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Rob Rogers - Fellowship talk, Fall 2002

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Geologic constraints on the late Mesozoic tectonic evolution of the Chortis block of northern Central America

By Rob Rogers, BP Fellowship.

Abstract:
The Chortis continental block of northern Central America forms the present-day northwest corner of the Caribbean plate, a plate otherwise composed of oceanic, oceanic plateau, or arc crust. Previous work has shown that the Chortis block was part of the southern Cordillera of Mexico during the Mesozoic prior to 1000 km of left-lateral strike-slip translation into Caribbean realm during the Cenozoic. This study documents major late Mesozoic structural and stratigraphic events of the Chortis block in eastern and central Honduras that constrain the structural amalgamation and tectonic reconstruction of the Chortis block.

As an introduction to this talk, I show a 90-0 Ma plate tectonic animation of the Chortis block that is constrained by all available kinematic data compiled by myself and the PLATES project at UTIG from surrounding plates and ocean basins. Key features shown in the reconstruction include: 1) large-scale, deformed Cretaceous belts of the southern Cordillera of Mexico (Alisitos volcanic arc; Morelos intra-arc basin) and central Honduras (Olancho volcanic arc and Fray Pedro intra-arc basin); and 2) ophiolite (Siuna terrane of Nicaragua) and 150-km-long, NE-trending deformed Cretaceous fold-thrust belt between the Caribbean oceanic plateau and southern Chortis block of eastern Honduras (Montañas de Colon). The remainder of the talk focuses on my field results from Honduras which are used to better constrain the lithologies, ages, style and time of deformation for the Fray Pedro intra-arc basin and Montañas de Colon.

Geochemistry of volcanic rocks and paleontological dates from sedimentary units of the Fray Pedro basin confirm an of Aptian-Cenomanian intra-arc origin. Thickness and facies variations indicate a 3.5-km-deep, fault-bounded basin with pre-Cenomanian syn-sedimentary erosion of the basin margins. The basin trends WNW in present geography and NS when reconstructed against the Guerrero-Morelos basin of southwest margin of Mexico. The Fray Pedro basin was deformed and inverted by thick-skinned style, south dipping reverse faults in post-Cenomanian time. The age of deformation correlates with early Laramide-age shortening in the Alisitos arc and Guerrero-Morelos basin of Mexico and is consistent with my proposed Chortis-southern Mexico reconstruction.

Mapping and paleontological dates from sedimentary units in the Montañas de Colon fold-thrust belt confirm a pre-Cenomanian south-facing continental margin setting. Shallow-water carbonate rocks and subareal clastic strata totaling 4 km in thickness were deformed by thin-skinned style, northwestward-directed thrusting in Campanian time. Deformation is attributed to oblique collision of the Caribbean oceanic plateau and Siuna oceanic terrane as these oceanic elements entered the Caribbean realm from their place of origin in the eastern Pacific.