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: Colorado R. Rate of crustal growth by deposition of sediment in basins

SOURCE - Colorado River: Catchment Area: 630,000 km 2 (4th largest in conterminous U.S.) Dissolved Load (TDS): ~ 400 ppm (early 1900’s) ~ 800 ppm (modern) Sediment Discharge: x 10 8 t/yr (pre-dam) ~ 1.0 x 10 5 t/yr (modern) Total Sediment Volume Eroded: ~ 230, ,000 km 3 (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)

2.65 and 2.60 Ma Oldest C-Sst Miocene Pliocene 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 Pacific Plate E C S Z S.N. Pre-Miocene Pliocene- Quaternary D.D. post 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 ~ 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 ~ 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 km 2 Volume of Sediments (areas 1 & 2): Minimum = 29,625 km 3 Maximum = 50,363 km 3 (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 km maximum = 12 km (5-12 km = 50% seds) Area (3 + 4): = 13,200 km 2 Volume of Sediments (areas 3 + 4): Minimum = 58,000 km 3 Maximum = 76,200 km 3 (3) 50 x 160 km (4) 0.5 * (65 x 160 km) 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 km 2 Volume of Sediments (area 5): Minimum = 79,900 km 3 Maximum = 119,850 km 3 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 Basin Delfin 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 km 2 Volume of Sediments (area 6): Minimum = 30,000 km 3 Maximum = 45,000 km 3 Gonzalez et al. (2005) Aragon & Martin (2007) Tiburon Basin

Sum the calculations: (1) Total volume of C.R. sediment in subsurface: ~ 197, ,815 km 3 Very rough estimate, lots of room for improvement. (2) Slight adjustment, convert to equivalent rock volume: ~ 182, ,590 km 3 (3) Compare to rock eroded from Colorado Plateau: ~ 230, ,000 km 3 (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, ,590 km 3 / 5.3 m.y. / 580 km along strike = km 3 / m.y. / km Compare to growth rates at seafloor spreading centers: = km 3 / m.y. / km (for slow and v. slow spreading rates) = km 3 / m.y. / km (for medium to fast spreading rates) Compare to rates at subduction-related magmatic arcs: = km 3 / m.y. / km (Philippines) = km 3 / m.y. / km (other west Pacific arcs) = km 3 / 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.