Working group proposal on Oceanic Transform Faults
Leading proponents and contacts:
Marcia Maia (marcia.maia@univ-brest.fr), France, geophysics, tectonics
Barry Hanan (bbhanan@mail.sdsu.edu), USA, isotope geochemistry
Daniele Brunelli (daniele.brunelli@unimore.it), Italy, petrology
WG co-proponents:
Diane Arcay, France, geophysics (subduction models)
Marco Cuffaro, Italy, geophysics (models)
Colin Devey, Germany, geochemistry, petrology
Joao Duarte, Portugal, tectonics, analogue models
Laurent Geoffroy, France, tectonics (passive margins)
Cédric Hamelin, Norway, isotope geochemistry
Seung-Sep Kim, Korea, geophysics
Serge Lallemand, France, tectonics (subduction)
Marco Ligi, Italy, geophysics
Christine Meyzen, Italy, petrology, geochemistry
Eric Mittelstaedt, USA, geophysics (models)
Ingo Grevemeyer, Germany, geophysics
Sven Petersen, Germany, hydrothermalism
Lars Ruepke, Germany, geophysics (models)
Pedro Terrinha, Portugal, tectonics, geophysics
Scientific objectives:
Transform faults, especially large-offset ones, have been thoroughly investigated by different teams around the world (e.g., Bonatti et al., 1979; Bonatti, 1978; Karson and Dick, 1983; Sinha and Louden, 1983; Detrick et al., 1982; Cormier et al., 1984; ten Brink and Brocher, 1988; Tucholke and Schouten, 1988; Detrick et al., 1993; Wolfe et al., 1993; Bonatti et al., 1994; Mueller et al., 2000; Bonatti et al., 2005). From their work, we derived the vision of transform faults as complex plate boundaries that could deform under the influence of far field stresses, especially changes in plate motion (e.g. Bonatti et al., 1994; Gasperini et al., 2001). However, not all transforms react equally to equivalent stress changes, suggesting the influence of parameters such as offset length, spreading rates and mantle temperature and heterogeneities (e.g. Fornari et al., 1989; Michael et al., 1994; Pockalny et al., 1997; Bonatti et al., 2003; Maia et al., 2016). Furthermore, together with numerical models, observational studies also reveal the role of transform faults in shaping the geometry of mantle flow and active processes at mid-oceanic ridge axes (e.g. Bonatti et al., 2001 & 2003; Ligi et al, 2008; Cipriani et al., 2009; Gregg et al., 2009). Many of the above processes are most evident at the extreme limits of spreading rate and transform offset size. For example, at slow and ultra-slow spreading ridges, the notion of mega transforms was applied to the large-offset Romanche and Andrew Bain transforms to explain their particularly complex morphologies, which reflect complex evolution of the transform domain through time. In contrast to most oceanic transform boundaries that consist of a single narrow strike-slip zone offsetting two mid-ocean ridge segments, the slowly slipping Romanche and Andrew Bain transforms are characterized by a broad and complex multifault zone of deformation similar to some continental strike-slip systems (Ligi et al., 2002; Sclater et al., 2005). Such faulting system may act as pathways for seawater and allow for extensive fluid-rock interactions. Oceanic transform faults and fracture zones have long been hypothesized to be sites of enhanced fluid flow and biogeochemical exchange (Boschi et al., 2013; Detrick et al., 1993; Francis, 1981; Gregg et al., 2007; Roland et al., 2010). In this context, the serpentine forming interaction between seawater and cold lithospheric mantle rocks is particularly interesting. The transformation of peridotite to serpentinite not only leads to hydration of oceanic plates and is thereby an important agent of the geological water cycle (Rupke et al., 2004), it is also a mechanism of abiotic hydrogen and methane formation (McCollom and Bach, 2009; Seyfried Jr et al., 2007), which in the present seafloor support archeal and bacterial communities (Kelley et al., 2005; Perner et al., 2007; Shock and Holland, 2004). Inferring the likely amount of mantle undergoing serpentinization reactions therefore allows estimating the amount of biomass that may be autotrophically produced at and around oceanic transform faults and mid-ocean ridges (Cannat et al., 2010). Although the above studies have advanced our understanding of the enormous complexity of these major plate boundaries and their role on fundamental processes building the oceanic lithosphere, such as fluid circulation, mantle exhumation and mantle flow, several questions remain to be addressed because they require a joint effort of different communities such as geochemists, petrologists, geophysicists, microbiologists, fluid and numerical modeling specialists. This working group, would like to focus on five questions that are likely of large interest to the Earth sciences community:
- How do large and mega- transform domains react to both far- and near-field stress changes?
- How do transforms interact with the underlying mantle. What are the effects of temperature, rheology and composition?
- What is the interplay between transform dynamics and magmatism?
- Which relationship exist between oceanic transform faults and their counterparts on continental margins?
- Are oceanic transform faults sites of intense fluid-rock interaction and biogeochemical exchange?
Organization:
The working group is composed of researchers with different specialties, spanning from structural geology to geochemistry and modeling. Specialists on subduction processes and on continental margins enlarge the scope of the group beyond the ridge community. The aim of this working group is to create a collaborative dynamic among different specialties and different communities in order to develop innovative and ambitious research projects on transform faults and fracture zones. Broadly, in the frame of this working group we intend:
- to exploit the large amount of available data on transform faults and fracture zones through collaborative research projects and the writing of synthesis papers;
- to improve the modeling approach through exchanges between different research groups as well as the joint work between model specialists and other specialties, such as tectonics, geochemistry and petrology;
- to target areas that would be “example systems”, where new data should be acquired in order to answer the above questions and proceed to develop multi-cruise large international operations.
We intend to organize a first meeting at the AGU Fall session this year with the colleagues that will attend in order to start the group work and organize the first group workshop, to be held in 2018. As a first goal, this workshop will aim on making a synthesis of knowledge about transforms and fracture zones, including comparative views of the main studied systems. One of the first outcomes will be synthesis papers to be submitted to journals such as Earth Science Reviews. This is an important goal as these review papers are widely used by researchers and students. This work will also allow clarifying and establishing priorities for future research targets. The first workshop will also build the basis upon which international cruise proposals can be developed. We plan a second workshop in 2021 where we will discuss the on-going new projects (new model approaches, new cruises and inter-disciplinary projects) and evaluate the advances the working group dynamics was able to trigger. This workshop will be the final one. Between the first and the second workshops, we plan to hold regular meetings at the main international meetings (EGU, AGU) to insure a follow-up of the working group actions.
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