Niveaux intercalaires dans les strates de basalte des plateaux de l'archipel de kerguelen

Bellair, Pierre; Carron, Jean-Paul; Nougier, J.; Trichet, Jean

doi:10.1007/bf01765771

Cited by 5 publications

(1 citation statement)

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“…In this part of the archipelago, outpouring of lava flows occurred at or above sea-level. Intercalated 0.1-0.5-m thick red layers correspond to hydrothermally altered vitreous ash falls (Bellair et al 1965). Breccias and conglomerates with up to 30-cm diameter boulders are exposed at various levels of the sequence.…”

Section: Country Rocksmentioning

confidence: 99%

The Neogene to Recent Rallier-du-Baty nested ring complex, Kerguelen Archipelago (TAAF, Indian Ocean): stratigraphy revisited, implications for cauldron subsidence mechanisms

Bonin

Ethien

Gerbe

et al. 2004

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The Kerguelen Archipelago is made up of a stack of thick piles of Tertiary flood basalts intruded by transitional to alkaline igneous centres at various times since 30 Ma ago. In the SW, the Rallier-du-Baty Peninsula is mostly occupied by two silicic ring complexes, each with an average diameter of 15 km, comprising dissected calderas cross-cut by subvolcanic cupolas. Previous radiometric determinations yield ages ranging from 15.4 to 7.4 Ma in the southern centre, and 6.2 to 4.9 Ma in the northern one. The felsic ring dykes were injected by coeval mafic magmas, forming, successively, swarms of early mafic enclaves, disrupted synplutonic cone sheets, and late cone-sheets. After the emplacement and subsequent unroofing of the plutonic ring complexes, abundant and thick trachytic pyroclastic flows and falls were emitted from the younger caldera volcanoes, while hawaiite and mugearite lava flows were erupted from marginal maars and cones. Huge trachyte ignimbritic flows filled the glacial valleys in the central Peninsula, and capped lacustrine deposits and older lava flows, while related pumice falls are widespread throughout the archipelago. This powerful plinian eruption took place after the network of glacial valleys was established, but before the Little Ice Age that occurred during the last centuries. In the south of the peninsula, even younger trachytic formations are exposed, and fumarolic vents are still active.The growth mechanisms of a caldera-related ring complex can be explained as a repetitive sequence of two eruptive episodes. The first episode of hydrofracturing, induced by volatile exsolution within the evolving magma chamber, creates a vertical circular fracture zone, along which highly vesiculated magmas are emitted during explosive eruptive events occurring at the surface in a caldera volcano. It is followed by a second episode of cauldron-subsidence of a crustal block down to the degassed magma chamber, induced by pressure release. Downward movement of the crustal block favours the emplacement at shallow depths within the older caldera-filling formations, of discrete magmatic sheets characterized by a 16-km mean diameter and a 1-km mean thickness, corresponding to an average unit volume of 200 km 3. Actually, the estimated volumes of the different igneous episodes within the Rallier-du-Baty nested ring complex vary from 60 to 900 km 3, and correspond to the production during 15 Ma of about 2800 • 850 km 3 of new materials and a net crustal growth of about 100 _+ 30 × 103 m 3 per year.Clough et al. (1909) on the district of Glen coe, Argyllshire, Scotland, where, for the first time, they describe a cauldron, in the sense of an eroded caldera with inverted relief, formed by subsidence having affected an area, roughly oval in shape, delineated by a boundary fault. Observing that uprise of a series of marginal intrusions accompanied the subsidence, they suggest that these intrusions could have been From:

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Section: Country Rocksmentioning

confidence: 99%