Determining Mantle Temperature and Composition from Discontinuities

Anna Courtier

James Madison University, courtiam@jmu.edu

This activity is part of the On the Cutting Edge Exemplary Teaching Activities collection and has been reviewed by 1 other review process

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This page first made public: May 17, 2010

Summary

This pair of activities uses observations of mantle discontinuity structure to examine mantle heterogeneity and differences in the depth extent of melt sources for ridges and "hotspots." The first activity focuses on interpretations linked with temperature anomalies, and the second activity emphasizes that contributions from variable composition (iron and water) are important to consider as well.

Tectonophysics, Geochemistry, Mineralogy | College Upper (15-16)

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Context

Audience

Upper level undergraduate. Previously used in a Special Topics course (Geochemistry and Geophysics of Hawaii from Top to Bottom). Could be used in Petrology or Geophysics/Solid Earth courses as well.

Skills and concepts that students must have mastered

Basic Excel calculations, Phase Diagrams

How the activity is situated in the course

These are a pair of exercises that led up to a "mantle plume debate" in a Special Topics course.

Goals

Content/concepts goals for this activity

Concepts addressed include: mantle heterogeneity, mantle potential temperature, mantle discontinuities/phase transitions, and phase diagrams.

Higher order thinking skills goals for this activity

Data manipulation, evaluation of errors, evaluation of potential interpretations.

Other skills goals for this activity

Description of the activity/assignment

This activity is divided into two parts - 1) Using data from primary literature to calculate mantle potential temperature beneath a ridge and an oceanic island ("hotspot"). 2) Using the transition zone thickness observed beneath a "hotspot" (Hawaii) to analyze contributions from anomalous temperature and composition. In addition to the student activity sheets, an Excel key, instructor notes, and student handouts are included below.

Determining whether students have met the goals

Calculations can be checked with the Excel key. Both activities include short-answer questions that can be graded to assess students' understanding of the material. An in-class discussion following the second part of the activity also worked well for assessment and helped students to detect "holes" in some of their own arguments or interpretations.

More information about assessment tools and techniques.

Teaching materials and tips

Activity Description/Assignment

#1: "Hotspot" vs Ridge Temperature Activity (Microsoft Word 638kB Feb25 10)

#2: Student Handout for Temperature vs Composition Interpretations (PowerPoint 346kB Feb25 10)

#3: Phase Diagrams (Acrobat (PDF) 274kB Feb25 10)
Instructors Notes:
For #1 above: Transition Zone Discontinuity Slides (PowerPoint 2.7MB Mar25 10). These slides include an overview of transition zone temperature and methods used to study mantle discontinuities.

For #2 and 3 above: Instructor Notes for Phase Diagram Interpretation (Microsoft Word 39kB Feb25 10). This document outlines the phase diagrams used for the temperature vs composition interpretations and suggests issues to address with students.
Solution Set:
For #1 above: Excel Key for Temperature Activity (Excel 33kB Feb25 10)

Other Materials

Supporting references/URLs

Courtier, A. M., B. Bagley, and J. Revenaugh (2007), Whole mantle discontinuity structure beneath Hawaii, Geophysical Research Letters, 34, L17304, doi:10.1029/2007GL031006.

Katsura, T., et al. (2003), Post-spinel transition in Mg2SiO4 determined by high P-T in situ x-ray diffractometry, Physics of the Earth and Planetary Interiors, 136, 11–24.

Katsura, T., et al. (2004), Olivine-wadsleyite transition in the system (Mg, Fe)2SiO4, Journal of Geophysical Research, 109, B02209, doi:10.1029/2003JB002438.

Lawrence, J.F., Shearer, P.M., 2006. A global study of transition zone thickness using receiver functions. Journal of Geophysical Research 111. doi:10.1029/2005JB003973.

Lawrence, J.F., Shearer, P.M., 2008. Imaging mantle transition zone thickness with SdS-SS finite-frequency sensitivity kernels. Geophysical Journal International, 174:1, 143-158.

Li, X., Kind, R., Priestley, K., Sobolev, S.V., Tilmann, F., Yuan, X., Weber, M., 2000. Mapping the Hawaiian plume conduit with converted seismic waves. Nature 405, 938–941.

Shen, Y., C. J. Wolfe, and S. C. Solomon (2003), Seismological evidence for a mid-mantle discontinuity beneath Hawaii and Iceland, Earth and Planetary Science Letters, 214, 143– 151.

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