Caribbean
tectonics website
My field area: Bonaire
IGCP Project on Tectonic
Evolution of the Caribbean
Caribbean discussion
group
Caribbean Group at
Texas
 |
The aim of the Workshop was for the main
research groups in this field to discuss recent research on the Caribbean
region, specifically on the Cretaceous Caribbean plateau, the island arc
terranes associated with it, and the tectonic evolution of the Caribbean
region. The workshop lasted 2 days: the first day was focussed on the
Mesozoic tectonic and structural evolution of the region whereas the
emphasis on the second day was on the magmatic evolution and geochemistry
of the Caribbean plateau, and the island arc terranes.
The
Workshop hosted 35 participants from six countries (Colombia, United
States, Italy, France, Germany and the UK). In addition, 30+ researchers
from 5 other countries registered interest in the proceedings, but were
not able to attend. Some of the main research groups were
1. Leicester,
UK; represented by Kerr (now Cardiff), Saunders, Tarney, Thompson and
White
2. Grenoble, France; represented by Arndt, Jaillard and Lapierre
and Mamberti
3. Palmero, Italy; represented by Coltorti and Giunta
4. Regional tectonic analysis group, represented by Draper, Maresch,
Pindell and Stanek
In total, 17 oral presentations were scheduled, though the emphasis was
on informal discussion. To facilitate this, a long discussion session was
scheduled at the end of each day, and the discussion chairs saught points
to discuss from other participants prior to this.
The chair of
the first day's discussion was Roz White (Leicester), who led a discussion
on how the geophysical and tectonic models discussed that day could fit in
with the existence of the Caribbean plateau. It was agreed that Pindell's
new comprehensive and detailed model for the tectonic evolution of the
Caribbean did not rely on the presence of the Caribbean plateau: indeed
the word plateau was never specifically mentioned in his talk. Plateau
workers counteracted this by saying that a thick buoyant oceanic plateau
would be very difficult to subduct, and would therefore significantly
affect the tectonics of the Caribbean region, in particular the subduction
polarity reversal. They cite the arrival of the buoyant and thick
Caribbean plateau at the eastward dipping subduction zone as a mechanism
for the flip, in a situation analagous to that seen in the Solomon Isles
with the attempted subduction of the Ontong Java oceanic plateau. However,
Pindell believes the subduction polarity reversal occurred at ca. 120 Ma
(before the bulk of the plateau was formed), on the basis of the following
pieces of evidence:
1. Abundant evidence for a large tectonic
event around that time
2. Unconformities in many arc-related sequences
at ca. 120Ma.
3. P-T paths from high-pressure metamorphic rocks
4.
Change in geochemical character from PIA to CA in many circum-Caribbean
arcs.
5. The earlier the flip occurred, the easier would occur
tectonically. At 120 Ma, the arc would have been short and straight and
there was a powerful potential mechanism available (the acceleration of
the opening of the Atlantic. At 75 Ma., the arc was ~2000km in length, and
may have been very highly arcuate in shape, which would require huge
internal deformation as the convex side changes from the SW to the SE.
However, in the discussion it was conceded that there is growing
evidence for an earlier (and possibly more voluminous (Diebold et al.,
1999)) pulse of plateau magmatism around 130-120 Ma. If that is the case,
an earlier plateau could have formed and caused the postulated subduction
flip, and the later plateau building events (78, 90) could have
represented the last pulses of magmatism.
Pindell's suggestion
(pers. com.) was for plateau workers to suggest possible mechanisms for
plateau emplacement within the 2500 km wide proto-Caribbean plate
following the flip, with perhaps only the first ~300 km of the leading
edge of the plate overlying the Benioff zone, hence allowing the Aruba
batholith etc to be formed at 85-82 Ma. from subduction of normal oceanic
crust beneath the plateau.
The second day's discussion focussed on
the following areas:
1. The possible older 120Ma. pulse of plume
magmatism
There appears to be growing evidence for it around the
Carribbean (eg Lapierre, 2001; Diebold et al., 1999)
2. Whether
the plateau was derived from the Galapagos plume
New palinispastic
reconstructions say it's impossible (Pindell, 2001). Trace element and
isotopic geochemistry, however, do not rule it out (Hauff
2000)
3. The cause of the spread to high 87Sr/86Sr for the
plateau lavas
Revillion (1999) analysed clinopyroxene separates
from the Gorgona komatiites for Sr and concluded that it was primary as it
correlates with the trace element abundances. This is supported by Kerret
al. (1996) who found that the high Sr composition of samples from the
Curacao plateau sequence stayed constant with increased leaching and
therefore attributed it to the incorporation of altered basalt into the
source of the basalts. However, Thompson et al found that for the Upper
Cretaceous arc lavas, which had initial 87Sr/86Sr of 0.7065, fresh apatite
separates had much lower 87Sr/86Sr than the whole rock, and concluded that
this spread to high 87Sr/86Sr was the result of alteration of the whole
rock.
4. How Gorgona relates to the rest of the plateau
The Gorgona komatiites have a depleted eHf-eNd isotopic composition
(Thompson et al. 2001), which is distinct from the rest of the Caribbean
plateau. This suggests that they are sampling an additional depleted
component. But we don't know the exact nature of their relationship to the
rest of the plateau.
5. Does the plume source contain a
non-DMM depleted component?
There is growing evidence that the plume
responsible for the Caribbean plateau contains a depleted component (eg
Kerr et al, 1995). Thompson et al. (2001) have identified two depleted
components using Hf-Nd systematics: a depleted component with an isotopic
composition similar to MORB, and a depleted component with a high eHf of
around +17. This component seems to be unique to Gorgona.
References
Diebold, J.; Driscoll, N. and 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 Venezuelan basin. In: Caribbean Basins, edited by Mann,
P., Elsevier, Amsterdam.
Hauff, F., K. Hoernle, et al.
2000. Age and geochemistry of basaltic complexes in western Costa
Rica: contributions to the geotectonic evolution of Central America. G
cubed 1(May 30).
Kerr, A. C., Saunders, A.D., Tarney, J.,
Berry, N.H. & Hards, V.L. 1995. Depleted
mantle-plume geochemical signatures: no paradox for plume theories.
Geology 23(9): 843-846.
Kerr, A.C.; Marriner, G.F.; Arndt,
N.T.; Tarney, J.; Nivia, A.; Saunders, A.D. and Duncan, R.A.
1996. The
petrogenesis of Gorgona komatiites, picrites and basalts: new field,
petrographic and geochemical constraints. Lithos 37, 245-260.
Kerr, A. C., Tarney, J., Marriner, G.F., Klaver, G.Th,
Saunders, A.D & Thirlwall, M.F. 1996. The
geochemistry and petrogenesis of the late-Cretaceous picrites and basalts
of Curaçao, Netherlands Antilles: a remnant of an oceanic plateau.
Contributions to Mineralogy and Petrology 124: 29-43.
Lapierre,
H.; Bosch, D; Mamberti, Dupuis, B.; Jaillard, E.; de Lépinay, B.; Maury,
R.; Hernandez, J.; Polvé, M. and Tardy, M. 2001. The Late
Cretaceous Duarte Complex (Hispaniola) revisited: comparison with the
Cretaceous oceanic plateaus from Ecuador. This meeting.
Pindell, James. 2001. Origin of
Caribbean terranes in a kinematic framework. This meeting.
Revillon, S.; Arndt, N. T. et al. 2000. Geochemical
study of ultramafic volcanic and plutonic rocks from Gorgona island,
Colombia: the plumbing system of an oceanic plateau. J. Pet 41(7):
1127-1153.
Thompson, P.M.E.; Kempton, P.D.; Tarney, J.; Saunders,
A.D.; White, R.V. and Kerr, A.C. 2001. New Isotopic and
Geochronological Constraints on the Origin of an Island Arc Sequence
Associated with the Cretaceous Caribbean Oceanic Plateau. This
meeting. |
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