Tectonic processes along the Middle America Trench inner slope

Summary The relationship between sedimentation and structural variations observed in geophysical data provides insight into tectonic processes on the convergent Middle America Trench margin. We observe that some of the hemipelagic and pelagic oceanic sediments seem to continue relatively undeformed beneath the lowermost slope. Trench sediment bodies restricted to ponds in the vicinity of submarine canyons are incorporated into the lower slope by folding and thrust faulting. This offscraping (shallow accretion) at the base of the Middle America Trench slope appears at least partly dependent on the presence of trench fill. The internal structure of the so-called accretionary zone, the top of which is usually identified on seismic reflection profiles by a prominent zone of diffractions, is rarely resolved in the seismic reflection data. The shallow part of the accretionary zone along much of the margin may consist of deformed slope sediments since down-section increase in both folding and other deformation are observed in the seismic reflection and drill data. Beneath the undeformed and deformed slope sediments, offscraped trench fill may occur if trench fill was present in the ancient trench. The deeper part of the accretionary zone representing the bulk of the volume is not resolved in the reflection data but may consist of other sediments or crustal rocks added by an underplating process at deeper structural levels.

[1]  N. Lundberg,et al.  Structural Features of the Middle America Trench Slope off Southern Mexico, Deep Sea Drilling Project Leg 66 , 1982 .

[2]  M. Arthur,et al.  Initial Tectonic Deformation of Hemipelagic Sediment at the Leading Edge of the Japan Convergent Margin , 1980 .

[3]  J. Curray,et al.  Structure of the Sunda Trench lower slope off sumatra from multichannel seismic reflection data , 1980 .

[4]  J. Curiale,et al.  Leg 67: The Deep Sea Drilling Project Mid-America Trench transect off Guatemala , 1980 .

[5]  J. L. Worzel,et al.  Continental margin and lower slope structures of the Middle America Trench near Acapulco (Mexico) , 1980 .

[6]  J. Leggett,et al.  Progressive accretion in the Middle America Trench, Southern Mexico , 1979, Nature.

[7]  G. Latham,et al.  Seismic refraction and reflection measurements in the Middle America Trench offshore Guatemala , 1979 .

[8]  C. Galli-Olivier.  Ophiolite and island-arc volcanism in Costa Rica , 1979 .

[9]  D. Cowan,et al.  A dynamic, scaled model of accretion at trenches and its implications for the tectonic evolution of subduction complexes , 1978 .

[10]  D. G. Moore,et al.  Late Cenozoic subduction and continental margin truncation along the northern Middle America Trench , 1978 .

[11]  Thomas H. Jordan,et al.  Present‐day plate motions , 1977 .

[12]  R. Hey.  Tectonic evolution of the Cocos-Nazca spreading center , 1977 .

[13]  B. Carson,et al.  Tectonically induced deformation of deep-sea sediments off Washington and northern Oregon: Mechanical consolidation , 1977 .

[14]  B. Lewis,et al.  Tectonic evolution of the northern Cocos plate , 1976 .

[15]  D. Karig,et al.  Subduction and Accretion in Trenches , 1975 .

[16]  D. Karig.  Evolution of Arc Systems in the Western Pacific , 1974 .

[17]  S. Kesler.  Basement Rock Structural Trends in Southern Mexico , 1973 .

[18]  P. Molnar,et al.  Tectonics of the Caribbean and Middle America Regions from Focal Mechanisms and Seismicity , 1969 .

[19]  D. Ross,et al.  Reflection profiles across the Middle America Trench , 1965 .

[20]  R. L. Fisher,et al.  Middle America Trench: Seismic-Refraction Studies , 1961 .

[21]  J. Moore,et al.  Sedimentation in different tectonic environments of the Middle America Trench, southern Mexico and Guatemala , 1982, Geological Society, London, Special Publications.

[22]  N. Lundberg.  Evolution of the slope landward of the Middle America Trench, Nicoya Peninsula, Costa Rica , 1982, Geological Society, London, Special Publications.

[23]  R. Buffler.  Geologic Structure of the Forearc Region off the West Coast of Costa Rica in the Vicinity of Nicoya Peninsula, Results of a multifold seismic reflection survey, 1982 , 1982 .

[24]  N. Lundberg,et al.  Accretion, underplating, subduction and tectonic evolution, , 1981 .

[25]  J. Stephan,et al.  Accretion, Underplating, Subduction and Tectonic Evolution, Middle America Trench, Southern Mexico: Results From DSDP Leg 66 , 1981 .

[26]  W. Dickinson,et al.  Structure and Stratigraphy of Forearc Regions , 1979 .

[27]  D. Seely.  The Evolution of Structural Highs Bordering Major Forearc Basins: Convergent Margins , 1979 .

[28]  Manik Talwani,et al.  Island arcs, deep sea trenches, and back-arc basins , 1977 .

[29]  M. S. Marlow,et al.  Sedimentary Sequence in Modern Pacific Trenches and the Deformed Circum-Pacific Eugeosyncline , 1974 .

[30]  G. A. Fowler,et al.  Oregon Continental Margin Structure and Stratigraphy: A Test of the Imbricate Thrust Model , 1974 .