Becky Dorsey - University of Oregon

Crustal Recycling by Surface Processes Along the Pacific-North America Plate Boundary: From the

Colorado Plateau to the Salton Trough and Gulf of California

NASA

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

• Thermal insulation, enhanced extraction of mantle melt (Lizzaradle et al.,

2007): earlier transition to narrow rift mode

• Reduction of differences in buoyancy forces (Bialas and Buck, 2007; submitted):

earlier transition to narrow rift mode

• Diffuse deformation, after transition to narrow rift mode (Persaud et al., 2003)

• Build new transitional crust at rifted margins (Fuis et al., 1984; Nicolas, 1985) …

Effects of sediment input on extension processes and rift architecture:

Colora

do R.

Rate of crustal growth by deposition of sediment in basins

SOURCE - Colorado River:

Catchment Area: 630,000 km2

(4th largest in conterminous U.S.)

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)

Total Sediment Volume Eroded:

~ 230,000 - 294,000 km3 (assuming pre-dam discharge over 5.3 m.y.)… work in progress (J. Pederson)

SINK - Basins in Salton Trough and northern Gulf of California

Volume ?

Age ?

Crustal Growth Rate ?

Implications for Rifted Margins ?

Why Sediment Budgets ?

Regional mass balance and landscape evolution

Rates & processes of erosion in source, dynamic feedbacks with tectonic & climate drivers

Efficiency of mass transfer to basins

Ultimate distribution & fate of sediments

Understand processes of crustal recylcing

Fish Creek - Vallecito Basin (FCVB)

Fish Creek - Vallecito Basin (FCVB)

2.65 and 2.60 Ma

Oldest C-Sst

Mio

cen

eP

lioce

ne

micropaleontology (K. McDougall)

= 5.3 Ma

Ongoing work with Mike Oskin, Tom Peryam, Kim Le: basin evolution and controls on progradation

(North America)

Colorado Plateau

Basin and Range

PacificPlate

E C S Z

S.N.

Pre-M

iocene

Pliocene-Quaternary

D.D.

post - 5.5 Ma (House et al., 2005)

post - 6 Ma (Spencer et al., 2001)

5.3 Ma

~ 200 kyr.

Colorado River sandstone: impressive in outcrop, lots of good information. But …

192°

Paleocurrent Data

… most Colorado R. sediment is buried in subsurface basins (Pliocene to modern).

What is the volume of sediment in subsurface basins?

Where to look?

Guaymas Basin is sediment-rich compared to southern Gulf, but …

Most sediment in Guaymas Basin derived from rivers in Sonora, not Colorado River (Curray et al., 1982; Einsele and Niemitz, 1982).

Estimate volume of C.R. sediment in subsurface

Depth of the basins?

Answer is model-dependent …

Aragon & Martin (2007)Gonzalez et al. (2005)

Fuis et al. (1984)

Pacheco et al. (2006)

(1) 30 x 60 km

(2) 55 x 75 km

(3) 50 x 160 km

(4) 0.5 * (65 x 160 km)

(5a) 65 x 180 km

(6) 50 x 120 km(5b) 40 x 90 km

(5c) 20 x 34 km

Preliminary analysis …

Schmitt and Vasquez (2006)

Bracket the estimate using two crustal models:(1) Lithosphere is fully ruptured, therefore:

Sed basins are 5 km deep, basement consists of [sediments + mafic intrusions] (Fuis et al., 1984)

Fuis and Mooney (1991)

5 km

12 km

Salton Trough

Bracket the estimate using two crustal models:(2) Lithosphere is not fully ruptured, therefore:

Sed basins are 5 km deep, and basement consists of thinned continental crust

This model is suggested by relatively shallow depth to crystalline basement in southern Salton Trough (Pacheco et al., 2006).

… large unknowns, under-constrained problem.

Pacheco et al. (2006)

Northern and Central Salton Trough

Fuis and Mooney (1991)

5 km

12 km

Depth of Basin Fill:

Minimum = 5 km … Assumes average sed accum rate of ~0.9-1.0 mm/yr (less than half of rate measured in upper 1.7 km)

Maximum = 12 km (between 5 and 12 km depth, assume crust is composed of half sediment and half mafic intrusions)

Assumes net sed accum rate of ~ 2.2-2.3 mm/yr: same as rate based on 0.76-Ma Bishop ash at 1.7 km (Herzig et al., 1988).

Area (1 + 2): = 5,925 km2

Volume of Sediments (areas 1 & 2):

Minimum = 29,625 km3

Maximum = 50,363 km3

(1) 30 x 60 km

(2) 55 x 75 km

Salton Trough

Southern Salton Trough Buried detachment fault in Altar Basin

Depth of Basin Fill:3. Altar Basin: 4 km (use one value)

4. Basin SW of CPF: minimum = 5 kmmaximum = 12 km (5-12 km = 50%

seds)

Area (3 + 4): = 13,200 km2

Volume of Sediments(areas 3 + 4):

Minimum = 58,000 km3

Maximum = 76,200 km3

(3) 50 x 160 km

(4) 0.5 * (65 x 160 km)

Pacheco et al. (2006)

Pacheco et al. (2006)

Pacheco et al. (2006)

(5a) 65 x 180 km

(5b) 40 x 90 km

Depth of Basin Fill:

Minimum = 5 km

Maximum = 10 km (5-10 km = 50% seds)

Area (5): = 15,980 km2

Volume of Sediments (area 5):

Minimum = 79,900 km3

Maximum = 119,850 km3

Gonzalez et al. (2005)

5 km

10 km

sediments

sediments + mafic intrusions?

sediments

Gonzalez et al. (2005)

Northern Gulf of California

lower crust, looks “continental” (?)

Tiburon BasinDelfin Basin

(5c) 20 x 34 km

(6) 50 x 120 km

Depth of Basin Fill:

Minimum = 5 km (Aragon and Martin, 2007)

Maximum = 10 km (5-10 km = 50% seds) (Gonzalez et al., 2005)

Area (6): = 6,000 km2

Volume of Sediments (area 6):

Minimum = 30,000 km3

Maximum = 45,000 km3

Gonzalez et al. (2005)

Aragon & Martin (2007)

Tiburon Basin

Sum the calculations:

(1) Total volume of C.R. sediment in subsurface:

~ 197,925 - 291,815 km3

Very rough estimate, lots of room for improvement.

(2) Slight adjustment, convert to equivalent rock volume:

~ 182,700 - 280,590 km3

(3) Compare to rock eroded from Colorado Plateau:

~ 230,000 - 294,000 km3

(also very approximate)

Aragon & Martin (2007)Gonzalez et al. (2005)

Fuis et al. (1984)

Pacheco et al. (2006)

(1) 30 x 60 km

(2) 55 x 75 km

(3) 50 x 160 km

(4) 0.5 * (65 x 160 km)

(5a) 65 x 180 km

(6) 50 x 120 km(5b) 40 x 90 km

(5c) 20 x 34 km

Rate of Crustal Growth by input of sediment to the Salton Trough & N. Gulf of California:

= volume / time / distance along strike

= 182,700 - 280,590 km3 / 5.3 m.y. / 580 km along strike

= 59 - 91 km3 / m.y. / km

Compare to growth rates at seafloor spreading centers:

= 50 - 160 km3 / m.y. / km (for slow and v. slow spreading rates)

= 250 - 800 km3 / m.y. / km (for medium to fast spreading rates)

Compare to rates at subduction-related magmatic 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)

Implications:

Gulf of Cal. & Salton Trough:

Highlights difference between the

alternate crustal models. Will affect

future attempts at sediment budget.

“Novel type of crust” produced by

rifting: intermediate velocities reflect

mix of seds and mafic intrusions(Fuis et al., 1984; Nicolas, 1985).

Crustal recycling by surface processes: Erosion, transport, and deposition of seds in basins

Important mechanism of crustal growth. Similar in scale and rate to magmatic accretion at subduction zones and slow spreading centers.

May occur at other rift and oblique-rift margins where large continental river is captured by subsidence of a pre-existing orogenic highland.