Major and trace element abundances, including highly siderophile elements, and 187Os and 182W isotopic compositions were determined for ca. 89 Ma mafic and ultramafic rocks from the islands of ...Gorgona (Colombia) and Curaçao (Dutch Caribbean). The volcanic systems of both islands were likely associated with a mantle plume that generated the Caribbean Large Igneous Provence. The major and lithophile trace element characteristics of the rocks examined are consistent with the results of prior studies, and indicate derivation from both a chemically highly-depleted mantle component, and an enriched, or less highly-depleted mantle component. Highly siderophile element abundances for these rocks are generally similar to rocks with comparable MgO globally, indicating that the major source components were not substantially enriched or depleted in these elements. Rhenium-Os isotopic systematics of most rocks of both islands indicate derivation from a mantle source with an initial 187Os/188Os ratio between that of the contemporaneous average depleted mid-ocean ridge mantle and bulk silicate Earth. The composition may reflect either an average lower mantle signature, or global-scale Os isotopic heterogeneity in the upper mantle. Some of the basalts, as well as two of the komatiites, are characterized by calculated initial 187Os/188Os ratios 10–15 % higher than the chondritic reference. These more radiogenic Os isotopic compositions do not correlate with major or trace element systematics, and indicate a mantle source component that was most likely produced by either sulfide metasomatism or ancient Re/Os fractionation. Tungsten-182 isotopic compositions measured for rocks from both islands are characterized by variable μ182W values ranging from modern bulk silicate Earth-like to strongly negative values. The μ182W values do not correlate with major/trace element abundances or initial 187Os/188Os compositions. As with some modern ocean island basalt systems, however, the lowest μ182W value (−53) measured, for a Gorgona olivine gabbro, corresponds with the highest 3He/4He previously measured from the suite (15.8 R/RA). Given the lack of correlation with other chemical/isotopic compositions, the mantle component characterized by negative μ182W and possibly high 3He/4He is most parsimoniously explained to have formed as a result of isotopic equilibration between the mantle and core at the core-mantle boundary.
The maximum crystallization temperature of mantle-derived melts provides constraints on the minimum temperature of their mantle source regions. This temperature can be estimated using ...phenocryst-based thermometry on primitive lavas that contain olivine and spinel phenocrysts using the Al-in-olivine thermometer. Application of an updated version of this thermometer to primitive basalts gives precise estimates of olivine-spinel crystallization temperatures in different geodynamic settings. These are minimum temperatures for melt extraction from the mantle due to both adiabatic cooling and cooling prior to co-saturation in these phases. Application of this thermometer to primitive MORB gives co-saturation temperatures of up to 1270°C (and a maximum olivine forsterite (Fo) content of Fo91.3) consistent with previous constraints (e.g. from the volume of melt produced at mid-ocean ridges). Substantially higher crystallization temperatures are recorded by Tertiary (~60Ma) picrites from Baffin Island (up to 1408°C; Fo91.3) and East Greenland (up to 1354°C; Fo90.1), Cretaceous (86Ma) picrites from Madagascar (up to 1486°C; Fo91.8) and Cretaceous (88Ma) komatiites from Gorgona (up to 1435°C; Fo91.7). Unlike olivine-melt based thermometers these temperature estimates are not significantly influenced by uncertainty in melt H2O content or fO2. These results indicate that the mantle source region of large igneous provinces is substantially hotter than the ambient upper mantle, supporting the standard thermal plume model.
•Al-in-olivine thermometer applied to MORB and LIP basalts•LIP basalt initial crystallization up to 200°C hotter than MORB•This supports the thermal plume model.
The mantle of the modern Earth is relatively oxidised compared to the initially reducing conditions inferred for core formation. The timing of the oxidation of the mantle is not conclusively resolved ...but has important implications for the timing of the development of the hydrosphere and atmosphere. In order to examine the timing of this oxidation event, we present iron isotope data from three exceptionally well preserved komatiite localities, Belingwe (2.7Ga), Vetreny (2.4Ga) and Gorgona (0.089Ga). Measurements of Fe isotope compositions of whole-rock samples are complemented by the analysis of olivine, spinel and pyroxene separates. Bulk-rock and olivine Fe isotope compositions (δ57Fe) define clear linear correlations with indicators of magmatic differentiation (Mg#, Cr#). The mean Fe isotope compositions of the 2.7–2.4Ga and 0.089Ga samples are statistically distinct and this difference can be explained by greater extent of partial melting represented by the older samples and higher mantle ambient temperatures in the Archean and early Proterozoic relative to the present day. Significantly, samples of all ages define continuous positive linear correlations between bulk rock δ57Fe and V/Sc and δ57Fe and V, and between V/Sc and V with TiO2, providing evidence for the incompatible behaviour of V (relative to Sc) and of isotopically heavy Fe. Partial melting models calculated using partition coefficients for V at oxygen fugacities (fO2s) of 0 and +1 relative to the fayalite-magnetite-quartz buffer (FMQ) best match the data arrays, which are defined by all samples, from late Archean to Tertiary. These data, therefore, provide evidence for komatiite generation under moderately oxidising conditions since the late Archean, and argue against a change in mantle fO2 concomitant with atmospheric oxygenation at ~2.4Ga.
► We measure iron isotopes in 2.7–0.089Ga komatiites. ► Iron isotopes are fractionated even at exceptionally high degrees of partial melting. ► Trends with V/Sc and V indicate melting under relatively oxidising conditions. ► No evidence is found for a change in mantle fO2 from 2.7 to 0.089Ga.
Abstract
During the austral winter, G-stock humpback whales, Megaptera novaeangliae, migrate to the Tropical Eastern Pacific to breed. To analyse if the whale migration times have changed over time, ...we analysed 31 years (1988–2018) of arrival and departure times to Gorgona National Park, Colombia, an important breeding site. During this period, whales have significantly changed their arrival time, coming now earlier, but their departure time has not changed significantly. Hence, humpback whales now stay 1 month longer than 31 years ago. Humpbacks arrived in Gorgona at the earliest during the beginning of May and stayed at the most until late December. The change observed in the arrival time to breeding grounds could be related to ice sheet mass changes in autumn in Antarctica and increase in population size over the past decades but we were unable to determine which factor is more important in explaining the observed trend. Management decisions in Colombia need to account for a longer stay, specifically restricting anthropogenic activities from 1May to 31December. We urge other researchers to review their data, in case this shift is evident in other regions and management plans need to be updated.
Island-mainland systems serve as natural laboratories for studying communication signals. We explored potential divergence in the song of the black-crowned antshrike between Gorgona Island, a ...land-bridge island off the Pacific coast of Colombia, and several mainland populations. We found that the perching song of this species, the so called loudsong, was distinctly different on Gorgona Island. This differentiation encompassed an increase in frequency bandwidth, a decrease in vocal performance, and a reduction in song duration. All are consistent with documented patterns of divergence observed in avian acoustic signals on oceanic islands. The observed distinctions in loudsong acoustics, including variations in frequency and temporal features, led to the inference that the population on Gorgona Island produces the least complex loudsong dialect across the entire species range. This pattern of how an innate vocalization manifests within a land-bridge island, which was connected to the mainland not long ago, lends support to the Character Release Hypothesis. To ensure an unbiased comparison, we considered genetic clusters and analyzed them by comparing ten acoustic signals between the land-bridge island and several mainland populations. Combined with the gene genealogy, this finding supports the validity of two geographic forms:
Thamnophilus atrinucha atrinucha
and
Thamnophilus atrinucha gorgonae
(island). However, they also reveal the existence of additional unrecognized dialects of loudsong that transcend current taxonomic classifications. We provide evidence that challenges the long-standing presumption suggesting minimal intraspecific geographic variation in the vocalization among non-vocal learning species.
Significance statement
Significant evolutionary implications exist for an intriguing pattern of variation of the loudsong behavior in the Black-crowned Antshrike over a land-bridge island. Our gene tree does provide evidence of the enormous haplotypic diversity accumulated in the
trans
-Andean region long after the final uplift of the northern Andes. The acoustic divergence of the loudsong suggests substantial geographic variation within a non-vocal learning suboscine. Genetic and loudsong divergence on a land-bridge island add to document that evolution of acoustic traits may be relaxed in islands as compared to those observed on the species-rich mainland. The island-mainland system is one of the few definitive biogeographic contexts for understanding evolution of acoustic behavior.
Given its biogeographical importance a study was performed on the diversity of fish in the streams of the Colombian Pacific Gorgona National Natural Park. This place is characterized by having the ...largest insular creeks system of the Colombian Pacific with 25 permanent streams and an estimated 75 temporary. The island was divided into east and west zones and the sampling was carried out in sites of nine streams, starting from the mouth upstream. The sampling sites were separated by paths of 50 meters with a total of seven points per stream. At each site, diversity data were taken through visual censuses modulated by time and additionally some physicochemical parameters were recorded. Nine species were registered, of which eight are of amphidrome origin and one primary freshwater. Differences were found in the species composition between some streams and between the zones. Flow rate and total dissolved solids were the variables that most contributed to the distribution of species, in this case diversity increased at points with lower flow levels and low values of dissolved solids.
Debido a la importancia biogeográfica del Parque Nacional Natural Isla Gorgona en el pacífico colombiano, se realizó un estudio de la diversidad de peces en sus quebradas. Este lugar se caracteriza por tener el sistema de quebradas insulares más grande del Pacifico colombiano con 25 quebradas permanentes y un estimado de 75 temporales. La isla se dividió en zonas este y oeste y el muestreo se realizó mediante sitios de conteo en nueve quebradas, partiendo de la desembocadura hacia aguas arriba. Los sitios estuvieron separados por trayectos de 50 metros y se muestrearon un total de siete sitios por quebrada. En cada sitio se tomaron datos de diversidad mediante censos visuales modulados por tiempo y adicionalmente se registraron parámetros fisicoquímicos. Se registraron nueve especies de las cuales ocho son peces anfídromos y una primaria dulceacuícola. Se hallaron diferencias en la composición de especies entre algunas quebradas y entre las zonas. El caudal y los sólidos disueltos totales fueron las variables más relacionadas con la distribución de las especies, en este caso la diversidad se incrementó en los sitios con menores valores de caudal y valores bajos de sólidos disueltos.
We report O isotopes in olivine grains (Fo89–93) and volatile contents (CO2, H2O, F, S, Cl) in olivine-hosted melt inclusions from one Gorgona picrite and five komatiites with the aim of constraining ...the origin of H2O in these magmas. These samples have previously been analysed for major and trace elements and volatile concentrations (H2O, S, Cl) and B isotopes in melt inclusions. A distinctive feature of the included melts is relatively high contents of volatile components and boron, which show positive anomalies in, otherwise depleted, primitive mantle normalised trace and rare earth element patterns and range in δ11B from −11.5 to 15.6‰. In this study, the olivines were systematically analysed for O isotopes (1) in the centre of grains, (2) near the grain boundaries and, (3) as close as possible to the studied melt inclusions. The majority of olivines (∼66%) are “mantle”-like, 4.8‰≤δ18O≤5.5‰, with a subordinate but still significant number (∼33%) above, and only 2 grains below, this range. There is no systematic difference between the central and marginal parts of the grains. Higher than “mantle” δ18OOl values are ascribed to low-T (<300 °C) serpentinisation along inner fractures and grain boundaries of olivine phenocrysts. The measured concentrations of volatile components in the melt inclusions corrected for the effects of post-entrapment crystallisation and H2O–CO2 exsolution in inclusion shrinkage bubbles are: 286–1748 μg/g CO2, 0.2–0.86 wt.% H2O, 48–82 μg/g F, 398–699 μg/g S and 132–198 μg/g Cl. They correspond to a pressure of 86±44MPa or ∼2.5-km crustal depth of olivine crystallisation. The correlations of S and, to a lesser extent, of H2O, with highly incompatible lithophile elements and the correlation of F with Cl, but no relationships of H2O with Cl, rule out shallow depth magma degassing and/or crustal contamination. Our new δ18O olivine and volatile component data combined with the existing, highly variable δ11B values for melt inclusions also support the deep mantle origin of H2O (and probably other volatiles) in the Gorgona mafic and ultramafic magmas.
•66% studied olivines reveal mantle δ18O, with the rest affected by serpentinisation.•H2O–CO2 melt inclusion data imply ∼2.5-km crustal depth of magma fractionation.•Relationships between volatile and trace elements preclude crustal contamination.•δ18O–δ11B data do not support magma contamination by crustal rocks as well.•Deep mantle origin of H2O and other volatiles in the Gorgona magmas is confirmed.
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