Pillow lava

Central Manus Basin Vienna Woods (3° ID S, 150°17 E) 2500 2-km-wide axial rift graben of the northeast spreading center. Mostly massive pillow lava floor. Sulfide chimneys up to 20 m high are venting clear, milky and black fluids. Sulfate smokers are also present. Sphalerite, wurtzite, pyrite, marcasite, chalcopyrite, galena, amorphous silica, barite. Sulfate chimney anhydrite, silica, barite. 

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. 

In the southern TCZ only Early Devonian rocks are exposed, and all of them are assigned to the Tobique Group. The Tobique and Dalhousie groups are in part coeval and are similar in terms of rock types. The depositional environment for the Tobique Group is, for the most part, thought to be outer shelf or slope based on sedimentary bed forms and ichnofauna and the presence of abundant pillow lava and hyaloclastite in mafic volcanic units. In... 

TACHYLYTE for Tachylite). Pure tachylite is a natural, basic black glass, which may form along the chilled contacts of dikes or sills. II also occurs as a rind on basic pillow lavas that have been suddenly chilled by plunging into water. Occasionally it forms entire flows from certain Hawaiian volcanoes. 

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... 

The Plio-Peistocene activity is by far the best studied (Beccaluva et al. 1998 Trua et al. 1998). It took place during Lower-Middle Pliocene (4.9 to 3.5 Ma) and Upper Pliocene-Lower Pleistocene (2.4 to 1.5 Ma). The earlier products are principally submarine and are represented by volcano-clastic products, pillow lavas and minor subaerial lava flows. The Upper Pliocene-Lower Pleistocene activity erupted lava in subaerial to shallow marine environments (Di Grande et al. 2002). 

Dobson et al. (1995) measured water contents in melt inclusions in pyroxenes in boninites from the Bonin Islands. These melt inclusions contained 2.8-3.2 wt.% H2O, whereas quenched glass from pillow lava rims had 2.2-2.4wt.% H2O, which Dobson et al. interpreted as a result of degassing between the time of entrapment of the melt inclusions and the eruption on the seafloor. They also measured the water content of the orthopyroxene, which contained 80-120 ppm H2O. 

Samples of the deepest oceanic crust are accessible in only one ocean drill core site 735B was drilled on 11 Myr old crust on the SW Indian Ridge (Dick et al., 2000). This hole penetrated a few tens of meters of pillow lavas and 1,200 m of gabbros, with 100% recovery. The site never reached cumulates (Dick et al., 2000). The lack of sheeted dikes and the near absence of pillow lavas is clearly quite different from the normal ophiolitic crust, but site 735 rock types are not very different from materials found in the upper plutonic section of ophiolites. Thus, site 735B is used to represent the deeper crust for the composite crust section. 

A third approach that is commonly used to constrain chemical fluxes compares differently altered materials, such as altered pillow margins and less altered pillow interiors, or samples with or without alteration haloes around veins (e.g., Alt et al., 1986), mineralized and unmineralized zones or differently altered gabbros (e.g., Bach et al., 2001) in order to constrain chemical changes associated with alteration. However, least altered samples only rarely reflect the original composition reliably. A second problem in this approach is the relatively small sample sizes typically analyzed from ocean drilling materials. Typical sample sizes are about 15 cm, which is small when compared with local variability in modal mineralogy. Indeed, individual phenocryst phases can be several millimeters in size. Local variability in modal mineralogy is particularly common in pillow lavas where phenocryst abundances can vary as a function of radial distance from the center or vertically within the center... 

Pillow lava—The form that basaltic lava takes when it is erupted deep under water. 

The Manjeri Formation is overlain by Reliance Formation (ultra-) mafic volcanic rocks (Fig. 3b). The contact between the two formations is a high-strain zone of 1-5 m width over-lain by relatively unstrained pillow lavas. It has been interpreted as (1) conformable but accommodating layer-parallel sUp during refolding of the belt (Blenkinsop et al. 1993), or (2) a thrust or detachment surface that accommodated obduc-tion of an oceanic plateau (Kusky Kidd 1992). 

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