Overview: The Subduction Factory Mini-lessons

Chris Kincaid, Bob Stern, Sarah Penniston-Dorland, Ben Edwards

Subduction boundaries are the main places where heat and mass are continuously cycled between Earth's interior and exterior. Subduction of oceanic lithosphere causes some of the most dangerous of all natural hazards: the most violent earthquakes and tsunamis and the most explosive volcanism. Subduction also gives rise to beneficial products, such as ore deposits, geothermal energy and the very ground we live on. The Subduction Factory recycles raw materials from the seafloor and underlying mantle, creates products on the upper plate in the form of melts, aqueous fluids and gases, and modulates the dynamics of plate tectonics.

The MARGINS Subduction Factory Initiative (SubFac) focused on three sub-themes:

  1. The relationship of magma output and composition to forcing functions such as convergence rate, plate age, and sedimentary input.
  2. The cycling of volatiles from the slab to the mantle wedge and ultimately to either the crust and surface reservoir or back into the deep mantle.
  3. The production rate of arc crust.

The Central American and Izu-Bonin-Mariana magmatic arcs were chosen during open meetings by the geoscientific community to be the foci for a wide range of geochemical and geophysical studies because they represent two different types of factories: one whose input is old oceanic crust (IZB) and the other young oceanic crust (CAVA).

To help integrate important results from SubFac into geoscience curricula, we have developed three mini-lessons intended to guide student exploration of heat and mass inputs and outputs of the Subduction Factory:

  • Subfac: Subduction zone metamorphism - this module introduces students to subduction zone metamorphism by examining what happens to basalts during subduction, calculating P-T-t paths, and comparing the paths to thermal model predictions. This module also provides an opportunity for instructors to obtain teaching samples of fresh Mid-Ocean Ridge Basalt, greenstone, blueschist, and eclogite.

  • Subfac: Central American arc volcanoes, petrology, and geochemistry - this module uses basic concepts in igneous petrology, from hand specimen identification of lavas to major element geochemistry, to teach students how to investigate processes that lead to the production of petrologic diversity in subduction zones using two Central American arc volcanoes as examples.

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