Overview of the Salton Trough Overview of the Salton Trough and Northern Gulf of and Northern Gulf of

CaliforniaCaliforniaWhat are the key scientific issues What are the key scientific issues

that can be addressed?that can be addressed?

Gary AxenGary Axen

New Mexico TechNew Mexico Tech

Tectonics Program

N. Gulf of CA & Salton TroughN. Gulf of CA & Salton TroughCascadiCascadiaa

Walker Walker LaneLaneMojaveMojave

Salton Salton TroughTrough

Northern Northern GulfGulf

Tectonic SettingTectonic Setting

New New magnetically magnetically lineated ocean lineated ocean crust in Gulf crust in Gulf mouthmouth

New ocean New ocean crust in S Gulfcrust in S Gulf

New New “transitional” “transitional” mafic/sedimentarmafic/sedimentary crust in N Gulf, y crust in N Gulf, thick thick sedimentary sedimentary layerlayer

Key QuestionsKey Questions• Extent, thickness, and distribution of new Extent, thickness, and distribution of new

lower crust - badly known in S Salton Trough lower crust - badly known in S Salton Trough and N Gulfand N Gulf

• Effects of thick sediments on melt extraction Effects of thick sediments on melt extraction and thermal structure in riftand thermal structure in rift

• Interactions between magmatic and mechanical Interactions between magmatic and mechanical riftingrifting

• 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

Gulf Extensional ProvinceGulf Extensional Province

Salton TroughSalton Trough

Northern GulfNorthern Gulf

(Transpression) (Transpression)

Strain Partitioning:Strain Partitioning:Transtension,Transtension,

Transpression, Transpression, CW Vertical-Axis CW Vertical-Axis

Rotation, Rotation, FoldingFolding

1

2

3

4

5

Comparison of Crustal StructureComparison of Crustal StructureSouthern Gulf of CaliforniaSouthern Gulf of California

3. 3. GuaymasGuaymas

2. 2. AlarcónAlarcón

1. Cabo - Puerto 1. Cabo - Puerto VallartaVallarta

Northern Gulf - Salton TroughNorthern Gulf - Salton Trough

5. Salton 5. Salton TroughTrough

Lizarralde et al. in review

González-Fernández et al., 2005

Fuis, USGS website

4. Delfín - 4. Delfín - TiburónTiburón

~20 ~20 kmkm

~200 km~200 km

New New crustcrust

? ?

Present Area of New CrustPresent Area of New CrustExtent of new Extent of new crust from crust from refraction lines, refraction lines, gravity, and 2 gravity, and 2 wells into wells into “granitic “granitic basement” (but basement” (but wells within new wells within new basement area basement area have hit juvenile have hit juvenile granite…)granite…)

New crust: New crust: forming in forming in Brawley and Brawley and Mexicali seismic Mexicali seismic zones; non-zones; non-orthogonal orthogonal spreading centers, spreading centers, asymmetric?asymmetric?

Southern extent Southern extent poorly knownpoorly known

New Crust at 2 MaNew Crust at 2 Ma

New Crust at 4 MaNew Crust at 4 MaIf most plate If most plate motion is motion is accommodated accommodated magmatically, magmatically, then new crust then new crust may be only ~ 4 may be only ~ 4 Ma. Ma.

LANFs on west LANFs on west side probably side probably much older (8? much older (8? Ma)Ma)

Salton Trough BasementSalton Trough Basement

• Does not incorporate folds, western LANFs

Fuis, USGS website

PrecambriPrecambrian an

basementbasementMetasedimentMetasedimentary basementary basement

New mafic New mafic lower crustlower crust

Sediments Sediments stripped offstripped off

Pre-San Jacinto, ElsinorePre-San Jacinto, Elsinore• Could we improve upon Could we improve upon

these models?these models?

• Southern extent of new Southern extent of new crustcrust

• Interaction of WSDS and Interaction of WSDS and magmatically magmatically accommodated riftingaccommodated rifting

• Vibroseis surveysVibroseis surveys

• Marine MCS in Salton Marine MCS in Salton SeaSea

• Noisy, but mostly ruralNoisy, but mostly rural

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

Less Oblique Than Less Oblique Than Southern GulfSouthern Gulf

About 15° difference in About 15° difference in trends of rift axis and trends of rift axis and western rift marginwestern rift margin

Well-constrained offset of Well-constrained offset of ~ 320 km across Gulf ~ 320 km across Gulf (Oskin et al., 2001), but less (Oskin et al., 2001), but less extension than inferred extension than inferred farther south (~ 450 km) farther south (~ 450 km) from seimsic surveysfrom seimsic surveys

Low-Angle Low-Angle Normal Faults Normal Faults Present in N. Present in N.

Gulf Gulf West Salton Detachment West Salton Detachment ~8-4 to 1.1 Ma~8-4 to 1.1 Ma

Cañada David Detachment Cañada David Detachment ~12-8? To 0 Ma ~12-8? To 0 Ma

Las Cuevitas & Santa Las Cuevitas & Santa Rosa Detachments(?) Rosa Detachments(?) ~12-8 to 4-2 Ma~12-8 to 4-2 Ma

Laguna Laguna SaladaSalada

Elsinore - Laguna Salada FltElsinore - Laguna Salada Flt

Cañada David DetachmentCañada David Detachment

Active Low-Angle Normal Fault?Active Low-Angle Normal Fault?

Cañada DavidCañada DavidDetachmentDetachment

Detachment-relatedDetachment-relatedfault scarps & grabenfault scarps & graben

(Axen et al., 1999; Spelz et al., in prep.)

View ~ NNWView ~ NNW

Cañada David DetachmentCañada David Detachment

Quaternary scarps follow Quaternary scarps follow detachmentdetachment

Many antithetic scarpsMany antithetic scarps

Heave:throw ratio yields Heave:throw ratio yields detachment dip equivalent to detachment dip equivalent to outcrop measurementsoutcrop measurements

Gravity & magnetic survey Gravity & magnetic survey extends low dip ~ 2 km extends low dip ~ 2 km

If all scarps formed in single If all scarps formed in single EQ: ~10 m slip event!EQ: ~10 m slip event!

Axen et al., 1999

ConclusionsConclusions• Northern Gulf & Salton Trough provide Northern Gulf & Salton Trough provide

significant, attainable ties between significant, attainable ties between EarthScope and MARGINS-RCL goalsEarthScope 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)