K-Ar radiometric ages of lavas from Cocos Island (Eastern Pacific)

Bellón, Hervé; Saenz, R.; Tournon, Jean

doi:10.1016/0025-3227(83)90004-x

Cited by 14 publications

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“…Two northern Cocos Ridge lavas from Cocos Island and a nearby seamount (64DR‐1 and 71DR‐1, see sites on Figure 3) extend to slightly higher εNd values compared to the Galápagos northern domain field (Figure 4b). Lavas from Cocos Island have been dated at 2 Ma [ Bellon et al , 1983] and therefore may not belong to the Cocos Ridge and Galápagos hot spot track but rather may represent a separate “Cocos Island magmatic event”. Combined Sr, Nd and Pb isotope ratios, and now Hf isotopes as well, indicate that Cocos Island and Galápagos Island lavas have the same characteristic isotope signature [ Castillo et al , 1988; Werner et al, submitted manuscript, 2003; this paper].…”

Section: Analytical Methods and Resultsmentioning

confidence: 99%

“…Two southern Cocos Ridge samples, 38DR-12 and 39DR-2 are more typical in terms of both eNd and eHf, of the northern and eastern Galápagos domains. Lavas from Cocos Island have been dated at 2 Ma[Bellon et al, 1983] and therefore may not belong to the Cocos Ridge and Galápagos hot spot track but rather may represent a separate ''Cocos Island magmatic event''. Combined Sr, Nd and Pb isotope ratios, and now Hf isotopes as well, indicate that Cocos Island and Galápagos Island lavas have the same characteristic isotope signature[Castillo et al…”

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confidence: 99%

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Hafnium isotopic variations in volcanic rocks from the Caribbean Large Igneous Province and Galápagos hot spot tracks

Geldmacher

Hanan

Blichert‐Toft

et al. 2003

Geochem Geophys Geosyst

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[1] We report Hf isotope compositions of 79 lavas that record the early ($5-95 Ma) history of the Galápagos plume volcanism. These include lavas from the Caribbean Large Igneous Province (CLIP; $95-70 Ma), the accreted Galápagos paleo-hot spot track terranes (54-65 Ma) of Costa Rica (Quepos, Osa and Burica igneous complexes), and the Galápagos hot spot tracks (<20 Ma) located on the Pacific seafloor (Cocos, Carnegie, Malpelo, and Coiba Ridges and associated seamounts). These samples have previously been well characterized in terms of major and trace elements, Sr-Nd-Pb isotopes and Ar/Ar ages. As a result of the relative immobility of the high field strength and rare earth elements during synand post-emplacement hydrothermal activity and low-temperature alteration, combined Lu-Hf and Sm-Nd isotope systematics, when used in conjunction with Pb isotopes, provide a particular powerful tool, for evaluating the source compositions of ancient and submarine lavas. The combined Nd-Hf isotope data suggest that three of the isotopically distinct source components found today in the Galápagos Islands (the Floreana-like southern component, the Fernandina-like central component, and the depleted Genovesa-like eastern component) were present in the CLIP already by 95-70 Ma. The fourth Pinta-like northern component is first recorded at about 83-85 Ma by volcanism taking place during the transition from the plume head/CLIP to plume tail stage and has then been present in the hot spot track continuously thereafter. The identification of the unique northern and southern Galápagos Plume Hf-Nd-Pb isotope Pb and lower DeHf, a signature typical of the northern Galápagos island Pinta.

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Section: Analytical Methods and Resultsmentioning

confidence: 99%

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confidence: 99%

Hafnium isotopic variations in volcanic rocks from the Caribbean Large Igneous Province and Galápagos hot spot tracks

Geldmacher

Hanan

Blichert‐Toft

et al. 2003

Geochem Geophys Geosyst

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“…The rocks from Cocos Island, located on the northwestern flank of Cocos Ridge approximately halfway between the CNS and the Central America (Figure 1), show ocean‐island‐basalt (OIB)‐type compositions similar to those of the enriched Galápagos domains but K/Ar and paleomagnetic dates indicate that the island is only 2 m.y. old [ Dalrymple and Cox , 1968; Bellon et al , 1983; Castillo , 1987; Castillo et al , 1988]. Castillo [1987] concludes that this late‐stage volcanism on Cocos Ridge was apparently caused by anomalously slow cooling of the lithosphere under the ridge whereas Meschede et al [1998] postulate a second hot spot near Cocos Island.…”

Section: Introductionmentioning

confidence: 99%

Geodynamic evolution of the Galápagos hot spot system (Central East Pacific) over the past 20 m.y.: Constraints from morphology, geochemistry, and magnetic anomalies

Werner¹,

Hoernle

Barckhausen

et al. 2003

Geochem Geophys Geosyst

130

164

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[1] We report results of magnetic data from the Nazca Plate and of geochemical (major element and Sr-NdPb-isotope) analyses of rocks dredged from the Galápagos hot spot tracks (Cocos, Carnegie, Malpelo and Coiba Ridges and adjacent seamounts) in the Central East Pacific. Magnetic anomalies indicate that the Malpelo and Carnegie Ridges were once attached and that seafloor spreading separated the two ridges between 14.5 Ma and 9.5 Ma. The variations in Sr-Nd-Pb isotopic composition show that three of the mantle components currently observed at the Galápagos (Central, Southern, and Eastern) existed in the hot spot for at least 20 m.y., whereas the Northern Galápagos mantle component has been present for at least $15 Ma. Our data are consistent with the existence of a compositionally zoned/striped Galápagos plume since $20 Ma. Combined constraints from the morphology of the hot spot tracks, the magnetic record, and the isotope geochemistry of the rock samples provide new insights into the hot spot-ridge geometry and interaction of the Galápagos hot spot with the Cocos-Nazca spreading center (CNS) over the past 20 m.y. At 19.5 Ma a ridge jump moved the spreading axis to the northern edge of the hot spot. Between 19.5 and 14.5 Ma, the spreading axis was located above the center of the hot spot. At 14.5 Ma, a new ridge jump moved the spreading axis to the south, splitting the paleo-Carnegie Ridge into the present Carnegie and Malpelo Ridges. The repeated ridge jumps reflect capture of the northwardly drifting spreading center by the Galápagos hot spot. At 11-12 Ma an offset of the spreading axis lay above the plume center. Spreading between the Carnegie and Malpelo Ridges continued until 9.5 Ma.

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“…A) as well as one of the world's largest, tropical, uninhabited islands. It is the only emergent part of the Cocos Ridge and was formed as a result of volcanic activity by the Galapagos hotspot between 1.9 and 2.4 million years ago (Bellon et al ; Castillo et al ). Its high annual rainfall (5000–7000 mm, Alfaro ) makes it one of the few islands in the Eastern tropical Pacific that harbors a tropical rainforest.…”

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A comparative analysis of island floras challenges taxonomy‐based biogeographical models of speciation

et al. 2015

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Using phylogenetic data from insular and mainland congeneric species, we show that all of the endemic species are derived from independent colonization events rather than in situ speciation. This is in sharp contrast to the results of a study carried out in a comparable system, Lord Howe Island (Australia), where as much as 8.2% of the plant species were the product of sympatric speciation. Differences in physiography and age between the islands may be responsible for the contrasting patterns of speciation observed. Importantly, comparing phylogenetic assessments of the modes of speciation with taxonomy-based measures shows that widely used island biogeography approaches overestimate rates of in situ speciation. K E Y W O R D S :Cladogenesis, Cocos Island, phylogeny, sympatric speciation.

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K-Ar radiometric ages of lavas from Cocos Island (Eastern Pacific)

Cited by 14 publications

References 9 publications

Hafnium isotopic variations in volcanic rocks from the Caribbean Large Igneous Province and Galápagos hot spot tracks

Hafnium isotopic variations in volcanic rocks from the Caribbean Large Igneous Province and Galápagos hot spot tracks

Geodynamic evolution of the Galápagos hot spot system (Central East Pacific) over the past 20 m.y.: Constraints from morphology, geochemistry, and magnetic anomalies

A comparative analysis of island floras challenges taxonomy‐based biogeographical models of speciation

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