Computer Science
Scientific paper
Dec 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990e%26psl.101..272c&link_type=abstract
Earth and Planetary Science Letters, Volume 101, Issue 2-4, p. 272-280.
Computer Science
9
Scientific paper
We present results of a preliminary paleomagnetic study devised as a test of a tectonic model proposed by Van Den Driessche and Brun [1] to interpret the main structural features of the Montagne Noire (South Massif Central, France). This model suggests that crustal extension during Stephanian to Permian times is responsible for a major flat-lying detachment. The inferred geometrical relationships between fault azimuth and extension direction is believed to induce a counter-clockwise rotation of the Paleozoic cover during its northward motion. In order to test this model, we have sampled Autunian (Lower Permian) grey and red sandstone beds within two basins opened during the extension, the Lodève and the St-Affrique basins. The paleomagnetic study of six sites (three in each basin) using thermal demagnetization procedures, reveals the presence of 3 magnetization components. A first one (A), which is unblocked below 400°C, is interpreted as a recent overprint due to weathering of the sandstones. The B component is unblocked between 400° and 575°C. This B component is assumed to be primary, although the gentle dip of the beds does not allow a fold test. It fits the Lower Permian field direction in the Lodève basin (in situ: Dm = 194°, Im = 6°, k = 50, tilt corrected: Dm = 194°, Im = -10°, k = 53). In contrast, it shows a systematic difference in declination in the St-Affrique basin (in situ: Dm = 173°, Im = 2.5°, k = 101, tilt corrected: Dm = 172°, Im = 6°, k = 37). This is interpreted as a post-Autunian counter-clockwise rotation of at least 20° of the St-Affrique basin, thus supporting one of the main implications of the tectonic model. Finally, red sediments from two sites of the Lodève basin yield a third component (C) with unblocking temperatures up to 670°C and carried by hematite. Its direction is also consistent with the Permian field direction, showing that hematite crystallisation occurred early in the diagenesis history of the sediments.
Brun Jean-Pierre
Cogné Jean-Pascal
van den Driessche J.
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