Ocean Drilling Program Hole 896A (1°13.01'N, 83°43.39'W) is
in 3440 m of water east of the Galapagos Platform in the equatorial
eastern Pacific Ocean. At this site in 5.9 Ma crust, basement rocks
were recovered over the depth range of 195.1 meters below seafloor
(mbsf) to 469 mbsf. These rocks...
The majority of the Earth's shallow crust is composed of basalt that erupted on the seafloor and was subsequently altered by chemical exchange with seawater. One aspect of this alteration is the replacement of glass by secondary minerals, including clays. Petrographic thin sections from ODP Holes 504B and 896A revealed...
Within the altered parts of the glass rim of pillow lavas of Hole 896A, at depths at least 432 m below seafloor (237 m below the top of volcanic basement), microbes have been identified. This is indicated by the size and shapes of alteration textures and verified by the presence...
The island of Tahiti, the largest in French Polynesia, comprises two major volcanoes aligned NW-SE, parallel with the general trend of the Society Islands hotspot track. Rocks form this volcanic system are basalts transitional to tholeiites, alkali basalts, basanites, picrites, and evolved lavas. Through K-Ar radiometric dating we have established...
The interaction of basalt melt with mantle harzburgite at low pressure might result in silica enrichment of the melt by assimilation of orthopyroxene. Experimental tests of this hypothesis show that silica-rich liquids (56 wt %) are produced by melt-orthopyroxene reaction at 1200° to 1250°C. These silica-rich liquids are enriched in...
The Hawaii Scientific Drilling Program (HSDP) cored and recovered igneous rock from the surface to a
depth of 3109 m near Hilo, Hawaii. Much of the deeper parts of the hole is composed of hyaloclastite
(fractured basalt glass that has been cemented in situ with secondary minerals). Some hyaloclastite units...
The alteration of subseafloor volcanic glass from three locations is qualitatively attributed to biological
(biotic) or chemical (abiotic) reactions on the basis of microscopic morphology of the boundary between
the unaltered and altered glass. Eleven-element composition of fresh basalt glass (sideromelane) and its
alteration products were determined by electron microprobe....
Bransfield Strait is a Quaternary, ensialic back arc basin at the transition from rifting
to spreading. Fresh volcanic rocks occur on numerous submarine features distributed
along the rift axis, including a discontinuous neovolcanic ridge similar to the nascent
spreading centers seen in some other back arc basins. Smaller edifices near...
We propose alternative mechanisms for the origin of three unusual rock suites, high-Mg andesites, NaTi basalts, and arclike rocks, that have been dredged from the Woodlark basin, southwest Pacific Ocean. We show that the high-Mg andesites and NaTi basalts are associated with an unusually cool ridge environment. The cooling is...
These first measurements of specific surface area (SSA)
of bulk samples of subsurface marine basalts were undertaken
to determine the potential area available for microbial
colonization. SSA ranged from 0.3 to 52 m2/g of basalt
with the lowest value coming from pillow basalt and the
highest value from breccia. The...