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  • 1
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    Mid-Cretaceous Hawaiian tholeiites preserved in Kamchatka (2008)
    GSA (Geological Society of America)
    In:  Geology, 36 (11). pp. 903-906.
    Details
    Publication Date: 2019-10-24
    Description: We report geochemical data on a peculiar group of Albian–Cenomanian (120–93 Ma) basalts preserved in ophiolites on the Kamchatsky Mys peninsula (Kamchatka, Russia) that share trace element and isotopic compositions with enriched tholeiites from the Detroit and Meiji Seamounts in the Hawaiian-Emperor Seamount chain. Melt inclusions in chromium spinel from these rocks, representative of melt composition unaffected by post-magmatic alteration, exhibit Hawaiian-type [Th/Ba]n (0.25–0.77; i.e., distinctively low compared to the majority of oceanic island basalts and mid-oceanic ridge basalts). Low 208Pb*/206Pb* of ~0.93 in rocks and high [Nb/La]n = 1.1–4.6 in melt inclusions suggest the presence of a distinctive “Kea”–type component in their source. We propose that the ophiolitic basalts represent older (Early to middle Cretaceous) products of the Hawaiian hotspot (older than preserved on the northwest Pacific seafloor) that were accreted to the forearc of Kamchatka. The presence of similar compositional components in modern and Cretaceous Hawaiian hotspot lavas suggests a persistent yet heterogeneous composition of the mantle plume, which may have sampled ≥15% of the core-mantle boundary layer over the past ~100 m.y.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/G25171A.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Lifetime and cyclicity of fluid venting at forearc mound structures determined by tephrostratigraphy and radiometric dating of authigenic carbonates (2008)
    GSA (Geological Society of America)
    In:  Geology, 36 (9). pp. 707-710.
    Details
    Publication Date: 2019-10-24
    Description: At convergent margins, fluids rise through the forearc in response to consolidation of the upper plate and dewatering of the subducting plate, and produce various cold-seep–related features on the seafloor (mud diapirs, mud mounds). At the Central American forearc, authigenic carbonates precipitated from rising fluids within such structures during active venting while typical mixed-mud sediments were ejected onto the surrounding seafloor where they became intercalated with normal pelagic background sediments, indicating that mud mounds evolved unsteadily through alternating active and inactive phases. Intercalated regional ash layers from Plinian eruptions at the Central American volcanic arc provide time marks that constrain the ages of mud ejection activity. U/Th dating of drill core samples of authigenic carbonate caps of mud mounds yields ages agreeing well with those constrained by ash layers and showing that carbonate caps grow inward rather than outward during active venting. Both dating approaches show that offshore Nicaragua and Costa Rica (1) active and inactive phases can occur simultaneously at neighboring mounds, (2) mounds along the forearc have individual histories of activity, but there are distinct time intervals when nearly all mounds have been active or inactive, (3) lifetimes of mounds reach several hundred thousand years, and (4) highly active periods last 10–50 k.y. with intervening periods of 〉10 k.y. of relative quiescence.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/G24806A.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Transition from arc to oceanic magmatism at the Kamchatka-Aleutian junction (2005)
    GSA (Geological Society of America)
    In:  Geology, 33 (1). pp. 25-28.
    Details
    Publication Date: 2019-10-24
    Description: Spatial geochemical variations of Quaternary lavas erupted along the northern segment of the Kamchatka arc are used to trace changes in magma generation across the subducting Pacific slab edge. The late Pleistocene–Holocene lavas of the northern end of the Central Kamchatka depression north of the Pacific slab edge show strong enrichment in high field strength elements and light rare earth elements, relatively unradiogenic strontium and lead but radiogenic neodymium isotope ratios, and oxygen isotope compositions similar to those of mid-oceanic-ridge basalts. These geochemical characteristics are distinct from the southern Central Kamchatka depression volcanoes located above the subducting Pacific slab. Extensive fluid-triggered mantle melting dominates magma genesis beneath the largest Kamchatka volcanoes in the south, whereas low-degree decompression melting of the Pacific asthenospheric mantle is the major magma generation process north of the Pacific slab edge. Quaternary detachment of the subducted Pacific plate fragment resulted in the influx of fertile mantle beneath Kamchatka. We propose that upwelling and southward flow of this hotter, more fertile mantle is the main reason for recent magmatism in northern Kamchatka and for the exceptional productivity of the Central Kamchatka depression volcanoes (Klyuchevskoy and Sheveluch), the most active arc volcanoes on Earth.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/G20853.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    The Missing History (16-71 Ma) of the Galápagos Hotspot: Implications for the Tectonic and Biological Evolution of the Americas (2002)
    GSA (Geological Society of America)
    In:  Geology, 30 . pp. 795-798.
    Details
    Publication Date: 2019-10-24
    Description: We present the results of volcanological, geochemical, and geochronological studies of volcanic rocks from Malpelo Island on the Nazca plate (15.8–17.3 Ma) belonging to the Gala´pagos hotspot tracks, and igneous complexes (20.8–71.3 Ma) along the Pacific margin of Costa Rica and Panama. The igneous complexes consist of accreted portions of ocean island and seamount volcanoes and aseismic ridges, representing the missing (primarily subducted) history of the Gala´pagos hotspot. The age and geochemical data directly link the Gala´pagos hotspot tracks on the Pacific Ocean floor to the Caribbean large igneous province (ca. 72–95 Ma), confirming a Pacific origin for the Caribbean oceanic plateau from the Gala´pagos hotspot. We propose that emplacement of this oceanic plateau between the Americas and interaction of the Gala´pagos hotspot tracks with the Central American Arc played a fundamental role in the formation of land bridges between the Americas in Late Cretaceous–Paleocene and Pliocene-Holocene time. The land bridges allowed the exchange of terrestrial faunas (e.g., dinosaurs, mastodons, saber-tooth cats, and ground sloths) between the Americas and served as barriers for the exchange of marine organisms between the central Pacific Ocean and the Caribbean Sea and the central Atlantic Ocean.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/0091-7613(2002)030〈0795:MHMOTG〉2.0.CO;2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Paired coral Sr/Ca and delta〈sup〉18〈/sup〉O records from the Chagos Archipelago: Late 20th century warming affects rainfall variability in the tropical Indian Ocean (2006)
    GSA (Geological Society of America)
    In:  Geology, 34 (12). pp. 1069-1072.
    Details
    Publication Date: 2019-10-24
    Description: Understanding the relationship between sea surface temperature (SST) and precipitation is a significant challenge for climate models, particularly for the tropics. Here we present a new monthly coral Sr/Ca record from the tropical Indian Ocean (Chagos Archipelago) that extends from 1950 to 1995. The coral Sr/Ca ratio shows a stationary relationship with local SST, and documents a warming of 0.3 °C since 1950. Previous work has shown that the δ18O values measured in the same coral core provide a proxy record of precipitation in the tropical Indian Ocean. The coral δ18O record shows a nonstationary relationship with local SST, and a correlation between δ18O and SST only emerges in the 1970s. It was proposed that this nonstationary behavior is due to an increase in mean SSTs in the tropical Indian Ocean. During the 1970s, SSTs reached a critical threshold (28.5 °C) beyond which small SST anomalies can have a significant impact on atmospheric convection. As a result, the covariance between SST and precipitation in the tropical Indian Ocean increased. Our new Sr/Ca data confirm that the warming of the Indian Ocean during the late twentieth century affects atmospheric convection and rainfall variability. Moreover, our proxy data show that the relationship between SST and precipitation is nonlinear and characterized by threshold behavior.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/G23162A.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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