Geochemistry and tectonomagatic setting of Tertiary volcanic rocks of the Kangan area, northeast of Sarbisheh, southern Khorasan

Abstract

Introduction The study area is located 12km away from the north east of Sarbisheh at the eastern border of the Lut block (Karimpour et al., 2011; Richards et al., 2012). The magmatic activity in the Lut blockhas begun in the middle Jurassic (165-162 Ma) and reached its peak in the Tertiary age (Jung et al., 1983; Karimpour et al., 2011). Volcanic and subvolcanic rocks in the Tertiary age cover over half of the Lut block with up to 2000 m thickness and they were formed due to subduction prior to the collision of the Arabian and Asian plates (Jung et al., 1983; Karimpour et al., 2011). In the Kangan area, the basaltic lavas cropped out beyond the above intermediate to acid volcanic rocks. In this area, bentonite and perlite deposits have an economic importance. The main purpose of this paper is to present a better understanding of the tectono-magmatic settings of volcanic rocks in the northeast of Sarbisheh, east of Iran based on their geochemical characteristics. Materials and methods Fifteen samples were analyzed for major elements by inductively coupled plasma (ICP) technologies and trace elements by using inductively coupled plasma mass spectrometry (ICP-MS), following a lithium metaborate/tetraborate fusion and nitric acid total digestion, at the Acme laboratories, Vancouver, Canada. Results The Kangan area is located at the northeast of Sarbishe, Southern Khorasan and the eastern border of the Lut block. In this area, basaltic lavas have cropped out above intermediate to acid lavas such as andesite, dacite, rhyolite (sometimes perlitic) .The main minerals in the basalt are plagioclase, olivine and pyroxene, in andesite contain plagioclase, pyroxene, biotite and amphibole and in acid rocks include plagioclase, quartz, sanidine, biotite and amphibole. Intermediate to acid rocks have medium to high-K calc-alkaline nature and basalt is alkaline. Enrichment in LREE relative to HREE (Ce/Yb= 21.14-28.7), high ratio of Zr/Y(4.79- 10.81), enrichment in LILE and negative anomaly of Eu, Nb, P, Ti, Ba and Sr in intermediate to acid lavas are characteristics of subduction related calc-alkaline magmatism. Geochemical characteristics such as high ratio of La/Yb (8.18), low content of Rb with tectonic setting discriminant diagrams show within plate environment for basalt. The constituent magma of the studied rocks originated from an enriched garnet lherzolite source in 100 to 110km depth. Discussion Enrichment in LREE relative to HREE (Ce/Yb= 21.14-28.7), high ratio of Zr/Y (4.79- 10.81), enrichment in LILE and negative anomaly of Eu, Nb, P, Ti, Ba and Sr in intermediate to acid lavas are characteristics of subduction related calc-alkaline magmatism. Tectonic setting discrimination diagrams show that andesite to dacitic rocks are located in active continental margin (Schandle and Gorton, 2002) and basalt is placed within the volcanic plate zone and continental rift type (Verma et al., 2006). Intermediate to acid rocks of Kangan area originated from lithospheric mantle (Moharami et al., 2014) that is enriched by sediment melt related metasomatism (Ersoy et al., 2010) whereas Kangan basaltic lava origin is Nb enriched (Wang et al., 2008; Sajona et al., 1996) mixed lithospheric - asthenospheric mantle (Moharamiet al., 2014). According to the trace elements diagrams (Ellam, 1992), partial melting depth for generation of Kangan area lavas was determined to be about 100 to 110Km. Because of absent crustal contamination instances in the basalt, it can be argued that ascending of magma has been rapid and probably similar to other alkali basalts in east of Iran, it may be related to deep fault systems. 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Keywords

• Andesite
• Alkali basalt
• Active continental margin
• Kangan
• Lut block