ژئوشیمی و پتروزنز سنگ‌های آتش فشانی کوه چهلتن؛ جنوب غرب بردسیر )استان کرمان)

احمدی مقدم, پریچهر; احمدی پور, حمید

ژئوشیمی و پتروزنز سنگ‌های آتش فشانی کوه چهلتن؛ جنوب غرب بردسیر )استان کرمان)

نویسندگان

دانشگاه شهید باهنر کرمان

چکیده

کوه چهلتن، در 16 کیلومتری جنوب غرب شهرستان بردسیر (استان کرمان) واقع شده و بخشی از مجموعه آتش فشانی هزار (کمربند ارومیه - دختر) با سن ائوسن است. سنگهای منطقهی مورد بررسی شامل تناوبی از گدازه، سنگهای پیروکلاستیک و اپی کلاستیک و تودههای نفوذی متعدد هستند. گدازهها بیشتر از جنس بازالتیک آندزیت و بازالت بوده و در آنها بلورهای درشت پلاژیوکلاز و کمی بلور پیروکسن در یک زمینهی ریزدانه تا شیشهای دیده میشود. بر اساس بررسیهای ژئوشیمیایی، گدازههای منطقه به سری ماگمای آهکی- قلیایی و پتاسیم آهکی- قلیایی بالا وابستهاند و در نمودارهای هارکر، روندی ترکیبی پیوسته را نشان میدهند که میتواند حاصل تبلور جدایشی کانیهایی نظیر الیوین باشد. در نمودارهای عنکبوتی گدازههای منطقه، بیهنجاریهای منفی Nb، Ti، Ta، HFSE و HREE و مثبت Ba، Rb، Th، LREE و Sr به خوبی دیده میشوند. این حالت، مشابه ویژگیهای ماگماهای وابسته به مناطق فرورانش بوده و پدیدهی آلایش پوستهای را در سنگها نشان میدهد. بر اساس بررسیهای سنگزایی، گدازههای منطقه به حاشیه فعال قارهای وابستهاند و همهی آنها خاستگاه مشترکی دارند. این بررسیهای نشان داد که ماگماهای مادر سنگهای منطقه، احتمالاً در اثر ذوب بخشی یک گوشتهی دگرنهاد، در محیط فرورانشی ایجاد شدهاند.

کلیدواژه‌ها

عنوان مقاله [English]

Geochemistry and petrogenesis of the Cheheltan Mountain volcanic rocks; south-west of Bardsir (Kerman Province)

چکیده [English]

The Cheheltan Mountain is located at south west of Bardsir, Kerman Province. It represents a part of the Eocene Hezar volcanic complex (Urumiyeh-Dokhtar volcanic belt) and consists of lava flows, pyroclastics, epiclastics and numerous intrusions. The lava flows comprise of basaltic-andesites and basalts and contain plagioclase and pyroxene phenocrysts that set in a vitreous or fine-grained matrix. Geochemical studies show that the lava flows belong to the calcalkaline and high-K calcalkaline magmatic series, and in the variation diagrams, they show continuous chemical trends, which can be formed due to fractional crystallization of minerals such as olivine. These rocks show negative anomalies of Nb, Ti, Ta, HFSE and HREE, and positive anomalies of Ba, Rb, Th, LREE and Sr in the spider diagrams, resembling the subduction related magmas. These evidences show that the parental magmas may have been affected by crustal contamination processes. According to the petrogenetic studies, these magmas belong to the active continental margin setting, and all of them have the same source. The present work shows that the parental magmas of the studied rocks, probably originated by partial melting of metasomatized mantle sources in a subduction zone environment.

کلیدواژه‌ها [English]

Urumiyeh-Dokhtar volcanic belt
calcalkaline series
active continental margin
crustal contamination

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