Detailed bathymetric survey data were collected along the Peruvian
continental margin and were compiled by the author and other
investigators to construct a new bathymetric map for the area between
6° to 18°S latitude. Based on this map and individual bathymetric
profiles, the continental shelf topography is essentially flat. Four
different physiographic provinces (A-D) are defined on the continental
slope. Each province apparently reflects the structural and tectonic
settings in a given area. The trench is separated into three provinces
on the basis of regional depth differences.
Three sedimentary basins, Sechura, Salaverry, and Pisco, are
recognized on the Peruvian continental shelf between 6° to 15°S. The
landward migration on the axis of deposition within these basins is
interpreted to be the sedimentary response to tectonism (uplift) taking
place along the outer edge of the continental margin. Prominent
sedimentary basins also occur on the upper continental slope; these
basins have been named with respect to their geographic position as
the Lima and Arequipa Basins. Landward and seaward migration of
the axis of maximum deposition in these basins is interpreted to be
the result of variable rates of uplift along the outer margin. Uplift
along the seaward edge of these basins suggests that the accretion of
trench and oceanic plate deposits is taking place along the lower and
middle continental slope.
Seismic reflection profiles, extrapolation of regional structural
trends onshore to offshore along the Peruvian margin, and positive
free-air gravity anomalies off southern Peru (Whitsett, 1975), show
that an outer continental shelf high is present off northern and central
Peru. This high is believed to be composed of Paleozoic rocks with
a possible Precambrian core. The high is linked with the Amotape
Mountains in northern Peru and the Coastal Ranges in southern Peru.
It is an important element in the development of the Peruvian continental
margin.
Using all of the data available, a four stage model is proposed
for the Mesozoic-Cenozoic evolution of the Peruvian continental margin.
Stage I describes conditions prior to the formation of the subduction
zone during Triassic time. Plate collision is postulated at the
beginning of Stage II with the formation of a Benioff Zone about 180
m.y. ago (Triassic-Jurassic boundary). Accretion of trench and
oceanic plate deposits occurs as a result of the initiation of under-thrusting
of the South America Block by the Nazca Plate. Stage III
describes the continuous seaward growth of the continental slope
during middle to late Cretaceous time. During late middle (Turonian)
and middle late Cretaceous (Santonian) time diastrophism in
southern Peru restricted the marine conditions to central and
northern Peru. During late Cenozoic time (Stage IV) the Peruvian
margin attained its present configuration through continuous seaward
growth of the continental slope and buildup of the sedimentary
sequences found in the Sechura, Salaverry, and Pisco Basins, in
central and northern Peru. Late Cenozoic volcanism in southern
Peru is apparently associated with the large amount of sediments
that reached the southern Peru Trench since late Cretaceous time.
The Nazca Ridge apparently approached the Peruvian continental
margin during Cenozoic time, and locally changed the morphology of
the continental slope. The proposed model shows that the Peruvian
continental margin is growing seaward and that continental erosion
of the crystalline continental block is not necessary along the
Peruvian continental margin. The model explains and justifies the
presence of the outer continental shelf high off northern and central
Peru. / Graduation date: 1976
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28513 |
| Date | 06 June 1975 |
| Creators | Masias Echegaray, Juan Antonio |
| Contributors | Kulm, LaVerne D. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
Page generated in 0.0132 seconds