The Trans-Atlantic Geotraverse hydrothermal field : a hydrothermal system on an active detachment fault

© The Author(s), 2015. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 121 (2015): 8-16, doi:10.1016/j.dsr2.2015.02.015.Over the last ten years, geophysical studies have revealed that the Trans-Atlantic Geotraverse (TAG) hydrothermal field (26°08’N on the Mid-Atlantic Ridge) is located on the hanging wall of an active detachment fault. This is particularly important in light of the recognition that detachment faulting accounts for crustal accretion/extension along a significant portion of the Mid-Atlantic Ridge, and that the majority of confirmed vent sites on this slow-spreading ridge are hosted on detachment faults. The TAG hydrothermal field is one of the largest sites of high-temperature hydrothermal activity and mineralization found to date on the seafloor, and is comprised of active and relict deposits in different stages of evolution. The episodic nature of hydrothermal activity over the last 140 ka provides strong evidence that the complex shape and geological structure of the active detachment fault system exerts first order, but poorly understood, influences on the hydrothermal circulation patterns, fluid chemistry, and mineral deposition. While hydrothermal circulation extracts heat from a deep source region, the location of the source region at TAG is unknown. Hydrothermal upflow is likely focused along the relatively permeable detachment fault interface at depth, and then the high temperature fluids leave the low-angle portion of the detachment fault and rise vertically through the highly fissured hanging wall to the seafloor. The presence of abundant anhydrite in the cone on the summit of the TAG active mound and in veins in the crust beneath provides evidence for a fluid circulation system that entrains significant amounts of seawater into the shallow parts of the mound and stockwork. Given the importance of detachment faulting for crustal extension at slow spreading ridges, the fundamental question that still needs to be addressed is: How do detachment fault systems, and the structure at depth associated with these systems (e.g., presence of plutons and/or high permeability zones) influence the pattern of hydrothermal circulation, mineral deposition, and fluid chemistry, both in space and time, within slowly accreted ocean crust?We acknowledge the National Science Foundation which has supported our research at the TAG hydrothermal field through many awards for cruises, technological advancement of equipment, analytical, and modeling work.2016-02-2

Investigation of a marine magnetic polarity reversal boundary in cross section at the northern boundary of the Kane Megamullion, Mid-Atlantic Ridge, 23°40′N

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 121 (2016): 3161–3176, doi:10.1002/2016JB012928.Near-bottom magnetic field measurements made by the submersible Nautile during the 1992 Kanaut Expedition define the cross-sectional geometry of magnetic polarity reversal boundaries and the vertical variation of crustal magnetization in lower oceanic crust exposed along the Kane Transform Fault (TF) at the northern boundary of the Kane Megamullion (KMM). The KMM exposes lower crust and upper mantle rocks on a low-angle normal fault that was active between 3.3 Ma and 2.1 Ma. The geometry of the polarity boundaries is estimated from an inversion of the submarine magnetic data for crustal magnetization. In general, the polarity boundaries dip away from the ridge axis along the Kane TF scarp, with a west dipping angle of ~45° in the shallow (<1 km) crust and <20° in the deeper crust. The existence of the magnetic polarity boundaries (e.g., C2r.2r/C2An.1n, ~2.581 Ma) indicates that the lower crustal gabbros and upper mantle serpentinized peridotites are able to record a coherent magnetic signal. Our results support the conclusion of Williams (2007) that the lower crust cools through the Curie temperature of magnetite to become magnetic, with the polarity boundaries representing both frozen isotherms and isochrons. We also test the effects of the rotation of this isotherm structure and/or footwall rotation and find that the magnetic polarity boundary geometry is not sensitive to these directional changes.2016-11-1

Behaviour change interventions to influence antimicrobial prescribing: a cross-sectional analysis of reports from UK state-of-the-art scientific conferences

Background To improve the quality of antimicrobial stewardship (AMS) interventions the application of behavioural sciences supported by multidisciplinary collaboration has been recommended. We analysed major UK scientific research conferences to investigate AMS behaviour change intervention reporting. Methods Leading UK 2015 scientific conference abstracts for 30 clinical specialties were identified and interrogated. All AMS and/or antimicrobial resistance(AMR) abstracts were identified using validated search criteria. Abstracts were independently reviewed by four researchers with reported behavioural interventions classified using a behaviour change taxonomy. Results Conferences ran for 110 days with >57,000 delegates. 311/12,313(2.5%) AMS-AMR abstracts (oral and poster) were identified. 118/311(40%) were presented at the UK’s infectious diseases/microbiology conference. 56/311(18%) AMS-AMR abstracts described behaviour change interventions. These were identified across 12/30(40%) conferences. The commonest abstract reporting behaviour change interventions were quality improvement projects [44/56 (79%)]. In total 71 unique behaviour change functions were identified. Policy categories; “guidelines” (16/71) and “service provision” (11/71) were the most frequently reported. Intervention functions; “education” (6/71), “persuasion” (7/71), and “enablement” (9/71) were also common. Only infection and primary care conferences reported studies that contained multiple behaviour change interventions. The remaining 10 specialties tended to report a narrow range of interventions focusing on “guidelines” and “enablement”. Conclusion Despite the benefits of behaviour change interventions on antimicrobial prescribing, very few AMS-AMR studies reported implementing them in 2015. AMS interventions must focus on promoting behaviour change towards antimicrobial prescribing. Greater focus must be placed on non-infection specialties to engage with the issue of behaviour change towards antimicrobial use

Manus 2006 : hydrothermal systems in the Eastern Manus Basin: fluid chemistry and magnetic structure as guides to subseafloor processes

Cruise Report R/V Melville MAGELLAN-06, Rabaul, Papua New Guinea to Suva, Fiji July 21st 2006 to September 1st 2006The hydrothermal systems in the Manus Basin of Papua New Guinea (PNG) were comprehensively investigated through a combination of sampling and mapping using the Remotely-Operated Vehicle (ROV) Jason, the autonomous underwater vehicle (AUV) ABE (Autonomous Benthic Explorer) and ship-based CTD work and multi-beam bathymetric mapping using the RV Melville. The objectives of the cruise (July 21st to Sept. 1st, 2006) were to identify the tectonic/geologic settings of the vent systems, examine the interactions of seawater with felsic rocks that constitute the high silica end-member range of seafloor basement compositions, determine the extent of volatile magmatic inputs into these systems and to examine the evolution of hydrothermal activity through time. The first 10-day portion of the cruise was funded by Nautilus Minerals in a collaborative research effort to examine the Manus Spreading Center and the Vienna Woods basalt-hosted hydrothermal vent systems. The second 32-day portion of the cruise, funded by the National Science Foundation (NSF), focused on the felsic-hosted hydrothermal systems of the PACMANUS (Papua New Guinea – Australia – Canada Manus) vents drilled by the Ocean Drilling Program (ODP) in 2000 and the nearby seafloor volcano vent systems of Desmos and SuSu Knolls. Nautilus Minerals generously funded the add-on use of ABE throughout the NSF program allowing for high resolution mapping to be completed on all the major vent sites within the eastern Manus Basin. A total of 30 ROV dives (497 operational hours) were completed collecting 198 vent sulfides, 83 altered substrate and 43 fresh lava samples along with 104 black, gray and clear fluid samples using gastight and major samplers. ABE successfully completed 14 high resolution bathymetric, CTD and magnetic field mapping dives covering a total of 364 line km of seafloor. We located and mapped in detail the Vienna Woods and nearby Tufar-2 and -3 vent areas on Manus Spreading Center documenting the strong tectonic control on the distribution of the vent systems and the presence of reduced magnetization i.e. “magnetic burnholes”, that help define the lateral extent of the vent fields. The Vienna Woods vent systems (273°-285°C) form treetrunk- like chimneys 5-15 m tall, that emit black to gray fluids with pH and compositions similar to other documented midocean ridge (MOR) systems like the East Pacific Rise. At PACMANUS, high-resolution mapping by ABE reveals a distinctive seafloor morphology associated with dacitic lava flows along with discrete magnetic burnholes associated with the active venting systems of Roman Ruins, Satanic Mills, Snowcap, Tsukushi and a new vigorous vent system discovered southeast of the Satanic Mills area named Fenway. Another vent field in its waning stages was also discovered ~8 km northeast of PACMANUS on the Northeast Pual Ridge. At PACMANUS, the 40 m diameter Fenway mound hosts outcrops of massive anhydrite on the seafloor beneath the sulfide chimneys, a rare occurrence as anhydrite is unstable at ambient seafloor conditions. Fenway is also boiling (356°C, 172 bar) with two-phase fluid producing a ”flashing” phenomenon when the Jason lights illuminated the vent orifices. The five PACMANUS vents (271° – 356°C) have ubiquitous low pH (2.3 to 2.8) relative to Vienna Woods and typical MOR fluids, presumably reflecting water-rock reaction with the felsic hosted lava, input of magmatic volatiles and the subsurface deposition of metal sulfides. We investigated two strongly magmatically influenced vent systems associated with seafloor volcanoes. Desmos is a breached caldera with white smokers (70°-115°C) that are highly acidic (pH 1 – 1.5) and sulfur lava flows. SuSu Knolls and the adjacent Suzette mound (Solwara-1 of Nautilus Minerals) were mapped in detail and sampled intensively. Hydrothermal activity at SuSu Knolls showed a remarkable range from boiling black smokers to white sulfur-rich fluids, native sulfur flows and massive anhydrite outcrops. Vent fluids from North Su (48° – 325°C) are 2 characterized by a measured pH of 0.87, more than an order of magnitude more acidic than any deep-sea vent fluid sampled to date. Many of the low pH fluids sampled at North Su and Desmos were actively precipitating native sulfur creating thick plumes of dense white smoke. In general, sampled fluids show a considerable range in pH and gas contents, sometimes within individual hydrothermal fields. The pronounced variability of fluid chemistry within 10’s to 100’s of m at North Su is probably unparalleled in systems studied to date. The most plausible explanation for the observed variability is that different fluid-rock reaction pathways are expressed in regimes of variable magmatic volatile input and extent of subsurface cooling. This hypothesis is supported by the distribution of alteration types at the seafloor, where the occurrence of advanced argillic alteration - that relates to interactions with acid-sulfate waters such as sampled at Desmos and North Su – is patchy and spatially confined to patches of active (Desmos, North Su) and past (Snowcap) venting of such fluids. In relationship to the ODP drilling results at PACMANUS we identified and sampled examples of advanced argillic rock alteration similar to that seen in the drill core. Good examples came from Snowcap and from the North Su pillar. We sampled highly clay-altered basement from just underneath extinct chimney complexes at two locations in the Satanic Mills hydrothermal field. Both samples have dense networks of sulfide veins and may represent the stockwork or feeder zone through which hydrothermal fluids rise up to the seafloor. These samples, in addition to the other altered rock types recovered, will provide useful stepping stones in bridging the knowledge gap between the extensive surface sampling now accomplished and the basement rocks recovered by ODP, where coring was almost nil shallower than 40 m subseafloor depth. Overall, the quality and quantity of solid and fluid samples that can be put in a direct geochemical context is remarkably high. This unique dataset encompasses a broad range of geological environments that includes hydrothermal activity in basalt-hosted oceanic style spreading centers to hydrothermal systems associated with arc-style volcanism. For the first time, alteration assemblages that are commonly observed in drillcore and outcrop on land have been observed in the aqueous environment responsible for their formation.NSF Grant – OCE0327448; NSF Grant – OCE042559

A new middle to late Jurassic Geomagnetic Polarity Time Scale (GPTS) from a multiscale marine magnetic anomaly survey of the Pacific Jurassic Quiet Zone

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 126(3), (2021): e2020JB021136, https://doi.org/10.1029/2020JB021136.The Geomagnetic Polarity Time Scale (GPTS) provides a basis for the geological timescale, quantifies geomagnetic field behavior, and gives a time framework for geologic studies. We build a revised Middle to Late Jurassic GPTS by using a new multiscale magnetic profile, combining sea surface, midwater, and autonomous underwater vehicle near-bottom magnetic anomaly data from the Hawaiian lineation set in the Pacific Jurassic Quiet Zone (JQZ). We correlate the new profile with a previously published contemporaneous magnetic sequence from the Japanese lineation set. We then establish geomagnetic polarity block models as a basis for our interpretation of the origin and nature of JQZ magnetic anomalies and a GPTS. A significant level of coherency between short-wavelength anomalies for both the Japanese and Hawaiian lineation magnetic anomaly sequences suggests the existence of a regionally coherent field during this period of rapid geomagnetic reversals. Our study implies the rapid onset of the Mesozoic Dipole Low from M42 through M39 and then a subsequent gradual recovery in field strength into the Cenozoic. The new GPTS, together with the Japanese sequence, extends the magnetic reversal history from M29 back in time to M44. We identify a zone of varying, difficult-to-correlate anomalies termed the Hawaiian Disturbed Zone, which is similar to the zone of low amplitude, difficult-to-correlate anomalies in the Japanese sequence termed the Low Amplitude Zone (LAZ). We suggest that the LAZ, bounded by M39–M41 isochrons, may in fact represent the core of what is more commonly known as the JQZ crust.This study is funded by National Science Foundation grants OCE-1029965 (Tominaga, Tivey, and Lizarralde) and OCE-1233000 (Tominaga and Tivey) and OCE-1029573 (Sager).2021-07-2

Magnetic Mineral Populations in Lower Oceanic Crustal Gabbros (Atlantis Bank, SW Indian Ridge): Implications for Marine Magnetic Anomalies

To learn more about magnetic properties of the lower ocean crust and its contributions to marine magnetic anomalies, gabbro samples were collected from International Ocean Discovery Program Hole U1473A at Atlantis Bank on the Southwest Indian Ridge. Detailed magnetic property work links certain magnetic behaviors and domain states to specific magnetic mineral populations. Measurements on whole rocks and mineral separates included magnetic hysteresis, first‐order reversal curves, low‐temperature remanence measurements, thermomagnetic analysis, and magnetic force microscopy. Characteristics of the thermomagnetic data indicate that the upper ~500 m of the hole has undergone hydrothermal alteration. The thermomagnetic and natural remanent magnetization data are consistent with earlier observations from Hole 735B that show remanence arises from low‐Ti magnetite and that natural remanent magnetizations are up to 25 A m−1 in evolved Fe‐Ti oxide gabbros, but are mostly \u3c1 A m−1. Magnetite is present in at least three forms. Primary magnetite is associated with coarse‐grained oxides that are more frequent in the upper part of the hole. This magnetic population is linked to dominantly “pseudo‐single‐domain” behavior that arises from fine‐scale lamellar intergrowths within the large oxides. Deeper in the hole the magnetic signal is more commonly dominated by an interacting single‐domain assemblage most likely found along crystal discontinuities in olivine and/or pyroxene. A third contribution is from noninteracting single‐domain inclusions within plagioclase. Because the concentration of the highly magnetic, oxide‐rich gabbros is greatest toward the surface, the signal from coarse oxides will likely dominate the near‐bottom magnetic anomaly signal at Atlantis Bank

Magnetic mineral populations in lower oceanic crustal gabbros (Atlantis Bank, SW Indian Ridge): implications for marine magnetic anomalies

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 21(3), (2020): e2019GC008847, doi:10.1029/2019GC008847.To learn more about magnetic properties of the lower ocean crust and its contributions to marine magnetic anomalies, gabbro samples were collected from International Ocean Discovery Program Hole U1473A at Atlantis Bank on the Southwest Indian Ridge. Detailed magnetic property work links certain magnetic behaviors and domain states to specific magnetic mineral populations. Measurements on whole rocks and mineral separates included magnetic hysteresis, first‐order reversal curves, low‐temperature remanence measurements, thermomagnetic analysis, and magnetic force microscopy. Characteristics of the thermomagnetic data indicate that the upper ~500 m of the hole has undergone hydrothermal alteration. The thermomagnetic and natural remanent magnetization data are consistent with earlier observations from Hole 735B that show remanence arises from low‐Ti magnetite and that natural remanent magnetizations are up to 25 A m−1 in evolved Fe‐Ti oxide gabbros, but are mostly <1 A m−1. Magnetite is present in at least three forms. Primary magnetite is associated with coarse‐grained oxides that are more frequent in the upper part of the hole. This magnetic population is linked to dominantly “pseudo‐single‐domain” behavior that arises from fine‐scale lamellar intergrowths within the large oxides. Deeper in the hole the magnetic signal is more commonly dominated by an interacting single‐domain assemblage most likely found along crystal discontinuities in olivine and/or pyroxene. A third contribution is from noninteracting single‐domain inclusions within plagioclase. Because the concentration of the highly magnetic, oxide‐rich gabbros is greatest toward the surface, the signal from coarse oxides will likely dominate the near‐bottom magnetic anomaly signal at Atlantis Bank.This work used samples and data provided by the International Ocean Discovery Program. Funding was provided by the U.S. Science Support Program (J.B.). I.L. has benefited from a Smithsonian Edward and Helen Hintz Secretarial Scholarship. We thank the members of the IODP Expedition 360 Science Party, and the captain and crew of the JOIDES Resolution. Part of this work was done as a Visiting Fellow at the Institute for Rock Magnetism (IRM) at the University of Minnesota. The IRM is made possible through the Instrumentation and Facilities program of the National Science Foundation, Earth Sciences Division, and by funding from the University of Minnesota. We would like to thank IRM staff M. Jackson, P. Solheid, and D. Bilardello for their generous assistance. Many thanks to A. Butula, K. Vernon, and J. Marquardt for their assistance with rock magnetic measurements at UWM and to L. McHenry for assistance with XRD. We also thank two anonymous reviewers for their thoughtful comments that improved the manuscript. Magnetic data associated with this manuscript are available in the Magnetics Information Consortium (MagIC) database at https://www.earthref.org/MagIC/doi/10.1029/2019GC008847. XRD data are available at https://zenodo.org/record/3611642.2020-08-2

Nature of the Jurassic Magnetic Quiet Zone

Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 42 (2015): 8367–8372, doi:10.1002/2015GL065394.The nature of the Jurassic Quiet Zone (JQZ), a region of low-amplitude oceanic magnetic anomalies, has been a long-standing debate with implications for the history and behavior of the Earth's geomagnetic field and plate tectonics. To understand the origin of the JQZ, we studied high-resolution sea surface magnetic anomalies from the Hawaiian magnetic lineations and correlated them with the Japanese magnetic lineations. The comparison shows the following: (i) excellent correlation of anomaly shapes from M29 to M42; (ii) remarkable similarity of anomaly amplitude envelope, which decreases back in time from M19 to M38, with a minimum at M41, then increases back in time from M42; and (iii) refined locations of pre-M25 lineations in the Hawaiian lineation set. Based on these correlations, our study presents evidence of regionally and possibly globally coherent pre-M29 magnetic anomalies in the JQZ and a robust extension of Hawaiian isochrons back to M42 in the Pacific crust.National Science Foundation Grant Numbers: OCE-1029965, OCE-1233000, OCE-10295732016-04-2

Subaqueous cryptodome eruption, hydrothermal activity and related seafloor morphologies on the andesitic North Su volcano

© The Author(s), 2016. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Volcanology and Geothermal Research 323 (2016): 80-96, doi:10.1016/j.jvolgeores.2016.04.041.North Su is a double-peaked active andesite submarine volcano located in the eastern Manus Basin of the Bismarck Sea that reaches a depth of 1154 m. It hosts a vigorous and varied hydrothermal system with black and white smoker vents along with several areas of diffuse venting and deposits of native sulfur. Geologic mapping based on ROV observations from 2006 and 2011 combined with morphologic features identified from repeated bathymetric surveys in 2002 and 2011 document the emplacement of a volcanic cryptodome between 2006 and 2011. We use our observations and rock analyses to interpret an eruption scenario where highly viscous, crystal-rich andesitic magma erupted slowly into the water-saturated, gravel-dominated slope of North Su. An intense fragmentation process produced abundant blocky clasts of a heterogeneous magma (olivine crystals within a rhyolitic groundmass) that only rarely breached through the clastic cover onto the seafloor. Phreatic and phreatomagmatic explosions beneath the seafloor cause mixing of juvenile and pre-existing lithic clasts and produce a volcaniclastic deposit. This volcaniclastic deposit consists of blocky, non-altered clasts next, variably (1-100 %) altered clasts, hydrothermal precipitates and crystal fragments. The usually applied parameters to identify juvenile subaqueous lava fragments, i.e. fluidal shape or chilled margin, were not applicable to distinguish between pre-existing non-altered clasts and juvenile clasts. This deposit is updomed during further injection of magma and mechanical disruption. Gas-propelled turbulent clast-recycling causes clasts to develop variably rounded shapes. An abundance of blocky clasts and the lack of clasts typical for the contact of liquid lava with water is interpreted to be the result of a cooled, high-viscosity, crystal-rich magma that failed as a brittle solid upon stress. The high viscosity allows the lava to form blocky and short lobes. The pervasive volcaniclastic cover on North Su is partly cemented by hydrothermal precipitates. These hydrothermally-cemented breccias, crusts and single pillars show that hydrothermal circulation through a thick layer of volcaniclastic deposits can temporarily increase slope stability through precipitation and cementation.The RV Melville work was funded by a combination of the US National Science Foundation grant OCE-0327448 and a collaborative research funding grant from Nautilus Minerals for the ABE surveys. The RV Sonne research cruise was funded through the BMBF (Grant G03216a). Additional funding, including salary support for JT, was provided by the German DFG Research Centre/Excellence Cluster ―The Ocean in the Earth System‖. WB acknowledges support from DFG research grant BA1605/4-1.2018-05-1