overview of the salton trough and northern gulf of california what are the key scientific issues...
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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)