1. Overview of the Salton Trough and Northern Gulf of California What are the key scientific issues that can be addressed? Gary Axen New Mexico Tech Tectonics Program

2. N. Gulf of CA & Salton Trough Cascadia Walker Lane Mojave Salton Trough Northern Gulf

3. Tectonic Setting New magnetically lineated ocean crust in Gulf mouth New ocean crust in S Gulf New “transitional” mafic/sedimentary crust in N Gulf, thick sedimentary layer

4. Key Questions Extent, thickness, and distribution of new lower crust - badly known in S Salton Trough and N GulfExtent, 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 riftEffects of thick sediments on melt extraction and thermal structure in rift Interactions between magmatic and mechanical riftingInteractions between magmatic and mechanical rifting Active strain field and strain partitioningActive strain field and strain partitioning Are LANFs still active in Laguna Salada?Are LANFs still active in Laguna Salada? Seismic hazards to El Centro, Mexicali, etc.Seismic hazards to El Centro, Mexicali, etc. Geothermal resourcesGeothermal resources

5. Gulf Extensional Province Salton Trough Northern Gulf (Transpression) Strain Partitioning: Transtension,Transpression, CW Vertical-Axis Rotation,Folding 1 2 3 4 5

6. Comparison of Crustal Structure Southern Gulf of California 3. Guaymas 2. Alarcón 1. Cabo - Puerto Vallarta Northern Gulf - Salton Trough 5. Salton Trough Lizarralde et al. in review González-Fernández et al., 2005 Fuis, USGS website 4. Delfín - Tiburón ~20 km ~200 km New crust ?

7. Present 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

8. New Crust at 2 Ma

9. New 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)

10. Salton Trough Basement Does not incorporate folds, western LANFs Fuis, USGS website Precambrian basement Metasedimentary basement New mafic lower crust Sediments stripped off

11. Pre-San Jacinto, Elsinore Could we improve upon these models?Could we improve upon these models? Southern extent of new crustSouthern extent of new crust Interaction of WSDS and magmatically accommodated riftingInteraction of WSDS and magmatically accommodated rifting Vibroseis surveysVibroseis surveys Marine MCS in Salton SeaMarine MCS in Salton Sea Noisy, but mostly ruralNoisy, but mostly rural

12. Obique view southeast from the shuttle shows bend in Main Gulf Escarpment near the south end of the cloud line

13. Less 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

14. Low-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

15. Laguna Salada Elsinore - Laguna Salada Flt Cañada David Detachment Active Low-Angle Normal Fault?

16. Cañada David Detachment Detachment-related fault scarps & graben (Axen et al., 1999; Spelz et al., in prep.) View ~ NNW

17. Cañada David Detachment Quaternary scarps follow detachment Many antithetic scarps Heave:throw 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

18. Conclusions Northern Gulf & Salton Trough provide significant, attainable ties between EarthScope and MARGINS-RCL goalsNorthern Gulf & Salton Trough provide significant, attainable ties between EarthScope and MARGINS-RCL goals Opportunities to study:Opportunities to study: Unusual crustal structure (EarthScope)Unusual crustal structure (EarthScope) Complex strain partitioning (PBO)Complex strain partitioning (PBO) Fault mechanics (SAFOD)Fault mechanics (SAFOD)