Sieve Texture

Plagioclase commonly exhibits a variety of disequilibrium textures in volcanic rocks, especially in orogeny andesites. These textures often include combinations of complex zoning patterns and resorption feature in plagioclase e that record changing physical conditions in magmatic system. Sieve texture is common in plagioclase or in pyroxene crystals in extrusive volcanic rocks; It is interpreted by some authors as the result of mixing processes(Nixon e Pearce, 1987). the above interpretation are reinforced by the experiments of Tsuchiyama, 1985 (see diagram 1).

If the An % of the phenocryst (plagioclase 1 and 2) is less than the plagioclase (plagioclase 3) in equilibrium with the melt (M), the corroded surface becomes very rough and finely indented to form a sieve texture, which is filled with magma, and in which plagioclase (plagioclase 1 and 2)reacts to become more calcic.
If basic and acid magma mix, sodic feldspar in the acid magma dissolves, develops sieve texture and the corroded parts react to become more calcic, when crystallization eventually resumes, the Sieve texture is coated by euhedral growth of more calcic plagioclase. Calcic plagioclase in the more basic magma simply continues to grow becomes more sodic (plagioclase 4).

It is also possible to achieve solution by decompression as magma rise toward the surface (Pearce et al.,1987), in which case there should be no evidence that corrosion was accompanied by change in the composition of the magma. In the case of feldspar, dissolutions takes place in hydrous magma because the liquidus and solidus curves are depressed as pressure decrease and volatiles are released.

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Diagram 1Results of mixing plagioclase crystals of various compositions with magma of composition M that is in equilibrium with a plagioclase of composition 3. A): Crystals of composition 1, mixed with M; crystals may melt, but in any case dissolve to give rounded shapes. If M penetrate the dissolving crystals (1), or if partial melting occurs internally, sieve texture is produced as (1) react with the melt to form more calcic rim (no more calcic than 3).
B): Crystals of composition (2) cannot melt completely and cannot simply dissolve in M, but they will react during partial solution or melting, to give a sieve texture and more calcic rim (no more calcic than 3). The former euhedral outline is preserved.
C): Crystals of composition (4) continue to grow with euhedral overgrowth of composition (3). From Shelley





Bibliography



• E. WM. Heinrich (1956): Microscopic Petrografy. Mcgraw-hill book company,inc
• David Shelley (1983): Igneous and metamorphic rocks under the microscope. Campman & Hall editori.
• Cox et al. (1979): The Interpretation of Igneous Rocks, George Allen and Unwin, London.

Photo
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Sieve texture in clinopyroxene. PPL image, 10x (Field of view = 2mm)
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Sieve texture in clinopyroxene. XPL image, 10x (Field of view = 2mm)
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Sieve texture in clinopyroxene. PPL image, 10x (Field of view = 2mm)
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Sieve texture in clinopyroxene. XPL image, 10x (Field of view = 2mm)
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Sieve texture in clinopyroxene. XPL image, 10x (Field of view = 2mm)
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Sieve texture in clinopyroxene. XPL image, 10x (Field of view = 2mm)
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Sieve texture in clinopyroxene. XPL image, 10x (Field of view = 2mm)
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Sieve texture in clinopyroxene. XPL image, 10x (Field of view = 2mm)
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Sieve texture in clinopyroxene. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystals with sieve texture. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. XPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. XPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Pyroxene crystal with sieve texture. XPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. XPL image, 10x (Field of view = 2mm)
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Plagioclase crystals with sieve texture. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. XPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. XPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. PPL image, 10x (Field of view = 2mm)
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Resorbed Plagioclase crystal with sieve texture. XPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture. PPL image, 20x (Field of view = 1mm)
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Plagioclase crystal with sieve texture, karapinar, Anatolian peninsula. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystals with sieve texture, karapinar, Anatolian peninsula. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture, karapinar, Anatolian peninsula. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture, karapinar, Anatolian peninsula. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture, karapinar, Anatolian peninsula. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture, karapinar, Anatolian peninsula. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystals with sieve texture, karapinar, Anatolian peninsula. PPL image, 2x (Field of view = 7mm)
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Hornblende and Plagioclase crystal with sieve texture from Bulgaria. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from Bulgaria. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from Bulgaria. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from Bulgaria. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from Bulgaria. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystals with sieve texture from Bulgaria. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystals with sieve texture from Bulgaria. PPL image, 10x (Field of view = 2mm)
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Plagioclase crystal with sieve texture from Bulgaria. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from Bulgaria. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from Bulgaria. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from Bulgaria. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from euganean hills, italy. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from euganean hills, italy. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from euganean hills, italy. XPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from euganean hills, italy. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from euganean hills, italy. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from euganean hills, italy. XPL image, 2x (Field of view = 7mm)
plg(sieve)(7).jpg

Plagioclase crystal with sieve texture from euganean hills, italy. PPL image, 2x (Field of view = 7mm)
plg(sieve)(8).jpg

Plagioclase crystal with sieve texture from euganean hills, italy. XPL image, 2x (Field of view = 7mm)
plg(sieve)(9).jpg

Plagioclase crystal with sieve texture from euganean hills, italy. PPL image, 2x (Field of view = 7mm)
plg(sieve)(11).jpg

Plagioclase crystal with sieve texture from euganean hills, italy. PPL image, 2x (Field of view = 7mm)
plg(sieve)(12).jpg

Plagioclase crystal with sieve texture from euganean hills, italy. PPL image, 2x (Field of view = 7mm)
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Plagioclase crystal with sieve texture from euganean hills, italy. PPL image, 2x (Field of view = 7mm)