Table 1.

Table 1. Summary of petrological and structural characteristics of three lava flows in Hole 990A.

	Unit 2 Plagioclase-olivine phyric basalt	Unit 3A Plagioclase-olivine phyric basalt	Unit 9 Aphyric olivine basalt
Thickness (m)	24.8	17.5	4.1
Recovery (%)	89	83	110
Flow type	Aa	Aa	Pahoehoe
	Boundary
Upper	Not found. 8R-1 (15 cm).	5 mm red soil. 12R-2 (18 cm).	Not found. 21R-1 (127 cm).
Lower	5 mm red soil. 12R-2 (15 cm).	Not found. 15R-4 (20 cm).	Not found. 21R-4 (145 cm).
	Internal Structure
Top breccia	Recovery = 1.9 m, max.* = 6.1 m. Dark reddish brown to dusky red.	Recovery = 3.7 m, max.* = 7.0 m. Dark reddish brown to dusky red.	None.
Interior	Massive. Subhorizontal flow-banding common. Medium gray; reddening towards base.	Massive. Flow-banding or mesostasis-rich wisps common. Medium gray; dusky red to pinkish red in top meter.	Massive. Pinkish gray changing to greenish gray downwards.
Basal breccia	Recovery = 0.2 m, max.* = 3.5 m. Dark reddish brown.	Recovery = 0.2 m, max.* = 0.5 m. Dark reddish gray.	None.
Vesicles	Breccia: 0%-5%, open in top; 10%-15% open and clay-filled in base. Interior: 1%, filled with clay; a few small highly vesicular patches. Up to 12% in lower 30 cm.	Breccia: 1%-20%, open and zeolite or clay-filled in top; 10%, open, in base. Interior: 1%, filled; open, high-vesicularity bands in upper 7 m. Increasing from 1% to 10% in lower 3 m.	Very vesicular. 15%-25 % in upper 3 m; lower meter fairy dense. Dominantly open; downward increase in size.
Veins/fractures	None to <1%, up to 4 mm wide, random to steeply inclined, filled with clay, zeolites and calcite. 5% subvertical fractures with slickensides in 1-m interval 10 m above base.	None to <1%, up to 2 mm wide, mainly steeply inclined, filled with clay, zeolites and calcite.	One 0.1 mm subvertical vein.
	Mineralogy & Alteration
Phenocrysts	Plagioclase: 5%-15 %, up to 5 mm, decreasing size and number in lower part. Olivine: <1%, up to 1-2 mm, replaced by green clay.	Plagioclase: 5%-10%, up to 3 mm. Olivine: 5%, up to 1 mm. Clinopyroxene: Traces, 0.5 mm, in lower part.	Aphyric. Traces of olivine.
Groundmass	Fine-grained; top-part microcrystalline.	Fine-grained; top-part microcrystalline.	Fine-grained.
Alteration	Breccia: high. Interior: moderate; high just above base.	Breccia: high. Interior: moderate, high just below top and above base. Olivine phenocrysts replaced by clay.	High; moderate in lower meter.

Notes: * = The maximum thickness is the sum of recovered and not recovered section in cores with breccia. Data from Duncan, Larsen, Allan, et al. (1996).