High-resolution geologic mapping of seafloor structures and identification of structural systematics

Two comprehensive geologic mapping projects, which were conducted in the eastern Manus Basin, Papua New Guinea, are the core of this dissertation. They provide new perspectives on the local geologic framework and distribution of hydrothermal discharge sites at felsic-hosted hydrothermal systems in an opening back-arc basin. Both mapped areas are interpreted as present-day analogs to volcanogenic massive sulfide (VMS) deposits preserved in the geologic record on land. Our results advance the knowledge of submarine volcanic eruption styles and related eruption products, the interplay of back-arc volcanism with the formation of VMS ore deposits and finally the spatial distribution and influence of hydrothermal activity at the resultant seafloor morphologies

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

Hochauflösende geologische Kartierung von Meeresbodenstrukturen und Identifikation von strukturellen Systematiken

Two comprehensive geologic mapping projects, which were conducted in the eastern Manus Basin, Papua New Guinea, are the core of this dissertation. They provide new perspectives on the local geologic framework and distribution of hydrothermal discharge sites at felsic-hosted hydrothermal systems in an opening back-arc basin. Both mapped areas are interpreted as present-day analogs to volcanogenic massive sulfide (VMS) deposits preserved in the geologic record on land. Our results advance the knowledge of submarine volcanic eruption styles and related eruption products, the interplay of back-arc volcanism with the formation of VMS ore deposits and finally the spatial distribution and influence of hydrothermal activity at the resultant seafloor morphologies

Volcanic Structures and Magmatic Evolution of the Vesteris Seamount, Greenland Basin

The formation of isolated seamounts distant from active plate boundaries and mantle plumes remains unsolved. The solitary intraplate volcano Vesteris Seamount is located in the Central Greenland Basin and rises ∼3,000 m above the seafloor with a total eruptive volume of ∼800 km3. Here, we present a new high-resolution bathymetry of Vesteris Seamount and a detailed raster terrain analysis, distinguishing cones, irregular volcanic ridges, volcanic debris fans, U-shaped channels and lava flows. The slope angles, ruggedness index and slope direction were combined with backscatter images to aid geologic interpretation. The new data show that the entire structure is a northeast to southwest elongated stellar-shaped seamount with an elongated, narrow summit surrounded by irregular volcanic ridges, separated by volcanic debris fans. Whole-rock geochemical data of 78 lava samples form tight liquid lines of descent with MgO concentrations ranging from 12.6 to 0.1 wt%, implying that all lavas evolved from a similar parental magma composition. Video footage from Remotely Operated Vehicle (ROV) dives shows abundant pyroclastic and hyaloclastite deposits on the summit and on the upper flanks, whereas lavas are restricted to flank cones. The seamount likely formed above a weak zone of the lithosphere possibly related to initial rifting parallel to the nearby Mohns Ridge, but the local stress field increasingly affected the structure of the volcano as it grew larger. Thus, we conclude that the evolution of Vesteris Seamount reflects the transition from deep, regional lithospheric stresses in the older structures to shallower, local stresses within the younger volcanic structures similar to other oceanic intraplate volcanoes. Our study shows how the combination of bathymetric, visual and geochemical data can be used to decipher the geological evolution of oceanic intraplate volcanoes.Peer reviewe

Multibeam bathymetry processed data (Kongsberg EM 712 working area dataset) of RV MARIA S. MERIAN during cruise MSM86

The hydroacoustic surveys carried out during MARIA S. MERIAN cruise MSM86 were aimed to acquire detailed information of the areas of interest (Boyd Seamount; Logi Ridge; Vesteris; Vestnesa Ridge) with respect to backscatter and bathymetry. The shallow to medium water Kongsberg EM 712 multibeam echosounder system was only operating in water depths above about 1000 m. Hydroacoustic surveys were usually conducted with a vessel speed of maximum 6 kn, while for some few sub-bottom profiles, a reduced speed of about 4 kn was applied. During transits the vessel speed was increased to 8-12 kn, depending on weather conditions. Sound velocity profiles were uploaded into the recording system online. Data has been processed according to the MB-System standard processing sequence

Multibeam bathymetry processed data (Kongsberg EM 122 working area dataset) of RV MARIA S. MERIAN during cruise MSM86

The hydroacoustic surveys carried out during MARIA S. MERIAN cruise MSM86 were aimed to acquire detailed information of the areas of interest (Boyd Seamount; Logi Ridge; Vesteris; Vestnesa Ridge) with respect to backscatter and bathymetry. During MARIA S. MERIAN cruise MSM86, the Kongsberg EM 122 multibeam echosounder was operating almost continuously. Hydroacoustic surveys were usually conducted with a vessel speed of maximum 6 kn, while for some few sub-bottom profiles, a reduced speed of about 4 kn was applied. During transits the vessel speed was increased to 8-12 kn, depending on weather conditions. Sound velocity profiles were uploaded into the recording system online. Data has been processed according to the MB-System standard processing sequence

Geologic setting of PACManus hydrothermal area — High resolution mapping and in situ observations

Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Marine Geology 355 (2014): 98-114, doi:10.1016/j.margeo.2014.05.011.This study presents a systematic analysis and interpretation of autonomous underwater vehicle-based microbathymetry combined with remotely operated vehicle (ROV) video recordings, rock analyses and temperature measurements within the PACManus hydrothermal area located on Pual Ridge in the Bismarck Sea of eastern Manus Basin. The data obtained during research cruise Magellan-06 and So-216 provides a framework for understanding the relationship between the volcanism, tectonism and hydrothermal activity. PACManus is a submarine felsic vocanically-hosted hydrothermal area that hosts multiple vent fields located within several hundred meters of one another but with different fluid chemistries, vent temperatures and morphologies. The total area of hydrothermal activity is estimated to be 20,279 m2. The microbathymetry maps combined with the ROV video observations allow for precise high-resolution mapping estimates of the areal extents of hydrothermal activity. We find the distribution of hydrothermal fields in the PACManus area is primarily controlled by volcanic features that include lava domes, thick and massive blocky lava flows, breccias and feeder dykes. Spatial variation in the permeability of local volcanic facies appears to control the distribution of venting within a field. We define a three-stage chronological sequence for the volcanic evolution of the PACManus based on lava flow morphology, sediment cover and lava SiO2 concentration. In Stage-1, sparsely to moderately porphyritic dacite lavas (68 - 69.8 wt. % SiO2) erupted to form domes or cryptodomes. In Stage-2, aphyric lava with slightly lower SiO2 concentrations (67.2 – 67.9 wt. % SiO2) formed jumbled and pillowed lava flows. In the most recent phase Stage-3, massive blocky lavas with 69 to 72.5 wt. % SiO2 were erupted through multiple vents constructing a volcanic ridge identified as the PACManus neovolcanic zone. The transition between these stages may be gradual and related to progressive heating of a silicic magma following a recharge event of hot, mantle-derived melts.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