Pillow basalts

The Tyrone Plutonic Group comprises a basic igneous association of layered, isotropic and pegmatitic gabbros, doleritic sheeted dykes and rare basaltic pillow lavas first recognized as ophiolitic by Hutton etal. (1985). 

The Tyrone Volcanic Group sequence comprises basaltic pillow lavas, tuffs of basic to intermediate composition, rhyolites, cherts, siltstones and dark grey mudstones representing up to three volcanic cycles. From base to top of each cycle and through the sequence as a whole, the Tyrone Volcanic Group becomes progressively more acidic in composition. 

Wiebe R. A., Frey H., and Hawkins D. P. (2001) Basaltic pillow mounds in the Vinalhaven intrusion, Maine. J. Volcanol. Geotherm. Res. 107, 171-184. 

Above the komatiites are thick basalt pillows and flows. At the top of the sequence is a further sequence of shallow-water sediments, including limestones that locally have extensive and very well preserved stromatolites (Figure 4). These too have evidence for mbisco fractionation (see Section 8.01.7.2), both in kerogen carbon, and in carbonate with Q%o. 

Fig. 16. Fields of lanthanide element patterns for co-existing unaltered basalt pillow interiors and altered palagonite margins from the Atlantic ridge (data are from Ludden and Thompson 1979). The enrichment of light lanthanides in the altered margins has been used as evidence for lanthanide mobility under...

Watanabe et al. (1993) have determined a whole rock isochron age of 107 15 Ma (yi b = 1.42 X 10 Vy) for well-preserved pillowed basalts in Western Shikoku with their basalt initial ratio of 0.70401. 

Fig. 2.58. Relationships between esr and Nd the pillowed basalts. MORB and OIB indicate midoceanic...

Watanabe et al. (1993) indicated Nd and sr for the pillowed basalt plot within the OIB region, but very close to the MORB region (Fig. 2.58), assuming 130 Ma is the age of the original basalt lavas (Isozaki and Itaya, 1990). 

A typical hydrothermal vent system. Included are basal mounds of mineral precipitates, pillow basalts, a black smoker, and various vent organisms. Source From Haymon, R. M. and K. C. Macdonald (1985). American Scientist, 73, 441 49. 

The palagonite is thermodynamically unstable and, hence, reacts with seawater to form various clay minerals, including smectites (montmorillonite, nontronite, and saponite), micas (celadonite), and zeolites (phillipsite). This chemical weathering involves uptake of Si, Al, Mg, Ca, Na, and K and the release of water, reversing to some extent, the elemental effect of palagonitization. These mineral alterations tend to proceed progressively from the outer margin of the pillow basalts to their interior. 

Pillow basalts Large mounds of basalt that form when lava is extruded onto the seafloor at active spreading centers. 

Four main evolution stages have been distinguished for Mount Etna activity (Gillot et al. 1994 Branca et al. 2004). The first stage (580 to 225 ka) was characterised by emplacement of tholeiitic basalts, which were erupted over a wide area from the Iblean Plateau in the south to the Pelori-tani mountains in the north, and presently crop out as pillow-lavas, hyalo-clastites and sills along the Ionian Sea coast north of Catania, between... 

Honda, M., McDougall, I., Patterson, D. B., Doulgeris, A., Clague, D. A. (1993a) Noble gases in submarine pillow basalt glasses from Loihi and Kilauea, Hawaii A solar component in the Earth. Geochim. Cosmochim. Acta, 57, 859-74. 

Fig. 16.4. Kolbeinsey Ridge. Network of hyphae of an unknown marine fungus in a pillow basalt pore from the Holocene oceanic crust of the Kolbeinsey Ridge (north of Iceland) from a water depth of nearly 1500 m. The old hyphae are partly covered with iron and manganese oxides. Fungi are very common in pillow basalts and play a central role during rock alteration and the formation of certain microbialites.

Fig. 16.5. Kolbeinsey Ridge. Terminal ends of an another type of unknown marine fungus from a pillow basalt of the Kolbeinsey Ridge. The thickened ends of the hyphae are probably conidia.

Nichols A. R. L., Carroll M. R., and Hoskuldsson A. (2002) Is the Iceland hot spot also wet Evidence from the water contents of undegassed submarine and subglacial pillow basalts. Earth Planet. Sci. Lett. 202, 11-Kl. 

Our knowledge of the architecture of the oceanic cmst derives from four main sources studies of portions of the oceanic cmst that have been obducted onto land (ophiolite complexes) drilling of the ocean cmst exposures of the deeper cmst at fracmre zones and rare tectonic windows and geophysical smdies of the seismic properties of the ocean cmst. These smdies have revealed that the general structure of the igneous ocean cmst, from top to bottom, consists of a carapace of basaltic lava flows and pillows... 

On Maliata the stratigraphic thickness of the accreted plateau reaches 3-4 km, and the succession is dominated by pillowed and massive basaltic flows (Petterson et al., 1997 Babbs, 1997). Like the CCOP, dykes are volumetrically minor. The DSDP/ODP drill holes have penetrated into the plateau to a depth of 216 m (Site 1185B Mahoney et at, 2001). The sampled sections consist predominantly of pillowed and massive basalts with occasional thin interlava sediments (Neal et al., 1997 Mahoney et al., 2001)... 

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