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Isotopic and petrological evidence of fluid-rock interaction at a Tethyan ocean-continent transition in the Alps: implications for tectonic processes and carbon transferduring early ocean formation
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
2007 (English)In: Geofluids, ISSN 1468-8115, E-ISSN 1468-8123, Vol. 7, no 4, 401-414 p.Article in journal (Refereed) Published
Abstract [en]

We report overprinting stable isotope evidence of fluid–rock interaction below two detachment faults along which mantle rocks were exhumed to the seafloor, between the respective landward and seaward limits of oceanic and continental crust, at a Tethyan ocean–continent transition (OCT). This OCT, which is presently exposed in the Tasna nappe (south-eastern Switzerland) is considered an on-land analogue of the well-studied Iberian OCT. We compare our results with the fault architecture (fault core–damage zone–protolith) described by Caine et al. [Geology (1996) Vol. 24, pp. 1025–1028]. We confirm the existence of a sharp boundary between the fault core and damage zone based on isotopic data, but the boundary between the damage zone and protolith is gradational. We identify evidence for: (1) pervasive isotopic modification to 8.4 ± 0.1‰ which accompanied or post-dated serpentinization of these mantle rocks at an estimated temperature of 67–109°C, (2) either (i) partial isolation of some highly strained regions [fault core(s) and mylonite] from this pervasive isotopic modification, because of permeability reduction (Caine et al.) or (ii) subsequent isotopic modification caused by structurally channelled flow of warm fluids within these highly strained regions, because of permeability enhancement, and (3) isotopic modification, which is associated with extensive calcification at T = 54–100°C, primarily beneath the younger of the two detachment faults and post-dating initial serpentinization. By comparing the volumetric extent of calcification with an experimentally verified model for calcite precipitation in veins, we conclude that calcification could have occurred in response to seawater infiltration, with a calculated flux rate of 0.1–0.2 m year−1 and a minimum duration of 0.2–4.0 × 104 years. The associated time-averaged uptake flux of carbon during this period was 8–120 mol m−2 year−1. By comparison with the estimated area of exhumed mantle rocks at the Iberian OCT, we calculate a maximum annual uptake flux for carbon of 2–30 Tg year−1. This is an order of magnitude greater than that for carbon exchange at the mid-ocean ridges and 0.1–1.4% of the global oceanic uptake flux for carbon.

Place, publisher, year, edition, pages
2007. Vol. 7, no 4, 401-414 p.
Keyword [en]
carbon transfer, fault architecture, fluid flow, ocean–continent transition, serpentinites
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:su:diva-22999DOI: 10.1111/j.1468-8123.2007.00194.xISI: 000250263000003OAI: oai:DiVA.org:su-22999DiVA: diva2:189875
Available from: 2006-10-26 Created: 2006-10-26 Last updated: 2011-03-01Bibliographically approved
In thesis
1. Deformation and fluid-flow in magma-poor margins: A study of the Tasna Ocean-Continent transition, SE Switzerland
Open this publication in new window or tab >>Deformation and fluid-flow in magma-poor margins: A study of the Tasna Ocean-Continent transition, SE Switzerland
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this study, interaction between fluids and deformation during the final stages of magma-poor rifting was investigated. The Tasna Ocean-Continent transition, located in the Swiss Alps, was studied and a large data set was obtained from profiles oriented perpendicular to two detachment faults. One of these juxtaposed serpentinized mantle against continental crust and the other exhumed both mantle and continental crust to the seafloor. Deformation associated with detachment faulting showed many common features but also some phenomena which were unique to each fault, confirming their sequential activity and differing roles in the exhumation process. Oxygen isotopes indicated the presence of both pervasive and channeled fluid phases, either accompanying or post-dating serpentinization. Deformation in the fault zone occurred in previously serpentinized mantle indicating that serpentinization pre-dated final exhumation. Most strain localization and displacement occurred in fault cores which are narrow zones beneath the detachments. These are underlain by wide zones characterized by more distributed strain. Transitional fabrics as well as reactivated and/or overprinted deformation structures indicated that the final phase of rifting is complex. Fault cores acted as fluid conduits or barriers. Thus, the most deformed zones may become the least permeable. Hence the coupling between deformation and fluid flow is complex in a study area subjected to several phases of deformation and fluid flow. Finally the importance of serpentinization in the evolution of magma-poor rifting was investigated. It was found that serpentinization is the consequence rather than the reason for strain localization at magma-poor margins. However, serpentinization may be an important process which can accelerate exhumation rates in the very latest stages of magma-poor rifting. The pre-existing deformation history of the crust may also be of importance for the development and location of margins.

Place, publisher, year, edition, pages
Stockholm: Institutionen för geologi och geokemi, 2006. 26 p.
Series
Meddelanden från Stockholms universitets institution för geologi och geokemi, ISSN 1101-1599 ; 328
Keyword
Magma-poor margins, Deformation, Fluid-flow, Serpentinization
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-1320 (URN)91-7155-333-9 (ISBN)
Public defence
2006-11-17, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:15
Opponent
Supervisors
Available from: 2006-10-26 Created: 2006-10-26Bibliographically approved

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