Atlas of alteration textures in volcanic glass from the ocean basins

摘要

We provide a comprehensive photographicnatlas of the intricate alteration featuresnfound in glass in igneous rocks from thenocean basins. The samples come from surfacenand subsurface rocks from oceanic risesnand seamounts of the ocean basins and somenmarginal seas. These textures have previouslynbeen termed “bioalteration textures”nby those who consider them as potentiallynbiogenic in origin, or as “etch pits” by thosenwho prefer a non-biogenic interpretation.nHere, transmitted-light color photomicrographsnare provided to illustrate the range ofngranular and tubular textures as well as theirnrelation to fractures, minerals, vesicles, andnmultiple episodes of alteration in the samensample. The tubular forms are describednusing seven morphological characteristics:n(1) length and width; (2) density; (3) curvature;n(4) roughness; (5) variations in width;n(6) branching; and (7) tunnel contents. Thenphotomicrographs are a starting point fornunderstanding the factors that control thenformation of the alteration textures, for evaluatingnthe biogenicity of the various forms,nfor inferring subsurface conditions duringnalteration, and for making comparisons tonsimilar textures in ancient ophiolites, some ofnwhich have been attributed to the earliest lifenon Earth.