Plate Tectonics as Expressed in Geological Landforms and Events part of MARGINS Data in the Classroom:MARGINS Mini-Lessons
This activity seeks to have students analyze global data sets on earthquake and volcano distributions toward identifying major plate boundary types in different regions on the Earth. While the focus of the activity as written is on two NSF-MARGINS focus areas, any region of the Earth for which this data is available can be targeted. A secondary objective of the activity is to familiarize students with two publicly available resources for viewing and manipulating geologically-relevant geospatial data: Google Earth(TM) and GeoMapApp, a Java-based marine geoscience data resource and visualization tool maintained by the Marine Geoscience Data Systems at Lamont-Doherty Earth Observatory.
Serpentinite in Subduction Zones: How do we find it, and how common is it? part of MARGINS Data in the Classroom:MARGINS Mini-Lessons
One of the interesting discoveries arising out of the MARGINS Subduction Factory Initiative is the recognition that serpentinites - metamorphically hydrated products of ultramafic rocks that are rich in serpentine group minerals - are significant constituents of both the mantle wedge and downgoing plate. Serpentine minerals are interesting mineralogically because of their distinctive physical properties, habits and appearance; and for their commonly close affinities for olivine and Mg-rich pyroxenes. As well, serpentine group minerals are interesting rheologically because, as sheet silicates, they can behave in a plastic fashion in rocks that are undergoing deformation. This activity leads students through a range of literature sources and activities, including GeoMapApp manipulations and some "back of the envelope" calculations about isostatic compensation and volumetric expansion during serpentinization to help them appreciate the different ways that the presence of serpentinite can be observed or inferred in subduction zone settings. A second but equally important goal is to familiarize students with some of the basic kinds of data and interpretive approaches used by geochemists and geophysicists in studying modern subduction zone environments. This activity is targeted for use in Junior- or Senior-level mineralogy and/or petrology courses. It makes use of published data and information from both of the MARGINS Subduction Factory focus sites (Izu-Bonin-Mariana and Central America), as well as information from meeting presentations posted on the NSF-MARGINS homepage site. It presumes a basic familiarity with examining geospatial data (primarily comparative elevations) using GeoMapApp. It is suggested that students be provided with thin sections or hand samples of actual serpentinites to give them a better understanding of what these materials are, and how they compare to olivine-rich ultramafic rock samples more typical of 'fresh' mantle.
Serpentine Seamounts in the Mariana Forearc: Shallow Material Releases from Downgoing Plates part of MARGINS Data in the Classroom:MARGINS Mini-Lessons
This is a resource of published images and diagrams, and GeoMapApp/Google Earth captures of geophysical survey results for use in describing the unique phenomenon of active serpentinite mud volcanism observed in the shallow forearc region of the Mariana subduction system. Students should be familiar with the concept of subduction and one of its primary petrologic implications - that materials (specifically sediments, ocean crust, and H2O-rich fluids) long residing at the Earth's surface are transported down deep sea trenches, with the release of bound fluids (and fluid-soluble chemical species from the downgoing plate) occurring progressively with increasing depth. These materials are intended to be used as aids in lecture or discussions of this phenomenon in the context of instruction on the process of subduction.t
What Goes into Making Volcanic Arc Magmas, and How Do We Know It? part of MARGINS Data in the Classroom:MARGINS Mini-Lessons
One of the challenges in teaching undergraduate petrology students about the origins of subduction-related magmas and igneous activity at volcanic arcs is that this system is much more complex than that encountered at mid-ocean or intraplate settings: the sources of magmas are variable (i.e., the mantle, the downgoing plate, and/or the overriding crust may provide part or all of the magmatic source materials), and their histories from their point of origin to eruption are complex. An additional complication is that much of what we know about the material contributors to subduction-zone magmas has been learned through arcane trace element and isotopic studies of arc lavas and associated subduction zone metamorphic rocks, a body of literature (and geologic subdiscipline) with which undergraduates are likely to have little experience. This activity is intended as a directed reading exercise for undergraduates in a junior- or senior-level petrology course aimed at leading them through the how and why of our current views on arc petrogenesis, while along the way familiarizing them with key aspects of trace element and isotope geochemistry: specifically, the concept of trace element solid/melt and solid/fluid partitioning, and its use in defining how a particular elemental signature in a rock can originate. The readings are key geochemical papers that track the development of our current views on the petrogenesis of arc lavas, and some associated controversies (i.e., melting of the subducting slab, and the role of subduction-related serpentinites).
Online Investigation of an Island Arc Volcano: Anatahan, Mariana Arc part of MARGINS Data in the Classroom:MARGINS Mini-Lessons
Current students have online access to nearly unlimited information in an entirely unfiltered state. As such, they need guidance in training in assessing information quality and identifying high-quality information resources for educational and research use. In this activity, students will conduct a directed Web surf/search effort for information on and datasets from the Anatahan arc volcano, which they will use in an interpretive study of recent magmatic activity in the Mariana arc. Students should have been exposed to concepts related to magma genesis and the nature of subduction zone magmatism before conducting this activity. As well, a rudimentary knowledge of trace element geochemistry and its application to the study of igneous rocks is expected, or should be prepared for if this activity is used. The activity is designed as an extended homework "project" exercise that complements hands-on laboratory work in volcanic rock description and analysis. An intent of the activity is to help students connect the volcanic rock samples they see in the lab to a real volcanic event that they discover through their own research efforts.