Transcript Overview of the Salton Trough and Northern Gulf

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
N. Gulf of CA & Salton Trough
Cascadia
Walker Lane
Mojave
Salton Trough
Northern
Gulf
Tectonic 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
Key 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
Gulf Extensional Province
(Transpression)
Strain Partitioning:
Transtension,
Transpression,
CW Vertical-Axis
Rotation,
Folding
Salton Trough
5
Northern Gulf
4
3
2
1
Comparison of Crustal Structure
Southern Gulf of California
3. Guaymas
Northern Gulf - Salton Trough
5. Salton Trough
~20 km
~200 km
2. Alarcón
Fuis, USGS website
1. Cabo - Puerto Vallarta
4. Delfín Tiburón
? ?
González-Fernández et al.,
2005
New crust
Lizarralde et al. in review
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; nonorthogonal spreading
centers, asymmetric?
Southern extent
poorly known
New Crust at 2 Ma
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)
Salton Trough Basement
Sediments
stripped off
Precambrian
basement
Metasedimentary
basement
New mafic
Fuis, USGS website
lower crust
• Does not incorporate folds, western LANFs
Pre-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
Obique view southeast from the shuttle shows bend in Main
Gulf Escarpment near the south end of the cloud line
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
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
Active Low-Angle Normal Fault?
Elsinore - Laguna Salada Flt
Laguna
Salada
Cañada David Detachment
Cañada David
Detachment
Detachment-related
fault scarps & graben
View ~ NNW
(Axen et al., 1999; Spelz et al., in prep.)
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
Conclusions
• 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)