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IGCP 433 home page Caribbean WorkshopTowards an Integrated Understanding of Caribbean Tectonics and Stratigraphy - Contributions From TexasUniversity of Texas Institute for Geophysics |
| Ian Dalziel | UTIG |
| Lisa Gahagan | UTIG |
| Sean Gulick | UTIG |
| Paul Mann | UTIG |
| Kirk McIntosh | UTIG |
| Tom Shipley | UTIG |
| Harm Van Avondonk | UTIG |
| Wulf Gose | UT Dept. of Geological Sciences |
| Samarjit Chakraborty | UT Dept. of Geological Sciences |
| Alejandro Escalona | UT Dept. of Geological Sciences |
| Mochammad Fachmi | UT Dept. of Geological Sciences |
| Martha Jaimes | UT Dept. of Geological Sciences |
| Robert Rogers | UT Dept. of Geological Sciences |
| Armando Sena | UT Dept. of Geological Sciences |
| Sean Sullivan | UT Dept. of Geological Sciences |
| Songul Yildiz | UT Dept. of Geological Sciences |
| Kathleen Howard | University of Texas |
| Carr Breton | UT Bureau of Economic Geology |
| Cem O. Kilic | UT Bureau of Economic Geology |
| Lesli Wood | UT Bureau of Economic Geology |
| André Droxler | Dept. of Earth Science, Rice Univ. |
| Lanette Marcha | Dept. of Earth Science, Rice Univ. |
| Alastair John | Dept. of Earth Science, Rice Univ. |
| Jinny Sisson | Dept. of Earth Science, Rice Univ. |
| Armando Altamira | Geosciences Dept., Univ. Houston |
| Dan Fernandez | Geosciences Dept., Univ. Houston |
| Mike Murphy | Geosciences Dept., Univ. Houston |
| Sonya Punch | Geosciences Dept., Univ. Houston |
| Isabel Serrano | Geosciences Dept., Univ. Houston |
| Charlotte Sullivan | Geosciences Dept., Univ. Houston |
| Yahya Ciftai | Yuzuncu Yil Univ. Van Turkey |
Industry
| Scot Krueger | Conoco |
| Stefan Boettcher | ExxonMobil |
| Steve Creaney | ExxonMobil |
| Bolaji Famakinwa | ExxonMobil |
| Ian Norton | ExxonMobil |
| Michael Sullivan | ExxonMobil |
| Pete Emmet | Brazos Valley Services |
Table 1 List of Presentations
Abstracts for Presentations
1. Overview of workshop, PLATES model for Caribbean evolution
By Gahagan, Lisa (UTIG)
The purpose of the Caribbean workshop, "Towards an Integrated Understanding of Caribbean Tectonics and Stratigraphy - Contributions From Texas," was to focus on Caribbean research conducted by Texas scientists and to promote communication between these scientists. The workshop is part of a series of meetings in Río de Janeiro, Leicester, Stuttgart, and Boston, as well as field meetings in Cuba, Guatemala and Barbados, that have provided venues for researchers to discuss Caribbean tectonics in support of the International Geological Correlation Programme (IGCP) Project 433 on Caribbean Plate Tectonics (co-leaders Manuel Iturralde-Vinent and Edward Lidiak).
The workshop provided an added impetus to the PLATES Project to improve its plate tectonic model for the Caribbean and Central America. Working with Robert Rogers, a UT Austin Ph.D. candidate, we added several key magnetic anomaly data sets and Euler pole data (e.g., Wilson and Hey, 1995; Wilson, 1996; Tebbens and Cande, 1997; Barckhausen et al., 2001) to the PLATES data set and plate model. These were used to provide a framework for our Central American/Caribbean reconstructions. Mr. Rogers and Paul Mann provided additional geological/geophysical information to help constrain the motion of the smaller blocks. The results were presented as a Powerpoint animation, "Plate Tectonic Evolution of Central America and the Caribbean (90 Ma to Present Day)."
References
Barckhausen, U., Ranero, C.R., von Huene, R., Cande, S.C., and Roeser, H.A., 2001 Revised tectonic boundaries in the Cocos plate off Costa Rica: Implications for the segmentation of the convergent margin and for plate tectonic models, Journal of Geophysical Research - Solid Earth, 106 (9), p. 19,207-19,220.
Tebbens, S. F. and Cande, S. C., 1997, Southeast Pacific tectonic evolution from early Oligocene to present, Journal of Geophysical Research, 102 (6), p. 12061-12084.
Wilson, D.S., 1996, Fastest known spreading on the Miocene Cocos-Pacific plate boundary, Geophysical Research Letters, 23(21): 3003-3006.
Wilson, D.S., and Hey, R.N., 1995, History of rift propagation and magnetization intensity for the Cocos-Nazca spreading center, Journal of Geophysical Research - Solid Earth, 100(B6): 10041-10056.
2. Geologic constraints on the late Mesozoic tectonic evolution of the Chortis block of northern Central America
By Rogers, Robert (Dept. of Geological Sciences and Inst. for Geophysics, University of Texas at Austin)
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.
3. Intercratonic Orogens: The Caribbean and Scotia Arcs
By Dalziel, Ian W.D., Lawver, L. A., Gahagan, L. M., Rogers, R. and Mann, P. (UTIG)
The Caribbean and Scotia arcs are two striking features of any tectonic map of the Earth and are in fact nearly identical in size. They are respectively located between North and South America, and South America and Antarctica, joining the North American Cordillera to the Andes, and the Andes to the West Antarctic continental margin orogen. Their tectonic evolutions can be related to the relative motion between the two pairs of cratons. Their evolving physiography produced critical controls, varying with time, on the movement of biota between the cratons, and between the Pacific and Atlantic Oceans.
The Caribbean arc differs from the Scotia arc with the presence of the Central American land bridge. Yet differential motion along the Shackleton Fracture Zone between Cape Horn and the tip of the Antarctic Peninsula has produced a ridge as shallow as 700 meters. This ridge with only minor changes in plate motions could develop into a subduction zone and generate an island arc. Absence of a South America-Antarctica land bridge permits a complete and vigorous wind-driven circum-Antarctic current and intense sediment scour in Drake Passage.
Cenozoic magnetic anomalies have been identified in Drake Passage and the eastern Scotia Sea where oceanic crust was formed as Antarctica separated from South America. High sedimentation rates, possible formation during the Cretaceous Normal Superchron, and a large igneous province obscure the equivalent history of the older Caribbean arc and seafloor. The nature and tectonic history of these 'fusible orogenic links' between the continental margin cordilleras of the western Americas and Antarctica are considered as are their evolutions in terms of possible 'mantle return flow' from the Pacific Ocean basin to the Atlantic Ocean basin. Possible analogs to the ancient geologic record such as a link between the Ordovician Taconic and Famatinian arcs of North and South America are also considered.
4. Two styles of Cenozoic continental growth observed in the Caribbean, Solomon Islands, and other convergent margin settings
By Mann, Paul (UTIG)
This talk describes two styles of Cenozoic continental growth using field examples from several different convergent margins. The first style, colloquially referred to as "sidestepping", involves the progressive fragmentation of an incoming, colliding plate along newly-formed strike-slip faults trending at a high-angle to the convergent zone. The strike-slip faults act as lateral ramps that divide a previously-collided area from an as-yet-to-collide area. Examples of large-scale crustal growth involving this process include the northern Caribbean, Alps and Carpathians, and Yakutat block of Alaska. Continental growth occurs by the progressive transfer of the strike-slip fault-bounded blocks from one plate to the other.
The second style, referred to as "stepout", involves the formation and propagation of thrust faults into thick crust unable to be subducted at subduction and oblique-subduction margins. Formation and growth of thrust faults transfers large blocks of little deformed-material from the underriding to overriding plate and results in net continental growth. Examples of large-scale crustal growth involving this process includes the Ontong Java Plateau-Solomon island arc collisional zone.
5. Current investigations of the S. Central America convergent margin
By McIntosh, Kirk (UTIG)
(*From a proposal submitted by K. McIntosh and C. Fulthorpe to NSF MG&G)
Project Summary*
Forearc basin sediments are influenced by both tectonic events associated with plate convergence and global sea-level (eustatic) fluctuations. However, sequence stratigraphic investigators have tended to avoid convergent margins because of the perception that tectonic forcing would overwhelm the eustatic effect. Recent seismic investigation of the offshore Eel River Basin, northern California, suggests that this is not the case and supports the hypothesis that unconformities generated by tectonic uplift are localized near structures and distinguishable from the more regional sequences that are of eustatic origin.
This proposal is designed with two overriding objectives: 1) Initiate a test of the hypothesis that eustatic and tectonic effects can be identified and distinguished by acquiring and interpreting high-resolution, multichannel seismic (MCS) data in the Sandino forearc basin, on the Pacific margin of Nicaragua. These data will be used to interpret unconformities and sequences across and along the margin to document their geometries and extent. Subsequent IODP drilling will date interpreted sequences for correlation with coeval sequences on other margins and with the deep-sea oxygen isotope proxy for sea-level change. 2) Evaluate the record of tectonic events in the form of local unconformities and/or tectonically controlled variations in the geometries and stacking patterns of regional eustatic sequences. These will be correlated with known and proposed tectonic episodes in the region, including changes in plate motion, and uplift and subsidence associated with hypothesized tectonic erosion and accretion.
A vital part of defining the environmental impact of future sea-level change is in understanding the stratigraphic record of past eustatic fluctuations. The relative importance of eustasy versus local tectonic and sedimentary processes in controlling continental-margin depositional cyclicity is integral to this effort. It is a fundamental question in sedimentary geology and a key to deciphering the long history of geological, climatic, and oceanographic processes imprinted on the preserved stratigraphic record. The proposed work would be a large step toward proving whether regional unconformities worldwide, in a wide range of tectonic settings, can be ascribed to eustatic control, a result that could be applied to similar unconformities throughout the stratigraphic record, including the Mesozoic. It would provide a much-needed refocusing of the debate over the stratigraphic response to sea level change. Likewise, determining uplift and subsidence histories and defining the roles of tectonic erosion versus accretion are fundamental to understanding mechanisms of subduction and the evolution of convergent margins. The proposed work builds on, and complements, ongoing research into the Central American convergent margin in support of the Subduction Factory and Seismogenic Zone Experiment components of NSF’s MARGINS initiative.
Recognition of the need for high-resolution MCS data arises from experience gained from work off northern California, New Jersey, and New Zealand. In all of these locations, commercial and/or academic, low-resolution MCS data were available, but proved inadequate for detailed sequence stratigraphic interpretation in preparation for ODP/IODP drilling. In all cases, high-resolution MCS data led to identification of additional sequence-bounding unconformities not revealed by lower-resolution data and were essential for unraveling complex stratigraphic and structural interactions. Academic, deep-penetration, low-resolution MCS data (EW00-05 survey) are available in the Sandino Basin and provide an excellent structural framework, but the stratigraphy and structures of interest are at the limits of seismic resolution and the existing profiles are widely spaced (~20 km). To document the three-dimensional variability in sequence geometries that reflects local control and to map complex structures the proposed seismic program will have high vertical resolution (~5 m in the upper 0.5 - 1 km), close line spacing (~2 km), and numerous cross lines.
Only by studying basins subject to a wide spectrum of tectonic and depositional controls can full understanding of the relative roles of eustasy, tectonics and local sedimentary processes in generating preserved continental margin stratigraphy be achieved. Precise, seismic delineation of sequence and structural geometries, including their along-strike variability, followed by drilling, is essential to develop criteria for assessing how local and global controls interact to form the stratigraphic record.
6. Structure and stratigraphy of the Gracias A Dios platform and the Mosquitia basin, offshore eastern Honduras, and implications for the tectonic history of the Chortis block
By Emmet, Pete (Brazos Valley Services, Cypress, Texas 77433 USA;
281-373-3035; BrazosVS@neosoft.com)
(An extended version of this abstract, with figures, can be found at http://www.ig.utexas.edu/CaribPlate/forum/emmet/emmet_abstract.htm)
Students from The University of Texas were instrumental in performing early (1968-1983) detailed geological and geophysical studies in Honduras under the supervision of W.R. Muehlberger. Most of this work was performed in a relatively small area in central Honduras, and in retrospect it appears that the geographical focus of this early work led to an under-appreciation of the variablility of stratigraphic units and the diversity of structural styles in Honduras. More recent work, some of it being performed at Institute for Geophysics (UTIG) at The University of Texas at Austin, is beginning to clarify that record. I have been personally involved in research in Honduras geology and geophysics as a Masters student at UT (MA, 1983) and as a professional in 1985-86 while working for a geophysical service company in Houston; Aero Service. In this context I was the lead interpreter for a country-wide aeromagnetic survey of Honduras and I also contributed to an assessment of the hydrocarbon potential of the country performed by the Litton Resources Group (LRG; Aero Service, Western Geophysical and Core Lab) that utilized a comprehensive exploration data base that was shipped from Honduras to Houston for that purpose. More recently I have been involved in efforts to salvage this database, still in storage at WesternGeco in Houston until earlier this year, in collaboration with UTIG, the Dirección General de Energía (DGE) of Honduras and the Japanese Geological Institute (JGI). This effort has resulted in the preservation of a large amount of paper exploration data (reports, well logs, seismic profiles, aeromagnetic contours and depth-to-basement maps, etc) and digital field records for approximately 150 offshore seismic profiles. The ongoing study of these data will serve the parallel goals of stimulating the exploration effort for hydrocarbon resources in Honduras and identifying and publishing important details of the geology and geophysics of this critical and poorly-understood area in the Caribbean.
The first focus of my work in the current UTIG / DGE / JGI collaboration has been to study the offshore area immediately adjacent to eastern Honduras over which a seismic survey was shot by Texaco in the early 1980s. A shallow area extends seaward along the Nicaragua Rise and is known as the Gracias a Dios platform. To the south is an area of thicker Tertiary sediments known as the Mosquitia basin. To the north of the Gracias a Dios platform is a deep Cenozoic trough known as the Tela basin. The water bottom is nearly flat across Gracias a Dios platform and Mosquitia basin and does not exceed 200 m except to the north in the Tela basin. A 2D seismic survey was shot by Texaco in this area in the early 1980s. The key structural and stratigraphic characteristics of this area may be seen in two key profiles, Lines 80-68 and 80-74, and a key exploration well, Main Cape-1. The Texaco seismic data were reprocessed in 1984 by Geophysical Services, Inc (GSI) and were interpreted by a consultant, Don Rockwell, who prepared a proprietary report that was illustrated by a set of interpreted seismic profiles and both two-way time and depth maps for three horizons: Top Eocene, Top Cretaceous and Top Yojoa (?) Limestone. The configuration at the Top Cretaceous horizon is a structural nose that projects to the northeast offshore beneath the Gracias a Dios Platform. A short seismic line segment (Line 80-68) shows the deep structural configuration beneath the platform where a profound angular unconformity (top Cretaceous) overlies a faulted structure that thrusts a high-velocity unit suspected to be carbonate strata of the Lower Cretaceous Yojoa Group to the north. This thrust-fold structure has the same vergence and is believed to be analogous to the thrust-fold structures described onshore in the Montañas de Colon. Cretaceous volcanic rocks are associated with the Cretaceous carbonate and siliciclastic rocks in the Montañas de Colon. The presence of mafic volcanics within the Cretaceous strata has been observed but is rare in central Honduras (onshore) but appears to be increasingly common to the east (onshore and offshore).
The Mosquitia basin is characterized by closely-spaced normal faults with displacement mainly down to the southeast. These faults cut a thick section of Eocene and younger strata, but most of the faults appear to sole-out at the top Cretaceous. The character of the extensional fabric is such that the top Eocene horizon at some locations in the survey area is elevated above a regional marker (a local horst block) suggesting that there was a period of regional extension in the Eocene (transtension?) followed by an episode of compression (transpression?) during the Neogene. Detailed mapping, including the preparation of time-thickness and isopach maps, would clarify the structural evolution of the Mosquitia basin and help to determine the timing and sense of shear, if any, that influenced the formation of these structures. Onshore studies along the Guayape fault zone in eastern Honduras have suggested a complicated shear history.
The Main Cape-1 well was drilled on a regional arch and yielded a significant test of light oil. The source rocks for the oil are believed to be within the high amplitude reflections in the lower part of the Eocene package which are believed to correlate to the Mosquitia and/or Coco Marina Formations of Middle to Upper Eocene age. Geochemical modeling performed recently by JGI has demonstrated that Eocene strata in the vicinity of the Main Cape-1 well are thermally mature for oil, and also demonstrate that the thermal maturation and source rock quality of Cretaceous strata penetrated by wells offshore Honduras are favorable for significant oil generation. The Main Cape structure cannot be shown to be a closed structure based only on the Texaco lines. Many older seismic lines of lesser quality exist in the surrounding areas but could be integrated into a more detailed study. These lines appear to be of acceptable quality for defining the major structural and stratigraphic elements of this offshore province.
The aeromagnetic survey of Honduras performed by Aero Service in 1985 included coverage of a large part of the offshore area in eastern Honduras. The range of total magnetic intensity values in the offshore area is in excess of 750 nT. The weaker anomalies arise from structural relief (faulting) of more-or-less uniformly magnetic rocks (crystalline basement) against essentially non-magnetic sedimentary strata. The higher-amplitude anomalies arise from highly magnetic mafic igneous intrusions. Many of these igneous bodies were intruded within the basement complex in ancient times. In places where the basement subcrop is an erosional unconformity the lithologic contrast between these ancient intrusions and less magnetic metamorphic basement gives rise to magnetic anomalies whose depth can be calculated and which corresponds to the top of basement. In some cases in this data set igneous bodies can be documented to have intruded as diapirs within the sedimentary section in more recent times. These observations are consistent with the late Mesozoic and Cenozoic isotopic ages of many intrusions exposed onshore. The most prominent magnetic anomaly in eastern Honduras is a low-high anomaly pair with an amplitude in excess of 700 nT. A depth-to-basement map interpreted from the aeromagnetic data shows that this major anomaly arises from a combination of causes, including the contrast of intrusive bodies of high mafic mineral content against non-magnetic strata, but also from structural relief along faults that bound the intrusion
In general areas of smooth, broad contours correspond to deep basement and areas of very irregular contours correspond with shallow basement or shallow volcanic cover. A depth-to-basement map interpreted from the aeromagnetic data shows depth contours on the inferred basement surface. Faults are inferred where basement depth contour values change abruptly. Areas of volcanic cover are recognized by the irregular contours and by shallow depth solutions to the anomalies. The shallowest depths to basement are less than 2,000 ft while the deepest basinal areas are shown to be in excess of 34,000 ft. Note that basement in the onshore areas is consistently shallower than in the offshore areas. Also, the east-northeast-trending structural arch seen in the Gracias a Dios platform at the top Cretaceous structural level appears to have, in part, a corresponding feature at the basement structural level and at least some of these structures may be related to the thrust-fold structure observed on Texaco Line 80-68. Deep basinal areas and intervening structural arches are present in the Mosquitia basin. To the north along the present-day shelf margin that separates the Gracias a Dios platform and the Tela basin a series of basement uplifts and deep troughs are suggested by the interpretation. The relationship of these abrupt structures to the broader structures to the south, including the onshore structures, is unclear and should be investigated.
In summary a reconnaissance study of the available geological and geophysical data from the Gracias a Dios platform and Mosquitia basin offshore eastern Honduras has yielded the following preliminary results. An Eocene basin is recognized offshore which has characteristics that suggest compressional reactivation of extension structures (a mild inversion event). Inferrence from onshore geology and from the plate-tectonic context suggest that the Eocene basin probably evolved in a transtensional environment and was deformed sometime in the Neogene by transpression. The sense of shear and timing of the inferred strike-slip deformation offshore and any relationship to documented strike-slip motions onshore along the Guayape fault are currently unknown but should be a focus of future study. The Eocene basin has not yet been documented onshore but may be exposed in the Punta Patuca area. The Cretaceous strata underlying the Gracias a Dios platform and Mosquitia basin appear to have been subjected to intense shortening similar to that which is seen in the Montañas de Colon area onshore. The structural arch underlying the Gracias a Dios platform is intruded by highly magnetic plutons and some intrude the sedimentary section and are therefore relatively young (late Cretaceous or younger). Volcanic flows or sills are documented in the magnetic data offshore and appear to be similar to Cretaceous and Tertiary volcanics described onshore. Therefore, the Mesozoic and Cenozoic stratigraphy and main structural elements of eastern Honduras extend with apparent continuity offshore. Any major structural boundaries within the Chortis block should recognize this continuity. A crustal boundary between the Chortis block and oceanic terrane to the south probably exists along a trend parallel to the Hess Escarpment in northern Nicaragua and offshore along the southern margin of the Nicaragua Rise.
7. Neogene Evolution of the Pedro Channel Carbonate System, Northern Nicaragua Rise
By Cunningham, Andrew David*
Presented by Droxler, André (Rice University)
Pedro Channel is the deepest, central-most seaway on the northern Nicaragua Rise. A revised bathymetric map illustrates a seafloor dissected by numerous canyons and gullies as well as portions of a drowned carbonate bank with keep-up bank morphology. The 3.5 kHz echogram data interpretation in Pedro Channel indicates the banks provide both a line and point source of sediment to the channel floor. Concentric facies belts along the bank margins illustrate the line source concept. Localized zones of coarser-grained deposits at the bases of canyons along the bank margins depict the point source concept. The synthetic seismograms for ODP Site 1000 have low correlation coefficients (0.321). Visual correlation of the synthetic seismogram with SCS data indicates a good correlation of seismic facies with various lithologic intervals. An interpretation of SCCS and MCS data reveals that periplatform sedimentation has dominated Pedro Channel from the early Miocene to recent. Dredge haul analysis suggests that a neritic carbonate bank drowned partially in the middle Oligocene and finally in the early Miocene. Erosion affects the edges of this drowned bank in the middle Miocene. Faults in Pedro Channel illustrate characteristics typical of sinistral strike-slip faults including vertical to sub-vertical faults, faults that splay upward, forced folds, and linear fault traces in map view.
*From PhD Dissertation at Rice University, 1998, 378 p.
8. A multi-disciplinary study of the subduction-to-strike-slip transition in Hispaniola and Puerto Rico: Crustal and upper mantle structure and related seismic hazards
By Van Avendonk, Harm (UTIG), P. Mann, S. Gulick, J. Pulliam
The oblique subduction of oceanic plateaus and seamounts often results in variations from strike-slip to subduction along plate boundaries. A recent worldwide compilation of earthquakes (Bilich et al., 2001) suggested that these settings may experience relatively few but large earthquakes, leading us perhaps to underestimate the seismic hazard in these regions. The northern Caribbean offers a good example of a strike-slip-to-subduction transition, where the relatively buoyant Bahamas platform resists subduction beneath Hispaniola. The eastward progressing collision of the Bahamas platform has uplifted central Dominican Republic for about 5 Ma, and it may currently extend as far as Mona Block between Hispaniola and Puerto Rico. The resistance against subduction of the Bahamas may have caused the southward overthrusting of Hispaniola over the Caribbean plate at the Muertos trench. The two slabs subducting beneath Hispaniola and Mona passage appear to be in contact at large depth. This year a multi-institutional and international project is proposed by UTIG, Purdue and the University of Barcelona that includes acquisition of seismic reflection, wide-angle seismic refraction and earthquake seismology, GPS and geodynamic modeling around the Dominican Republic. Our goal is to capture the variability in crustal structure on both sides of the plate boundary, and to investigate the effect of platform collision by comparing the deep structure east and west of the current locus of deformation. Two imminently testable models are 1) underthrusting of the Bahamas, leading to large crustal thickness and continuing slab-pull forces beneath Hispaniola, and 2) tearing of the North American slab from east to west, leading to asthenospheric upwelling and pure strike-slip beneath Hispaniola. The new survey that we propose will provide the necessary boundary conditions for geodynamic modeling to validate the proposed models.
9. Tectonic Evolution of Cretaceous to Recent Orogenic Belts of northern Venezuela
By Virginia B. Sisson, Virginia B. and H. G. Avé Lallemant (Department of Earth Science,
MS-126, Rice University, Houston, TX 77005-1892, jinnys@rice.edu)
The Caribbean Mountain system (Venezuela) records a complicated interaction with the Caribbean plate. At first glance, this mountain range appears to be a classical orogenic belt with a metamorphic "Hinterland" and a non-metamorphic "Foreland" fold and thrust belt. However, metamorphism of the hinterland belt took place in mid-Cretaceous time, whereas the non-metamorphic foreland rocks were deformed in Cenozoic time. This situation resulted from marked right-oblique convergence of the Caribbean and South American plates. The metamorphic rocks contain blueschists and eclogites and have formed in the Leeward Antilles subduction zone along which the Atlantic plate was subducted. Blueschists and eclogites were partially exhumed by arc-parallel stretching resulting from displacement partitioning along an oblique plate margin. The collision of the Leeward Antilles arc with South America resulted in obduction of the accretionary wedge onto the South American margin. This obduction took place in Paleocene time in the west and is still occurring in the east. The development of foreland basins and the foreland fold and thrust belt was diachronous as well and young from west to east. The oblique convergence rate vector was strongly partitioned into a plate-boundary normal component that resulted into the south-vergent fold and thrust belt and a plate-boundary parallel component resulting in boundary parallel right-lateral strike slip faults along which the metamorphic belts were displaced toward the east.
In addition, subduction related processes vary along strike. The Cordillera de la Costa belt contains eclogites that were formed at ~70 km depth. Eclogites on Margarita formed at ~45 km depth. The Villa de Cura belt blueschist formed at ~30 km depth. The age of exhumation varies from mid-Cretaceous (Villa de Cura and Margarita) to Eocene (Cordillera de la Costa). The dependence of depth of metamorphism and timing of exhumation of these high-P rocks on plate tectonic configuration is complicated, because of Tertiary overprint.
New data on the evolution of the Foreland fold and thrust belt, particularily in the Guárico basin combined with apatite fission-track dating in the states of Guárico, Sucre, and Monagas (Pérez de Arma, 1998; Locke, 2001) reveals that convergence between North and South America in Tertiary time resulted in deformation along the South American margin in Venezuela long before the Caribbean plate arrived and collided with South America.
10. Paleomagnetic results from the Perijá Mountains, Venezuela: An Example of Vertical Axis Rotation
By Gose, Wulf A. (Department of Geological Sciences, The University of Texas at Austin
Austin, Texas, USA), A. Perarnau1 and J. Castillo (Departamento de Física, Universidad Simón Bolívar, Caracas, Venezuela)
1Now at Baker Atlas, Maturin, Venezuela
Paleomagnetic analyses of 161 samples of Jurassic through Eocene age from 11 sites in the Venezuelan foothills of the Perijá Mountains yield a pole position at 44.1°N, 6.6°E with an error of A95=9.6°. These data indicate that the sampling sites underwent a 50°±12° clockwise rotation. The rotations are interpreted to be the result of Neogene compression which caused the rotation of fault-bounded blocks. Model calculations suggest a shortening between 8 km and 20 km across the eastern portion of the Perijá Mountains.
11. Three-dimensional structural architecture and evolutionary history of an Eocene pull-apart basin, Maracaibo basin, Venezuela
By Escalona, Alejandro1 and P. Mann2
1Jackson School of Geosciences, Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78713, USA (email: escalonaa@mail.utexas.edu; phone:512-346-6881)
2Jackson School of Geosciences, Institute for Geophysics, The University of Texas at Austin, 4412 Spicewood Springs Road, Building 600, Austin, Texas 78759, USA (email: paulm@ig.utexas.edu; phone: 512-471-0452)
Three-dimensional seismic mapping of interpretative subsurface time slice maps that incorporate age data and detailed structural observations places constraints on the structural architecture and stratigraphic evolution of the Icotea pull-apart basin in the central part of the Maracaibo basin, Venezuela. The development of this 6-km-deep strike-slip basin within the much larger Maracaibo basin provides a good observational basis for testing two models for the formation of pull-apart basins in general, because all four fault-bounded sides of the Icotea basin, its ~3-km-thick Eocene basin fill of sandstone and shale, and faults pre-dating the opening of the basin can be mapped in three dimensions. The two models of pull-apart formation include (1) the simple model of pull-apart opening at a stepover between strike-slip faults and (2) formation of the basin by a component of extension normal to the strike of the strike-slip fault. The amount of fault extension (0.8 - 2.3 km) responsible for basin opening provides a minimum estimate for the amount of Eocene age left-lateral strike-slip displacement along the Icotea fault zone.
Three main fault trends produced at different periods in the formation of the Cretaceous-Recent Maracaibo basin are present: 1) N-NE normal faults, including the Icotea fault, formed originally during late Jurassic-early Cretaceous rifting and reactivated as left-lateral strike-slip faults during Eocene convergent deformation between the Caribbean and South American plates; 2) NW faults were formed by overthrusting of the Caribbean plate and downward flexure of the South American plate forming a major foreland basin depocenter in late Paleocene-Eocene time; and 3) NE normal faults formed also during late Jurassic-earliest Cretaceous rifting and were reactivated during Eocene plate convergence.
Three-dimensional architecture of the Icotea basin interpreted from five time slices through the basin and its flank areas supports the simple pull-apart model for the Eocene opening of the Icotea basin. The amount of extension across normal faults ranges between 0.8 and 2.25 km. This range of offset is consistent with some previous estimates of minor left-lateral displacement along the Icotea fault but is inconsistent with either low-angle or high-angle thrusting during Eocene time, as proposed by previous workers who based their interpretations on widely spaced two-dimensional seismic lines. Normal faults forming the pull-apart basin nucleated on pre-existing normal faults formed during plate flexure. The stratigraphic thickness, juxtaposition of Eocene sandy facies and Cretaceous source rocks across large-displacement normal faults and possibly higher heat flow, make the Icotea pull-apart basin a promising area for future hydrocarbon exploration.
12. Tectonic origin of the Cariaco basin, Venezuela: Pull-apart, extinct
pull-apart or fault-normal extension?
By Jaimes, Martha (Dept. of Geological Sciences and Inst. for Geophysics, University of Texas at Austin)
The Cariaco basin (CB) forms the largest and deepest fault-bounded, late Neogene basin along the northern shelf of Venezuela. Previous models have been proposed for its origin: 1) pull-apart formed at stepover between the right-lateral Moron and El Pilar faults; and 2) the basin formed by a component of extension parallel to Moron-El Pilar strike-slip faults. Using 2500 km of MCS tied to 12 wells, we present a structural and stratigraphic interpretation for the basin. Merged data sets suggest that faults of the CB can divided into four groups: 1) throughgoing Moron-El Pilar fault zone - expressed as a narrow seafloor valley overlying a negative flower structure that diagonally crosses both deeps; 2) EW normal-faults bounding the walls of the deeps - these faults exhibit mainly down-to-basin throws and may combine both normal and strike-slip displacement; 3) EW normal-faults south of the twin deeps - these faults are downthrown to north and south and form a large horst structure separating the CB from a middle Miocene-recent prograding clastic margin along the Unare shelf; and 4) NW-striking Urica fault zone - this fault is a large lateral ramp formed by thrusting in the Serrania del Interior and truncates EW faults of group 3. Correlation of well and seismic data shows that the main phase of basin subsidence was Pliocene-Pleistocene. We interpret the continuity of Moron-El Pilar fault through a blanket of Holocene deep-marine sedimentation as evidence for the process of "pull-apart extinction" or straightening of the fault zone at the expense of normal-fault systems framing the stepover area.
13. Integrating GIS and Quantitative Seismic Geomorphology for understanding the Deep Marine Architecture of the southeastern Caribbean Margin
By Wood, Lesli (UT BEG)
14. Provenance & depositional environments of Paleogene Sedimentary units of Trinidad and Barbados
By Punch, Sonya (Dept. of Geosciences, University of Houston, Houston, TX 77204, USA)
The island of Barbados is the only emergent portion of the accretionary prism formed by Neogene subduction beneath the Caribbean Plate. Paleogene sedimentary rocks within the wedge are unusual, however, as they are mostly compositionally mature quartz arenites interpreted deposited as a series of submarine fans deposited along the passive margin of South America (e.g., Larue & Speed, 1983; Larue 1985; Kasper & Larue, 1986). Petrographic studies indicate a composite of cratonic and recycled orogen sources, probably drained by the ancestral Orinoco River, formerly located near the present-day Araya Peninsula.
The Caribbean Plate is presently thought to have arrived in the Trinidad region in the Late Oligocene. Previous work suggests Paleogene rocks in Trinidad were deposited as deep marine sediments, shed from the passive margin of South America, similar to the source described for Barbados. Pindell et al. (2001), however, have suggested a more complicated source for the Paleogene sedimentary rocks of Trinidad. They proposed a Paleogene highland to the north of Trinidad as a probable source for the Paleogene sedimentary rocks of Trinidad. My research combines fieldwork and lab work and will test this hypothesis.
My recent fieldwork includes an examination and sampling of facies within the section in Barbados measured by Larue and Speed (1983). The Paleogene outcrops in Trinidad are not as laterally continuous nor as well preserved as those on Barbados. I sampled the Pointe-a-Pierre Formation at classic published locations including, the Petroluem Company of Trinidad and Tobago (Petrotrin) compound, the St. Fabien Road Quarry, the Navet Dam and Mt. Harris. I have had access to cores and archived reports of the Paleogene in Trinidad. A primary goal of this investigation is to determine provenance trends pre- and post-deposition of the Pointe-a-Pierre Formation. Provenance will be determined primarily through petrographic analysis, including heavy minerals, of the sandstones. Geochemical studies will be conducted as warranted.
15. Lithospheric Structure and Supracrustal Hydrocarbon Systems, Offshore Eastern Trinidad
By Boettcher, Stefan (ExxonMobil), L. Jackson, Jack E. Neal, and Michael J. Quinn
To facilitate an evaluation of hydrocarbon systems elements in offshore eastern Trinidad, we generated regional cross sections and a 1000 km long conceptual, lithospheric-scale cross section from the Aves ridge to the Demerara plateau. The sections are based on interpretation of 2D and 3D seismic data, gravity and magnetics surveys, and published literature. Our results indicate that convergent margin tectonism and rapid sedimentation first impacted the deepwater area of offshore eastern Trinidad in the latest Miocene. Up to 12 km of post-Middle Miocene sediments are present south and east of the Caribbean-South American plate boundary zone in the Columbus basin foredeep. The basin formed in response to subduction, tectonic loading, and progradation of the Orinoco delta. Well-imaged, northeast-trending buckle folds occur above the detachment fault(s) and are an important trap-forming element in the deepwater area. Deep-penetrating, active growth faults are the principal hydrocarbon migration pathways on the continental shelf but are absent in the deepwater exploration area. Seismic quality diminishes rapidly to the north of 11ºN latitude, in an area where highly irregular seafloor topography marks active deformation and dewatering in the internal part of the Barbados accretionary complex.
We propose that the change in crustal type across the Mesozoic passive margin of northern South America controls the style and magnitude of strain above the main décollement associated with the Cenozoic convergent margin. Contractional structures developed in Trinidad when continental lithosphere of the South American plate impinged on the subduction zone at the leading edge of the Caribbean plate. The positive buoyancy of continental lithosphere resists subduction, resulting in more earthquakes, a fold thrust belt from eastern Venezeula to offshore eastern Trinidad with up to 100 km shortening, and the southern limit of the Lesser Antilles volcanic arc. The transition to oceanic crust in offshore eastern Trinidad marks a change in tectonic environment from continental fold thrust belt to accretionary prism above subducting oceanic crust.
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