MRT to magma chamber: field inquiry on plate
tectonics and the rock cycle at Little Guilin, Singapore
Jamie McCaughey
Earth Observatory of Singapore, Nanyang Technological University
Singapore
[email protected]
INTRODUCTION
Field inquiry approach
This site and the suggested questions and activities below provide an
excellent opportunity for guided inquiry learning in the field. However, being in
the field does not, by itself, ensure that inquiry learning is taking place.
In inquiry learning, students pose questions, seek out relevant
information, then evaluate the information in an effort to answer the original
questions (e.g. Margaret, 2003). In practice, inquiry is guided to varying
degrees by the teacher, depending on student prior knowledge, available
time, and the complexity of the topic or available information. To promote
inquiry learning, answer student questions with guiding questions rather than
direct answers (Table 1).
Table 1. Possible teacher responses to a student who asks, "What rock is this?" Direct
answers (including confirmations of student guesses) inhibit inquiry learning, whereas
guiding questions foster inquiry learning.
Pedagogy
Didactic teaching in the
field
Inquiry learning in the field
Teacher role
Teacher as knowledge
dispenser
Teacher as guide and learning coach
Student role
Student as knowledge
recipient
Student as investigator
Teacher
responses to
the student
question,
"What rock
is this?"
• It's a norite.
• It's a norite, which is
high in iron and cooled
slowly underground
from a magma.
• See the coarse
mineral grains and
dark colour? Look
right there. That's
how you know it's a
norite, and that it
cooled slowly
underground from an
iron-rich magma.
• Tell me something about this rock.
• What colour is the rock?
• Can you see individual mineral grains
in this rock? What is their size?
• What does the colour tell you about
the composition of the rock?
• What does the grain size tell you
about how this rock formed?
• If a rock had a lot of iron, would it be
darker or lighter in colour?
• If liquid rock cooled slowly, would the
mineral crystals grow large in size?
• Where would liquid rock cool more
slowly - deep underground or on the
Earth's surface?
Field learning lends itself to an inquiry-learning approach (Mogk and
Goodwin, 2012). When the two are combined, students can benefit greatly.
Field inquiry helps students critically evaluate simplications and abstractions
of natural systems that are presented in textbooks and in the classroom
(Stillings, 2012). Field inquiry also helps students to form a more integrated,
less compartmentalised understanding of natural systems through both
sensory experiences and the process of integrating observations and
concepts into a coherent whole (Mogk and Goodwin, 2012). In geography
education in Singapore, both the Ministry of Education and National Institute
of Education are advocating for field-based inquiry learning to become a
standard component of students' geography learning.
A key habit for inquiry learning is the practice of separating
observations from interpretations. Students might be tempted to leap
immediately to the interpretation, "It's granite!" Instead, guide them to start
with describing what they see and using that information as evidence to
support their interpretations.
Student preparation
Students should already be familiar with:
• The rock cycle
• The processes that produce the three rock types (igneous, sedimentary,
and metamorphic)
• General physical features that distinguish the three rock types
• Rocks are made of minerals
• Minerals are crystals that occur in a range of sizes
• Isostatic adjustment: if significant erosion occurs, the lithosphere rises up
in response
Logistics
The field site is walking distance from Bukit Gombak MRT (Figure 1). As a
well-manicured and easily accessible park, the risks are generally low.
Students should not climb on steep rocks, enter closed areas, or swim.
BUKIT GOMBAK SMRT
SITE1
SITE 3
SITE 2
SITE 4
North
0
100m
Figure 1. Location of field sites at Little Guilin. (Basemap from streetdirectory.com)
SITE 1: OBSERVING AND INTERPRETING ROCKS IN
THE FIELD
Learning objectives
1a) Distinguish bedrock from loose soil/regolith.
1b) Distinguish fresh and weathered rock surfaces.
1c) Interpret whether rocks are igneous, sedimentary, or metamorphic
Objective 1a) Distinguish bedrock from loose soil/regolith.
Here there are dramatic exposures of bedrock, which in geological terms
means solid rock that is physically connected to the rest of the crust. Note
that "bedrock" does not mean a particular rock type, only that the rock is
connected to the rest of the crust. In contrast, loose soil or regolith sits on top
of bedrock but is not physically connected to it.
What is bedrock? What is soil? Find, sketch, and describe examples of each.
If we break a piece of rock off of the cliff, is it still bedrock? Why or why not?
Why is there a cliff here? Why is there a pond here?
Objective 1b) Distinguish fresh and weathered rock surfaces.
Some of these boulders have heavily weathered surfaces. Other boulders
have fresh surfaces, which are much closer to the original colour of the rock.
Which are which?
What are some processes that may have weathered these boulders?
Objective 1c) Interpret whether rocks are igneous, sedimentary,
or metamorphic
Students should already know the rock cycle and general characteristics of
the rock types (Table 2).
Table 2. The main rock types.
Rock type
Igneous
Common mode of
Liquid rock (magma
formation
or lava) cools and
crystallises
Common
distinguishing
characteristics
Mineral crystals are
interlocking
Sedimentary
Rock particles
(gravel, sand, or
clay) are deposited
and later compacted
and cemented
together
Grains of sediment
do not interlock;
layers might be seen
Metamorphic
A pre-existing rock is
changed by heat and
pressure
Mineral crystals align
and sometimes
separate into bands
of different
compositions
"It's not the shape, it's what's inside." People tend to focus on the
outward shape of rocks. However, the outward shape does not tell us very
much about the processes that formed the rocks. Instead, focus students'
attention on the materials and texture within the rocks. As an analogy, if you
wanted to know the taste of a new ice cream, you shouldn't focus on whether
the ice cream is in a bowl or in a cone - you should take a taste to see what's
inside.
Are these rocks igneous, sedimentary, or metamorphic? How do you know?
Sketch the defining characteristics of the rock.
SITE 2: DESCRIBE AND INTERPRET ROCKS
Learning objectives
2a) Describe and classify the rocks.
2b) Interpret how the rocks formed.
Objective 2a) Describe and classify the rocks.
How many distinct rock units are present?
For each rock unit, describe the grain size, grain relationships (interlocking or
not?), colour, and any characteristics of the minerals that you can observe.
Which rock unit has more iron and magnesium? How do you know?
Objective 2b) Interpret how the rocks formed.
Student questions
If liquid rock cools slowly, the mineral crystals grow large. If liquid rock cools
quickly, however, the resulting mineral crystals are too small to see without a
microscope. Which process would happen underground, and which process
would happen in a volcanic eruption onto the Earth's surface? Why?
Did this igneous rock cool slowly underground, or did it cool quickly on the
surface after being erupted from a volcano? How do you know?
SITE 3: INTERPRET GEOLOGIC HISTORY
Learning objectives
3a) Interpret the relative ages of the Gombak norite and Bukit Timah granite
3b) Interpret the geologic history of Little Guilin.
Objective 3a) Interpret the relative ages of the Gombak norite and
Bukit Timah granite
Going back to Hutton and Lyell, the principle of cross-cutting relations holds
that a geological feature that cuts another is the younger of the two features.
This is actually quite a simple idea: by analogy, you have to bake a cake
before you can cut it.
Which is younger, the Bukit Timah granite or the Gombak norite? How do you
know?
Objective 3b) Interpret the geologic history of Little Guilin.
Student questions
Develop a geologic history of Little Guilin by listing events from the oldest to
the youngest. Note where there is a gap in time in your history.
Radiometric dating allows for estimations of absolute rock ages based on the
decay of radioactive isotopes since the time of crystallisation of the rock.
Radiometric dating studies of Singapore rocks provide estimated ages of 250260 million years for the Gombak norite and 230-245 million years for the
Bukit Timah granite (Oliver et al., 2011; and pers. comm.)
Are these dates consistent with your geologic history? What does it mean
about the period of erosion?
These rocks are how much older than you?
These rocks crystallised from a magma more than 200 million years ago.
What does that mean about the plate tectonic setting of Singapore at that
time?
Based on your tectonic interpretation, what kinds of natural hazards would
have been common in the area that is now Singapore at about 230-260 million
years ago?
SITE 4: CONTRAST JURONG FORMATION AND
INTERPRET AGE RELATIONS
Learning objectives
4a) Describe rock at Block 503
4b) Interpret how the rock formed
4c) Hypothesise age relations between Little Guilin and Block 503
Objective 4a) Describe rock at Block 503
Describe the rock, including grain size, grain relationships, colour, and any
other features that you can observe. Note that the rock here is much less well
exposed than at Little Guilin; be sure that the features that you are describing
are part of the rock itself.
Objective 4b) Interpret how the rock formed
Based on your description, what rock type is this? How do you know?
How did this rock form?
Objective 4c) Hypothesise age relations between Little Guilin and
Block 503
From our observations, is it possible to determine whether the Jurong
Formation is older or younger than the Bukit Timah granite and Gombak
norite?
If you could find a place where the contact between these rock units is
exposed, what evidence would you look for to know the correct age
sequence?
REFERENCES
Lee, K. W., and Zhou, Y. (2009) Geology of Singapore, 2nd Ed., Defense
Science and Technology Agency, Singapore, 90 p.
Mogk, D. W., and Goodwin, C. (2012) Learning in the field: Synthesis of
research on thinking and learning in the geosciences, in Kastens,
K. A., and Manduca, C. A., eds., Earth and mind II: A synthesis of
research on thinking and learning in the geosciences: Geological
Society of America Special Paper 486, p. 131-163.
Oliver, G., Zaw, K., and Hotson, M. (2011) Dating rocks in Singapore,
Innovation Magazine, v. 10, no. 2, p. 22-25.
Roberts, M. (2003) Learning through enquiry: Making sense of geography in
the key stage 3 classroom: Geographical Association, 212 p.
Stillings, N. (2012) Complex systems in the geosciences and in geoscience
learning, in Kastens, K. A., and Manduca, C. A., eds., Earth and
mind II: A synthesis of research on thinking and learning in the
geosciences: Geological Society of America Special Paper 486, p.
97-111.