Active Margins—Caribbean Margin of South America, Profiles C-1422, C-1412, and C-1413
P. Lehner, H. Doust, G. Bakker, P. Allenbach, J. Gueneau, 1983. "Active Margins—Caribbean Margin of South America, Profiles C-1422, C-1412, and C-1413", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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Seismic lines C 1422 and C 1412, and C 1413 illustrate the structural configuration of the northern margin of South America, which is an active plate boundary between the Caribbean plate and the American plate.Plate models predict east to west trending strike slip movement along the southern margin of the Caribbean plate but leave little room for differential northward movement of South America.
Seismic profiles across the Caribbean margin, however, display characteristic features of a subduction zone. They show the plunge of the Caribbean basement southward below an accretionary prism of folded and imbricated sediments. The front of the prism forms an arc which extends from western Colombia along the foot of the continental slope to the region of the islands of Curacao and Bonaire.
A similar southward-facing fold belt extends from the Merida range of southern Venezuela to Trinidad along the northern rim of Guyana Craton.
The apparent contradiction between a plate model of global scale and the local geology can be solved by assuming that the Caribbean margin of South America consists of a converging wrench system with predominant east-west slip and a subordinate, north-south compressive component possibly related to the wrench systems in the Andean mobile belt.
The absence of a Benioff zone and the lack of a volcanic arc along the Caribbean margin of South America also indicate that subduction along the Caribbean front has been rudimentary, at least during Tertiary time.
Results of the JOIDES core hole 153, and seismic evidence, suggest that the basement of the Colombia basin in the Caribbean sea is of Late Cretaceous age. It is called Caribbean basement because its thickness and velocity distribution are different to those of a typical oceanic basement. This, however, may be due to the complexities of back-arc spreading.
The geology of the coastal ranges of Colombia and Venezuela is unusually complex. A major orogenic pulse with granitic intrusions and metamorphism in mid-Cretaceous time was followed by repeated tectonic phases, the most important ones being at the base of the Tertiary, during late Oligocene and early Pliocene times. The sediment fill of the coastal basins is of late Oligocene and Neogene age.
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Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces
Until a few decades ago, structural and regional geology were traditionally the preserve of field geologists. They usually mapped areas of outcropping deformed rocks and supplemented their work by laboratory studies of rock deformation and by theoretical work. Structural geology became tied to the geology of uplifts, folded belts, and underground mines, all of which were accessible to direct observation. Since World War II we have witnessed a tremendous development of geophysics in oceanography and in petroleum geology. Academic geophysicists in oceanography led their geological colleagues into modern plate tectonics and industry geophysicists developed reflection seismology into a superb structural mapping tool that penetrated the subsurface.
Today we are facing a situation where instruction and textbooks in structural geology are almost entirely dedicated to rock deformation, analytical techniques in detailed field geology and summaries of plate tectonics. Illustrations based on reflection seismic profiles are virtually absent in textbooks of structural geology. These texts illustrate only the parts of the proverbial elephant, together with some conjecture, but without ever offering a glimpse of the whole elephant.
Some of the reason cited for the relative scarcity of published reflection profiles are: 1) the confidentiality of exploration data; 2) difficulties in the photographic reduction and reproduction of seismic profiles for a book format; 3) the two-dimensional nature of vertical reflection profiles; and 4) the obvious distortions in reflection profiles that are typically recorded in time.
The AAPG leadership felt that it was time to attempt to correct the situation and to produce this picture and work atlas. The first volumes, of what may become a series of volumes, are addressing an audience that includes: petroleum geologists concerned with structural interpretations; exploration companies that provide in-house training; the AAPG continuing education program; and academic colleagues interested in updating their curricula in structural geology by inclusion of reflection profiles from the “real world” in their teaching.
The atlas is not meant to be a textbook in reflection seismology (instead we listed some at the end of this introduction) nor a text in structural and/or regional geology. Our intent is simply to provide a teaching tool.