U.S. Geological Survey Newberry 2 was drilled to a depth of 932 m within Newberry caldera. The bottom‐hole temperature of 265°C is the highest reported temperature of any drill hole in the Cascades region of the United States. The upper part of the stratigraphic section penetrated by Newberry 2 consists of caldera fill below which are increasingly more mafic lavas ranging from rhyodacite at 501 m to basalt at 932 m. Measured temperatures shallower than 300 m are less than 35°C, and rock alteration consists of hydration of glass and local palagonitization of basaltic tuffs. Incipient zeolitization and partial smectite replacement of ash and pumice occurred throughout the pumiceous lithic tuffs from 300 to 500 m. Higher‐temperature alteration of the tuffs to chlorite and mordenite occurs adjacent to a rhyodacite sill at 460–470 m; alteration minerals within the sill consist of pyrrhotite, pyrite, quartz, calcite, and siderite. Below 697 m the rocks are progressively more altered with depth mainly because of increased temperature along a conductive gradient from 100°C at 697 m to 265°C at 930 m. Fluid inclusions in quartz and calcite indicate that temperatures in the past have been higher than at present, most likely due to local confining pressures between impermeable lava flows. Flow breccias are more altered than the adjacent dense massive lava flows, regardless of composition, because of their much higher permeability. Hydrothermal minerals in this zone are mainly mixed‐layer chlorite‐smectite, quartz, calcite, and pyrite. Chlorite becomes more abundant than mixed‐layer clays near the bottom of the hole. In the lowest two lava flows, epidote, anhydrite, and scarce hematite occur locally. Alteration and leaching in the basal 2 m are unique and have led to the postulation of a localized two‐phase fluid zone consisting mainly of steam and CO2. The hydrothermal system of Newberry 2 is a simple evolving system associated with the evolution of Newberry Volcano. Only a few localized highly altered intervals where fracturing controlled fluid access occur in the core. There are no crosscutting fractures to indicate multiple hydrothermal systems. Chemical analyses of altered rocks and equivalent fresh rocks indicate that little chemical migration has taken place.

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Six flow units of basalt were penetrated at the base of Hole 315A, located near Fanning Island in the Line Islands chain; intercalated sedimentary rocks, if present, were not recovered. Ten flow units of basalt were penetrated in Hole 317A, located on the high Manihiki Plateau; four of these flow units are intercalated with thin beds of baked volcaniclastic siltstone. Basement was not reached in Hole 316, near Christmas Island in the Line Islands chain, nor in Hole 318, between Ahe and Arutua atolls in the Tuamotu Islands chain, but centimeter-sized pebbles of volcanic rocks were recovered from breccia beds at both these sites. The basaltic rocks in Hole 315A are highly altered, chiefly to montmorillonite group minerals and calcite, but not to the extent that their textures, original mineralogy, and major-and minor-element abundances could not be established. The flow units show textural differences, but their composition is similar to basalts of the oceanic island type, intermediate between Hawaiian tholeiite and alkalic basalt. The pebbles of Hole 316 may also be of this type. These basalts are much less alkalic than the amphibolebearing basalts drilled in the more northerly Line Islands on Leg 17, which appear to resemble Hawaiian post-erosional basanites and nephelinites. It would appear from existing analyses that the Line Islands are composed of basaltic rocks that are very similar to those of the Hawaiian chain.Basalts drilled in Hole 317A differ in character from those of Hole 315A. They are less altered, and their textures, mineralogy, and major and minor element compositions unquestionably show them to be basalts of the oceanic ridge tholeiite type. They resemble basalts drilled beneath the Ontong-Java Plateau during Leg 30. Basalts from both areas are similar to rocks forming at present-day spreading centers, and do not support the contention that these plateaus are subsided microcontinents. The basalts are, however, exceedingly vesicular, and must have been erupted at water depths of less than 400 meters, or perhaps even subaerially. This implies that the Manihiki Plateau has subsided between 3000 and 3500 meters during the last 110 to 120 m.y.Basaltic pebbles from the northwestern end of the Tuamotu chain are also of the oceanic island type. Age data down the chain are scanty, and it is not possible at present to say whether this part of the Tuamotu chain is of the progressively propagating type.

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