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Late Cretaceous magmatism in Madagascar: palaeomagnetic evidence for a stationary Marion hotspot

1998; Elsevier BV; Volume: 164; Issue: 1-2 Linguagem: Inglês

10.1016/s0012-821x(98)00206-4

1385-013X

Trond H. Torsvik, Robert D. Tucker, Lewis D. Ashwal, Elizabeth A. Eide, N. A. Rakotosolofo, Maarten J. de Wit,

Paleontology and Stratigraphy of Fossils

Late Cretaceous basaltic volcanics in the Morondava Basin (SW Madagascar) possess high-quality and pre-fold palaeomagnetic data (declination 353.5°, inclination −54.8°, α95 = 2.4°). The palaeomagnetic data are all of normal magnetic polarity, and remanence acquisition is linked to the terminal stages of the Cretaceous Normal Superchron (≥83 Ma). This is sustained by an 40Ar/39Ar age of 83.6±1.6 Ma from one of the tested basaltic flows. A precise U/Pb zircon–baddeleyite age from northeast Madagascar demonstrates magmatism at least back to 91.6±0.3 Ma; thus reliable isotope ages for the Madagascar Cretaceous igneous province span a range of 8 million years. Late Cretaceous palaeomagnetic data obtained from volcanics and dolerites all over Madagascar are directionally concordant, and the combined palaeomagnetic pole (latitude 68.5°N, longitude 230.3°E, A95 = 5.5°, N=8 studies; sampling age range ca. 84–90 Ma) represents one of the best Late Cretaceous poles for the former Gondwanan elements. The collective palaeomagnetic data yield a palaeolatitude of 45.3°S+5.3−4.7 for the proposed focal point of the Marion plume (Volcan de l'Androy, southeast Madagascar) during the Late Cretaceous. This is in perfect agreement with hotspot-controlled reconstructions that place the Marion hotspot (46.0°S) beneath southeast Madagascar during the Late Cretaceous. Setting true polar wander aside, hotspot movements in the Indian Ocean do not appear to exceed ca. 0.75 cm/yr, and the Marion hotspot appears stationary within the resolution power of palaeomagnetic data.