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Chemical characteristics of biotite from Boroujerd Granitoid complex (Middle Jurassic), Western Iran | ||
| Geopersia | ||
| مقاله 7، دوره 3، شماره 1، شهریور 2013، صفحه 69-78 اصل مقاله (352.88 K) | ||
| نوع مقاله: Research Paper | ||
| شناسه دیجیتال (DOI): 10.22059/jgeope.2013.31933 | ||
| نویسندگان | ||
| Dariush Esmaeily1؛ Reza Maghdour-Mashhour* 1؛ Amir Ali Tabbakh Shabani2 | ||
| 1Department of Geology, University College of Sciences, University of Tehran, Tehran, Iran | ||
| 2Faculty of Earth Sciences, Kharazmi University, Tehran, Iran | ||
| چکیده | ||
| Biotite samples from different units of Boroujerd Granitoid Complex (BGC) of the Sanandaj-Sirjan Zone, western Iran, have been analyzed by electron microprobe for major elements. Biotite analyses from three units of quartzdiorite, granodiorite and monzogranite of BGC have their own distinct non-overlapping compositional fields in the annite – siderophyllite – phlogopite – eastonite quadrilateral (ASPE), reflecting their host rock compositions. Biotite from each rock unit has an increasing trend of Al contents at almost fixed Fe/(Fe+Mg) values. In quartzdiorite it shows an approximately constant range of Fe/(Fe+Mg) with a low to moderate Al content from 2.5 to 3 atoms per formula unit (apfu). Biotite from granodiorite exhibits a fairly wide range of Al values reaching up to 3.32 apfu, at Fe/(Fe+Mg) from 0.6 to 0.7, whereas biotite from monzogranite have a relatively narrow range of Fe/(Fe+Mg) and total Al values of limited range of 3.1 to 3.3 apfu. Biotite compositions from these two latter units considered to be derived entirely from crustal material, characterized by a remarkable increase in total Al at relatively high Fe contents. Biotite samples of quartzdiorites define a distinct and non-overlapping trend from those of granidiorites and monzogranites and hence interpreted to be derived from a parental magma with different composition. Calculation of log(XMg/XFe) ranges from -0.09 to -0.02 and most of samples from quartzdiorite fall within weakly and moderately contaminated I-type field of log(XF/XOH) versus log(XMg/XFe) diagram, whereas the other two units, containing biotites with log(XMg/ XFe)< -0.21, classified as strongly contaminated reduced I-type. Oxygen fugacity (log ƒO2) of -15.4 to -17.5 bars and ƒH2O of 200 to 560 bars were calculated for quartzdiorite. Likewise, log (ƒO2) of –17.66 bars and water fugacity (ƒH2O) of 400 and 700 bars were also calculated for granodiorite and monzogranites respectively. In the FeO*–MgO–Al2O3 biotite discrimination diagram, biotite compositions from BGC are distributed between the calc-alkaline and peraluminous fields, i.e., biotite from the qaurtzdioritic rocks fall principally in the calc-alkaline field, whereas those from the granodioritic and monzogranitic units plot almost exclusively in the peraluminous field consistent with their host rock nature | ||
| کلیدواژه‌ها | ||
| biotite؛ chemical composition؛ Petrogenesis؛ Oxygen fugacity؛ Granitoid؛ Sanandaj-Sirjan zone؛ Iran | ||
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