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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.