is concluded that the studied volcanic rocks have resulted from FC of a parental magma which formed by partial melting of the subducted oceanic crust and the overlying mantle wedge with spinel-lherzolite composition. Zircon UPb dating indicates an age of 38.6 to 38.9 Ma for volcanic rocks (Middle Eocene, Bartonian). Initial 87Sr/86Sr and 143Nd/144Nd ratios (0.704350–0.704820 and 0.512619–0.512779, resp.), are compatible with parental melts formation in a subduction mantle wedge. The ɛNdi values (+0.60 to +3.73) are in the range of mantle-derived melts. We suggest that volcanic rocks of the Lut Block are part of the Paleogene volcanism resulted from the Sistan oceanic crust subduction under the Lut Block during the Cretaceous.
Highlights
Iran is situated in the middle part of the Alpine–Himalayan orogenic belt that represents the Tethys Sea during the Paleozoic–Mesozoic transition (Ghorbani, 2013)
We present new geochemical, isotopic (Rb-Sr and Sm-Nd), and geochronological (U-Pb) data from the Kuh-e-Shah volcanic rocks with a comparison to other scattered volcanic rocks throughout the Lut Block (Pang et al, 2013; Saadat & Stern, 2016; Javidi Moghaddam et al, 2019) to better understanding the Paleogene magmatism evolution of the Lut Block and to place constraints to the timing and onset of volcanism, its tectonic implications, the geochemical features of the mantle source involved in volcanic rocks genesis, petrogenetic processes and the controls of magma generation processes, the probable effects of fractional crystallization and crustal contamination, and geodynamic evolution of volcanic rocks which exposed in the western part of the Kuh-e-Shah volcano-plutonic complex
In addition to the Urumieh–Dokhtar, and Alborz geological zones, eastern Iran encludes extensive Eocene–Oligocene magmatic rocks that covered over half of the Lut block and are manifestations of a Paleogene magmatic flare-up in Iran
Summary
Iran is situated in the middle part of the Alpine–Himalayan orogenic belt that represents the Tethys Sea during the Paleozoic–Mesozoic transition (Ghorbani, 2013). According to the structural and geological divisions, Iran is divided into several structural units (Fig. 1a) and the eastern part of Central Iran is divided into two parts. A western part, known as the Lut Block (Stöcklin et al, 1965), and a strongly folded eastern part which has been named East Iranian Ranges (Berberian, 1977), Sistan Suture Zone (e.g., Tirrul et al, 1983; Walker et al, 2009) or Flysch zone (e.g., Ghorbani, 2013). The Lut Block is surrounded by highly deformed domains of oceanic affinity and ophiolitic series along with flysch-type rocks especially at the eastern border with the Afghan Block (Fig. 1b; Stöcklin et al, 1972). It is believed that these rocks are remnants of a narrow arm of the subducted Neo-Tethys Ocean (Bagheri & Stampfli, 2008) in the east of Iran, i.e. the Sistan Ocean. The volcanoplutonic rocks covered over half of the Lut block with up to 2000 m thickness, the Tertiary period was of special importance, especially at the eastern part of the Lut Block
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