IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS014 Poster presentation 2292
Large scale features of the south-easternmost TTZ as inferred from
geophysical data
Dr. Lucian Besutiu
Dynamics of the Solid Earth Institute of Geodynamics of the Romanioan Academy IAG
Unlike its northern and central part, thoroughly studied from the North Sea to the state-border of
Romania through the large amount of works carried out during the EUROPROBE program and some
later large scale seismic experiments, the path and structure of the SE extension of the Tornquist-
Teisseyre Zone (TTZ) are still subject to debate. The paper represents an attempt to reveal TTZ largescale
peculiarities on the Romanian territory based on the available geophysical data interpretation.
Several issues were targeted: (i) path, (ii) structure, (iii) nature, and (iv) SE end of the contact. The
study started with the examination of the TTZ geophysical fingerprints along its known track. The TTZ
path has been firstly outlined within the pattern of the airborne geomagnetic anomaly as separating the
warmer (less magnetic) lithosphere of the Central European Plate (CEP) from the colder Precambrian
lithosphere of the East European Plate (EEP) which allows the geomagnetic expression of its lower
crust. The effect is still preserved at the altitude of the geomagnetic satellites. Both gravity and some
DSS lines previously performed revealed a graben-like, or at least a step structure at the bottom of the
crust all along the TTZ track. The TTZ path on the Romanian territory has been outlined both in the
geomagnetic anomaly and heat-flow images, where parts of the CEP and EEP are clearly discriminated.
The contact is also visible in pattern of the geomagnetic induction vectors. Modelling the TTZ large scale
structure on the Romanian territory has been performed mainly based on gravity data interpretation
under depth constraints provided by MTS and seismic data. More than 40,000 core samples from oil
wells, and rock samples collected from hundreds outcrops located within East Carpathians and
surrounding area were analysed in order to provide an appropriate density model for the main
geological formations as known within the region. Gravity modelling confirmed the previous
assumptions on the intricate alpine structures of East Carpathians with about 10 km thick nappes stack.
Deeper on, the model revealed a graben-like structure at the bottom of the crust, with a 10 km step at
the both Conrad and Moho discontinuities, quite similar to the TTZ features previously outlined along its
north-western track. The regional stress tensor within Transylvanian Depression, pointing towards TTZ,
and an accented crust deformation within the area seem to advocate for a compression contact in
nature. The Moho keel seems to be well outlined in the gravity low (within both Bouguer and isostatic
anomalies) extending from the North Sea to the bending area of East Carpathians (the Vrancea
intermediate seismicity zone) where it suddenly ends. There is no gravity evidence on the TTZ extension
towards the Black Sea as previously postulated. Due to data insufficiency, some speculations on the
possible TTZ SE extent, beyond Vrancea zone, are made only. Acknowlegements. The research has
been supported through the Romanian National Agency for Scientific Research grant CEEX-MENER
no.732/2006.
Keywords: tornquist teisseyre, geophysics, romania