Download (Yuan and Dueker 2005) Southern margin: The Cheyenne slab

Lithosphere in craton margins and adjacent
orogens: seismic structure and tectonic
implications
Huaiyu Yuan
CCFS-Macquarie University, University of WA, Geological Survey WA
Australia
IGG-CAS Jan. 17 2014
 Building craton lithosphere
Lee et al., Annu. Rev. Earth Planet. Sci, 2011
 Destroying craton lithosphere
Lee et al., Annu. Rev. Earth Planet. Sci, 2011
 High resolution image along craton margins/orogens
 High resolution image along craton margins/orogens
o Temporary line/2D array setup; 1-2 year deployments
o Array processing methods: body wave tomography; receiver functions;
ambient noise
o Few 100s km lateral structure with 10s km lateral resolution: better than TA
resolution
 Observations regarding craton stabilization and
reworking
 High resolution image along craton margins/orogens
o Temporary line/2D array setup; 1-2 year deployments
o Array processing methods: body wave tomography; receiver functions;
ambient noise
o Few 100s km lateral structure with 10s km lateral resolution: better than TA
resolution
 Observations regarding craton stabilization and
reworking
o Examples in Wyoming craton and surrounding orogens/margins
o Building a craton: subduction polarity reversal; Wedge tectonics
o Destroying mechanism: plume erosion; mid-crustal sill; lower crustal flow;
magmatic underplating (7.x layer).
Wyoming craton
Yuan et al. 2011; Modified from Whitmeyer and Karlstrom 2007
Wyoming craton
Yuan et al. 2011; Modified from Whitmeyer and Karlstrom 2007
o Proterozoic orogens along 3 sides
o Cheyenne belt extensively studied
o West margin unclear; affected by
Yellowstone hotspot system
Foster et al., 2006
Wyoming craton
Yuan et al. 2011; Modified from Whitmeyer and Karlstrom 2007
o Upper mantle dipping reflectors
from active imaging along north
border: imbricated slab
Gorman et al., 2002
Foster et al., 2006
Geophysical lines/arrays
Yuan and Dueker 2010; Modified from Mueller and Frost 2006
Southern margin: The Cheyenne slab
 Archean/Proterozoic (1.78-1.76 Ga;
Karlstrom 1988) southward
subduction;
o lack of subduction related rocks on the
Archean side;
o dip of mylonite zones along the shear
zone on the surface
Southern margin: The Cheyenne slab
 CD-ROM lines image the structure using Pand S-wave body wave tomography (Yuan
and Dueker 2005)
Southern margin: The Cheyenne slab
 North dipping high velocity found beneath
the Cheyenne belt
P-wave
S-wave
Model
Error
Spike
test
Southern margin: The Cheyenne slab
 North dipping high velocity found beneath the Cheyenne belt
P-wave
S-wave
Model
Error
Spike
test
 Proposed as a fossil slab segment,
the Cheyenne slab
 Consistent with north-dipping
anisotropy modelled by shear
wave splitting
 Requires anisotropy present in the
“slab”
Southern margin: The Cheyenne slab
 Subduction polarity reversal is proposed
Southern margin: The Cheyenne slab
 High velocity Cheyenne slab observed along the whole southern margin
 Receiver function CCP
structure follows the slab
interface
Yuan and Dueker, 2010
Southern margin: Imbricated Moho
 Receiver function CCP image across the Cheyenne belt
 Laramie array: 30 sites with 2-km spacing; 1 year operation
 No Moho in active reflection images
Southern margin: Imbricated Moho
 Imbricated Moho: Archean + Proterozoic Moho
 Consistent with northward subduction
P-wave CCP Stacking
Proterozoic Moho
Archean Moho
Southern margin: Imbricated Moho
 Imbricated Moho: Archean + Proterozoic Moho
 Consistent with northward subduction
S-wave CCP Stacking
P-wave CCP Stacking
Archean Moho
Proterozoic Moho
Hansen and Dueker 2009
Southern margin: The Wedge tectonics
 The Wedge tectonics: stronger Archean lithosphere vs weaker (more
deformable) juvenile terrane lithosphere
Archean Moho
Proterozoic Moho
Snyder 2002
Southern margin: The Wedge tectonics
 The Wedge tectonics along the Cheyenne belt
Note red is positive gradient in 2 and 3!
Yuan and Dueker, 2010
Western margin: Yellowstone plume
 Plume interacting with the Archean lithosphere
 Ambien noise image of the crust and shallow
upper mantle
USGS website
Western margin: Yellowstone plume
 Plume interacting with the Archean lithosphere
 Ambien noise image of the crust and shallow
upper mantle
Stachnik et al. 2008
Western margin: Yellowstone plume
 Thinning of lithosphere under the hotspot track
Stachnik et al. 2008
Western margin: Yellowstone plume
 Consistent with body-wave Yellowstone plume image
Stachnik et al. 2008; Yuan et al. 2005
Western margin: Yellowstone plume
 Magma injection into the crust: mid-crustal sill and lower
crustal flow
Mid-crustal sill (MCS)
Stachnik et al. 2008
Western margin: Yellowstone plume
 Magma injection into the crust: mid-crustal sill and lower
crustal flow
Peng and Humphreys, 1998
Western margin: Yellowstone plume
 Magma injection into the crust: mid-crustal sill and lower
crustal flow
Stachnik et al. 2008
Western margin: Yellowstone plume
 Earlier magma injection in the Archean crust: 7.x layer
7.x P-wave velocity from active source modeling
Stachnik et al. 2008
7.x layer
Western margin: Yellowstone plume
 7.x layer in receiver functions, active source imaging and
gravity modeling
Yuan et al. 2010
Snelson et al. 1998
Summary
 Paleo-subduction and imbrication played an important
role in craton stabilization by docking Proterozoic
terranes to the Archean craton
 Inconsistent observations with surface geology suggest
subduction polarity reversal
 Yellowstone plume strongly modified Archean craton by
eroding (thinning) the lithosphere;
 Also increased crust volume by injecting magma into the
crust
Magma injection & forming of Mid-crustal sill
Mid-crustal sill induces lower crustal flow