نشریه علوم زمین خوارزمی

نشریه علوم زمین خوارزمی

گابرودیوریت های ماجراد در جنوب شرق شاهرود: شاهدی بر آغاز بازشدگی حوضه سوپراسابداکشن نئوتتیس شاخه سبزوار در ژوراسیک میانی

نویسندگان
مرضیه ویس کرمی 1
محمود صادقیان 1
پیام شاهولی کوه شوری 1
حبیب الله قاسمی 1
مینگو ژای 2
1 دانشگاه صنعتی شاهرود، دانشکدۀ علوم زمین، گروه پترولوژی و زمین‌شناسی اقتصادی
2 مؤسسه زمین شناسی و ژئوفیزیک آکادمی علوم چین (پکن) و دانشگاه نورث وست (شیان)
10.29252/gnf.5.2.293
چکیده
مجموعه پی­سنگی دگرگونی- آذرین ماجراد به سن نئوپروتروزوئیک پایانی با روند شمال­خاوری- جنوب­باختری، در 150 کیلومتری جنوب­خاوری شاهرود و در حاشیۀ شمالی پهنه ساختاری ایران مرکزی قرار دارد. همانند دیگر مجموعه­های پی­سنگی جنوب­خاوری شاهرود، در شمال تنگه ماجراد، این مجموعه نیز به‌وسیلۀ چند تودۀ نفوذی گابرودیوریتی کوچک­مقیاس و تعدادی دایک­ دیابازی قطع شده است. در این توده­های گابرودیوریتی، شواهد صحرایی تفریق­یافتگی از گابرو تا تونالیت مشاهده شده است. این گابرودیوریت­ها بافت­های دانه­ای، افیتی، ساب­افیتی و پوئی­کیلیتی را نشان می­دهند و از کلینوپیروکسن اوژیتی، هورنبلند سبز، پلاژیوکلاز و بیوتیت (به‌عنوان کانیهای اصلی) تشکیل شده­اند. ماگمای سازنده این سنگ­ها دارای ماهیت کالک­آلکالن است، از عناصر سنگ­دوست بزرگ ­یون (LILEs) و عناصر خاکی ­نادر سبک (LREEs) غنی­شدگی و از عناصر با قدرت ­میدانی زیاد (HFSEs) و عناصر خاکی ­نادر سنگین (HREEs) تهی­شدگی نشان می‌دهند. برای اولین­بار سن­سنجی انجام شده به‌روش U-Pb روی زیرکن­های استخراج­شده از گابرودیوریت­های مورد نظر، میانگین سنی پیرامون 166 میلیون­سال (معادل با ژوراسیک ­میانی) برای تشکیل آن‌ها ارئه کرده است. این ماگماها، از ذوب‌بخشی یک منبع گوشته­ای زیرقاره­ای متاسوماتیسم ­شده با ماهیت اولیه اسپینل­لرزولیتی در یک محیط­ کششی درون قاره­ای پشت کمانی واقع روی زون فرورانش حوضه نئوتتیس زاگرس در لبۀ ­شمالی پهنۀ ­ساختاری ایران­ مرکزی در زمان ژوراسیک میانی ایجاد شده­اند.


کلیدواژه‌ها
گابرودیوریت
ژوراسیک­میانی
نئوتتیس­
ماجراد
شاهرود

عنوان مقاله English

Majerad Gabbrodiorites in the Southeast of Shahrood: Evidence to Starting of Opening of the Supra-Subduction Basin of the Sabzevar Neotethyian Branch in the Middle Jurassic

نویسندگان English

Marzieh Veiskarami 1
Mahmoud Sadeghian 1
Payam Payam Shahvali kohshori 1
, Habibollah Ghasemi 1
Minggou Zhai 2
1 Shahrood University of Technology
2 - State Key Laboratory of Lithospheric Evolution, Northwest University Xian
چکیده English

Late Neoproterozoic Majerad igneous - metamorphic complex basement with NE-SW trend is located in the 150 km southeast of Shahrood and north edge of the Central Iran structural zone. Similar to the other complex basement of southeast Shahrood, in the north of Majerad- passage, this complex crosscut by several small scale gabbrodioritic intrusions and numerous diabasic dikes. Field evidences of fractionation from gabbro to tonalite are observed in these gabbrodiorite intrusions. These gabrrodiorites show granular, ophitic, subophitic and poikilitic textures and composed of augitic clinopyroxene, green hornblende, plagioclase and biotite (as an essential minerals). Magma forming of these rocks has calc-alkaline nature and is enriched in large ion lithophile elements (LILEs) and also light rare earth elements (LREEs) and depleted in high field strength elements (HFSEs) and heavy rare earth elements (HREEs). For the first time U-Pb age dating on zircons seperated from the gabbrodiorites, represented an average age around 166 million years (equivalent to middle Jurassic) for their formation. These magmas originated from the partial melting of the metasomatized subcontinental lithosoheric mantle source with spinel- lherzolithic primary nature in an extensional intracontinental back arc basin tectonic setting located on the subduction zone of the Zagros Neothetyan basin on the northern edge of Central Iran structural zone during the middle Jurassic.


کلیدواژه‌ها English

Gabbrodiorites
Middle Jurassic
Neothetys
Majerad
Shahrood
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