High Resolution Apparent Polar Wander Path from Kimmeridgian-Aptian Umbro-Marchean Sections (Northern Apennines, Italy)
Abstract
A new high resolution apparent polar wander path (APWP) segment have been obtained from four Kimmeridgian to lower Aptian Northern Apennines (Italy) sections. Apennines are a fold and thrust belt developed during Neogene in response to the convergence between Africa and Europe and are formed by Meso-Cenozoic sedimentary succession, deposited along the Tethyan margin of Adria. On the basis of paleomagnetic data, it has been shown that Adria is a promontory of the African plate since at least Permian times. Whereas paleomagnetic data from Africa are of poor quality for this period, we used data from Adria to improve quality of the APWP in the 150-120 Ma range. We collected 861 samples from the four sections, with a sampling space varying from 30 to 50 cm. The cores have been measured in the paleomagnetic laboratories of the Istituto Nazionale di Geofisica e Vulcanologia of Rome and of the Institut de Physique du Globe of Paris by 2G DC-SQUID cryogenic magnetometers. Samples were cleaned both using thermal and alternating field demagnetization, depending on their lithologies and on their paleomagnetic behavior. The sections show a detailed record of polarity chrons from M21n to M14 and from M9 to M0, however with a magnetostratigraphic recording gap between M14n to M11. The magnetic stratigraphy obtained is consistent with the sequence of polarity chrons as inferred from oceanic magnetic anomaly analysis. We investigated the evolution of directions vs. time. The use of the paleomagnetic data for determination of APWP is hampered by the large local tectonic rotations linked to the Apennines tectonics. To solve this problem, we computed relative rotation between sections and realigned them in a common declination reference frame. We synthesized a new high resolution 150 to 120 Ma APWP for Adria and compared it with similar age APWP segment for Africa. The shape of the new segment is very similar to the time-equivalent segment of the synthetic APWP of Besse & Courtillot (2002). We obtained a perfect overlap between the two APWP segments by a 28° counterclockwise (CCW) rotation of our common frame section. This overlap confirms that Adria promontory moved coherently with Africa during this time span, whereas the rotations were introduced during Apenninic orogenesis. Finally, we address the geometry of the earth magnetic field for this important time interval, and discuss, in relation with worldwide plate evolution, the peculiar shape of our APWP, which displays a hairpin turn during Berriasian with absolutely no standstill.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFMGP23A0034S
- Keywords:
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- 1500 GEOMAGNETISM AND PALEOMAGNETISM;
- 1520 Magnetostratigraphy;
- 8157 Plate motions: past (3040)