Atlas of alteration textures in volcanic glass from the ocean basins

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1 tlas of alteration textures in volcanic from the ocean basins Martin Fisk 1 and Nicola McLoughlin 2 1 College of Earth, Ocean and tmospheric Sciences, Oregon State University, Corvallis, Oregon 97330, US 2 Department of Earth Sciences, Centre for Geobiology, University of ergen, 5020 ergen, Norway STRCT We provide a comprehensive photographic atlas of the intricate alteration features found in in igneous rocks from the ocean basins. The samples come from surface and subsurface rocks from oceanic rises and seamounts of the ocean basins and some marginal seas. These textures have previously been termed bioalteration textures by those who consider them as potentially biogenic in origin, or as etch pits by those who prefer a non-biogenic interpretation. Here, transmitted-light color photomicrographs are provided to illustrate the range of granular and tubular textures as well as their relation to fractures, minerals, vesicles, and multiple episodes of alteration in the same sample. The tubular forms are described using seven morphological characteristics: (1) length and width; (2) density; (3) curvature; (4) roughness; (5) variations in width; (6) branching; and (7) tunnel contents. The photomicrographs are a starting point for understanding the factors that control the formation of the alteration textures, for evaluating the biogenicity of the various forms, for inferring subsurface conditions during alteration, and for making comparisons to similar textures in ancient ophiolites, some of which have been attributed to the earliest life on Earth. INTRODUCTION ND PREVIOUS WORK ims and Scope of This tlas The interaction of sub-seafloor volcanic with circulating fluids produces secondary minerals as well as alteration textures that penetrate into the (e.g., Thorseth et al., 1995; Fisk et al., 1998a; lt and Mata, 2000; Furnes et al., 2001a; Josef, 2006). These alteration textures are found in basalts from the flanks of ocean rifts, seamounts, back-arc basins, and marginal seas. The alteration textures include micronsized etch pits and tunnels that are located at the interface of fresh and its alteration products. This petrographic atlas aims to bring together and illustrate the full spectrum of alteration textures in marine lavas to show the variety of alteration textures found in vol canic and hyaloclastites collected from the ocean crust. In particular we focus on the size, morphology, distribution, and infilling of granular cavities and tubular tunnels. selection of annotated petrographic images from a collection of 119 samples spanning the world s ocean basins is provided to systematically illustrate the key textural characteristics of alteration. guide and glossary to the principal features is provided and an accompanying classification scheme is given to identify the key morphotypes of alteration. This expands on earlier classification schemes (Furnes and Staudigel, 1999; Josef, 2006; Staudigel et al., 2006, 2008; McLoughlin et al., 2009) and identifies several previously unrecognized morphotypes. The atlas is intended as an illustrated guide for geologists, microbiologists, and astrobiologists studying alteration. We realize that as researchers further explore their collections and as more deep-sea environments are sampled, new forms of alteration will be found and documented; thus, this guide represents the current state of knowledge. Some alteration textures have previously been argued to represent biological alteration products and trace fossils (e.g., Fisk et al., 1998a; Torsvik et al., 1998; Furnes et al., 2001a, 2001b, 2002, 2008; Furnes and Muehlenbachs, 2003; anerjee and Muehlenbachs, 2003; Thorseth et al., 2003; McLoughlin et al., 2009; Staudigel et al., 2008); however, this study is not designed to support or refute claims of biogenicity of the alteration of basaltic. lso, this work does not investigate the secondary mineralogy of altered, referred to as palagonite, a mixture of iron oxyhydroxides and phyllosilicates (Stronick and Schmincke, 2002), and we have not characterized the secondary minerals, such as carbonates, zeolites, and phyllosilicates, that occur in voids and fractures in the. These minerals are indicative of conditions in the seafloor and may be useful for correlating conditions of alteration with alteration features; however, this is the subject of an ongoing study. If the alteration textures are biotic and if specific textures can be correlated with subsurface conditions, then they could help researchers understand the evolution of the marine subsurface environment from the rchean to the present. Previous Work Granular and tubular alteration textures of oceanic volcanic have been illustrated in transmitted-light photomicrographs since the 1960s (Morgenstein, 1969). In that first study, /palagonite alteration boundaries and linear features in black-and-white photographs were described as micro-channels and hair channels. More recently, transmitted-light photomicro graphs of alteration features in seafloor and sub-seafloor basalt have been published by a number of authors (e.g., Giovannoni et al., 1996; Fisk et al., 1998a, 2006; Furnes and Staudigel, 1999; Fisk and Giovannoni, 1999; Christie et al., 2001; Furnes et al., 2001a, 2002; anerjee and Muehlenbachs, 2003; Storrie- Lombardi and Fisk, 2004; Ivarsson et al., 2008; Staudigel et al., 2008; Cockell and Herrera, 2008; McLoughlin et al., 2009, 2010; Heberling et al., 2010). These studies have, in general, included a limited number of images to illustrate the granular or tubular structures, and they have not documented the full range of alteration textures now known from oceanic igneous. n extensive unpublished collection of photomicrographs also exists (Josef, 2006). Over this more recent period (1996 to the present), alteration features in oceanic basalt have also been illustrated in backscattered electron images, transmission electron images, and energy-dispersive X-ray spectroscopy (EDS) maps (e.g., Furnes et al., 1996, 1999; Torsvik et al., 1998; lt and Mata, 2000; Thorseth et al., 2003; Kruber et al., 2008; Cockell et al., 2009). lso, similar features have been documented Geosphere; pril 2013; v. 9; no. 2; p ; doi: /ges ; 31 figures; 2 tables. Received 26 May 2012 Revision received 17 November 2012 ccepted 20 November 2012 Published online 5 February 2013 For permission to copy, contact editing@geosociety.org 2013 Geological Society of merica 317

2 Fisk and McLoughlin with transmitted-light photo graphs of metamorphosed pillow-lava rims from rchean to Phanero zoic ophiolites (Furnes et al., 2001b, 2004, 2008; Furnes and Muehlenbachs, 2003; Staudigel et al., 2006, 2008) and an rchean mafic tuff (Lepot et al., 2011). Photographs of granular and tubular alteration in basalts from the marine/land transition have also been published (Fisk et al., 2003; Walton and Schiffman, 2003; Walton, 2008; Cousins et al., 2009; Montague et al., 2010). Interestingly, similar transmitted-light photomicrographs of alteration features in pillow lavas erupted into fresh water are not evident in the literature. Common alteration textures, such as tunnels in volcanic, were until recently informally classified by several authors, so synonyms for these textures exist in the literature. more formal ichnotaxonomic classification was suggested by McLoughlin et al. (2009), which considered potential bioalteration textures as trace fossils and recognized two ichnogenera and five ichnotaxa based on a selection of samples from the in situ oceanic crust and Phanerozoic ophiolites. This atlas expands on these five ichnotaxa or morphotypes, and outlines seven morphological criteria and provides names for features that can help unify discussion of the morphotypes. bundance and Distribution of the lteration Textures The percentage of alteration in subseafloor basalts can be estimated visually, and the percent of that total alteration that is attributed to biotic versus abiotic processes has been derived by point counting of thin sections from the Mid-tlantic Ridge, the Costa Rica Rift, and Lau asin (Furnes et al., 2001a). From 2% to 60% of the was altered, with about half of this alteration being granular and tubular and the remainder being abiotic secondary minerals. The amount of granular and tubular alteration has also been visually estimated in basalt at the marine/land transition (Cousins et al., 2009; Montague et al., 2010). One of these studies (Cousins et al., 2009) from the glacial/ marine transition of James Ross Island, ntarctica, found that the samples exposed to sea water tended to have more granular and tubular alteration than samples exposed to fresh water. lteration of a Hawaiian subsurface hyalo clastite was indexed from 1 to 6, with 1 being no alteration to 6 being complete alteration (Montague et al., 2010). Indices were mostly 2 3. From these three studies, it appears that granular and tubular alteration is ubiquitous and more abundant in marine water than fresh water. lthough most photographic documentation of tunnels has come from basalts, there are examples of tunnels from other silicates. There are two examples from felsic rocks one of these is from a rhyolite tuff from central Oregon (United States) (Fisk et al., 1998b) and the other is from a submarine clastic tuff from the western Pacific (anerjee and Muehlenbachs, 2003). lso, tunnels have been documented in olivine from an olivine basalt collected from the marine/land transition in Hawaii and in dunites from central Oregon and northern California (Fisk et al., 2006). Origin of lteration Textures in Volcanic Glass It has been hypothesized based on several lines of evidence that some of the tunnel and granular alteration features are produced biotically. In support of this, biological staining has revealed that nucleic acids can be found at the interface of fresh and altered near tubular and granular textures and in some tubular forms (e.g., Furnes et al., 1996; Giovannoni et al., 1996; Torsvik et al., 1998; anerjee and Muehlenbachs, 2003). It has been shown theoretically that basaltic can yield sufficient energy to support chemolithoautotrophic growth (ach and Edwards, 2003), and culture-independent sequencing studies have shown that the microbial population inhabiting the sub-seafloor is distinct from that found in both overlying seawater and seafloor sediments and is up to 4 times larger (Mason et al., 2009; Santelli et al., 2008). Controlled laboratory experiments have found that enhanced, localized dissolution occurs in volcanic inoculated with microorganisms, relative to abiotic controls (Thorseth et al., 1995; Staudigel et al., 1995). Comparative analysis of pillow-basalt rims and interiors suggests that biological activity has lowered the δ 13 C of the rim relative to the basalt interior (e.g., Furnes et al., 2001c). Partially fossilized, mineral-encrusted microbial cells have been observed in or near etch pits on altered surfaces, and these pits have forms and sizes resembling the associated microbes suggesting that the microbes are involved in pit formation (Thorseth et al., 1992, 2001, 2003). lthough these studies support the hypothesis of biologically mediated tunnels, it has not yet been possible to cultivate microorganisms that create tunnel shapes, and abiotic mechanisms of tunnel production have been proposed such as for the rchean mafic tuffs, which experienced conditions very different from basalts in our collection (e.g., Lepot et al., 2011). So although the weight of evidence is in favor of the biological formation of complex tunnels, the question has not been answered. In attempts to understand the origin of the alteration textures, several geochemical tools have been used to examine the contents of tunnels and the chemistry of the surrounding and alteration products. These studies have included: electron probe micro analysis (Furnes et al., 1996; Torsvik, et al., 1998; Storrie- Lombardi and Fisk, 2004); scanning and transmission electron microscopy (lt and Mata, 2000; Thorseth et al., 2003; enzerara et al., 2007; McLoughlin et al., 2011; Knowles et al., 2012); Raman and/or infrared spectroscopy (Preston et al., 2011); and synchrotron-based X-ray microprobe techniques (enzerara et al., 2007; Staudigel et al., 2008; Knowles et al., 2011, 2012; Fliegel et al., 2012). It has been hypothesized that Fe(II) is an energy source for microbial metabolism, and electron microprobe analyses of palagonite near biotic alteration has higher Fe than palagonite near abiotic alteration (Storrie-Lombardi and Fisk, 2004). nalysis of the nm-wide rim of a tunnel in shows that the lost Fe (lt and Mata, 2000) and this loss of Fe is consistent with a gain in Fe in the alteration material near biotic alteration (Storrie-Lombardi and Fisk, 2004). Transmission electron microscopy and synchrotron-based X-ray microprobe analysis show the presence of partially oxidized Fe (enzerara et al., 2007; Knowles et al., 2011; Fliegel et al., 2012) and organic carbon in tunnel-filling smectite (enzerara et al., 2007). The X-ray microprobe analysis also shows that tunnels are produced by the dissolution of the. Nano-Secondary Ion Mass Spectrometry analyses of carbon, nitrogen, and manganese associated with micropores in suggest that these are remnants of manganese-oxidizing bacteria (McLoughlin et al., 2011). Raman spectroscopy indicates that tunnels contain complex organic compounds such as amides and esters, which could be left by microbial inhabitants (Preston et al., 2011). These studies show that microbes and microbial processes are associated with some of the alteration features described in this paper. The biogeochemical controls on the abundance, distribution, and diversity of alteration textures in volcanic, however, are yet to be identified, and we hope that the framework presented herein will aid future investigations of the these controls on (bio)alteration. In addition, this collection of alteration textures may be an informative companion for those studying the alteration of (meta)volcanic in ophiolites and/or Precambrian greenstone belts and provide a context for interpreting proposed trace fossils that are hypothesized to represent some of the earliest evidence for life on Earth (Furnes et al., 2004). Likewise, for astrobiologists who 318 Geosphere, pril 2013

3 lteration textures of oceanic basalt may one day study alteration in igneous rocks from other planetary bodies (cf. Fisk et al., 2006), this will provide a terrestrial reference frame for the range of currently known textures. SMPLES Samples for this study are from existing collections and are primarily cored sub-seafloor igneous rocks that were collected and archived by the Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP). The location of volcanic within the archived cores was determined by first reviewing Initial Reports volumes of the Deep Sea Drilling Project and the Initial Results volumes of the Ocean Drilling Program. Then, during visits to the sample repositories at Scripps Institution of Oceanography, Texas &M University, and Lamont-Doherty Earth Observatory, the presence of was verified visually and samples were collected from the working halves of the cores. This collection of DSDP and ODP samples was supplemented with a small number of samples from an Integrated Ocean Drilling Program (IODP) expedition as well as from seafloor outcrops that were collected by submersibles. In total, the samples come from 21 DSDP expeditions, 15 ODP and IODP expeditions, and 5 manned and unmanned submersible expeditions. Samples are from the Pacific, Indian, and tlantic Oceans, the Mediterranean Sea, and some adjacent seas. asalts from ocean rifts, seamounts, and back-arc spreading ridges are included in the study. The cored samples come from a range of depths into the volcanic basement, ranging from the sediment/ basalt contact (<0.5 m into basement, mib) to 320 mib. Samples collected by submersible are from outcrops on the seafloor. The samples are primarily the rims of pillow basalts, sheet-flow margins, and interflow breccias. The youngest cored basalt examined was <0.4 Ma and the oldest was 167 Ma. t some cored sites, samples from multiple depths were examined. Standard 26 mm 46 mm polished petrographic thin sections were examined. These are listed in Table 1, and Figure 1 shows the global distribution of samples. ll samples, except 482D 11R2 32, which appears to have been at 150 C at the time of collection (Duennebier and lackinton, 1980), were from the seafloor or shallow subsurface where ambient temperatures were compatible with life (<100 C). METHODS The petrographic thin sections listed in Table 1 were examined with a petrographic microscope fitted with objective lenses with 4, 10, 20, and 40 magnification. Thin sections are nominally 30 μm thick, which is 3 30 times the diameter of most tunnels and thus permits viewing tunnels in three dimensions by changing the elevation of the microscope stage. The observation strategy was to survey the whole thin section with the 4 objective lens to locate areas of. These es were then viewed at 10 and/or 20 to locate regions that contained altered and -alteration textures. Glass commonly was limited to less than 25% of the thin section area and most regions of altered were examined at one of these two higher magnifications. The alteration was photographed at 40 and sometimes at 10 for larger features or to show the context of the feature being illustrated. ll of the morphotypes of alteration found in our selection of thin sections are illustrated in the figures. The optical images shown here were obtained using a Nikon LV100Pol polarizing microscope at the Centre for Geobiology in ergen, Norway, and photographed using an DS-Fi1 color camera with 5.24-megapixel resolution coupled to NIS-Elements R 2.30 software. The images were saved in Joint Photographic Experts Group (.jpg) format ( pixels). RESULTS Guide to Illustrations The alteration features are summarized in line drawings in Figure 2, and each line drawing references a photograph that illustrates the feature (Figs. 3 31). The diversity of alteration features can be illustrated with a subset of 26 thin sections (identified by bold italics font in Table 1). Each photograph is labeled with the sample identification, a scale bar, and descriptive terms. lso the and major features such as fractures, vesicles, and minerals are annotated. Features are first separated into major categories of granular and tubular forms (Fig. 2, upper left panel) as previously described (Furnes et al., 2001a). In addition to the granular form, a bud-shaped form is recognized here that is an intermediate form between granular and tubular. The photographs are grouped by the primary feature that is being illustrated such as granular forms, simple tubes, branching, distribution, and overprinting. In many photographs, more than one textural feature is present but typically only the feature being demonstrated is described. glossary of terms is provided in Table 2 to aid in the description of the alteration features. In the text below, terms that are from the glossary are italicized. Tubular lteration The tunnel forms are more complex and varied than granular textures and are therefore further characterized by their shape, density, contents, and their relationship to other features in the thin sections such as fractures and vesicles. Seven major characteristics are used to describe the variety of tunnel morphologies. These are: (1) size (length and width); (2) spacing between similar tunnels; (3) curvature; (4) roughness; (5) changing width along the length of the tunnel; (6) branching; and (7) tunnel contents. In addition we recognize differences in how tunnels are distributed relative to fractures, minerals, and vesicles, and we note that some thin sections have a single type of alteration but others exhibit multiple forms. The term thin is applied to tunnel widths (diameters) less than 3 µm from edge to edge (Fig. 8) and long tunnels are more than 50 times longer than they are wide (Fig. 6). The length of short tunnels is less than 10 times their width (Fig. 6). The density term (Fig. 2) is based on how closely packed the tunnels are along the fracture or other surface from which they originate: close tunnels have a center-to-center distance that is less than 10 times the tunnel width (Fig. 7), whereas the center-to-center distance of separated tunnels are apart by more than 10 times their diameters (Fig. 7). Tunnels are usually curved and directed, such as away from a fracture (e.g., Figs. 5, 6). These directed tunnels can be nearly linear (curvilinear), kinked with sharp changes in direction (Figs. 5, 9), or appear have a tangled knotted appearance along their length (Fig. 8). Convoluted tunnels turn back toward their point of origin (e.g., Fig. 24) and do not appear to be directed away from their point of origin. Some tunnels have nearly constant width ±20% over their entire lengths (Figs. 5, 7), but others are variable (e.g., Figs. 14, 15, 20). Some taper from their origin at a free surface to a point in the (Fig. 13). Others have repeated variations in their width resulting in a rhythmic annulated tunnel (Fig. 13), or have a single bump between the tunnel origin and end termed engorged tunnels (Figs. 11, 22), or multiple irregular bumps (Fig. 12). Rarely, a tunnel will broaden into a mushroom shape (Fig. 14) or central disk (Fig. 12). In addition to tunnels of variable width, there are round bud and bubble textures that are present at the margins of fractures (Figs. 16, 17). The surfaces of some tunnels are smooth, having irregularities that are less than 0.5 μm (Fig. 10). Rough tunnel walls (Figs. 7, 10, Geosphere, pril

4 Fisk and McLoughlin TLE 1. SMPLES EXMINED FOR THIS STUDY Leg Thin section asin Feature Lithology R3 46 tlantic West flank, Mid-tlantic Ridge asalt R1 67 Indian Ninety East Ridge, hotspot track asalt R1 30 Indian West flank Carlsberg Ridge, Somali asin asalt R1 64 Indian South flank Southeast Indian Ridge asalt R2 106 tlantic West flank Mid-tlantic Ridge Ol-plag basalt R3 7 tlantic West flank Mid-tlantic Ridge Plag-ol basalt R5 46 tlantic West flank Mid-tlantic Ridge Plag-ol basalt breccia R2 77 tlantic East of egir Rift, Norway asin asalt breccia R3 128 Mediterranean Central Tyrrhenian byssal Plain asalt breccia R1 83 tlantic North Pond, west flank Mid-tlantic Ridge Plag-ol-cpx basalt R1 91 tlantic North Pond, west flank Mid-tlantic Ridge Plag-ol-cpx basalt R1 131 tlantic North Pond, west flank Mid-tlantic Ridge Plag-ol-cpx basalt R3 8 tlantic North Pond, west flank Mid-tlantic Ridge phyric basalt R2 112 tlantic North Pond, west flank Mid-tlantic Ridge Hyaloclastite R1 102 tlantic North Pond, west flank Mid-tlantic Ridge phyric basalt R1 146 tlantic North Pond, west flank Mid-tlantic Ridge phyric basalt R6 108 tlantic East flank Mid-tlantic Ridge Plag-ol basalt R3 108 tlantic East flank Mid-tlantic Ridge Plag-ol basalt D 54R1 129 tlantic West flank Mid-tlantic Ridge Plag-cpx-ol pillow basalt D 66R6 35 tlantic West flank Mid-tlantic Ridge Plag-cpx-ol pillow basalt R3 41 tlantic West flank Mid-tlantic Ridge Plag-cpx-ol pillow basalt R3 87 tlantic West flank Mid-tlantic Ridge Plag-cpx-ol pillow basalt R2 81 tlantic West flank Mid-tlantic Ridge Plag-cpx-ol pillow basalt R1 17 Pacific Shikoku asin, Philippine Sea phyric basalt R8 33 Pacific Shikoku asin, Philippine Sea phyric basalt R3 105 Pacific Shikoku asin, Philippine Sea phyric basalt R2 34 Pacific East flank Palau-Kyushu Ridge, Philippine Sea Plag-ol basalt R1 124 Pacific East flank Palau-Kyushu Ridge, Philippine Sea Plag-ol-cpx basalt R3 118 Pacific East flank Palau-Kyushu Ridge, Philippine Sea Plag-ol-sp pillow basalt R2 48 Pacific East flank Palau-Kyushu Ridge, Philippine Sea Plag-ol-sp pillow basalt R2 142 Pacific Palau Ridge, Philippine Sea phyric basalt R2 18 Pacific Palau Ridge, Philippine Sea Plag-ol basalt R2 32 Pacific Palau Ridge, Philippine Sea Volcanic breccia R1 23 Pacific West of Palou-Kyushu Ridge, Philippine Sea Plag-ol-sp pillow basalt R2 17 Pacific ase of Patton Escarpment, California orderland phyric basalt R1 26 Pacific aja Seamount Province phyric basalt R1 102 Pacific aja Seamount Province phyric pillow basalt R1 92 Pacific Mouth, Gulf of California Plag pillow basalt D 11R2 32 Pacific Flank of East Pacific south of Tamayo Fracture Zone phyric basalt R2 34 Pacific Flank of East Pacific south of Tamayo Fracture Zone Plag-cpx-ol basalt R2 80 Pacific South flank Costa Rica Rift Plag-ol pillow basalt R1 18 tlantic East flank Mid-tlantic Ridge phyric basalt R1 105 tlantic ngola byssal Plain, east flank Mid-tlantic Ridge phyric pillow basalt R3 11 tlantic East of arbados Ridge, west flank Mid-tlantic Ridge Plag-ol pillow basalt R7 60 tlantic East of arbados Ridge, west flank Mid-tlantic Ridge Plag-ol basalt R1 21 tlantic East flank Mid-tlantic Ridge Phyric basalt R4 33 tlantic West flank Mid-tlantic Ridge phyric basalt R4 108 tlantic West flank Mid-tlantic Ridge Plag basalt R1 37 tlantic West flank Mid-tlantic Ridge phyric pillow basalt R2 37 tlantic West flank Mid-tlantic Ridge phyric pillow basalt R1 39 tlantic West flank Mid-tlantic Ridge Plag pillow basalt R1 107 Mediterranean Vavilov asin, Tyrrhenian Sea asalt R1 34 Mediterranean Vavilov asin, Tyrrhenian Sea asalt C 2R2 76 Indian Mascarene Plateau, Reunion Hotspot track Plag basalt R5 89 Indian Chagos Ridge, Reunion Hotspot track Plag basalt hawaiite R5 98 Indian Chagos Ridge, Reunion Hotspot track Plag basalt hawaiite R6 24 Indian Chagos Ridge, Reunion Hotspot track Plag basalt R2 133 Indian Ninety East Ridge, hotspot track phyric pillow basalt D 5R1 12 Indian rgo byssal Plain, eastern Indian Ocean asalt D 5R1 53 Indian rgo byssal Plain, eastern Indian Ocean asalt D 5R8 81 Indian rgo byssal Plain, northeastern Indian Ocean asalt D 13R1 96 Indian rgo byssal Plain, eastern Indian Ocean reccia D 24R3 142 Indian rgo byssal Plain, eastern Indian Ocean Pillow breccia R3 142 Pacific Celebes Sea Plag-ol basalt C 4R1 14 Pacific Celebes Sea Plag-ol basalt breccia R1 106 Pacific Izu-onin back arc asalt breccia R1 134 Pacific Isu-onin forearc asalt breccia C 12R1 85 Pacific West flank East Pacific Ol-plag basalt C 17R3 85 Pacific West flank East Pacific phryic basalt C 48R2 121 Pacific West flank East Pacific phryic basalt C 42R2 126 Pacific West flank East Pacific phryic basalt R2 97 Pacific West flank East Pacific Ol-plag basalt D 69R1 50 Pacific Ontong Java Plateau phryic basalt D 70R2 117 Pacific Ontong Java Plateau phryic basalt C 75R2 8 Pacific Ontong Java Plateau phryic basalt C 82R5 14 Pacific Ontong Java Plateau phryic basalt C 92R2 110 Pacific Ontong Java Plateau phryic basalt R2 73 Pacific Interarc basin, New Hebredes Plag basalt H7 Pacific Western Lau asin backarc phryic basalt (continued) 320 Geosphere, pril 2013

5 lteration textures of oceanic basalt TLE 1. SMPLES EXMINED FOR THIS STUDY (continued) Leg Thin section asin Feature Lithology R1 20 Pacific Western Lau asin backarc Cpx-ol basalt R1 1 Pacific Western Lau asin backarc Cpx-pl basaltic andesite R1 11 Pacific Forearc, Tonga Ridge Rhyolite breccia C 5R1 24 Pacific Taitao Ridge, Chile Triple Junction Plag-hbl dacite R1 Pacific East flank, Juan de Fuca Ridge asalt breccia R1 81 Indian Kerguelen Plateau, hotspot platform Plag basalt R1 31 Indian Kerguelen Plateau, hotspot platform Plag-cpx basalt R2 24 Pacific Emperor Seamounts, Hawaii-Emperor hotspot track Plag-ol basalt R1 118 Pacific Emperor Seamounts, Hawaii-Emperor hotspot track Plag-ol basalt E 11R1 83 Pacific Ridge flank phyric basalt F 2R3 53 Pacific West flank East Pacific phyric basalt F 5R1 27 Pacific West flank East Pacific phyric basalt F 6R1 0 Pacific West flank East Pacific phyric basalt F 9R1 78 Pacific West flank East Pacific phyric basalt F 11R1 108 Pacific West flank East Pacific phyric basalt F 13R2 102 Pacific West flank East Pacific phyric basalt F 13R2 120 Pacific West flank East Pacific phyric basalt F 13R3 20 Pacific West flank East Pacific phyric basalt DSV lvin Pacific Warwick Seamount, Cobb-Eichelberger hotspot track asalt DSV lvin 3816 F Pacific Coxial segment, Juan de Fuca Ridge asalt DSV lvin Pacific Warwick Seamount, Cobb-Eichelberg hotspot track Hyaloclastite DSV lvin 3823G Pacific Cobb Seamount, Cobb-Eichelberg hotspot track asalt DSV lvin 3825 C Pacific rown ear Seamount, Cobb-Eichelberg hotspot track asalt DSV lvin 3853 R Pacific Crest, East Pacific asalt DSV lvin C Pacific Denson Seamount asalt DSV lvin , 3, 8, 15 Pacific Denson Seamount asalt DSV lvin Pacific Dickins Seamount asalt DSV lvin , 3, 8, 11 Pacific Dickins Seamount asalt DSV lvin , 4, 8 Pacific Dickins Seamount asalt DSV lvin Pacific Dickins Seamount asalt DSV lvin Pacific Welker Seamount asalt DSV lvin , 5, 9, 10 Pacific Welker Seamount asalt DSV lvin Pacific Pratt Seamount asalt DSV lvin , 30 Pacific Pratt Seamount asalt DSV lvin Pacific Giacomini Seamount asalt DSV lvin Pacific Giacomini Seamount asalt DSV lvin Pacific Giacomini Seamount asalt DSV Sea Cliff MR3-3 Pacific Mendocino Ridge, transform fault asalt ROV Tiburon MRF1-10R Pacific Mendocino Ridge, transform fault asalt ROV Tiburon MRF1-8R Pacific Mendocino Ridge, transform fault asalt Note: For drilled samples, the Leg indicates the Deep Sea Drilling Project (DSDP), Ocean Drilling Program (ODP), or Integrated Ocean Drilling Program (IODP) expedition. Thin section number includes the core site number, the hole at that site, the core barrel number, the type of core (R for rotary rock core, H for hydraulic piston core, and CC for core catcher), section of core (the cored material was archived in 1.5 m sections), and distance in centimeters from the top of the section to the sample. (For example, R2 106 indicates: Site 332, Hole, Core 20, a core type of rotary, Section 2, and 106 cm from the top of Section 2). Numbers for the samples collected with submersibles are the vehicle designation, the dive number, and the sample number assigned when the rocks were archived. Entries in bold italic font are illustrated in Figures In addition, the ocean basin, geological feature, and lithology are indicated. Data are from the DSDP Initial Reports volumes and the ODP Preliminary Reports and Scientific Results volumes. DSDP data are available online from the National Geophysical Data Center ( ODP data are available online from the Ocean Drilling Program (Publications Leg-Related Publications) ( The table is modified from a previously compiled table (Josef, 2006). Figure 1. Locations of all samples examined as part of this study. Larger (white) circles indicate the locations of samples that are documented with photographs in this article; other samples examined are indicated by smaller (blue) circles. The map was generated with Geo- Mappp, (Ryan et al., 2009). 11) are embellished with fine (>1 μm) extensions into the uniformly or periodically distributed along the tunnel. The widths of individual extensions from the walls of tunnels are much thinner than the width of the tunnel. In contrast to this, branches (Fig. 2) are commonly the same width as the main tunnel. ranching may be simple with the nodes widely spaced along a tunnel, (Fig. 17), or mossy (Fig. 4), or networks (Figs. 18, 19), where branches are crowded together and branch repeatedly. In the case of simple, mossy, or network branching, daughter branches are the same diameter as the parent branch. In other cases branches are narrower than their parent tunnels (Figs. 20, 21). Some tunnels have crowns, composed of multiple radiating tunnels that have a different form than the tunnel from which they originate (Figs. 21, 23, 25). Geosphere, pril

6 Fisk and McLoughlin Figure 2. Schematic diagram summarizing the morphological characteristics used to describe alteration textures. The box (top left) shows the main alteration morphotypes: tubular, granular, and the less common sub-types of buds and bubbles. In the rest of the figure, seven characteristics are illustrated with line diagrams: (1) length and width; (2) density; (3) curvature; (4) roughness; (5) variations in width; (6) branching; and (7) tunnel contents. Each of the morphological forms is given a simple descriptive term, and a typical example from our photographic atlas is given. Descriptive terms are defined in Table 2. This diagram expands on the ichnotaxonomic classification scheme shown in McLoughlin et al. (2009, their figure 1). 322 Geosphere, pril 2013

7 lteration textures of oceanic basalt phenocryst light granular border palagonite Figure 3. () Tan (upper and lower areas of photo) with a fracture filled with banded, yellow to tan palagonite. The border of the with the palagonite (arrows) has a granular texture. The lower border is darker than the upper border. () Light-tan in the lower part of the photo, palagonite in the upper part of the photo with a granular boundary at the palagonite/ interface. crystalline quench feature (variole) is on the right side; a microphenocryst is below the focal plane in the center of the palagonite. filled fracture darker granular border R1 31 micro phenocryst palagonite micro phenocrysts variole granular R1 92 mossy granular 803D 69R1 50 variole palagonite granular palagonite Figure 4. () Circular alteration features along a fracture. The center of the fracture is palagonite, which is surrounded by a band of dark granular texture at the palagonite/ border. mossy texture extends from the granular band into the. () Short, dark, rough tunnels <5 μm wide and < long at the /granular-alteration boundary. Mossy tunnels appear to be random as opposed to directed tunnels. mossy dark zone variole 765D 5R8 81 Geosphere, pril

8 Fisk and McLoughlin granular mossy random Figure 5. () Five styles of alteration are illustrated: (i) granular, (ii) mossy, (iii) simple directed tunnel with constant width, (iv) kinked directed tunnel, and (v) random tunnels. () Simple 50-μm-long, 3 5-μm-wide tunnels radiate from a central point on the edge of a fracture at high angles R1 124 radia ng tunnels Sea Cliff MR3 3R palagonite long granular mossy 765D 5R1 53 variole 500 μm bubble texture Figure 6. () Long, directed tunnels extend more than 500 μm from the granular and mossy texture at the right edge of the. Tunnels are ~3 μm wide. () Simple, short, close tunnels extending from clay along the margin of an olivine grain and from an area of bubble texture. These tunnels are 1 2 μm wide and 10 μm long and 1 or 2 μm apart. Nearby bubble texture has no tunnels emerging from it. short tunnels olivine R Geosphere, pril 2013

9 lteration textures of oceanic basalt R2 89 Figure 7. () Close, smooth tunnels are 5 7 μm wide and μm apart along the fracture. () Separated tunnels (the spacing along the fracture is more than 10 times the tunnel width). In this case, the tunnel width is 5 7 μm and the distance between them is 100 μm. These channels are ornamented with 3 5 μm extensions and contain septa. smooth tunnels separated by 30 μm at their intersec ons with the fracture separated 765D 5R R1 102 short wide tunnels or granular incursions R6 108 tangles granular palagonite Figure 8. () Thin, <3-μm-wide, directed, hair tunnels originating from the edge of the fracture. The fracture contains a 10-μm-wide layer of brown material adjacent to the. The image also contains tunnels that randomly change direction within a segment of the tunnel. tunnel may have more than one of these tangled regions. () lternating dark and light concentric rings in yellow palagonite are centered along the fracture. Granular texture extends from the fracture or from the concentric rings to a dark granular zone. Short, wide, granular incursions emerge from the dark, granular texture. The fracture is filled with an undetermined white transparent mineral. concentric rings fracture Geosphere, pril

10 Fisk and McLoughlin 765D 5R8 81 Figure 9. () Directed, simple, empty tunnels with a constant width of 5 μm emerge from granular material. The granular alteration is separated from an original fracture by a crack that was produced possibly during the manufacture of the thin section. Yellow granular material has replaced along the original fracture. () Kinked, directed, opaque tunnels ~3 μm wide emerge from the dark granular material. fracture just visible in the upper right of the photo is surrounded by palagonite that grades from yellow to brown to black. empty tunnel kinked tunnels palagonite R R3 11 smooth smooth R3 46 quench crystals Figure 10. () Smooth, simple, 5 10-μm-wide tunnels emerge from yellow granular alteration. Two tunnels are indicated with arrows. () Simple tunnels with rough surfaces emerge from brown alteration at the edge of a fracture. Tunnels are 5 10 μm wide. altera on rough 326 Geosphere, pril 2013

11 lteration textures of oceanic basalt microphenocryst Figure 11. () 15-μm-wide tunnel with rough exterior expands at the end to ~35 μm wide. The tunnel also has an enlargement in the midsection. Short tunnels, 5 10 μm long, also emerge from the fracture in lower part of the photo. () Fracture in the lower left contains brown fill and is surrounded by altered. From this comes wide (10 15 μm), rough tunnels that taper to 10 μm or less at their ends and have an intermediate enlargement (15 wide) with a single ovoid body with dark edges. 807C 75R2 8 terminal enlargement intermediate enlargement microphenocryst short 807C 75R2 8 intermediate enlargements (engorged) 10 μm granular mossy altera on R1 81 terminal enlargement annulated tunnels disk Figure 12. () Fractures with several styles of alteration. Yellow granular alteration occurs at the margins of the fractures. Mossy alteration and 3-μmwide tunnels with variable width emerge from the fracture on the left. nnulated tunnels and tunnels with club-shaped ends emerge from the fracture with yellow fill. () Fracture surrounded by several styles of alteration, one of these (arrow) being a smooth tunnel, 5 μm wide, that has a 25-μm-wide, dark disk 100 μm from the fracture and 60 μm from the tunnel terminus R1 146 Geosphere, pril

12 Fisk and McLoughlin Figure 13. () Smooth, 10-μmwide tunnel with spiral filament has repeated rings (annulations) every 3 5 μm near its end. The photo also contains smooth, thin, simple tunnels on both sides of a fracture that runs vertically through the image, and thin, kinked, dark tunnels on the left side of the image. () Fracture with little alteration has three smooth fingers or tunnels of variable width that taper from 10 μm at their bases to points ~30 μm from the fracture. rown patches are areas of quench crystals and varioles. annula ons tapered fingers 765D 5R8 81 variole R5 8 Quench crystals 807C 92R2 110 petal (ii) R2 77 honeycomb petal with honeycomb pa ern Figure 14. () There is a fracture in the lower left from which a tunnel that is wide expands to 40 μm just below a mushroom-shaped cap that is 70 μm wide. () Fracture runs diagonally from the upper left corner and has smooth tunnels, three of which are broad and flattened, petal shapes. One (i) has a honeycomb constructed of 5 10-μm-wide cellular pattern. nother (ii) has dark lineaments spaced 5 μm apart. oxed areas are shown in Figure 15. Spotted texture is an artifact of thin section production. (i) NM μm 328 Geosphere, pril 2013

13 lteration textures of oceanic basalt R2 77 petals petals with honeycomb pa ern Figure 15. () Flattened petalshaped tunnels have a 10-μmwide cell-like pattern of dark partitions. () Flattened petalshaped tunnel with ribs separated by 5 μm. Smooth tunnel with spiral filament is on the left side of the photograph R2 77 petal ribs spiral 765D 5R8 81 buds bubble texture granular upper trunca on of tunnel lower trunca on of tunnel R1 26 Figure 16. () Two short, wide (15 ), smooth, round, yellow-brown buds extend from the granular area next to the fracture. lso present is a row of tunnels that are truncated at the upper and lower surfaces of the thin section. () Coalesced 5 8-μm-diameter spheres produce a bubble texture. The bubbles grade from transparent yellow spheres on the left to brown spheres with dark rims. Geosphere, pril

14 Fisk and McLoughlin 482D 11R2 32 Figure 17. () 10-μm-wide fracture has 5 10-μm-diameter spherical buds along its edge. The buds lack any internal structure and are not granular. () Simple branching; a single tunnel can have more than one node. ranches have the same diameter as the trunk. Tunnel width varies in a sawtooth or thorny pattern. buds nodes R R5 43 dark, kinked tunnels networks mass of dark, kinked tunnels granular palagonite Figure 18. () Dark, 1-μmwide, separated, branched tunnels form random networks that extend μm from the fracture. () Semicircular palagonite area is centered on a fracture (top of photo) and surrounded by a black mass of kinked tunnels. ranched, straight, dark tunnels are 3 5 μm wide. 30-μm-long tunnels with undulating, smooth outlines emerge from the black mess. The branches fork at ~60 angles from each other. Most appear to have only one branch per tunnel. oxed area enlarged in Figure 19. branched tunnel with single node 50 μm R1 26 NM Geosphere, pril 2013

15 lteration textures of oceanic basalt Figure 19. () nnulated tunnels branch at 60 angle. Mossy, kinked tunnels also branch. () Fracture at the bottom of the photo has granular alteration along one side that grades into a dark zone. Emerging from the dark zone are kinked, dark, branched, random tunnels that are ~3 μm wide and μm long. This is the type specimen of Tubulohyalichnus stipes isp., first described in McLoughlin et al. (2009). annulated branched tunnels R R1 26 mossy branched tunnels dark, kinked, branched network of tunnels fracture dark zone altera on NM 2012 NM 2012 palmate branching bulbs fracture nodes 50 μm annulated crowns bulb palagonite petal shape kinked, dark, branched blunt R22 77 Figure 20. () Fracture at the bottom of the photo has tunnels up to 300 μm long emerging from it. One tunnel branches at nodes into a palmate arrangement of tunnels that terminate in 2 μm bulbs. Some tunnels are annulated; one has a petal shape. Some branches emerge from an expanded node; some tunnels are partitioned with a filigree of dark material. () Fracture (out of view below the bottom of the photo) is surrounded by reddish palagonite (granular texture), which grades into a dark zone. Emerging from the dark zone are dark, simple tunnels that are 5 10 μm wide. Some have blunt terminations as close as 10 μm to the dark zone. Others penetrate into the and expand to wide or produce crowns of 3 5-μmwide tunnels that end in bulbs R1 102 NM 2012 Geosphere, pril

16 Fisk and McLoughlin lvin tunnel crowns Figure 21. () Separated, smooth tunnels, 3 4 μm wide and long, with crowns composed of multiple, dark helixes that are 1 μm wide. () Three forms of tunnel filling of simple, directed, smooth tunnels: granular, intermittent dark material, and continuous dark material. constant width dark, helical tunnels R2 48 intermi ent dark contents con nuous dark contents granular contents 765D 5R1 53 septae ovoid bodies intermediate enlargements Figure 22. () Smooth, simple, 2-μm-wide tunnels contain 2 μm ovoid bodies spaced 10 apart and septae that divide the tunnel at 2 μm intervals. () Tapering tunnels with intermediate enlargements that are divided by dark partitions. enlargement with divisions 807C 75R Geosphere, pril 2013

17 lteration textures of oceanic basalt crown septae 807C 75R2 8 Figure 23. () Dark alteration at the right of the figure has a single, rough, variable-width tunnel that is 100 μm long and expands from 12 μm at its base to just below the 30-μmwide, rough crown. The tunnel has prominent septae and an enlarged segment below the crown. () Smooth, simple, 5-μm-wide tunnels contain spiral filaments. One tunnel may also have a filament and septae. microphenocryst enlarged segment variable width R3 11 spiral filaments septae R1 124 variole convoluted dark object in annulated tunnel Figure 24. () Fracture at the left has separated patches of dark, granular material. From one of these patches emerges a 1 2-μm-wide, simple, directed, convoluted tunnel with dark contents. () nnulated tunnel contains a 10-μm-wide and 20-μm-long, brown oval R2 89 Geosphere, pril

18 Fisk and McLoughlin ovals Figure 25. () group of tunnels radiate from a center on a fracture at the right of the photo. One smooth, 8-μm-wide tunnel in the group contains numerous 8 μm 5 μm ovals that are 5 10 μm apart. second tunnel also contains ovals. () 3 5-μm-wide fracture with granular alteration along its edges and rough, simple tunnels (5 10 μm wide and up to 40 μm long) with rough crowns, 10 wide. Tunnels vary in width and several have three bulges plus the crown. bumpy crown R R2 34 fracture tunnel tunnels 765D 5R1 53 vesicle fracture olivine microphenocryst 765D 5R1 53 olivine vesicle tunnel emerging upward and turning to the right tunnels 1 to 2 μm bodies Figure 26. () fracture cuts across the center of the photo. Two spherical vesicles, one 70 μm in diameter and the other 30 μm in diameter, are above the fracture. Empty, rough tunnels with broadened crowns extend from the rims of the vesicles. () Smooth, simple, 1 3-μm-wide tunnels emerge from the rim of a vesicle. The vesicle contains tan clay and an opaque sulfide. The tunnels extend from the vesicle in opposite directions. Some tunnels contain ovoid bodies. The photo also shows two smooth tunnels with ovoid bodies that are not connected to the vesicle and which wrap around an olivine microphenocryst. tunnels wrapping around olivine 334 Geosphere, pril 2013

19 lteration textures of oceanic basalt Figure 27. () vesicle lined with light-tan clay. The rim of the vesicle has been altered to granular palagonite. Granular incursions into the are 5 wide at their contact with the granular/ boundary and have rough crowns that are wide. () dark brown, 150-μm-long and 70-μm-wide variole has numerous empty, smooth tunnels that are 1 3 μm wide and up to 80 μm long that emerge from the contact of the spherule with. The tunnels only emerge from the side of the variole that faces the fracture. t the top of the photo, there is a fracture surrounded with light-colored alteration with a dark border and associated, dark, kinked tunnels. granular incursions altered clay precipitate empty vesicle Tiburon MRF1 8R fracture altered tunnels variole rough crowns R R3 11 fracture network variole Figure 28. () fracture on the left and a dark quench feature (variole) on the right are connected by clear, smooth tunnels that are 1 3 μm wide and μm long. () thin, directed network of branched tunnels between the fracture on the left and olivine micropheno cryst on the right. In some locations, the network appears to initiate from the olivine and in others, it emerges from the fracture R5 43 olivine microphenocryst Geosphere, pril

20 Fisk and McLoughlin Figure 29. () Glass that once surrounded a vesicle has been replaced with palagonite. The outlines of smooth, tapered tunnels with dark tips that surround the vesicle are preserved. () Fracture in the lower part of the photo has dark networks of tunnels that were overprinted with secondary alteration that left parallel dark laminations outlining the groups of tunnels. second episode of similar tunnels formed along the dark upper margin of the alteration. microphenocrysts preserved vesicle preserved, smooth, tapered, short tunnels 765D 5R1 53 second genera on of tunnels 100 μm fracture R3 105 preserved network parallel dark lamina ons R2 17 (4) granular texture tunnels (3) preserved altera on textures fracture (1) (2) overprinted tunnels 100 μm Figure 30. () fracture across the lower part of the photo is bordered by an early stage of dark, granular alteration (1). This is followed by hemispherical alteration centered on what is assumed to be the edge of an advancing alteration front (2). second dark zone (3) is associated with dark, mossy alteration. The final /alteration boundary is dark and rough (4). The white crack occurred during or after sample collection. () Granular texture surrounded by 5 8-μm-wide, tapered channels. Similar but slightly larger tunnels are present to the right of the granular texture and are overprinted with palagonite. 765D 5R Geosphere, pril 2013

21 lteration textures of oceanic basalt Figure 31. Simple, smooth, empty tunnels start at the granular boundary of the fracture and extend parallel to the fracture. Tunnels are 5 μm wide and 40 μm long or longer. Granular texture extends 5 from the edge of the fracture. Content of lteration Textures The contents of tunnels can vary as well. Some tunnels appear to be empty (Fig. 9), but others are partially or completely filled (Fig. 21) with opaque material. Tunnel contents can be segregated into oval or ovoid bodies typi cally 1 2 μm in diameter that are commonly evenly distributed along the interior of the tunnel (e.g., Figs. 22, 25). However, a single, large, ovoid body is present in some tunnels and the tunnel walls swell around the body (Fig. 11). In one example the large ovoid body is divided by dark septae into five separate bodies (Fig. 22). Septae can also divide a tunnel into multiple chambers that are 5 10 μm long (e.g., Figs. 22, 23). road flat tunnels are divided by a honeycomb or patterned with a filigree of dark material (Figs 14, 15). Tunnels may also have spiral filaments (e.g., Figs. 13, 23). Distribution and Directionality of lteration The distribution of alteration textures within has also been documented in this study. Tunnels are usually found distributed along fractures (e.g., Figs. 5, 6) but sometimes they are distributed around vesicles (Figs. 26, 27, 29), varioles (Figs. 27, 28), or phenocrysts and microphenocrysts (Figs. 6, 28). Tunnels are commonly directed away from fractures, but sometimes they are parallel to fractures (Fig. 31). Tunnels may also radiate from a point at the edge of a fracture (Fig. 5). Some tunnels turn sharply from their initial direction perpendicular to the surface where they originate to a direction parallel to the alignment of other tunnels in the (Fig. 26). In one example, the alignment of tunnels is parallel to the major axis of elongation of vesicles in the (not shown). parallel to fracture Timing of lteration The photographs also illustrate the temporal relationship of alteration in some samples. For example, Figure 29 shows tapered tunnels radiating from a vesicle. Originally the tunnels extended into, but the vesicle, tunnels, and surrounding have now been replaced with phyllosilicate. Overprinting of a network is obvious in Figure 29. Here a granular border evolves into a dark network in in the upper half of Figure 29. In the lower half of the figure, containing a previous dark network has been transformed into a yellow phyllosilicate. In Figure 30 a semicircular alteration pattern, which is similar to that in Figure 8, has been replaced by a subsequent phase of alteration, which suggests conditions changed during the formation of this alteration boundary. STTE OF KNOWLEDGE ON LTERTION TEXTURES IN VOLCNIC GLSS 765D 5R8 81 This tlas Compared to Earlier Studies Morgenstein (1969) illustrated granular and tubular textures in three dredged basalts from the Mid-tlantic Ridge and one from a fracture zone along the Pacific-ntarctic Ridge. His transmitted-light images showed granular alteration forming a semicircle around a fracture (similar to Fig. 4) and 20-µm-wide zones between and palagonite along fractures (similar to Fig. 4). His photographs also include what he called hair tunnels (see Table 2) extending 50 μm from a granular texture into (similar to Fig. 6) and from fractures into (similar to Fig. 9). He also described a solid solution border that is similar to the dark zone between and palagonite (Fig. 4). It was not until 1996 that tubular and granular features were again emphasized and documented with transmitted-light photomicrographs (Giovannoni et al., 1996). lso at this time and from the same Costa Rica Rift site, granular and tubular features were illustrated in backscattered electron images (Furnes et al., 1996). More detailed close-up photomicrographs (Fisk et al., 1998a) illustrated that the tubular phenomenon was more varied than the tunnels seen in Costa Rica Rift basalts. In these new photographs, mossy and branching tunnels, granular alteration, as well as tunnels with pronounced septae and cell-sized inclusions were illustrated from separate seamounts in the Pacific Ocean (one dredged and one cored basalt), from the Mid-tlantic Ridge (two cored basalts), and from the Indian Ocean (one cored basalt) (Fisk et al., 1998a). In the 2000s the growing literature of oceanic alteration reported additional morphologies including: budding along a tunnel (Furnes et al., 2000a), similar to what we have called tangled texture (Fig. 8), and bifurcating tunnels (Furnes et al., 2001a, 2002). nnulated and convoluted tunnels were described by anerjee and Muehlenbachs (2003) in basalts from the Ontong Java Plateau, which we have also illustrated with samples from Chagos Ridge (Fig. 13) and from the Philippine Sea (Fig. 24), respectively. Josef (2006) identified a number of textures not previously described, such as mushroom (Fig. 14) and engorged (Fig. 11). Networks of branched tunnels were first described by McLoughlin et al. (2009), and the type example is illustrated in Figure 19. Here we also report networks made of thinner branched tunnels (Figs. 18, 28). Comparison to an Ichnotaxonomic Classification n ichnotaxonomic framework was advanced for alteration by McLoughlin et al. (2009) that considers the textures as trace fossils, and two new ichnogenera were proposed, corresponding to the two broad granular and tubular morphotypes discussed here and in earlier reports. Five ichnospecies were also defined on the basis of morphological characteristics and these are compared to the range of textures illustrated here, which includes new morphological variants: 1. Granulohyalichnus vulgaris isp. has a granular form (McLoughlin et al., 2009, their figure 2), and is very common and comparable to the examples illustrated here (e.g., Figs. 3 and 4). 2. Tubulohyalichnus simplus isp. has an un orna mented tubular form (McLoughlin et al., 2009, their figure 3). This alteration morphology is also illustrated here (Figs. 5 31) and with further descriptors including short or long, thick Geosphere, pril

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