Transcript PPT - Margins

Crustal Recycling by Surface Processes Along the PacificNorth America Plate Boundary: From the Colorado Plateau to
the Salton Trough and Gulf of California
Becky Dorsey - University of Oregon
satellite view looking SE along the Pac-NAM plate boundary, GoC and S.T.
Effects of sediment input on extension
processes and rift architecture:
• 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) …
NASA
Rate of crustal growth by deposition
of sediment in basins
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
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 ?
Fish Creek - Vallecito Basin (FCVB)
Fish Creek - Vallecito Basin (FCVB)
Ongoing work with Mike
Oskin, Tom Peryam, Kim
Le: basin evolution and
controls on progradation
Miocene
Pliocene
2.65 and 2.60 Ma
micropaleontology (K. McDougall)
Oldest C-Sst
= 5.3 Ma
Basin and Range
PlioceneQuaternary
S.N.
post - 6 Ma
(Spencer et al., 2001)
post - 5.5 Ma
(House et al., 2005)
D.D.
~ 200 kyr.
5.3 Ma
Pacific
Plate
Colorado
Plateau
(North America)
Paleocurrent Data
192°
Colorado River sandstone: impressive in outcrop, lots of good information. But …
… 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
Preliminary analysis …
(1) 30 x 60 km
Depth of the basins?
Fuis et al. (1984)
Answer is model-dependent
…
(2) 55 x 75 km
(3) 50 x 160 km
Pacheco et al. (2006)
(4) 0.5 * (65 x 160 km)
(5a) 65 x 180 km
Aragon & Martin (2007)
Gonzalez et al. (2005)
(5b) 40 x 90 km
(5c) 20 x 34 km
(6) 50 x 120 km
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)
Salton Trough
5 km
12 km
Fuis and Mooney (1991)
Schmitt and Vasquez (2006)
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
Salton Trough
5 km
12 km
Fuis and Mooney (1991)
Depth of Basin Fill:
(1) 30 x 60 km
Minimum = 5 km … Assumes average sed accum rate of ~0.91.0 mm/yr (less than half of rate measured in upper 1.7 km)
(2) 55 x 75 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
Southern Salton Trough
Buried detachment fault in Altar Basin
Pacheco et al. (2006)
Pacheco et al. (2006)
Depth of Basin Fill:
3. Altar Basin: 4 km (use one value)
4. Basin SW of CPF: minimum = 5 km
maximum = 12 km (5-12 km = 50% seds)
Area (3 + 4): = 13,200 km2
(3) 50 x 160 km
Volume of Sediments
(areas 3 + 4):
Minimum = 58,000 km3
(4) 0.5 * (65 x 160 km)
Maximum = 76,200 km3
Pacheco et al. (2006)
Northern Gulf of California
Delfin Basin
Tiburon Basin
sediments
sediments
sediments + mafic intrusions?
lower crust, looks “continental” (?)
Gonzalez et al. (2005)
Depth of Basin Fill:
Minimum = 5 km
(5a) 65 x 180 km
Maximum = 10 km (5-10 km = 50% seds)
Area (5): = 15,980 km2
Volume of Sediments (area 5):
(5b) 40 x 90 km
(5c) 20 x 34 km
Minimum = 79,900 km3
Maximum = 119,850 km3
5 km
10 km
Tiburon Basin
Aragon & Martin (2007)
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
(6) 50 x 120 km
Sum the calculations:
(1) Total volume of C.R.
sediment in subsurface:
~ 197,925 - 291,815 km3
(1) 30 x 60 km
Very rough estimate, lots of
room for improvement.
Fuis et al. (1984)
(2) 55 x 75 km
(2) Slight adjustment, convert
to equivalent rock volume:
(3) 50 x 160 km
Pacheco et al. (2006)
~ 182,700 - 280,590 km3
(4) 0.5 * (65 x 160 km)
(3) Compare to rock eroded
from Colorado Plateau:
(5a) 65 x 180 km
Aragon & Martin (2007)
Gonzalez et al. (2005)
(5b) 40 x 90 km
(5c) 20 x 34 km
(6) 50 x 120 km
~ 230,000 - 294,000 km3
(also very approximate)
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 obliquerift margins where large continental
river is captured by subsidence of a
pre-existing orogenic highland.