An Izu-Bonin-Mariana Arc Thematic Mini-Lesson Package. Initiated by Jeff Ryan (University of South Florida), Rosemary Hickey-Vargas (Florida International University) & Leslie Peart (JOI/Smithsonian) at the Margins Education Mini-Workshop: Bringing MARGINS Science to the Classroom, April 5-6, 2007, Arlington, VA Rationale: The idea is to develop a set of mini-lessons using the IBM subduction factory to illustrate geologic concepts that would normally be taught in an upper level undergraduate course, like Petrology, Sedimentology, Geophysics or Geochemistry. The rationale for using the IBM arc system is twofold. First, this focus area was chosen because many important subduction parameters vary along its length and width, so it is ideally suited for illustrating how subduction processes operate. A second rationale is that by making the mini-lessons, IBM researchers can determine what aspects of IBM science, observations and findings get into our college classrooms. Question for IBM Education Group: What aspects of IBM science, observations and findings are most important to get into our college classrooms? V) Backarc Basins 1) How is the development of a back arc spreading center related to stress in the overlying plate? Compare bathymetric maps of the Izu-Bonin and Mariana segments of the IBM arc, your findings in I to answer this question. 2) What is the difference between flux melting and decompression melting? What aspects of magma geochemistry suggest that IBM arc magmatism is dominated by flux melting and back arc magmatism is dominated by decompression melting.. 3) How is the subducted crust metamorphosed? Look at published P-T diagrams for the stability of the minerals in sediments from II-1 and for seafloor basalt. Make a possible sequence of minerals that would appear in the subducted plate with depth. Which minerals would release water and which could carry water to the greatest depths. 4) Using published cross-sections of the Izu-Bonin and Mariana segments, estimate the difference in depth to the top of the Pacific plate beneath the back arc regions. How would this difference affect the sequence of minerals determined in V-3? IV) Arc volcanoes and arc crust 1) What influences the location of volcanoes? Look at a bathymetric map and measure the distance between adjacent active volcanoes, and distance to the trench. Is there a regular spacing? Based on your answer to I-2, are the volcanoes located the same distance above the subducting plate? Why or why not? 2) The Anatahan volcano has erupted several times since the IBM Focus area was established. What is the average composition of lava erupted from this volcano? How does this compare with “average continental crust”. Assume that the IBM crust is like average “continental crust” and think of explanations for differences between the crustal composition and erupted lava. 3) Look at seismic profiles of arc crust in the Izu-Bonin and Mariana arc segments. How does the observed layering of the crust support or refute your arguments from IV-2. Are the profiles like continental crust? 4) How much water is recycled by IBM arc volcanoes? Find a recent estimate for the water content for undegassed IBM arc magma and published estimates of magma production rates for the arc. Estimate how much water can be recycled by magmatic degassing (per km arc length per unit time) and compare this with your estimate of subducted water in II-3 and II-4. 5) How are elements recycled from the slab to arc magmas? Do the calculation of II-2 for the elements Ba, Th and K. Compare these with the composition of IBM arc volcanic rocks from the Izu, Bonin and Mariana segments. Consider both the actual concentrations of the elements, and their ratios (i.e., Ba/Th, K/Th, K/Ba). Think of some reasons that the elemental abundances may or may not match. I Subduction parameters 1) How does the convergence direction and rate vary along the IBM arc? Use Pacific and Philippine Sea plate velocities and vectors to estimate the change in the rate and direction of convergence along the arc. 2) How does the dip of the Pacific Plate vary along the IBM arc? Use the location of earthquake foci and seismic tomographic images to estimate the dip at different locations along the arc. II) The downgoing Pacific Plate 1) What is the sedimentology/lithology of the downgoing plate? Use the sediment column for the Reference Site to understand oceanic sedimentology, the Geologic Time scale and the interpretation of sediments in terms of depositional environments. How are the sediments different along the arc? This is the oldest seafloor on Earth, where did this seafloor originate? 2) What is the bulk composition of the downgoing plate? Use the Reference column to calculate a bulk major elemental composition, using average compositions for basalt, clay, etc. Compare this weighted average with a typical arc basalt or andesite (see IV-2). How do they compare? 3) What is the water content of the downgoing plate? Use ODP data for pore water content/sample and density to estimate the mass of water in a cubic kilometer section of downgoing plate. 4) How long would it take to recycle an “ocean’s” worth of water? Use part II-3) and the rate of convergence (I-1) to estimate the amount of water delivered per kilometer arc length per year. III) Forearc 1) What are mud volcanoes and how do they compare with “magma” volcanoes? Look at maps, sonar images, cross-sections of serpentinite seamounts and compare with the cross section of well known stratocones of 2000 meter height. Why are the shapes different? 2) What is serpentine and why does it form in the forearc? Outline the serpentinization process: water + olivine, temperature constrained by polymorphs, alkaline water. Where is there paleo-evidence for this process? 3) What kinds of vent communities live on mud volcanoes? Research examples of cold versus hot, alkaline versus acid, low alkalinity versus high alkalinity vents. 4) How much water can be held in the forearc? Use III-2 and the breadth of the forearc to estimate how much water could be contained in the forearc. How does this compare with the total calculated in II-3? These are some sample ideas for IBM mini-lessons - “learning activity snippets”. What is missing? Feel free to add more. Which are most important? What is a mini-lesson? ( MARGINS Mini-Lessons are modular learning materials that repurpose the data resources, visualizations, and other information sources developed through MARGINS and MARGINS-related research for use in examining fundamental earth processes in undergraduate classrooms from a multidisciplinary perspective. Several different types of learning materials are being developed: Web-deliverable Laboratory/Classroom Exercises: exercises and activities that can be downloaded in their entirety from the website. These are available at several scales and are suitable for use in either introductory or upper-level geoscience courses. Larger Mini-Lessons are scaled for use as a full laboratory session or across several lecture meetings, while the smaller Lessons may be annotated sets of visualizations, short interactive activities, or other materials for use within a lecture or laboratory session. Virtual Expeditions: These aim to bring the results of the MARGINS research across a number of courses (oceanography, marine geology, tectonics, geophysics, structural geology, petrology). Each module consists of linked web pages that trace the development of specific research projects through a combination of short video segments, process-based animations, interactive graphics, and real-time data from land and ocean observatories. This approach to learning is driven by a series of linked questions that progressively increase in sophistication, much like the evolution of a research project. These questions lead students through the process of scientific discovery while learning about MARGINS research.