شیمی کانی‌ها و شرایط فشار – دمای تبلور توده‌های گرانیتوئیدی حاشیه‌ی رودخانه‌ی زاینده‌رود، پهنه‌ی برشی شمال شهرکرد با نگرشی ویژه به حضور اپیدوت ماگمایی

نویسنده

دانشگاه شهرکرد

چکیده

ناحیه مورد بررسی در پهنه­ی برشی شمال شهرکرد قرار دارد. در این منطقه تعداد زیادی پلوتون گرانیتوئیدی کوچک و متوسط به سن ژوراسیک میانی حضور دارند که در سنگ‌های دگرگون منطقه نفوذ کرده‌اند. این سنگ‌ها برگواره و خطواره میلونیتی بارزی را در نتیجه­ی دگرشکلی شدید نشان می‌دهند. اغلب این پلوتون‌های گرانیتوئیدی دارای مجموعه­ی کوارتز + فلدسپات پتاسیم + پلاژیوکلاز + بیوتیت + هورنبلند + آلانیت + تیتانیت + مگنیت + اپیدوت ماگمایی + آپاتیت + زیرکن ± گارنت در شرایط تعادل بافتی ظاهری قرار گرفته­اند. ویژگی‌های بافتی و ترکیبی اپیدوت‌ها دلالت بر خاستگاه ماگمایی آن­ها دارد. این پلوتون‌های گرانیتوئیدی حاوی اپیدوت ماگمایی، بایستی در فشارهای نسبتاً بالا تشکیل شده باشند. زمین فشارسنجی محتوای Al در هورنبلند مقادیر فشار 3/7 تا 1/8 کیلو بار (متوسط 7/7 کیلو بار) را ارایه می‌دهد که با عمق حدود 28 کیلومتری پوسته همخوانی دارد. همچنین، زمین فشارسنجی آمفیبول – پلاژیوکلاز دماهایی از 663 تا 711 درجه­ی سانتیگراد را به دست می‌دهد. این نتایج زمین دما - فشارسنجی با حضور اپیدوت ماگمایی در این سنگ‌های گرانیتوئیدی سازگار است.

کلیدواژه‌ها


عنوان مقاله [English]

Mineral chemistry and P-T conditions of crystallization of the granitoid plutons in the Zayandeh-Rood river area, shear zone of north of Shahrekord with special reference to magmatic epidote

چکیده [English]

The study area is located within the shear zone of north Shahrekord. There are many small and medium granitoid plutons that have intruded in the metamorphic rocks with Middle Jurassic in age. These rocks show sharp mylonitic foliation and lineation as the results of undergoing strong deformation.  Most of these granitoid plutons contain the assemblage of quartz + K-feldspar + plagioclase + biotite + hornblende + allanite + titanite + magnetite + magmatic epidote + apatite + zircon ± garent in apparent textural equilibrium. Epidotes exhibit textural and compositional characteristics implying their magmatic origin. The granitoid plutons bearing magmatic epidote must have formed under moderately high pressures, corresponding to lower crustal depths. The Al – in – hornblende geobarometry yields pressures of 7.3 - 8.1 kbar (average 7.7 kbar) corresponding to a depth of about 28 Km. Also, amphibole–plagioclase geothermometry gives temperatures from 663 to 711 °C. The geothermobarometry results are in agreement with the presence of magmatic epidote in the granitods.

کلیدواژه‌ها [English]

  • deformed granitoid
  • Middle Jurassic
  • geobarometry
  • geothermometry
  • magmatic epidote
  • north of Shahrekord
]1[ زاهدی م.، "نقشه زمین‌شناسی چهارگوش شهرکرد"، مقیاس 1:250000، سازمان زمین‌شناسی کشور. 1371.

]2[ داودیان دهکردی ع.، "تحول تکتونو متامورفیک و ماگماتیک در ناحیه شهرکرد – داران (زون سنندج – سیرجان، ایران)", پایان نامه دکتری دانشگاه اصفهان، (1384) 217 صفحه.

[3] Davoudian A.R., "Petrological and geochemical constraints on the evolution of the Cheshmeh-Sefid granitoid complex of Golpayegan in the Sanandaj-Sirjan zone, Iran", Neues Jahrbuch Fur Mineralogie-Abhandlungen 184 (2007) 117-129.

[4] Shabanian N., Khalili M., Davoudian A.R., Mohajjel M., "Petrography and geochemistry of mylonitic granite from Ghaleh-Dezh, NW Azna, Sanandaj-Sirjan zone, Iran", Neues Jahrbuch Fur Mineralogie-Abhandlungen‎ 185 (2009) 233-248.

[5] Maniar P.D., Piccoli P.M., "Tectonic discrimination of granitoids", Geological Society of American Bulletin 101 (1989) 635-643.

[6] Anderson J.L., "Regional tilt of the Mount Stuart batholith, Washington, determined using aluminum-in-hornblende barometry: Implications for northward translation of Baja British Columbia: Discussion and Reply", Geological Society of America Bulletin 109 (1997) 1223-1227.

[7] Stöklin J., "Structural history and tectonics of Iran; a review", American Association of Petroleum Geologists Bulletin 52 (1968)1229-1258.

[8] Davoudian A.R., Genser J., Dachs E., Shabanian N., "Petrology of eclogites from north of Shahrekord, Sanandaj-Sirjan zone, Iran", Mineralogy and Petrology 92 (2008) 393–413.

[9] Dachs E., "PET: Petrological elementary tools for Mathematica: an update", Computers and Geoscience 30 (2004) 173-182.

[10] Droop G.T.R., "A general equation for estimating Fe+3 concentrations in ferromagnesian silicates and oxides from microprobe analyses, using stoichiometric criteria", Mineralogical Magazine 51 (1987) 431-435.

[11] Holland T.J.B., Blundy J.D., "Non-ideal interactions in calcic amphiboles and their bearing on amphibole-plagioclase thermometry", Contributions to Mineralogy and Petrology 116 (1994) 433-447.

[12] Leake B.E., "Nomenclature of amphiboles. Report of the subcommittee on amphiboles of the International Mineralogical Association on new minerals and mineral names", European Journal of Mineralogy 9 (1997) 623-651.

[13] Leake R., "On aluminous and edenitic hornblendes", Mineralogical Magazine 38 (1971) 389 – 405.

[14] Fleet M.E., Barnett R.L., "Partitioning in calciferous amphiboles from the Frood mine, Sudbury, Ontario", The Canadian Mineralogist 16 (1978)527 – 532.

[15] Hollister L.S., Grissom G.C., Peters E.K., Stowell H.H., Sisson V.B., "Confirmation of the empirical correlation of Al in hornblende with pressure of solidification of calc-alkaline plutons", American Mineralogist 72 (1987) 231-239.

[16] Enami M., Suzuki K., Liou J.G., Bird D.K., "Al – Fe3+ and F– OH substitutions in titanite and constrains on their P–T dependence", European Journal of Mineralogy 5 (1993) 231-291.

[17] Franz G., Spear F.S.‎, "Aluminous titanite (sphene) from the Eclogite Zone, South-Central Tauern Window, Austria", Chemical Geology 50 (1985) 33-46.

[18] Schmidt M.W., Poli S., "Magmatic Epidote", Reviews in Mineralogy and Geochemistry 56 (2004) 399-430.

[19] Naney M.T., "Phase equilibria of rock -forming ferromagnesian silicates in granitic systems", American Journal of Science 283 (1983) 993-1033.

[20] Zen E-an, Hammarstrom M.‎, "Magmatic epidote and its petrologic significance", Geology 12 (1984) 515-518.

[21] Crawford M.L., Hollister L.S., "Contrast of metamorphic and structural histories across the Work Channel lineament, Coast Plutonic Complex, British Columbia", Journal of Geophysical Research 87 (1982) 3849-3860.

[22] Schmidt M.W., Thompson A.B., "Epidote in calc-alkaline magmas: an experimental study of stability, phase relationships, and the role of epidote in magmatic evolution", American Mineralogist 81 (1996) 462-474.

[23] Brandon A.D., Creaser R.A., Chacko T., "Constraints on rates of granitic magma transport from epidote dissolution kinetics", Science 271 (1996)1845-1848.

[24] Tulloch A.J., "Comment on "Implications of magmatic epidote - bearing plutons on crustal evolution in the accreted terranes of northwestem North America" and "Magmatic epidote and its petrologic significance", Geology 14 (1986) 186-187.

[25] Vyhnal C.R., McSween H.Y., Speer J.A., "Hornblende chemistry in southern Appalachian granitoids: Implications for aluminum hornblende thermobarometry and magmatic epidote stability". American Mineralogist 76 (1991) 176-188.

[26] Zen E-an., "Tectonic significance of high-pressure plutonic rocks in the Western Cordillera of North America. In Ernst W.G., ed., Metamorphisrn and crustal evolution of the western United States", Rubey Volume VII: Englewood Cliffs, New Jersey, Prentice Hall (1988) 41-67.

[27] Brasilino R.G., Sial A.N., Lafon J.M., "Magmatic Epidote, Hornblende Barometric Estimates, and Emplacement of the Conceicao das Creoulas Pluton, Alto Pajeu Terrane, NE Brazil", Anais da Academia Brasileira de Ciências 71(1999) 1-16.

[28] Tulloch A.J., "Secondary Ca-Al silicates as low-grade alteration products of granitoid biotite", Contributions to Mineralogy and Petrology 69 (1979) 105-117.

[29] Pal N., Pal D.C., Mishra B., Meyer F.M.‎,

" The evolution of the Palim granite in the Bastar tin province, Central India". Mineralogy and Petrology 72 (2001) 281-304.

[30] Helmy H.M., Ahmed A.F., El Mahallawi M. M., Ali S.M‎, "Pressure, temperature and oxygen fugacity conditions of calc-alkaline granitoids, ‎Eastern Desert of Egypt, and tectonic implications",. Journal of African Earth Sciences 38 (2004) 255-268.

[31] Anderson J.L., Smith. D.R., "The effect of temperature and oxygen fugacity on Al-in-hornblende barometry", American Mineralogist 80 (1995) 549-559.

[32] Johnson M.C., Rutherford M.J., "Experimental calibration of the aluminum-in-hornblende geobarometer with application to Long Valley caldera (California) volcanic rocks", Geology 17 (1989) 837-841.

[33] Schmidt M.W., "Amphibole composition in tonalite as a function of pressure: an experimental calibration of the Al-in-hornblende barometer", Contributions to Mineralogy and Petrology 110 (1992) 304-310.

[34] Anderson J.L., Smith. D.R., "The effect of temperature and oxygen fugacity on Al-in-hornblende barometry", American Mineralogist 80 (1995) 549-559.

[35] Blundy J.D., Holland T.J.B., "Calcic amphibole equilibria and a new amphibole-plagioclase geothermometer", Contributions to Mineralogy and Petrology 104 (1990) 208-224.