Kevin Konrad

We present new observations on the dynamics and locations of deep mantle reservoirs derived from the ages and compositions of Voyager Seamount Chain lava flows. The previously unexplored Voyager Seamount Chain trends NW–SE between the Mid‐Pacific Mountains and the Northwestern Hawaiian Ridge. Volcanic samples were recovered from the chain during the Ocean Exploration Trust expedition NA134. The lava flows are alkalic to highly alkalic in composition. Ages ranged from 81 to 86 Ma ( n = 8), with the oldest ages in the NW and an age‐progression toward the SE. The Voyager age‐progression continues southward through the Northern Line Islands region until at least 69 Ma. Mantle flowlines using absolute plate motion models indicate that the Voyagers were emplaced near the modern Marquesas Hotspot location approximately 86–69 Ma. The Sr‐Nd‐Pb‐Hf isotope systematics show the influence of an EMII component and overlap the compositions of Pliocene volcanism from the Marquesas Islands, consistent with the plate motion age model. These data imply a long‐lived plume as the source of the Voyager seamounts and the Marquesas. However, the lack of a clear and continuous seamount chain between the 86–69 Ma Voyager Seamount Chain and the 6–0 Ma Marquesas Islands implies that the mantle plume displays variable buoyancy flux over time. The surface expression of this mantle reservoir experienced a potential hiatus of up to ∼60 m.y. These new data indicate that the mantle beneath the Marquesas Islands region has been discontinuously producing age‐progressive, EMII‐like hotspot volcanism since at least the Late Cretaceous.

Recent changes in US oceanographic assets are impacting scientists' ability to access seafloor and sub‐seafloor materials and thus constraining progress on science critical for societal needs. Here we identify national infrastructure needs to address critical science questions. This commentary reports on community‐driven discussions that took place during the 3‐day FUTURE of US Seafloor Sampling Capabilities 2024 Workshop , which used an “all‐hands‐on‐deck” approach to assess seafloor and sub‐seafloor sampling requirements of a broad range of scientific objectives, focusing on capabilities that could be supported through the US Academic Research Fleet (US‐ARF) now or in the near future. Cross‐cutting issues identified included weight and size limitations in the over‐boarding capabilities of the US‐ARF, a need to access material at depths greater than ∼20 m below the seafloor, sampling capabilities at the full range of ocean depths, technologies required for precise navigation‐guided sampling and drilling, resources to capitalize on the research potential of returned materials, and workforce development.

Upwelling and decompression of mantle plumes is the primary mechanism for large volumes of intraplate volcanism; however, many seamounts do not correlate spatially, temporally, or geochemically with plumes. One region of enigmatic volcanism in the ocean basins that is not clearly attributable to plume‐derived magmatism is the Geologist Seamounts and the wider South Hawaiian Seamount Province (∼19°N, 157°W). Here we present new bathymetric maps as well as ⁴⁰Ar/³⁹Ar age determinations and major and trace element geochemistry for six remote‐operated vehicle recovered igneous rock samples (NOAA‐OER EX1504L3) and two dredged samples (KK840824‐02) from the Geologist Seamounts. The new ages indicate that volcanism was active from 90 to 87 Ma and 74 to 73 Ma, inferring that in conjunction with previous ages of ∼84 Ma, seamount emplacement initiated near the paleo Pacific‐Farallon spreading ridge and volcanism spanned at least ∼17 m.y. Geochemical analyses indicate that Geologist Seamount lava flows are highly alkalic and represent low‐degree partial mantle melts primarily formed from a mixture of melting within the garnet and spinel stability field. The ages and morphology inferred that the seamounts were likely not related to an extinct plume. Instead, we build upon previous models that local microblock formation corresponded to regional lithospheric extension. We propose that the microblock was bounded by the Molokai and short‐lived Kana Keoki fracture zones. Regional deformation and corresponding volcanism among the Geologist Seamounts associated with the microblock potentially occurred in pulses contemporaneous to independently constrained changes in Pacific Plate motion—indicating that major changes in plate vectors can generate intraplate volcanism.

Iceland records over fifteen million years of complex volcanism resulting from the intersection of mid-ocean ridge and mantle plume upwelling. The Iceland mantle plume has been active for at least 70 Ma, with surface expressions in Greenland, the North Atlantic, and Iceland. The Iceland hotspot may exhibit periods of increased volcanic output linked to pulses of upwelling within the plume. Understanding Iceland’s magmatic history and potential pulsation could provide key insights into dynamic topography driving changes in deep-water oceanic circulation, late Cenozoic climate change and mantle plume – mid-ocean ridge interaction. Detrital geochronology is a powerful tool for capturing the magmatic history of a region. However, Iceland's fine-grained extrusive volcanic lithologies lack the typical detrital mineral phases such as zircon, sanidine, hornblende, and rutile that current geochronology methods utilize. Here we present a new methodology for capturing the magmatic history of fine grained extrusive volcanic rocks using single grain detrital ⁴⁰Ar/³⁹Ar incremental heating geochronology. The DARL (or Detrital Argon Lithics) method thus far has consisted of ⁴⁰Ar/³⁹Ar total fusion analyses, which pose a problem in the case of Iceland, due to the nature of its young glassy lava flows commonly displaying subatmospheric ⁴⁰Ar/³⁶Ar isochron intercepts and low ⁴⁰Ar*. This work represents a ⁴⁰Ar/³⁹Ar incremental heating pilot study on 19 single grains of Icelandic river sand (1–3 mm), collected from five different catchments. Fifteen of the 19 basaltic grains produced concordant age experiments that ranged from 0.2 to 13.5 Ma and uncertainties (2σ) from 1 % to 86 % with the grains under 1 Ma having the largest uncertainties. Preliminary results show that basaltic grains with less alteration (and corresponding lower atmospheric argon concentration) yield more accurate age determinations, though altered basaltic grains can still produce statistically valid age determinations. Results presented here show the validity of the incremental heating DARL methodology for capturing the magmatic history of mafic terrains. The long analysis time required for incremental heating experiments makes it infeasible to produce the large number of ages required for a detrital study. For this reason, we propose combining the aspects of the total fusion and incremental heating DARL methodologies to acquire age data for the large N values needed for detrital studies while improving the accuracy of total fusion DARL analysis.

Iceland records over fifteen million years of complex volcanism resulting from the intersection of mid-ocean ridge and mantle plume upwelling. The Iceland mantle plume has been active for at least 70 Ma, with surface expressions in Greenland, the North Atlantic, and Iceland. The Iceland hotspot may exhibit periods of increased volcanic output linked to pulses of upwelling within the plume. Understanding Iceland’s magmatic history and potential pulsation could provide key insights into dynamic topography driving changes in deep-water oceanic circulation, late Cenozoic climate change and mantle plume – mid-ocean ridge interaction. Detrital geochronology is a powerful tool for capturing the magmatic history of a region. However, Iceland's fine-grained extrusive volcanic lithologies lack the typical detrital mineral phases such as zircon, sanidine, hornblende, and rutile that current geochronology methods utilize. Here we present a new methodology for capturing the magmatic history of fine grained extrusive volcanic rocks using single grain detrital ⁴⁰Ar/³⁹Ar incremental heating geochronology. The DARL (or Detrital Argon Lithics) method thus far has consisted of ⁴⁰Ar/³⁹Ar total fusion analyses, which pose a problem in the case of Iceland, due to the nature of its young glassy lava flows commonly displaying subatmospheric ⁴⁰Ar/³⁶Ar isochron intercepts and low ⁴⁰Ar*. This work represents a ⁴⁰Ar/³⁹Ar incremental heating pilot study on 19 single grains of Icelandic river sand (1–3 mm), collected from five different catchments. Fifteen of the 19 basaltic grains produced concordant age experiments that ranged from 0.2 to 13.5 Ma and uncertainties (2σ) from 1 % to 86 % with the grains under 1 Ma having the largest uncertainties. Preliminary results show that basaltic grains with less alteration (and corresponding lower atmospheric argon concentration) yield more accurate age determinations, though altered basaltic grains can still produce statistically valid age determinations. Results presented here show the validity of the incremental heating DARL methodology for capturing the magmatic history of mafic terrains. The long analysis time required for incremental heating experiments makes it infeasible to produce the large number of ages required for a detrital study. For this reason, we propose combining the aspects of the total fusion and incremental heating DARL methodologies to acquire age data for the large N values needed for detrital studies while improving the accuracy of total fusion DARL analysis.

Iceland records over fifteen million years of complex volcanism resulting from the intersection of mid-ocean ridge and mantle plume upwelling. The Iceland mantle plume has been active for at least 70 Ma, with surface expressions in Greenland, the North Atlantic, and Iceland. The Iceland hotspot may exhibit periods of increased volcanic output linked to pulses of upwelling within the plume. Understanding Iceland’s magmatic history and potential pulsation could provide key insights into dynamic topography driving changes in deep-water oceanic circulation, late Cenozoic climate change and mantle plume – mid-ocean ridge interaction. Detrital geochronology is a powerful tool for capturing the magmatic history of a region. However, Iceland's fine-grained extrusive volcanic lithologies lack the typical detrital mineral phases such as zircon, sanidine, hornblende, and rutile that current geochronology methods utilize. Here we present a new methodology for capturing the magmatic history of fine grained extrusive volcanic rocks using single grain detrital ⁴⁰Ar/³⁹Ar incremental heating geochronology. The DARL (or Detrital Argon Lithics) method thus far has consisted of ⁴⁰Ar/³⁹Ar total fusion analyses, which pose a problem in the case of Iceland, due to the nature of its young glassy lava flows commonly displaying subatmospheric ⁴⁰Ar/³⁶Ar isochron intercepts and low ⁴⁰Ar*. This work represents a ⁴⁰Ar/³⁹Ar incremental heating pilot study on 19 single grains of Icelandic river sand (1–3 mm), collected from five different catchments. Fifteen of the 19 basaltic grains produced concordant age experiments that ranged from 0.2 to 13.5 Ma and uncertainties (2σ) from 1 % to 86 % with the grains under 1 Ma having the largest uncertainties. Preliminary results show that basaltic grains with less alteration (and corresponding lower atmospheric argon concentration) yield more accurate age determinations, though altered basaltic grains can still produce statistically valid age determinations. Results presented here show the validity of the incremental heating DARL methodology for capturing the magmatic history of mafic terrains. The long analysis time required for incremental heating experiments makes it infeasible to produce the large number of ages required for a detrital study. For this reason, we propose combining the aspects of the total fusion and incremental heating DARL methodologies to acquire age data for the large N values needed for detrital studies while improving the accuracy of total fusion DARL analysis.

Upwelling and decompression of mantle plumes is the primary mechanism for large volumes of intraplate volcanism; however, many seamounts do not correlate spatially, temporally, or geochemically with plumes. One region of enigmatic volcanism in the ocean basins that is not clearly attributable to plume-derived magmatism are the Geologist Seamounts and the wider South Hawaiian Seamount Province (∼19°N, 157°W). Here we present new bathymetric maps as well as 40Ar/39Ar age determinations and major and trace element geochemistry for six remote-operated vehicle recovered igneous rock samples (NOAA-OER EX1504L3) and two dredged samples (KK840824-02) from the Geologist Seamounts. The new ages indicate volcanism was active from 90–87 Ma and 74–73 Ma, inferring that, in conjunction with previous ages of ~84 Ma, seamount emplacement initiated near the paleo Pacific-Farallon spreading ridge and volcanism continued for at least ~17 m.y. Geochemical analyses indicate that Geologist Seamounts lava flows are highly alkalic and represent low-degree partial mantle melts primarily formed from a mixture of melting within the garnet and spinel stability field. The ages and morphology infer the seamounts were likely not related to an extinct plume. Instead, we build upon previous models that local microblock formation corresponded with regional lithospheric extension. We propose the microblock was bounded by the Molokai and short-lived Kana Keoki fracture zones. Regional deformation and corresponding volcanism among the Geologist Seamounts associated with the microblock potentially occurred in pulses contemporaneous to independently constrained changes in Pacific Plate motion —indicating that major changes in plate vectors can generate intraplate volcanism.

Iceland records over fifteen million years of complex volcanism resulting from the intersection of mid-ocean ridge and mantle plume upwelling. The Iceland mantle plume has been active for at least 70 Ma, with surface expressions in Greenland, the North Atlantic, and Iceland. The Iceland hotspot may exhibit periods of increased volcanic output linked to pulses of upwelling within the plume. Understanding Iceland’s magmatic history and potential pulsation could provide key insights into dynamic topography driving changes in deep-water oceanic circulation, late Cenozoic climate change and mantle plume – mid-ocean ridge interaction. Detrital geochronology is a powerful tool for capturing the magmatic history of a region. However, Iceland's fine-grained extrusive volcanic lithologies lack the typical detrital mineral phases such as zircon, sanidine, hornblende, and rutile that current geochronology methods utilize. Here we present a new methodology for capturing the magmatic history of fine grained extrusive volcanic rocks using single grain detrital ⁴⁰Ar/³⁹Ar incremental heating geochronology. The DARL (or Detrital Argon Lithics) method thus far has consisted of ⁴⁰Ar/³⁹Ar total fusion analyses, which pose a problem in the case of Iceland, due to the nature of its young glassy lava flows commonly displaying subatmospheric ⁴⁰Ar/³⁶Ar isochron intercepts and low ⁴⁰Ar*. This work represents a ⁴⁰Ar/³⁹Ar incremental heating pilot study on 19 single grains of Icelandic river sand (1–3 mm), collected from five different catchments. Fifteen of the 19 basaltic grains produced concordant age experiments that ranged from 0.2 to 13.5 Ma and uncertainties (2σ) from 1 % to 86 % with the grains under 1 Ma having the largest uncertainties. Preliminary results show that basaltic grains with less alteration (and corresponding lower atmospheric argon concentration) yield more accurate age determinations, though altered basaltic grains can still produce statistically valid age determinations. Results presented here show the validity of the incremental heating DARL methodology for capturing the magmatic history of mafic terrains. The long analysis time required for incremental heating experiments makes it infeasible to produce the large number of ages required for a detrital study. For this reason, we propose combining the aspects of the total fusion and incremental heating DARL methodologies to acquire age data for the large N values needed for detrital studies while improving the accuracy of total fusion DARL analysis.