Paleomagnetic Lab

Tectonic implications of paleomagnetic data

Here you may find paleomag data set from the whole Carpatho-Pannonian area are obtained by different European laboratories (Márton & Márton, 1989; Márton & Mauritsch, 1990; Krs et al., 1991; Krs et al., 1993, Márton et al., 1996; Tuny & Márton, 1996; Patrascu 1993; Patrascu et al., 1990, 1992, 1994, 1995; Hambach et al., 1994, 1996; Panaiotu et al., 1995, 1997). Data have been grouped in several age windows to suggest better the tectonic implications. Tectonic maps after Liviu Matenco, 1997.

If you use these informations please refer to Panaiotu, 1998 (Panaiotu, C., 1998. Paleomagnetic constrains on the geodynamic history of Romania. In: Sledzinski J. (ed.), Monograph of Southern Carpathians., Reports on Geodesy, 7: 205-216) or to this web page.

Main conclusions

I. The declination data and block rotations

From the point view of paleomagnetic data, the Carpatho-Pannonian region can be separated in two domains with different senses of rotation during Tertiary. Large areas from these domains have not only an identical sense of rotation but also the same amplitude of post Eocene rotation. According to Westaway (1990) this kind of organisation style of paleomagnetic directions in large domains reflect the movement of the blocks in the brittle layer of the crust in response to the viscous torque acting on their base from the underlying plastic deformation of the lithosphere. Local deviations from the general pattern probably reflect changes in the vertical vorticity of the viscous flow of the lithosphere or the response to the frictional torque acting at the margins of the blocks. The main boundary between the two large domains is along the Mid Hungarian Line and North Transylvanian Fault. On the Romanian territory the clockwise rotation is well sustain by paleomagnetic data for the Transylvanian Basin and internal parts of the South Carpathians. Preliminary paleomagnetic results suggest that this rotation affected also the southern border of the South Carpathians.

During the Tertiary northward drift of the area, only 20° of clockwise rotation took place between Eocene and Middle Miocene and there is no rotation between Maastrichtian and Eocene.
Most of the clockwise rotation of the central part of the Transylvanian Basin took place during Late Badenian - Early Sarmatian. The age of the rotation in the S-E corner of basin is clear post-Eocene and taking into account the inclination of remagnetizations probably post-Paleogene. So, it is probably contemporaneous with the rotation of the central part of the basin. This rotation took place after the cessation of counterclockwise rotation of the North Pannonian Paleogene Basin. Contemporaneous counterclockwise rotations are recorded only in the Sarmatian volcanic areas from Zemplen and Ignis Mountains (Fig. 3). During Late Badenian, the Pannonian area was characterised by a major stretching phase, leading to the eastward escape of the basin. A system of NW-SE normal faults developed in the Pannonian Basin and the Apuseni Mountains (Fig. 2). The development of this faults system was probably the answer of the brittle upper crust to accommodate the rotation imposed by the continuum deformation of the lower crust and mantle lithosphere. It must be point out that present direction of this faults system corresponds to the position of the faults when the rotation was finished. It is quite probably that the faults also rotate to accommodate the distributed deformation (e.g. Jackson and McKenzie, 1989). In the Outer Romania Carpathians the Sarmatian tectonic episode was characterised by large scale eastward motion of the inner East Carpathians and South Carpathians, causing differential contraction and uplift, accompanied by the disruption of the roll-back process in the East Carpathians and right-lateral shearing along a roughly E-W trending corridor between the South Carpathians and the Moesian Platform. The most advanced East Carpathians nappes reached the East European block in the central sectors and this probably produced the cessation of the rotation. Such a fast clockwise rotation (20°/Ma to 30°/Ma) was probably the answer of the upper plate to a very rapid migration to the east of the slab's hinge (Dvorkin et al., 1993). This retreating was probably accelerated by the slab breakoff (Wortel and Spakman, 1992).
After Late Sarmatian, the paleomagnetic data show the absence of significant rotation. It must be point out that all the data come only from volcanics rocks and that the paleomagnetic directions indicate the absence of rotation after the emplacement of studied volcanic rocks. So present paleomagnetic data did not exclude the presence of rotations on the eastern border of Transylvanian Basin after Late Sarmatian. The mean paleomagnetic direction has a declination around 90° indicating a large clockwise rotation that is not present in paleomagnetic data from younger rocks of the Calimani Mountains and the Gurghiu Mountains. Rotations in the SE part of the East Carpathians are not unexpected since the structural analyses indicate the ESE advancement of this part during latest Miocene. The northern segments of the East Carpathians remained blocked, while in this transition zone the roll-back process continued, and is still presently recorded in the seismically active Vrancea area. The paleomagnetic data from the Northern Harghita Mountains and the Persani Mountains do not support significant rotations in the transition zone in the last 5 Ma. From geological point of view, the late Sarmatian marks the beginning of the common evolution of the Outer Carpathians and the Intra-Carpathians units and this aspect is probably reflected in the absence of important rotation.

II. The inclination data and the northward drift

According to the geocentric axial dipole hypothesis, inclination data are connected with the paleolatitude of the sampling area during the magnetization. In order to give a quantitative estimate of the latitudinal drift with respect to the stable Africa and Europe, the expected paleolatitudes with 95% confidence limits are also plotted. These paleolatitudes were computed in the hypothesis of a rigid connection of the studied area in the present day position with one of the two major plates in the last 200 Ma. It is obviously that the sampled areas from Transylvanian Basin and Southern Carpathians were to the south of Europe at lest until post Eocene. Only the paleolatitudes from the Miocene volcanics are closed to the present day position. This implies a northward drift of the studied area to the north during Oligocene - Lower Miocene to reach the present day position with respect to Europe. According to the Debiche and Watson' method (1995) the latitudinal movement of Transylvanian Basin with respect to Africa is not significant statistical during Eocene. So the northward drift of Transylvanian basin has the same order of magnitude like the drift to the north of Africa with respect to Europe.

The paleolatitudes obtained for the Jurassic rocks from Piatra Craiului and Bucegi Mountains, for the Upper Cretaceous magmatic rocks from the Apuseni Mountains, Poiana Rusca, Hateg Basin and Banat area and for the Neogene volcanics rocks from the Apuseni Mountains and East Carpathians are represented here.

References

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