Project

marine hydrothermal systems; isotopes; Ligurian ophiolites; carbonate precipitation; fluid fluxes; Mid-Atlantic Ridge; strontium; carbonate precipitation; ODP/IODP; Lost City; serpentinization; detachment faulting

Lead
Entlang gewisse mittelozeanische Rücken (z.B. im Atlantik Ozean) werden ultramafische Gesteine (Bestandteile des oberen Erdmantels) durch grosse Abscherungsbrüche (sogenannte Detachment Faults) am Meeresgrund verfrachtet. Diese grosse Deformationszonen lassen Meerwasser in die Gesteine eindringen und führen zur Serpentinisierung (Hydrationsreaktionen in Mantelgesteinen), zur Freisetzung von H2- und CH4-reiche Fluiden, und zur Bildung von hoch- und tief-Temperatur hydrothermale Systeme.
Lay summary
Inhalt und Ziel des Forschungsprojekts Serpentinisierung ist ein wesentlicher Prozess, welche entscheidende geophysikalische, geochemische und biologische Auswirkungen auf das globale marine System hat. In den Alpen und Apenninen findet man Überreste der ozeanischen Lithosphäre der Tethys in Jurassichen Ophiolitsequenzen, wo Umwandlungs- und Deformationsprozesse untersucht werden können. Unser Projekt ist eine Fortsetzung des SNF Projekts Nr. 200021-134947 und ist Bestandteil der Doktorarbeit von Monica Vogel. Unser Ziel ist es, die Zusammenhängen zwischen Alterationsprozessen, Deformation und hydrothermale Ablagerungen (Sulfide und Karbonate) in den Bracco-Levanto and Val Graveglia Ophiolit-Komplexen (Italien) zu untersuchen, und diese mit moderne hydrothermale Prozessen entlang der Mittelatlantischer Rücken zu vergleichen. Wir werden petrologische, geochemische und isotopische (Sr, O, C) Analysen durchführen, um Fluidbahnen und chemischen Austausch zu quantifizieren und um zu einem verbesserten Verständnis der Rolle von Abscherungsprozessen für hoch- und tief-temperatur hydrothermale Aktivität beizutragen.   Wissenschaftlicher Kontext des Forschungsprojekts Unsere Arbeit wird neue und wichtige Informationen über die Entwicklung von hydrothermalen Systemen in Serpentiniten liefern und wird dazu beitragen, ausführliche, integrierte Modelle über hydrothemale Zirkulation in mafische und ultramafische Gesteinen entlang Mittelozeanischen Rücken zu entwickeln.

Direct link to Lay Summary

Last update: 25.03.2013

Lead
Ultramafic rocks are tectonically emplaced along major, large-scale offset normal faults (detachment faults) and are important components of the seafloor at slow spreading ridges. In these environments oceanic detachment faults lead to the formation of oceanic core complexes, which are characterized by extensive exposure of gabbro and serpentinized mantle rocks. Detachment faults zones also provide conditions for fluid flow and hydrothermal systems with varying temperatures of venting.
Lay summary
The interaction of seawater with mantle rocks exposed on the seafloor results in serpentinization, which is a fundamental process that has geophysical, geochemical and biological importance for the global marine system and for subduction zone processes. A number of the Tethyan ophiolites in the Alps and northern Apennines are now considered relicts of oceanic lithosphere and contain lower crustal and upper mantle sequences that are believed to have been exposed by detachment faults onto the seafloor. This project is a continuation of SNF project No 200021-134947 (2011-2013) to complete the PhD thesis work of Monica Vogel. The aim of this project is to study the links among fluid-rock interaction, hydrothermal deposits and deformation processes recorded in the Jurassic Bracco-Levanto and Val Graveglia ophiolite complexes in Liguria (Italy) and to compare these processes to modern oceanic hydrothermal systems hosted in ultramafic and gabbroic rocks along the Mid-Atlantic Ridge (MAR). We will conduct petrological, major element, trace element and isotopic (O, C, Sr) analyses of basement rocks and the hydrothermal deposits in Liguria to investigate fluid flow paths, mass transfer, and fluid fluxes during high and low temperature hydrothermal activity, with emphasis on processes leading to the formation of carbonate-vein systems in serpentinites, so-called ophicalcites. We will compare these data to new and published data from the MAR and from the Lost City hydrothermal field. This comparative study will provide a better understanding of evolving, subsurface processes in serpentinite-hosted hydrothermal systems and will contribute to a comprehensive, integrated model of end-member hydrothermal systems in oceanic sequences formed at slow spreading ridge environments.

Direct link to Lay Summary

Last update: 25.03.2013

Active participation

Number	Title	Start	Funding scheme

Ultramafic rocks are tectonically emplaced along major, large-scale offset normal faults (detachment faults) and are important components of the seafloor at slow spreading ridges. In these environments oceanic detachment faults lead to the formation of oceanic core complexes (OCCs), characterized by extensive exposure of gabbro and serpentinized mantle, and provide conditions for fluid flow and hydrothermal systems with varying temperatures of venting. Mantle rocks exposed on the seafloor constitute a highly reactive chemical and thermal system, in which interaction with seawater to produce serpentinite has major consequences for lithospheric cooling, global geochemical cycles, and microbial activity. A number of the Tethyan ophiolites in the Alps and northern Apennines are now considered relicts of oceanic lithosphere formed in these environments and contain lower crustal and upper mantle sequences that are believed to be exposed by detachment faults onto the seafloor. This project is a continuation of SNF project No 200021-134947 (2011-2013) to complete the PhD thesis work of Monica Vogel. The aim of this project is to study the links among fluid-rock interaction, hydrothermal deposits and deformation processes recorded in the Jurassic Bracco-Levanto and Val Graveglia ophiolite complexes in Liguria (Italy) and to compare these processes to modern oceanic hydrothermal systems hosted in ultramafic rocks along the Mid-Atlantic Ridge (MAR). A focus will be on investigating fluid flow paths, mass transfer, and fluid fluxes during high and low temperature hydrothermal activity, with emphasis on processes leading to the formation of carbonate-vein systems in serpentinites, so-called ophicalcites. Our project targets two distinct temperature regimes that represent different stages of hydrothermal circulation during the evolution of the Jurassic seafloor: (1) low temperature alteration, carbonate precipitation and deformation in serpentinites and ophicalcites exposed in quarries; and (2) high temperature alteration in serpentinites and gabbros, locally resulting in massive sulfide deposits. We will conduct petrological, major element, trace element and isotopic (O, C, Sr) analyses of basement rocks and the hydrothermal deposits in Liguria and will compare these data to new and published data from the MAR and from the Lost City hydrothermal field. Lost City is unlike all known marine hydrothermal systems: it hosts extensive carbonate-brucite structures that are deposited from 25-90°C, high pH (9-11) fluids emanating from fault zones, which tap a region of active serpentinization in mantle peridotites that have been uplifted through detachment faulting during formation of the Atlantis Massif as an oceanic core complex.This comparative study will provide a better understanding of evolving, subsurface processes in serpentinite-hosted hydrothermal systems and will contribute to a comprehensive, integrated model of end-member hydrothermal systems in oceanic sequences formed at slow spreading ridge environments. The collected data will compliment a wealth of data available from previous studies of Lost City and will further allow us to test the hypothesis that the Lost City vent field is a modern analogue for hydrothermal processes that produced ancient ophicalcites. In addition, the proposed project will allow us to test the hypotheses that the Bracco-Levanto and Val Graveglia ophiolite complexes were formed in a similar setting to many OCCs and preserve records of variable temperature hydrothermal activity similar to present-day systems along the MAR.