شکل‌گیری گارنت‌های موجود در توده‌ی گرانیتوئیدی دهنو، شمال‌غرب مشهد

نویسندگان

1 دانشگاه فردوسی مشهد

2 دانشگاه آزاد اسلامی

چکیده

توده­ی گرانیتوئیدی دهنو که در شمال­غرب مشهد، در مجاورت بلافصل با هورنفلس­های سرشار از گارنت واقع شده است، حاوی درشت بلورهایی از گارنت است  که فرصتی را برای بررسی پدیده­ی آلایش ماگما با سنگ­های دیواره فراهم کرده است. بلورهای گارنت حاوی میانبارهای فراوانی بوده که نشان­دهنده­ی فازهای آذرین هستند و به­صورت دوائر متحد المرکز درون بلور آرایش یافته­اند. حاشیه­ی سرشار از بیوتیت و هورنبلند در پیرامون بلورهای گارنت نشان می­دهد که این گارنت­ها در تعادل با ماگمای میزبانشان نبوده و به­وسیله­ی فازهای فرومنیزین ماگمای گرانیتی جایگزین شده­اند. به­دلیل این که ماگمای شبه رخشانی تشکیل دهنده­ی گرانیتوئیدهای منطقه، آلومینیوم کافی برای تشکیل و پایداری گارنت را ندارد. به نظر می­رسد که بلورهای گارنت در منطقه­ی مورد بررسی، بلورهای پرتیکیتکی هستند که نخست در سنگ میزبان وجود نداشته و فراورده­های ذوب نامتجانس زینوکریست­ها و زینولیت­های مشتق شده از سنگ­های دیواره هستند.

کلیدواژه‌ها


عنوان مقاله [English]

Genesis of garnets in the granitoid intrusion of Dehnow, NW Mashhad

چکیده [English]

The granitoid intrusions of Dehnow, which is located  in northwest of Mashhad in immediate contact with garnet-rich hornfels, contain large crystals of garnets. They provide an excellent opportunity to study the effect of host rocks in contamination of a garnet-bearing granitoid magma. The garnet crystals contain abundant inclusions that are indicative of igneous phases and are arranged in a circular pattern in crystal. Biotite and hornblende-rich rim around garnet crystals show that the garnets are not in equilibrium with the host magma and is replaced by ferromagnesian phases of the granite magma. Dehnow granitoids  are metaluminous  in nature. As normally metaluminous magmas  have not enough aluminum for garnet stability, it seems that these garnets are peritectic crystals  and formed as a result of heterogeneous melting of xenocrysts and xenoliths derived from host rocks.

کلیدواژه‌ها [English]

  • granitoid intrusion
  • Dehnow
  • contamination
  • peritectic crystals
[1] Deer W. A., Howie R. A., Zussman J., “An Introduction to the Rock forming Minerals”, Second Longman ed. Longman, London (1992) 696pp.

[2] Thöni M., Miller C., “Ordovician meta-pegmatite garnet (N–W Ötztal basement, Tyrol, Eastern Alps): preservation of magmatic garnet chemistry and Sm–Nd age during mylonitization”, Chemical Geology 209 (2004) 1–26.

[3] Miller C.F., Stoddard E.F., “The role of manganese in the paragenesis of magmatic garnet: an example from the Old Woman-Piute Range, California”, Journal of Geology 89 (1981) 233-246.

[4] Kebede T., Koeberl C., Koller F., “Magmatic evolution of the Suquii-Wagaa garnet-bearing two-mica granite,Wallagga area, western Ethiopia”, Journal of African Earth Sciences 32 (2001) 193-221.

[5] Chappell B.W., White A.J.R., “Two contrasting granite types”, Pacific Geology 8 (1974) 173-174.

[6] Clemens J.D., “S-type granitic magmas petrogenetic issues, models and evidence”, Earth-Science Reviews 61(2003) 1-18.

[7] Wu F.Y., Sun D.Y., Jahn B.M., Wilde S., “A Jurassic garnet-bearing granitic pluton from NE China showing tetrad REE patterns”, Journal of Asian Earth Sciences 23 (2004) 731-744.

[8] Yu J.H., Zhao L., Zhou X., “Mineralogical characteristics and origin of garnet-bearing I-type granitoids in southeastern Fujian province”, Geological Journal of China Universities 10 (2004) 364-377.

[9] Zhang J., Changqian Ma,C., She Z., “An Early Cretaceous garnet-bearing metaluminous A-type granite intrusion in the East Qinling Orogen, central China: Petrological, mineralogical and geochemical constraints”, Geoscience Frontiers (2012) 1-12.

[10] Erdmann S., Clarke D. B., MacDonald M. A. “Origin of chemically zoned and unzoned cordierites from the SouthMountain and Musquodoboit batholiths”, Transactions of the RoyalSociety of Edinburgh, Earth Sciences 95 (2005) 99-110.

[11] Fourcade S., Capdevila R., Ouabadi A., Martineau F., ”The origin and geodynamicsignificance of the Alpine cordierite-bearing granitoids of northern Algeria”, A combined petrological,mineralogical, geochemical and isotopic (O, H, Sr, Nd) study.Lithos 57 (2001) 187-216.

[12] Gottesmann B., Forster H.-J., “Sekaninaite from the SatzungGranite (Erzgebirge, Germany); magmatic or xenolithic?”, EuropeanJournal of Mineralogy 16 (2004) 483-491.

[13] Dahlquist J. A., Rapela C.W., Baldo E. G., “Petrogenesis ofcordierite-bearing S-type granitoids in Sierra de Chepes,Famatinian orogen, Argentina”, Journal of South American EarthSciences 20 (2005) 231-251.

[14] Beard J. S., Ragland P. C., Crawford M. L., “Reactive bulk assimilation: A model for crust-mantle mixing in silicic magmas”, Geology 33 (2005) 681-684.

[15] Stevens G., Villaros A., Moyen J.-F., “Selective peritecticgarnet entrainment as the origin of geochemical diversity in S-type granites”, Geology 35 (2007) 9-12.

[16] Plimer I. R., Moazez-Lesco Z., “Garnet Xenoerysts in the Mashhad Granite, NE Iran”, Geologische Rundschau, Bd. 89 (1980) 801—810.

[17] Samadi R., Mirnejad H., Kawabata H., Harris Ch., Valizadeh M.V., Gazel E., “Magmatic garnet in the Triassic(215Ma) Dehnow pluton of NE Iran and its petrogenetic significance”, International Geology Review, (2014).

[18] طاهری ج.، قائمی ف.، نقشه 100000/1 مشهد، سازمان زمین‌شناسی ایران، 1994.

[19] صمدی ر.، میرنژاد ح.، شیردشت‌زاده ن.، کاواباتا ه.،"کاربرد شیمی گارنت در بررسی‌های ترمودینامیکی تونالیت دهنو (شمال غرب مشهد)"، مجله بلورشناسی و کانی‌شناسی ایران، شماره 2 (1391) ص 253 - 264.

[20] Karimpour M.H., Stern C.R., Farmer G.L., “Zircon u-pb geochronology, Sr-Nd isotope analyses and petrogenetic study of the Dehnow diorite and Kuhsangi granodiorite (paleo-Tethys),NE Iran”, Journal of Asian Earth Sciences 37 (2010) 384-393.

[21] Razavi M.H., Masoudi F., Alaminia Z., ”Garnet-Biotite Chemistry for Thermometry of Staurolite Schist from South of Mashhad, NE Iran”, Journal of Sciences, Islamic Republic ofIran 19(3) (2008) 237-245.

[22] Karimpour M.H., Farmer L., Ashori C., Saadat S., “Major, Trace and REE geochemistryof Paleo-Tethys Collision-Related Granitoids from Mashhad, Iran", Journal of Science IslamicRepublic of Iran, 17 (2006) 127-145.

[23] Mirnejad H., Lalonde A.E., Obeid M., Hassanzadeh J., "Geochemistry and petrogenesis of Mashhad granitoids: An insight into the geodynamic history of the Paleo-Tethys in Northeast of Iran", Lithos v 170–171 (2013) 105–116.

[24] Harangi S.Z., Downes H., Kόsa L., Szabό C.S., Thirlwall M.F., Mason P.R.D., "Almandine garnet in calc-alkaline volcanic rocks of the Northern Pannonian Basin (Eastern- Central Europe), geochemistry, petrogenesis and geodynamic implications", Journal of Petrology, v 42 (2001) 1813–1843.

[25] Shand S.J., "Eruptive rocks. Their genesis, composition, classification, and their relations to ore-deposits", Wiley, New York (1943) 444 pp.

[26] Irvine T. N., Barager W. R. A., “A guide to the chemical classification of the common volcanic rocks”, Canadian Journal of Earth Science, 8(1971) 235-458.

[27] Chappell B. W., "Aluminium saturation in I- and S-type granites and the characterization of fractionated haplogranites", Lithos 46 (1999) 535–551.

[28] Yardley B. W. D., “An empirical studyof diffusion in garnet”, American Mineralogist 62 (1977) 793-800.

[29] Askren D.R., Roden M.F and Whitney J.A., “Petrogenesis of Tertiary Andesite Lava Flows Inter-layered with Large-Volume Felsic AshFlow Tuffs of the Western USA”, Journal of Petrology, 38(1999) 1021–1046.

[30] Erdmann S., "Country rock contamination and assimilation in the South Mountain Batholith”, Unpublished Ph.D thesis, Dalhousie University, Halifax, Nova Scotia, (2006) 212 pp.

[31] Erdmann S., Scaillet B., Kellett D.A., "Textures of peritectic crystals as guides to reactive minerals in magmatic systems: New insights from melting experiments", Journal of Petrology 11 (2013) 2231- 2258.

[32] Dorias M.J., Tubrett M., “Detecting pritectic garnet in the peraluminous cardigan pluton,New Hampshire”, journal of petrology 53 (2012) 299-324.