Filed and Textural Evidences of Magma Mingling Recorded in the Tekyeh-Bala Area Granitoid Rocks, Southeast of the Kordestan Province, West Iran

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1 Australian Journal of Basic and Applied Sciences, 5(12): , 2011 ISSN Filed and Textural Evidences of Magma Mingling Recorded in the Tekyeh-Bala Area Granitoid Rocks, Southeast of the Kordestan Province, West Iran 1 Farhad Aliani, 2 Mohammad Maanijou and 3 Mirmohammad Miri 1,2,3 Department of Geology, Bu-Ali-Sina University, Hamedan, Iran. Abstract: The Tekyeh-Bala area is located in west Iran and belongs to the Sanandaj-Sirjan zone. During Mesozoic and Cenozoic, igneous activity due to subduction of Neo-Tethys beneath Iran microplate led to generation of several igneous rocks throughout the Sanandaj-Sirjan zone (e. g., intrusive complex in the southeast of the Kordstan province). In the study area there are several quartzmonzonite (QM) and quartz-monzodiorite (QMD) regular dykes which host mafic microgranular enclaves (MME). These enclaves are rounded, ellipsoidal and, in some cases, elongated in shape and their size of them is vary between 10 cm to 100 cm. They also have chilled margines. Moreover, QM and QMD have anti-rapakivi texture, sieved plagioclase and acicular apatite crystals. These textures together with MMEs with various shapes and chilled margins are interpreted as evidences of magma mingling. Key words: magma mingling, anti-rapakivi, sieved plagioclase, mafic microgranular enclaves, Tekyeh-Bala area, Sanandaj-Sirjan, Iran. INTRODUCTION The study area is located in the southeast of Kordestan province in west Iran with coordinates of ' to ' E and ' to ' N. There are several igneous bodies (plutonic and volcanic) in the study area which have different geochemical (Miri, 2011), mineralogical and textural properties. These differences does show that these rocks not only were generated by a single magmatic process but also were generated by different process and under different conditions; i.e., fractional crystallization, partial melting from different source and magma mixing and mingling (Miri, 2011). In this paper we want to study the field and textural evidences of magma mixing and mingling in the Tekyeh-Bala area. It should be noted that magma mixing and mingling evidences in the southeast of Kordestan province (Qorveh area) have been studied by several researchers (e.g., Torkian, 2011) but the field and textural evidences of magma mingling in the Tekyeh-Bala area have not been studied specially. Field and textural evidences of magma mixing and mingling recorded in the granitiod rocks are widely reported and documented over the world. Mafic microgranular enclaves (MME) which commonly occur in alkali-granite, monzogranite and granodiorite (Didier, 1984) are reported as field evidence for magma mixing and mingling by several authors (e.g., Willey, 1984; Barbarin and Didier, 1992). Moreover, anti-rapakivi, sieved plagioclase and poiclitic textures are interpreted as textural evidences of magma mixing and mingling (e.g., Sabah, 2008; Debon, 1991). These evidences are visible in the QM and QMD rocks in the study area. Geological Setting and Field Observations: Tekyeh-Bala area belongs to the Sanandaj-Sirjan zone based on the new classification of Iran structural zone (Mohajjel et al., 2003) which endured Cimmerian and late-cretaceous orogenic events that led to emplacement of several plutons in it. According to the geological map of Sonqor (Eshraghi et al., 1996) there is a complex of intrusive rocks in the study area which is Eocene-Oligocene in age (Fig. 1). This complex generally composed of granite, quartz-monzonite (QM), quartz-monzodiorite (QMD), monzonite, diorite and small amount of gabbro (Miri, 2011). The age differences between the rocks in the complex is not reported, however, regarding to the presence of MMEs in QM and QMD unites and also penetration of granite veins in the diorite and gabbro unites, it can be proved that felsic units are younger than mafic unites. The MMEs in the study area have various shapes including rounded, elongated and ellipsoidal (Fig. 2) and their size vary between 10 cm to 100 cm (Fig. 2). The contact of the MMEs with QM and QMD is generally sharp but in some cases is partly gradational. MATERIALS AND METHODS As the field and textural evidences of magma mixing and mingling are recorded in QM, QMD and MMEs, a total about 45 samples from these rocks which were closer to the objectives of the study are collected. Thirty thin sections from these representative samples were prepared and were studied by polarized light microscope. Corresponding Author: Department of Geology, Faculty of Science, Bu-Ali Sina University, Mahdieh Ave. Hamedan-Iran. Tel: ; Fax: ; Miri.mirmohammad@gmail.com 1513

2 Fig. 1: Regional geological map of the study area (modified from Eshraghi et al., 1996). Petrography: Quartz-Monzonite (QM) and Quartz-Monzodiorite (QMD): These rocks occurred as little dykes with E-W trend. They are light to dark grey in color, mezocratic and middle to fine grained. These rocks consist of plagioclase and orthoclase (60-75%), quartz (5-15%), augite (10-15%) and biotite (>5%). Sphene, zircon, apatite and magnetite are accessory minerals. Secondary minerals are actinolite, epidote, chlorite and sericite. Hydrothermal alteration effected plagioclases and augites and converted them to epidote and actinolite respectively. QM and QMD have anheral to subhedral granular, anti-rapakivi (Fig. 3a, b) and sieve-textured plagioclase (Fig. 3c, d). Sabah (2008) and Arsalan and Aslan (2006) suggested that anti-rapakivi texture is an evidence of magma mingling or coeval felsic and mafic magmas. Debon (1991) and Hibbard (1991) noted that anti-rapakivi texture can be an evidence of magma hybridization and mingling. Also sieved plagioclase texture is reported as mixing and mingling evidence by many researchers (e. g., Dungan and Rhodes, 1978; Tsuchiyama, 1985). Acicular apatite crystals (Fig. 3e, f) are other evidences for mixing and mingling in these rocks (Janousek et al., 2000). Mafic Microgranular Enclaves (MME): The MMEs have black to dark gray color and are melanocratic and fine grained. They are consisting of plagioclase (40-45%), hornblende (25-30%), biotite (10-15%), orthoclase (>10%), quartz (>5%). Magnetite and apatite are accessory minerals. Chlorite is only secondary mineral which resulted from hornblende alteration. The mineral assemblages of MMEs show that their chemical composition is similar to diorite. General textures of MMEs are microgranular and porphyritic (Fig. 4) whit plagioclase and hornblende phenocrysts (0.5-2mm in size). Also some hornblende crystals have biotite inclusion [poiclitic texture (Fig. 4d) which is reported as magma mixing and mingling evidence (Janousek et al., 2000). Other important feature of MMEs is their sharp and chilled contact with host rocks (Fig. 4c, d). Discussion: Petrogenetic Considerations: The origins of MMEs have been considered by many authors (e.g., Vernon, 1983, Willey, 1984) and most of them have suggested that MMEs are resulted from mixing/mingling between felsic and mafic magmas, also Barbarin and Didier (1992) believed that MMEs are field evidences of interaction between the felsic and mafic magmas. 1514

3 Fig. 2: Various shapes and size of the MMEs in the QM and QMD in the study area. On the other hands, Chappell and White (1992) interpreted MMEs as remnants of igneous protolith partial melting. In the case of the study area, however, regarding to the presence of anti-rapakivi and sieved plagioclase textures and acicular apatite crystals it is more plausible that know MMEs as consequence mixing and mingling. As mentioned above, the MMEs in the study area are rounded, elongated and ellipsoidal (Fig. 2) which is evidence of felsic-mafic interaction and mingling (Kumar et al., 2004). Also Vernon et al. (1988) have emphasized that rounded to ellipsoidal shapes of enclaves are a strong indication of magma mingling and flow. Also as noted, the contacts of MMEs with QM and QMD are generally sharp and chilled (Fig. 2; Fig. 4 b, c). Wiebe (1991) believed that chilled margin of mafic enclaves is a mingling evidence. According to the various shapes of the MMEs, their sharp and chilled contacts and presence of anti-rapakivi texture it seems that sieved plagioclase and poiclitic textures and acicular apatite crystals also were resulted from magma mingling and mixing is not occurred vastly. However, it should be considered that difference between temperature and density of mafic and felsic magmas do not permit to complete mixing between two magmas. It is noteworthy Torkian (2011) has suggested that magma mingling was the main factor in generation of some granitoids in south of the Qorveh area. Conclusion: The quartz-monzonite and quartz-monzodiorite rocks in the Tekyeh-Bala area have mafic micrograular enclaves that are accompanied by anti-rapakivi and sieved plagioclase textures and acicular apatites, also, MMEs have various shapes and chilled margins together with poiclitic texture (biotite inclusion in hornblende) which all of these features are interpreted as field and textural evidences of magma mingling and mixing. Referring to the various shapes and chilled margins of the enclaves and presence of anti-rapakivi texture in QM and QMD, it is more plausible that magma mingling played the main role in the generation of quartz-monzonite and quartz-monzodiorite. However there are not sufficient evidences demonstrating magma mixing in the study area. 1515

4 Fig. 3: a) and b) anti-rapakivi texture in the QM and QMD; c) and d) sieved plagioclase texture in the QM and QMD; e) and f) acicular apatite inclusions in the orthoclases crystals of the QM and QMD. Abbreviations: Pl= plagioclase; Or= orthoclase; Epi= epidote; Ap= apatite; Aug= augite (Whitney and Evans, 2010). Fig. 4: a) microgranular and porphyritic textures (with plagioclase and hornblende phenocrysts); b) and c) chilled and sharp contacts of MMEs with their host rocks; d) biotite inclusions in a hornblende phenocryst (poiclitic texture). Abbreviations: Pl= plagioclase; Hbl= hornblende; Bi= biotite (Whitney and Evans, 2010). 1516

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