@article { author = {Bakhtiari, Hossein and Moghimi, Ebrahim and Servati, Mohammad Reza}, title = {An Assessment about the Effect of Mineralogical Composition of Alvand Pluton Rock Units on Outcrops Resistance against Weathering and Erosion}, journal = {Physical Geography Research}, volume = {46}, number = {1}, pages = {1-18}, year = {2014}, publisher = {University of Tehran}, issn = {2008-630X}, eissn = {2423-7760}, doi = {10.22059/jphgr.2014.50616}, abstract = {IntroductionIn general, strength of rocky outcrops is associated with two factors, feature lithology thatincludes mineralogical composition, texture and rock Structure and environmental factors that isthe area stones are located in (Hafezy moghadas, 2011, 229 after Ulusay, 1994). Themineralogical composition determines sensitivity of rocks against physical, chemical andbiochemical attacks (Mahmoodi, 2010). Rocks because of containing different minerals showvarious stability against the degradation factors (Nikoodel, 2011). This is the first time researchto use classification system of in geology for naming rocks to determine the degree of resistanceof the stones against weathering and erosion.MethodologyThe Alvand Pluton is one of the largest intrusive masses in Sanandaj- Sirjan metamorphic zone(Sepahi, 2008).The exposed area of this mass are approximately 362.92 square kilometers(excluding Quaternary deposits). Alvand Plutonism was started from middle Cretaceous andcontinued till early Tertiary (Paleocene) (Sepahi & Moeen vaziry, 2000).Alvand pulotonic rocks have been marked on the geological map (Tuyserkan and􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯∗E-mail: moghimi_ir@yahoo.com Tel: +98 91243927902 Physical Geography Research Quarterly, 46 (1), Spring 2014Hamadan1:100,000 scale) in 100 limited areas with 8 different symbols. That usually has lightgrey to white color and fine to coarse grains (2-5mm in diameter). About 9 square kilometers ofcordierite andalousites and cordierite hornfelses (metamorphic rocks) in the 23 areas withdifferent extent are over the surface of porphyroid granite which mostly matches top heights(especially Heights Gavboreh). This shows diapirism in placement of the mass.In this research, library and field observation have been used as the methods of datacollection, (sampling and observation) and the research method has been descriptive andanalytical. For evaluating the effect of mineralogical composition of the Alvand pluton rock onoutcrop resistance some steps have been taken. In next step, the classification was proposed bythe International Union of Geological Sciences (IUGS), and diagram (QAPF)1 associated withit, was selectedwith range diagram, according to the mineralogical composition. Numericalvalues are determined for the degree of outcrop resistance of each area against weathering anderosion. In order to determine the degree of Alvand pulotonic outcrops resistance we havespecified surface of QAPF diagram. The resistance specified as numerical value is ranged from1 to 10 classes started from foidolites with least degree of resistance and with ratio of decreasingF and P and increasing A and Q. It is the most sensitive igneous rocks against chemicalweathering considering mineralogical composition. Thus, quartz-rich granitic-rocks are in 9areas and finally quartzolit (silexite) which is the most resistant intrusive igneous rock againstweathering.To test the proposed method, 10 types of Alvand pulotonic rocks which gathered by Zarianet al., 1972 with Modal analysis method was studied and selected by using diagram QAPF forresistance range. In addition, finding equivalent name in classification system of IUGS, thedegree of the resistance against weathering and destruction in terms of mineralogicalcomposition is given in.Results and DiscussionNaming Alvand plutonic rock units on geological maps is based on IUGS classification. Thus,based on provided method, relative strength of the rock outcrop in terms of the effects ofmineralogical composition on the resistance against weathering and erosion have been identifiedand presented in Table 1. Specific degree of resistance for Alvand plutonic rock units arepresented on Table 4. Rock units of this mass can be classified in four groups, the least ofresistance is related to Olivine gabbro outcrops with 2 degree which cover 14.8% of the massarea.The most resistant rock outcrops are the unit pegmatitic granite, pegmatic- aplite granite,tourmalin granite and granite bearing garnet with a resistance degree of 8. Among other unitsthis later covers just 3.15% of surface area. Degree resistance was determined for different rockunits in Alvand pluton and it shows 6 degree resistance differences between them.Thisdifference can be affected by weathering and differential erosion between different units.Average weighted degree rock units outcrop resistance of Alvand in terms of mineralogical􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯􀀯1. Q = Quartz, A= Alkali Feldspar, F= Feld spathoids, P= Plagioclase.Physical Geography Research Quarterly, 46 (1), Spring 2014 3composition is obtained for total mass about 6.59. It shows resistence of the mineralogicalcomposition of the outcrops and the results can be found in relation to high percentage of quartzand alkali feldaspar, and the approximate homogeneity in mineralogical composition of the rockmass. In order to determine the applicability of the results obtained from the proposed method ingeomorphological and hydrological analyses, the Digital Elevation Model (DEM) of Alvandpluton was provided.ConclusionIn this paper, the effect of mineralogical composition of Alvand plutonic outcrops against theweathering and erosion with the numeric range 1-10 and using QAPF diagrams have beendetermined. In this method, Surface of QAPF diagram between Q and F has been divided intoten areas with in numerical range of 1-10. The range of values represents the effect of themineralogical composition on degree of resistance of outcrops of rock units. According todegree resistance designated for Alvand pluton rock units in terms of the effects, this mass canbe classified in four groups.In this classification the least resistance is related to Olivine gabbrooutcrops with degree resistance of 2 and the most resistant rock outcrops with resistance degreeof 8 are the units including pegmatitic granite pegmatitic– aplite granite, tourmaline granite, andgranite bearing granite. According to average weighted degree granitic outcrop resistance ofAlvand in terms of mineralogical composition, the degree is obtained 6.59for total mass..Determining resistence of Alvand rock units in quantitative mineralogical composition and theproperties of texture and structure characteristics can be used for geomorphological analysis andexplanation of predominant form over Alvand mass.}, keywords = {Alvand Ploton,Mineralogical Composition,Outcrops,QAPF Diagram,Resistance Degree}, title_fa = {ارزیابی اثر ترکیب کانی‎شناسی واحدهای سنگی تودۀ نفوذی الوند بر مقاومت رخنمون‎ها در برابر هوازدگی و فرسایش}, abstract_fa = {تودۀ نفوذی الوند، یکی از بزرگترین توده‎های نفوذی در کمربند دگرگونی سنندج ـ سیرجان است. این مقاله به ارزیابی اثر ترکیب کانی‎شناسی واحدهای سنگی بر مقاومت آنها در برابر هوازدگی و فرسایش پرداخته است. این کار با ارائۀ یک روش پیشنهادی، یعنی استفاده از نمودار QAPF انجام گرفته است. در این روش با توجه به قرارگیری کانی‎های کوارتز و فلدسپاتوئیدها در دو قطب مخالف نمودار و نقش تعیین‎کنندۀ آنها در مقاومت رخنمون‎ها، ابتدا سطح نمودار QAPF به ده محدوده تقسیم و ارزش‎گذاری شد که ارزش هر محدوده به‎صورت نسبی، معرف تأثیر ترکیب کانی‎شناسی بر مقاومت سنگ‎های داخل آن در برابر هوازدگی و فرسایش است. سپس درجه مقاومت رخنمون واحدهای سنگی توده نفوذی الوند تعیین و ضمن طبقه‎بندی در چهار گروه، نقشۀ پهنه‎بندی مربوطه تهیه شده است. با تعیین درجه مقاومت کانی‎شناسی رخنمون واحد‎های سنگی، می‎توان نقش ترکیب کانی‎شناسی را به‎صورت یک متغیر کمّی در تحلیل‎های ژئومورفولوژیکی برای تبیین فرم و فرآیند‎های حاکم بر ناهمواری‎ها مورد توجه قرار داد.}, keywords_fa = {تودۀ نفوذی الوند,رخنمون,ترکیب کانی‎شناسی,درجۀ مقاومت,نمودار QAPF}, url = {https://jphgr.ut.ac.ir/article_50616.html}, eprint = {https://jphgr.ut.ac.ir/article_50616_e2e0857cc2511edcbd273ba52b40b71e.pdf} }