7/31/2019 Cross Section Canada and USA G95A_Hammer_Insert_HighRes

1/1

f)

-1 30 -125

WRCB

OL CR

PR

HA

BR

S

eattl

e

JUANDE FUCA

PLATE

EXPLORERPLATE

5 0

4 8

Reflection

R/WARTeleseismic

Subduction trench

EE

E

EOMR OM T

a)

Asthenosphere

J u a n d e F u c a

e l t n a M c i r e h p

s o h t i L

Garibaldi Volcanic Belt

VancouverVancouver Island

WrangelliaC

Cascadia MegathrustInterface

SerpentinizedMantle

E

b)

d)

e)

[Clowes et al., 1987b]

C

SW-NE E -WEN-WS

5.0

8.28.0

6.2

7.06.8

6.66.2

7.06.6

7.0

6.66.66.8

6.87.0 6.8

6.6

8.0

6.25.8

7.87.67.6

[Dre w and C low es , 1990 ] [Ramachand ran e t a l . , 2006 ] [Ze l t e t al . , 19 93 ]

c)

F

FOM T

OMR

E

C

FOMR

OM T

Va n c

o v e ru

D e p

t h ( k m

)

40

60

0

20

80

200 km0 100

200 km0 100

200 km100100

40

60

0

20

80

D e p

t h ( k m

)

D e p

t h ( k m

)

100

40

60

0

20

80

40

60

0

20

D e p

t h ( k m

)

40

0

20

D e p

t h ( k m

)

[Calvert et al., 2006] [Nicholsonet al., 2005]

Inset Figure A: Results from the Cascadia subduction zone. Heterogeneous structure along strike complicates interpretation and resolution of discrepancies between theactive source seismic and teleseismic studies. (a) Simplified tectonic map locating seismic profiles. Navy and turquoise linesnear-vertical incidence (NVI) seismic

reflection profiles; green linesrefraction/wide-angle reflection (R/WAR) profile; pink lineteleseismic profile. CBCoast belt; CRCrescent; BRBridge; HAHarrison;OLOlympic; PRPacific Rim; WRWrangellia. (b) Schematic interpretation based on multidisciplinary studies. (c) P-wave velocity models based on R/WAR data (adaptedfrom Drew and Clowes, 1990; Ramachandran et al., 2006; Zelt et al., 1993). Thick black lineswide-angle reflections. (d) Offshore and onshore seismic reflection crossingcentral Vancouver Island (Clowes et al., 1987a). C and E strongly reflective bands. Blue dotted line (F reflector)interpreted top of oceanic crust; blue dashed lineMoho of subducting oceanic plate (OM R). (e) Offshore seismic reflection projected onto a line crossing Vancouver Island (Calvert et al., 2006). Pink dashed linelow-velocity zonedefined from an overlapping teleseismic profile (see f). The base of this zone is interpreted as representing the tele seismic Moho of the subducting oceanic plate (OM T).(f) Migrated teleseismic image using the scattered P-p-s phase (Nicholson et al., 2005). Broad dipping red bandlow-velocity zone interpreted as dehydrating oceanic crust(the base of which is the OM T). Dotted black lineE-zone, defined by active source reflectivity; dashed blue lineMoho defined by seismic reflection.

B

A

Inset Figure B: Results from the Western Superior transect. (a) Simplified tectonic map of the current sub-provincescrossed by Lithoprobe profiles. EREnglish River terrane; KIKeweenawan intrusives; WRTWinnipeg River terran

(b) Simplified interpretation along Line 2 (adapted from White et al., 2003; Musacchio et al., 2004). Numbers in mantle areP-wave velocities in km/s. (c) Migrated reflection seismic section for line 2. (d) Refraction velocity model superimposed onthe reflection section. The lower crust and upper mantle are strongly anisotropic, consistent with relic oceanic lithospheretectonically accreted at the base of the crust. (e) Location map of teleseismic results from Frederiksen et al. (2007).Redactive source corridor; map in (a) noted by the black box. 100 km-depth slice through P-wave tomographic model isdisplayed. (f) AA slice through Frederiksen et al. (2007) P-wave model shown in (e). Downgoing lithospheric slabs are notvisible in the teleseismic model but may contribute to the overall high velocity of the western Superior province. The slowvelocity region is attributed to the Nipigon Embayment (a branch of the 1.1 Ga Mid-Continent Rift).

BA

Trans-Continental Profile: The lithospheric cross section provides a continental-scale synthesis of more than two decades of multidisciplinary research carried out byLITHOPROBE and complementary projects. This plate-scale perspective emphasizes the relationships between orogens and permits visual comparisons regarding structureand tectonic development. The cross section includes merged interpretations, near-vertical incidence seismic reflection profiles, and P-velocity structure models.The trans-continental profile spans 6000 km. Earth curvature is incorporated. See text for details.

The interpreted lithospheric structure is displayed in conjunction with seismic reflection and seismic P-wave velocity compilations; no vertical exaggeration. Transect (orexperiment name if not part of a Lithoprobe transect) and seismic line names are given for each segment. Direction headings note changes in the general orientation of the profile segments. In general, the reflection fabric and velocity models are coincident; offsets are noted where present. In the migrated reflection profiles, thin red linesrepresent the most prominent reflections and denote fabrics and faults. The composite P-wave velocity model panels are presented using a common color scale. Velocitiesare also shown using numbers (km/s) and thin, dashed contour lines. Black lines represent interpreted wide-angle reflector locations. Interpretation panels represent acurrent synthesis of published work. Colors indicate tectonic age (see map and text). Heavy black lines represent major reflective or compositional boundaries inferredfrom seismic data. Anisotropic and/or heterogeneous structure in the l ithospheric mantle is noted by short dashed zones. In the Western Superior transect segment,teleseismic velocity and resistivity anomalies in the lithospheric mantle are denoted by shaded ovals and corresponding annotation for average velocity (AV),high velocity (HV), l ow velocity (LV), and high resistivity (HR) regions (Percival et al., 2006). The teleseismic dataset revealed lateral compos-itional changes in the lithospheric mantle that corresponded closely with the orogenic boundary and possible subduction anddelamination that were inferred from the active-source dataset (Musacchio et al., 2004; White et al., 2003). Estimatesof lithospheric thickness are based on the work of Shapiro and Ritzwoller (2002) and Artemieva (2009).

The many references used in the compilation of the interpreted cross section and thetwo data panels are included i n the data repository accompanyingthis article (Appendix DR2; see text footnote 1).

100km-depth slice

5 0 0 .

4 0 0 .

3 0 0 .

2 0 0 .

1 0 0 .

0 .

D e

p t h ( k m

)

A : ( 4 6 . 0 0 N , 8 9 . 2 5 W ) A : ( 5 6 . 0 0 N , 8 9 . 2 5 W )

0 . 8

400

100

300

200

500

D e p

t h ( k m

)

0

Distance (km) 0040030020010

) m k ( h t p e D

0

20

40

60

80

100

120Line 2

Moh

o

Mantle Vp (km/s)

8 .0 8 .5 8 . 9

SuperterraneN Uchi English RiverWabigoon

Winnipeg River

8.38.0

8.4

8.4

8.68.6

8.2/8.7 (?)

9.0/8.5 (?)

North Caribou Superterran

e Basement

SutureSuture

Subcreted ocean crust

Imbricate ZoneWinnipeg River

Northern Caribou

1 A 1 D

D e p t h ( k m )

0 1 0

2 0

3 0 4 0

5 0

6 0

Moho MohoMoho

6 . 0 6 . 5 7 . 5 8 . 57.0V (km/s)p

8.0

b)

c)

d)

0

8

16

24

) s ( e m i T

SutureSuture

Refraction velocity ) m k ( h t p e D

0

20

40

60

SutureSuture

MohoMoho

n fabric

4 8 o

52 o

-94 o -92 o - 90 o -88o -86 o

4 9 o

50 o

51 o

53 o

100500

km

N. CaribouSuperterrane

Quetico

Uchi

English RiverER

WabigoonW

aw

a

W

Line 2

WRT

Line 2 Refraction andReflection Profile

Line 1 Refraction Profile

Other Reflection Profiles2001000km

a)

f)

A

A

e)

Lithoprobe Transect

NipigonEmbayment

A A

a)

f)

d)

e)

b)

c)

7.2 6.96.7

5.96

8.38.48.0

LakeSuperior

KI

KI