Table T5. Brief petrographic descriptions of analyzed basalts and X-ray diffraction of secondary minerals from fine fraction removed from altered volcanic rocks, Hole 1138A.
Core, section, interval (cm)
Description
Alteration
XRD identification
183-1138A-


78R-1, 60-64 Crystal-lithoclastic tuff. High (50%-60%); secondary minerals represented by chlorite. Oxidation of basalt is moderate (total ~20% of rock). Smectite, clinoptilolite, and heulandite
80R-4, 35-40 Aphyric basalt, vesicular (20%-25%; 0.4-3.5 mm), incompletely crystallized, with microdoleritic texture. Rock represented by plagioclase lathe (labradorite-oligoclase) with size 0.1-0.3 mm (40%-45%), small crystals of clinopyroxene (40%-45%), opaque minerals, and glass (5%-10%). 15%-20%; interstitial glass replaced by chlorite; vesicles infilled with chlorite. Oxidation of basalt is very low (total ~1% of rock). Smectite
81R-1, 34-39 Aphyric basalt, vesicular (10%-15%), incompletely crystallized, with intersertal texture. Rock is represented by plagioclase lathe (40%-45%), clinopyroxene (30%-35%), opaque minerals (5%), and glass (10%). 15%-20%; vesicles infilled with smectite and chlorite with admixture of zeolite in central part of vesicles; veins represented by smectite, chlorite, and zeolite. Rock is nonoxidized.
81R-2, 51-57 Plagioclase microphyric basalt, weakly vesicular (2%-3%; 0.3-1 mm), incompletely crystallized, with intersertal texture. Microphenocrysts (5%) are tabular plagioclase (labradorite-andesine) (0.2-1.2 mm), single crystals of clinopyroxene (0.2-0.3 mm), and olivine(?). Groundmass is plagioclase (40%-45%), clinopyroxene (30%-35%), opaque minerals (5%), and interstitial glass. ~20%; olivine completely replaced by chlorite; interstitial glass completely replaced by smectite and chlorite; vesicles infilled with smectite and chlorite. Oxidation of basalt is low (~5%).
82R-2, 76-81 Aphyric basalt, vesicular (10%-15%; up to 10 mm), incompletely crystallized, with microlitic texture. Rock consists of small plagioclase lathe to 0.1 mm, cryptocrystalline clinopyroxene, and glass with opaque minerals. ~20%; vesicles infilled with brown and green chlorite and small crystals of zeolites (natrolite and tomsonite). Oxidation of rock is very low (total ~1%).
82R-5, 19-23 Aphyric basalt, weakly vesicular, incompletely crystallized, with intersertal texture. Rock consists of small plagioclase lathe (40%-45%; 0.1- to 0.2 mm), isometric crystals of clinopyroxene, opaque minerals (5%), and interstitial glass (10%). ~20%-25%; single vesicles zonally infilled (from wall to center) with chlorite, smectite, and then chlorite. Oxidation of rock is very low. Smectite
83R-4, 19-24 Aphyric basalt, weakly vesicular, incompletely crystallized, with intersertal texture. Rock is same as Sample 183-1138A-82R-5, 19-23 cm.
Smectite
83R-5, 106-109 Aphyric basalt, vesicular (20%; 0.2-4 mm), incompletely crystallized, with intersertal texture. Rock is same as Sample 183-1138A-82R-5, 19-23 cm, but is more vesicular (20%; 0.2-4 mm). ~30%; vesicles infilled with chlorite, smectite, and admixture chlorite. Oxidation of rock is very low.
84R-5, 20-25 Sparsely plagioclase microphyric basalt, vesicular (5%-10%; 1.5-7 mm), almost completely crystallized, with intergranular texture. Microphenocrysts (35%-40%), opaque minerals (5%), and interstitial glass (5%). Plagioclase (2%-3%) is represented by tabular crystals (0.2-0.7 mm). Plagioclase is zonal. Groundmass of plagioclase lathe (40%-45%), isometric clinopyroxene. Moderate (~30%); central parts of zonal plagioclases replaced by mica-type mineral, sometimes with admixture of opaque minerals; interstitial glass completely replaced by chlorite and smectite; vesicles completely infilled with chlorite and smectite, central parts infilled by zeolites, sometimes with admixture of chlorite and opaque minerals. Oxidation of basalt is low.
86R-1, 130-137 Aphyric basalt, weakly vesicular (2%-3%; 1-1.5 mm), incompletely crystallized, brecciated rock, with microlitic, partly hyaline, texture. Rock consists of plagioclase lathe and brown interstitial glass with opaque minerals. Moderate (~30%); vesicles infilled with chlorite and smectite, and zeolites. Oxidation of basalt is low (total ~1%-2% of rock).
86R-2, 21-25 Aphyric basalt, weakly vesicular (30%-35%; 0.1-6 mm), incompletely crystallized, with microlitic, partly hyaline, texture. Rock of long lathe of plagioclase (0.1-0.2 mm) and brown interstitial glass with opaque minerals. Moderate to high (~ 40%); vesicles infilled (from wall to center) with chlorite and smectite, and zeolites, sometimes vesicles infilled by glass. Oxidation of basalt is low (total ~1% of rock).
86R-3, 72-74 Aphyric basalt, vesicular (up to 1.5 mm), incompletely crystallized, with intersertal texture. Rock of long lathe of plagioclase, small crystals of clinopyroxene, opaque minerals, and fresh glass. ~10%; walls of vesicles encrusted with chlorite and smectite. Rock is nonoxidized.
87R-1, 4-9 Plagioclase glomerophyric basalt incompletely crystallized, with microlitictexture. Phenocrysts (5%) of plagioclase (labradorite-oligoclase; to 0.2-0.6 mm and 0.4-2 mm). Groundmass represented by plagioclase, brown interstitial glass, and opaque minerals. Vesicles (~5%). Low (~10%); phenocrysts of plagioclase partly replaced by chlorite; vesicles infilled with light green chlorite. Rock is nonoxidized.
87R-2, 76-81 Aphyric basalt, weakly vesicular (<1%; up to 2 mm), incompletely crystallized, with interstitial, partly trachytic, texture. Rock consists of lathe of plagioclase (oligoclase, labradorite-oligoclase), prismatic crystals of clinopyroxene, and brown interstitial glass with opaque minerals. ~20%; interstitial glass partly replaced by chlorite and smectite; vesicles partly or completely infilled with brown-green chlorite and smectite. Oxidation of basalt is low (total ~5%-7% of rock).
88R-2, 47-53 Aphyric basalt, vesicular (20%-25%; 0.3-7 mm), incompletely crystallized, with vitrophyric-microlitic texture. Rock consists of lathe of plagioclase and brown interstitial glass with opaque minerals. High (~50%); walls of vesicles encrusted by green-brown chlorite and smectite, then to center vesicles infilled by zeolites (natrolite and tomsonite). Oxidation of basalt is low (total ~3%-5% of rock).
88R-2, 91-96 Aphyric basalt, vesicular (5%; 0.3-3 mm), incompletely crystallized, with intersertal texture. Rock of lathe of plagioclase, long and isometric crystals of clinopyroxene, and brown interstitial glass. Moderate (~20%-25%); interstitial glass replaced by chlorite and smectite; vesicles infilled by chlorite and smectite. Oxidation of basalt is very low (total ~1% of rock).

Note: XRD = X-ray diffraction.