The gravity field and plate boundaries in Venezuela
Citable URI
https://hdl.handle.net/1912/2209Location
7°N - 13°N60°W - 72°W
Venezuelan continental margin
DOI
10.1575/1912/2209Keyword
Marine geophysics; Plate tectonics; Atlantis II (Ship : 1963-) Cruise AII54; Chain (Ship : 1958-) Cruise CH55Abstract
Free-air and simple Bouguer anomaly maps of the Venezuelan
continental margin (from 60°W to 72°W and from 7°N to 13°N)
are presented. The major features of the free-air map are:
the large lows associated with the deep sedimentary basins,
-200 mgal in the Eastern Venezuela basin and -164 mgal in the
Maracaibo basin; the high of greater than 300 mgal over the
Venezuelan Andes; and a belt of highs associated with the offshore
islands extending from Blanquilla to Curacao and then
over the Guajira peninsula, where they terminate. The Bouguer
anomaly map shows a large low (-196 mgal) over the Eastern
Venezuela basin and relative minimums over the coastal mountains.
A minimum associated with the Venezuelan Andes is
shifted to the northwest of the topographic axis and lies
over the flank of the Andes and part of the Maracaibo basin.
Using the gravity data, structural sections were constructed
for a series of profiles across the Venezuelan Andes and
Caribbean mountains. They show that there is no light crustal
root under the Andes, the relative mass excess is as much as
600 kg/cm2, and that there is an excess of low density material
under the Maracaibo basin. This appears to be caused by a
combination of a southeastward dipping shear zone in the
lithosphere under the basin-mountain boundary and a component
of compressive stress perpendicular to this zone, both of
which have resulted in the uplift of the crust under the Andes,
and downwarp under the basin. The apparent flexural rigidity
of the lithosphere under the Maracaibo basin is 0.6 x 1023
newton-m, a normal value for lithosphere deformations of
Miocene age.
The Caribbean mountains have a light crustal root which
has been formed by the sliding of blocks of crustal material
from the north over the rocks to the south, and perhaps by the
underthrusting of oceanic crust under the continental crust.
This underthrusting may have been a result of the formation of
a downgoing slab of lithosphere along the Venezuelan continental
margin during the late Cretaceous. The downgoing slab may have
existed until mid-Eocene time. The gravity minimum over the
Eastern Venezuela basin is due to the downwarping of lighter
crustal material into the higher density mantle. This may be
a result of compression from the north along a north-south
direction causing plastic downbuckling of the lithosphere.
The present deformation along the northern boundary appears to
be due to differences in relative motion between the North
and South American plates.
Because the Caribbean mountains are partially isostatically
compensated, while the Venezuelan Andes are above isostatic
equilibrium, this suggests that the relative motion
of the Caribbean plate with respect to the South American
plate is eastward. The compressive stress across the boundary
in the region of the Venezuelan Andes is probably greater than
the compressive stress across the Caribbean mountains.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January 1972
Collections
Suggested Citation
Thesis: Folinsbee, Robert Allin, "The gravity field and plate boundaries in Venezuela", 1972-01, DOI:10.1575/1912/2209, https://hdl.handle.net/1912/2209Related items
Showing items related by title, author, creator and subject.
-
The relationship between plate curvature and elastic plate thickness : a study of the Peru-Chile Trench
Judge, Anne Victoria (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1988-05)The age of the Nazca plate where it enters the Peru and northern Chile trenches varies from 30 Ma in the north to 45 Ma in the south as its dip beneath the South American continent steepens from 13° to 30°. If the elastic ... -
Structure and mechanics of the subducted Gorda plate: constrained by afterslip simulations and scattered seismic waves
Gong, Jianhua (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2021-02)Subduction zones host the greatest earthquakes on earth and pose great threat to human society. The largest slip in megathrust earthquakes often occurs in the 10–50 km depth range, yet seismic imaging of the material ... -
Acoustic diffraction from a semi-infinite elastic plate under arbitrary fluid loading with application to scattering from Arctic ice leads
Dahl, Peter H. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1989-05)The problem of a low-frequency acoustic plane wave incident upon a free surface coupled to a semi-infinite elastic plate surface, is solved using an analytic approach based on the Wiener-Hopf method. By low-frequency it ...