San Francisco 14-18 December 2009. AGU Fall Meeting. Session
"T22 Evolution of the Caribbean Plate: Linking its Tectonic, Magmatic,
Metamorphic and Stratigraphic Records"
San Francisco 14-18 December 2009. AGU Fall Meeting. Session
"T22 Evolution of the Caribbean Plate: Linking its Tectonic, Magmatic,
Metamorphic and Stratigraphic Records"
Abstracts
Session T22: Evolution of the Caribbean Plate: Linking its Tectonic, Magmatic, Metamorphic and Stratigraphic Records
This session is devoted to further understanding the convoluted tectonic evolution of the Caribbean plate and its interactions with the North American and South American plates. The session aims at integrating new data from all fields of geophysics, geochemistry, and geology in an actualistic paleogeographic and geodynamic model for the Caribbean plate that accounts for its current tectonic configuration. Contributions on both ancient and active tectonic processes are welcome, as well as new work on sutures, divergent margins, strike-slip boundaries, sedimentary basins, development of arcs, evolution of spreading centers, and terrane transferal, among others. This session will include, but not be limited to, scientific results from IGCP Project 546 “Subduction Zones of the Caribbean”. Therefore contributions on current and fossil subduction zones in the Caribbean area are especially encouraged.
This session will include, but not be limited to, results from IGCP Project 546 “Subduction Zones of the Caribbean”.
Our session proposal for the upcoming 2009 AGU Fall Meeting was approved by the Fall Meeting Program Committee and is already listed on the AGU Web site:
http://www.agu.org/meetings/fm09/
or go directly to:
http://www.agu.org/meetings/fm09/program/scientific_session_search.php?show=detail&sessid=448
We invite you to present contributions from all fields of geophysics, geochemistry and geology applied to convergent tectonics and geodynamics of the Caribbean. Field-based, geochemical or petrologic studies of sutures and subduction complexes are welcome. We especially encourage contributions establishing links, contrasts and correlations among current and fossil subduction zones in the Caribbean area.
Please, note that the abstract submission deadline is 3 September 2009. THERE IS NO GUARANTEE THAT OUR SESSION WILL BE SCHEDULED AS AN ORAL SESSION, but the higher the number of abstracts submitted, the greater the possibility. So, we are asking you to submit abstracts for our session and promote it to your colleagues and students.
Useful Links
Free abstract submission for 'Low Income' or 'Lower Middle Income' Countries There is no abstract fee for participants from these countries.
3 September Abstract Deadline for Electronic Submissions – No Exceptions!
10 September Scheduler Software Distributed to Program Committee
15 September Scheduler Software Distributed to Conveners
21 September Scheduler Software Closed to Conveners
23-25 September Fall Meeting Program Committee Planning Scheduling Meeting
15 October Program Posted on AGU Website
19 October Acceptance Letters Sent to Presenters and Session Chairs
12 November Pre-Registration Deadline (after this date registration rates will increase). Housing Deadline
25 November Last Day to Register Before the Meeting
14-18 December 2009 Fall Meeting in San Francisco
Esteban Gazel. "Petrological and Geochemical Evolution of the Galapagos Plume". Earth and Planetary Sciences, Rutgers University, NJ, U.S.A
Andrew C Kerr. "Mantle plume or slab window?: Physical and geochemical constraints on the origin of the Caribbean oceanic plateau". School of Earth and Ocean Sciences, Cardiff University UK.
Robert Rogers. "Transtensional Tectonics of the M 7.5, May 2009 Honduras Earthquake and Aftershocks". Department of Physics and Geology, California State University, Stanislaus, U.S.A
24 Abstracts
PRESENTATION TYPE: Invited
CONTROL ID: 689042
TITLE: Middle Jurassic – Early Cretaceous rifting on the Chortis Block in Honduras: Implications for proto-Caribbean opening
AUTHORS (FIRST NAME, LAST NAME): Robert D Rogers1, Peter A Emmet2
INSTITUTIONS (ALL): 1. Physics and Geology, Califonia State University Stanislaus, Turlock, CA, USA.
2. Brazos Valley GeoServices, Cypress, TX, USA.
ABSTRACT BODY: Regional mapping integrated with facies analysis, age constraints and airborne geophysical data reveal WNW and NE trends of Middle Jurassic to Early Cretaceous basins which intersect in southeast Honduras that we interpret as the result of rifting associated with the breakup of the Americas and opening of the proto-Caribbean seaway. The WNW-trending rift is 250 km long by 90 km wide and defined by a basal 200 to 800 m thick sequence of Middle to Late Jurassic fluvial channel and overbank deposits overlain by transgressive clastic shelf strata. At least three sub-basins are apparent. Flanking the WNW trending rift basins are fault bounded exposures of the pre-Jurassic continental basement of the Chortis block which is the source of the conglomeratic channel facies that delineate the axes of the rifts. Cretaceous terrigenous strata mantle the exposed basement-cored rift flanks. Lower Cretaceous clastic strata and shallow marine limestone strata are dominant along this trend indicating that post-rift related subsidence continued through the Early Cretaceous. The rifts coincide with a regional high in the total magnetic intensity data. We interpret these trends to reflect NNE-WSW extension active from the Middle Jurassic through Early Cretaceous. These rifts were inverted during Late Cretaceous shortening oriented normal to the rift axes.
To the east and at a 120 degree angle to the WNW trending rift is the 300 km long NE trending Guayape fault system that forms the western shoulder of the Late Jurassic Agua Fria rift basin filled by > 2 km thickness of clastic marine shelf and slope strata. This NE trending basin coincides with the eastern extent of the surface exposure of continental basement rocks and a northeast-trending fabric of the Jurassic (?) metasedimentary basement rocks. We have previously interpreted the eastern basin to be the Jurassic rifted margin of the Chortis block with the Guayape originating as a normal fault system.
These two rifts basin intersect at near 120 degree angle in southeastern Honduras. We suggest that the intersection of these two trends represents part of a R-R-R triple junction during the breakup of the Americas. The WNW trending rift produced the WNW trending fabric of the central Chortis block and failed in the Early Cretaceous while the NE trending rift continued opening to form the south-facing passive margin of the northern proto-Caribbean basin.
PRESENTATION TYPE: Invited
CONTROL ID: 691629
TITLE: Eclogites and related metamorphism in the North America-Caribbean plate boundary: An example from the Motagua fault zone, Guatemala
AUTHORS (FIRST NAME, LAST NAME): Tatsuki Tsujimori1, Guillermo A Hernandez Pineda1
INSTITUTIONS (ALL): 1. Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori, Japan.
ABSTRACT BODY: Active volcanic arcs and strike-slip fault systems characterize the present-day Caribbean Plate margins. The northern boundary of the Caribbean plate in Guatemala is the Motagua fault zone (MFZ). Along the MFZ in central and eastern Guatemala, eclogite- and jadeitite-bearing serpentinite-matrix mélange are exposed stretching ∼200 km on either side of the Motagua-Polochic fault system. The MFZ eclogites and related high-pressure metamorphic rocks represent key evidence for testing existing competing Caribbean plate tectonic models (e.g., Harlow et al., 2008, GSA Abs. Prog. 40:452).
The presence of lawsonite-eclogite and jadeite-eclogite with lawsonite-blueschist-facies overprinting in the south of the MFZ (Tsujimori et al., 2006, GSA Spec. Paper 403:147-68) indicates that the geotherm in the paleo-subduction zone is very low. Protoliths for these high-pressure rocks consist of uppermost oceanic crust including MORB-origin greenstones and cherts with minor trench turbidites. Epidote-paragonite-eclogites of layered gabbroic origin occur in the north of the MFZ. Although some N-MFZ eclogites record amphibolite-facies hydration and new mineral growth, eclogitic garnets preserve lawsonite-pseudomorph and glaucophane, suggesting a cold subduction zone. The lack of ubiquitous lawsonite in northern eclogites may be attributed to due to water under-saturated conditions.
Considering recent geochronology that implies a coeval eclogite-facies metamorphism at ∼130 Ma (Bruekener et al., 2009, EPSL284:228–35) and petrologic similarities of host serpentinized spinel-lherzolite on either side of the MFZ, we can tentatively reconstruct the succession of a fragmented eclogite-facies metamorphosed oceanic crust. However, the correct interpretation of the paleo-subduction record and further understanding of a cold subduction-zone process at paleo-Caribbean plate margin requires a more comprehensive approach to focus on in-situ geochemical and isotopic analyses of prograde metamorphic minerals. In this contribution new insights into the metamorphic evolution of the MFZ eclogites are presented.
PRESENTATION TYPE: Invited
CONTROL ID: 706379
TITLE: Life Cycle of Mantle Plumes: A perspective from the Galapagos Plume
AUTHORS (FIRST NAME, LAST NAME): Esteban Gazel1, Claude T Herzberg2
INSTITUTIONS (ALL): 1. Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA.
2. Earth and Planetary Sciences, Rutgers University, Piscataway, NJ, USA.
ABSTRACT BODY: Hotspots are localized sources of heat and magmatism considered as modern-day evidence of mantle plumes. Some hotspots are related to massive magmatic production that generated Large Igneous Provinces (LIPS), an initial-peak phase of plume activity with a mantle source hotter and more magmatically productive than present-day hotspots. Geological mapping and geochronological studies have shown much lower eruption rates for OIB compared to lavas from Large Igneous Provinces LIPS such as oceanic plateaus and continental flood provinces. Our study is the first quantitative petrological comparison of mantle source temperatures and extent of melting for OIB and LIP sources. The wide range of primary magma compositions and inferred mantle potential temperatures for each LIP and OIB occurrence suggest that this rocks originated form a hotspot, a spatially localized source of heat and magmatism restricted in time. Extensive outcrops of basalt, picrite, and sometimes komatiite with circa 65-95 Ma ages occupy portions of the pacific shore of Central and South America included in the Caribbean Large Igneous Province (CLIP). There is general consensus of a Pacific-origin of CLIP and most studies suggest that it was produced by melting in the Galapagos mantle plume. The Galapagos connection is consistent with isotopic and geochemical similarities with lavas from the present-day Galapagos hotspot. A Galapagos link for rocks in South American oceanic complexes (eg. the island of Gorgona) is more controversial and requires future work. The MgO and FeO contents of lavas from the Galapagos related lavas and their primary magmas have decreased since the Cretaceous. From petrological modeling we infer that these changes reflect a cooling of the Galapagos mantle plume from a potential temperature of 1560–1620 C in the Cretaceous to 1500 C at the present time. These temperatures are higher than 1350 C for ambient mantle associated with oceanic ridges, and provide support for the mantle plume model of the CLIP. The exact form of the secular cooling curve depends on whether the Gorgona komatiites were produced by the Galapagos or another plume. Iceland also exhibits secular cooling, in agreement with previous studies. In general, mantle plumes for LIPS with Paleocene-Permian ages were hotter and melted more extensively than plumes of more modern oceanic islands. This is interpreted to reflect episodic flow from lower mantle domains that are lithologically and geochemically heterogeneous. The majority of lavas from the present-day Galapagos plume formed in a column where melting ended at pressures less than 2 GPa, and this pressure is highly variable. Melting ended at much lower pressures for lavas from the Cocos and Carnegie Ridges, consistent with the channeling of the Galapagos plume to locations of thinner lithosphere. Low pressures of final melting are also inferred for older CLIP lavas, which suggest that the plume head impacted a mid-ocean ridge system.
PRESENTATION TYPE: Invited
CONTROL ID: 689041
TITLE: Mantle plume or slab window?: Physical and geochemical constraints on the origin of the Caribbean oceanic plateau
AUTHORS (FIRST NAME, LAST NAME): Andrew Craig Kerr1, Alan Hastie1
INSTITUTIONS (ALL): 1. School of Earth and Ocean Sciences, Cardiff University, Cardiff, United Kingdom.
ABSTRACT BODY: The Caribbean oceanic plateau formed in the Pacific realm when it erupted onto the Farallon plate due to melting of (possibly) the Galapagos hotspot at ~93 Ma. The plateau was subsequently transported to the northeast and collided with the Great Arc of the Caribbean thus initiating subduction polarity reversal and the consequent tectonic emplacement of the Caribbean plate between the North and South American continents. The plateau represents a large outpouring of mafic volcanism, which has been interpreted as having formed by melting of a hot mantle plume. Conversely, some have suggested that a slab window could be involved in forming the plateau. However, the source regions of oceanic plateaus are distinct from N-MORB (the likely source composition for slab window mafic rocks). Furthermore, melt modelling using primitive (high-MgO) Caribbean oceanic plateau lavas from Curaçao, shows that the primary magmas of the plateau contained ~20 wt.% MgO and were derived from 30-32 % partial melting of a fertile peridotite source region which had a potential temperature (Tp) of 1564-1614 °C. Thus, the Caribbean oceanic plateau lavas are derived from decompression melting of a hot upwelling mantle plume with excess heat relative to ambient upper mantle. Extensional decompression partial melting of sub-slab asthenosphere in a slab window with an ambient mantle Tp cannot produce enough melt to form a plateau. The formation of the Caribbean oceanic plateau by melting of ambient upper mantle in, or close to, a slab window setting, is therefore, highly improbable.
Reference
Hastie, A.R., Kerr, A.C. 2010. Mantle plume or slab window?: Physical and geochemical constraints on the origin of the Caribbean oceanic plateau. Earth Science Reviews, in press.
Oral
CONTROL ID: 718904
TITLE: Evidence for subduction of upper plate serpentine at the western edge of the Caribbean plate
AUTHORS (FIRST NAME, LAST NAME): Michael D Tryon1, Charles Geoffrey Wheat2, David R Hilton1
INSTITUTIONS (ALL): 1. Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA.
2. Global Undersea Research Unit, University of Alaska Fairbanks, Fairbanks, AK, USA.
ABSTRACT BODY: The margins community has only relatively recently begun to examine the substantially different tectonics and associated hydrologic systems of erosive convergent margins as compared with accretionary margins. One type example is the Costa Rica system, the western edge of the Caribbean plate. Such erosive margins can subduct significant amounts of upper plate material, altering the chemistry of fluids expelled at the forearc. In some cases these fluids may be diagnostic of the nature of the upper plate. Pore fluids collected from a recent mud flow at Mound 11 on the mid-slope of the forearc south of Nicoya have extremely high B/Li molar ratios while fluids expelled nearer the wedge toe in the ODP Leg 170/205 area have very low B/Li ratios. Since the formation of serpentinite is the only common subduction zone process that significantly fractionates B and Li, the fluid composition suggests that serpentinite minerals are involved in the fluid genesis. We hypothesize that the mound fluid source is just above the seismogenic zone at ~120-150°C and is composed of up to 90% altered igneous and ultramafic rock [Vannucchi et al., 2003] rich in serpentine mixed with ~10% lower plate sediment. In this zone, dehydration and illitization of smectite drives fluid production and some B and Li is released. The phase change in serpentine from low to high temperature forms releases significantly more B into the fluid, driving up the B/Li molar ratio. These deep sourced B-rich fluids pass upwards through the fractured upper plate to the slope sediment layer where they fluidize mud before extruding onto the seafloor. The deep fluid source may be unique to the Mound 11 area due to the heterogeneity of the source region but, more likely, is only evident here due to a recent eruptive cycle. Fluid sampled at other mounds may have had a longer residence time in the slope sediments where B would be adsorbed and the fluid diluted. This deep-sourced fluid only represents a minor component of fluids reaching the wedge toe via the décollement. Dilution by the more intense dewatering occurring toe-ward would likely make this deeper signal nearly undetectable. The dominant fluid source at the toe is further updip along the décollement at temperatures <100°C. Consolidation and early diagenitic reactions including the loss of interlayer water in smectite drives fluid production and releases B and Li into the fluid. This B/Li molar ratio is, however, unusually low for smectite dehydration, suggesting that some low-temperature serpentinization of upper plate materials may occur in the upper portions of the subduction channel, consuming B and leaching Li from the source rock, thus reducing the B/Li molar ratio to that seen in the Leg 170 area.
Serpentinized ultramafic assemblages are known from the eastern Caribbean Large Igneous Province (CLIP) including picrites and komatiites. Kerr et al., [1998] suggest that such assemblages may be present throughout the CLIP. The results presented here support this suggestion.
CONTROL ID: 696128
TITLE: Geochemistry and geochronology of Tobago Island: a preliminary re-appraisal.
AUTHORS (FIRST NAME, LAST NAME): Iain Neill1, Andrew Craig Kerr1, Arthur W Snoke2, Alan Hastie1, James L Pindell1, 3, Kevin Chamberlain2, Ian L Millar4
INSTITUTIONS (ALL): 1. School of Earth and Ocean Sciences, Cardiff University, Cardiff, Wales, United Kingdom.
2. Department of Geology and Geophysics, University of Wyoming, Laramie, WY, USA.
3. Tectonic Analysis Ltd., Chestnut House, Burton Park, Duncton, West Sussex , United Kingdom.
4. NERC Isotope Geoscience Laboratories, Keyworth, Nottingham, United Kingdom.
ABSTRACT BODY: A unifying model to constrain the sources, polarity and geometry of the Great Arc of the Caribbean during the Jurassic-Cretaceous remains elusive. The arc was the leading edge of the Caribbean plate prior to, and during, its late Cretaceous tectonic emplacement between the Americas1,2. Tobago Island in the SE Caribbean has long been considered a partial cross-section through at least two generations of mid-Cretaceous Great Arc magmatism3. ICP-OES/MS and Nd-Hf-Pb radiogenic isotope whole rock determinations are combined with three new U-Pb zircon LA-ICP-MS and several existing mineral ages to present a geochemical and geochronological re-appraisal of the origin of the igneous suites on Tobago.
The North Coast Schist (>115 Ma3) is a suite of tholeiitic mafic-felsic tuffs and volcanic breccias with variable Nb-Ta, Ti and slight Th depletions indicative of an arc or back-arc origin. This suite was deformed and metamorphosed to greenschist facies prior to the formation of the Tobago pluton and volcanic suite. The pluton (104±1 Ma3) comprises peridotite cumulates, gabbro-diorites and hornblende pegmatites. It is cogenetic with the volcanic suite, which consists of mafic volcanic breccias, tuffs and lavas (~104 Ma3), and a suite of mafic dykes (~105-91 Ma3). The volcano-plutonic suite has a tholeiitic island arc composition and appears geochemically similar to the North Coast Schist. A 6 km-long tonalite body cross-cuts the pluton and has a trondhjemitic composition, with high Si, Al, La/Yb and Sr/Y, low MgO, Y and Nb. It may be derived from partial melting of an enriched, garnet-bearing basaltic or amphibolitic source region. Furthermore, several mafic-to-granitic dykes have non-arc highly enriched signatures consistent with a plume source and may be related to the ~90 Ma Caribbean Oceanic Plateau2.
The data indicate a more complex magmatic history for the igneous rocks of Tobago than suggested by previous studies3 and thus they require a more detailed tectonomagmatic interpretation. Radiogenic isotopes provide a unique opportunity to study in detail the changing nature of the mantle sources involved in both arc and plume magmatism on Tobago and to test potential links with arc outcrops of a similar age throughout the Caribbean. A vital test will be to place constraints upon whether or not subduction polarity reversal occurred between eruption of the North Coast Schist and the Tobago Volcanic Group, a key tenet of the work by Pindell et al.1.
1: Pindell, J.L. et al., 2009. In: James, K., Lorente, M. A. & Pindell, J. (eds), The geology and evolution of the region between North and South America, Geological Society, London, Special Publication, in press.
2: Kerr, A.C. et al., 2003. AAPG Memoir 79: 126-168.
3: Snoke, A.W. et al., 2001. GSA Special Paper 354: pp.54.
CONTROL ID: 713748
TITLE: Integrated Provenance Studies in Northwestern South America, Linking Tectonic and Sedimentary Processes
AUTHORS (FIRST NAME, LAST NAME): Camilo Montes1, AGUSTIN Cardona1, Victor Orlando Ramirez3, German Bayona2, Carolina Ayala2, 1, Victor Valencia4
INSTITUTIONS (ALL): 1. Smithsonian Tropical Research Institute, Panama, Panama.
2. Corporacion Geologica Ares, Bogota, Colombia.
3. Ecopetrol, Bogota, Colombia.
4. University of Arizona, Tucson, AZ, USA.
ABSTRACT BODY: Post-collisional late Eocene to Oligocene extensional basins (Plato-San Jorge basin in Colombia) and syn-collisional basins to the east contain the record of drainages and source areas as a former passive margin obliquely collided with the Caribbean deformation front. A 2 to 8 km thick, shallowing-upward and almost entirely fine-grained, upper Eocene and younger sedimentary sequence contains the record of post-collisional paleogeography behind the advancing deformation front. Sedimentation in the syn-collisional margin is fragmentary along the northern margins of Colombia and Venezuela in the Guajira province. An integrated provenance approach is being undertaken with detrital zircon geochronology, whole rock geochemistry, heavy mineral analysis and tectonic modeling. Source areas contain distinctive assemblages that should be diagnostic and include cratonic contributions with Grenville and older provinces, Andean contributions with Mesozoic-age signatures and Caribbean contributions with latest Cretaceous and Paleogene contributions. The complex Paleogene tectonic interactions along the northwestern South American margin include the simultaneous opening of basins (Plato-San Jorge basin in Colombia), micro-block rotation (Santa Marta massif), shortening and mountain building (Perija range) and oblique accretionary wedges along the margin (Sinu-San Jacinto deformed belts). Rivers draining the interior of South America to the north would have been deflected by this Paleogene configuration, and local drainages would have similarly developed in response to changing depocenters. Distinctive signatures should have developed in the sedimentary sequence as the sources dynamically changed from cratonic (Grenville and older cratonic) to Andean (Mesozoic continental crust and reworked) to Caribbean (volcanic arcs and collision zones).
CONTROL ID: 712235
TITLE: An evaluation of Neogene tectonic reconstructions for the eastern Caribbean using tomography
AUTHORS (FIRST NAME, LAST NAME): Steven van Benthem1, Rob M A Govers1, Wim Spakman1
INSTITUTIONS (ALL): 1. Earth Sciences, Utrecht University, Utrecht, Utrecht, Netherlands.
ABSTRACT BODY: Recent reconstructions of the Caribbean plate for the Neogene agree on the large-scale tectonic evolution. These reconstructions are based mostly on surface observations. Here, we investigate whether predictions of upper mantle structure that result from the reconstructions match our recent high-resolution tomographic model. In this study we interpret the upper mantle structure beneath the Caribbean plate east of 75°W. The spatial resolution of the tomographic model is variable; in most regions we resolve features larger than 200 km. The model shows extensive high velocity anomalies under the Lesser Antilles and along the northern Caribbean plate boundary.
Subduction under the Lesser Antilles is evidenced by a Wadati-Benioff zone, which extends until 300 km depth. A prominent gap in the seismicity of the slab exists around 14.5°N. The Wadati-Benioff zones north and south of this gap have different dips. The Lesser Antilles Wadati-Benioff zones coincide with high P-wavespeed anomalies, but in the tomography the anomaly extends to (at least) the 660km discontinuity. The shape of the anomaly indicates that it was draped on the 660km discontinuity, possibly due to roll-back. This agrees with the amount of subducted material as predicted by tectonic reconstructions. The southern anomaly is clearly separated from the northern anomaly by a low velocity anomaly, which coincides with the observed seismic gap.We interpret this as a gap in the Lesser Antilles slab.
Reconstructions show that north and South America moved westward with respect to the Caribbean plate, subducting under the Lesser Antilles island arc. Subduction ended at the southern end of the arc, which resulted in a vertical tear (or STEP) fault along the southeast boundary of the Caribbean plate. Recent seismic and geodetic studies agree with STEP faulting at the scale of the crust. In the tomographically imaged upper mantle, the southward termination of the Southern Antilles anomaly is well resolved, which supports the interpretation of STEP faulting.
In contrast with the southeastern Caribbean plate boundary, the northern plate boundary east of the Bahamas is a mature subduction zone, as is evidenced by observations of seismicity, gravity and bathymetry. The Wadati-Benioff zone of this Puerto Rico subduction zone, and that of the intra-plate Muertos slab to the south, extends to a depth of 200km. This northern plate boundary is not a STEP, and it was previously suggested that here North America lithosphere is brought into the mantle by westward convergence at the Lesser Antilles, perhaps in combination with oblique convergence at the Greater Antilles. The subducted lithosphere thus remains attached to the surface North America plate, creating a hanging “flap” of lithosphere under the Greater Antilles. The tomographically imaged anomaly agrees with the interpretation of a flap. This Puerto Rico anomaly extends to the base of the upper mantle, whereas an anomaly under the Muertos trough extends no deeper than 200 km. The tomographic anomalies of the Puerto Rico slab and Greater Antilles slab seem to be connected.
We speculate that the mechanical contrast between the northern and southern ends of the Lesser Antilles slab, i.e., flap versus STEP, was responsible for the tear down the middle of the slab.
CONTROL ID: 700329
TITLE: Finite-Frequency Tomographic Images of Subducting Slabs in the Southeast Caribbean.
AUTHORS (FIRST NAME, LAST NAME): Maximiliano J Bezada1, Alan Levander1, Brandon Schmandt2
INSTITUTIONS (ALL): 1. Earth Science, Rice University, Houston, TX, USA.
2. Geological Sciences, University of Oregon, Eugene, OR, USA.
ABSTRACT BODY: We present a tomographic P-wave velocity model for the eastern Caribbean – South America plate boundary in northern Venezuela. The data were collected by the BOLIVAR (Broadband Ocean and Land Investigation of Venezuela and the Antilles arc Region) passive seismic array that included the 39 stations from the Venezuelan National Seismological Network (VNSN) as well as a temporary deployment of 35 IRIS-PASSCAL, 8 Rice broadband stations and 11 OBSIP ocean bottom seismographs. The temporary stations were deployed for a period of ~17 months. The array covers the eastern part of Venezuela with typical station spacing of ~50-100 km. Coverage is more sparse in the west of the study area and relies on the stations of the VNSN and an ongoing deployment of 8 PASSCAL and Rice instruments. Stations were located from south of the Orinoco river at latitude 6°N, across the northern Guayana Shield, to the Caribbean Sea at latitudes up to 14°N.
We used data from 86 stations, and inverted traveltime residuals from 462 teleseismic events with good azimuthal and epicentral distance distribution. Traveltime delays were obtained by cross-correlation of waveforms in frequency bands centered on 1.0, 0.5 and 0.3 Hz. A total of 6619 delays were used in the inversion. Crustal corrections were computed using a 3-D crustal velocity model constructed from five, boundary normal, 2-D active source seismic refraction models and gravity data. The inversion algorithm we applied uses approximate finite-frequency sensitivity kernels and calculates static event and station terms.
The tomographic image shows the subducting Atlantic slab very clearly to a depth of > 500 km in the east of the study area. The location of the southern edge of the slab corresponds roughly to the plate boundary in the surface down to ~400 km depth and extends southwards at greater depths. West of the Atlantic slab, the Caribbean mantle is dominated by low velocity anomalies, while the Guayana Shield is characterized by small positive anomalies. A second, eastward dipping, subducting slab is imaged in the western Venezuela (longitudes 72°W to 69°W); we interpret this to be a subducted portion of the Caribbean plate. In both cases, the position of the imaged slabs correlates well with anomalously high transition zone thickness as determined by receiver function analysis [Huang et al., 2009]. We find no clear evidence for south or southeastwards dipping shallow subduction of the Caribbean under the Southern Caribbean Deformed Belt.
CONTROL ID: 721890
TITLE: Nature of crustal terranes and the Moho in northern Costa Rica
AUTHORS (FIRST NAME, LAST NAME): Lepolt Linkimer1, Susan L Beck1, Susan Y Schwartz2, George Zandt1, Vadim L Levin3
INSTITUTIONS (ALL): 1. Department of Geosciences, The University of Arizona, Tucson, AZ, USA.
2. Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA, USA.
3. Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ, USA.
ABSTRACT BODY: The Central American land bridge is built upon blocks and terranes with differing origins and there is no consensus on the location of their boundaries. By analyzing the Moho beneath both the subducting Cocos Plate and the overriding Caribbean Plate with receiver functions we investigate the nature of crustal terranes within the Caribbean Plate in northern Costa Rica. We analyze high-quality P- and PP- wave receiver functions calculated from recent broadband experiments and estimate the depth and vertically averaged Vp/Vs to Moho. Our results show regions with distinct Vp/Vs which we describe in terms of the previously proposed Mesquito, Nicoya, and Chorotega terranes. Both the Nicoya and Chorotega terranes display high Vp/Vs (1.80-1.93) consistent with an oceanic character. In contrast, the Mesquito Terrane, which is thought to be oceanic, mostly displays lower Vp/Vs (1.62-1.80) more compatible with continental crust and may indicate that the current subduction zone magmatism is modifying the crust resulting in a more continental character. We found that the upper plate Moho has a relatively strong velocity contrast and it is deepest (~42 km) in the volcanic arc region and shallowest (~28-33 km) in parts of the fore-arc and back-arc regions. In addition, our analysis of the subducting Cocos Plate Moho revels a drier oceanic mantle subducting beneath the southernmost part of the Nicoya Peninsula as compared to a serpentinized oceanic mantle subducting beneath the northern part.
Poster
CONTROL ID: 703375
TITLE: Seismic anisotropy and mantle flow beneath western Venezuela
AUTHORS (FIRST NAME, LAST NAME): Jeniffer Masy1, Fenglin Niu1, Alan Levander1
INSTITUTIONS (ALL): 1. Earth Science MS 126, Rice University, Houston, TX, USA.
ABSTRACT BODY: We measured shear wave splitting from SKS and SKKS data recorded by the national seismic network of Venezuela and a linear broadband PASSCAL/Rice seismic array across the Merida Andes. The linear array was installed as a second phase of the passive seismic component of the BOLIVAR project (Broadband Onshore-offshore Lithospheric Investigation of Venezuela and the Antilles arc Region) to better understand the complicated regional tectonics in western Venezuela. Polarization direction (φ) of the faster S wave and delay time (δt) between the fast and slow wavelets from 20 stations were obtained using a stacking method proposed by Wolfe and Silver (1998). For each station, SKS or SKKS waveform data from 2 to 36 earthquakes, mostly from the Tonga subduction zone, were selected for splitting analysis. We assumed that shear wave splitting observed at each station is caused by upper mantle seismic anisotropy beneath the station. The best splitting parameters (φ,δt) were estimated when the summed eigenvalue ratio ∑(SNRi[λ2i(φ,δt)/λ1i(φ,δt)]) of the covariance matrix of the corrected particle motion reaches its minimum. We used signal-to-noise ratio (SNR) calculated from a noise time window before SKS as the weight of the summation.
The fast polarization directions can be divided into 3 zones, all in agreement with local GPS data: The first zone is the stations north of the dextral strike-slip Oca fault, an extinct part of the San Sebastian-El Pilar plate boundary zone. These stations show the largest split times (1.6-2.0s), oriented in a roughly EW direction, and are similar to splitting observations made further to the east along the strike slip plate boundary. Zone two is the Maracaibo block, bounded on the southeast by the right lateral Bocono fault, where split orientations are at N45°E, suggesting that the observed seismic anisotropy is likely caused by lithospheric deformation parallel to the Bocono. Zone three is east of the Bocono fault inside the Barinas-Apure Basin, where the measured split times are smaller (0.6-1.0s) with an EW fast direction that is consistent with those observed at the Guarico Basin, Maturin Basin and the Guayana shield in the east (Growdon et al., 2009), and are interpreted as orientation with the motion of the continent. Russo and Silver (1994) proposed that the rollback of the Nazca plate induced a trench-parallel NS flow that passes around the northwest corner of the subducting plate and along the northern edge of South America, forming an eastward flow beneath the southern Caribbean plate. The observed seismic anisotropy in western Venezuela can be roughly explained by a combination of this corner flow, the westward drift of the South America continent due to the opening of Atlantic Ocean, modulated by the northward escape of the Maracaibo block.
CONTROL ID: 703401
TITLE: Geochemistry and Geochronology of the Virgin Islands Batholith
AUTHORS (FIRST NAME, LAST NAME): Kevin L Schrecengost1, Allen F Glazner1, Drew Steven Coleman1
INSTITUTIONS (ALL): 1. Geological Sciences, UNC Chapel Hill, Chapel Hill, NC, USA.
ABSTRACT BODY: The Virgin Islands batholith is an extensive (>250 km2) compositionally heterogeneous series of plutonic rocks ranging from gabbro to granodiorite on the northeastern corner of the Caribbean plate. The Virgin Islands batholith represents the youngest documented magmatism in the Greater Antilles before subduction shut off during the transition to sinistral transtension. Here we present new major and trace whole-rock compositions, Sr, Pb, and Nd isotopic data, and U/Pb zircon geochronology.
Zircon ID-TIMS geochronology suggests that emplacement of the batholith occurred over at least 13 Myr beginning at 43.5 Ma with the emplacement of at least 4 discrete plutons. Preliminary ages from other plutons within the batholith are 42.6, 37.6, and 30.7 Ma which young to the southwest. Geochemical data show significant variation in the petrogenetic processes involved in the evolution of the Virgin Islands batholith, marked by wide variation in HREE enrichment and four distinct REE patterns. Silicic rocks in northern Virgin Gorda and Beef Island express negative Eu anomalies whereas those in southern Virgin Gorda and Peter Island show depleted HREE with no Eu anomalies. A gabbroic cumulate on Virgin Gorda exhibits a positive Eu anomaly whereas other mafic units of the Virgin Islands batholith have flat REE patterns. 87Sr/86Sr initial and Pb isotopic values suggest the Virgin Islands batholith evolved from mantle-derived melts with limited incorporation of isotopically evolved components.
Geochronology and geochemistry of the Virgin Islands batholith imply a southwestward migration of magmatism during the transition from active subduction to sinistral transtension that is accompanied by a shift in petrogenetic processes resulting in less enriched plutonism over time.
CONTROL ID: 703585
TITLE: Genesis of Guatemala jadeitite and related fluid characteristics: an insight from zircon
AUTHORS (FIRST NAME, LAST NAME): Tzen-Fu Yui1, Kenshi Maki1, Tadashi Usuki1, Uwe Martens2, Chao-Ming Wu3, Tsai-Way Wu4, Juhn G Liou2
INSTITUTIONS (ALL): 1. Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan.
2. Department of Geological and Environmental Sciences, Stanford University, Stanford, CA, USA.
3. Department of Applied Arts, Fu-jen Catholic University, Hsinchung, Taiwan.
4. Department of Earth Sciences, University of Western Ontario, London, ON, Canada.
ABSTRACT BODY: Zircons from one jadeitite sample, collected from north of the Motagua fault, Guatemala, were separated for SHRIMP U-Pb dating and trace element analyses. The sub- to anhedral crystal form, lack of typical magmatic oscillatory zone, the presence of fluid and albite/quartz/jadeite inclusions, and the low Th/U ratios (<0.005) indicate that these zircons are of hydrothermal origin. The U-Pb concordia intercept age of these zircons, 95.1 ± 3.6 Ma, is much older than the reported 40Ar/39Ar phengite age (i.e., 77-65 Ma) of jadeitites and related rocks from the same area. The age of 95 Ma is considered as the time of jadeitite formation and the age of 77-65 Ma, time of cooling. The formation temperature of the jadeitite would therefore be higher than the phengite 40Ar/39Ar blocking temperature and probably in the range of 400-450oC. The presence of quartz inclusions in zircons also indicates that the maximum pressure condition for jadeitite formation might be 13-14 kbar. It is further concluded that metasomatic replacement and solution precipitation are two end-member mechanisms for jadeitite genesis.
Both the jadeitite sample and separated zircons have very low REE contents, ~ 1 ppm and 0.5-42 ppm, respectively. The jadeitite shows a flat and slightly concave REE pattern with Eu/Eu* = 1.24. Zircons give HREE enriched patterns and can be divided into two groups: one with negative Eu anomaly and one with positive Eu anomaly. The latter tends to have smaller positive Ce anomalies. The responsible fluid might have evolved with time becoming more reducing and more dominated by albite decomposition reactions. Alternatively, trace element compositions of zircons simply demonstrate complicated variations of fluid chemistry during jadeitite formation.
A reducing fluid with high pH values capable of mobilizing Al, Na, Zr and Hf is inferred to be the media during jadeite/zircon formation. The fluid was most probably derived from serpentinization processes where (partially serpentinized) peridotites contain olivine as the major primary mineral (left). Other requirements for jadeitite formation include (1) albite-bearing felsic protoliths occurring as tectonic inclusions within peridotites and survived from rodingitization during initial serpentinization, and (2) fluid channels as well as pulses of in/out-flux fluid. These preconditions in subduction zones may make the jadeitite genesis scarce.
CONTROL ID: 714868
TITLE: Shallower structure of the collision zone between the Muertos fold-and-thrust belt and the aseismic Beata Ridge in the NE Caribbean Plate
AUTHORS (FIRST NAME, LAST NAME): Maria Pilar Llanes Estrada1, Andres Carbo-Gorosabel1, Jose Luis Granja 1, Alfonso Munoz Martin1, Maria Druet Vélez2, Maria Goméz Ballesteros2, Uri S Ten Brink3, Joseph M Davila4, Antonio Pazos4, Manuel Catalan4, Jesús Quijano4, Octavio López5
INSTITUTIONS (ALL): 1. GEODINAMICA, UNIVERSIDAD COMPLUTENSE DE MADRID, Madrid, Spain.
2. INSTITUTO ESPAÑOL DE OCEANOGRAFIA, MADRID, Spain.
3. U.S. GEOLOGICAL SURVEY, WOODS HOLE, MA, USA.
4. REAL INSTITUTO Y OBSERVATORIO DE LA ARMADA, CADIZ, Spain.
5. DIRECCION GENERAL DE MINERIA, SANTO DOMINGO, Dominican Republic.
ABSTRACT BODY: The CaribeNorte cruise held in the spring of 2009 aboard the Spanish R/V Hesperides studied the NE of the Caribbean plate in the zone of interaction and collision between the Muertos fold-and-thrust belt and the aseismic Beata Ridge. Swath bathymetry data and three-channel seismic profiles combined with reprocessed multi-channel profiles were used to analyze the morphology of the western end of the Muertos fold-and-thrust belt. In the surveyed area this 650 km-long deformed belt progressively changes its orientation from E-W to NW and then becomes narrower and disappears in the collision zone with the NE-SW trending Beata Ridge. The collision takes places because the active Muertos thrust belt has a southward transport direction and the NE-SW trending Beata Ridge acts as a basement high in the foreland area. The deep and elongated Muertos Trough located at the toe of the thrust belt becomes narrower and progressively shallower and then sharply disappears at 70.9°W and 18.1°N. Both the thrust belt and the trough are replaced westward by a steep insular slope characterized by a dense network of submarine canyons draining to the south and east from the Bahoruco peninsula and the Ocoa and Azua Bays. The northern Beata Ridge is strongly asymmetrical, with a main steep fault-scarp in the western side and a gentler eastern slope formed by terraces and ridges. Two of the ridges trend to the N, consistent with the orientation of the Beata Ridge, while a third and arcuate one has a shape and orientation suggesting its implication in the collision with the Muertos fold-and-thrust belt. The reflection seismic images suggest that these ridges could be volcanic constructions that had a later tectonic control.
CONTROL ID: 718513
TITLE: Relocating San Miguel Volcanic Seismic Events for Receiver Functions and Tomographic Models
AUTHORS (FIRST NAME, LAST NAME): Ezer Patlan1, Aaron A Velasco1, Jasper Konter1
INSTITUTIONS (ALL): 1. Geological Sciences, University of Texas at El Paso, El Paso, TX, USA.
ABSTRACT BODY: The San Miguel volcano lies near the city of San Miguel, El Salvador (13.43N and -88.26W). San Miguel volcano, an active stratovolcano, presents a significant natural hazard for the city of San Miguel. Furthermore, the internal state and activity of volcanoes remains an important component to understanding volcanic hazard. The main technology for addressing volcanic hazards and processes is through the analysis of data collected from the deployment of seismic sensors that record ground motion. Six UTEP seismic stations were deployed around San Miguel volcano from 2007-2008 to define the magma chamber and assess the seismic and volcanic hazard. We utilize these data to develop images of the earth structure beneath the volcano, studying the volcanic processes by identifying different sources, and investigating the role of earthquakes and faults in controlling the volcanic processes. We will calculate receiver functions to determine the thickness of San Miguel volcano internal structure, within the Caribbean plate. Crustal thicknesses will be modeled using calculated receiver functions from both theoretical and hand-picked P-wave arrivals. We will use this information derived from receiver functions, along with P-wave delay times, to map the location of the magma chamber.
CONTROL ID: 723186
TITLE: Incorporation of island-arc rocks into a Caribbean subduction channel: Geochemical constraints from eclogite boulders and greenschist rocks, Guajira region, Colombia.
AUTHORS (FIRST NAME, LAST NAME): Marion Weber1, Agustin Cardona2, 3, Uwe Altenberger4, Antonio Garcia-Casco5, Victor Valencia6, Monica Tobón1, Sebastián Zapata1
INSTITUTIONS (ALL): 1. Universidad Nacional de Colombia, Medellin, Colombia.
2. Smithsonian Tropical Research Institute, Panama City, Panama.
3. Corporación Geológica Ares, Bogotá, Colombia.
4. Universität Potsdam, Potsdam, Germany.
5. Universidad de Granada, Granada, Spain.
6. University of Arizona, Tucson, AZ, USA.
ABSTRACT BODY: Characterization of the protoliths of a subduction-accretion complex can provide major insights into the dynamics of the subduction channel. Geochemistry of eclogites found as boulders in a Tertiary conglomerate from the Guajira Peninsula, Colombia, indicate that these rocks are mainly metamorphosed basalts. A negative Nb-anomaly and flat to enriched REE patterns suggest that the eclogite protoliths evolved in a subduction related tectonic setting, with island arc affinities.
The geochemical characteristics are similar to low-grade greenschists from the nearby Etpana Formation, which is interpreted as part of a Cretaceous intra-oceanic arc. This further supports evidence that the deposition and metamorphism of these units record the ongoing Late Cretaceous continental subduction of the South American margin beneath the advancing Caribbean arc. This gave way to an arc-continent collision between the Caribbean and the South American plates. Arc-rocks were incorporated into the subduction channel and the accretionary wedge, either though influx of tectonically eroded arc material (subduction erosion) or incorporation into the accretionary wedge during arc-continent collision.
CONTROL ID: 723272
TITLE: Provenance of the Pendales Fm in the Sinu-San Jacinto Basin of Colombia's Caribbean margin
AUTHORS (FIRST NAME, LAST NAME): Alejandra Abreu1, Dayana Schonwalder2, Jose Maria Jaramillo1, Uwe Martens3
INSTITUTIONS (ALL): 1. Universidad Nacional de Colombia, Bogota, Colombia.
2. GMAS Ltda, Bogota, Colombia.
3. GES, Stanford University, Stanford, CA, USA.
ABSTRACT BODY: Petrography of the Pendales Formation at Arroyo Henequén (Atlantico) revealed that conglomeratic lithoarenites and polymictic conglomerates contain detrital quartz, potassium feldspars, plagioclase, serpentinite, chert, epidote, tourmaline, actinolite and volcanic rock fragments. This composition indicates provenance from two sources, one mainly composed of ocean floor materials, and another composed of granites. Twenty U-Pb ages of detrital zircon form a single population ranging 80-65 Ma. This age is interpreted to reflect the time of magmatism of the granitic source. Taking into account paleogeographic reconstructions, the most likely source was the Leeward Antilles Arc. We propose that Pendales Formation was derived from a recycled orogen uplifted by the Pre-Andean orogeny during the Middle Eocene.
CONTROL ID: 714515
TITLE: Is there Subduction in the Muertos Trough (NE Caribbean)? : Insights from gravity
AUTHORS (FIRST NAME, LAST NAME): Jose Luis Granja Bruna1, Andres Carbo-Gorosabel1, Alfonso Munoz Martin1, Uri S Ten Brink2, Maria Pilar Llanes Estrada1, Diego Cordoba Barba3, Joseph M Davila4, Manuel Catalan4
INSTITUTIONS (ALL): 1. GEODINAMICA, UNIVERSIDAD COMPLUTENSE DE MADRID, Madrid, Spain.
2. U.S. GEOLOGICAL SURVEY, WOODS HOLE, MA, USA.
3. FISICA DE LA TIERRA Y ASTROFISICA 1, UNIVERSIDAD COMPLUTENSE DE MADRID, MADRID, Spain.
4. REAL INSTITUTO Y OBSERVATORIO DE LA ARMADA, CADIZ, Spain.
ABSTRACT BODY: The interpretation of the Muertos Trough as a subduction zone from seismicity has proven to be problematic and the compressive deformational features observed in the upper crust do not suggest necessarily a subduction process. We tested the hypothesized subduction of the Caribbean plate’s interior beneath the eastern Greater Antilles island arc using gravity modeling. Gravity models simulating a subduction process yield a regional mass deficit beneath the island arc independently of the geometry of the subducted slab used in the models. This mass deficit results from sinking the less dense Caribbean slab beneath the lithospheric mantle replacing denser mantle materials and suggests that there is not a subducted Caribbean plateau beneath the island arc. The geologically more realistic gravity model which would explain the 30km N-S shortening observed in the upper crust requires an underthrusted Caribbean slab extending at least 60 km northward from the deformation front with a progressive increase in the thrusting angle from 8° to 30°, reaching a maximum depth of 22 km beneath the insular slope. The results of gravity modeling allowed us to propose a new tectonic model for the Muertos Margin as a retroarc thrust. This model is in agreement with the deformational features of the upper crust, the inferences from sandbox kinematic modeling, the deep seismic sounding modeling and the earthquake focal solutions. In this tectonic model the thrusting takes place with a gentle dipping basal detachment which yields at least 30 km of N-S shortening in the upper crust. This shortening has to be accommodated in the lower crust by means of a single or a more or less complex plate interface. The thickening of the crust beneath the insular slope can be associated with basal accretion and/or subduction erosion resulting in the partial imbrication and thickening of the Caribbean oceanic plateau. The use of gravity modeling has provided targets for future wide-angle seismic surveys in the Muertos Margin. This methodology used has proven efficiently to approach the research of other subduction or compressive retroarc zones around the world where there is not much information about the deep structure.
CONTROL ID: 723260
TITLE: Caribbean affinities of mafic crust from northern Colombia: preliminary geochemical results from basaltic rocks of the Sinu-San Jacinto belt
AUTHORS (FIRST NAME, LAST NAME): CAMILO BUSTAMANTE1, Agustin Cardona1, 2, Victor Valencia3, Marion Weber4, Georgina Guzman5, Camilo Montes1, 2, Mauricio Ibañez3, Mario Lara4, Maria Isabel Toro6
INSTITUTIONS (ALL): 1. Smithsonian Tropical Research Institute, Panama, Panama.
2. Corporacion Geologica Ares, Bogota, Colombia.
3. Department of Geosciences, University of Arizona, Tucson, AZ, USA.
4. Escuela de Geociencias y Medio Ambiente, Universidad Nacional de Colombia, Medellin, Colombia.
5. INVEMAR, Santa Marta, Colombia.
6. Universidad de Cordoba, Monteria, Colombia.
ABSTRACT BODY: The petrotectonic characterization of accreted mafic remnants within the northern Andes and the Caribbean yield major insights on the growth and evolution of oceanic plates, as well as in the identification of the role of terrane accretion within the northern Andes orogeny. Within the northern termination of the Andes, in northern Colombia, several exposures of mafic and ultramafic rocks have been identified. However, extensive sedimentary cover and difficulties in field access have left the petogenetic analysis and tectonic implications of this rocks scarcely studied. Preliminary geochemical constrains from volcanic rocks obtained in outcrops and as clasts from a Paleocene-Eocene conglomerate indicate that the mafic rocks are mainly andesitic in composition, with well defined enrichment in Th and Ce and depletion in Nb and flat to weakly enriched LREE. These features suggest a relatively immature intra-oceanic volcanic arc setting for the formation of these rocks. Hornblende-dioritic dikes in peridotites also attest to the role of water in the magmatic evolution, and the affinity to a subduction related setting. The tectonic implications of this arc remnants and the relation between these rocks and other oceanic domains in the northern Andes suggest that the compositional and tectonic setting on the different accreted margins of the Caribbean plate are heterogeneous.
CONTROL ID: 703951
TITLE: Intra-arc Deformation in Mona Passage, Northeast Caribbean
AUTHORS (FIRST NAME, LAST NAME): Jason D Chaytor1, Uri S Ten Brink1
INSTITUTIONS (ALL): 1. U.S. Geological Survey, Woods Hole, MA, USA.
ABSTRACT BODY: Intra-arc deformation, which accompanies the subduction process, can present seismic and tsunami hazards to the surrounding islands. Diffuse tectonic deformation within the Northeast Caribbean Plate Boundary zone likely led to the development of the submerged Mona Passage between Puerto Rico and the Dominican Republic. GPS geodetic data and significant levels of seismicity indicate that extension within the region is ongoing. Newly-collected high-resolution multibeam bathymetry and multi-channel seismic reflection profiles and previously-collected samples are used to investigate the tectonic evolution of the Mona intra-arc region. The passage is floored almost completely by an Oligocene-Pliocene carbonate platform, which has undergone extensive submarine and subaerial erosion. Structurally, the passage is characterized by W- to NNW-trending normal faults that offset the entire thickness of the Oligocene-Pliocene carbonate platform. The orientation of these faults is compatible with the NE-oriented extension vector given by GPS measurements. Evaluation of kinematic deformation models for the region supports poly-phase and oblique rifting models, rather than previously proposed single-phase, active arching, and rotation models. The interaction of these generally NW-trending faults in Mona Passage with the N-S oriented faults of Mona Canyon (rift) may reflect differing responses of the brittle upper crust along an arc-forearc rheological boundary, to oblique subduction along the Puerto Rico trench. Several faults within the passage, if ruptured completely, are long enough to generate earthquakes with magnitudes exceeding Mw 6.5, and their seafloor displacement could generate local tsunamis.
CONTROL ID: 712463
TITLE: Micro plate tectonics in the Virgin Islands Basin, north eastern Caribbean
AUTHORS (FIRST NAME, LAST NAME): Sara Raussen1, Holger Lykke-Andersen2
INSTITUTIONS (ALL): 1. Reservoir, Petroleum Geo-Services, Weybridge, Surrey, United Kingdom.
2. Department of Earth Sciences, Aarhus University, Aarhus, Denmark.
ABSTRACT BODY: The formation of the Virgin Islands Basin in the north eastern part of the Caribbean is controlled by the plate boundary between the Puerto Rico-Virgin Islands Micro Plate and the stable part of the Caribbean Plate. The Puerto Rico-Virgin Islands Micro Plate is one of three micro plates located in a complex plate boundary zone in the north eastern part of the Caribbean where the Caribbean Plate borders the North American Plate. These micro plates move differently than the stable part of the Caribbean plate.
There exists a lot of contradicting theories about the course of formation of the Virgin Islands Basin, including counter clockwise rotation of the micro plate and dextral or sinistral strike-slip movements between the plates.
In connection with the Danish Galathea 3 expedition, the most extensive exploration of the basin to date was conducted in March 2007. Cores, CTD measurements, multi beam bathymetric data and 2D seismic data were acquired.
The results from the multi beam and seismic data are presented in this study. The main observations are of extensional features, which show both on the sea bed and in the sedimentary package. Furthermore, evidence of strike-slip movements is found.
Based on the observations, a tectonic model is presented. The model consists of a primary north-south to north west-south east directed extension combined with east-west trending sinistral strike-slip. It implies that the Puerto Rico-Virgin Islands Micro Plate is moving slower towards the east-north east than the stable part of the Caribbean Plate. The model is supported by the newest GPS-measurements.
CONTROL ID: 714042
TITLE: Uplift of late Quaternary marine terraces in the forearc of the Middle America Trench due to active thrusting inboard of the Panama Triple Junction, Burica Peninsula
AUTHORS (FIRST NAME, LAST NAME): Kristin D Morell1, T W Gardner2, Donald M Fisher1, Allison Teletzke2, Danny Davidson2
INSTITUTIONS (ALL): 1. Geosciences Department, PennState University, University Park, PA, USA.
2. Geosciences Department, Trinity University, San Antonio, TX, USA.
ABSTRACT BODY: The Burica Peninsula, a ~30 km long and ~3-10 km-wide outer forearc peninsula, lies only 15 km inboard of the CO-NZ-CA triple junction, along the border between Costa Rica and western Panama. At the triple junction, the Panama Fracture Zone, separating the CO and NZ plates, subducts under the Caribbean plate to form a trench-trench-transform triple point. To the northwest of the triple junction, the Cocos plate subducts more rapidly, nearly orthogonally and contains a significantly thicker and shallower slab than the Nazca plate to the southeast. The abnormal thickness (>20 km) and gentle dip of the Cocos plate adjacent to the triple junction is due to the Cocos Ridge, a hot-spot generated aseismic ridge that is abruptly truncated on its eastern edge by the Panama Fracture Zone. This plate tectonic configuration results in the presence of a large (~ 2 km) bathymetric step located ~20 kms offshore of the eastern coastline of the Burica Peninsula. With migration of the triple junction to the southeast at ~55 mm/yr, the Caribbean plate overrides the bathymetric step between the two plates, causing uplift and deformation of the Burica Peninsula.
Deformation on the peninsula is produced by at least 2-3 deeply-rooted NE-dipping reverse faults and a seaward-dipping backthrust. The frontal thrust exposes highly-sheared basalt sea cliffs in its hanging wall along the northwestern portion of the peninsula. Arcward splays of this fault strike parallel to the main fault, yet decrease in slip laterally to the south-southeast until they eventually merge with the frontal thrust offshore.
Late Quaternary marine deposits, including terraces and shelfal-facies growth strata are well-preserved throughout the eastern half of the peninsula. A flight of up to six terraces are recognized, the highest of which does not exceed ~70 m. Terraces grade from thin, sediment-starved strath deposits to ~10 m thick bay-filled shelfal sediments. Eleven C14 dates indicate these deposits range in age from MIS 3 (38, 460 +/- 400 BP) to latest Holocene (510 +/- 60 BP). Uplift rates calculated from terrace C14 ages and high-precision DGPS surveys range between 1.3 +/- 0.5 and 3.4 +/- 0.3 mm/yr. The consistent elevation of inner edges (PHTL, paleo-high tide line) indicates that uplift is spatially uniform on the hanging-wall ramp of the rear-most thrust. Our results indicate that active, rapid deformation of the Burica Peninsula is occurring due to basement-involved thrusting as the upper plate overrides the eastern flank of the Cocos Ridge.
CONTROL ID: 717715
TITLE: North America - Caribbean plate motion as constrained by provenance of Eocene beds in Central Guatemala
AUTHORS (FIRST NAME, LAST NAME): Uwe Martens1, Axel Gutierrez2
INSTITUTIONS (ALL): 1. Stanford University, Stanford, CA, USA.
2. Universidad San Carlos, Coban, Guatemala.
ABSTRACT BODY: The continental Subinal Formation of Central Guatemala is composed of red conglomerates and sandstones that outcrop along the Motagua Valley. The geographic distribution of the Subinal basin is elongate and constrained by the faults of the Motagua system. This suggests the basin developed as a trans-extensional feature associated with strike-slip tectonics at the Caribbean-North American plate boundary. Stratigraphic position of the Subinal implies a post-Cretaceous depositional age, possibly Eocene. This chronologic constraint is supported by detrital zircon geochronology by the LA-ICPMS U-Pb method. The presence of eclogite in conglomerate indicates that HP belts of the Guatemala Suture Complex were already exposed at that time. The study of pebbles in conglomerate indicates that the relative abundance of some clast groups correlates with the rock units exposed north, across the San Agustín fault. This implies provenance from the North American plate and minor motion along this fault. We hypothesize that the Subinal basin was formed as an onland response to the opening of the coveal Cayman Trough.
CONTROL ID: 717715
TITLE: CARIBENORTE Project: Studying the deep structure of the NE Caribbean Plate
AUTHORS (FIRST NAME, LAST NAME): Andres Carbo-Gorosabel1, Joseph M Davila2, Diego Cordoba Barba4, Jose Luis Granja1, Maria Pilar Llanes Estrada1, Alfonso Munoz Martin1, Maria Druet3, Maria Gomez3, Antonio Pazos2, Manuel Catalan2, Uri S Ten Brink5, Juan Payero7, Octavio Lopez6, Jesús Quijano2
INSTITUTIONS (ALL): 1. Geodinámica, Universidad Complutense de Madrid, Madrid, Spain.
2. Real Instituto y Observatorio de la Armada, San Fernando, Cádiz, Spain.
3. Instituto Español de Oceanografía, Madrid, Spain.
4. Departamento de Física de la Tierra y Astrofísica I, Universidad Complutense de Madrid, Madrid, Spain.
5. U.S. Geological Survey, Woods Hole, Woods Hole, MA, USA.
6. Dirección General de Minería, Santo Domingo, Dominican Republic.
7. Instituto Sismológico Universitario, Universidad Autónoma , Santo Domingo, Dominican Republic
ABSTRACT BODY: Despite the high number of studies carried out in the NE Caribbean there is still not a geodynamic model that is capable of integrating all of the local tectonic settings present in the area. The CaribeNorte Project aims to analyze the geodynamics of the area by studying the deep crustal structure of the North-eastern Caribbean Plate Boundary Zone across the Dominican Republic (DR) and by analyzing the morphostructure of the southern insular slope because most works have focused on the northern side of the arc. The main objectives of the project are: 1) to define the deep structure from north to south across the island arc and to test whether the Caribbean Plate’s interior is subducting beneath the DR, as has been hypothesized, 2) to analyse the deep and shallow structure of the northern Beata Ridge and to assess its origin and evolution, 3) to study the morphostructure of the zone of collision between the Muertos fold-and-thrust belt and the aseismic Beata Ridge, and 4) to evaluate the seismic and tsunami risk in the area. The new data was acquired during a research cruise held in the spring of 2009 aboard the Spanish R/V Hesperides. Swath bathymetry was obtained covering an area of 34.460 km2 in the south of the DR, overlapping by the east with data from our previous cruise Geoprico-Do. Along the track lines we have continuously collected gravity and magnetic data and high-resolution seismic profiles (TOPAS system). The active seismic experiment consisted on 3 deep seismic soundings profiles with a total of 16 OBS, deployed from the DR’s ship Orion, and 340 seismic land stations. For the deep seismic experiment the R/V Hesperides was shooting every 90 s with airguns having a total power of 3.850 ci. In addition, the Dominican Republic’s DGM collaborated with 3 drill-hole explosions on-shore. The five seismic profiles have a total of 980 km offshore and 650 km onshore, running across the Bahamas Carbonate platform, the DR island along two transects, the Muertos fold-and-thrust belt and the Beata ridge. Additional tree-channel seismic reflection profiles were collected shooting every 15 s a total of 860 ci, and were used together with reprocessed multichannel profiles to analyze the morphostructure of the southern slope of the DR. Preliminary results are presented here.
We look forward to seeing you in San Francisco in December!
last modified: 09.22.09 01:51 +0200
