Dynamics of the Ocean Floor

Tyrrhenis

TYRRENIan sea Seismic experiment on continental break-up and structure of conjugated rifted margins

Duration: 01.01.2010-31.12.2012

Applicants: Priv. Doz. Dr. Ingo Grevemeyer, Prof. Dr. Christian Berndt

Sponsered by: Deutsche Forschungsgesellschaft (DFG)

 

Rifted margins are areas of dense population and host major energy resources in the sub-surface. However, the geological processes that control the formation of continental margins are yet not well understood. It is the aim of the proposed project to constrain the temporal and spatial distribution of stretching and crustal thinning of conjugate margins to gain insight into the geological processes underlying continental margin formation. The Tyrrhenian Basin is a confined rift basin with active rifting at its edges and it has the advantage of well preserved, un-deformed conjugate margins in its central part. This makes it an ideal natural laboratory to study the formative processes of rifted margins.
We propose a collaborative project with partners from Spain and Italy to address these questions in a multi-disciplinary project. New data will be acquired during a two ship operation in April 2010. The Spanish R/V Sarmiento de Gamboa will collect multi-channel seismic (MCS) data and operate airguns for seismic refraction and wide-angle work. Ocean-bottom stations for the refraction work will be deployed and recovered from the Italian vessel R/V Urania. Several geophysical transects will cross the Tyrrhenian Basin, sampling conjugate margins that have been formed under different amount of stretching. The comparison of the crustal and upper mantle structure derived from seismic reflection and seismic refraction data along different transects will permit to unravel the evolution of the processes of continental margin formation by trading space (different areas with different stretching factors) for time (evolution of extension).

 

Objectives

The project is going to address a number of goals/objectives:

1. Characterization of the structure and physical properties of the crust and uppermost mantle
To determine the distribution of the seismic velocity in the crust, uppermost mantle and the geometry of the crust-mantle boundary (Moho), as well as their uncertainty ranges along seismic profiles in the Tyrrhenian and South-Balearic basins. All models will be integrated in a 3D analysis to establish the variation in crustal thickness from the continental margins to the oceanic basins. Furthermore, crustal and uppermost mantle density distribution as well as their uncertainty ranges will be obtained, from gravity data by means of existing empirical velocity-density relationships for continental and oceanic rocks.

2. Classification of crustal domains within the extensional basin
To characterize the continent-ocean transition based on the changes in seismic velocity and crustal thickness, defining the boundaries of the oceanic basins. Furthermore, to determine the petrological composition of the continental crust, transitional crust (e.g. serpentinized peridotite, thinned and intruded continental crust) and oceanic crust, based on their physical properties. To determine the nature of the lower continental crust to evaluate the volume of decompression melting during extension and underplating/intrusions into the lower crust.

3. Study of the mantle melting process and the generation of oceanic crust
To characterize the process of mantle melting based on the seismic structure of the oceanic crust and the relation between seismic and petrologic parameters (pressure, rock melting fractions), to estimate the relative importance of mantle temperature, upwelling rate and composition. To investigate the distribution of upper mantle density anomalies and compensation depth, to evaluate the thermal influence of the magmatism associated to the subduction under the Calabrian arc.

4. Characterization of extensional processes of margin formation
To determine the tectonic structure and construct balanced cross sections of the entire crust across the basin using depth seismic images and velocity models. To integrate the 2D cross sections with the tectonic structure imaged in the bathymetry to investigate the 3D tectonic evolution. To identify active faults and evaluate related potential natural hazards.

5. Formation of sedimentary deposits
 To study the seismic stratigraphy and tectono-sedimentary evolution of the basin. To determine the space-time evolution of extensional processes studying the relationship between tectonics and syntectonic sedimentation to estimate opening rates of the basin.

6. Evolution of the Western Mediterranean basin in the context of subduction-related context of slab rollback
To integrate marine observations and numerical modelling done by English project partners with onshore observations to obtain a model of formation of the Tyrrhenian Basin and its comparison with the structure Alborán and South-Balearic basins obtained from the data of the R/V Meteor cruise M69/2 (Chief scientist I. Grevemeyer).

Research area

Bathymetric map of the working area of MEDOC cruise (the Thyrrenian Sea). The different seismic profiles to be acquired and corresponding waypoints are labelled A-B to M-N. The red lines show the WAS profiles to be acquired during the first phase and the MCS profiles to be acquired in the second phase. The black lines correspond to those profiles that will be acquired only with MCS. The yellow dots show the approximate locations of the OBS deployment (this may change slightly depending on the detailed bathymetry).

 

Arbeitsgebiet im Tyrrhenischen Meer

Methods

  • MCS: Multi-channel reflection seismics
  • WAS: wide angle refraction and reflection seismics

Instruments

  • Ocean bottom seismometers and hydrophones
  • 6 km digital multi-channel seismic streamer
  • 140 litre airgun array

Contact

Project leader
Dr. Ingo Grevemeyer
Phone: +49 431 600-2336
Fax: +49 431 600-2922
e-mail: igrevemeyer(at)geomar.de

 

Project partners

Prof. Dr. C.R. Ranero - Instituto de Ciencias del Mar (ICM), Barcelona, Spanien
Dr. V. Sallares - Instituto de Ciencias del Mar, Barcelona, Spanien
Prof. Dr. N. Zittelini - Instituto di Scienze Marine (ISMAR), Bologna, Italien
Dr. M. Pérez-Gussinyé - Royal Holloway University of London