1. Geochemistry and tectonic setting of extrusive rocks in the southeast of Maimeh, northwest of Isfahan
- Author
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Shahzad Sherafat and Zahra Heidari Fetrat
- Subjects
basic to intermediate volcanic rocks ,active continental margin ,maimeh ,urumieh- dokhtar magmatic arc ,Geology ,QE1-996.5 - Abstract
Introduction The studied area is situated 15 km away from the southwest of Maimeh at the western part of Urumieh-Dokhtar magmatic arc. This zone is a part of the Zagros orogenic belt formed due to the subduction of the Neo-Tethyan oceanic crust under the Central Iran block. The magmatic activity in the Urumieh-Dokhtar magmatic arc has begun in Eocene (Alavi, 2004) and continued until Quaternary (Ghasemi and Talbot, 2006). In the middle part of the studied area, several outcrops of the post-Early Cretaceous volcanic rocks with basaltic to andesitic composition have been seen (Vahdati Daneshmand, 2006). Until now, no petrological and geochemical data about these rocks are present. Therefore, in this study, petrographic and the geochemical features of these rocks are discussed in detail. This study aims to reveal a better understanding of the petrology and petrogenesis of volcanic rocks in the southeast of Maimeh and the middle part of the Urumieh-Dokhtar magmatic arc as a part of the Zagros orogenic belt. Materials and methods To reach the goal of the research, after collecting basic information using geological maps and works done in the study area, all volcanic outcrops systematically sampled, and more than 50 fresh samples were chosen and studied. Afterward, seven samples were chosen for geochemical analyses by using inductively coupled plasma mass spectrometry (ICP-MS) at the ACME Laboratories, Vancouver, Canada. The results of chemical analyses are listed in table 1. Discussion Based on the field observations, the volcanic rocks have basaltic to andesitic composition with plagioclase, clinopyroxene, olivine, amphibole, biotite, and opaque microphenocrysts. Clinopyroxene (probably augite) is the main minerals as phenocrysts and small mineral in the groundmass. Olivine phenocryst has undergone limited alteration to iddingsite and amphiboles show burned margin. Opacitization in amphibole occurs due to a decrease in water pressure with magma rising or as a result of the increase in temperature (Plechov et al., 2008). These rocks have microlithic porphyry, glomeroporphyry and vesicular textures. According to geochemical analysis, intermediate rocks have calc-alkaline nature and basalt is alkaline. They display enrichment in LILEs (Rb, Ba, K, Sr, U, and Th) relative to HFSEs (especially Nb, Ti, and P) and coherent REE patterns characterized by enrichment in LREEs relative to HREEs without negative Eu anomaly. These features are characteristics of subduction-related magmatism (Woodhead et al., 1993). U and Th enrichment may be due to crustal contamination (Kuscu and Geneli, 2010) or the addition of pelagic sediments and/or altered oceanic crust to the source of magma (Fan et al., 2003). The tectonic discrimination diagrams show an active continental arc setting for these rocks. Geochemical evidence shows that the volcanic rocks were originated from low degree partial melting (1) partial melting of a garnet- lherzolitic mantle source that enriched by slab-derived fluids. The magma has undergone AFC processes during ascending and alkaline affinity changed to calc-alkaline nature. The volcanic rocks occurred as a result of the subduction of the Neo-Tethyan oceanic crust beneath the Central Iran microplate. References Alavi, M., 2004. Regional stratigraphy of the Zagros fold-thrust belt of Iran and its proforeland evolution. American Journal of Science, 304(1): 1–20. http://doi.org/10.2475/ajs.304.1.1 Fan, W.M., Guo, F., Wang, Y.J. and Lin, G. 2003. Late Mesozoic calc-alkaline volcanism of post-orogenic extension in the northern Da Hinggan Mountains, northeastern China. Journal of Volcanology and Geothermal Research, 121(1–2): 115–135. http://doi.org/10.1016/S0377-0273(02)00415-8 Ghasemi, A. and Tabatabaei Manesh, S.M. 2015. Geochemistry and petrogenesis of Ghohroud igneous complex (Urumieh–Dokhtar zone): Evidence for Neotethyan subduction during the Neogene. Arabian Journal of Geosciences, 8(11): 9599–9623. http://doi.org/10.1007/s12517-015-1883-7 Kuscu, G.G. and Geneli, F., 2010. Review of post collisional volcanism in the Central Anatolian volcanic province (Turkey), with special reference to the Tepekoy volcanic complex. International Journal of Earth Sciences, 99(3): 593–621. https://doi.org/10.1007/s00531-008-0402-4 Plechov, P.Y., Tsai, A.E., Shcherbakov, V.D. and Dirksen, O.V., 2008. Opacitization conditions of hornblende in Bezymyannyi volcano andesites (March 30, 1956 eruption). Petrology, 16(1): 19–35. http://doi.org/ 10.1134/S0869591108010025 Vahdati Daneshmand, F., 2006. Geological map of Maimeh, Scale 1:100000, Sheet No. 6256. Geological Survey of Iran. Tehran, Iran. Woodhead, J., Eggins, S. and Gamble, J., 1993. High field strength and transition element systematics in island arc and back-arc basin basalts: Evidence for multi-phase melt extraction and a depleted mantle wedge. Earth and Planetary Science Letters, 114(4): 491–504. https://doi.org/10.1016/0012-821X(93)90078-N
- Published
- 2021
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