North American-Caribbean Plate Boundary Research Articles

Late Cenozoic subduction and continental margin truncation along the northern Middle America Trench

The narrow inner trench slope and the truncated igneous and metamorphic terrane along the west coast of Mexico between Cabo Corrientes and the Gulf of Tehuantepec indicate that part of the continental margin has in some way been removed during the process of subduction. However, a detailed marine geophysical survey of the inner trench slope near Acapulco indicates that this removal is not occurring now. South-southwest–trending magnetic anomalies produced by the Xolapa metamorphic complex extend seaward only 20 to 30 km. Oceanic magnetic anomalies that trend N50°W extend as much as 30 km landward of the trench. The boundary between these two magnetic patterns lies landward of the trench-slope break and beneath the upper-slope sediment pile. The nonmagnetic material forming the acoustic basement trenchward of the metamorphic rocks is interpreted to consist of late Miocene to Holocene deformed trench-floor turbidites. Deformation associated with subduction has reversed the gradients of several submarine canyons and tilted the seaward edge of the upper-slope sediment pile away from the trench. The morphology and structure of the inner trench slope is typical of accreting trench-arc systems, although the morphotectonic units in this system are smaller than usual. Accretion since late Miocene time is suggested by the age of dredged slope sediments and by analysis of offshore magnetic anomalies, which indicate a change from right-lateral oblique to perpendicular subduction at that time. Removal of the continental margin probably occurred intermittently between Late Cretaceous and late Miocene time. Possible mechanisms include subduction of continental crust (tectonic erosion), left-lateral translation associated with the Caribbean–North American plate boundary, and right-lateral translation associated with oblique subduction between the Farallon or Cocos plates and the North American plate. Geological data favor right-lateral offset and suggest that some of the missing margin may be the slivers of subduction complex found along the west coast of Baja California and possibly even farther north.

Offset across the Polochic fault of Guatemala and Chiapas, Mexico

Research Article| June 01, 1978 Offset across the Polochic fault of Guatemala and Chiapas, Mexico Burke Burkart Burke Burkart 1Department of Geology, University of Texas at Arlington, Arlington, Texas 76019 Search for other works by this author on: GSW Google Scholar Author and Article Information Burke Burkart 1Department of Geology, University of Texas at Arlington, Arlington, Texas 76019 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1978) 6 (6): 328–332. https://doi.org/10.1130/0091-7613(1978)6<328:OATPFO>2.0.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Burke Burkart; Offset across the Polochic fault of Guatemala and Chiapas, Mexico. Geology 1978;; 6 (6): 328–332. doi: https://doi.org/10.1130/0091-7613(1978)6<328:OATPFO>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Polochic fault is seen on LANDSAT imagery to continue its westward path from northwestern Guatemala across the Chiapas massif to the Pacific coastal plain. The fault has had 132 ± 5 km of left-lateral displacement that is recorded in the offset of Cenozoic fold and thrust belt structure and stratigraphy. The trace of the Polochic fault has been folded into what approximates a sinusoidal curve of about 130-km wave length and 7-km amplitude by an essentially east-west compressive stress. The curious similarity in displacement and fold wavelength results in a premovement reconstruction that reveals not only a match across the fault in geology, but an almost perfect fit of one block against the others. Some segments of the fault across which recorded slip took place are probably locked and not active. Strain has shifted to other shears in western Guatemala and Chiapas and to the Motagua fault. Parts of the Polochic and the newer shears may be alternating with the Motagua as the Caribbean-North American plate boundary. With the 132 km of slip removed, segments of the now fragmented Cenozoic fold belt can be brought into coincidence in a clear-cut arcuate trend that is convex southwest. The major fault displacement is believed to have occurred within the interval from middle Miocene to middle Pliocene time. Eastern Guatemala has undergone a counterclockwise rotation of about 25° that reoriented the fault trace and all other structural fabric from due east to the present east-northeast azimuth. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.