IGCP Project short title: Caribbean Plate Tectonics Duration and ...
IGCP Project short title: Caribbean Plate Tectonics Duration and ... IGCP Project short title: Caribbean Plate Tectonics Duration and ...
Project 433 Caribbean Plate 2 2000-2001 By- Annual Report of IGCP Project 433 (October 2001) Summary of major past achievements of the project As this is our first by-annual report for the years 2000-2001: the achievements embrace both years. During these two years some important results are already evident as a consequence of focused discussion and selected presentations during the workshops and meetings. This approach has highlighted many problems that are currently among topics of research: Origin of the Present-day Caribbean Plate. The concept that the present-day Caribbean Plate is allochthonous from the Pacific produce models that explain many aspects of the evolution of the Caribbean. Some advocates of the autochthonous models have reconsidered their points during the meetings in Stuttgart and Leicester. However, the allochthonous models still present major problems pending adequate solution. The Galapagos hotspot and Caribbean plateau. There are two fundamental points of view regarding the role of the Galapagos hotspot in the geology of the Caribbean, which were the subject of extensive debate in Stuttgart and Leicester. One group holds that the Galapagos hotspot has nothing to do with the ProtoCaribbean crust or the Caribbean Plateau basalts, because the hot spot was always positioned west of both of them, and, consequently, was not the source of the so-called Caribbean plateau basalts. The other interpretation holds that the Galapagos hotspot actually produced the Caribbean plateau basalts and the ridges within the Nazca and Cocos plates. Pindell’s new unpublished palinispastic reconstructions say that it is impossible that the Galapagos hotspot produced the Caribbean plateau basalts. Trace element and isotopic geochemistry, however, do not rule it out (Hauff et al., 2000). Subduction reversal in the Caribbean. The polarity of subduction of the Caribbean plate in Cretaceous time has been an intriguing topic since Mattson (1979) proposed that a reversal in subduction direction occurred during plate development. A summary of the evidence relevant to a reversal and the possible timing of the event is given by Jolly et al (1998). Most models seemingly require a change in subduction direction. For example, Pindell (1994, 2001) proposed a flip in the polarity of the 2
3 arc at about 120 Ma. However, several researchers consider that the arc’s subduction flip required by Pindell’s model about 120 Ma ago is problematic for several reasons. Those investigating the origin of the plateau basalts disagree because a thick buoyant oceanic plateau would be very difficult to subduct, and would therefore significantly affect 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 Islands with the attempted subduction of the Ontong Java oceanic plateau. However, Pindell’s latest unpublished model suggests that the 120 Ma polarity reversal occurred before the bulk of the plateau was formed, on the basis of the following pieces of evidence: a. Abundant evidence for a large tectonic event around that time b. Unconformities in many arc-related sequences at ca. 120Ma. c. P-T paths from high-pressure metamorphic rocks d. Change in geochemical character from PIA to CA in many circum-Caribbean arcs. e. 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 at Leicester 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 Ma) could have represented the last pulses of magmatism. Other authors also disagree with the subduction reversal because this flip does not explain the geochemical evolution of the Cretaceous arc magmatism in Cuba (Iturralde- Vinent, 1994, 1998; Kerr et al., 1999), neither the tectonics of north central Cuba (Iturralde- Vinent, 1994, 1998). Iturralde-Vinent (op.cit.) postulated a major change in the geometry of the convergent plate boundary between latest Campanian and Paleocene, involving deformation and almost complete extinction of arc volcanism, modification of the trend of the arc axis, and a major change in the orientation and geochemistry of the arc. The alleged Albian-Campanian arc in Central America. Another subject that did not find agreement is the existence of an active Albian-Campanian island arc in Central America, and its evidence in the Nicoya Complex. According to a paper by Calvo and Bolt (1994), there is an arc-derived volcaniclastic calcalkaline section in Costa Rica, but several other attendees at the Stuttgart meeting (K. Hoernle, A. Astorga) stated that their geochemical and geological investigations in the Nicoya Complex do not confirm its presence. An Albian-Campanian island arc as part of present-day southern Central America 3
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<strong>Project</strong> 433<br />
<strong>Caribbean</strong> <strong>Plate</strong><br />
2<br />
2000-2001 By- Annual Report of <strong>IGCP</strong> <strong>Project</strong> 433<br />
(October 2001)<br />
Summary of major past achievements of the project<br />
As this is our first by-annual report for the years 2000-2001: the achievements embrace both<br />
years.<br />
During these two years some important results are already evident as a consequence of<br />
focused discussion <strong>and</strong> selected presentations during the workshops <strong>and</strong> meetings. This<br />
approach has highlighted many problems that are currently among topics of research:<br />
Origin of the Present-day <strong>Caribbean</strong> <strong>Plate</strong>. The concept that the present-day<br />
<strong>Caribbean</strong> <strong>Plate</strong> is allochthonous from the Pacific produce models that explain many aspects<br />
of the evolution of the <strong>Caribbean</strong>. Some advocates of the autochthonous models have<br />
reconsidered their points during the meetings in Stuttgart <strong>and</strong> Leicester. However, the<br />
allochthonous models still present major problems pending adequate solution.<br />
The Galapagos hotspot <strong>and</strong> <strong>Caribbean</strong> plateau. There are two fundamental points of<br />
view regarding the role of the Galapagos hotspot in the geology of the <strong>Caribbean</strong>, which<br />
were the subject of extensive debate in Stuttgart <strong>and</strong> Leicester. One group holds that the<br />
Galapagos hotspot has nothing to do with the Proto<strong>Caribbean</strong> crust or the <strong>Caribbean</strong> <strong>Plate</strong>au<br />
basalts, because the hot spot was always positioned west of both of them, <strong>and</strong>, consequently,<br />
was not the source of the so-called <strong>Caribbean</strong> plateau basalts. The other interpretation holds<br />
that the Galapagos hotspot actually produced the <strong>Caribbean</strong> plateau basalts <strong>and</strong> the ridges<br />
within the Nazca <strong>and</strong> Cocos plates. Pindell’s new unpublished palinispastic reconstructions<br />
say that it is impossible that the Galapagos hotspot produced the <strong>Caribbean</strong> plateau basalts.<br />
Trace element <strong>and</strong> isotopic geochemistry, however, do not rule it out (Hauff et al., 2000).<br />
Subduction reversal in the <strong>Caribbean</strong>.<br />
The polarity of subduction of the <strong>Caribbean</strong> plate in Cretaceous time has been an intriguing<br />
topic since Mattson (1979) proposed that a reversal in subduction direction occurred during<br />
plate development. A summary of the evidence relevant to a reversal <strong>and</strong> the possible timing<br />
of the event is given by Jolly et al (1998). Most models seemingly require a change in<br />
subduction direction. For example, Pindell (1994, 2001) proposed a flip in the polarity of the<br />
2
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