A Middle‐Triassic Paleomagnetic Pole for the Eurasian Plate from Heming (France)

Summary Palaeomagnetic dating techniques have been applied to determine the age of fluid migration that produced the Mississippi Valley‐type (MVT) Pb–Zn–Ba–F deposits in the Cévennes region of southern France. 15 sampling sites in two gently deformed areas around the Largentière and Croix‐de‐Pallières mines on the Cévennes border were selected for palaeomagnetic study. They yielded a very well‐defined direction of remagnetization corresponding to an Early‐Middle Eocene age. This remagnetization cannot be related to the formation of magnetite as a result of the transformation of smectite to illite because the latter has been well dated as a Mesozoic event. The magnetic overprint in this area is related to a chemical phenomenon during fluid migration. The age of remagnetization corresponds to a major uplift in the Pyrénées mountains, located to the south of the Cévennes. This implies that fluid migration occurred from the south to the north as a result of hydraulic head established in the Pyrénées orogenic belt during orogenesis and suggests that the MVT deposits in the Cévennes region formed from a gravity‐driven fluid system as described by Garven & Freeze (1984a,b).

Section: Age Of the Two Chrmsmentioning

confidence: 99%

Palaeomagnetic dating of widespread remagnetization on the southeastern border of the French Massif Central and implications for fluid flow and Mississippi Valley-type mineralization

Henry

Rouvier

Goff

et al. 2001

“…4), removed at 550-580 and 680"C, respectively, were isolated during heating. The high-temperature component NSTa, which is carried by haematite, has a pole position close to the Ladinian (Muschelkalk) pole of Heming (HEM) (Theveniaut et al 1992) and the new results obtained from the Keuper marls (OSH and ENT, see below). The intermediate-temperature component NSTb has a high inclination and a more northerly declination, which locates the VGP close to the mean Lower Jurassic pole of Europe (Van der Voo 1990).…”

Section: Induan (Annweiler) Sandstonesmentioning

confidence: 86%

The apparent polar wander path of the European plate in Upper Triassic-Lower Jurassic times and the Liassic intraplate fracturing of Pangaea: new palaeomagnetic constraints from NW France and SW Germany

Edel

Duringer

1997

Self Cite

S U M M A R YIn order to constrain the European plate motions during Triassic-Lower Jurassic times, new palaeomagnetic data were acquired from various Triassic-Liassic sediments of northeastern France and southwestern Germany. A Carnian palaeopole 49"N/13 1 "E, K = 193, A,, = 7", N = 4 was obtained for Keuper marls with consistent directions of normal and reversed polarities. Rhaetian sandstones, also with both polarities, and Carnian dolomites with a magnetization of probable secondary origin, provide a mean pole 51°N/112"E, K = 109, Ag5=6", N = 6 , more westerly than that given above. The Lower Hettangian, sampled in limestones of the Xeuilley quarry near Nancy shows a N-R-N polarity sequence with well-defined anti-parallel directions. The mean Hettangian pole is 55"N/10OoE, K = 123, Ag5 = 1 lo, N = 3. Induan sandstones from the northern Vosges show two distinct overprints, one consistent with the LadinianCarnian magnetizations already observed in the same region, the second consistent with the recalculated mean Lower Jurassic pole of Europe. Five other sites with different rock types also exhibit late overprints with Lower Jurassic directions. The mean pole calculated from these overprints is 74"N/124"E, K = 125, A,, = 6", N = 6.The revised apparent polar wander path (APWP) presented here shows that for the mid-Permian to the earliest Jurassic the palaeopoles of Europe stayed around 50" latitude, while the longitudes drifted from 185"E to 100"E. The previously established Upper Triassic-Lower Jurassic loop of the APWP is shifted westwards by about 25". The revised APWP involves the following plate motions. After the late Alleghanian tectonic phase, which marked the end of the Variscan orogeny, central western Europe rotated counterclockwise during about 70 Myr, up to the earliest Jurassic. The southnorth drift in latitude by 35" (nearly 4000 km) remained regular from 320 to 205 Ma, with a constant rate of 3.4cmyr-'. Around 205 Ma, this motion ceased, probably because of a collision somewhere in the north of Eurasia. Then, in the Lower Liassic, the plate underwent a rapid counterclockwise rotation with a Eulerian pole located in northeastern Asia, synchronous with fracturing in the Atlantic and the Neotethys areas. It is proposed that the intraplate fracturing of Pangaea was initiated by the rapid change of the megacontinent motion at the end of the Trias.

“…Italics indicate calculations done using directions. References: (1) Yang et al (1996); (2) Edel & Duringer (1997); (3) Edel & Duringer (1997); (4) Briden & Daniels (1999); (5) Edel & Duringer (1997); (6) Symons et al (1995); (7) Theveniaut et al (1992); (8) Torsvik et al (1998); (9) Biquand (1977); (10) Merabet & Daly (1986); (11) Nawrocki (1997); (12) Chen et al (1997); (13) Merabet & Guillaume (1988); (14) Berthold et al (1975); (15) Konrad & Nairn (1972); (16) Halvorsen (1970); (17) Mauritsh & Rother (1983); (18) Thorning & Abrahamsen (1980); (19) Thomas et al (1997); Soffel & Harzer (1991); (20) Nawrocki (1997); (21) Merabet & Guillaume (1988); (22) Krs et al (1992); (23) Smith & Piper (1979); (24) Harcombe‐Smee et al (1996).…”

Section: Methods and Apw Pathsmentioning

confidence: 99%

Pre-drift extension of the Atlantic margins of North America and Europe based on paths of Permo-Triassic apparent polar wander

Beck

Housen

2003

SUMMARY We reconstruct the relative configuration of North America and Europe prior to separation using paths of apparent polar wander (APW) for the interval 300 to 200 Ma. The Bullard et al. (1965) reconstruction closely superimposes the 300 Ma points on the two APW paths but leaves the 200 Ma points far apart. Conversely, anomaly‐based reconstructions for later times approximately superimpose the 200 Ma ends of the paths but leave the older ends far apart. This indicates that separation of the interiors of the two continents began during the interval 300 to 200 Ma, long before surficial rifting commenced in the late Mesozoic. This in turn requires pre‐rift extension in the two continental margins. Extension appears to have occurred in two phases of approximately equal magnitude but significantly different direction; the change in direction occurred at about 200 Ma. The earlier (300 to 200 Ma) episode of extension appears to have involved a strong element of sinistral shear. Based on our preferred reconstruction, the total amount of pre‐rift extension of the two continental margins may have been as much as 1400 km.