Geol 406 (Igneous and Metamorphic Petrology) Outcomes Assessment
Big Idea 1
Observations of mineral assemblages and rock textures can be used to interpret a rock’s origin and any subsequent changes in its environment. Rock descriptions, which consist of rock names and detailed mineral and hand sample textures, are the critical foundation for communication and interpretation.
Prerequisite skills
Mineral identification, Mineral composition, Bowen’s reaction series
Learning Targets and Success Criteria
| Learning Target | Success Criteria |
|---|---|
| 1.1 The minerals found in an igneous rock are controlled by the rock composition and Bowen’s reaction series. | 1.1.1 Correctly predict what minerals will be found in mafic, intermediate and felsic igneous rocks. |
| 1.2 An IUGS igneous rock name is based on the mineral mode and texture of the rock, and is a critical component of a rock description. |
1.2.1 Accurately identify minerals and determine their percentages in an igneous rock 1.2.2 Choose the correct IUGS triangular classification diagram and use the modal percentages of minerals to name the rock (this requires knowledge of how to normalize mineral percentages and plot on a triangular diagram) 1.2.3 Successfully describe an igneous rock using protocols described for igneous rocks, using appropriate igneous textural terminology |
| 1.3 The sizes, shapes, and relationships between minerals, as well as other structures can be used to interpret rock formation processes. |
1.3.1 Mineral growth relationships in igneous rocks can be used to interpret order of crystallization 1.3.2 By looking at a hand sample and thin section, interpret whether the products of silicic volcanism were produced explosively or by a lava flow 1.3.3 Porphyroblast growth and foliation relationships in metamorphic rocks can be used to interpret the relative timing of metamorphism and deformation. |
| 1.4 The mineralogy of a metamorphic rock is a function of its protolith group (ultramafic, mafic, shale, carbonate, quartzofeldspathic) | 1.4.1 Show your knowledge of the five different protolith groups by categorizing different types of metamorphic minerals with different protolith groups (recognizing that there is some overlap,but that some minerals are diagnostic of a particular protolith group). |
| 1.5 An IUGS metamorphic rock name is based on the protolith, mineralogy, and texture of the rock, and is a critical component of a rock description. |
1.5.1 Accurately identify minerals and determine their percentages in a metamorphic rock 1.5.2 Successfully name a metamorphic rock, using one of the four protocols (protolith name, rocks with >70% of one mineral, texture-based names, random historical names) 1.5.3 Successfully describe a metamorphic rock using appropriate metamorphic textural terminology.LT 1.6 Within a protolith group the mineralogy of a metamorphic rock is a function of pressure and temperature |
| 1.6 Within a protolith group the mineralogy of a metamorphic rock is a function of pressure and temperature | 1.6.1 (same as 4.4.1) List distinctive assemblages in mafic and pelitic rocks at specific facies |
Big Idea 2
Magmas are formed by partial melting of the mantle or the deep crust. The magma produced has a different composition than the residue left behind
Prerequisite skill
General understanding of structure of the Earth
Learning Targets and Success Criteria
| Learning Target | Success Criteria |
|---|---|
| 2.1 The bulk composition of the Earth is known from meteorites. Earth has differentiated into distinct compositional and mechanical layers | 2.2.1 Describe the major mechanical and chemical subdivisions of the Earth’s interior |
| 2.2 The geothermal and geobarometric gradients show how T&P changes inside Earth | 2.2.1 Draw a simple sketch of the shape of the geothermal and geobarometric gradient from the surface to the core-mantle boundary. |
| 2.3 The temperature and pressure at which a given rock composition melts (with or without H2O) can be shown on a simple P-T diagram. From these diagrams we can interpret P-T paths for melting. | 2.3.1 Illustrate on a P-T diagram how melting of peridotite might occur |
| 2.4 The partial melt composition is not the same as the bulk rock composition. | 2.4.1 Use a binary eutectic phase diagram to show how the bulk composition of a rock stays the same during melting but the partial melt and residual solid compositions change and are different from each other |
Big Idea 3
Magma differentiation is the key process by which magma compositions change as they traverse through earth’s crust
Prerequisite skill
Bowen’s reaction series as a backdrop for changing magma and mineral compositions (the what but not the how) (G211 and 306)
Learning Targets and Success Criteria
| Learning Target | Success Criteria |
|---|---|
| 3.1 Magmas are composed of liquid, crystals, and dissolved or exsolved vapor. Magma behavior is controlled by viscosity, temperature and density |
3.1.1 Explain how network formers and modifiers affect magma viscosity 3.1.2 Describe how temperature affects magma viscosity 3.1.3 Describe how volatiles affect magma viscosity |
| 3.2 Two component phase diagrams can be used to track changing liquid and crystal compositions as well as relative abundances |
3.2.1 Describe the difference between a eutectic vs. solid solution phase diagram. Define the terms liquidus, solidus, eutectic 3.2.2 Track changing liquid composition on a phase diagram during cooling 3.2.3 Track changing solid composition on a solid solution phase diagram during cooling 3.2.4 Track relative proportions of liquid versus solid on a phase diagram during cooling |
| 3.3 Closed system magma differentiation can occur by separating crystals from liquid through gravity driven processes |
3.3.1 Using Stoke’s Law, describe if crystal settling is a viable mechanism for magma differentiation given specified values for Stoke’s law variables. 3.3.2 After a given amount of fractional crystallization, determine what you would need to calculate the composition of the remaining magma. |
| 3.4 Open system magma differentiation can occur by mixing magmas of different compositions | 3.4.1 Sketch and describe simple scenario(s) for how magma mixing may occur |
| 3.5 Graphic visuals of changing magma composition (Harker diagrams) can be used to interpret how differentiation occurs |
3.5.1 Using a Harker diagram, identify a parental magma for a magma series 3.5.2 Using a Harker diagram, determine whether magma mixing was a viable process for magma differentiation 3.5.2 Using a Harker diagram, describe whether an element is behaving compatibly or incompatibly. If the former, what mineral might be responsible, and when did it begin to crystallize? |
| 3.6 Highly silicic magmas are either the extremes of magma differentiation or crustal melts. These are either emplaced as large batholiths, erupted in caldera-forming eruptions, or less commonly, erupted as silicic lava flows |
Big Idea 4
Rocks change through metamorphism and the mineral assemblage produced depends on protolith, P-T conditions, and fluid availability
Learning Targets and Success Criteria
| Learning Target | Success Criteria |
|---|---|
| 4.1 (Builds upon 2.1) The geothermal and geobarometric gradients show how P&T vary inside Earth. Temperature defines the grade of metamorphism and pressure defines the depth |
4.1.1 Define what metamorphism is, and what three important variables play a role (considered “agents” of metamorphism) 4.1.2 Draw isotherms (lines of constant temperature) in a cross section of Earth (and later in the course, at a subduction zone) |
| 4.2 Different metamorphic environments are defined by their geothermal gradient and amount of deformation |
4.2.1 Compare and contrast the effects and tectonic settings of the 6 different metamorphic environments –contact, regional, hydrothermal, hiP/lowT, cataclastic, and shock 4.2.2 Utilize the concept of metamorphic facies to name, sketch, and describe common regions in PT space that metamorphism occurs |
| 4.3 There are 5 basic protolith groups that form metamorphic rocks: ultramafic, mafic, shale, carbonate, and quartzo-feldspathic |
4.3.1 Explain why rocks from a similar protolith group would have the exact same minerals in a particular facies 4.3.1 Explain why rocks from different protolith groups have different minerals in a particular facies |
| 4.4 Rocks with similar bulk composition metamorphosed at similar P-T will develop the same set of minerals. This is defined as metamorphic facies. |
4.4.1 (same as 1.6.1) List distinctive assemblages in mafic and pelitic rocks at specific facies 4.4.2 Predict what minerals a rock would have given the facies and the protolith group (or predict the facies given the minerals and the protolith group) |
| 4.5 A metamorphic facies series (field gradient) is defined by zones of increasing metamorphic grade that develop in response to gradients in P and T. The three most common facies series/field gradients are high P/T, medium P/T, and low P/T. Zones are separated by isograds (lines of constant grade) and are marked by the appearance of index minerals. |
4.5.1 Be able to list the index minerals for pelitic and carbonate rocks 4.5.2 Use the concept of facies series to predict on a map which direction was higher P&T, and explain using the terms isograd and index mineral |
| 4.6 The high temperature limit of metamorphism is melting and this is strongly influenced by the presence of H2O | 4.6.1 Using a P-T diagram that has both metamorphic reactions and rock solidi for pelitic rocks, explain how the 2ndsillimanite isograd may contribute to the production of magmas |
Big Idea 5
The changes in mineral assemblage and mineral chemistry occur through metamorphic reactions
Learning Targets and Success Criteria
| Learning Target | Success Criteria |
|---|---|
| 5.2 Composition diagrams provide a method to analyze the effect of bulk composition on mineral assemblage at a particular grade. In general we use ACF diagrams for mafic and carbonate assemblages and AFM and AKF diagrams for pelitic assemblages |
5.2.1 Use tie lines drawn on composition diagrams to determine which minerals are stable together at a given P&T (facies), or conversely, determine the P&T (facies) of the rock based on the minerals that are stable together 5.2.2 Be able to predict the mineral assemblage of a given protolith type if you know the mineral assemblage of another protolith type at the same P-T conditions 5.2.3 Use composition diagrams, a petrogenetic grid, and observations of stable mineral assemblages to assign regions in P-T space where the assemblages could have been metamorphosed (homework) |
| 5.3 Metamorphic reactions will change the geometry of composition diagrams. Each facies is represented by a diagram that differs from the next by a reaction. |
5.3.1 Given two or more different composition diagrams derive the reaction that occurs between them 5.3.2 (same as 5.4.3) Use tie-line flips or terminal reactions on composition diagrams to determine the metamorphic reactions that have occurred between two different P-T conditions 5.3.3 Derive reactions for the index minerals in pelitic rocks going up grade through Barrovian metamorphism |
| 5.4 There are multiple types of metamorphic reactions. These are phase transformations, solid-solid reactions, devolatilization reaction, continuous reactions, ion exchange reactions. |
5.4.1 Be able to explain, in the briefest way, how ion exchange reactions can be used as geothermometers and net transfer reactions as geobarometers 5.4.2 Use a P-T diagram to show the shift in a dehydration reaction as pore-fluid pressure varies 5.4.3 (same as 5.3.2) Use tie-line flips or terminal reactions on composition diagrams to determine the metamorphic reactions that have occurred between two different P-T conditions |
| 5.5 Continuous reactions span an interval of metamorphic grade where the reactants are progressively consumed, products are generated and the composition of each varies systematically. |
5.5.1 Track changing reactant and product compositions on aT-X phase diagram during heating 5.5.2 Track relative proportions of reactants versus products on a T-X phase phase diagram during heating |
Big Idea 6
The types of igneous and metamorphic rocks are controlled by their plate tectonic environment
Prerequisite skill
Knowledge of plate tectonic environments and associated P-T conditions
Learning Targets and Success Criteria
| Learning Target | Success Criteria |
|---|---|
| 6.1 Trace element discrimination diagrams can be used to determine tectonic setting of magmas | 6.1.1 Using the geochemical data from the Fidalgo field trip rocks, determine their tectonic setting of formation |
| 6.2 Oceanic divergent boundaries produce basalt through decompression melting. This process forms ophiolites |
6.2.1 Draw a concept sketch of a divergent boundary and the magmatic processes active there. 6.2.2 How do the processes in 6.3.1 create an ophiolite? |
| 6.3 Intraplate settings are the dominant locations that produce Si-undersaturated magmas by decompression melting. Si-saturation is | 6.3.1 Sketch a cross section of a ”plume” and relate the different OIB magma series (Si-saturated, Si-undersaturated, and strongly Si-undersaturated) to the Hawaiian eruptive cycle related to the amount of melting and depth of melting |
| 6.4 Convergent margins produce basalt by flux melting in the mantle but are also the most common sites for magma differentiation to produce wide ranging compositional suites. This is the only setting that produces calcalkaline magmas |
6.4.1 Sketch and explain how mantle melting occurs in magmatic arcs and compare to melting processes in a mid ocean ridge. Ultimately, where does the H2O come from? 6.4.2 Explain how crustal thickness in arcs (continental versus oceanic) plays a role in differentiation of arc magmas |
| 6.5 (related to 4.5) The three metamorphic facies series/field gradients are related to tectonic environments |
6.5.1 Show the trajectory of common facies series for mafic rocks on a P-T diagram (Subduction, Barrovian, Contact) 6.5.2 Sketch the hypothesized location for formation of blueschist facies rocks, and a simple model for getting those rocks to the surface 6.5.3 Draw a cross section of a convergent margin and show where you would find the three common facies series/field gradients. Describe the metamorphic facies you would find at each location. Be able to transfer this information to the Cascadia subduction zone. |