ژئوشیمی و پتروژنز سنگ‌های ولکانیک پلیوکواترنری سبلان: کاربردی از ولکانیسم بعد از برخورد

نویسندگان

1 دانشگاه محقق اردبیلی

2 دانشگاه دامغان

چکیده

تراکی آندزیت­ها، تراکیت­ها و لاتیت­ها همراه با ایگنیمبریت­ها و سنگ­های پیروکلاستیک که دارای سرشت شوشونیتی می­باشند از اصلی­ترین سنگ­های ولکانیکی پلیوکواترنر منطقه سبلان می­باشند. پلاژیوکلاز، فلدسپار پتاسیم، بیوتیت همراه با کلینوپیروکسن و شیشه از مهمترین تشکیل دهندگان این سنگ­های ولکانیکی هستند. پلاژیوکلازها دارای ترکیب آندزین تا لابرادوریت بوده در حالی که کلینوپیروکسن­ها دارای ترکیب اوژیت می­باشند. سنگ­های ولکانیکی سبلان غنی شدگی در عناصر نادر خاکی سبک نسبت به عناصر نادر خاکی سنگین نشان داده و با غنی شدگی در عناصر با شعاع یونی بزرگ و تهی شدگی در عناصر با قدرت میدانی بالا مشخص می­گردند. مشاهدات پترولوژیکی همراه با ژئوشیمی عناصر نادر خاکی و کمیاب این گدازه­ها نشان دهنده سرشت شوشونیتی و مشتق شدن از یک زون فرورانش می­باشد. سنگ­های ولکانیکی سبلان از نظر ایزوتوپی، از یک گوشته غنی شده (همراه یا بدون آلودگی با مواد پوسته­ای) مشتق شده و در دیاگرام تغییرات ایزوتوپ نئودیمیم در مقابل ایزوتوپ­های استرانسیوم در محدوده بازالت­های قوس­های آتش فشانی پلات می­گردند. این خصوصیات ژئوشیمیایی و ایزوتوپی برای گدازه­های سبلان نشان دهنده اشتقاق ماگمای آنها از ذوب بخشی درجه پائین یک گوشته لیتوسفری قاره­ای که توسط ورقه فرورانش شده دچار متاسوماتیزم شده است،
می­باشد. تشکیل این گدازه­ها می­تواند در ارتباط با پرشیب شدن و شکست ورقه اقیانوسی فرورانش شده در یک محیط بعد از برخورد باشد.

کلیدواژه‌ها


عنوان مقاله [English]

Geochemistry and petrogenesis of the Sabalan Plio-Quaternary volcanic rocks: implication for post-collisional magmatism

چکیده [English]

Trachyandesites, trachytes and latites associated with ignimbrite and pyrocalstic rocks, characterized by shoshonitic affinity are the main Plio-Quaternary volcanic rocks in the Sabalan region (Ardabil). Plagioclase, K-feldspar, biotite associated with clinopyroxene and glass are the main constituents of these lavas. Plagioclases are andesine to labradorite while clinopyroxenes have augitic composition. The Sabalan volcanic rocks show enrichment in LREE relative to HREE and are characterized by enrichment in LILE and depletion in HFSE. Petrological observations along with geochemistry of rare earth and trace elements of these lavas suggest shoshonitic affinity and derivation from a subduction zone. The Sabalan volcanic rocks are isotopically characterized by derivation from an enriched mantle source (with/without crustal influence) with tendency to plot in a field defined by island-arc basalts (IAB) and OIBs (in εNd vs. 87Sr/86Sr diagram). The geochemical and isotopic signatures of the Sabalan lavas suggest that their magma has been issued via low degree partial melting of a subduction-metasomatized continental lithospheric mantle. The formation of these lavas is linked to slab steepening and break-off in a post-collisional regime.

کلیدواژه‌ها [English]

  • Geochemistry
  • Sr-Nd isotopes
  • petrogenesis
  • Plio-Quaternary lavas
  • Sabalan
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