Download South American Plate Relationships

Outline
South American Plate
Relationships
Rebecca Williams
Kelly McGuire, Sarah Craig
z Introduction
z South American Plate
z Coupling Theory: Relationship to African
Plate
z Relationship with North American Plate
z Caribbean Plate
z North American Analogy?
South American Plate
z General
westward
movement
from Mid
Atlantic Ridge
(MAR) since
break up of
Gondwana.
z Has variations
in lithosphere
thicknesses.
Coupled with African Plate
z The South Atlantic Ridge has had constant
spreading rate for 80 Myrs.
z African Plate slowed abruptly 30 Myrs ago.
z Caused westward acceleration of SA
Plate.
z Seen by increase in cordilleran activity
along western edge-Andean Deformation.
z Plate velocity ~2-2.8 cm/yr
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Affect on Andean Deformation?
Relationship of SA and NA Plates
z Assuming SA Plates trenchward velocity,
since 30Ma, is taken up entirely by E-W
shortening, the predicted amount of
cordilleran shortening from plate motion is
120 km.
z Estimate comparable to previous
estimates for the Central Andes.
z Present day shortening rate of 1cm/yr.
z Diverged from Late Triassic to E
Campanian (84 Myrs ago).
z Time when Gulf of Mexico and ProtoCaribbean Seaway formed.
z Since then only minor relative motion.
z Only meet (present day) east of
Caribbean.
Is the North American Plate coupled?
Evidence from Mud Diapirism
z Westward acceleration of NA Plate
expected from SA-AF plate analysis.
z If the NA Plate is not coupled, an E-W
differential motion between N and S
America should be evident.
z Motion of NA Plate relative to Iceland Hot
Spot is consistent with westward
acceleration.
z Mud Diapirs
ahead of
Barbados
accretionary
wedge.
z Triggered by
change in
relative plate
motion from
Compression to
Dextral Strikeslip.
Evidence from Mud Diapirism
Northern SA Border
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Northern SA Border
z NA Plate, discussed previously.
z Caribbean Plate: Atlantic Seafloor part of
Northern SA is subducting beneath Caribbean
Plate.
z In NE Venezuela, deformation dominated by
right lateral, strike slip along E-W striking faults.
z N-S Compression
z Caribean Plate moving E/SE @ 1-1.5 cm/yr
relative to SA.
z Subduction occurring @ 1.5cm/yr
Relation to Caribbean Plate
Terranes
z Northern SA border is most complex
border of Caribbean Plate
z Undergone diachronous, right-oblique
collision with overriding Lesser Antilles arc
system.
z Began 35-40Ma.
z Drove Caribbean Terranes from west to
east to point North of Trinidad-present day
collision.
z 3 Caribbean Terranes between arc
system and SA continent:
1. Tobago Terrane
2. Paria-Trinidad Terrane: exhumed
schists.
3. Araya-Margarita Terrane.
z P-T Terrane thrust above Mesozoic shelf
strata and locally, Miocene Strata:
¾ Piggy-Backed Foreland Basin
¾ Obducted Terranes
Piggy Backed Foreland Basin
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Subduction?
Spatial Variation in
Subduction
z Irregular Seismicity
z Dipping zone below continent but attached
to SA lithosphere.
z Contradicts normal thinking-would expect
seismicity north of exposed plate edge.
z Continent has detached from slab and
moved north above slab.
z Wedged between overriding terranes and
underriding slab.
Tectonic Wedging Model
North American Analogy?
z Mechanism for
thickening
crust
z Rationale for
depressing
mantle.
z Supported by
P Wave
Velocities
z Supported by
gravity model.
z Oblique convergence common in
Cordillera e.g. Offshore British Colombia.
z Thrust belts common along western
margin.
z No known analogy for slab detachment
and continent wedging.
References
z Bosch & Rodriguez, 1992. North Venezuela collisional crustal
block: The boundary between the Caribbean and South American
Plates. J of South American Earth Sciences 6 (3) 133-143.
z Mantovani et al, 2001. Tidal gravity anomalies as a tool to measure
rheological properties of the continental lithosphere: application to
the South American Plate. J of South American Earth Sciences 14
(2001) 1-14.
z Meijer & Wortel, 1992. The dynamics of motion of the South
American Plate. Journal of Geophysical research 97 (8) 1191511931.
z Pindell et al, 1988. A plate-kinematic framework for models of
Caribbean evolution. Tectonophysics 155 (1-4) 121-138.
z Russo & Speed, 1992. Oblique collision and tectonic wedging of the
South American continent and Carribean Terranes. Geology 20.
447-450.
z Silver et al, 1998. Coupling of South American and African Plate
Motion and Plate Deformation. Science 279 (5347) 60-63.
z Sumner & Westbrook, 2001. Mud diapirism in front of the Barbados
accretionary wedge: the influence of fracture zones and North
America-South America plate motions. Marine and Petroleum
Geology 18. 591-613.
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