Laboratory Modelling of 3-D Flow and Temperatures in Subduction Zones with Back-arc Spreading and Plumes

Chris Kincaid 1 , Ross Griffiths 2 , John Foden 3 , Charles Langmuir 4 , Richard Carlson 5 , David James 5

1 Graduate School of Oceanography, University of Rhode Island , Narragansett , RI , USA
2 Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
3 School of Earth and Environmental Sciences , University of Adelaide , Adelaide , SA 5005, Australia
4 Department of Earth and Planetary Sciences, Harvard University , Cambridge , MA , USA
5 Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington DC , USA

Subduction of lithospheric plates back into the mantle at subduction zones (ocean trenches) provides the dominant driving force for plate tectonics and causes thermal and chemical exchange with the Earth's interior. We have developed a laboratory apparatus for modeling 3D aspects of flow in subduction zones in response to various modes by which plates move and subduct into the mantle. These include both slab rollback, when the slab sinks with a backward retreating or horizontal component of motion, and periods where the angle of descent (slab dip) either increases or decreases with time. Previous work has documented the importance of these modes of plate motion on 3D shallow mantle return flow and both slab and mantle wedge temperatures (Kincaid and Griffiths, 2003; 2004). During a recent visit to RSES, Kincaid has been studying the role of back-arc spreading (BS) on slab/mantle evolution and the interaction between subduction and buoyant mantle upwellings (plumes). A series of experiments started in 2004 and completed here in 2006 (with collaborator C. Langmuir) characterize spatial and temporal patterns in slab and mantle wedge temperatures for various modes of plate sinking and back-arc spreading, including extension produced by slab/arc retreat versus motion of the overriding plate. Parameters explored include subduction style, width of the BS center, extension rate and the BS center–to–trench separation distance. Results show dramatic differences in the plate and overlying mantle wedge evolution depending on conditions. For example, BS due to trench/plate rollback produces very shallow flow trajectories in the wedge (which are unfavorable for decompression melting) but extreme lateral variations in slab heating and shallow back-arc temperatures (Figure 1). Extension produced by retreat of the overriding plate away from the arc/trench produces laterally uniform slab/wedge temperatures and steep return flow trajectories (favorable for decompression melting). Results are being related to recent data sets collected by C. Langmuir in the Tonga-Lau system.

During his 2006 visit to the GFD facility at RSES, Prof Kincaid (with ARC collaborator J. Foden) has considered what temporal changes in plate motions (slab and BS) allow material from a hydrated boundary layer above the downgoing slab to be brought up into the melting zone beneath either the arc or the back-arc. Results are being related to geological data on the spatial and temporal distributions of Boninite magmas in subduction environments. This work is related to another long term NSF funded project involving a multidisciplinary, multi-institutional approach to studying the continental evolution of the northwestern USA (http://www.dtm.ciw.edu/research/HLP). The project includes geological and geochemical field work (T. Grove, MIT; A. Grunder & R. Duncan, OSU; W. Hart, Miami; R. Carlson, Carnegie), seismic imaging (D. James, Carnegie; M. Fouch, Arizona; R. Keller, UO; S. Harder, UTEP) and geodynamic modeling (Kincaid/Griffiths). We have added to the existing apparatus the ability to introduce plumes (with a controlled location, temperature and buoyancy flux) to model how both plume heads and tails are deformed by extreme three-dimensional shear flows that are produced in subduction zones with rollback and back-arc extension (Figure 2). Both generic cases to document basic plate-plume interaction modes and experiments with parameters (e.g., plate motion histories) specific to the Cascades-Yellowstone system will be run.

Figure 1. Plots of temperature perturbations produced along the surface of the subducting slab (A) and beneath the back-arc spreading center. Values are plotted as a function on distance from either the center of the slab or the back-arc spreading axis. Values are laboratory perturbations, produced by subtracting off initial reference values (5°C for the slab, ~15°C for the back-arc). Slab surface temperatures are from a scaled depth of 160 km after ~30 Ma of subduction. Sub-back-arc values are from a scaled depth of 20 km after 30 Ma of extension for cases with a 250km trench - back-arc separation. (OP=overriding plate)  

Figure 2. Side view movie of a laboratory experiment that includes a subducting plate (rollback sinking), backarc extension and a buoyant plume.

 

References: Kincaid, C., and R. W. Griffiths (2003) Thermal evolution of the mantle during rollback subduction, Nature , 425 , 58-62

Kincaid, C. and R. W. Griffiths (2004) Variability in mantle flow and temperatures within subduction zones. Geochem. Geophys. Geosyst. , 5, Q06002, doi:10.1029/2003GC000666