MM Magma Chamber Handout rev 10-2022
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Orange Coast College *
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A110
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Geology
Date
Jan 9, 2024
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docx
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Differentiation of Magmas By Fractional Crystallization
Objective
The objective of this exercise is to gain first-hand knowledge of the process of magmatic differentiation by fractional crystallization. The activity also provides an opportunity to utilize your knowledge of mineral stoichiometry, apply the IUGS classification system, and work with spreadsheets.
A Bit of History and Terminology
In the course you will learn about Bowen’s reaction series and the importance of crystal-melt fractionation in generating the spectrum of observed igneous rock compositions (e.g., basalt, andesite, rhyolite). Magmatic differentiation
is the process by which diverse rock types are generated from a single magma. Differentiation is accomplished by crystal-melt fractionation
, a two-stage process that involves the formation and mechanical separation of compositionally distinct phases. In 1844 Charles Darwin described flows from the Galápagos Islands in which the
lowest flows contained greater proportions of feldspar crystals. These observations led Darwin to propose that density differences between crystals and melt would result in mechanical separation of these two phases and the formation of different magma types. This process, known today as gravity settling, was the focus of detailed experimental studies by N.L. Bowen. Constructing the Magma Chamber (DONE IN CLASS)
1.
Each major cation (e.g., Si, Ti, Al) will be represented by a different M&M
color. If needed, count out the appropriate number of M&Ms for each cation (refer to data sheet). Mix the M&M’s and pile them in your magma chamber.
Crystallization and Fractionation of the Magma (DONE IN CLASS – SEE PHOTOS ON CANVAS)
2.
Before you begin, note the general proportions of the different cations (colors) in the magma chamber. Determine the composition and stoichiometry of each of the minerals involved in the crystallization process using the first table on the spreadsheet (on Canvas). 3. For the first increment of crystallization, move the appropriate number of M&Ms from the magma chamber to the “floor” of the magma chamber. For each cation, record the number that remains in the magma chamber in the appropriate table on the spreadsheet.
4.
For each increment of crystallization, move the appropriate number of cations (M&Ms) from the melt to the floor of the chamber and complete the table. (
Note
: it is helpful to group the cations that were removed in each crystallization step in separate layers. In other words, move the M&Ms that were crystallized during the first step the furthest away
from the magma chamber; cations from each additional crystallization step will be successively closer to the magma chamber.)
5.
After each crystallization step, you should observe the proportions of the different colors of cations (M&Ms) in the remaining liquid and in the cumulus layers, recording this data in your tables as well.
6.
Before your experiment is dismantled (or consumed), describe the general trends you observed during the fractional crystallization of the magma
. This is your chance to ask questions and double-check your work during the experiment!
Analyzing the Results (SUBMIT TO CANVAS PORTAL – DATA SHEET AND CHARTS)
7.
Complete each data table and enter your data into a spreadsheet (provided on Canvas).
8.
Generate x-y plots of the following:
a. % Al, Mg, Fe, Ca, Na, K, and Ti remaining in the melt versus % magma remaining
b.
These plots are already generated in the Excel worksheet (you may need to modify the spreadsheet to connect the data sets to the plots) Reflecting on What You’ve Learned (SUBMIT TO CANVAS PORTAL – REFLECTION QUESTIONS)
A. With reference to Bowen’s Reaction Series, compare the chemistry of the minerals removed at the beginning of crystallization with those removed in the middle and at the end of crystallization. (1 pt)
-At the beginning of crystallization is was only olivine crystalizing because of the temp. Once we started getting cooler we see more minerals crystallizing. Magnesium primarily with silicon to form mg-olivine but towards the middle it started opting to bond with other chemicals where we see pyroxene get introduced. It was finally towards the end where the chemical comps
quartz happening.
B. Which elements increase in relative abundance in the remaining liquid over time? (1 pt)
- Relative abundance would be silicon and calcium where there overall abundance increased from the start of the cooling.
C. Which elements decrease in relative abundance in the remaining liquid over time? (1 pt)
- The Elements that decrease are aluminium, Iron, magnesium, and sodium
D. Are there any elements that display more complex behavior? If so, briefly describe the pattern. (1 pt)
-Sodium naturally abundance was increasing throughout the time but it was only at the end it decreased.
E. Explain how the concentration of silicon (Si) in the remaining liquid can increase during crystallization, even though almost all of the minerals being removed are silicates? (1 pt)
- Because the overall percent of other minerals were taken. Each time silicon is used its only a small portion because of its starting size. Where other minerals were taken at a faster rate
due to high amounts and lower starting amount.
F. Using the classification of magmas discussed on the separate handouts (on Canvas), based on the amount of SiO2 (or Si in this case) assign a name (i.e. basalt, andesite, rhyolite) to the initial liquid magma, and the liquid remaining after the 2
nd
, 6
th
, and 10
th
crystallization steps. (2 pts)
- I think it goes from basalt, to basaltic andesite, finally to andesite.
G. Using an appropriate igneous rock classification diagram, assign a rock name to the igneous rocks produced by fractional crystallization during the 2
nd
, 4
th
, 6
th
, 8
th
, and 10
th
stages of crystallization. (2 pts)
- I think step 2 is ultramafic/mafic. Step 4 and 6 are mafic and intermediate. Step 8 is between intermediate/felsic and step 10 is in felsic.
H. Reflect on the activity. What surprised you? What are you more interested in learning about? How has this activity impacted your understanding of the processes of fractional crystallization or magma evolution in general? (1 pt)
- It was interesting to see how the m&m represented the elements that form these rocks
and what share they make up in the lava. Im interested in why they prefer to bond to one another at the different temps and what makes them bond. Its very cool to see what magma really is and not just hot orange stuff.
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