Transcript A Simple Model for the Caribbean

Geology of the Caribbean Plateau
Keith James
Institute of Geography & Earth Sciences,
Aberystwyth, Wales, UK,
[email protected]
This model: the plate formed in place,
Paradigm:
between N and S America.
-the Caribbean Plate is oceanic and
came from the Pacific.
--the
it is Plateau
mostly extended
continental
formed over
a mantlecrust.
plume.
-the plateau consists of NE trending continental
blocks, Palaeozoic and older, flanked by TriassicJurassic seaward-dipping wedges and overlain by
Cretaceous basalts.
K. H. James 07
“Middle America”
Atlantic Plate
35°
NORTH
AMERICA
Yucatán
Basin
20°
Cayman
Trough
Cayman
Ridge
“Accreted
volcanic arc”
Bahamas
Gulf of
Mexico
Greater
Antilles
Grenada
Basin
Maya
Block
Chortis
Block
U
Chorotega
Block
Colombia
Basin
L
Venezuela
Basin
Lesser
Antilles
Beata and Aves ridges
5°
Pacific Plate
Chocó
Block
- 85°
- 55°
SOUTH AMERICA
- 70°
K. H. James 07
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
The Caribbean Plateau
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 88 - 90
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.
Several oceanic plateaux (Ontong-Java, Iceland, Kerguelen, Vøring,
Rockall) are known to have continental roots.
Is this true of the Caribbean Plateau?
Popular model: The Caribbean Plate is oceanic and migrated
from the Pacific (successive arc locations).
Arc volcano
Extinct
MEoc
20 °
Mas
LA
Tur
Brm
MMio
5°
CAP
-8 5 °
-7 0 °
Popular model: The Caribbean Plateau formed above a
mantle plume (Galapagos Hotspot).
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Caribbean
Banda
NORTH AMERICA
ATLANTIC OCEAN
Plate boundary
Continent margin
Shoreline
Volcanic arc
SOUTHEAST ASIA
30°
Gulf of Mexico
Bahamas
Philippines
Hispaniola
Puerto Rico
Yucatán
Maya Basin
BR
15°
15°
AR
Chortis
PACIFIC OCEAN
Lesser
Antilles
0°
Sumatra
Borneo
Sulawesi
PapuaNew Guinea
PACIFIC OCEAN
-100°
SOUTH AMERICA
-85°
-70°
Scotia
PACIFIC
OCEAN
SOUTH
AMERICA
ATLANTIC
OCEAN
N Scotia Ridge
Java
INDIAN OCEAN
105°
Timor
120°
AUSTRALIA
135°
The plates are strikingly similar.
Scotia and Banda formed in-place by
back-arc spreading.
-55°
S Sandwich
Islands
Shackleton
Fracture Zone
-75°
Antarctic
Peninsula
S. Scotia Ridge
-45°
-30°
Scotia and Banda carry marginal and
interior continental fragments.
Is there continental material in the
Caribbean?
K. H. James 07
Indications of continent in the Caribbean
35°
Cayman Trough walls
-continental grantitoids, red beds,
greywackes, arkose.
Cuban Cretaceous arc rocks
-carry Precambrian, Palaeozoic
zircons,
20°
Jamaica
-crustal thickness 20 km,
-flysch from N.NE contains
gneiss, schist, quartzite, slate,
marble
5°
- 85°
Southern Central America
-crustal thickness 40 - 45 km,
-gravity: continental density,
-high silica ignimbrites,
granulite xenoliths
-Albian and Miocene
quartz sandstones.
- 70°
- 55°
K. H. James 07
Indications of continent in the Caribbean
35°
NE Caribbean:
20°
-crustal thickness 30 km
-gravity: continental density
-continental rocks on Hispaniola,
Puerto Rico Trough, Cretaceous
stratigraphic continuity with Bahamas
-Silica content up to 76%
Siuna Cretaceous “oceanic
terrane”
-conglomerates with abundant
quartz, fragments of schist
5°
and quartzite
Aves Ridge
-underlain by granitic rocks
- 85°
- 70°
- 55°
K. H. James 07
The Caribbean “plateau”
35°
shelf edge
plate boundary
thick crust
NORTH AMERICA
"accreted plateau"
DSDP locations
ridge
ATLANTIC
20°
5°
PACIFIC
-100°
.
SOUTH AMERICA
The original
“plateau”
has NE structural
grain (not the radial
pattern expected of a
plume)
-55°
K. H. James 07
It conforms with the regional tectonic pattern
.
N35°E Palaeozoic structural
trend
35°
Next slide
5°
-100°
This extends along the Atlantic seaboard of N. America into the N.
Atlantic
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Seismic line 1293
“Seamount”
(after Diebold & Driscoll, 1999)
Ridge
Wedge
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Seaward-dipping wedges
are common
features of continental margins (e.g. N. Atlantic, after Parson et al.)
Jan
Jan Mayan and Iceland:
Mayan
Greenland
continental roots.
Seismic line
Iceland
Rockall and Vøring:
subaerial-shallow marine
basalts.
Vøring
Plateau
Faroe
Vøring: andesite-dacite at
(ODP Site 642) shows
continental input.
Rockall: 5 km sedimentary section,
including 1.5 km basalt, on ~13 km
highly stretched continental crust.
Rockall
Plateau
Wales,
etc.
Seaward-dipping wedges,
A
Caribbean
and Vøring plateaux
convex-up reflections
NW
SE
smooth B"
Caribbean
“plateau”
B
C
C
NW
Vøring
margin
Convex up reflections
Basalt
SE
Eastern N America (after Manspeizer, 1988).
Next slide
300
Km
Onshore:
Triassic clastic basins
Offshore:
Triassic - Jurassic basins
with salt
Seaward-dipping wedges: offshore N America; note
presence of salt (after Benson & Doyle, 1988).
NW
SE
SW
NE
Shore line
COST
Neogene
U Cret - Pal
Km
Mid. JJ Early KK
5
Pre-Mesozoic
basement
10
Post rift
unconformity
15
100 Km
20
V/E x10
Rift
basin
Salt
Wedge
Interpretation of plateau
(after Diebold & Driscoll,
1999)
volcanic mounds with dipping flanks
A - Early volcanic thickening
depleted source
Mantle
ve = 25
“Seamount”
B - Extension - final volcanics
additional depletion
K. H. James 07
Diapirs: - Gulf of Mexico and Caribbean
NW
SE
Caribbean:
Line 1293, after Diebold &
Driscoll, 1999
10 km
Not a seamount but a
diapir (salt, shale,
serpentinite?)
SW
NE
Gulf of Mexico:
Sigsbee Knolls, after Burk
et al., 1969
SW
1 km
5 km
Challenger Knoll:
drilled - salt diapir
Seismic line 1293:
1000 CDP
interpretation - this study (James 2007)
10000
5000
25000
20000
15000
6 s/twt
8
9
10
11
“Ski jump”? = marginal
SE
reef/mound
NW
Diapir - ?salt
Sea floor
SB"
?
TriassicPz basement
?
NE-trending continental blocks, seawarddipping wedges, salt, covered by subaerial
Cretaceous basalts - SB smooth Horizon B”.
RB - rough Horizon B” - serpentinized mantle
(“oceanic” crust).
Mio - Rec
A"
U - E0 - Mio
M - U Cret
oceanized crustRB"
U-Jur L - Cret
CVFZ
U Tr
?
L Jur
Moho
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Atlantic spreading
JJ
KK
N60°W drift, Late Jurassic - Early
Cretaceous, of N America from
Gondwana involved Middle America
extension
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Middle America:
mostly extended continental
crust. Greatest extension produced serpentinized mantle.
The only true
oceanic crust (spreading
ridge, magnetic anomalies)
North
America
Extended continent: thick
Cretaceous carbonates
JJ
*
Highly extended
continent: NE-trending
KK
continental blocks,
CZ seaward-dipping wedges
(Tr-JJ), Cretaceous
basalts
South
America
Extreme extension:
serpentinized mantle
(Jurassic and Cretaceous)
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Caribbean crustal types
Continental crust
Extended
continental crust
Oceanized crust
Accreted ocean/arc
Oceanic crust
Shelf edge
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Restoration:
Jurassic
rift
300 km
offset
removal of extension
Seawarddipping wedge
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Pangean reconstruction
Appalachians
Palaeozoic
suture
Florida
Maya
Cuba
Bahamas
Chortis
S. America
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Triassic-Jurassic rift/drift
Rifts
Seaward-dipping
wedges with salt Baltimore Canyon,
Carolina Trough, Blake
Plateau, Gulf of Mexico,
Caribbean, (?Yucatán
and Colombian Basins).
Regional tectonic fabric is inherited from Palaeozoic and older
structures (e. g. Appalachian suture).
K. H. James 07
SUMMARY
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.
K. H. James 07
Last thought:
if Scotia, Banda and the Caribbean are so alike, why is there an LIP in the
Caribbean alone?
Caribbean Plate.
Caribbean Plateau was an impact involved?
K. H. James 07
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. 561-589.
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. 57-68.
Manspeizer, W., 1988, Triassic-Jurassic rifting and opening of the Atlantic: An Overview: In: Manzpeizer, W. (Ed.),
Triassic-Jurassic Rifting, Part A, Elsevier, p. 41-79.
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. 99-127.
Burk, C. A., M. Ewing, J. L. Worzel, A. O. Beall, W. A. Berggren, D. Bukry, A. G. Fisher and E. A. Pessagno, 1969, DeepSea Drilling into the Challenger Knoll, Central Gulf of Mexico: AAPG Bull., v. 53, p. 1338-1347.
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.