Middle Eocene magmatism in the Khur region (Lut Block, Eastern Iran): implications for petrogenesis and tectonic setting

Abstract

Late Mesozoic-Cenozoic magmatic rocks constitute the main lithological units of the Lut Block and occur in an area of 60000 km 2. Our field observation from the eastern Lut (Khur region) indicate intrusive rocks occur as dike (granitoid and mafic dikes) and shallow plutons (monzonites) in the Lut Block. Volcanic rocks (basaltic andesites, andesites, trachyandesites, dacites, rhyodacites) are also abundant and are intruded into pyroclastic rocks. U-Pb zircon ages indicate that granitic-dioritic dikes and monzonite were emplaced at 44.97 to 40.86 Ma and 41.11 Ma, respectively. Granitoid dikes are high-K calc-alkaline and metaluminous and geochemically belong to I-type granitoids. Monzonites show I-type (and rarely A-type) signatures, with typical enrichments in alkalis, Zr and Ce, high FeO t /(FeO t +MgO) ratio and depletion in Sr and Nb. Geochemical data, including major and trace elements and Sr-Nd isotopes indicate that the volcanic and intrusive rocks are products of a mantle source, presumably modified by sediment melts/fluids. The genesis of these rocks is suggested to be associated with extension above the subducting Sistan Ocean slab beneath the Lut Block. Subduction-related extension was also responsible for the high magmatic rate during Late Cretaceous-Oligocene and was associated large-scale Cu-Au mineralization in the Lut Block.

Crustal Lg Attenuation Beneath the Iranian Plateau: Implications for Cenozoic Magmatism Related to Slab Subduction, Slab Break‐Off, and Mantle Flow

“…Parallel to the Sistan suture, Cretaceous ophiolites crop out on the eastern edge of Iran and represent remnants of ancient Sistan oceanic crust. Between the Lut and Afghan Blocks, the Sistan Ocean opened in the Early Cretaceous and possibly subducted westward beneath the Lut Block during the Late Cretaceous (Moghaddam et al., 2021). The Lut volcanism is therefore suggested to have been triggered by the westward subduction of the Sistan oceanic lithosphere beneath the Lut Block, which led to the dehydration of the subducted slab (e.g., Samiee et al., 2016), the production of fluid and melt from subducted sediments (Beydokhti et al., 2015) and partial melting in the suprasubduction mantle wedge (Arjmandzadeh et al., 2011).…”

“…However, the magmatic accumulation pattern in the crust and mantle is not well documented. In eastern Iran, the N‒S‐trending Lut Block might have overridden the subducted Early Cretaceous Sistan Ocean and then collided with the Afghan Block after the ocean closed (S. A. Babazadeh & Wever, 2004; Moghaddam et al., 2021). The formation mechanism behind Lut volcanism is also controversial.…”

The composite Triassic–Eocene Poshteh pluton, eastern Iran, an Eo-Cimmerian element south of the main Paleotethys suture

“…Emplacement of the younger granite G2 at 41.23 ± 0.31 Ma coincides with a period of intense magmatism across the entire region, and especially in the Sistan suture zone (Camp and Griffis 1982;Shafaroudi et al 2013;Golmohammadi et al 2015;Mohammadi et al 2016;Javidi Moghaddam et al 2020;Shahbazi et al 2021;Rezaei-Kahkhaei et al 2021). There are geochemical similarities between the G2 granite of the Poshteh Pluton and similar coeval intrusions such as at Sangan (Fig.…”

Segmented Up‐Bending of the Arabian Continental Plate Revealed by Pn Attenuation Tomography

“…In the Lut Block, diffuse magmatism is almost continuous from the Early Cretaceous to the Quaternary (Jentzer et al., 2020). The formation of Lut volcanism may be related to WE‐dipping Sistan Oceanic subduction (e.g., Moghaddam et al., 2021; Saccani et al., 2010) and lithospheric delamination during the Lut‐Afghan collision (Pang et al., 2013). A low‐ Q Lg belt spans the northern Lut Block, the Sabzevar zone and the Kopet‐Dogh Mountains.…”