توزیع اندازه بلوری در سنگهای دگرگونی: مثالی از تأثیر دمای ماورای تعادل در نرخ هسته‌بندی و رشد

نویسنده

انشگاه علوم پایه

چکیده

توزیع اندازه بلوری در سنگهای دگرگونی اطلاعات اساسی را در ارتباط با سرعت هسته‌بندی، سرعت رشد، زمان رشد و میزان حرارت ماوراء در تعادل ارائه می‌کند. بررسی توزیع اندازه بلوری برای بلورهای استرولیت، کیانیت و آندالوزیت در هاله دگرگونی آردارا بیانگر این است که کانیهای نخست تشکیل یافته (گارنت) دارای بالاترین چگالی جمعیت و کوتاهترین زمان رشد، و  کانیهای تشکیل یافته در فاز نهائی دگرگونی (آندالوزیت) دارای پایین‌ترین چگالی جمعیت و طولانی‌ترین زمان رشد هستند. چگالی جمعیت و زمان رشد استرولیت و کیانیت یکسان بوده و از این حیث حد واسط گارنت و آندالوزیت قرار میگیرند. این اطلاعات مؤید تأثیر درجه ماوراء تعادل بر روی  سرعت هسته‌بندی و رشد کانیها در دگرگونی است.

کلیدواژه‌ها


عنوان مقاله [English]

Crystal size distribution in metamorphic rocks: an example for the relationship between nucleation and growth rates with overstepping

چکیده [English]

Crystal size distribution (CSD) in metamorphic rocks provide fundamental information about crystal nucleation and growth rate, growth time and the degree of overstepping. CSD data for garnet, staurolite, kyanite and andalusite crystals from the aureole demonstrate that the earliest formed of these minerals, garnet, has the highest population density and the shortest growth time. The last formed mineral, andalusite, has the lowest population density and longest growth time. Kyanite  and  staurolite  have  the  similar  population  density  and  growth  times  intermediate  between those of garnet and andalusite. These data demonstrate the effect of the degree of overstepping on the nucleation and growth rates of minerals during metamorphism.

کلیدواژه‌ها [English]

  • crystal size distribution
  • Overstepping
  • Nucleation
[1] BarkerA.J., Introduction to metamorphic textures and microstructures, Stanley Thornes, Oxford (1998) pp. 264.

[2] Roselle G.R., Baumgartner L.P., Chapman J.A., Nucleation-dominated crystallisation of forsterite in the Ubehebe Peak contact aureole, California, Geology 25 (1997) 823-826.

[3] Ridley J., Thompson A.B., The role of mineral kinetics in the development of metamorphic microtextures In: Walther J.V. and Wood B.J. (eds.) Fluid-Rock Interactions During Metamorphism, Springer-Verlag, New York (1986) pp. 154-193.

[4] McLean D., The science of metamorphism in metals, In: Pitcher W.S. and Flinn G.W. (eds.), Controls of Metamorphism, John Wiley&Sons, New York (1965) pp. 103-118.

[5] Fisher G.W., Rate laws in metamorphism, Geochim. Cosmochim. Acta 42 (1978) pp. 1035-1050.

[6] Jones K.A., Galwey A.K., Size distribution, composition and growth kinetics of garnet crystals in some metamorphic rocks from the west of Ireland, Geological Society of London Quaternary Journal 122 (1966) pp. 29-44.

[7] Galwey A.K., Jones K.A., An attempt to determine the mechanism of a natural mineral-forming reaction from examination of the products, Journal of Chemical Society, London Dec. (1963) pp. 5681-5686.

[8] Galwey A.K., Jones K.A., Crystal size frequency distribution of garnets in some analysed metamorphic rocks from Mallaig, Inverness, Scotland, Geological Magazine 103 (1966) pp. 143-152.

[9] Kretz A., Grain-size distribution for certain metamorphic minerals in relation to nucleation and growth, Journal of Geology 74 (1966) pp. 147-173.

[10] Jones K.A., Morgan G.J., Galwey A.K., The significance of the size distribution function of crystals formed in metamorphic reactions, Chemical Geology 9 (1972) pp. 137-143.

[11] Randolph A.D., Larson M.A., Theory of particulate processes, Academic Press, New York (1971) p. 251.

[12] Marsh B.D., Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallisation: I. Theory, Contribution to Mineralogy and Petrology 94 (1988) pp. 277-91.

[13] Cashman K.V., Marsh B.D., Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallisation: II. Makaopuhi lava lake, Contribution to Mineralogy and Petrology 99 (1988) pp. 292-305.

[14] Cashman K.V., Ferry J.M., Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystalization: III. Metamorphic crystallisation, Contribution to Mineralogy and Petrology 99 (1988) pp. 401-415.

[15] Akaad M.K., The Ardara granitic diapir of Co. Donegal, Ireland, Geological Society of London Quaternary Journal 112a (1956) pp. 263-88.

[16] Akaad M K., The northern aureole of the Ardara pluton of County Donegal, Geological Magazine 93b (1956) pp. 377-92.

[17] Naggar M.H., Atherton M.P., The composition and metamorphic history of some aluminum silicate-bearing rocks from the aureoles of the Donegal granites, Journal of Petrology 11 (1970) pp. 549-589.

[18] Homam S.M., A chemical and textural study of aluminium silicate-bearing rocks from the contact aureole of the Ardara pluton, Co. Donegal, Ireland, Ph.D Thesis, University of Liverpool (2000).

[19] Kerrick D.M., Fibrolite in contact aureoles of Donegal, Ireland, American Mineralogist 72 (1987) pp. 240-254.

[20] Peterson T.D., A refined technique for measuring crystal size distribution in thin section, Contribution to Mineralogy and Petrology 124(3-4) (1996) pp. 395-405.

[21] Shelley D., Igneous and metamorphic rocks under the microscope, Chapman and Hall, London (1992) p. 445.

[23] Thompson A.B., Mineral reactions in pelitic rocks: II. Calculation of some P-T-X (Fe,Mg) Phase relations, American Journal of Sciences 276 (1976) pp. 425-454.