Title: Overview of the Salton Trough and Northern Gulf of California
1Overview of the Salton Trough and Northern Gulf
of California
- What are the key scientific issues that can be
addressed? - Gary Axen
- New Mexico Tech
2N. Gulf of CA Salton Trough
Cascadia
Walker Lane
Mojave
Salton Trough
Northern Gulf
3Tectonic Setting
New transitional mafic/sedimentary crust in N
Gulf, thick sedimentary layer
New ocean crust in S Gulf
New magnetically lineated ocean crust in Gulf
mouth
4Key Questions
- Extent, thickness, and distribution of new lower
crust - badly known in S Salton Trough and N Gulf - Effects of thick sediments on melt extraction and
thermal structure in rift - Interactions between magmatic and mechanical
rifting - Active strain field and strain partitioning
- Are LANFs still active in Laguna Salada?
- Seismic hazards to El Centro, Mexicali, etc.
- Geothermal resources
5Gulf Extensional Province
(Transpression)
Salton Trough
Strain Partitioning Transtension, Transpression,
CW Vertical-Axis Rotation, Folding
Northern Gulf
6Comparison of Crustal Structure
Southern Gulf of California
Northern Gulf - Salton Trough
3. Guaymas
5. Salton Trough
20 km
200 km
2. Alarcón
Fuis, USGS website
4. Delfín - Tiburón
1. Cabo - Puerto Vallarta
González-Fernández et al., 2005
Lizarralde et al. in review
7Present Area of New Crust
Extent of new crust from refraction lines,
gravity, and 2 wells into granitic basement
(but wells within new basement area have hit
juvenile granite) New crust forming in Brawley
and Mexicali seismic zones non-orthogonal
spreading centers, asymmetric? Southern extent
poorly known
8New Crust at 2 Ma
9New Crust at 4 Ma
If most plate motion is accommodated
magmatically, then new crust may be only 4 Ma.
LANFs on west side probably much older (8? Ma)
10Salton Trough Basement
Sediments stripped off
Precambrian basement
Metasedimentary basement
New mafic lower crust
Fuis, USGS website
- Does not incorporate folds, western LANFs
11Pre-San Jacinto, Elsinore
- Could we improve upon these models?
- Southern extent of new crust
- Interaction of WSDS and magmatically accommodated
rifting - Vibroseis surveys
- Marine MCS in Salton Sea
- Noisy, but mostly rural
12Obique view southeast from the shuttle shows bend
in Main Gulf Escarpment near the south end of the
cloud line
13Less Oblique Than Southern Gulf
About 15 difference in trends of rift axis and
western rift margin
Well-constrained offset of 320 km across Gulf
(Oskin et al., 2001), but less extension than
inferred farther south ( 450 km) from seimsic
surveys
14Low-Angle Normal Faults Present in N. Gulf
West Salton Detachment 8-4 to 1.1 Ma Cañada
David Detachment 12-8? To 0 Ma Las Cuevitas
Santa Rosa Detachments(?) 12-8 to 4-2 Ma
15Active Low-Angle Normal Fault?
Elsinore - Laguna Salada Flt
Laguna Salada
Cañada David Detachment
16Cañada David Detachment
Detachment-related fault scarps graben
View NNW
(Axen et al., 1999 Spelz et al., in prep.)
17Cañada David Detachment
Quaternary scarps follow detachment Many
antithetic scarps Heavethrow ratio yields
detachment dip equivalent to outcrop
measurements Gravity magnetic survey extends
low dip 2 km If all scarps formed in single
EQ 10 m slip event!
Axen et al., 1999
18Conclusions
- Northern Gulf Salton Trough provide
significant, attainable ties between EarthScope
and MARGINS-RCL goals - Opportunities to study
- Unusual crustal structure (EarthScope)
- Complex strain partitioning (PBO)
- Fault mechanics (SAFOD)