1. Final cooling and textures of igneous rocks (mostly plutonic)

2. Growth and nucleation Textures related to the crystallization sequence Textures related to the chemical evolution of the magma during cooling Textures related to deformation in a partially molten system Textures related to sub-solidus deformation Sub-solidus textures

3. 1- Growth and nucleation Textures related to the growth rate of crystals

4. Nucleation and growth Many nuclei Few nuclei

5. Growth and nucleation rates are a function of the degree of undercooling Strong undercooling = Nucleation >> growth (fine texture) Moderate undercooling = Growth >> nucleation (coarse texture)

6. Plutonic and volcanic textures

7. Glass, groundmass Groundmass= microcrystals Glass= No crystals

8. Porphyritic textures 2 Grain-size populations = 2 growth events? (magma chamber & eruption)

9. Porphyroid textures Faster growth, or earlier crystals?

10. Aplites & pegmatites Close association of (very) coarse pegmatites and (very) fine aplites Water influences both nucleation and growth rates => complex, highly variable grain size associations

11. A complex pegmatite body

12. 2- Textures related to the crystallization order

13. 1274 Di 2040 60 80 An 1200 1300 1400 1500 1600 T o C Anorthite + Liquid Liquid Liquidus Diopside + Liquid Diopside + Anorthite 1553 1392 Wt.% Anorthite

14. Figure 3-7. Euhedral early pyroxene with late interstitial plagioclase (horizontal twins). Stillwater complex, Montana. Field width 5 mm. © John Winter and Prentice Hall.

15. Figure 3-8. Ophitic texture. A single pyroxene envelops several well- developed plagioclase laths. Width 1 mm. Skaergård intrusion, E. Greenland. © John Winter and Prentice Hall.

16. Poekilitic texture Crystallization sequence Biotite > Feldspar

17. Simultaneous growth Classical eutectic diagram. First minerals are either Qz or K-spar Then, at the eutectic…

18. Micrographic textures

19. Graphic texture: coeval growth of quartz and K-spar

20. Figure 3-9. a. Granophyric quartz-alkali feldspar intergrowth at the margin of a 1-cm dike. Golden Horn granite, WA. Width 1mm. b. Graphic texture: a single crystal of cuneiform quartz (darker) intergrown with alkali feldspar (lighter). Laramie Range, WY. © John Winter and Prentice Hall.

21. 3- Textures related to the evolution of the magma during cooling

22. Igneous Textures Figure 3-5. a. Compositionally zoned hornblende phenocryst with pronounced color variation visible in plane-polarized light. Field width 1 mm. b. Zoned plagioclase twinned on the carlsbad law. Andesite, Crater Lake, OR. Field width 0.3 mm. © John Winter and Prentice Hall.

23. Zoned K-spar (Hercynian granite, France)

24. Binary diagrams with complete solid solution 1118 Ab204060 80 An 1100 1200 1300 1400 1500 1557 T C o Plagioclase Liquid plus L i q u i d u s S o l i d u s Weight % An Plagioclase The crystals formed change composition as the liquid cools (and changes its composition too)

25. Complex zoning A complex sequence of cryst. And magma chamber « refill »

26. Figure 3-6. Examples of plagioclase zoning profiles determined by microprobe point traverses. a. Repeated sharp reversals attributed to magma mixing, followed by normal cooling increments. b. Smaller and irregular oscillations caused by local disequilibrium crystallization. c. Complex oscillations due to combinations of magma mixing and local disequilibrium. From Shelley (1993). Igneous and Metamorphic Rocks Under the Microscope. © Chapman and Hall. London. Complex zonings

27. Plag sieving

28. Crystal resorption

29. Everything is not chemical effects!! Fast ascent can also dissolve crystals…

30. 4- Textures related to deformation of a partially molten system Movements in a partially molten « mush » Syn-plutonic deformation

31. Magmatic flow

32. Late magma movement Leucocratic magma expulsed from the cooling « mush »

33. « ellipsoids », « snail structures », « diapirs » www.earth.monash.edu.au/~weinberg

34. Pipes of late magmatic liquids in the mush

35. K-feldspar accumulation (flow segregation?)

36. Rheology of partially molten systems

39. Magmatic foliation « Proto-shear zone » Shear zones with late melts Shear zones filled with aplites and pegmatites C/S structures Orthogneissification Outcrop-scale structures Closepet granite, south India (2.5 Ga)

40. MagmaticSub-solidus Micro-structures

41. Quartz subgrains

42. Qz grain-size reduction

43. Continuous sequence of textures Feldspar alignment/accumulation Expulsion of late melts Strain partitionning on the latest melts C/S movement on weak planes (phyllosilicates) Ductile deformation of quartz (sub-grains, etc.) Orthogneissification, deformation/recrystallization of all minerals

45. Sub-solidus evolution

46. Mineral transformations Secondary minerals Fluids expulsion and movement –Pegmatite/aplite veins –Mineralized veins Hydrothermal alteration –Episyenites, endoskarns, greisens –Exoskarns

47. Mineral transformations Polymorphs Exsolutions (solvus)

48. Phase diagram for SiO 2

49. Feldspar solvus

50. Perthites

51. Opx-Cpx exsolution

52. Secondary minerals « Autometamorphism »

53. Water-saturated solidus (granites)

54. Secondary minerals Px => Amp => Bt Px, Amp, Bt => chlorite (phyllosilicate) K-feldspar, feldspathoids => sericite (fine white mica) Ca-plagioclase => saussurite (epidote) Olivine => serpentine (complex phyllosilicate), iddingsite (a mixture of various Fe-Mg silicates)

55. Figure 3-20. a. Pyroxene largely replaced by hornblende. Some pyroxene remains as light areas (Pyx) in the hornblende core. Width 1 mm. b. Chlorite (green) replaces biotite (dark brown) at the rim and along cleavages. Tonalite. San Diego, CA. Width 0.3 mm. © John Winter and Prentice Hall. Pyx Hbl Bt Chl

56. Sericitization K-feldspar to sericite: 3 KAlSi 3 O 8 + 2 H + > KAl 3 Si 3 O 10 (OH) 2 + 6 SiO 2 + 2 K +

57. Saussuritization Dolerite from ODP leg 180 (sea of Java)

58. Olivine with iddingsite alteration

59. Calcite vein

60. Fluid expulsion Typical water contents: 2-4% in a granite Water content of a biotite: ~2 % Biotite: max. 5-10 % of the rock Excess water = ? + meteoric water also feeding the hydrothermal system

61. Hydrothermal circulations Most of the water in hydrothermal systems comes from meteoric, surface waters (cf. O isotopes, G214)

62. Effect of free, hot water Overpressure, fractures, etc. Very aggressive solvent! Aplite/pegmatite veins

63. Pegmatites recording the same strain pattern as ductile structures Cape de Creus, Spain

64. Quartz solubility in hydrothermal fluids G.B. Arehart, http://equinox.unr.edu/homepage/arehart/Courses/713/Syllabus.htm 0.5 mol/kg water = 30 g/l 1 km 3 of pluton At 3 wt% H2O = 2.7 10 12 kg rock ≈ 10 11 kg water Can dissolve 3 10 9 kg of SiO 2, or 10 6 m 3

65. Composition of hydrothermal fluids G.B. Arehart, http://equinox.unr.edu/homepage/arehart/Courses/713/Syllabus.htm Acidic water dissolve less SiO 2 pH changes can precipitate SiO 2

66. Evidence for Si-rich hydrothermal fluids Tatio hydrothermal field, Peru

67. Network of pegmatites/apl ite dykes

68. Mineralized veins Very incompatible elements (large ions, typically) concentrated in last liquids, then in fluids The same elements are leached from an already cooled rock (igneous intrusion or its wall-rock) Precipitate with hydrothermal veins

69. Analysis of hydrothermal fluids from inclusions in pegmatites

70. Gold-quartz veins See economic geology (GEOL344)

71. pH control on solubility G.B. Arehart, http://equinox.unr.edu/homepage/arehart/Courses/713/Syllabus.htm Changes of pH can precipitate ore bodies: mixing with acid groundwater Interaction with rocks of very different chemistry (e.g., carbonates, very mafic rocks…)

72. Barberton gold fields

73. Hydrothermal modifications of rocks Around the intrusion –Exoskarns, etc. In the intrusive rocks –Episyenites –Endoskarns, greisens

74. Summary: deposits around a magmatic body

75. Around the pluton

76. Deposits by chemical reactions

77. Outside the pluton: skarn

80. In the pluton

81. pH control on solubility G.B. Arehart, http://equinox.unr.edu/homepage/arehart/Courses/713/Syllabus.htm High pH helps to dissolve SiO 2

82. In the pluton Loss of quartz => « syenites » (Episyenites)

83. Fedlspar alteration in the pluton K-feldspar to sericite: 3 KAlSi 3 O 8 + 2 H + > KAl 3 Si 3 O 10 (OH) 2 + 6 SiO 2 + 2 K + Sericite to kaolin: 2 KAl 3 Si 3 O 10 (OH) 2 + 2 H + + 3 H 2 0 > 3 Al 2 Si 2 O 5 (OH) 4 + 2 K + Requires acidic fluids!

84. In the pluton Episyenites are plutonic rocks from which the quartz has been dissolved away (therefore, they become syenites) (high pH) Greisens are plutonic rocks where the feldspar has been transformed into clays (kaolinite) by hydrothermal reactions (low pH)