Journal of Economic Geology (Oct 2024)
Petrogenesis of Intrusive body in Northeast of Joveinan, North of Isfahan, Urumieh- Dokhtar magmatic zone
Abstract
Middle Miocene igneous rocks are located in the Northeast of Joveinan, the middle part of the Urumieh-Dokhtar Magmatic Belt. The igneous rocks have intruded into the Eocene volcano-sedimentary units. The rocks consist of diorite, quartzdiorite, and monzodiorite. They contain plagioclase, hornblende, biotite, pyroxene, orthoclase, quartz, and opaque minerals, and have granular to porphyroid textures. Field and petrographic evidence such as a lack of thermal metamorphism and graphic texture suggests that the rocks crystallized at a shallow depth. The rocks exhibit characteristics of I-type granitoids and a calc-alkaline nature with metaluminous affinities. The enrichment of large ion lithophile elements (LILEs) and the negative anomaly of Ta, Nb, and Ti elements in the primary mantle normalized diagram demonstrate subduction-related magmatism in the continental arc setting. The chondrite normalized pattern of the rocks (Lan/Ybn= 3.68-5.64) suggests a low degree of partial melting and the absence of garnet as a permanent phase in the source region. Based on the petrological data, the parental magma has been produced in the subduction setting of the collisional zone. The primary magma resulting from the partial melting of the subducted lithospheric mantle intruded into the continental crust. The magma underwent numerous changes and evolution during ascent and created the intrusive rocks of Northeast Joveinan. Introduction The study area is located 130 km north of Isfahan and 10 km northeast of Joveinan which is a part of the Urumieh-Dokhtar magmatic Belt. The Urumieh-Dokhtar magmatic belt resulted from the subduction of the Neotethys oceanic crust under the Central Iranian continental plate (Agard et al., 2005; Mohajjel and Fergusson, 2014). The Urumieh-Dokhtar zone experienced severe Tertiary magmatism during the Eocene (Alavi, 2004) that persisted until the Quaternary (Agard et al., 2011). The variations in the composition and origins of the melts at different periods have been demonstrated in previous research (Omrani et al., 2008; Chiu et al., 2013; Honarmand et al., 2014). However, no geochemical or petrological data have been reported from the Northeast Joveinan intrusive body. The only available information is derived from investigations carried out during the preparation of the Kashan geological map 1:100000 and Ghohroud geological map 1.25000. The research on the North Jovian intrusive body provides valuable insights into Cenozoic magmatism and the geology of the middle part of the magmatic belt of Zagros orogeny. This study aims to understand the nature, tectonic setting, origin, and various processes involved in the magmatic evolution of the Northeast Joveinan intrusive rocks. Material and Methods After field studies and the sampling of outcrops, 52 microscopic thin sections were prepared and studied using an Olympus polarizing microscope model BX-2. Subsequently, 6 samples with the least amount of alteration were chosen and sent to the ACME Canadian laboratory for ICP-OES inductively coupled plasma emission spectroscopy and ICP-MS inductively coupled plasma mass spectrometry analysis. The data from field, petrographic, and geochemical studies were used for the best conclusion. Result and Discussion The main rock units found in the research area include sedimentary rocks belonging to the formations of Niur (Early Silurian), Padeha (Late Devonian), Bahram (Late Devonian), Shotori (Middle Triassic), Shemshak (Jurassic), Cretaceous carbonate rocks, Eocene volcanic rocks, and Neogene intrusive bodies. The widespread intrusive bodies and Cenozoic volcanic rocks are exposed in the area. Eocene volcanic-sedimentary rocks, including andesitic lavas, hyaloclastite tuffs, and sandy tuffs are the Cenozoic units in the area. In the western part of the area, the Ghohroud batholith, consisting of granite, monzonite, and granodiorite, intruded into the Lower Miocene formations, leading to significant contact metamorphism. North Joveinan post Lower Miocene intrusive body intrudes Eocene volcanic and pyroclastic rocks. These rocks comprise diorite, monzodiorite, and quartzdiorite with granular to porphyroid, poikilitic, and micrographic textures. The marginal parts of intrusive rocks are more microcrystalline and have a porphyroid texture, while the middle parts have a granular, poikilitic, and graphic texture. The main minerals of the rocks include plagioclase, clinopyroxene, hornblende, biotite, opaque minerals, minor quartz, sphene, apatite, and zircon, and secondary minerals including calcite, clay minerals, sericite, and chlorite. The igneous rocks exhibit a composition range of amounts of SiO2 (53.18-59.46 wt.%), Al2O3 (15.27-16.14 wt.%), Na2O (2.79-5.76 wt.%), K2O (1.42-2.56 wt.%) and variable concentrations of Fe2O3* (7.61-11.13 wt.%), MgO (2.92-3.87 wt.%), CaO (5.15-7.80 wt.%) and LOI (1.4-2.7 wt.%). Geochemical data show these rocks are mainly calc-alkaline diorite, monzodiorite, and quartzdiorite with metaluminous affinities. The primary mantle normalized pattern shows the enrichment of large ion lithophile elements (LILE) and depletion of high field strength elements (HFSE), which is one of the geochemical characteristics of the magma related to the subduction zone (Kuscu and Geneli, 2010). The chondrite-normalized rare earth elements diagrams show a medium enrichment of LREE compared to HREE, a weak negative anomaly of Europium, and a flat pattern of heavy rare earth elements. The rare earth element (REE) patterns indicate low amounts or absence of garnet in the source (Rollinson, 1993), also the magma could be formed at a depth where the garnet is not stable. Based on the discrimination diagrams, the rocks are formed in a magmatic arc setting. Geochemical data, such as the negative anomaly of Ti, Ta, P, and Nb, and the positive anomaly of Rb, Th, and K, along with the enrichment of LILE and LREE, suggest that the North Joveinan intrusive body is comprised of normal calc-alkaline I-type granitoids, which are produced in an active continental margin. The samples in various diagrams fall within the range of melts formed from the metasomatized mantle (MM) and continental crust (CC). This suggests that the magma results from a mixture of melts from the mantle and crust or a combination of mafic magma with crustal components. The ratio of mantle to crust in the final magma is approximately 50%. Conclusion The North Joveinan intrusive rocks in the middle part of the Urumieh-Dokhtar magmatic Belt are formed due to the subduction of the Neo-Tethys oceanic crust. This causes the release of fluids and melts from the subducted slab into the lithospheric mantle, leading to the melting of the mantle and generating primary mafic magma. The heat needed for partial melting and contamination of crustal rocks is provided with the ascent and placement of basic magma in the lower continental crust. The contamination in the magma reservoir caused the primary magma to change, forming intermediate magma. Keywords
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