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Understanding Magma: Classification, Textures, and Genesis

Explore the world of magma, from its composition to formation stages, with diagrams and explanations to deepen your knowledge of igneous rocks.

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Understanding Magma: Classification, Textures, and Genesis

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  1. Magma, Rocks Classification & Textures

  2. MAGMA

  3. MAGMA • Larutan silikat yang sangat panas • Mengandung oksida, sulfida serta volatiles (CO2, sulfur, chlorine, fluorin, boron dll) • Temperatur antara 600°C (magma asam) sampai 1250°C (magma basa)

  4. JENIS KONVERGEN

  5. 7 3 2 5 1 4 6 200 km Continental Crust Oceanic Crust 400 Source of Melts Lithospheric Mantle ? ? ? ? Sub-lithospheric Mantle 600 km Plate Tectonic - Igneous Genesis

  6. Environments of Magma Formation

  7. Environments of Magma Formation

  8. Stages in ascent • Eruption • (Fragmentation) • Vesiculation • Renewed ascent • Storage • mixing • assimilation • crystallization • Buoyant ascent • Partial melting

  9. Crust Depth (km) The Earth’s Interior 60 Upper Mantle 220 410 Transition Zone 660 Mantle Crust: Granite/Andesite (felsic) Mantle: Peridotite (ultramafic) Core: Metal alloy/liquid Lower Mantle 2898 Outer Core (liquid) Core 5145 Inner Core (solid) 6370

  10. Ca Al S Si 1.4% 3.0% 1.0% 14.4% O 50.7% Fe 15.2% Mg 15.3% Most important elements Figure 1-5. Relative atomic abundances of the seven most common elements that comprise 97% of the Earth's mass. An Introduction to Igneous and Metamorphic Petrology, by John Winter , Prentice Hall.

  11. Partial Melting: The Origin of Basalt and Granite Basaltic magma = 50% silica (1100o C) Forms the rock basalt Melting Asthenosphere 40% Silica

  12. Partial Melting: The Origin of Basalt and Granite Granitic magma ~ 70% silica (700-900o C) Forms granite (a mixture of quartz and feldspar) Melting Continental Crust (Mainly low melting point minerals such as quartz, feldspar, mica)

  13. Urutan pembekuan magma • Padapembekuan magma, padaawalnya mineral yang terbentukadalah yang anhydrous (tidakmengandung air)  tidakmengandunggugus OH, disebut mineral pyrogenetik. • Cairanselanjutnyaakanlebihbanyakmengandungkomponen gas danterbentuk mineral-mineral yang mengandunggugusanhydroksil (OH), disebut mineral hydratogenetik.

  14. Diferensiasi Magma • Prosesdiferensiasimeliputisemuakegiatan yang mengakibatkansuatujenis magma induk yang semularelatifhomogenterpecah-pecahmenjadibeberapabagianataufraksidengankomposisi yang berbeda-beda. Hal inidisebabkankarenamigrasi ion ataumolekuldalamlarutan magma karenaadanyaperubahantemperaturdantekanan. Yang padaakhirnyaakanmembentukberbagaijenisbatuanbekudengankomposisi yang berbeda-beda pula.

  15. Bowen reaction series

  16. DIAGRAM FASE • Fase : padat, cair, gas • Diagram fase : menggambarkan kondisi magma pada kondisi P & T tertentu • Parameter penting dalam sistem magma : fase, komponen, variabel intensif

  17. DIAGRAM fASE • fase : padat, cair • komponen : komponen terkecil yang diperlukan utk pembentukan fase-fase • dalam sistem (OH, H2O, MgO, NaAlSi3O8, dll) • variabel intensif : temperatur dan tekanan, jumlah komponen

  18. DIAGRAM FASE • Rumus fase : F = C – P + 2 • F : degree of freedom : jumlah kondisi minimum • C : jumlah komponen; • P : jumlah fase • contoh utk air – es ------ C = 1 (H2O) ; P = 2 (es dan air) • F = C – P + 2 ---- F = 1 – 2 + 2 = 1 (unary system)

  19. SISTEM 1 KOMPONEN

  20. SISTEM 2 KOMPONEN (BINER) DGN TITIK EUTEKTIK h : titik eutektik; titik terendah fase cair ; kondisi terbentuknya 2 komponen

  21. SISTEM 2 KOMPONEN SOLID - SOLUTION

  22. SISTEM 2 KOMPONEN INCONGRUENT MELTING

  23. Why storage? Why do some magmas stall and pond in chambers during ascent? crust denser stronger crust

  24. Processes during storage in magma chambers Fractional Crystallization http://www.geolsoc.org.uk/webdav/site/GSL/shared/images/geoscientist/Geoscientist%2019.2/7%20Volcano%20and%20magma%20chamber%20James%20Island2resized.jpg

  25. Processes during storage in magma chambers Gravity settling http://www.geolsoc.org.uk/webdav/site/GSL/shared/images/geoscientist/Geoscientist%2019.2/7%20Volcano%20and%20magma%20chamber%20James%20Island2resized.jpg

  26. Gravity settling and cumulates http://www.geol.lsu.edu/henry/Geology3041/lectures/12LayeredMafic/Fig12-15.jpg

  27. Buoyancy, sinking: Stoke’s Law r - r 2 2gr ( ) = s l V = the settling velocity (cm/sec) g = the acceleration due to gravity (980 cm/sec2) r = the radius of a spherical particle (cm) rs = the density of the solid spherical particle (g/cm3) rl = the density of the liquid (g/cm3) h = the viscosity of the liquid (1 c/cm sec = 1 poise) V h 9

  28. Sinking olivine in basalt Olivine in basalt • Olivine (rs = 3.3 g/cm3, r = 0.1 cm) • Basaltic liquid (rl = 2.65 g/cm3, h = 1000 poise) • V = 2·980·0.12 (3.3-2.65)/9·1000 = 0.0013 cm/sec • that’s ~1m per day

  29. Sinking x’talin rhyolite Rhyolitic melt • h = 107 poise and rl = 2.3 g/cm3 • hornblende crystal (rs = 3.2 g/cm3, r = 0.1 cm) • V = 2 x 10-7 cm/sec, or 6 cm/year • feldspars (rl = 2.7 g/cm3) • V = 2 cm/year • = 200 m in the 104 years that a stock might cool • If 0.5 cm in radius (1 cm diameter) settle at 0.65 meters/year, or 6.5 km in 104 year cooling of stock

  30. IGNEOUS ROCKS CLASSIFICATION

  31. Ternary diagrams

  32. Classification of Igneous Rocks Figure 2-1a. Method #1 for plotting a point with the components: 70% X, 20% Y, and 10% Z on triangular diagrams. An Introduction to Igneous and Metamorphic Petrology, John Winter, Prentice Hall.

  33. Know how to classify a rock

  34. Volcanic rocks: aphanitic

  35. Ultra-mafic rocks & felsic vs. mafic

  36. Olivine Dunite 90 Peridotites Wehrlite Lherzolite Harzburgite 40 Pyroxenites Olivine Websterite Orthopyroxenite 10 Websterite 10 Clinopyroxenite Orthopyroxene Clinopyroxene Classification of Igneous Rocks Figure 2-2. A classification of the phaneritic igneous rocks. b. Gabbroic rocks. c. Ultramafic rocks. After IUGS. (c)

  37. Classification of Igneous Rocks Figure 2-4. A chemical classification of volcanics based on total alkalis vs. silica. After Le Bas et al. (1986) J. Petrol., 27, 745-750. Oxford University Press.

  38. Classification of Igneous Rocks Ash (< 2 mm) Lapilli (2-64 mm) Lapilli- Tuff stone Lapilli Tuff 30 30 Lapilli - Tuff Breccia 70 70 Pyroclastic Breccia or Agglomerate Blocks and Bombs (> 64 mm) (b) Figure 2-5. Classification of the pyroclastic rocks. a.Based on type of material. After Pettijohn (1975) Sedimentary Rocks, Harper & Row, and Schmid (1981) Geology, 9, 40-43. b.Based on the size of the material. After Fisher (1966) Earth Sci. Rev., 1, 287-298.

  39. TEXTURES IN IGNEOUS ROCKS

  40. Textures: result of nucleation+growth

  41. Grain size

  42. a Fast growth Ocean Drilling Program

  43. Crystal zoning

  44. Crystal shape

  45. Growth order

  46. Quartz - feldspar intergrowth

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