زمین شناسی، پتروگرافی، دگرسانی، کانی سازی و پتروژنز توده های نفوذی در محدوده اکتشافی هَمِچ، جنوب‌ غرب بیرجند

زمین شناسی اقتصادی

مقاله 5، دوره 10، شماره 1 - شماره پیاپی 18، 1397، صفحه 113-137   

نوع مقاله: علمی- پژوهشی

شناسه دیجیتال (DOI): 10.22067/econg.v10i1.62625

نویسندگان

عباس اعتمادی؛ محمد حسن کریم پور^* ؛ آزاده ملکزاده شفارودی

فردوسی مشهد

چکیده

محدوده اکتشافی هَمِچ در شرق بلوک لوت و در فاصله 85 کیلومتری جنوب‌غرب بیرجند واقع شده است. منطقه شامل برون‌زدهایی از سنگ‌های آذرین پالئوسن- ائوسن است که در برگیرنده طیف گسترده ای از توده های آذرین نیمه عمیق (دیوریت تا مونزونیت پورفیری) به‌همراه واحدهای نفوذی بازی، آتشفشانی حدواسط و سنگ‌های آذرآواری و رسوبی است. انواع دگرسانی آرژیلیک، سیلیسی، کوارتز- سرسیت- پیریت، پروپلیتیک و کربناته در محدوده اکتشافی قابل مشاهده است. کانی سازی در سطح به شکل پیریت پراکنده و رگه‌چه های اکسید‌ آهن و در عمق به‌صورت کانی سازی پراکنده پیریت، کالکوپیریت، گالن و اسفالریت و پیریت رگه‌چه ای دیده می شود. توده های نفوذی حدواسط از نوع کالک‌آلکالن پتاسیم بالا (K2O بین 42/2 تا 4 درصد) و توده های گابرو و گابرودیوریتی مربوط به دسته تولئیتی (K2O بین 15/0 تا 27/0 درصد) است. توده های نفوذی منطقه همه از نوع متاآلومینوس است و در دسته مگنتیت (نوع I) طبقه بندی می‌شوند. نمودارهای عنکبوتی بیانگر غنی شدگی توده های نفوذی حدواسط از عناصر LREE، LILE و تهی شدگی از عناصر HREE به‌همراه مقدار جزئی ناهنجاری منفی Eu (81/0 تا 02/1) و حضور ناهنجاری مثبت Sr است که نشان‌دهنده حضور کم و یا نبود پلاژیوکلاز در سنگ منشأ به‌عنوان کانی باقی‌مانده و وجود شرایط ذوب در حالت اکسیدان است. پایینبودن نسبت N(La/Yb) در سنگ‌های نفوذی محدوده همچ (85/6 تا 72/9) می تواند بیانگر درجه پایین ذوب‌بخشی گوشته اولیه باشد. تهی شدگی Nb به‌همراه نسبت بالای Zr/Nb نشان‌دهنده اشتقاق ماگما از پوسته اقیانوسی با میزان آلودگی پوسته ای کم است. ماگمای مولد توده های نفوذی حدواسط از حدود 1 تا 5 درصد ذوب‌بخشی اسپینل- گارنت لرزولیت (با مقدار کم گارنت) در عمق حدود 65 تا 67 کیلومتری گوشته بالایی و توده های بازی از 5 تا 20 درصد ذوب‌بخشی اسپینل لرزولیت (گوشته تهی‌شده) تشکیل شده‌‌اند. در نمودارهای پتروژنیک و تعیین محیط تکتونوماگمایی، توده‌های نفوذی در جایگاه زمین‌ساختی کمربند آتشفشانی زون فرورانش (VAG1) قرار می گیرند. تنوع واحدهای نیمه عمیق با ماهیت کالک‌آلکالن پتاسیم بالا، گسترش و نوع دگرسانی ها و کانی سازی سولفیدی پراکنده و رگه‌چه ای در محدوده، نشانه هایی از وجود سیستم پورفیری در عمق است.

کلیدواژه‌ها

زمین شناسی؛ دگرسانی؛ کانی سازی؛ پتروژنز؛ مس پورفیری؛ هَمِچ، بیرجند؛ بلوک لوت

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