Source: http://www.gsjournal.ir/article_68698_8823.html
Timestamp: 2019-04-19 02:35:06+00:00

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سنگ‎های آتشفشانی نشوه در شمال باختر ساوه واقع شده، بخشی از کمربند ماگمایی ارومیه- دختر محسوب می‎شوند. این سنگ‎ها عمدتاً از نوع بازالت، آندزی‎بازالت، آندزیت تا تراکی‎آندزیت هستند. در بررسی‎های میکروسکوپی این سنگ‏ها شواهدی از عدم تعادل بلور با ماگما نیز دیده می‎شود که از آن جمله می‎توان به بافت غربالی، وجود دو نسل سالم و دگرسان شده پلاژیوکلاز، حاشیه واکنشی، خوردگی و گردشدگی فنوکریست‏ها اشاره کرد. بررسی‎های ژئوشیمیایی مربوط به نمودارهای عناصر اصلی و کمیاب نشان می‎دهد که اگر چه تبلور تفریقی در تکامل سنگ‏های آتشفشانی منطقه مؤثر بوده است؛ اما در برخی از نمودارها نوعی پراکندگی و روندهای غیر عادی نسبت به روند تفریق به چشم می‎خورد، که این حالت می‎تواند بیان کننده اختلاط و آلودگی ماگمایی باشد. ناهماهنگی و تغییرات زیاد در غلظت برخی عناصر نظیر Sr و همچنین نمودارهای دوتایی Nb-Nb/Y و Zr/Rb-Rb نقش اختلاط ماگمایی را در شکل‏گیری سنگ‏های آتشفشانی منطقه نشوه نشان می‎دهد. با توجه به موارد ذکر شده می‎توان گفت که مهم‎ترین فرایند تشکیل سنگ‎های آتشفشانی منطقه نشوه تفریق و اختلاط ماگمایی است. همچنین اختلاط پالس یا پالس‌های ماگمایی جدید با ماگمای تفریق یافته مؤثرترین مکانیزم برای تحول ماگمایی سنگ‎های آتشفشانی منطقه مورد مطالعه است.
Neshveh volcanic rocks located in the NW Saveh are parts of the Uromeyeh-Dokhtar magmatic arc. The rocks are mainly basalt, basaltic andesite, andesite and trachyandesite in composition. Petrographical studies represent some evidences for the lack of equilibrium between crystals and magma, such as sieve texture, two generation of fresh and altered plagioclase, reaction rim, corrosion and rounding of phenocrysts. Major and trace element diagrams show, although crystal differentiation was effective in the evolution of the study rocks, the scatter and unusual trends, which are observed in some diagrams in comparing with fractionation trend, reflect magma mixing and contamination were also important during magma generation. Inconsonance and high variations in Sr concentrations together with binary diagrams of Nb/Y-Nb and Rb-Zr/Rb reveal magma mixing role in the evolution of Neshveh volcanic rocks. Considering the above facts, we can conclude that magma mixing and magmatic differentiation were the important processes in formation of the Neshveh volcanic rocks. As well as, the incorporation of new magmatic pulse(s) with differentiation magma is the most effective mechanism for the evolution of volcanic rocks from the study area.
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