Terrane transfer: Lessons from Baja California

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Terrane transfer Lessons from Baja
California
C. Plattner R. Malservisi LMU München,
Germany T. Dixon RSMAS, FL, USA F.
Suarez-Vidal CICESE, Mexico R.
Govers Universiteit Utrecht Netherlands G.
Iaffaldano Harvard University USA
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Baja California is a typical example for
terranes
NA
PA
Fletcher et al., 2007
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Motivation
While large plates are driven by mantle
convection...
... terranes, located within the plate boundary
zone, are likely dragged by neighbouring plates
through lithospheric coupling forces.
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Baja transfer by partial coupling with the
Pacific plate

• Quantify the coupling (dynamics)
• Kinematic response of such dynamics
• Implications for NAM - PAC plate boundary region

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GPS data
Baja California Permanent Campaign GPS
network of CICESE, Univ. Miami, LMU
Munich Pacific plate Permanent stations of
IGS, WING, SPSLCMP North America Permanent
stations (Sella et al., 2006)
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Numerical model should reproduce the geodetic
rigid plate motions Pacific (PAC) - Baja
California - North America (NAM) (Plattner et
al., 2007 GJI).
Geodetic Sierra Nevada motion from Psencik et
al., 2006
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2D spherical shell model simulates BAJA dragged
by Pacific plate
G-TECTON Govers and Meijer, 1998
FE Model with plane stress spherical elements
100 km lithosphere thickness Viscosity 1023
Pa.s
s
Plattner et al., 2007
Fault with strike-slip motion and differential
shear stress
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Scale shear stress from zero until geodetic plate
motion is fitted
FEM GPS
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Scale shear stress from zero until geodetic plate
motion is fitted
FEM GPS
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Geodetic plate relative motion is fitted with 10
MPa
Plattner et al., in press _at_ Geology
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Geodetic plate relative motion is fitted with 10
MPa
Plattner et al., in press _at_ Geology
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Rigid plate motions and geologic deformation
validate the model
Fit velocity vectors in rigid microplate Fit
velocity magnitudes in deformation zone
Geodetic and neotectonic fault rates as
summarized in Becker et al., 2005
Plattner et al., Geology, in press
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Additional coupling in the Gulf of
California decreases motion of BAJA with respect
to NAM
Plattner et al., in press _at_ Geology
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Influence of incomplete decoupling in the Gulf of
California
For higher stresses the Pacific - Baja plate
boundary is continuously deforming, instead of
localized faulting.
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Implications of a constant shear stress over the
last gt6 Myrs
Gravitational coupling suggest constant shear
stress. Rupture of Gulf of California should have
increased Baja - NAM motion, and slowed
Pacific-BAJA motion.
Fletcher et al., 2007
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Western NAM imposes resisting forces for BAJA
motion Fault evolution since 3 Ma suggests
decreasing resisting forces
in the past
lower velocity of
BAJA w.r.t. NAM?
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Constant Baja velocity since 3 Ma
GEOLOGIC GEODETIC
PAC - BAJA coupling decreased?
NA-PA
NA-PA
NA-PA
NA-Baja
NA-Baja
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CONCLUSIONS
Coupling stresses along the Pacific BAJA plate
boundary reproduces the observed kinematics of
BAJA. NAM - PAC plate boundary region, in
particular the Sierra Navada microplate are
strongly affected by BAJA motion. Since 3 Ma
PAC - BAJA coupling decreased if velocities were
constant as suggested by comparison of geological
and geodetic plate motions. Since 6 Ma BAJA
velocity with respect to NAM increased due to
Protogulf rupture and fault evolution in western
NAM, AND/OR coupling decreased.
Funding provided by Deutsche Forschungsgemeinschaf
t and Graduate School THESIS of the Elitenetzwerk
Bayern
USGS
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(No Transcript)
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Evidence for presence of coupling zone
High phase velocity zone supports presence of
lithospheric coupling along Western Baja
California (Zhang et al., 2007).
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Results from GPS study Rigidity of Baja
California microplate
Residual velocity 1.708 mm/yr
Convergent strain between northern and southern
network 10-16 s-1
Plattner et al. (GJI, 2007)
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Pure kinematic reference model
Broad scale needs simplification of plate and
microplate boundaries Test if fault geometry and
assumptions do not violate the kinematics (does
the model reproduce the kinematic input?)
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Pure kinematic reference model
The model is self-consistent and reproduces the
geodetic fault velocity and GPS velocity vectors
within the microplate.
GPS FEM
FEM GPS
w.r.t. fixed NA
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Lithospheric coupling model
FE code G-Tecton (Govers, 1993) as elastic, 2D,
shell Homogeneous rheology.
R. B. Smith et al., 2001