The Pliocene seamount series of La Palma/Canary Islands

Abstract

A Pliocene submarine series of alkali basaltic pillow lavas, hyaloclastites, and breccias (A), a sheeted dike swarm (B), and a basal suite of gabbro and ultramafic rocks (C) from La Palma (Canary Islands) is interpreted as a cross section through an uplifted seamount. This series has been tilted to its present orientation of 50ø/230 ø (plunge and azimuth), probably by upwarping due to intrusions in the central portion of the island. The basal plutonic complex (C) also includes intrusives coeval with up to 2000 m of younger subaerial alkali basaltic lavas unconformably overlying the submarine series. The plutonic suite (C) is overlain abruptly by more than 1800 m of sills (B), 0.4-1 m thick on average, with minor screens of lavas and breccias. Extrusives (A) form a 1750 m thick sequence of pillow lavas, breccias, and hyaloclastites. The clastic rocks increase in abundance upward and are of four main types: (1) breccias, consisting of partly broken pillows, formed nearly in situ, (2) heterolithologic pillow fragment breccias, (3) hyaloclastites composed dominantly of highly vesicular lapJill and ash sized shards, the latter thought •to have formed by near surface explosive eruptions and been subsequently transported downslope by mass flows, (2) and (3) being interpreted to have been resedimented, and (4) pillow scoria breccias from the upper 700 m of the extrusive section consisting of amoeboidal, highly vesicular "pillows" and lava stringers and local bombs, probably formed by cracking and "bleeding" of gas-rich expanding pillow lava and some shallow submarine/subaerial lava fountaining. The extrusive series is chemica!ly and mi•eralogically crudely zoned, with the most differentiated rocks (metatrachytes and mugearires) at the base and most picritic: lavas occurring near the top of the series. Subsequent to emplacement, the entire extrusive and intrusive series has been hydrothermally altered, the lower part to greenschist and the upper part to smectite--zeolite facies mineral assemblages. The La Palma succession, combined with evidence from surface studie s of seamounts, suggests that seamounts are formed by intrusive and extrusive processes in approximately equal portions. The nature of eruptive clasti c and depositional mechanisms changes drastically during growth of a seamount if the critical depth for major magmatic degassing is surpassed and especially if magmatic explosive processes can occur at very shallow water depth, the critical depth dependi'ng on magma and thus volatile composition. •Changes in slopes of a seamount influence depositional processes. Based on these factors, at least three major depositional sites develop as a seamount grows' summir, flank, and apron facies. Nonexplosive, extrusive processes prevail in the Deep Water Stage, dominant•!y producing pillow lavas (75%). These consist of individual pillow volcanoes'Up to 200 m high, with large pillows near the base and decreasing pillow size toward the top Of a volcano. Pillow breccias•, and pillow fragment breccias comprise approximately 20...

Facies architecture and Late Pliocene – Pleistocene evolution of a felsic volcanic island, Milos, Greece

“…9), resembling the primary and redeposited products of weakly explosive, strombolian eruptions (cf. Staudigel and Schmincke 1984;Cas et al 1989;Houghton and Landis 1989;Dolozi and Ayres 1991;Kano 1998). They conformably overlie thick submarine pumice breccia and are overlain by partly subaerial facies.…”

Physical volcanology, stratigraphy, and lithogeochemistry of an archean volcanic arc :

“…A deep submarine environment was inferred based on the absence of vesicles and broken pillows, along with minor hyaloclastites Imreh, 1985). Up section, hyaloclastites become more abundant and the transition to the Val d'Or Formation is marked by the recognition of pillowed basalt flows and isolated pillow breccia of calc-alkaline affinity (Imreh, 1985), both of which are consistent with a shoaling sequence (e.g., Staudigel and Schminke, 1984 …”

Volcanologie physique et géochimie des komatiites de Spinifex Ridge, formation de La Motte-Vassan, Abitibi /

“…Il était alors décrit comme des débris ou morceaux de verre provenant des coussins basaltiques. Nous utilisons le terme hyaloclastite comme étant un dépôt de volcanoclastite dans lequel on retrouve des fragments de verre ou échardes volcaniques provenant d'une fragmentation, explosive ou non-explosive, au contact de l'eau et du magma lors de l'écoulement de laves sous-marines (Staudigel et Schmincke, 1984;Fisher et Schmincke, 1984). Ces dépôts sont généralement associés aux coulées de laves mafiques effusives sous-marines plus particulièrement sur les flancs des monts de mer (seamounts) de faible pente (20-30°) (Londsdale et Batiza, 1980;Smith et Batiza 1989, Fouquet et al, 1998Clague et al, 2000;Maicher et al, 2000).…”