Transcript presentation

Crustal Recycling Along an Oblique-Divergent Plate
Boundary: From the Colorado Plateau to the Salton Trough
and Gulf of California
Becky Dorsey - University of Oregon
NSF MARGINS Program
Rupturing Continental Lith (RCL)
Source to Sink (S2S)
Salton Trough
Gulf of California and Salton Trough:
Growth of an active oblique-rift boundary:
• Basinal response to deformation
• Erosion, transport, deposition
• Role of Sedimentation in crustal evolution
(not just a passive recorder of E. history)
Gary Axen
COLLABORATORS
(N.M. Tech)
Amy Spears
(WWU)
Susanne Janecke
(Utah State Univ.)
Bernie Housen
(WWU)
Mike Oskin
(U.C. Davis)
Molly Keogh
(U. Oregon)
Kim Le
(U.C. Davs)
Tom Peryam
(U. Oregon)
Influence of Sediments on Crustal Architecture and Evolution
• Build Transitional Crust (O.C.T.)
at rifted margins (Fuis et al., 1984; Nicolas,
1985; Wu et al., 2006)
• Thermal Effect of thick sediment:
- Warm the lithosphere due to
insulation (Lizzaradle et al., 2007) ?
- Cool the lithosphere due to
addition of cold seds ?
Nova Scotia margin (Wu et al., 2006)
Bialas and Buck (2009)
Extension
without
Sedimentation
Extension
with
Sedimentation
Sediment
Wide Rift Mode
Narrow Rift Mode
• Rift Architecture: sediment load
promotes early transition to narrow
rift mode (Bialas and Buck, 2009).
Sediments are one of the main recorders of
tectonic events, but they may also affect the way
compression or extension proceeds. It is now
accepted that the unloading effect of erosion can
change the pattern of compressional deformation in
areas of continental convergence … In a similar
way, we suggest that the load of sediments may
promote localized deformation in areas of
continental extension (Bialas and Buck, 2009).
The weight of sediments reduces the difference in crustal buoyancy forces between adjacent blocks, allowing strain to localize.
Gulf of California and Salton Trough
Today’s Talk:
* Brief Overview of Gulf-Trough Region
1. Exposed Late Cenozoic Section, Western Salton Trough:
+ Initiation (?) and growth of Pacific - North Am. plate boundary
+ First arrival of Colorado River sediment in tectonic lowland
+ Colorado River delta progradation and basin filling
2. Regional Sediment Budget, Mass Balance:
+ Estimate volume of sediment in subsurface basins
+ Compare to volume eroded from Colorado Plateau
+ Explore implications for crustal growth and recycling
~ 120 km E-W extension in
B&R ~ 16 to 10 Ma (Wernicke
?
and Snow, 1998; Fitzgerald et al.,
2009; Colgan and Henry, 2009).
Inversion of Topography …
prob. low by about 8-10 Ma.
Colorado River drainage
integrated at 6 Ma.
(Spencer et al., 2001; House et al., 2005),
Entered Salton Trough ~5.3 Ma
36 Ma
10 Ma
20 Ma
6 Ma
(Dorsey et al., 2007)
0 Ma
McQuarrie and Wernicke (2005)
12.3 Ma
12.3 to 6 Ma
6 to 0 Ma
TWO CONTRASTING MODELS
for kinematic evolution of the
Pac. - North America plate
boundary: 12 to 6 Ma.
1. Regional Strain Partitioning
Stock and Hodges (1989)
Oskin and Stock (2003)
12.3 Ma
Late Miocene
12.3 - 6 Ma
6 to 0 Ma
2. Regional Integrated Strain
Gans (1997), Fletcher et al. (2007)
Models agree on past 6 m.y.
Fletcher et al. (2007) GSAB
Basins of the Gulf of California & Salton Trough
Northern Gulf
past 5-6 Myr
• Water depth: ≤200 m
• Sed Thickness: 8-12 km
accum. in past 6-8 Myr.
• Total Crust: 15-20 km
• No true Ocean Crust
Central Gulf
•
•
•
•
Water depth: ~1,600 m
Sed Thickness ~3 km
Total Crust: 9-10 km
Ocean Crust since ~3 Ma
Southern Gulf
•
•
•
•
Dorsey and Umhoefer (in press)
Water depth: ~2,500 m
Sed Thickness ~1 km
Total Crust: ~6 km
Ocean Crust since ~3 Ma
Lizarralde et al. (2007), and others
1. Late Cenozoic Basin Development, Western Salton Trough
Southern San Andreas Fault System
scec
M 7.2 Earthquake
(April 4, 2010)
Fish Creek - Vallecito Basin
mod. from Winker (1987); Axen and Fletcher (1998)
Top of Sxn ~0.95 Ma
Marine Turbidites (6.3 Ma)
FishEarliest
Creek
- Vallecito Basin, western Salton Trough
2.65 and 2.60 Ma
Large Rock Avalanche
Alluvial-Fan Conglomerate
Base of Marine ~ 6.3 Ma
Active Rift Basin, Steep Local Topography
Base of Sxn ~ 8.0 ± 0.4 Ma
Initiation of paleo-San Andreas fault at ~7-8 Ma?
Present Day
7-8 Ma
Top of Sxn ~0.95 Ma
A. Diablo Fm., Palm Spring Gp.
2.65 and 2.60 Ma
marine turbidites, Latrania Fm.
Oldest Col. R. sand
= 5.3 Ma
Locally - Derived
Sand Composition
Subsurface
Herzig et al. (1988)
volc.
C-suite
L-suite
chert
mixedsource
qtz
qtz
Colorado River - Derived
metam.
Outcrop
biotite
plag.
Locally - Derived
Top of Sxn ~0.95 Ma
~ 4 Ma
Delta Prograded
during abrupt increase in
subsidence rate, fluvial
conditions persisted
during rapid subsidence.
2.65 and 2.60 Ma
Requires large increase
in sediment flux rate.
Seen in other supplydriven delta systems
(Goodbred and Kuehl, 2000;
Carvajal and Steel, 2006)
Colorado Delta Progradation Continuous Fluvial
Base of Sxn ~ 8.0 ± 0.4 Ma
Colorado R.
Axen (2008)
Linked slip on southern SAF and west Salton detachment fault. Space
created by lithospheric rupture is filled with basaltic intrusions from below
and voluminous sediment input from above (mainly Colorado River).
2. Regional Sediment Budget, Mass Balance
satellite view looking SE along the Pac-NAM plate boundary, GoC and S.T.
Rapid Sediment Input to active obliquerift basins during past 5-6 Myr.
Sediment builds new (recycled) crust as
it is buried and metamorphosed ...
North
America
Regional-scale crustal recycling system.
Pacific
Plate
Next:
• Calculate Volume of sediment in basins
• Rate of crustal growth
• Implications for rift-margin evolution
NASA
SOURCE: Colorado River
Catchment Area: 630,000 km2
4th largest in conterminous U.S.;
~10-15 times the area of the sink.
Dissolved Load (TDS):
~ 400 ppm (early 1900’s)
~ 800 ppm (modern)
Sediment Discharge:
1.2-1.5 x 108 t/yr (pre-dam)
~ 1.0 x 105 t/yr (modern)
(Meade and Parker, 1985)
SINK: Basins in Salton Trough
and northern Gulf of California
• Opened by oblique divergence along
plate boundary since ~6-8 Ma.
• Colorado River sediment arrived in
Salton Trough at ~5.3 Ma ...
• has dominated basin fill since then.
• Rapid subsidence and sediment
accumulation (~2-3 mm/yr)
• High heat flow: greenschist facies
metam. (~300°) at 2-4 km depth.
Estimate VOLUME of Colorado
River - derived sediment in
subsurface basins …
Estimate VOLUME of Colorado
River - derived sediment in
subsurface basins …
DATA: recent seismic studies,
information about basin depth
and crustal structure.
Estimate VOLUME of Colorado
River - derived sediment in
subsurface basins …
DATA: recent seismic studies,
information about basin depth
and crustal structure.
AREA of 6 main depocenters;
multiply by depth …
UNCERTAINTIES:
• total basin depth
(requires crustal model)
• sed. composition and age
• volume of intrusions at depth
Shallower, unmetamorphosed basins: well imaged in sesimic-reflection studies
Altar Basin
Pacheco et al. (2006)
Tiburon Basin
Aragon & Martin (2007)
For deeper basins, use crustal model of Fuis et al. (1984) – Salton Trough:
Lithosphere is fully ruptured: Unmetamorphosed seds are 4-5 km deep; Basement = [metaseds + mafic intrusions]
Salton Trough
0
sediments
metaseds + intrusions
12 km
10
20
basaaltic crust
30
Fuis and Mooney (1991)
40
… explains seismic refraction data, velocity structure
0
unmetamorphosed
basinal sediments
4-5
Increasing seismic velocity (Vp) is
10-12
km in 5.3 m.y.
requires
typical
of sedimentary
basin
fill.
accum.
rate
(gradual
transition)
of 1.9-2.3 mm/yr …
consistent with measured rates
Average Vp (5.65 km/s) is too slow for
(Van Andel, 1964; Herzig et al., 1988;
old crystalline
(5.9-6.0
km/s).
Dorseyrock
et al.,
in press).
Consistent w/ metaseds & intrusions.
meta-sedimentary
rock and intrusions
“sub-basement”
= basaltic crust
or
partially serpentin.
mantle
Fuis et al., (1984)
Depth (km)
10-12 (abrupt increase in Vp)
20
Faster velocities (7.5-8.0 km/s) could
be basaltic crust (Fuis et al., 1984) or
partially serp. mantle (Nicolas, 1985).
For deeper basins, use crustal model of Fuis et al. (1984) – Salton Trough:
Lithosphere is fully ruptured: Unmetamorphosed seds are 4-5 km deep; Basement = [metaseds + mafic intrusions]
Salton Trough
0
sediments
metaseds + intrusions
12 km
10
20
basaaltic crust
30
Fuis and Mooney (1991)
40
Northern Gulf of California
Delfin Basin
Tiburon Basin
sediments
sediments
metasedim. rx + intrusions
lower crust
Gonzalez et al. (2005)
5 km
10 km
BRACKET VARIABLE PARAMETERS:
Salton Trough
Northern Gulf
Depth to base of unmetamorphosed sediments
4-5 km
4-5 km
Depth to base of metased. rocks and intrusions
10-12 km
8-10 km
10-40%
10-40%
100-1000 m
100-1000 m
Volume % of intrusions in metasedim. rocks
Thickness of non-C.R. seds at base of section
Depth x Area: min. and max. volumes for the 6 basinal domains …
Domain #
Area (km 2)
1
1,730
2
3,545
3
7,300
4
5,130
5
17,000
min.
max.
4
5
4
5
0.4
0.1
1
0.1
105,400 159,800
6
4,750
min.
max.
min.
max.
min.
max.
min.
max.
min.
Sediments*
4
5
4
5
4
4
4
5
4
Metaseds*
6
7
6
7
0
0
4
5
4
ž
Intrusions
0.4
0.1
0.4
0.1
n.a.
n.a.
0.4
0.1
0.4
Non-C.R. •
1
0.1
1
0.1
1
0.1
1
0.1
1
Volume
11,418
19,376
23,397
39,704
21,900
28,470
27,702
48,222
29,450
TOTAL: Minimum Volume = 2.2 x 10 5 km 3; Maximum Volume = 3.4 x 10 5 km 3
* Thickness (km); ž Fraction of metasediments volume occupied by intrusions; •Thickness of non-Colorado River sediment (km)
RESULT: Total volume of Colorado R. sediment in subsurface basins
is ~ 2.2 - 3.4 x 105 km3
max.
5
5
0.1
0.1
44,650
Compare to volume of rock eroded
from Colorado River catchment
(two estimates):
(1) Spatially averaged erosion on Plateau
(Pederson et al., 2002), corrected for ratio
of pre- to post-6 Ma erosion (Flowers et al.,
2008), plus modest inputs from the Virgin
and Gila rivers: ~ 2.0 x 105 km3.
(2) Multiply pre-dam sediment discharge
(1.2-1.5 x 108 t/yr; Meade and Parker, 1985) by
time since first arrival of C.R. sand in the
Salton Trough (5.3 Ma), and simple density
conversion: 2.5-3.1 x 105 km3.
* Preliminary, needs more work *
Volume of sediment stored in plate-boundary basins (~ 2.2 - 3.4 x 105 km3)
is roughly equal to volume of rock eroded from Colorado R. in past 5-6 m.y.
Rate of Crustal Growth:
1. Input of sediment to plate-boundary basins
= volume / time / distance along strike
= 2.2 - 3.4 x 105 km3 / 5.3 m.y. / 500 km along strike
= ~ 80 - 130 km3 / m.y. / km
2. Magmatic accretion at seafloor spreading centers:
= 50 - 160 km3 / m.y. / km (slow and v. slow spreading rates)
= 250 - 800 km3 / m.y. / km (medium to fast spreading rates)
3. Magmatic accretion at island arcs:
= 25 - 67 km3 / m.y. / km (Philippines)
= 30 - 95 km3 / m.y. / km (other west Pacific arcs)
= 80 - 200 km3 / m.y. / km (Izu-Bonin arc)
Lithospheric Rupture, Sedimentation, and Crustal Recycling
sediments
metaseds + intrusions
basaaltic crust
Fuis and Mooney (1991)
Salton Trough and
Northern Gulf of California
Nova Scotia margin (Wu et al., 2006)
Insights into crustal evolution and
structure at ancient rifted margins.
• “Novel type of crust”: rifting and basin filling (Moore, 1973; Fuis et al., 1984; Nicolas, 1985) .
• Surface Processes: Important mechanism of crustal growth and recycling … similar in
scale and rate to magmatic accretion at subduction zones and slow spreading centers.
• May be important at other rift and oblique-rift margins where large continental drainage is
captured following tectonic collapse and subsidence of a pre-existing orogenic highland.