Outline

South American Plate zIntroduction zSouth American Plate Relationships zCoupling Theory: Relationship to Rebecca Williams zRelationship with Kelly McGuire, Sarah Craig zCaribbean Plate zNorth 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 zThe South Atlantic Ridge has had constant spreading rate for 80 Myrs. zAfrican Plate slowed abruptly 30 Myrs ago. zCaused westward acceleration of SA Plate. zSeen by increase in cordilleran activity along western edge-Andean Deformation. zPlate velocity ~2-2.8 cm/yr

1 Affect on Andean Deformation? Relationship of SA and NA Plates zAssuming SA Plates trenchward velocity, zDiverged from Late Triassic to E since 30Ma, is taken up entirely by E-W Campanian (84 Myrs ago). shortening, the predicted amount of zTime when Gulf of Mexico and Proto- cordilleran shortening from plate motion is Seaway formed. 120 km. zSince then only minor relative motion. zEstimate comparable to previous zOnly meet (present day) east of estimates for the Central Andes. Caribbean. zPresent day shortening rate of 1cm/yr.

Is the North American Plate coupled? Evidence from Mud Diapirism zWestward acceleration of NA Plate z Mud Diapirs expected from SA-AF plate analysis. ahead of zIf the NA Plate is not coupled, an E-W accretionary differential motion between N and S wedge. America should be evident. z Triggered by change in zMotion of NA Plate relative to Iceland Hot relative plate Spot is consistent with westward motion from acceleration. Compression to Dextral Strike- slip.

Evidence from Mud Diapirism Northern SA Border

2 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 , 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 occurring @ 1.5cm/yr

Relation to Caribbean Plate zNorthern SA border is most complex z 3 Caribbean Terranes between arc border of Caribbean Plate system and SA continent: zUndergone diachronous, right-oblique 1. collision with overriding Lesser arc 2. Paria- Terrane: exhumed system. schists. zBegan 35-40Ma. 3. Araya-Margarita Terrane. z P-T Terrane thrust above Mesozoic shelf zDrove Caribbean Terranes from west to strata and locally, Miocene Strata: east to point North of Trinidad-present day ¾ Piggy-Backed collision. ¾ Obducted Terranes

Piggy Backed Foreland Basin

3 Spatial Variation in Subduction? Subduction zIrregular Seismicity zDipping zone below continent but attached to SA lithosphere. zContradicts normal thinking-would expect seismicity north of exposed plate edge. zContinent has detached from slab and moved north above slab. zWedged between overriding terranes and underriding slab.

Tectonic Wedging Model North American Analogy? z Mechanism for zOblique convergence common in thickening Cordillera e.g. Offshore British . crust zThrust belts common along western z Rationale for depressing margin. mantle. zNo known analogy for slab detachment z Supported by and continent wedging. P Wave Velocities z Supported by gravity model.

References z Bosch & Rodriguez, 1992. North Venezuela collisional crustal block: The boundary between the Caribbean and South American Plates. J of South American 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) 11915- 11931. 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 : the influence of zones and - plate motions. Marine and Geology 18. 591-613.

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