Tectonostratigraphic evolution of the Sinu accretionary prism and Lower Magdalena forearc basin formed above a shallow-dipping subduction zone, Caribbean margin of Colombia

This dissertation is an integrated geologic and geophysical study of the slowly converging (20 mm/yr), amagmatic, and shallowly subducting (4-8˚) system of the Caribbean margin of Colombia that includes both its offshore accretionary prism (Sinu belt) and its overlying deep (8-9 km) and wide (150-200 km) forearc basin (Lower Magdalena basin, LMB). Based on 29000 earthquake relocations, interpretations of ~1200 km of offshore deep-penetration seismic reflection lines recorded to depths of 20 km along with coincident gravity models, and 7000 km2 of onshore seismic reflection lines tied to 33 wells, I define an east-southeastward (110˚) dipping zone of shallow subduction beneath northwestern Colombia, an actively deforming accretionary prism, and an Oligocene to Recent forearc basin. Low angle subduction occurs as a 13-16 km thick Late Cretaceous oceanic plateau subducts beneath South America. Tomographic data reveal that the subducted slab exhibits an unusual negative velocity anomaly at depths greater than 80 km that I interpret as an incipient slab break off related to the clogging of the trench by the 30-km-thick Panama arc. In the accretionary prism, Pliocene-Pleistocene deformation developed on an imbricated backward breaking imbricated fan of thrust faults with out-of-sequence thrust faulting (OOST) within inner and outer parts of the prism. Inactive strike-slip faults were identified in a trench-parallel orientation where the subduction convergence direction is more oblique (>13mm/yr). In the forearc basin, I describe initial Oligocene subsidence of the forearc basin along 70˚-110˚striking normal faults that remained active until Early Miocene. An angular unconformity spanning the interval of 11 to 7 Ma seems to evidence the initiation of low angle subduction. The Lower Magdalena basin (LMB) overfills with sediments of shallow marine- transitional facies and spills offshore along the proto-delta of the Magdalena fan where up to 5 km deposited during the Pleistocene to Recent. I propose that this change from the steeper to shallowing dipping slab in the Middle Miocene led to increasing elevation of the forearc high and the western part of LMB where a clear unconformity is subsequently deformed.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Geology

Grantor

University of Houston

Year dc:date.issued

2014

Author dc:creator

• Bernal-Olaya, Rocio 1985-

Advisor dc:contributor.advisor

• Mann, Paul

Committee members dc:contributor.committeemember

• Murphy, Michael A.
• Khan, Shuhab D.
• Bird, Dale

• Subduction
• Accretionary prism
• Forearc basin
• Flat subduction

Statement dc:rights

• The author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10657/1567

OAI identifier oai:identifier

oai:uh-ir.tdl.org:10657/1567