1 / 21

Diversification of Magmas

Diversification of Magmas. Today. Updates: Have fun next week Topics: Evolving melt compositions: Partial melting Fractional crystallization Crystal settling Cumulates. Magmatic Differentiation. ?. B. A. Magmatic Differentiation. Partial Melting. Anorthite. M. T. Forsterite.

adara
Download Presentation

Diversification of Magmas

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Diversification of Magmas

  2. Today • Updates: • Have fun next week • Topics: • Evolving melt compositions: • Partial melting • Fractional crystallization • Crystal settling • Cumulates

  3. Magmatic Differentiation ? B A

  4. Magmatic Differentiation

  5. Partial Melting

  6. Anorthite M T Forsterite Effects of only partially melting+segregating

  7. Partial melt and grain boundaries The ability to form an interconnected film is dependent upon the dihedral angle () a property of the melt Figure 11-1 After Hunter (1987)In I. Parsons (ed.), Origins of Igneous Layering. Reidel, Dordrecht, pp. 473-504.

  8. Minimum amount of melt http://www.ldeo.columbia.edu/~benh/matos/portfolio/index_rocks.html http://www.whoi.edu/oceanus/viewImage.do?id=4981&aid=2390

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

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

  11. Processes during storage in magma chambers

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

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

  14. Gravity settling and cumulates

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

  16. Frax crystallization example: majors Melt Cumulate Figure 11-2 After Murata and Richter, 1966 (as modified by Best, 1982)

  17. Buoyancy, sinking: Stoke’s Law 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) r - r 2 2gr ( ) = s l V h 9

  18. 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

  19. Sinking xls in 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

  20. Caution

  21. Consequences Figure 11-3 From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall

More Related