CCFS-Macquarie University, University of WA, Geological - PowerPoint Presentation

Slide1

CCFS-Macquarie University, University of WA, Geological Survey WA

Australia

IGG-CAS Jan. 17 2014

 Lithosphere in craton margins and adjacent orogens: seismic structure and tectonic implications

Huaiyu YuanSlide2

Building craton lithosphere

Lee et al., Annu. Rev. Earth Planet. Sci

, 2011Slide3

Destroying craton lithosphere

Lee et al., Annu. Rev. Earth Planet. Sci, 2011Slide4

High resolution image along craton margins/orogensSlide5

High resolution image along craton margins/orogens

Temporary line/2D array setup; 1-2 year

deploymentsArray processing methods: body wave tomography; receiver functions; ambient noise

Few 100s km lateral structure with 10s km lateral

resolution: better than TA resolutionObservations regarding craton stabilization and reworkingSlide6

High resolution image along craton margins/orogens

Temporary line/2D array setup; 1-2 year

deploymentsArray processing methods: body wave tomography; receiver functions; ambient noise

Few 100s km lateral structure with 10s km lateral

resolution: better than TA resolutionObservations regarding craton stabilization and reworking

Examples in Wyoming craton and surrounding orogens/marginsBuilding a craton: subduction polarity reversal; Wedge tectonicsDestroying mechanism: plume erosion; mid-crustal sill; lower crustal flow;

magmatic

underplating (7.x layer).Slide7

Wyoming craton

Yuan et al. 2011; Modified from Whitmeyer and Karlstrom 2007Slide8

Wyoming craton

Yuan et al. 2011; Modified from Whitmeyer and Karlstrom 2007

Foster et al., 2006

Proterozoic orogens along 3 sides

Cheyenne belt extensively studied

West margin unclear; affected by Yellowstone hotspot systemSlide9

Wyoming craton

Yuan et al. 2011; Modified from Whitmeyer and Karlstrom 2007

Foster et al., 2006

Upper mantle dipping reflectors from active imaging along north border: imbricated slab

Gorman et al., 2002Slide10

Geophysical lines/arrays

Yuan and Dueker 2010; Modified from Mueller and Frost 2006Slide11

Southern margin: The Cheyenne slab

Archean/Proterozoic (1.78-1.76 Ga; Karlstrom 1988) southward subduction;

lack of subduction related rocks on the Archean side;

dip of mylonite zones along the shear zone on the surface Slide12

Southern margin: The Cheyenne slab

CD-ROM lines image the structure using P- and S-wave body wave tomography (Yuan and Dueker 2005)Slide13

Southern margin: The Cheyenne slab

North dipping high velocity found beneath the Cheyenne belt

P-wave

S-wave

Model

Error

Spike

testSlide14

Southern margin: The Cheyenne slab

North dipping high velocity found beneath the Cheyenne belt

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”

P-wave

S-wave

Model

Error

Spike

testSlide15

Southern margin: The Cheyenne slab

Subduction polarity reversal is proposedSlide16

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, 2010Slide17

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 imagesSlide18

Southern margin: Imbricated Moho

Imbricated Moho: Archean + Proterozoic Moho

Consistent with northward subduction

Archean Moho

Proterozoic Moho

P-wave CCP StackingSlide19

Southern margin: Imbricated Moho

Imbricated Moho: Archean + Proterozoic Moho

Consistent with northward subduction

Archean Moho

Proterozoic Moho

P-wave CCP Stacking

S

-wave CCP Stacking

Hansen and Dueker 2009Slide20

Southern margin: The Wedge tectonics

The Wedge tectonics: stronger Archean lithosphere vs weaker (more deformable) juvenile terrane lithosphere

Archean Moho

Proterozoic Moho

Snyder 2002Slide21

Southern margin: The Wedge tectonics

The Wedge tectonics along the Cheyenne belt

Note red is positive gradient in 2 and 3!

Yuan and Dueker, 2010Slide22

Western margin: Yellowstone plume

Plume interacting with the Archean lithosphere

Ambien noise image of the crust and shallow upper mantle

USGS websiteSlide23

Western margin: Yellowstone plume

Plume interacting with the Archean lithosphere

Ambien noise image of the crust and shallow upper mantle

Stachnik et al. 2008Slide24

Western margin: Yellowstone plume

Thinning of lithosphere under the hotspot track

Stachnik et al. 2008Slide25

Western margin: Yellowstone plume

Consistent with body-wave Yellowstone plume image

Stachnik et al. 2008; Yuan et al. 2005Slide26

Western margin: Yellowstone plume

Magma injection into the crust: mid-crustal sill and lower crustal flow

Stachnik et al. 2008

Mid-crustal sill (MCS)Slide27

Western margin: Yellowstone plume

Magma injection into the crust: mid-crustal sill and lower crustal flow

Peng and Humphreys, 1998Slide28

Western margin: Yellowstone plume

Magma injection into the crust: mid-crustal sill and lower crustal flow

Stachnik et al. 2008Slide29

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 layerSlide30

Western margin: Yellowstone plume

7.x layer in receiver functions, active source imaging and

gravity modeling

Yuan et al. 2010

Snelson

et al.

1998Slide31

SummaryPaleo-subduction and imbrication played an important role in craton stabilization by docking Proterozoic terranes to the Archean cratonInconsistent observations with surface geology suggest subduction polarity reversalYellowstone plume strongly modified Archean craton by eroding (thinning) the lithosphere; Also increased crust volume by injecting magma into the crustSlide32
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Magma injection & forming of Mid-crustal sillSlide34

Mid-crustal sill induces lower crustal flow