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بررسي فرايند اختلاط ماگمايي در توده نفوذي قوشچي با استفاده از مطالعات كاني‌شناسي

چکیده
منطقه قوشچي‏‎ٌ در شمال غرب ايران شامل طيف وسيع سنگ‌شناسي از گابروديوريت تا آلكالي‌گرانيت است كه در بخش‌هايي در هم نفوذ كرده و حجم­هاي مختلفي از آنكلاوهاي مافيك را شكل داده و يا در برخي موقعيت‌ها با هم ادغام شده و سنگ حدواسط را تشكيل داده است. آنكلاوهاي موجود با تركيب سنگ‌شناسي گابروديوريت دانه ريز بوده، به طوري كه با نزديك شدن به حاشيه آنكلاو ريز دانه‌تر شده و براثر تجمع كاني‌هاي مافيك در حاشيه تيره‌تر به نظر مي‌رسد. اين آنكلاوها به اشكال مختلفي مانند گرد، بيضوي تا اشکال نامنظم با سطوح صاف، مواج، کنگره­‌اي و زائده‌دار قابل رويت هستند. حضور درشت بلورهاي فلدسپار و كوارتز در آنكلاوهاي مافيك و يا هجوم ماگماي گرانيتي در توده‌هاي بزرگ گابروديوريتي به عنوان ديگر شواهد صحرايي قابل ذكر هستند. علاوه بر آن شواهدي چون بافت‌ پوئي‌كيليتيك در درشت بلورهاي فلدسپار، لخته‌هاي مافيك، آپاتيت‌هاي سوزني، پلاژيوكلاز دو نسلي حاكي از فرايند اختلاط ماگمايي است. تركيب پلاژيوكلازهاي مورد مطالعه از آلبيت تا لابرادوريت تغيير مي‌كند، به طوري كه آنكلاوهاي مافيك با سنگ‌هاي گابروديوريتي هم‌پوشاني دارد و سنگ‌هاي آلكالي گرانيت با درشت بلورهاي فلدسپار قابل مقايسه هستند. بررسي تغييرات سيستماتيك ميزان آنورتيت و عناصر Fe، Ti، Ba و Sr از حاشيه به مركز در بلورهاي پلاژيوكلاز بيانگر نوساناتي در الگوي منطقه­بندي پلاژيوکلاز و مويد نقش موثر اختلاط ماگمايي در شكل‌گيري توده نفوذي مورد مطالعه است
واژگان کلیدی
آنكلاو، اختلاط ماگمايي، اروميه، فلدسپار، قوشچي

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