شواهد عدم وابستگی توالی‌های بالشی و دایکی افیولیت نورآباد-میانراهان (استان کرمانشاه) به محیط فرافرورانشی

نویسنده

استادیار مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی استان کرمانشاه، سازمان تحقیقات، آموزش و ترویج کشاورزی، کرمانشاه، ایران

چکیده

گدازه‌های بالشی و توالی دایکی هرسین- نورآباد و میانراهان بخشی از مجموعه افیولیتی کرمانشاه به شمار می‌آیند. دایک‌های دیابازیک با بافت‌های افیتیک، دولریتی و گلومروپورفیریک، متشکل از پلاژیوکلاز دارای زونینگ و کلینوپیروکسن‌اند و گدازه‌های بالشی بافت‌های اینترگرانولار تا میکروپورفیریک با خمیره هیالومیکرولیتیک داشته و از پلاژیوکلاز، دیوپسید-اوژیت و پسودومورف‌های الیوین تشکیل گردیده‌اند. الگوی نمودارهای عنکبوتی، محیط تشکیل فرافرورانشی این توالی‌ها را رد و نشان از موقعیت تکتونوماگمایی جزایر درون صفحه اقیانوسی (OIB) در واحد پیلولاوایی گشور و دایک‌های دیابازیک و نیز شواهد ژئوشیمیایی P-MORB در واحد پیلولاوایی تمرک و میانراهان دارد. شواهد ژئوشیمیایی مورب در منطقه گشور و دایک‌های دیابازیک می‌تواند نشان­دهنده­ی وقوع ذوب بخشی در یک منشاء غنی شده از نوع OIB باشد که منجر به تولید بازالت‌های آلکالن شده است، اما در مقابل در واحد پیلولاوایی محدودهای تمرک و میانراهان، ذوب بخشی گوشته از نوع MORB که بصورت نامتجانس دارای اجزائی از OIB بوده شرایط تولید P-MORB های این را مناطق فراهم آورده است. لذا شاید بتوان جنوب نئوتتیس را بصورت یک حاشیه ریفتی حدواسط با ریفتینگ غیرمتقارن تلقی نمود که در آن شرایط رخنمون گوشته فوقانی زیر قاره‌ای مهیا گردیده و منجر به پیدایش حالتی حد واسط بین افیولیت‌های حاشیه قاره و پلوم در مجموعه مورد بررسی شده است.

کلیدواژه‌ها


عنوان مقاله [English]

Evidences of undependence of pillow basalt and dyke swarm of Nurabad-Miyanrahan Ophiolite (Kermanshah) to suprasubduction zone

نویسنده [English]

  • A. Moradpour
Assist. Prof., of Agricultural and Natural Resources Research and Education Center of Kermanshah, AREEO, Kermanshah, Iran
چکیده [English]

The pillow lavas and dyke swarm of Harsin-Nurabad and Miyanrahan are part of Kermanshah Ophiolite complex. Diabasic dykes with ophitic, doleritic and glomeroporphyritic textures consist of zoned plagioclase and clinopyroxen and pillow lavas have intergranular and microporphyritic textures with hyalomicrolitic matrix and consist of plagioclase, augite-diopside and pseudomorphic olivines.The resalts of N-MORB-normalized multielement and chondrite-normalized REE patterns indicate that these rocks not formed in supra-subduction zone but overall geochemistry of Gashor pillow baslte and diabasic dykes resembles that of alkaline basalts generated at within-plate ocean island settings (OIB), meanwhile Tamark and Miyanrahan pillow baslte show P-MORB geochemical signature. MORB evidence in studied rocks is interpreted to be the partial melting of an OIB-type enriched source led to the production of the Gashor and diabasic dykes alkaline basalts whereas the partial melting of MORB-type mantle heterogeneously modified by OIB-type components resulted in the production of Tamark and Miyanrahan P-MORBs. Therefore, it may be considered that, southern Neo-Tethys was characterized by an intermediate rifted margin type where asymmetrical rifting, exhumed sub-continental upper mantle provided combination of continental margin- and plume-type in the investigated ophiolites.

کلیدواژه‌ها [English]

  • Pillow basalt
  • Dyke swarm
  • Harsin-Miyanrahan
  • Kermanshah
  • Neo-Tethys
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