COMPO- SITION. Euhedral skeletal. Twinned, zoned. Euhedral. Calcic. Anhedral. Mafic. brown clay.

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1 SITE 9-9A-24X-CC (Piece,-2 cm) ROCK NAME: Basaltic vitrophyre. GRAIN : y to 2.2 mm. TEXTURE: Spherulitic; microporphyritic; subophitic. WHERE SAMPLED: At top of contact with volcaniclastic. Green clay Zeolites or vesicles. Vein Anhedral. Mafic. Euhedral skeletal. Twinned, zoned. Most is devitrified. Yellow to clove-brown glass remains in the center of some spherulites. Spherulites have altered to clays. Bright green; interstitial to spherulites. Zoned; vein is lined with green clays. Vein 2 Zeolites; green to brown clay. Perpendicular to contact, : Some of the more altered glass was removed during thin section preparation. The altered basaltic vitrophyre is in contact with a felsic volcaniclastic. Angular feldspars are in a very fine-grained matrix containing phyllosilicates. The contact is a finely banded, sharply scalloped edge, concave upward. -9A-2X- (Piece, -4 cm) ROCK NAME: Tholeiitic basalt. GRAIN : y to.8 mm. TEXTURE: Microporphyritic; subophitic; intersertal. WHERE SAMPLED: Iceland Plateau; pillow interior. 2 4 ^ Green clay Orange clay 2-4 < Bladed. Subhedral, tabular. Subhedral. Skeletal, euhedral. One grain is present and it is partially plucked. Interlayered with. Some is altered. Present also as plumose sheaves. Tabular, anhedral, and equant. Partially sericitized. Ilmenite and magnetite are present. Some is replacing interstitial s or glass. Completely altered; apparently variable in composition. Found only in strip at edge of thin section. Strong resemblance to iddingsite. It is probably best described as a oid. Fibrous, often radiating or axiolitic. Cavity <2 At edge of second section. Spherical. Best seen in thin section chip. Spherical. Two coalesced nearly spherical cavities. Perhaps are vesicles. : in "groundmass" is partially altered to a very fine-grained material (Mg-amphibole?). Edge of thin section contains a strip of altered material where intersertal glass has altered to brilliant olive green and orange fibrous clay 88

2 SITE 9-9A-2X- (Piece A, -6 cm) GRAIN : y to 2. mm. TEXTURE: Microporphyritic; subophitic; glomeroporphyritic. WHERE SAMPLED: Center of pillow, away from vesicles. Altered olivine -4 Silica <. <.-.2 In amygdules and in veins. and olivine. Replacing quenched clinopyroxene. Euhedral to anhedral. Euhedral to subhedral. Euhedral tabular. Euhedral, skeletal. Found in clots with. Found in clots of only or of and clinopyroxene. Completely altered to fibrous brown s and iron-oxide Tabular and plumose. Larger grains are fresh. Plumose sheaves are partially altered. Zoned, very fresh. Magnetite and ilmenite are present, with no secondary titanite. Generally in amygdules with a green clay. Granular to fibrous. Cryptocrystalline and granular with first order birefringence. Always found with fibrous radiating brown clay. Possibly opal or chalcedony. Vein Void to.8.-. Clay or empty.. and a a green clay. Irregularly shaped and spherical. Irregularly shaped. Amygdaloidal. -2 cm long; 2 present. : Groundmass is mostly radiating sheaves of quenched pyroxene altering to an unknown, possibly actinolite. -9A-2X- (Piece, 8-84 cm) WHERE SAMPLED: Iceland Plateau; massive pillow center. GRAIN : y to 2 mm. TEXTURE: Subophitic; quenched; microporphyritic. Brown Mineraloid Sericite? Chalcedony Replacing glass and in amygdules.... Subhedral; equant. Subhedral to tabular. Subhedral skeletal. Skeletal to euhedral. Zoned. Fresh; one grain present. Completely altered to brown fibrous Rims and cores are compositionally distinct. Some are platy, some are skeletal with altered melt inclusions. Some of the smaller grains are altered. Intergrown with. Ilmenite and magnetite. Some is cryptocrystalline (devitrified glass). Completely altered to brown clay s and iron-oxide Euhedral cubes, generally clustered. Probably several different s; fibrous; different rims and cores. Always with brown clay in interstices. Possibly an amphibole, but granular and very finegrained. : Identification of olivine is tenuous because the alteration product is so similar to the alteration product of intersertal glass. It is difficult to tell whether the is altering or whether inclusions in have altered.

3 SITE 9-9A-2X- (Piece, 8-9 cm) ROCK NAME: Slightly aphyric basaltic vitrophyre. GRAIN : y to. mm. TEXTURE: Vesicular; glomeroporphyritic; spherulitic. WHERE SAMPLED: Iceland Plateau; in glassy pillow rind. 8 6 Iron oxide - 6 and vesicles <O.l Intermediate. Mafic. Tabular; skeletal; euhedral. Subhedral. Skeletal. Spherulitic. Twinned. Clustered skeletal grains. Altered to brown clay s and iron oxides. Altered spherulites are dark brown and are surrounded by yet a darker brown material. Fracture Even..-. -l Yellow and brown clay None. Spheroidal to irregular. Most are plucked of the fibrous filling. Lined with a mustard-yellow, fibrous clay, which is perhaps an altered glass. : Spherulites and surrounding matrix have been completely altered to palagonite or a smectite. -9A-2X-2 (Piece C, cm) WHERE SAMPLED: Iceland Plateau; pillow center. GRAIN : y to 2 mm. TEXTURE: Variolitic (radiating; plumose); micro-glomeroporphyritic; subophitic; intersertal.? Clay Veins; interstitial areas Bladed skeletal. Skeletal tabular. Skeletal, euhedral. Euhedral, skeletal. Mostly fresh. Intergrown with pyroxene. Some sericitization. Fresh. inclusions. Completely altered to brown and tan fine-grained fibrous and granular material along with an iron-oxide. Ilmenite and magnetite. Contain altered melt inclusions, clinopyroxene inclusions, and are partially sericitized. Almost completely altered to brown clay s and a colorless granular. Altered to brown material. Colorless and granular. Edge of slide.. and brown clay. Irregular. Have mostly been plucked of clays. : Distinctive domains throughout thin section where grain size increases or where a trachytic texture is well developed. 88

4 SITE 9-9A-2X-2 (Piece B, - cm) GRAIN : y to 2. mm. TEXTURE: Micro-glomeroporphyritic; subophitic; quenched; variolitic. WHERE SAMPLED: Iceland Plateau; pillow center. Chalcedony Vein; segregated melt.. and olivine Anhedral. Anhedral. Skeletal, zoned. Skeletal; anhedral. Skeletal or equant. Devitrified. Quenched; intergrown with clinopyroxene. Swallowtails present. Zoned; cores are browner. Swallowtails common. Contain pyroxene cores. Colorless to yellow-brown. Plumose crystals are slightly altered. Some contain opaque inclusions. Mostly magnetite, but ilmenite is common. Fresh grains could be "hidden" in the groundmass; however, most are completely altered. Some fresh glass could remain in the quenched pockets. Most is altered to a brownish clay (s). Is perhaps primary in the immiscible melt droplets. Circular, radiating features. Plumose, quenched sheaves altering to unknown that is perhaps amphibole..2-., quenched crystals, and clay. Spherical laths wrapped around periphery. Quenched feldspar and opaque in altered(?) glass, commonly with a large core of pyrite. Probably an immiscible melt segregation. : Pods of quenched glass containing skeletal opaque s, clinopyroxene, and reach. mm in diameter. Some glass may remain. Phenocrysts are best described as microphenocrysts. -9A-2X-2 (Piece, 42-4 cm) GRAIN : to. mm. TEXTURE: Microporphyritic; subophitic; variolitic. WHERE SAMPLED: Iceland Plateau; towards pillow center. Mineral clay s Fracture Amygdules/vesicles. Vein Euhedral, broken. Glomeroporphyritic in places. Zoned. Poikilitic, Poikilitic grains are few, are intergrown subhedral. with and may be xenocrystic. Equant and euhedral. In a clot with clinopyroxene and. Bladed, skeletal. Bladed, skeletal. Equant, euhedral. Devitrified. Spherical. Spherical. Swallowtails are common. Plumose grains are beginning to alter and are intergrown with crystals. Some skeletal. Probably magnetite and ilmenite. Completely altered; zoned. Dark and light brown fibrous; cracked and plucked. Colorless, green, and brown; fibrous. Fibrous; darker at the edge. Very fine-grained, perhaps amphibole. Plucked. : The plumose clinopyroxene may not be very altered. It is intimately intergrown with needles, therefore more than % clinopyroxene could still be present.

5 SITE 9-9A-26X- (Piece, -6 cm) GRAIN : y to. mm. TEXTURE: Spherulitic; vitrophyric; microporphyritic; fractured..2-. Orange-red clay Green clay Green/brown clay < Mafic. Veins and vesicles. Veins and vesicles. Spherulites... WHERE SAMPLED: Iceland Plateau; glassy rind. Twinned. Euhedral, skeletal. Euhedral or equant. Bladed; skeletal. Skeletal; tabular. Some within the glassy portion are slightly altered. Some are zoned. Iddingsite. Interleaved with altered pyroxene(?). Plumose crystals are altered. Completely altered to brown clay and iron-oxide Dark brown fraction could be partially devitrified, but not discernibly so. % is devitrified (spherulitic with microlites). Bright green, often rimming orange clay In crystallized part of thin section. May be replacing something other than clinopyroxene. Amygdules 8 Even Clays, opaque Clay s and opaque Irregular to spherical. Spherical to irregular. In the glassy section, vesicles are clayfilled. In the crystallized section, "vesicles" are melt segregations with quenched iron-oxide s and brown clay : Groundmass contains radiating, plumose structures: fine-grained tablets and a very fine-grained birefringent. It is possibly altered pyroxene considering the textures seen in several of the other units. However, it is difficult to distinguish altered plumose pyroxene from altered spherulites in this section. Section ranges from cracked and hydrated glass to devitrified glass, a quenched groundmass with quenched crystals, and the groundmass typical of pillow centers.

6 SITE 9-9A-26X- (Piece 6, -8 cm) GRAIN : y to 2. mm. TEXTURE: Microporphyritic; variolitic; subophitic; glomeroporphyritic. WHERE SAMPLED: Iceland Plateau; center of pillow. Green clay Red oid Colorless clay ?? 4-. ; vesicles. ; pyroxene <O.Ol-O.l.-.2 Amygdules; glass; olivine. Amygdules. Vein; glass. Euhedral, bladed. Zoned. Corroded/resorbed. No sieve-textured grains. Euhedral-anhedral. Usually with laths. Completely altered; zoned. Subhedral tabular. Also as radiating slender crystals intergrown with pyroxene. Euhedral, skeletal. Probably magnetite and ilmenite. Equant or plumose. The two apparent habits seem odd: small and euhedral (.2 mm) or plumose (variolitic?). Well-preserved pyroxene grades into the plumose very fine material, so at least in many instances, the pyroxene was perhaps quenched to form plumose sheaves. Zoned, with iron-oxide rims. Completely altered to brown and green clay plus iron-oxide Devitrified. Altered to brown clay and perhaps devitrified to the plumose fibrous or acicular material. The acicular, radiating sheaves could also be altered pyroxene. Bright green clay: chlorite or celadonite. Resembles iddingsite. Disseminated along a vein, and replacing intersertal glass. Grainy, often surrounded by brown fibrous clay, or lining a vesicle. Relief suggests a pyroxene or amphibole, rather than a clay. Vein Green and red clay.. Spherical. Comprised of disseminated pyrite grains, : Groundmass is devitrified. The plumose radiating sheaves in the groundmass are either altering devitrification products or altering pyroxene. The abundance of finegrained opaque s is indicative of devitrification. 89

7 SITE 9-9A-26X- (Piece A, 8-89 cm) GRAIN : y to. mm. TEXTURE: Microporphyritic; subophitic; variolitic. WHERE SAMPLED: Iceland Plateau; pillow interior. Sericite Chalcedony ? -2 < -2 Amygdules... /olivine. Pyroxene <.2-. Anhedral- Equant grains are possibly xenocrysts. Anhedral. Some poikilitically enclose clinopyroxene. Zone Skeletal tabular. Swallowtails are common. Melt inclusions and some sericitization are in cores. Euhedral-Anhedral. Mostly fresh, but beginning to alter. Equant to oblong. Euhedral-skeletal. Probably magnetite and ilmenite present. In clots with brown clay. Radiating fibers, always found in brown clay. Very fine-grained. Amygdules Brown Clay. and pyrite. Irregular. Vein of altered glass. : One of the least-altered rocks recovered. -9A-26X-2 (Piece IB, 6- cm) GRAIN : y to. mm. TEXTURE: Vesicular; variolitic; microporphyritic. WHERE SAMPLED: Iceland Plateau; center of small pillow. Green Clay Iron Oxide Brown Clay Brown Clay ? 2- -, glass., olivine.. Devitrified glass Skeletal tabular. Euhedral tabular. Skeletal. Skeletal tabular. Zoned, with more calcic cores. In radiating clots with clinopyroxene. Twinned. Probably all magnetite. Devitrified/spherulitic. Spherulites have altered to a brown clay. In vesicles with orange clay. Hematite or iddingsite. Diagenetic or hydrothermally altered devitrified glass.. Brown and green clay Spherical. Plucked. : Orange glass remains, interstitial to spherulites. Most of the glass devitrified to spherulites and fine-grained iron-oxide The spherulites have been replaced by or hydrated and baked to a dark brown clay that is perhaps a chlorite. 89

8 SITE 9-9A-26X-2 (Piece A, 6-9 cm) GRAIN : y to 2. mm. TEXTURE: Subophitic; variolitic; vesicular. WHERE SAMPLED: Iceland Plateau; center of pillow ? Groundmass; vesicles; vein... Euhedral-subhedral Tabular. Skeletal. Ovoid. Equant; euhedral. Tabular; plumose. Zoned. Intergrown with clinopyroxene. Slightly altered. Some alteration. Probably magnetite. Some alteration of plumose clinopyroxene sheaves, particularly in "cores." Disseminated around vesicles and along a Some of this could be an alteration produc feldspar or glass. It is difficult to discern. It is probably a poorly formed amphibole..8-. Quenched Spherical Contains quenched iron-oxide s, melt. to irregularly clinopyroxene, and in addition shaped. to brown clay. Fracture None. is disseminated along the fracture. : It is very difficult to distinguish altered olivine from what may be pockets of altered glass. 892

Page 499 PERCENT PRESENT. SIZE (mm) PERCENT ORIGINAL COMPO- SITION MORPHOLOGY COMMENTS

Page 499 PERCENT PRESENT. SIZE (mm) PERCENT ORIGINAL COMPO- SITION MORPHOLOGY COMMENTS 168-1025B-11X-CC (Piece 2, 028-040 cm) ROCK NAME: Aphyric plagioclase-pyroxene-olivine basalt GRAIN SIZE: Aphanitic: microcrystalline TEXTURE: Sheaf-spherulitic to intersertal. SIZE (mm) Olivine Tr Tr