rock record constraints on the seismic signature of ...rock record constraints on the seismic...

2.4

2.2

2.0

1.8

1.6

VP / V

S

mod

ern

subd

uctio

n zo

nes*

rock

s &

min

eral

s*Lz

dQ

tz

isot

ropi

cca

lcul

ated

usi

ngA

bers

& H

acke

r[2

016]

Con

drey

Mou

ntai

n Sc

hist

She

ar Z

one

cum

ulat

ive

sign

uatu

re o

fm

iner

al a

niso

trop

y &

frac

ture

sca

lcul

ated

usi

ng M

SAT

**A

udet

& K

im, 2

016

Stage 1Stage 2Stage 3

1. Rapid underplating

downgoing plate

interfaceshear zone

increasingthicknessover time

overriding plate

up to4 km

ė ~ 10-13

2. Non-accretionary period

downgoing plate

interface shear zone

up to0.5 km

overriding plate

3. Onset of underplating

ė ~ 10-13

downgoing plate up to2 km

overriding plate

interfaceshear zone

Carolyn M. Tewksbury-Christle1*, Dr. Whitney M. Behr1, & Dr. Mark A. Helper2

1: Department of Earth Sciences, ETH Zürich, 2: Department of Geological Sciences, Jackson School of Geology, University of Texas at Austin

Rock record constraints on the seismic signature of subduction interface shear zones SGTETHZ

VP

/ VS

oceanic mantleov

errd

ing

plat

e

sediments

oceanic crust

viscous interface shear zone

MOHO

dow

ngoi

ngpl

ate

plate interface

Low Velocity Zone

LowVelocityZone3-5 km

SubductionInterfaceShear Zone0.5 - 4+ km

overriding platedowngoing plate

shear zone thickness & occupying lithologies vary temporallycombined detailed geochronology & structural mapping to track strain localization evolution

seismic signature is highly anisotropic & VP/VS are elevatedaccounted for mineral anisotropy & fracture porosity measured from the CMS rock record

The fossil subduction interface shear zone preserved in the CMS records:

1) distributed deformation comparable to or within modern LVZ thicknesses

2) comparable seismic signatures to modern LVZs

VP

/ VS

VP

/ VS

ė ~ 10-12

© Tewksbury-Christle, Behr, & Helper. All rights reserved. Work is in preparation for submission to Geophysical Research Letters. Please contact carolyn.tewksbury-christle@erdw.ethz.ch with questions.

Used to characterize:

1) thickness & lithologies of the actively deforming interface

2) seismic signature for comparison to modern subduction zones

Condrey Mountain Schist (CMS) records Late J - Early K subduction and punctuated underplating at 350-450°C and 0.8-1 GPa

Graphitic Mica SchistEpidote Blueschist

CMSi (Epidote Blueschist Facies)

Serpentinite Dioritic to tonaliticorthogneiss

Greenschist

Graphite Phyllite

CMSo(Greenschist Facies)

X X’

0 5 km V.E. = 1x

fault

thrust fault

inferred fault

contact

map & cross-section after Helper, 1985additions as in Tewksbury-Christle et al., in prep

prograde ductile thrusts

mappedductilethrust

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.04

1.23

2.00

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

2.39

1.60

2.26

1.5

1.6

1.7

1.8

1.9

2.00

1.47

1.83

OR

CA

after Snoke &Barnes, 2006

42°00’

41°45’

X X’

123°00’ 123°10’

0 5 km

ORCA

124° 123°

43°

42°

41°

Medford

Redding0 30 km

KlamathTerranes

Franc

iscan

CondreyMountain

Schist

Compl

ex