GEOL 399
Fall 2004
PROJECT ONE
Volcan Mocho-Choshuenco, 40oS lat, Chile
(100 points)
deadline: 10:30 a.m., Friday, 1 October 2004
Volcan Mocho-Choshuenco is a young shield volcano located in the active volcanic
Andean arc at 40oS latitude in Chile. The most recent eruption was during the winter of 18641865. There are 13 samples in the Mocho-Choshuenco suite, which represent the compositional
variety of lavas at Mocho-Choshuenco.
Samples
The samples have two sample numbers. The SA numbers are the NMSU numbering system (SA
stands for Southern Andes). The numbers that consist of numbers and letters are the numbers
assigned during field work.
Lavas:
SA-1 = 16-1L
SA-5 = 17-1H
SA-9 = 01-1H
SA-13 = 12-2L
SA-2 = 05-3L
SA-6 = 27-2H
SA-10 = 23-2H
SA-3 = 12-3H
SA-7 = 27-4H
SA-11 = 05-3H
SA-4 = 15-2H
SA-8 = 22-3H
SA-12 = 27-1M
Assignment
Write a report, due at 10:30 a.m., Friday, 1 October 2004, on the mineralogy,
geochemistry, and tectonic setting of the samples from Mocho-Choshuenco. You are given hand
samples, thin sections, and major element and trace element data for 13 samples.
Work you will have to do prior to writing. Identify the minerals, estimate the mode,
describe the texture, and classify each sample using the IUGS modal classification system. Plot
the samples on appropriate major element diagrams, and classify the samples using a chemical
classification system. Plot incompatible trace element diagrams for the samples. Determine the
evolutionary order for the suite using mineralogy, major element, and incompatible trace
elements.
Format of your paper. Your paper will use the format of a scientific paper and will be
similar to a thesis. It should have the following sections:
Abstract
The abstract is the condensed version of the paper. It contains data as well
as conclusions. Write it last.
Introduction
The introduction lets the reader know about the topic of the paper and why
the paper is important. You may have to do some background reading to
write a snazzy introduction. A good introduction engages the reader and
makes her/him want to keep reading. Write this section second to last.
Data presentation
Present the data you have generated and are given in text with tables
and/or diagrams. You should have modal data, major element and trace
element geochemistry. In this section, describe the relationships in the
1
Interpretations
Discussion
Summary
data set but do not interpret! Rock descriptions and classifications belong
in this section.
Interpret the data you have presented and answer these questions:
1) Are the rock names from modal classification and chemical
classification systems the same? If not, why not? What are the
strengths and weaknesses of each system?
2) Are the rocks are placed in the same evolutionary order using
the modes, the major elements, and the incompatible trace
elements? What does this tell you about the magmatic system?
3) Use the data to discuss magmatic processes by which the
different compositions evolved.
4) Use the data to discuss the tectonic setting of the lavas.
The discussion section ties the interpretations together to address broader
issues. For instance, is this a typical continental arc volcano? If so, what
characteristics make it typical? If not, what makes it anomalous? Are the
magmatic processes at Mocho-Choshuenco unusual or fairly typical? You
will definitely have to read your text to get ideas for this section!
The summary section provides a quick overview of the interpretations and
implications of the paper. It does not summarize the data like the abstract
does! The reader should be able to turn to this section to get the punch
line without having to read the entire paper. The use of bullets to list your
conclusions is fine.
Reading Assignments
The following chapters of your text will be very useful while working on this project.
Chapter One—Overview of Fundamental Concepts
Chapter Two—Composition and Classification of Magmatic Rocks
Chapter Six—Chemical Dynamics of Melts and Crystals
Chapter Seven—Kinetic Paths and Fabric of Magmatic Rocks
Chapter Nine—Magma Ascent and Emplacement: Field Relations of Intrusions
Chapter Ten—Magma Extrusion: Field Relations of Volcanic Rock Bodies
Chapter Eleven—Generation of Magma
Chapter Twelve—Differentiation of Magma
Chapter Thirteen—Magmatic Petrotectonic Associations
Other chapters could very well prove useful as well!
2
Schedule
Notes:
1
The deadline for Friday assignments is the beginning of class on each Friday. Late work does not
receive credit.
2
Weekly assignments are graded in various ways. Assignments with * are graded on content. In
contrast, assignments with ** will receive full credit if they are turned in on time, complete, and neat. I
will give you written responses on the content.
Monday
Wednesday
Friday
8/25—start rock ID, lecture 8/27—lecture on rock
on rock classification
classification
Assignment due
none
8/30--more rock
classification, work
on modes
9/1--continue work on
mineralogy and modes
*mineralogy, modes,
textures, and rock
names
9/6--no class
Labor Day
9/8--arrange in evolutionary 9/10--lecture on trace element**major element
order, plot major element
geochemistry of igneous
diagrams,
diagrams
rocks
Microtheme #1
9/3-lecture on major
elements, problem
on major elements
9/13--continue
9/15--plot trace element
lecture on trace
diagrams
element geochemistry
9/17--make mindmap for
the paper (in class)
**trace element
diagrams,
Microtheme #2
9/20--write for first
hour (in class!!);
lecture on
volcanology
9/22--finish lecture on
volcanology
9/24--peer review in
class (NMGS conference)
**rough draft due
9/27--Start Project
Two
9/29--final discussion of
Project One; lecture on
Modal classification of
plutonic rocks
10/1-work on modes
for Project Two
*final draft due
3
Grades
Due Assignment
9/3
Brief rock descriptions, mineralogy, and modes for 13 samples
9/10 Microtheme with major element diagrams. See attached
assignment for Microtheme #1. Be sure to separate your
descriptions of the data set from your interpretations!
9/17
9/24
9/24
10/1
Microtheme with trace element diagrams. See attached
assignment for Microtheme #2. Be sure to separate your
descriptions of the data set from your interpretations!
The rough draft of your paper.
Participation in peer review of your classmates' papers. You
will review two rough drafts in class.
Final draft due. You must turn in the following:
-your final draft
-two peer reviews of your paper, including the rough drafts
Grading method
graded on content (10 points)
full credit (10 points)
if timely & complete. You
will also receive my written
response.
full credit (10 points) if
timely & complete. You will
also receive my response.
full credit (10 points) if
timely & complete. I will not
give you a written response.
5 points each for reviews of
two papers
Your paper will be graded
holistically, based on the
criteria listed below. (50 pts.)
Evaluation Criteria
Content of the paper
Paper presents the following data: mineralogy, modes, major element, and trace element data for 13
samples.
The 13 samples are classified using a modal and chemical classification system.
Differences between the modal and chemical classification systems are discussed.
Chemical analyses are used to discuss the tectonic setting of the lavas.
Chemical and modal data are used to discuss fractionation processes.
Technical aspects of the paper
Writer describes the relationships within the data set, including mineralogy, modes, major elements, and
trace elements.
Writer supports interpretations using data and diagrams.
Interpretations reflect clarity of thought and depth of analysis.
Discussion section used the interpretations to address broader issues.
Summary section provides a quick overview of interpretations and implications.
Abstract provides data and conclusions.
Standard edited English is used effectively.
Writing process
Revision is based on instructor responses to microthemes.
Revision is based on peer reviews.
Paper has been edited and proofread.
4
GEOL 399
Igneous and Metamorphic Petrology
Fall 2004
Project One: Evaluation Criteria
Evaluation by Dr. McMillan
Content of the paper
_____ Paper presents the following data: mineralogy, modes, major element, and trace element data for
13 samples
_____ The 13 samples are classified using a modal and chemical classification system
_____ Differences between the modal and chemical classification systems are discussed
_____ Chemical analyses are used to discuss the tectonic setting of the lavas
_____ Chemical and modal data are used to discuss fractionation processes
Technical aspects of the paper
_____ Writer describes the relationships within the data set, including mineralogy, modes, major
elements, and trace elements
_____ Writer supports interpretations using data and diagrams
_____ Interpretations reflect clarity of thought and depth of analysis
_____ Discussion section used the interpretations to address broader issues
_____ Summary section provides a quick overview of interpretations and implications
_____ Abstract provides data and conclusions
_____ Standard edited English is used effectively
Writing process
_____ Revision is based on instructor responses to microthemes
_____ Revision is based on peer reviews
_____ Paper has been edited and proofread
Holistic summary score: _____
Letter grade: _____
Points: _____
*
Mineralogy and modes
Microtheme 1
Microtheme 2
Rough draft
Peer review
Paper
Total
*
*
_____/10
_____/10
_____/10
_____/10
_____/10
_____/50
_____/100
*
* * * *
Project grade
*
*
*
*
GEOL 399
Igneous and Metamorphic Petrology
Fall 2004
Project One
Peer Review
Author's name: _______________________ Reviewer's name: __________________________
Evaluate each of these criteria using the holistic scoring method, using scores from 6
(distinguished) to 1 (clearly incompetent). Write additional comments in the margins or on the back of
the reviewed paper.
Content of the paper
_____ Paper presents the following data: mineralogy, modes, major element, and trace element data for
13 samples
_____ The 13 samples are classified using a modal and chemical classification system
_____ Differences between the modal and chemical classification systems are discussed
_____ Chemical analyses are used to discuss the tectonic setting of the lavas
_____ Chemical and modal data are used to discuss fractionation processes
Technical aspects of the paper
_____ Writer describes the relationships within the data set, including mineralogy, modes, major
elements, and trace elements
_____ Writer supports interpretations using data and diagrams
_____ Interpretations reflect clarity of thought and depth of analysis
_____ Discussion section used the interpretations to address broader issues
_____ Summary section provides a quick overview of interpretations and implications
_____ Abstract provides data and conclusions
_____ Standard edited English is used effectively
Writing process
_____ Paper has been edited and proofread
GEOL 399
Igneous and Metamorphic Petrology
Fall 2004
Holistic scoring
Accomplished Work
6 = Distinguished. The strengths of the work far outweigh its weaknesses. All the required topics are discussed
clearly. Data presentation is separated from interpretation. Interpretations are fully supported by data, diagrams,
and discussion. The writing is well-organized and communicates effectively with style and clarity. The work also
exhibits depth, fullness, and complexity of thought. The work responds to issues brought up in the peer reviews.
5 = Strong Competent. This work is similar to a “6” but not to the same extent. Strengths clearly outweigh its
weaknesses. All required topics are discussed, data presentation is separated from interpretation, and
interpretations are fully supported by data, diagrams and discussion, but not as fully or consistently as a “6”. Also,
while the writing is focussed and effective, problems may exist with depth, fullness, and complexity of thought.
The work responds to issues brought up in the peer reviews.
Competent Work
4 = Competent. This work is clearly competent. Its strengths outweigh or slightly outweigh its weaknesses. All
required topics are discussed, data presentation is separated from interpretation, and interpretations are supported at
some level by the data, diagrams, or discussion, although not to the extent of a “5” or “6.” For example, while the
topics are discussed, the relationship between the data and interpretations may not be fully explored or
interpretations not supported in the text although the diagrams and/or data are presented. Writing at this level
exhibits competence (i.e., few structural or grammatical problems), but may have clarity or organizational problems
or may be deficient in depth, fullness, and complexity of thought.
3 = Minimally Competent. This work is competent at the level approaching a “4” but not to the same extent. Its
strengths and weaknesses tend to be balanced. For example, writing at this level may address all the required
topics and separate data presentation from interpretation, but these strengths would be counterbalanced by being so
brief so that the data and ideas are not fully developed. On the other hand, some topics may be fully developed but
others not addressed at all. Minor problems with structure or grammar are present, but the paper lacks clarity.
Unsatisfactory Work
2 = Incompetent. This work does not separate data presentation from interpretation and does not address all of the
required topics. Its weaknesses outweigh its strengths. While work at this level may have few grammatical
problems, the paper is brief and superficial.
1 = Clearly Incompetent. The weaknesses of this work far outweigh its few strengths. Data presentation is
mingled with interpretation, and interpretations are not supported by the data. The required topics are not all
discussed. Work at this level indicates that little thought or effort was used during the writing process.
Holistic score
6
5
4
Letter grade
A
A-
B
B-
C
40
35
30
25
Points
50
45
3
2
1
C-
D
F
20
15
10
GEOL 399
Igneous and Metamorphic Petrology
Fall 2004
Project One: Volcano Mocho-Choshuenco
Microtheme #1: Major Element Data
Assignment: Write a three-paragraph microtheme that includes the information listed below. You don
need to introduce the paper--pretend that these are three paragraphs out of the middle of your final paper.
Paragraph 1: Use this paragraph to describe the major element data. For instance, state the range of
composition for some of the elements. Do the rocks fall along well-defined trends for all elements?
Which elements increase during evolution (increasing SiO2), and which elemental trends decrease? Do
some elements have greater scatter than others? If you put the rocks in evolutionary order using SiO2 or
MgO, do you get the same order as you did when you used the modes?
Paragraph 2: Use this paragraph to discuss the chemical classification of the rocks. What are their
names? Are they subalkaline (calc-alkaline or tholeiitic?), alkaline, or peralkaline?
Paragraph 3: Use this paragraph to discuss the most likely differentiation mechanism, based on the major
element data and the textures. Use the data and your graphs to support your interpretations. For
instance, instead of writing “The truck is broken,” write “The observation that the front axle is resting on
the ground in a pool of brown gooey liquid (Fig. 1) indicates that the truck broken.” Be specific!
GEOL 399
Igneous and Metamorphic Petrology
Fall 2004
Project One: Volcano Mocho-Choshuenco
Microtheme #2: Trace Element Data
Write a two-paragraph microtheme that describes and interprets the trace element data you have
been given. There is no need to introduce the project, because these paragraphs are part of the interior of
your final paper.
Paragraph 1: Describe the data in this paragraph. There are two aspects of the trace elements that you
should consider describing: changes in concentration during evolution, and ratios of elements that would
indicate the tectonic environment. The incompatible trace elements, such as Ba, Rb, and La should all
increase during evolution, and thus should be positively correlated with SiO2. The compatible trace
elements Ni, Cr, and Sc should all decrease during evolution and be negatively correlated with SiO2.
When considering tectonic environment, remember that Ba is usually enriched in arc magmas because it
is soluble in subduction fluids and that Ta is usually very low in arc magmas because it is retained by the
subducted slab. These variations could be illustrated on a “spidergram” or on a ratio plot, as discussed
in class. Remember that you don’t want to interpret the data in this paragraph---just describe the data.
For instance, don’t say that the magmas are typical arc magmas because they have low Ta. Leave that
for the next paragraph, and just say that the samples have very low Ta and high Ba, as illustrated by the
trough at Ta on the spidergram.
Paragraph 2: Use this paragraph to interpret your data! Is there any evidence for assimilation in addition
to fractional crystallization when you look at the trace elements in addition to the major elements? What
do the trace elements have to tell you about the tectonic environment of this volcano?