Document Type : Original Research Paper

Authors

1 PhD. Student, Department of Geology, School of Science, University of Tehran, Tehran, Iran

2 Assistant Professor, Department of Geology, Faculty of Science, Shahid Bahonar University of Kerman, Kerman, Iran

3 Professor, Department of Geology, Faculty of Science, Shahid Bahonar University of Kerman, Kernam, Iran

Abstract

Gandom Beriyan, as a part of Quaternary volcanism of Iran, is a kind of messa which is covered by very dark lava flows. The flows are generally fresh to rarely altered alkali olivine basalts and cover an area around 480 km2 in southern part of the Lut desert in northeast of Kerman. The common textures of basaltic lava flows are porphyry to glomeroporphyry with an intersertal to intergranular groundmass. Their major minerals are olivine and clinopyroxene phenocrysts along with plagioclase microlites. Plagioclase microlites are recognized as the major silicate phase in these rocks. Three-dimensional shape of plagioclase crystals and also rate of nucleation and growth time was estimated by thin section image processing and using crystal size distribution (CSD) method. Based on this, it is revealed that the shape of plagioclase microlites is tablet with aspect ratio of 1:10:10 for short: intermediate: long axes, respectively. The uniformity of CSD graph and its constant slope show that the effect of physical processes such as magma mixing was limited during ascent of basaltic magma toward the surface. Based on these calculations, growth time (t) and rate of nucleation (J) were estimated 2.53 to 3.21 years and 10.17×10-9 to 9.53×10-9 mm-3/s-1, respectively. The results are completely matched with nature of alkali basalt magmas.

Keywords

Cashman, K. V. & Marsh, B. D., 1988- Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallisation II. MakaopuhiLavaLake. Contributions to Mineralogy and Petrology, 92: 292-305.
Cashman, K. V., 1990- Textural constraints on the kinetics of crystallization of igneous rocks. In: Nicholls, J., Russell, J.K. (Eds.), Modern methods of igneous petrology: understanding magmatic processes. Mineralogical Society of America,.p: 259–314.
Cashman, K. V., 1993- Relationship between plagioclase crystallization and cooling rate. Contributions to Mineralogy and Petrology, 113: 126 -142.
Garrido, C. J. & Kelemen, P. B., Hirth, G., 2001- Varation of cooling rate with depth in lower crust formed at an aceanic spreading ridge; plagioclase crystal size distributions in gabbros from the Oman ophiolite. Geochemistry Geophysics Geosystems, 2: 10.1029/2000GC000136.
Higgins, M. D., 2002- Closure in crystal size distribution (CSD), verification of CSD calculations and the significance of CSD fans. American Mineralogist, 87, 160–164.
Higgins, M. D. & Roberge, J., 2003- Crystal size distribution (CSD) of plagioclase and amphibole from Soufriere Hills volcano, Monteserrat: evidence for dynamic crystallization textural coarsening cycles. Journal of Petrology, 44: 1401-1411. .
Higgins, M. D., 1994- Numerical modeling of crystal shapes in thin sections: estimation of crystal habit and true size. American Mineralogist, 79: 113–119.
Higgins, M. D., 1996- Magma dynamics beneath Kameni Volcano Thera Greece, as revealed by crystal size and shape measurements. Journal of Volcanology and Geothermal Research, 70: 37-48.
Higgins, M. D., 1998- Origin of  anorthosite by  textural  coarsening: quantitative measurements of  ural sequence of textural development. Journal of Petrology 39: 1307–1325.
Higgins, M. D., 2000- Measurement of crystal size distributions. American Mineralogist, 85: 1105- 1116 .
Higgins, M. D., 2006- Quantitative textural measurement in igneous and metamorphic petrology. Cambridge university press, 265p.
Jerram, D. A. &Higgins, M. D., 2007- 3D analysis of rock textures: Quantifying igneous microstructures. ELEMENTS. 3: 239-245.
Marsh, B., 1988- Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization I. Theory Contributions to Mineralogy and Petrology, 99: 277–291.
Marsh, B. D, 1998-  On the interpretation of crystal size distribution in magmatic systems. Journal of Petrology, 39, 553-599.
Mock, A. & Jerram. D. A., 2005- Crystal Size Distributions (CSD) in Three Dimensions: Insights from the 3D Reconstruction of a Highly Porphyritic Rhyolite. Journal of Petrology, 46: 1-17.
Monfaredi, B., Masoudi, F. & Tabbakh, A. A., 2009- Magmatic Interaction as Recorded in Texture and Composition of Plagioclase Phenocrysts from the Sirjan Area, Urumieh-Dokhtar Magmatic Arc, Iran. Journal of Sciences, Islamic Republic of Iran, 20: 243-251.
Morgan, D. J. & Jerram, D. A., 2006- On estimating crystal shape for crystal size distribution analysis. Journal of Volcanology and Geothermal Research, 154: 1–7.
Peterson, T. D., 1996- A refined technique for measuring crystal size distribution in thin section. Contributions to  Mineralogy and Petrology, 7: 99-105.
Proussevitch, A. A. & Sahagian, D. L., 2001- Recognition and separation of discrete objects within complex 3D voxelized structures. Computers & Geosciences, 27: 441–454.
Randolph, A. D. & Larson, M. A., 1971- Theory of Particulate Processes, Academic Press, New York. 251 p.