Paléomagnétisme et datation du volcanisme permien, triasique et crétacé du Maroc

Westphal, M.; Montigny, R.; Thuizat, R.; Bardon, C.; Bossert, A.; Hamzeh, R.; Rolley, J. P.

doi:10.1139/e79-202

Cited by 84 publications

(22 citation statements)

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“…The Southalpine poles agree with paleopoles from broadly coeval volcanic rocks from Morocco [35,36], the only two Q v 3 poles from volcanic rocks of comparable age from West Gondwana ( [1] ; Global Paleomagnetic Database 2003). These volcanic rocks, which accumulated in transtensional basins, are intercalated with continental sediments yielding Early Permian (Autunian) £o-ras [37].…”

Section: Data From Gondwanamentioning

confidence: 52%

Early Permian Pangea ‘B’ to Late Permian Pangea ‘A’☆

Muttoni¹,

Kent²,

Garzanti³

et al. 2003

Earth and Planetary Science Letters

222

151

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The pre-drift Wegenerian model of Pangea is almost universally accepted, but debate exists on its pre-Jurassic configuration since Ted Irving introduced Pangea 'B' by placing Gondwana farther to the east by V3000 km with respect to Laurasia on the basis of paleomagnetic data. New paleomagnetic data from radiometrically dated Early Permian volcanic rocks from parts of Adria that are tectonically coherent with Africa (Gondwana), integrated with published coeval data from Gondwana and Laurasia, again only from igneous rocks, fully support a Pangea 'B' configuration in the Early Permian. The use of paleomagnetic data strictly from igneous rocks excludes artifacts from sedimentary inclination error as a contributing explanation for Pangea 'B'. The ultimate option to reject Pangea 'B' is to abandon the geocentric axial dipole hypothesis by introducing a significant non-dipole (zonal octupole) component in the Late Paleozoic time-averaged geomagnetic field. We demonstrate, however, by using a dataset consisting entirely of paleomagnetic directions with low inclinations from sampling sites confined to one hemisphere from Gondwana as well as Laurasia that the effects of a zonal octupole field contribution would not explain away the paleomagnetic evidence for Pangea 'B' in the Early Permian. We therefore regard the paleomagnetic evidence for an Early Permian Pangea 'B' as robust. The transformation from Pangea 'B' to Pangea 'A' took place during the Permian because Late Permian paleomagnetic data allow a Pangea 'A' configuration. We therefore review geological evidence from the literature in support of an intra-Pangea dextral megashear system. The transformation occurred after the cooling of the Variscan mega-suture and lasted V20 Myr. In this interval, the Neotethys Ocean opened between India/Arabia and the Cimmerian microcontinents in the east, while widespread lithospheric wrenching and magmatism took place in the west around the Adriatic promontory. The general distribution of plate boundaries and resulting driving forces are qualitatively consistent with a right-lateral shear couple between Gondwana and Laurasia during the Permian. Transcurrent plate boundaries associated with the Pangea transformation reactivated Variscan shear zones and were subsequently exploited by the opening of western Neotethyan seaways in the Jurassic.0012-821X / 03 / $^see front matter ß

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Section: Data From Gondwanamentioning

confidence: 52%

Early Permian Pangea ‘B’ to Late Permian Pangea ‘A’☆

Muttoni¹,

Kent²,

Garzanti³

et al. 2003

Earth and Planetary Science Letters

222

151

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“…A A =Permian: 11, 15, 16 (Martin et al 1978), 12 (Hamzeh 1973), 13 (McElhinny & Opdyke 1968, 14 (Morel et al 1981), 17 (Kent et al 1984). + Triassic, Jurassic, Cretaceous (Westphal et al 1979). 0.…”

Section: Discussion a N D Conclusionmentioning

confidence: 99%

Carboniferous palaeomagnetic investigations in Morocco: Permian remagnetizations and possible large Carboniferous rotations occurring in Mesetian sedimentary and Jebilets intrusive rocks

Salmon¹,

Edel²,

Piqué³

et al. 1988

Geophysical Journal International

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Carboniferous limestone and sandstone formations from the Moroccan Meseta and Visean gabbros from the Jebilets massif have been investigated. Palaeomagnetic results reveal the occurrence of different magnetic components. These are (i) a Permian component: Dm = 141.5", Zm = -1.7", N = 4 [Virtual Geomagnetic Pole (VGP) = 33"S, 43.9"E], similar to that found in the Anti-Atlas and in other parts of the Hercynian chain, (ii) a Carboniferous component Dm = 116.6", Zm = 25. lo, N = 9 (VGP = 7.4"S, 54.5"E), consistent with other Carboniferous data from Central Sahara and Morocco, and (iii) a component not previously described from Africa and still undated, with a direction Dm = 77.4", Im = 1.5"; this direction and it's opposite polarity counterpart were found only at one site (21 specimens) in the Jebilets, and at two sites (20 specimens) in the Meseta (opposite polarity). It may represent an older magnetization possibly of Lower Carboniferous age which would imply important rotations of Africa during this period.

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“…Two sieve fractions were used, 100-160 µm and 160-250 µm. The analytical procedure, described more extensively elsewhere (Westphal et al, 1979) is as follows. Potassium was measured by flame photometry with a lithium internal standard.…”

Section: Analytical Techniquesmentioning

confidence: 99%

K-Ar and 40Ar/39Ar Ages of Central Kerguelen Plateau Basalts

Whitechurch¹,

Montigny²,

Sevigny³

et al. 1992

Proceedings of the Ocean Drilling Program

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Conventional K-Ar and 40 Ar/ 39 Ar analyses on whole-rock samples are reported for basaltic samples retrieved on the Central and Southern Kerguelen plateaus during Ocean Drilling Program Leg 120. Sites 747, 749, and 750 recovered basalts from the plateau basement, whereas Site 748 drilled a lava flow interbedded with sediments of probable Albian age.The freshest core basalts from the basement yielded dates falling in the 110-100 m.y. interval. Sample 120-749C-15R-3 (26-31 cm) gave conventional K-Ar, total fusion, and plateau ^Ar/^Ar ages that are closely concordant: 111.5 ± 3.2 m.y., 109.9 ± 1.2 m.y., and 109.6 ± 0.7 m.y., respectively. Sample 120-750B-15R-5 (54-60 cm), when taking into account the analytical uncertainties, yields conventional K-Ar and 40 Ar/ 39 Ar plateau ages that can be considered similar: 101.2 ± 7.5 and 118.2 ± 5 m.y., respectively. Inspection of the 39 Ar/ 40 Ar vs. 36 Ar/ 40 Ar diagram does not reveal the occurrence of an initial argon component of radiogenic composition in the two samples. Accordingly, our results suggest that the formation of the basement of the Central Kerguelen Plateau was closed at 110 m.y.. Furthermore, these results are in agreement with a K-Ar age of 114 ± 1 m.y. mentioned in the literature for a basalt dredged in the 77°E Graben.The still scant amount of data indicates that the outpourings of the Central Kerguelen Plateau correspond rather well with widespread continental magmatism in Gondwanaland that is believed to mark the incipient opening of the eastern Indian Ocean. This implies a huge head for the mantle plume at the source of these liquids. Nevertheless, on land and at sea the exact duration of magmatism remains unknown. Therefore, a catastrophic pattern similar to that currently invoked for the Deccan Traps at the end of the Cretaceous, though possible, is not yet required by present geochronologic data.

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Paléomagnétisme et datation du volcanisme permien, triasique et crétacé du Maroc

Cited by 84 publications

References 0 publications

Early Permian Pangea ‘B’ to Late Permian Pangea ‘A’☆

Early Permian Pangea ‘B’ to Late Permian Pangea ‘A’☆

Carboniferous palaeomagnetic investigations in Morocco: Permian remagnetizations and possible large Carboniferous rotations occurring in Mesetian sedimentary and Jebilets intrusive rocks

K-Ar and 40Ar/39Ar Ages of Central Kerguelen Plateau Basalts

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