one of the least altered Hawaiites from Karin Ridge and should be considered a minimum age. Preliminary results of 40Ar/39Ar incremental heating experiments of mugearites from SOJIR yielded slightly discordant ages of about 71 MA.
X-ray Diffraction Mineralogy And PetrographyThe various types of limestone are composed of calcite and, when partly phosphatized, carbonate fluorapatite (Table 3). Most of the Paleogene limestone is bioclastic and composed of recrystallized fragments of pelecypods, gastropods, echinoids, calcareous algae, foraminifers, and many unidentifiable grains, all in calcite cement. Coarse-grained mosaic calcite cements some breccias (e.g. CD20-2, CD24-2), and drusy-and dog-tooth spar calcite line vugs in breccia. Calcite is also mixed with other minerals in mudstone and in mud infilling burrows and borings in the rocks. Dolomite has not been previously reported to occur in rocks from environments like those sampled here, but we may have found it as the dominant mineral in two samples of mud (Table 3); however, the X-ray reflections can also be assigned to kutnahorite, which may be a more likely mineral to occur in these rocks.Phosphorite is composed of carbonate fluorapatite that, in most samples, completely replaced limestone. Foraminiferal sand is the most common carbonate replaced by carbonate fluorapatite and ghosts of foraminifera are commonly present. Carbonate fluorapatite also cements the fine-grained clastic rocks and breccia, infills fractures, and infills vesicles in basalt. Some phosphorite contains minor amounts of volcanic rock fragments, and all gradations exist from grain-supported phosphorite-cemented breccia to phosphorite.Primary volcanogenic minerals that occur in basalt, fine-grained clastic rocks, and breccia include plagioclase, pyroxene, magnetite, and amphibole. Most of the volcanic rocks and volcaniclastic rocks have altered to phillipsite, smectite, goethite, and lesser amounts of clinoptilolite, chlorite, mixed-layer clay minerals, and anatase. Nearly all volcanic rock fragments in clastic rocks and hyaloclastites are altered to goethite. Phillipsite is a common cement in the clastic rocks, and is only exceeded as a cement by phosphorite. Phillipsite forms blocky or tabular radially arranged crystals as cement or forms an acicular rim cement. Clinoptilolite is the predominant mineral in only one sample (CD7-9C), a mudstone, and probably was produced from the reconstitution of the alteration products of volcanic debris with the addition of silica. Smectite is commonly a helped with the Q-mode factor analysis, and Randolph Koski, kindly reviewed this report.