Geol. 342. Petrology Homework:- - Present a neat report in a bound form

Objectives:. 1) Calculate normative composition of rocks. Plot normal and modal compositions by using IUGS schemes -Streckeisen (QAPF) diagrams, and identify the specific rock names.

2) Identify specific rock names from major oxide composition of rocks by using the IUGS scheme -LeBas (TAS).

3) Determine rock suites a) ultramafic, mafic, intermediate, and felsic types (silica saturation); b) peraluminous, peralkaline suites (alumina saturation).; c) Tholeiites, calcalkaline, and alkaline kindred (discrimination diagrams).

4) Determine the tectonic environments in which suites of igneous rocks formed.

5) Determine the origin of magmas, degrees of partial melting in magma generation, and if different rocks of a region are co-magmatic.

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Part A. Write the chemical formulae and specific characteristics such as color and cleavage of the common rock forming minerals, i. e. minerals found in Bowen's Reaction Principle, in Barrovian Sequence, and calcite, dolomite, pyrite, and hematite.

Part B. Present diagrams or maps that show the physiographic provinces of the Appalachians Division, and the mid province boundaries, which separate lithotectonic units of the Appalachians. Give details of the belts within the Eastern Blue Ridge sub-province. Present diagrams that show the lithotectonic units of Costa Rica. Use these maps to locate the tholeiitic and calcakaline rocks, which you will identify in subsequent questions.

Part C. Study the Chemical analysis of rocks from Costa Rica and USA. Samples from Southeastern USA are given at the bottom of the list. Samples A1 and A2 refer to analysis of rocks from Pumpkinvine Formation, just east of Allatoona Fault (a continuation of the Hayesville Thrust Fault) on I -75, GA, and B-1 refers to analyses of Corben Gneiss, a Grenvillian age rock at Red Top Mountain, just west of Allatoona Fault, GA. Winding Stair Gap is just east of Glade Gap, Chunky Gal Mountain, North Carolina on US- 64. Buck Creek dunite is just north of Glade Gap. Glade Gap, Winding Stair Gap, and Buck Creek are east of the Hayesville Thrust Fault.

Discrimination diagrams (Use Igpet99 software, and data in CostaRica-USA.xls.text)

1. Plot: K20 vs SiO2. [K20 increases away from a trench. The slope angle helps discriminate between tholeiites and calc alkaline suites.]

[Procedure. Double click on Igpet99 - from file open CostaRica-USA.xls.text [which may be within the Igpet99 folder or on desktop]. From Plot click on XY. For X-axis click on SiO2, for Y- axis click on K2O. A K20 SiO2 plot of all the data is displayed.

Learn the various ways of modifying the diagram and the type of data displayed.

a) Changing tick marks on the axis. Select Axes, change 10 to 1 tick interval, and click OK. Tick marks on X-axis are now at 1 wt.% SiO2 apart.

b) Finding regression curve. [If it is not already displayed, plot K2O vs SiO2.] Select Regress, read slope amount (0.08), click on Done, click on Diagram, click on use endpoints. The best fitting curve to the data is displayed. Click on delete the line to deselect the regression line and to return to previous position.

c) Identify data numbers on the plot. [If it is not already displayed, plot K2O vs SiO2.] Select Name to see or to remove data IDs of samples. Remove IDs. Click on ID ON, ID OFF until Next Prev, and Pick are active. Click on Pick to see the selection of IDs in a column, and double click on any ID number to find its position identified by a cross on the diagram. Click on Next or Prev to see the sample ID in a sequence. You could eliminate data points by going to the original data, which is entered in an excel or text-delimited data set, and either expunging the data or better yet by assigning a different pattern (by means of corresponding number under the K-column- see below on modifying data).

d) Modify the data set to be examined.

(d1)- Click on Symbol, see the numbers that correspond to symbols (e.g., 0 = small black circle; 1= unfilled green triangle, 2 = filled green triangle; 4 = filled blue triangle, 5 = unfilled diamond, 7 = unfilled red circle, 8 = filled red circle). This exercise will show you how to prepare your data for use with Igpet99. If you wish to change the patterns in the original data set, select from Igpet99 the numbers that correspond to symbols, go back to the original data set and enter the number that correspond to the selected pattern, under the K-column in the row adjacent to the sample ID (given under column S$). Change the pattern for sample Corben Gneiss from small circle to unfilled red diamond in the data set.

d2- Double click Igpet99 - File- CostaRica-USA.xls.text - Plot - XY - For plotting K20 vs SiO2, click on, for X- axis SiO2, for Y-axis click on K2O. K2O - SiO2 diagram appears. Click on Symbol, click on 8 to remove data set identified by filled Red circles, and click OK to view the diagram. The red circles are removed .

(1d2a) Click on Symbol, refresh, and deselect all, and click on # 8 to select only the filled red circles. Plot only the filled red circles, with their ID Numbers shown, and include the diagram in your report. Click on Label, and write a label for the diagram, place arrow at exactly the place that you wish to place the label. [To save the plot, you must enter a diskette in the computer. From Igpet99, click on Save, yes, open the diskette, and then save the diagram. You may export the diagram from your diskette to a drawing-software such as canvas, and work some more on your diagram.] The samples of filled red circles are siliciclastic sedimentary rocks. Which among them is a likely diatomaceous earth? What can be said about the alumina, amnesia, and silica content?

(1d2b) Plot only the data of igneous rocks from Costa Rica [Symbol, Refresh, click on 0, 1, 2, and 8 to deselect them}. Place a regression line on it, and include the diagram in your report by describing what the data show.

2) Plot: IUGS, TAS LeBas diagram.

Read data of CostaRica-USA.xls.text in Igpet, then click on Plot - Diagrams - double click PETROL.DGM, double click on TAS alkalies-silica LeBas et al, 86. The program plots all the data to show the names of the rocks.

(2a1) Select only the open circles of CostaRica-USA.xls.text . Show the ID numbers and include the plot in your report. Also, tabulate the Wt.% SiO2 values for ultramfic, mafic, intermdiate and felsic rocks. Give names of individual subalkaline volcanic rocks that correspond to ultramfic, mafic, intermediate, and felsic rocks. Give the ID numbers of at least one Costa Rica rock for each class of igneous rock as appropriate. Give the anticipated mineralogical composition for each rock by using a Bowen's Rection diagram as a guide.

(2a2) Give examples of alkali volcanic rock names for felsic, intermediate and mafic rock suites. Mark with bold blue line the slope values that separate alkali rocks from transitional ones, and the transition from subalkaline rocks. [Hint. Use Canvas to draw the line over the LeBas diagram]

(2b) Select only the filled blue symbols of Costa Rica rocks, and indicate the rock suites to which they belong. Include the plot and your response in the homework report.

3a) Plot: TAS (Total alkali versus silica) diagram.

Read data of CostaRica-USA.xls.text in Igpet99, then click on Plot, XY. For X-axis click on SiO2. For Y-axis click on A+B, then for A click on K2O, and for B click on Na2O, and then for Y-axis click on K2O + Na2O. This example shows you to use the calculator in Igpet99. The Diagram that appears shows all the data. Select only the ones for Costa Rica igneous rocks and include the result in your report by comparing it to the LeBas diagram.

3b) Alakali- Silica Cox-Bell-Pank, 79 - Identify which samples are picrite and which are andesite.

3C) SiO2-K20 andesite types Gill81-- Identify which samples are medium K and which are high K

3d) SiO2-F/M Miyashiro 74. This a preferred mode for distinguishing tholeiites from alkaline

3f) Nb/Y vs Zr/Ti Winchester and Boyd 1977

4) Plot: Harker and Fenner Diagrams [useful for determining co-magmatism (smooth curves) of continental and oceanic rocks, respectively, and magma mixing (straight lines)]

(4a) Plot a Harker Diagram for the filled red rocks of Costa Rica. Read data of CostaRica-USA.xls.text in Igpet, then click on Plot, Symbol (deselect all and select # 8), Diagrams, highlight HARKER.DGM, highlight Al203 vs SiO2, Done. Save the diagram. Do similarly for all the oxides. Resize the diagrams , and by using Canvas place them in a vertical sequence to show the variations. Describe if Harker Diagram indicates co-magmatism. [Plot all rocks on an Fe2O3 vs SiO2, place a regression curve, and discuss how linearity may not indicate co-magmatism]. [Optional: Plot Costa Rica tholeiitic rocks on a Fenner Diagram.]

5) Plot: AFM diagram. [Tholeiitic and calcalkaline differentiation trends]

(5a) Read data of CostaRica-USA.xls.text in Igpet, then click on Plot, Tri . For X left -variable click on A+B. for A click on Na2O, for B click on K2O, for x left -variable click on Na20 +K2O. [This gives A for alkalies]. For top apex, first click constant and enter 0.8889, then click on A*B, for A click on 0.8889, for B click on Fe2O3, this gives 0.8889 *Fe2O3, then click on A + B, for A click on FeO, for B click on 0.8889*Fe2O3, [This gives Fe as FeO* = FeO + 0.8889Fe2O3], For Y-top variable click on FeO + 0.8889Fe2O3 For Z right variable click on MgO. This gives M for MgO]. All the data appear on an AFM diagram. Select only the unfilled red circles of igneous rocks from Costa Rica to show a calcalkaline trend typical of island arcs. Include diagram in your report.

(5b) IRVBAR.DGM. Read data of CostaRica-USA.xls.text in Igpet99, then click on Plot, Diagram -, double click on IRVBAR.DGM, Done.

(5b1) select AFM thol vs calc-alk diagram showing the plot of all the samples appears.

Click Symbol and selectblue squares of igneous rocks from Costa Rica. Compare this diagram with the one from 4a. Explain how tholeiitic rocks are incorporated in an island arc setting as in Costa Rica. On which side of Costa Rica would the tholeiitic rocks be found and why? Repeat work for unfilled red circles.

Click Symbol and select only the rocks from USA. Explain the possible origin of these rocks by also using tectonic discrimination diagram.

(5b2) SiO2-alk alk vs subalk

(5b3) after performing CIPW calculation use Ne'-0l' -Q' to differentite between anlkaline and tholeiites.

6. Plot: DIAGRAM; TECTONIC.DGM Tectonic Discrimination Diagram.

Read data of CostaRica-USA.xls.text in Igpet99, then click on Plot - Tectonic, Done,

(6a) Mgo-FeO -Al2O3, Pearceet al, 77,

(6b) MnO- TiO2/10 -P2O5, Mullen, 83.

(6c) Zr - Ti/100 - Y*3, Perce & Cann 1973

(6d) Zr - Ti/100 -Sr/2 , Pearce & Cann, 1973

For each of these prepare separate diagrams for filled blue patterns of Costa Rica, unfilled red pattern of Costa Rica, and unfilled triangles of USA. Indicate ID numbers of samples. Describe the meanings of the plot in each diagram, and compare theses to data obtained from previous diagrams in 1, 2, 3, and 4 above.

7. Plot: REE. First work on one example by using a calculator.

Read data of CostaRica-USA.xls.text in Igpet99, then click on Plot, Spider .

Note, before you plot an REE diagram, go to symbols and select the samples you wish to work on. Also, double click on samples until a * appears in front of the ID numbers.

7a) Rees-Nakamura, chondrites

7b) REEs-sun & MCD-89 Chondrites

7c) Rees-INVERSE chondrites - for high REE values only

7d) Thompson -RN-1982-double chondrites -- includes Ba, Rb,Th, etc.

7e) Thompson -RN-1982-nodouble chondrites -- includes Ba,Rb, Th etc. check to see if slab component

7f) Wood -D.A. et al.-1979 primordial mantle -- includes Cs,Ba,Rb, Th etc. check to see if slab component is involved in magma.

7g) etc.

Plot REE patterns for USA rocks. Describe the meaning of the pattern

Plot REE pattern for Costa Rica, tholeiitic rocks. Describe the meaning

Plot the REE pattern for Costa Rica unfilled red circle pattern. Describe the meaning.

8. DIAGRAM. REEINV.DGM Plot La/Sm vs La separtely for Costa Rica tholeiites, calcalkaline suite, and for USA tholeiites. Place regression curves to determine slope and interpret either crystal fractionation or degree of partial melting.

9. Make a column for Mg # for the rocks.

What is the use of magnesium number?

10. Normative mineral composition. First work on one exmple by using a calculator.

(10a) Calculate , by using a CIPW table in the text book, the mineral composition of Costa Rica rock #86.

(10b) Determine its aluminum saturation (peraluminus, peralkaline, etc,)

(10c) Give the name of the rock by using a QAPF (Streckeisen) diagram.

(10d) Name the same rock by using the IUGS, LeBas diagram.

(10e) Use Igpet99 to determine the normative compositions of samples 9,70, 86, 88

(10f) Examine the differentiation index (the sum of normative albite + orthoclase + quartz- petrogenyÕs residua system minerals for rocks, 9,70, 86, 88). Which rocks have low index? How does the Magnesium number correspond to the differentiation index?

Part D. Phase Equilibria.

Consider a magma of composition A₂₀B₈₀, where B has a higher crystallization temperature than A. On T-X space show equilibrium solidification of magma by using: a) binary use solid solution. B) binary with a simple eutectic, and c) binary with a peritectic, and d) binary with a minimum

Part E. Metatmorphic Rocks

Plot the composition of the Corben gneiss and sample B-1 on ACF metamorphic Phase diagram, and indicate what the protoliths of these metamorphic rocks likely were? Also, assuming that they have been metamorphosed to lower amphibolite facies, determine the equilibrium mineral assemblages for both rocks?