Transcript Moho comparison

Comparison of crustal structure
along the Caribbean-South
American plate boundary
from wide-angle seismic velocity
models
70W - Maria C. Guedéz
67W - Colin A. Zelt
65W - Maximiliano Bezada
64W - Stephen A. Clark
TRIN - Gail L. Christeson
TRIN
64W
65W
67W
70W
Crustal structure domains
Five wide-angle profiles on regional gravity map with seven crustal structure domains
trending roughly east-west from (1) in the north representing the Venezuela Basin, to (7)
in the south representing the South American continent. The domains are not tectonic
provinces, although they resemble those defined by Mann (1999).
5 velocity models
5 wide-angle velocity profiles arranged from
west (top) to east (bottom). Each model was
obtained by a combination of first-arrival
tomography to derive upper/middle crust, and
joint PmP and Pn inversion to derive lower
crust, Moho and upper mantle.
The boundaries of the crustal structure
domains are indicated by dashed lines; each
domain is numbered 1 through 7.
Corresponding average velocity-depth
functions in each domain for each wide-angle
profile has been calculated.
The Oca-San Sebastian-El Pilar strike-slip
fault indicated by thick gray dashed line.
1. Venezuela Basin
All of the profiles, except 67W,
sample oceanic plateau crust in
the north with Moho depths of
19-27 km. Profile 67W shows
close to normal oceanic crust.
2. South Caribbean
Deformed Belt
The 3 western profiles image
the SCDB which consists of a
thick sedimentary wedge. Profile
67W’s crustal thickness is less
due to normal oceanic crust
versus plateau crust.
3. Leeward Antilles
and Aves Ridge
The Aves Ridge and Leeward
Antilles Arc are very similar in
terms of velocity and crustal
thickness, except profile 70W in
the west shows much thicker
crust.
4. Bonaire and
Grenada Basins
The Grenada Basin along TRIN
and 64W are very different,
likely because 64W samples the
very edge. However, the basins
along 64W and 70W appear
very similar, as do those along
65W and 67W.
5. Falcon and Bonaire
Basins, Margarita High
and Lesser Antilles
The Lesser Antilles and
Margarita High along TRIN,
64W and 65W are quite
different. The Bonarie and
Falcon Basins along 67W and
70W are very different.
6. Cariaco, Araya
and Tobago Basins
These three basins along TRIN,
64W and 65W appear quite
different.
7. South American
continent
The South American continent
appears quite similar along the
four onshore profiles, except
profile 64W shows much thicker
crust.
Comparison of
Caribbean arc profiles
Aves and Leeward Antilles Arcs
are very similar (except along
70W), and the Lesser Antilles
(TRIN) and Margarita High
(65W) are somewhat similar to
these arcs, but the Margarita
High along 64W is very different
from all the rest.
Comparison of average
Caribbean arc and S.A.
continent with global
continent average
Comparison of average Caribbean arc
crust (domains 3 & 5) and average
South American continent crust (domain
7) with global continent average
(Christensen & Mooney 1995). Between
5 and 25 km depth, the arc crust is
consistently ~0.25 km/s faster than the
S.A. continent, but similar to the global
average. The S.A. continent is
consistently slower than the global
average to 35 km depth. [Note that the
average arc and S.A. continent profiles
below 25 km and 35 km, respectively,
are not very meaningful because of the
way in which the lateral averages were
calculated without regard to the Moho
depth.]
7:1 Moho comparison
Comparison of Mohos with zero distance corresponding to 12oN, a vertical exaggeration
of 7, and offset from each other for clarity. Generally, the Moho contains steeper
segments in the east.
1:1 Moho comparison
Comparison of the 5 Mohos aligned at the position of the major
strike-slip fault, with a vertical exaggeration of one, and offset from
each other for clarity.
2:1 Moho comparison
Comparison of the 5 Mohos aligned at the position of the major strike-slip fault, with a
vertical exaggeration of 2, and offset from each other for clarity.
Conclusions - part 1
(1). Thick oceanic plateau crust exists at the north end of all profiles, except
67W; thick sedimentary wedge (the South Caribbean Deformed Belt) present
along the western 3 profiles.
(2). The Aves Ridge and Leeward Antilles Arc are very similar in terms of
velocity and crustal thickness.
(3) The Lesser Antilles and Margarita High are quite different. In addition, the
Bonarie and Falcon Basins are very different; the Leeward/Aves and Lesser
Antilles are somewhat similar.
(4) The South American continent is quite homogeneous in terms of velocity
and crustal thickness, except it is ~8 km thicker along profile 64W.
(5) The average Caribbean arc crust is consistently ~0.25 km/s faster than the
S.A. continent, but similar to the global average (consistent with Yemi’s 3D
model); the South American continent is consistently slower than the global
average.
(6) The Moho has steeper segments in the east compared to the west.
Conclusions - part 2
(1) strong support for continuity of the Aves and Leeward Antilles
Arc based on velocity and crustal thickness.
(2) high crustal velocities at all depths within the arcs compared to
the adjacent South American continent.
(3) a general smoothing and flattening of Moho topography from
the youngest to oldest parts of the margin (east to west),
suggesting a “relaxation” of the Moho.
Moho comparison
Comparison of Mohos with zero distance corresponding to 12oN,
and a vertical exaggeration of 7. Generally, the Moho contains
steeper segments in the east (TRIN and 64W) and is smoother to
the west.