GEOL 399
Fall 2006
PROJECT TWO
Florida Mountains Intrusion
(90 points)
Due 10:30 a.m., Friday, 3 November 2006
The southern half of the Florida Mountains south of Deming, New Mexico, comprises the
Florida Mountains intrusion, dated by U-Pb on zircons at 513 + 10 Ma. The age and
geochemistry of these rocks are very interesting and more than a little controversial! At the time
of emplacement (Latest Cambrian-Early Ordovician), southern New Mexico is supposed to have
been a passive continental margin formed by the rifting of the Laurentian plate. Several
aulacogens, or fossil continental rifts, extend into the western or North American side of the
passive margin, but most geologists do not place an aulocogen in the New Mexico region. The
presence of the Florida Mountains intrusion and other similar intrusions, including carbonatites,
throughout New Mexico suggest that a continental rift developed and produced rift magmas.
The other interesting feature of the Floridas Mountains intrusion is its relationship with
the overlying Lower Ordovician Bliss Sandstone. The Bliss Sandstone, which has been
interpreted as a sheet of deltaic sands deposited on the passive margin, nonconformably overlies
the intrusion and, in the Florida Mountains, is derived from the intrusion. The timing of
intrusion (513 + 10 Ma), cooling (491 + 5 Ma), and deposition of the Bliss Sandstone (ca. 480
Ma) implies rapid erosion and unroofing of the pluton. Thus, one of the important questions in
this project is the depth of intrusion. If the pluton crystallized in the lower crust, at
approximately 30 km depth, then uplift rates were about 1.36 km/Ma (that's 1.36 m every
thousand years or 1.36 mm every year!). But if the pluton was very shallow, perhaps at 2 km,
uplift rates were only about 0.09 km/Ma (or 0.09 mm every year—that’s pretty slow!). That’s a
big difference, so it is important to look for any mineralogic, geochemical, or textural clues for
the depth of crystallization.
Samples
595GR106
595GR108
595SY110
595SY113
995SY114
995SY115
995GR116
995GR118
995GR119
995GR120
1095GR121
1095GR123
1095GR127
silicic hand specimen and thin section
silicic hand specimen and thin section
hand specimen almost all silicic; both silicic and mafic in thin section
hand specimen is silicic; both silicic and mafic in thin section
silicic hand specimen and thin section
silicic hand specimen and thin section
silicic hand specimen and thin section
mafic and silicic hand specimens and thin sections
mafic and silicic hand specimens and thin sections
mafic and silicic hand specimens and thin sections
silicic hand specimen and thin section
mafic hand specimen and thin section
silicic hand specimen and thin section
1
Assignment
Write a report, due at 10:30 a.m., Friday, 3 November 2006, on the mineralogy,
geochemistry, fractionation, geologic history, and tectonic history of the Florida Mountains
Intrusion. You are given hand samples, thin sections, major and trace element geochemistry, and
we will visit the pluton on a field trip.
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 incompatible trace element diagrams.
Determine the evolutionary order for the samples using mineralogy, modes, and major element
and trace element compositions.
Format for your paper. The format is very similar to Project One; in fact, only the
questions have been changed to annoy the innocent!
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 it 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
data set but do not interpret! Rock descriptions and classifications belong
in this section.
Interpretations
Interpret the data you have presented and answer these questions:
1) Estimate the depth of intrusion. What is there about the
mineralogy, texture, or geochemistry of the rocks that allows you
to say whether this was a very shallow intrusion, or one in the
lower crust?
2) Use the data to discuss the magmatic processes by which the
different compositions evolved.
3) Use the data to discuss the tectonic setting of the intrusion. Are
the trace element data similar to continental arc plutons or
continental rift plutons?
4) Draw a geologic cross section on the line indicated on the
geologic map. Describe the geologic history of the intrusion, from
its intrusion to the present.
Discussion
The discussion section ties the interpretations together to address broader
issues. For instance, is this pluton typical of passive margins? Do the data
support the hypothesis of a continental rift? How much rock would have
been eroded off of the pluton prior to deposition of the Bliss Sandstone?
Is this a fast or slow uplift rate?
Summary
The summary section provides a quick overview of the interpretations and
2
implications of the paper. It does not summarize the data like the abstract.
The reader should be able to turn to this section to get the “punch line”
without having to read the paper. The use of “bullets” to list your
conclusions is fine.
Reading Assignments
Chapter One—Overview of Fundamental Concepts
Chapter Two—Composition and Classification of Magmatic Rocks
Chapter Three—Thermodynamics and Kinetics: An Introduction
Chapter Five—Crystal-Melt Equilibria in Magmatic Systems
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 Eleven—Generation of Magma
Chapter Twelve—Differentiation of Magma
Chapter Thirteen—Magmatic Petrotectonic Associations
Other chapters could very well prove useful as well!
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
Assignment due
10/2—Start Project 10/4--final discussion of
10/6-work on modes *final draft of Project
Two
Project One; lecture on
for Project Two
One
Modal classification of
plutonic rocks
10/9--work on
10/11--lecture on intrusions 10/13—work on
*mineralogy, modes,
mineralogy and
and criteria for intrusive
trace element
textures, and rock
modes
contacts
diagrams
(NJM in Carlsbad)
10/16--lecture on
10/18--work on trace
10/20—lecture on
**major and trace
phase diagrams
element diagrams
phase diagrams
element diagrams;
Microtheme on
geochemistry
10/23- work on
10/25- draw cross10/27- peer
**rough draft
Supplemental Lab
sections in class; work on
review rough draft
One (NJM at GSA) Supplemental Lab One
(NJM at GSA)
10/30- lecture11/1- discuss Supplemental 11/3-Start Project
*final draft due
introduction to
Lab One
Three
metamorphism
3
Grades
Due date
10/13
10/20
10/27
10/27
11/3
Assignment
Brief rock descriptions, mineralogy, and modes for 13
samples
Major and trace element geochemical diagrams with a
microtheme that : 1) describes the data, and 2) interprets
the data. In this little paper, you will place the samples
in evolutionary order and discuss the relationship between
the degree of fractionation and the mineralogy. You will
also discuss the tectonic setting of the intrusion, based on
your interpretation of the trace element data. The first
paragraph should describe the data; the second should
interpret.
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
4
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.
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 classification system
Chemical analyses are used to discuss the tectonic setting of the pluton
Chemical and modal data are used to discuss fractionation processes
Modal, textural, and/or chemical data are used to estimate the depth of intrusion
Geologic cross-section is provided
Geologic history of the intrusion is discussed
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.
REFERENCES:
Clemons, R.E., 1983, Geology of Gym Peak Quadrangle, Luna County, New Mexico: New
Mexico Bureau of Mines and Mineral Resources, Geologic Map 58.
Evans, K.V., and Clemons, R.E., 1988, Cambrian-Ordovician (500 Ma) Alkalic Plutonism in
Southwestern New Mexico: U-Th-Pb Isotopic Data from the Florida Mountains: American
Journal of Science, V. 288, p. 735-755.
GEOL 399
Igneous and Metamorphic Petrology
Fall 2006
Project Two: 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 classification system
_____ Chemical analyses are used to discuss the tectonic setting of the pluton
_____ Chemical and modal data are used to discuss fractionation processes
_____ Modal, textural, and/or chemical data are used to estimate the depth of intrusion
_____ Geologic cross-section is provided
_____ Geologic history of the intrusion is discussed
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
Rough draft
Peer review
Paper
Total
*
_____/10
_____/10
_____/10
_____/10
_____/50
_____/90
* * * *
Project grade
*
*
*
*
GEOL 339
Igneous and Metamorphic Petrology
Fall 2006
Project Two
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 classification system
_____ Chemical analyses are used to discuss the tectonic setting of the pluton
_____ Chemical and modal data are used to discuss fractionation processes
_____ Modal, textural, and/or chemical data are used to estimate the depth of intrusion
_____ Geologic cross-section is provided
_____ Geologic history of the intrusion is discussed
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
Accomplished work:
6 = Distinguished
5 = Strong Competent
Competent work:
4 = Competent
3 = Minimally Competent
Unsatisfactory work:
2 = Incompetent
1 = Clearly Incompetent
GEOL 339
Igneous and Metamorphic Petrology
Fall 2006
Project Two: Florida Mountains Intrusion
Microtheme on Major and Trace Element Data
Write a two-paragraph microtheme that describes and interprets the major and 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 One: Describe the major element data. Describe the trends in the data: are the samples
well-correlated? What elements increase with increasing SiO2? Which elements decrease?
Describe the trace element data. What do the spidergrams for these samples look like? Do the
incompatible trace elements increase in abundance with increasing SiO2?
Paragraph Two: Interpret the geochemical data. Pay special attention to two of the questions you
are asked to address in your final paper: what magmatic processes were involved in the evolution
of these magmas, and what was the tectonic setting of the pluton.