Presentation on theme: "K. H. James 07 Geology of the Caribbean Plateau Keith James Institute of Geography & Earth Sciences, Aberystwyth, Wales, UK, This model:"— Presentation transcript:
K. H. James 07 Geology of the Caribbean Plateau Keith James Institute of Geography & Earth Sciences, Aberystwyth, Wales, UK, This model: the plate formed in place, between N and S America. - it is mostly extended continental crust. Paradigm: -the Caribbean Plate is oceanic and came from the Pacific. -the Plateau formed over a mantle plume. -the plateau consists of NE trending continental blocks, Palaeozoic and older, flanked by Triassic- Jurassic seaward-dipping wedges and overlain by Cretaceous basalts.
5° 20° 35° -85°-70°-55°NORTHAMERICA SOUTH AMERICA U L Atlantic Plate Pacific Plate Middle America LesserAntilles K. H. James 07CaymanTrough CaymanRidge Grenada Basin YucatánBasin Beata and Aves ridges MayaBlock ChortisBlock Bahamas Greater Antilles Antilles Chorotega Block Chocó Block Gulf of Mexico Colombia Basin Venezuela Basin Accreted volcanic arc
Problems with Caribbean geology Geology is spread over many different countries. Some areas are poorly mapped (access, vegetation, weathering). There are no spreading ridges or magnetic anomalies in the whole of middle America, save for the central 300 km of the Cayman Trough (Miocene - Recent). Most data are collected/interpreted under the assumption that the Caribbean Plate is oceanic and came from the Pacific. K. H. James 07
Caribbean Plate crust in the western Venezuela Basin-Beata Ridge area is up to 20 km thick. This is the original Caribbean Plateau. Five ODP/DSDP sites have penetrated Cretaceous basalts, dated Ma, at the very top of the thick, uncalibrated section. Overlying sediments are shallow marine carbonates. Peripheral to thick Caribbean crust, supposed original oceanic crust is thin, 3 km, not drilled, not dated. Other parts of the Caribbean Plate interior (in the Colombia, Grenada and Yucatán basins) also are thick. Together with the original plateau and accreted rocks around the Caribbean and in Colombia, they are seen to comprise an oceanic plateau or large igneous province. Some of the accreted sections include palaeosols. The Caribbean Plateau Several oceanic plateaux (Ontong-Java, Iceland, Kerguelen, Vøring, Rockall) are known to have continental roots. Is this true of the Caribbean Plateau?
5° 20° -85°-70° Arc volcano Extinct Brm Tur Mas MEoc MMio LA CAP K. H. James 07 Popular model: The Caribbean Plate is oceanic and migrated from the Pacific (successive arc locations). Popular model: The Caribbean Plateau formed above a mantle plume (Galapagos Hotspot).
ATLANTIC OCEAN PACIFIC OCEAN -70°-85° 15° 30° -100° Gulf of Mexico Yucatán Basin Maya Chortis Hispaniola Puerto Rico Lesser Antilles Bahamas BR AR PACIFIC OCEAN K. H. James 07 Caribbean Banda Scotia AUSTRALIA 120°135°105° 0° 15° Java Borneo Sulawesi Timor Papua- New Guinea Philippines Plate boundary Continent margin Shoreline PACIFIC OCEAN INDIAN OCEAN Volcanic arc SOUTHEAST ASIA Sumatra The plates are strikingly similar. Scotia and Banda formed in-place by back-arc spreading. Scotia and Banda carry marginal and interior continental fragments. Is there continental material in the Caribbean?
5° 20° 35° -85°-70°-55° Indications of continent in the Caribbean K. H. James 07 Southern Central America - crustal thickness km, - high silica ignimbrites, granulite xenoliths - Albian and Miocene quartz sandstones. -gravity: continental density, Cayman Trough walls Jamaica Cuban Cretaceous arc rocks - crustal thickness 20 km, - flysch from N.NE contains gneiss, schist, quartzite, slate, marble - continental grantitoids, red beds, greywackes, arkose. - carry Precambrian, Palaeozoic zircons,
5° 20° 35° -85°-70°-55° Indications of continent in the Caribbean K. H. James 07 NE Caribbean: Aves Ridge -crustal thickness 30 km -continental rocks on Hispaniola, Puerto Rico Trough, Cretaceous stratigraphic continuity with Bahamas -Silica content up to 76% -gravity: continental density - underlain by granitic rocks Siuna Cretaceous oceanic terrane -conglomerates with abundant quartz, fragments of schist and quartzite
NORTH AMERICA shelf edge plate boundary 5° 20° 35° -55°-100° SOUTH AMERICA ATLANTIC PACIFIC thick crust. "accreted plateau" DSDP locations ridge K. H. James 07 The Caribbean plateau has NE structural grain (not the radial pattern expected of a plume) The original plateau
. 5° 35° -100° K. H. James 07 Next slide It conforms with the regional tectonic pattern N35°E Palaeozoic structural trend This extends along the Atlantic seaboard of N. America into the N. Atlantic
K. H. James 07 Wedge Ridge Seamount Seismic line 1293 (after Diebold & Driscoll, 1999)
Seaward-dipping wedges are common features of continental margins (e.g. N. Atlantic, after Parson et al.) Jan Mayan Iceland Greenland Rockall Plateau Vøring Plateau Seismic line Faroe Wales, etc. Rockall: 5 km sedimentary section, including 1.5 km basalt, on ~13 km highly stretched continental crust. Rockall and Vøring: subaerial-shallow marine basalts. Vøring: andesite-dacite at (ODP Site 642) shows continental input. Jan Mayan and Iceland: continental roots.
NW SE NW smooth B" convex-up reflections A BC C Seaward-dipping wedges, Caribbean and Vøring plateaux Caribbean plateau Caribbean plateau Vøring margin Convex up reflections Basalt
300 Km Eastern N America (after Manspeizer, 1988). Next slide Onshore: Triassic clastic basins Offshore: Triassic - Jurassic basins with salt
Shore line COST Pre-Mesozoic basement Rift basin Wedge Mid. JJ - Early KK Neogene NWSESWNE Post rift unconformity U Cret - Pal Km 100 Km V/E x10 Seaward-dipping wedges: offshore N America; note presence of salt (after Benson & Doyle, 1988). Salt
K. H. James 07 Interpretation of plateau (after Diebold & Driscoll, 1999) Seamount ve = 25 A - Early volcanic thickening volcanic mounds with dipping flanks Mantle B - Extension - final volcanics depleted source additional depletion
10 km SE NW SW NE 1 km SW 5 km Diapirs: - Gulf of Mexico and Caribbean Caribbean: Line 1293, after Diebold & Driscoll, 1999 Gulf of Mexico: Sigsbee Knolls, after Burk et al., 1969 Challenger Knoll: drilled - salt diapir Not a seamount but a diapir (salt, shale, serpentinite?)
SB" A" RB" Sea floor ? CVFZ 11 K. H. James 07 Seismic line 1293: interpretation - this study (James 2007) Ski jump? = marginal reef/mound NE-trending continental blocks, seaward- dipping wedges, salt, covered by subaerial Cretaceous basalts - SB smooth Horizon B. RB - rough Horizon B - serpentinized mantle (oceanic crust).
K. H. James 07 Atlantic spreading JJ KK N60°W drift, Late Jurassic - Early Cretaceous, of N America from Gondwana involved Middle America extension
* North America South America K. H. James 07 Middle America: mostly extended continental crust. Greatest extension produced serpentinized mantle. CZ Extended continent: thick Cretaceous carbonates Extreme extension: serpentinized mantle (Jurassic and Cretaceous) Highly extended continent: NE-trending continental blocks, seaward-dipping wedges (Tr-JJ), Cretaceous basalts JJ KK The only true oceanic crust (spreading ridge, magnetic anomalies)
Continental crust Extended continental crust Oceanized crust Shelf edge Oceanic crust Accreted ocean/arc K. H. James 07 Caribbean crustal types
Restoration: removal of extension K. H. James km offset Jurassic rift Seaward- dipping wedge
K. H. James 07 Pangean reconstruction Palaeozoic suture Florida Bahamas Cuba S. America Maya Chortis Appalachians
K. H. James 07 Triassic-Jurassic rift/drift Regional tectonic fabric is inherited from Palaeozoic and older structures (e. g. Appalachian suture). Rifts Seaward-dipping wedges with salt - Baltimore Canyon, Carolina Trough, Blake Plateau, Gulf of Mexico, Caribbean, (?Yucatán and Colombian Basins).
K. H. James 07 The Caribbean Plate formed in place during American drift. It consists mainly of extended continental crust. The Caribbean plateau is built of NE trending Palaeozoic/older blocks, flanked by basins with Triassic - Jurassic seaward dipping wedges, Jurassic - Cretaceous shales/salt, covered by Cretaceous igneous flows. S UMMARY
Last thought : if Scotia, Banda and the Caribbean are so alike, why is there an LIP in the Caribbean alone? K. H. James 07 Caribbean Plate. Caribbean Plateau - was an impact involved?
References: Diebold, J., N. Driscoll, and the EW-9501 Science Team, 1999, New Insights on the Formation of the Caribbean Basalt Province Revealed by Multichannel Seismic Images of Volcanic Structures in the Venezuela Basin: IN: Mann, P. (ed.), Caribbean Sedimentary Basins, Sedimentary Basins of the World, Elsevier, p Parson, L.M. & the ODP Leg 104 Scientific Party: Dipping reflector styles in the NE Atlantic Ocean: In: Morton, A. C., and L.M.Parson, Early Tertiary Volcanism and the Opening of the NE Atlantic: GSL Special Publication No. 39, p Manspeizer, W., 1988, Triassic-Jurassic rifting and opening of the Atlantic: An Overview: In: Manzpeizer, W. (Ed.), Triassic-Jurassic Rifting, Part A, Elsevier, p Benson, R. N. and R. G. Doyle, 1988, Early Mesozoic rift basins and the development of the United States middle Atlantic continental margin: In: Manzpeizer, W. (Ed.), Triassic-Jurassic Rifting, Part A, Elsevier, p Burk, C. A., M. Ewing, J. L. Worzel, A. O. Beall, W. A. Berggren, D. Bukry, A. G. Fisher and E. A. Pessagno, 1969, Deep- Sea Drilling into the Challenger Knoll, Central Gulf of Mexico: AAPG Bull., v. 53, p Diebold et al. (1999) discuss seaward-dipping wedges, the Vøring Plateau, unusually thin oceanic crust and serpentinization. However, their interpretation (shown in this presentation) of the Caribbean Plateau is that it formed by two phases of volcanic extrusion on extended oceanic crust. They remark that their volcanic mounds have magnetic signature, so the diapirs discussed in this presentation could be igneous/serpentinitic. However, the magnetic data could record old intrusions and structural relief along basement faults. Salt diapirism is often focussed along fault zones. Diebold et al. (1999) note that their volcanic mounds trend NE or E-W. Sigsbee Knoll and NE Mexican salt diapirs in the Gulf of Mexico trend NE, following the regional fabric highlighted by this presentation.