سن سنجی، ژئوشیمی رادیو ایزوتوپ‌ها و منشا مونزوگرانیت پالئوتتیس سنگ بست مشهد، ایران

نویسندگان

1 دانشگاه فردوسی مشهد

2 دانشگاه کلرادو

چکیده

منطقه مطالعه در شمال شرق ایران و در جنوب مشهد واقع شده است. اقیانوس پالئوتتیس در اردویسین شروع به باز شدن نمود و فرورانش صفحه اقیانوسی به زیر صفحه توران از اواخر دونین آغاز گردید. راندگی صفحه توران روی صفحه ایران در آواخر کارنین (Ma225) شروع شد و در این مقطع زمانی هیچگونه صفحه اقیانوس پالئوتتیس باقی نمانده بود. دو مرحله دگرگونی ناحیه شناسایی شدند: اولین با گوهزایی هرسینین (اواخر پالئوزوئیک) و دومین با گوهزایی سیمیرین (ژوراسیک) مرتبط است. مونزوگرانیت در بقایای پوسته اقیانوس پالئوتتیس نفوذ نموده است (متاافیولیت و متافلیش). مونزوگرانیت به لحاظ شیمیایی گرانیت نوع S و فوق آلومینیوم متوسط است. عدد پذیرفتاری مغناطیسی مونزوگرانیت پایین است [(5 to 11) × 10-5 SI] و لذا مربوط به سری ایلمینیت هستند. مونزوگرانیت دارای غنی شدگی عناصر کمیاب سبک و کاهیدگی عناصر کمیاب سنگین هستند. تمامی نمونه­ها دارای بی­هنجاری منفی Eu هستند ((Eu/Eu* = 0.62 to 0.88. میزان کل عناصر کمیاب بینppm  212-481 است. سن سنجی مونزوگرانیت به روش  U-Pb در کانی زیرکون انجام و سن 201.3 ± 3.6 Ma تعیین شد (راتین، تریاس فوقانی). نسبت ایزوتوپ اولیه (87Sr/86Sr)i و i(143Nd/144Nd)  در مونزوگرانیت به ترتیب 0.706776 و 0.512219 اندازه­گیری و محاسبه شد (با توجه به سن 201 میلیون سال). نسبت ایزوتوپ اولیه (87Sr/86Sr)i و i(143Nd/144Nd)  اسلیت به ترتیب 0.72061 و 0.511601 محاسبه شد (با توجه به سن 201 میلیون سال). ایزوتوپ اولیه εNd در مونزوگرانیت -3.13  و در اسلیت -15.19 اندازه گیری شد. براساس داده­های ایزوتوپی و عناصر کمیاب ماگمای اولیه مونزوگرانیت از بخش تحتانی پوسته قاره­ای یا از جبه منشا گرفته و در پوسته قاره­ای ضمن بالا آمدن آلودگی صورت پذیرفته است.

کلیدواژه‌ها


عنوان مقاله [English]

Geochronology, Radiogenic Isotope Geochemistry, and Petrogenesis of Sangbast Paleo-Tethys Monzogranite, Mashhad, Iran

چکیده [English]

The study area is located in northeastern Iran (south of Mashhad). Paleo-Tethys Ocean opened during Silurian time and subduction under Turan plate was started in Late Devonian. By Late Triassic (225 Ma) there was no Paleo-Tethys left on an Iranian transect, therefore Turan plate obducted over Iran Plate. Two stages of low grade regional metamorphism are exposed, that are related to Hercynian (Late Paleozoic) and Cimmerian (Jurassic) orogenies. The Paleo-Tethys remnants (meta-ophiolite and meta-flysch) were intruded by Sangbast monzogranite. Chemically, monzogranite is moderately peraluminous S-type granitoid. It has low values of magnetic susceptibility [(5 to 11) × 10-5 SI] therefore it is classified as belonging to the ilmenite-series of reduced type granitoids. Monzogranite is characterized by strong light rare earth element (LREE) enrichment and less low heavy REE (HREE). All samples have very small negative Eu anomalies (Eu/Eu* = 0.62 to 0.88). Total REE content of monzogranite is between 212-481 ppm. The result of U-Pb zircon age dating of monzogranite is 201.3 ± 3.6 Ma (Upper Triassic, Rhaetian time). The initial 87Sr/86Sr and 143Nd/144Nd ratios for monzogranite is (0.706776 and 0.512219) when recalculated to an age of 201 Ma, consistent with the new radiometric. The initial 87Sr/86Sr and 143Nd/144Nd ratios for slate is (0.720613 and 0.511601) respectively when recalculated to an age of 201 Ma, consistent with the new radiometric results. Initial εNd isotope values for monzogranite is -3.13 and the slate is -15.19. Based on radiogenic isotopic data and REE monzogranite magma originated either from lower continental crust which was very different from slate or it is originated from mantle and contaminated in continental crust during ascending.

کلیدواژه‌ها [English]

  • Mashhad
  • Paleo-Tethys
  • monzogranite
  • Rb-Sr
  • Sm-Nd
  • U-Pb
[1] Jarchovski T., Momenzadeh M., Tadayon A., Ziegler V., “Mineral reconnaissance in Mashhad Quadrangle”, Geological Survey of Iran (1973) 192.

[2] Alberti A., Moazez. Z., “Plutonic and metamorphic rocks of the Mashhad area (northeastern Iran, Khorasan)”, Boll. Soc. Geol. Italy 93 (1974) 1157-1196.

[3] Alberti A., Nicoletti M., Petrucciani C., “K-Ar Ages of micas of Mashhad granites”, Period Miner. 42 (1973) 483-493.

[4] Plimer I.R., Moazez Lesco Z., “Garnet xenocrysts in the Mashhad Granite, NE Iran”, Geologische Rundschau. 69, 3, (1980) 801-810.

[5] Majidi B., “The ultrabasic lava flows of Mashhad, North East Iran., Geological Magazine 118 1 (1981) 49-58.

[6] Alavi Mehdi, “The Virani ophiolite complex and surrounding rocks”, Geologische Rundschau, 68 (1979) 334-341.

[7] Alavi Mehdi, “Sedimentary and structural characteristics of the Paleo-Tethys remnants in northeastern Iran”, Geological Society of America Bulletin 103 8 (1991) 983-992.

[8] Alavi Mehdi, “Thrust tectonics of the Binaloud region; NE Iran”, Tectonics. 11 2 (1992) 360-370.

[9] Valizadeh M., Karimpour M.H., “Origin and tectonic setting of Mashhad granitoids”, Journal of Sciences, University of Tehran, V. 21 No. 1 (1995) 71-82.

[10] Mirnejad H., “Geochemistry and petrography of Mashhad granites and pegmatites”, M.Sc. thesis, Tehran University. (1991)

[11] Iranmanesh J., Sethna S.F., “Petrography and geochemistry of the Mesozoic granite at Mashhad, Khorasan Province, northeastern part of Iran”, Journal of the Geological Society of India. 52 1 (1998) 87-94.

[12] Abbasi H., “Petrology of regional and contact metamorphic rocks south of Mashhad”, M.Sc. thesis. Tehran University. (1998).

[13] Ghazi M., Hassanipak A.A., Tucker P.J., Mobasher K., “Geochemistry and 40Ar-39Ar ages of the Mashhad Ophiolite, NE Iran”, abstracts as: Eos. Trans. AGU, 82(47), Fall Meet. (2001).

[14] Stampfli G.M., “The Intra-Alpine terrain: a Paleo-Tethyan remnant in the Alpine”, Variscides. Eclogae geol. Helv. 89 (1) (1996) 13-42.

[15] Stampfli G.M., Tethyan oceans. In: E. Bozkurt, J.A. Winchester and J.D.A. Piper (Eds.), “Tectonics and magmatism in Turkey and surrounding area”, Geological Society of London, Special Publication 173 (2000) 163-185.

[16] Stampfli G.M., “Opening and closure of Paleo-Tethys in Iran”, Personal communication (2002).

[17] Stampfli G.M., Pillevuit A., “An alternative Permo-Triassic reconstruction of the kinematics of the Tethyan realm”, In: J. Dercourt, L.-E. Ricou and B. Vrielinck (Eds.), Atlas Tethys Palaeoenvironmental Maps. Explanatory Notes. Gauthier-Villars Paris, (1993) 55-62.

[18] Stampfli G.M., Marcoux J., Baud A., “Tethyan margins in space and time”, In: J.E.T. Channell, E.L. Winterer and L.F. Jansa (Eds.), Paleogeography and paleoceanography of Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology 87 (1991) 373-410.

[19] Stocklin J., “possible ancient continental margins in Iran”, The Geology of Continental Margins, Edited by C.A. Burk & C.L. Drake, (1974) 873-887.

[20] Khatonie Molayossefi M., “The study of stratigraphy and plants fossils of Shemshak Formation in Shandiz area”, M.S thesis. (2000) 222.

[21] Gehrels G. E., Valencia V. A., “Pullen in Geochronology: Emerging Opportunities”, ed. T. Loszewski and W. Huff, Paleo. Soc. Pap., 12 (2006) 67-76.

[22] Barker F., “Trondhjemite: definition, environment and hypotheses or origin”, In Barker, F. (ed) Trondhjemites, dacites, and related rocks, 1-12 New York : Elsevier. (1979).

[23] Whalen J.B., Currie K.L., Chappell B.W., “A-type granites. geochemical characteristics, discrimination and petrogenesis”, Contributions to Mineralogy and Petrology 95 (1987) 407-419.

[24] Barbarin B., “A review of the relationships between granitoid types, their origin and their geodynamic environments”, Lithos 46 (1999) 605-626.

[25] Villaseca C., Barbero L., Herreros V. A. “Re-examination of the typology of peraluminous granite types in intra continental orogenic belts”, Transaction of the Royal Society of Edinburgh; Earth Sciences 89 (1998) 113-119.

[26] Batchelor R.A., Bowden P., “Petrogenetic interpretation of granitoid rock series using multicationic parameters”, Chem. Geol., 48 (1985) 45-55.

[27] Taylor S.R., McLennan S.M., “The Continental Crust; Its composition and evolution; an examination of the geochemical record preserved in sedimentary rocks”, Blackwell, Oxford. (1985) 312.

[28] Boynton W.V., “Cosmochemistry of the rare earth elements; meteorite studies. In: Rare earth element geochemistry.” Henderson, P. (Editors), Elsevier Sci. Publ. Co., Amsterdam. . (1984) 63-114.

[29] Pearce J.A., Harris N.B.W., Tindle A.G. , “Trace element discrimination diagrams for the tectonic interpretation of granitic rocks”, Journal of Petrology 25 (4) (1984) 956-983.

[30] Majidi B., “The geochemistry of ultrabasic and basic lava flows occurrences in northeastern Iran”, In Geodynamic project in Iran. Geological Survey of Iran Report No. 51 (1983) 463-477.

[31] Garrido C. J., Bodinier J.-L, Burg J.-P, Zeilinger G., Hussain S., Dawood H., Chaudhry M.N., Gervilla F., “Petrogenesis of mafic garnet granulite in the lower crust of the Kohistan Paleo-arc Complex (Northern Pakistan): Implications for intra-crustal differentiation of island arcs and generation of continental crust”, Journal of Petrology 47 (2009) 1873–1914

[32] Zhengfu G., Wilson M., Liu J., Mao Q., “Post-collisional, Potassic and Ultrapotassic Magmatism of the Northern Tibetan Plateau: Constraints on Characteristics of the Mantle Source”, Geodynamic Setting and Uplift Mechanisms. Journal of Petrology Volume 47 Number 6 (2006) 1177-1220.

[33] Ishihara S., “The magnetite-series and ilmenite-series granitic Rocks”, Mining Geology 27 (1977) 293-305.