MRT to magma chamber: field inquiry on plate tectonics and the rock cycle at Little Guilin, Singapore Education and Outreach 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 Teacher role Student role Teacher responses to the student question, "What rock is this?" Didactic teaching in the field Teacher as knowledge dispenser Student as knowledge recipient 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. Inquiry learning in the field Teacher as guide and learning coach Student as investigator 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 wellmanicured 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: Participants will be able to... 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. Find, sketch, and describe one example of bedrock and one example of soil. If we break a piece of rock off of the cliff, is it still bedrock? Why or why not? Are the cliff and pond natural or human-made features? What is the evidence?
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. Find an example of each and describe the evidence that indicates that the surface is fresh or weathered. 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 Sedimentary Metamorphic Common mode of formation Common distinguishing characteristics Liquid rock (magma or lava) cools and crystallises Mineral crystals are interlocking Rock particles (gravel, sand, or clay) are deposited and later compacted and cemented together Grains of sediment do not interlock; layers might be seen 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: Participants will be able to... 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. 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: Participants will be able to... 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 250-260 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 the geologic history that you wrote above? What does it mean about the period of erosion? These rocks are how many times older than you? These rocks crystallised from a magma more than 200 million years ago. At that time, might this area have been found at: Plate tectonic setting Collision zone Yes, no, or maybe? Based on what evidence? What additional information would help to confirm or disprove this hypothesis? Subduction zone Divergent boundary Transform boundary Hot spot within a plate
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: Participants will be able to... 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? Why? 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.