CLIP - Entstehung der karibischen Flutbasaltprovinz im Zusammenhang mit der geodynamischen Entwicklung der Zentralkaribik
Zusammenfassung der Projektergebnisse
The project “CLIP” is based on the evaluation of magmatic rock samples collected at two submarine structures in the Caribbean, the Beata Ridge and the Hess Escarpment, during cruise M81/2, Legs A and B in 2010. New 40Ar/39Ar age determinations confirm that the Caribbean Large Igneous Province (CLIP) was not formed during a geological short period of only a few million years, as often assumed for Large Igneous Provinces (LIPs). Instead, magmatic activity at least at the Beata Ridge ranges from ~94 to 50 Ma comprising three phases, a first main phase (~94-87 Ma) and two weaker phases (~81-74 Ma and ~62-50 Ma), confirming the results of Révillon et al. (2000) that younger volcanism took place between 81-74 Ma and 56-55 Ma ago. Our results are the first to show that the main CLIP stage of volcanism (~94-87 Ma) is also present at the Beata Ridge and that volcanism continues to 50 Ma, representing the youngest age associated with the CLIP thus far. At the Hess Escarpment, only the younger periods of volcanism were found, based on the one robust age of 56 Ma determined during this project for the structure and published age data of ~81 Ma from ODP Leg 165 Site 1001. Whereas a later magmatic pulse between ~81-69 Ma has been associated with the Caribbean Large Igneous Province, possibly caused by a pulsing Galápagos hotspot, the third phase present both at Beata Ridge and the Hess Escarpment may be caused by late-stage volcanism related to extension in the Caribbean. The extension could have resulted in upwelling and decompression (re)melting of residual plume material and upper mantle material. Picritic rocks, which are found in the basement sequences of the Beata Ridge, indicate high source temperatures during the early stages of magmatism consistent with melting of hot mantle plume material. Trace element and Sr-Nd-Hf-Pb isotope analyses show that the majority of samples from the Beata Ridge display relatively flat chondrite-normalized rare earth element (REE) patterns and intermediate radiogenic isotope ratios typical for the Caribbean Plateau, but some samples also have enriched and some have depleted signatures in both trace elements and radiogenic isotopes. This indicates that the mantle source region consists of enriched and a depleted components, which were variably mixed to generate the intermediate compositions. The high geochemical variability observed in the rocks suggests insufficient mixing in the plume head. In particular, the sampling of profiles conducted with the remotely operated vehicle (ROV) Kiel 6000 shows that these heterogeneities occur on a small scale of possibly only tens of kilometers. Additionally, our analytical data show that the oldest volcanic rocks are almost exclusively enriched and the depleted component seems to become more pronounced with time, since most of the younger samples show depleted characteristics. This depleted character is predominantly found in the southern part of the Beata Ridge. For the Hess Escarpment and the region to the north on the Lower Nicaraguan Rise, we produced the first representative geochemical dataset. Since we solely sampled volcanic and carbonate rocks but no metamorphic rocks, we assume that the region is of volcanic origin and does not belong to the adjacent continental Chortís block, as proposed by several authors. The Hess Escarpment seems to form an extensional horst and graben structure together with the Beata Ridge and the Colombian and Haiti Basins in between, indicating a connection to the CLIP. Similarities in geochemical composition to the common CLIP compositions of some rocks interpreted to form the basement of the Hess Escarpment support the assumption that the region is part of the CLIP. The majority of rocks from the Hess Escarpment and the Lower Nicaraguan Rise, however, show highly depleted compositions in both incompatible elements and radiogenic isotope ratios. These compositions are similar but not identical to the highly depleted komatiites, which are found on Gorgona Island off the west coast of Colombia and thought to have also been generated during the CLIP event, and not identical to MORB either. Thus the depleted compositions of the Hess Escarpment lavas may be the result of mixing of a depleted component intrinsic to the mantle plume responsible for the formation of the CLIP with depleted upper mantle material.
Projektbezogene Publikationen (Auswahl)
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(2019) Age and geochemistry of the Beata Ridge: Primary formation during the main phase (~89 Ma) of the Caribbean Large Igneous Province. Lithos 328-329 69–87
Dürkefälden, Antje; Hoernle, Kaj; Hauff, Folkmar; Wartho, Jo-Anne; van den Bogaard, Paul; Werner, Reinhard
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(2019) Second-stage Caribbean Large Igneous Province volcanism: The depleted Icing on the enriched Cake. Chemical Geology 509 45–63
Dürkefälden, Antje; Hoernle, Kaj; Hauff, Folkmar; Werner, Reinhard; Garbe-Schönberg, Dieter
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(2016). Submarine structures of the Caribbean Large Igneous Province: Age and geochemistry of the Beata Ridge and Hess Escarpment. In: 2nd European Mineralogical Conference, September 2016, Rimini, Italy
Schwindrofska, A., Hoernle, K., van den Bogaard, P., Hauff, F., Werner, R.
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(2016). The composition of mantle plumes and the deep Earth. Earth Planet. Sci. Lett. 444, 13-25
Hastie, A.R., Fitton, J.G., Kerr, A.C., McDonald, I., Schwindrofska, A., Hoernle, K.
