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Igneous Rock Textures GLY Spring, 2012

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Presentation on theme: "Igneous Rock Textures GLY Spring, 2012"— Presentation transcript:

1 Igneous Rock Textures GLY 4310 - Spring, 2012
Petrology Lecture 3 Igneous Rock Textures GLY Spring, 2012

2 Primary Form during solidification
They result from interactions between mineral crystals and melt

3 Secondary Develop by alteration of the rock after crystallization

4 Nucleation Clusters of a few tens of ions are essentially all surface
Ratio of surface area/volume is fantastically high Ions on the surface have unbalanced charges because they are not surrounded completely by other ions, and are easily disrupted Nucleation usually requires undercooling

5 Growth Involves the addition of ions to the nucleated cluster
Some crystals have preferred directions of growth

6 Rate of Diffusion Controls movement of ions in many magmas
Determines the rate of dissipation of the heat of crystallization

7 Cooling Rate Slow cooling allows system to maintain thermodynamic equilibrium Rapid cooling contributes to a non-equilibrium system

8 Nucleation vs. Growth

9 Blue Glassy Pahoehoe Large embayed olivine phenocryst with smaller plagioclase laths and clusters of feathery augite nucleating on plagioclase. Magnification ca. 400 X. © John Winter and Prentice Hall.

10 Blue Glassy Pahoehoe Feathey quenced augite crystal nucleating on plagioclase and growing in a semi-radiating form outwards Mag. 2000x © John Winter and Prentice Hall.

11 Available Liquid The volume of liquid available to the edge of a crystal is larger than to a face, and a corner has even greater available liquid. (left) The end of a slender crystal will have the largest available liquid. (right) b a © Chapman and Hall. London.

12 Zoned Hornblende © John Winter and Prentice Hall. Field of view 1 mm

13 Zoned Plagioclase Carlsbad twin Field of view o.3 mm
© John Winter and Prentice Hall. Carlsbad twin Field of view o.3 mm

14 Grain Shape Mineral Term Rock Term Euhedral Idiomorphic
Subhedral Hypidomorphic Anhedral Xenomorphic

15 Euhedral Crystal © John Winter and Prentice Hall. Euhedral early pyroxene with late interstitial plagioclase Field of view 5 mm

16 Dimension Relationships
Mineral term Rock term Equant Massive Prismatic Lineated Tabular Foliated

17 Ophitic Texture Pyroxene envelops plagioclase laths Field of view 1 mm
© John Winter and Prentice Hall. Pyroxene envelops plagioclase laths Field of view 1 mm

18 Granophyric Texture Quartz-alkali fldspar intergrowth
© John Winter and Prentice Hall. Quartz-alkali fldspar intergrowth Field of view 1 mm

19 Graphic Texture © John Winter and Prentice Hall. Single crystal of cuniform quartz intergrown with alkali feldspar

20 Pyroxene Replacing Olivine
Left – Olivine mantled by pyroxene, ppl Right – CN – Olivine is extinct, Opx stands out © John Winter and Prentice Hall.

21 Dehydration Rim © John Winter and Prentice Hall. Hornblende phenocryst dehrates to Fe-oxides plus pyroxene due to pressure release on eruption Width 1 mm

22 Embayed Texture Field of view 0.3 mm
© John Winter and Prentice Hall. Field of view 0.3 mm Partially resorbed olivine phenocryst

23 Sieve Texture Plagioclase phenocrysts Field of view 1 mm
© John Winter and Prentice Hall. Plagioclase phenocrysts Field of view 1 mm

24 Trachytic Texture Sub-parallel alkali feldspar laths form sheaves and swirls around earlier-crystallised minerals CN, medium power

25 Pilotaxic or Felty Texture
© John Winter and Prentice Hall. Microphenocrysts are randomly aligned

26 Flow Banding Andesite, Mt. Rainier Long-handled hammer for scale
© John Winter and Prentice Hall. Andesite, Mt. Rainier Long-handled hammer for scale

27 Intergranular Texture
© John Winter and Prentice Hall. Columbia River Basalt Group Width 1 mm

28 Carlsbad Twin Form as the result of mistakes during growth
© John Winter and Prentice Hall. Form as the result of mistakes during growth Field of view ≈ 1 mm

29 Albite Twinning © John Winter and Prentice Hall. Also thought to be form as the result of mistakes during growth Field of view ≈ 1 mm

30 Tartan Twinning Microcline Field of view ≈ 1 mm
© John Winter and Prentice Hall.

31 Deformational Albite Twinning
© John Winter and Prentice Hall. Typically occurs in nearly pure Ab Note that twins “pinch-out” at the edge Width 1 mm

32 Exsolution Textures Perthite - The host is K-spar, with albite lamellae appearing as a coherent intergrowth Coherent means the exsolved phase lattices have a specific relationship to the host lattice. Antiperthite - The host is albite, with K-spar lamellae showing a coherent intergrowth

33 Types of Perthite In perthite, intergrowths may sometimes be seen by the unaided eye In microperthite, however, they are distinguishable only microscopically In cryptoperthite the crystals are so small that the separation can be detected only by X-ray diffraction Perthite was originally thought to be a single mineral, described at a locality near Perth, Ontario, from which its name is derived

34 Bronzite Photomicrograph
Bronzite crystal from an ultramafic rock Thin lamellae of a calcium-rich species, probably pigeonite, have separated from the bronzite, and the host (grayish) thus has a very low calcium content (magnified about 40×) By courtesy of G. Malcolm Brown —EB Inc., from Encyclopædia Britannica Deluxe Edition 2005 CD. Copyright © Encyclopædia Britannica, Inc.

35 Augite - Pigeonite Complex separation of augite from an inverted pigeonite (magnified about 70.4×) By courtesy of G. Malcolm Brown —EB Inc., from Encyclopædia Britannica Deluxe Edition 2005 CD. Copyright © Encyclopædia Britannica, Inc.

36 Ocelli Liquid immiscibility can produce spherical to ovoid inclusions, ranging in size from mm's to a few cm's Intermixing of magmas may form ocelli by the suspension of blobs of one magma in another

37 Post-Solidification Processes
Autometamorphic Deuteric Diagenetic

38 Deuteric Reactions Uralization Biotitization Chloritization
Symplectite Biotitization Chloritization Seritization Saussuritization Serpentization

39 Uralite Pyroxene largely replaced by hornblende Width 1 mm Pyx Hbl
© John Winter and Prentice Hall Pyroxene largely replaced by hornblende Width 1 mm

40 Chloritization © John Winter and Prentice Hall Photo John D. Winter Chlorite (light) replaces biotite (dark) at the rim and along cleavages Width 0.3 mm

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