A study of microstructures of granitoids from the Alvand plutonic complex, Sanandaj-Sirjan zone, Iran: with special reference to myrmekitedevelopment

Document Type : Research Paper

Authors

Abstract

Many plutonic complexes occur in the Sanandaj-Sirjan Zone (SSZ), Iran. The Alvand Plutonic Complex (APC), as a major complex, is located in the northwestern part of the SSZ (near Hamedan). The APC is composed of various mafic to felsic plutonic rocks, such as olivine gabbro, gabbro, norite, diorite, tonalite, granodiorite, monzogranite, syenogranite, leucocratic granitoids, aplite, and pegmatite. In this study, our  research is concentrated on the granitoid part of the APC which is a major part of the pluton and consists of granodiorite and granites with porphyroid texture. Various microstructures, including magmatic, sub-magmatic, and solid-state structures can be distiguished in the APC. Alignment of feldspar phenocrysts and mafic enclaves are common magmatic structures.  Fractures filled with quartz and micas inside deformed feldspar phenocrysts are major submagmatic microstructures. Flame perthite and myrmekite in deformed rocks are common solid-state features in the granitoids. Various mechanisms for the genesis of  myrmekite are reviewed with special attention to myrmekite of the granitoids of the APC. Myrmekite was mostly generated from replacement of K-feldspar by sodic plagioclase in the presence of fluids with/without deformation and is more abundant in deformed rocks than in undeformed rocks, but occurs in some undeformed rocks, as well. Myrmekite was formed at the interface of K-feldspar/plagioclase, K-feldspar/K-feldspar, quartz/K-feldspar and biotite/K-feldspar; and within K-feldspar and plagioclase, as well. So, in contrast to ideas in several publications,  plagioclase/K-feldspar interface is not prequisite factor for development of myrmekite, although it make easier the process.

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منابع
[1] ایرانی، م (1372) بررسی پترولوژی توده گرانیتی الوند و هاله دگرگونی آن. پایان­نامه کارشناسی­ارشد، دانشکده علوم زمین، دانشگاه شهید بهشتی.
[2] بهاری­فر، ع.، ا (1383) پترولوژی سنگ­های دگرگونی منطقه همدان، رساله دکتری، دانشکده علوم، دانشگاه تربیت معلم.
[3] بهاری­فر، ع.، ا (1376) نگرش جدید بر پتروژنز سنگ­های دگرگونی ناحیه­ای منطقه همدان، پایان­نامه کارشناسی ارشد، دانشگاه تربیت معلم تهران.
[4] سپاهی­گرو، ع.، ا (1378) پترولوژی مجموعه نفوذی الوند بانگرشی ویژه برگرانیتوئیدها. رساله دکتری، دانشکده علوم، گروه زمین­شناسی، دانشگاه تربیت معلم.
[5] شهبازی، ح (1389) پترولوژی مجموعه سنگ­های آذرین و میگماتیت­های کمپلکس الوند و توده نفوذی آلموقلاغ همدان و ارتباط ژنتیکی بین آن­ها، رساله دکتری، دانشگاه شهید بهشتی.
[6] صادقیان، م (1374) بررسی پترولوژی سنگ­های آذرین و دگرگونی منطقه چشمه قصابان همدان، پایان­نامه کارشناسی­ارشد، دانشگاه تهران.
[7]     Ahadnejad V., Valizadeh M. V., Deevsalar R.,  Rezaei-Kahkhaei M (2011) Age and geotectonic position of the Malayergranitoids: Implication for plutonism in the Sanandaj-Sirjan Zone, W Iran. NeuesJahrbuchfürGeologie und Paläontologie, Abhandlungen 261(1): 61-75.
[8]     Ahmadi-Khalaji  A., Esmaeily  D., Valizadeh M. V., Rahimpour-Bonab H (2007) Petrology and geochemistry of the granitoid complex of Boroujerd, Sanandaj-Sirjan Zone, Western Iran, Journal of Asian Earth Sciences  29(5-6): 859-877.
[9]     Alavi  M (2004) Regional stratigraphy of the Zagros fold-thrust belt of Iran and its proforeland evolution, American  Journal of Science 304: 1-20.
[10] Alavi M (1994) Tectonics of Zagros orogenic belt of Iran: New data and interpretation, Tectonophysics 229: 211-238
[11] Arvin  M., Pan, Y., Dargahi S., Malekizadeh A.,  Babaei A (2007) Petrochemistry of the Siah-Kuhgranitoid stock southwest of Kerman, Iran: Implications for initiation of Neotethyssubduction, Journal of Asian Earth Sciences 30(3-4): 474-489.
[12] Ashworth J. R (1972) Myrmekite of exsolution and replacement origins, Geological Magazine 109: 45–62.
[13] Blenkinsop T. G (2000) Deformation microstructures and mechanisms in minerals and rocks, Kluwer Academic Publishers, Dordrecht, 150 pp.
[14] Esna-Ashari A., Tiepolo M., Valizadeh M. V., Hassanzadeh J., Sepahi A. A (2012) Geochemistry and zircon U–Pb geochronology of Aligoodarzgranitoid complex,  Sanandaj-Sirjan Zone, Iran, Journal of Asian Earth Sciences 43(1): 11-22.
[15] Hibbard M. J (1987) Deformation of incompletely crystallised magma systems: granitic gneisses and their tectonic implications", Journal of Geology 951:543–561.
[16] Mahmoudi S., Corfu F., Masoudi F., Mehrabi B., Mohajjel M (2011) U-Pb dating and emplacement history of granitoid plutons in the northern Sanandaj–Sirjan Zone, Iran", Journal of Asian Earth Sciences 41: 238–249.
[17] Masoudi  F (1997) Contact metamorphism and pegmatites development in the region SW of Arak, Iran,  Ph. D. thesis, University of Leeds, UK.
[18] Menegon L., Pennacchioni G., Stünitz H (2006) Nucleation and growth of myrmekite during ductile shear deformation in metagranites, Journal of Metamorphic Geology  24: 553-568.
[19] Michel Lévy A. M (1874) Structuremicroscopique des rochesacidesanciennes,  SociétéFrancaise de Mineralogie et de Crystallographie Bulletin, 3: 201-222.
[20] Passchier C. W., Trouw R. A. J (2005) Microtectonics, Springer-Verlag Berlin Heidelberg, 366 pp.
[21] Paterson S. R., Vernon R. H., Tobisch O. T (1989) A review of criteria for the identification of magmatic and tectonic foliations in granitoids, Journal of Structural Geology 11:  349-364.
[22] Phillips E. R (1980) On polygenetic myrmekite, Geological Magazine 117: 29-36.
[23] Phillips E. R (1974) Myrmekite-one hundred years later, Lithos  7: 181-194.
[24] Pryer L. L., Robin P. Y. F (1995) Retrograde metamorphic reactions in deforming granites and the origin of flame perthite", Journal of Metamorphic Geology 14: 645- 658.
[25] Pryer L. L., Robin P. Y. F (1996) Differential stress control on the growth and orientation of flame perthite: a Palaeostress-direction indicator", Journal of Structural  Geology 18: 1115-1116.
[26] Rashidnejad-Omran N., Emami M. H., Sabzehei  M., Rastad  E., Bellon  H (2002) Lithostratigraphy and Paleozoic to Paleocene history of some metamorphic complexes from Muteh area, Sanandaj-Sirjan zone (southern Iran), ComptesRendus Geosciences 334 (16): 1185-1191.
[27] Sepahi A. A (2008) Typology and petrogenesis of granitic rocks in the Sanandaj-Sirjan metamorphic belt, Iran: with emphasis on the Alvand plutonic complex, NeuesJahrbuchFuerGeologie und Paleontologie, Abhandlungen 247(3): 295-312(18).
[28] Sepahi A. A., Whitney D. L., Baharifar A. A (2004) Petrogenesis of andalusite-kyanite-sillimanite veins and host rocks, Sanandaj-Sirjan metamorphic belt, Hamedan, Iran,  Journal of Metamorphic Geology 22: 119-134.
[29] Shahbazi H., Siebel W., Pourmoafee M., Ghorbani  M., Sepahi  A. A., Shang  C. K., Vousoughi-Abedini  M (2010) Geochemistry and U-Pb zircon geochronology of the Alvand plutonic complex in Sanandaj–Sirjan Zone (Iran): New evidence for Jurassic magmatism, Journal of Asian Earth Sciences 39(6-9): 668-683.
[30] Sheikholeslami R., Bullen H., Emami M. H., Sabzehei M., Pique A (2003) New structural and K40-Ar40 data for the metamorphic rocks in Neyriz area (Sanandaj-Sirjan zone, southern Iran): Their interest for an overview of the Neo-Tethyan domain in the Middle East, ComptesRendus Geosciences 335(13):  981-991.
[31] Shelley  D (1964) On myrmekite, American Mineralogist 49: 41–52.
[32] Simpson C., Wintsch R. P (1989) Evidence for deformation-induced K-feldspar replacement by myrmekite, Journal of Metamorphic Geology 7: 261–275.
[33] Spencer E (1938) The potash-soda-feldspars. II. Some applications to petrogenesis, Mineralogical Magazine  25: 87–118.
[34] Tsurumi J., Hosonuma H., Kanagawa K (2003) Strain localization due to a positive feedback of deformation and myrmekite-forming reaction in granite and aplitemylonite along the Hatagawa Shear Zone of NE Japan, Journal of Structural Geology  25: 557-574.
[35] Valizade M. V., Cantagral J. M (1975) Premieres donneesradiometriques (K-AretRb-Sr) sur les micas du complexemagmatique du Mont AlvandpresHamedan (Iran Occidental), ComptesRendusHebdomadares des Seances de l’Academie des Sciences, Serie D. Sciences Naturelles 281:1083-1086.
[36] Vernon R. H (2000) Review of microstrucrtural evidence of magmatic and solid-state flow, Electronic Geosciences, 5, 2.
[37] Vernon R. H (2004) A practical guide to rock microstructure", Cambridge University Press, 580 pp.
[38] Vernon R. H (1991) Questions about myrmekite in deformed rocks, Journal of Structural Geology 13: 979-985.
[39] Vernon R. H (1999) flame perthite in metapelitic gneisses at Cooma, SE Australia, American Mineralogist 84: 1760-1765.
[40] Yuguchi T., Nishiyama T (2008) The mechanism of myrmekite formation deduced from steady-diffusion modeling based on petrography: Case study of the Okueyama granitic body, Kyushu, Japan, Lithos 106(3-4): 237-260.