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

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)

Salton Trough

Gulf of Cal.

Rupturing Continental Lith (RCL)

NSF MARGINS Program

Source to Sink (S2S)

Mike Oskin(U.C. Davis) Molly Keogh

(U. Oregon) Kim Le(U.C. Davs)

Tom Peryam(U. Oregon)

Bernie Housen(WWU)

Gary Axen(N.M. Tech)

COLLABORATORS

Susanne Janecke(Utah State Univ.)

Amy Spears(WWU)

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)

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).

Extensionwith

Sedimentation

Extensionwithout

Sedimentation

Wide Rift Mode Narrow Rift Mode

• Rift Architecture: sediment load promotes early transition to narrow rift mode (Bialas and Buck, 2009).

The weight of sediments reduces the difference in crustal buoyancy forces between adjacent blocks, allowing strain to localize.

Sediment

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

McQuarrie and Wernicke (2005)

20 Ma

10 Ma6 Ma 0 Ma

~ 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.

topography

remnant

?

Colorado River drainage integrated at 6 Ma.

(Spencer et al., 2001; House et al., 2005), Entered Salton Trough ~5.3

Ma (Dorsey et al., 2007)

Colorado R.

Colorado R.

36 Ma

12.3 Ma

12.3 Ma

12.3 to 6 Ma

12.3 - 6 Ma

6 to 0 Ma

6 to 0 Ma

Baja

Ca

lif.B

aja C

alif.

Fletcher et al. (2007) GSAB

TWO CONTRASTING MODELS for kinematic evolution of the Pac. - North America plate boundary: 12 to 6 Ma.

1. Regional Strain PartitioningStock and Hodges (1989)Oskin and Stock (2003)

2. Regional Integrated StrainGans (1997), Fletcher et al. (2007)

Models agree on past 6 m.y.

Late Miocene

Basins of the Gulf of California & Salton Trough

Northern Gulf• Water depth: ≤200 m• Sed Thickness: 8-12 km

accum. in past 6-8 Myr.• Total Crust: 15-20 km• No true Ocean CrustCentral Gulf• Water depth: ~1,600 m• Sed Thickness ~3 km • Total Crust: 9-10 km• Ocean Crust since ~3 MaSouthern Gulf• Water depth: ~2,500 m• Sed Thickness ~1 km• Total Crust: ~6 km• Ocean Crust since ~3 Ma

Lizarralde et al. (2007), and othersDorsey and Umhoefer (in press)

past 5-6 Myr

scec

Southern San Andreas Fault System

1. Late Cenozoic Basin Development, Western Salton Trough

M 7.2 Earthquake(April 4, 2010)

Fish Creek - Vallecito Basin

mod. from Winker (1987); Axen and Fletcher (1998)

WSDF

Fish Creek - Vallecito Basin, western Salton Trough

2.65 and 2.60 Ma

Alluvial-Fan Conglomerate

Large Rock Avalanche

Earliest Marine Turbidites (6.3 Ma)

Active Rift Basin, Steep Local TopographyBase of Sxn ~ 8.0 ± 0.4 Ma

Base of Marine ~ 6.3 Ma

Top of Sxn ~0.95 Ma

Initiation of paleo-San Andreas fault at ~7-8 Ma?

Present Day 7-8 Ma

2.65 and 2.60 Ma

Oldest Col. R. sand= 5.3 Ma

marine turbidites, Latrania Fm.

A. Diablo Fm., Palm Spring Gp.

Locally - Derived

Top of Sxn ~0.95 Ma

C-suite

L-suitemixed-source

Herzig et al. (1988)

chert

volc.

metam.Colorado River - Derived

Locally - Derived

Sand Composition

biotite

plag.

qtz

qtz

Subsurface

Outcrop

2.65 and 2.60 Ma

Top of Sxn ~0.95 Ma

Colorado Delta Progradation Continuous Fluvial

Delta Prograded during abrupt increase in subsidence rate, fluvial conditions persisted during rapid subsidence.

Requires large increase in sediment flux rate. Seen in other supply-driven delta systems (Goodbred and Kuehl, 2000; Carvajal and Steel, 2006)

~ 4 Ma

Base of Sxn ~ 8.0 ± 0.4 Ma

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).

Axen (2008)

Colorado R.

NASA

satellite view looking SE along the Pac-NAM plate boundary, GoC and S.T.

Colora

do R.

Rapid Sediment Input to active oblique-rift basins during past 5-6 Myr.

Sediment builds new (recycled) crust as it is buried and metamorphosed ...

Regional-scale crustal recycling system.

Pacific Plate

NorthAmerica

Tro

ugh

Cal

if.

Gul

f o

f

Sal

ton

Next:

• Calculate Volume of sediment in basins

• Rate of crustal growth

• Implications for rift-margin evolution

2. Regional Sediment Budget, Mass Balance

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

Aragon & Martin (2007)

Tiburon Basin

Altar Basin

Pacheco et al. (2006)

Shallower, unmetamorphosed basins: well imaged in sesimic-reflection studies

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

Fuis et al., (1984)

… explains seismic refraction data, velocity structure

unmetamorphosedbasinal sediments

meta-sedimentary rock and intrusions

“sub-basement”= basaltic crust

orpartially serpentin.

mantle

4-5

10-12Depth (km)

0

20

Increasing seismic velocity (Vp) is typical of sedimentary basin fill.

Average Vp (5.65 km/s) is too slow for old crystalline rock (5.9-6.0 km/s).Consistent w/ metaseds & intrusions.Faster velocities (7.5-8.0 km/s) could be basaltic crust (Fuis et al., 1984) or partially serp. mantle (Nicolas, 1985).

sediments

metaseds + intrusions

basaaltic crust

(gradual transition)

(abrupt increase in Vp)

Fuis and Mooney (1991)

10-12 km in 5.3 m.y. requires accum. rate of

1.9-2.3 mm/yr … consistent with measured rates (Van Andel, 1964; Herzig et al.,

1988; Dorsey et al., in press).

10

0

20

30

40

12 km

Gonzalez et al. (2005)

5 km

10 km

sediments

metasedim. rx + intrusions

sediments

lower crust

Tiburon BasinDelfin Basin

Northern Gulf of California

Fuis and Mooney (1991)

Salton Troughsediments

metaseds + intrusions

basaaltic crust

12 km10

0

20

30

40

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]

Domain #Area (km2)

min. max. min. max. min. max. min. max. min. max. min. max.Sediments* 4 5 4 5 4 4 4 5 4 5 4 5Metaseds* 6 7 6 7 0 0 4 5 4 5 4 5IntrusionsΩ 0.4 0.1 0.4 0.1 n.a. n.a. 0.4 0.1 0.4 0.1 0.4 0.1Non-C.R.∑ 1 0.1 1 0.1 1 0.1 1 0.1 1 0.1 1 0.1Volume 11,418 19,376 23,397 39,704 21,900 28,470 27,702 48,222 105,400 159,800 29,450 44,650

1 2 3 4

TOTAL: Minimum Volume = 2.2 x 105 km3; Maximum Volume = 3.4 x 105 km3

* Thickness (km); Ω Fraction of metasediments volume occupied by intrusions; ∑Thickness of non-Colorado River sediment (km)

5 61,730 3,545 7,300 5,130 17,000 4,750

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

Volume % of intrusions in metasedim. rocks 10-40% 10-40%

Thickness of non-C.R. seds at base of section 100-1000 m 100-1000 m

Depth x Area: min. and max. volumes for the 6 basinal domains …

RESULT: Total volume of Colorado R. sediment in subsurface basins

is ~ 2.2 - 3.4 x 105 km3

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.

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)

Rate of Crustal Growth:

Lithospheric Rupture, Sedimentation, and Crustal Recycling

• “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.

Fuis and Mooney (1991)

sediments

metaseds + intrusions

basaaltic crust

Salton Trough and Northern Gulf of California

Insights into crustal evolution and structure at ancient rifted margins.

Nova Scotia margin (Wu et al., 2006)