All of the analyses presented here were obtained by classical gravimetric analysis in U.S. Geological Survey laboratories in Denver and Reston. The earliest analyses [job nos. 955{DCS) and PD99 in the tables] were done in Denver, following the procedures described in Peck (1964). All subsequent analyses were done in Reston, following the procedures outlined in Kirschenbaum (1983). These analyses include FeO, H2O ±, and CO2 determinations, made as described in the references cited. in addition to those components determined by standard gravimetric analysis, most of these analyses include determinations of Cr, Cl and F. Cr was originally analyzed using a colorimetric determination (E. Engleman and H. Kirschenbaum analyses, plus the J.W. Marinenko analyses in jobs BD02 and BD25). The method used was that of Maxwell (1968) and Sandell (1959). Subsequently (in the later J. W. Marinenko analyses), Cr was determined by flame AA, as described in Aruscavage and Crock (1987). Cl was analyzed colorimetrically in the Engleman and Kirschenbaum analyses, while F was analyzed by ion-specific electrode, as described in Jackson and others (1987). Later analyses (major elements by J. W. Marinenko) used the ion specific electrode method for both Cl (as described in Jackson and others, 1987) and F (as modified by Kirschembaum, 1988). In addition, all samples in job 955(DCS), originally done in Denver, were reanalyzed by H. Kirschenbaum for F and Cl using the ion chromatograph in Reston (under new job no. BJ25). Samples in several of the earlier jobs (nos. PE74, PH48, BA23, BA56 and BD02, comprising 80 samples) were analyzed for total sulfur, as described in Jackson and others (1987). However, as sulfur was always found to be below the limit of detection, this determination was not made for subsequent samples. Many analytical chemists of the U.S. Geological Survey have been involved in obtaining this data set. The bulk of the analyses were the work of coauthors H. Kirschenbaum and J. W. Marinenko, including many of the Cr, Cl and F analyses. Other analysts who performed gravimetric analyses include G. Riddle [job no. 955(DCS)], and E. Engleman (job no. PD99). Some of the minor and trace element work involved other members of the Branch of Analytical Chemistry: some of the Cr determinations were done by J.G. Crock, M. Doughten and W.M. d'Angelo, while C. Skeen and D. Kobilis helped with the Cl and F analyses.
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.
characteristic of mid-plate Cretaceous seamounts. The channels act as conduits for sediment and talus debris. The bathymetry shown for the other seamounts (Figs. 7-12) is modified from Chase and Menard (1973) by changing the water depths from fathoms to meters (Chase, Seekins, and Young, U.S. Geological Survey, unpublished data, 1988). Airgun and 3.5 kHz Lines This section provides a brief description of each of the 37 seismic lines collected on F10-89-CP (Table 3; Figs. 13-' 9). The 156 km long Line 1 crosses Ruwituntun and Look Seamounts from the southeast to the northwest (Figs. 13-17). The shallowest water depth over the summit of Ruwituntun Seamount is 1215 m. Hie rugged summit platform of Ruwituntun Seamount consists of a series to basement knolls and basins filled or partly filled with sediment. Craters can be distinguished on the volcanic pinnacles to the southeast. Sediment thickness varies from 104 m in the summit-edge basins to 32 m for interior basins. The sediment drape is thicker on the southeast sides of volcanic pinnacles. The summit platform may tilt slightly to the southeast. 1 he upper to lower flank slope angles increase from 11° to 28° for the southeast flank and from 13° to 17° for the northwest flank. The pass between the two seamounts is rugged, showing volcanic pinnacles, sediment fill, slump deposits, and talus. The summit of Look Seamount shallows to 1000 m water depth aid consists of mostly small volcanic pinnacles draped by a thin layer of sediment. Sediment thickness varies from 0 m to 40 m on the summit and slumps and talus occur on the lower slopes. Slope angles range between 1 \ and 14°, although the lower northwest slope is 33°. The 33 km long Line 2 crosses the lower north-northwest flank of Look Seamount (Figs. 18, 19). The line shows mostly talus debris and slump structures, with abyssal sediment covering the lowermost slope at the northeast end of the line. Hie 46 km long Line 3 crosses Look Seamount from north to south (Figs. 20, 21). The summit shaUows to 999 m water depth, consistent with the line 1 crossing. The summit topography is irregular with small sediment-filled basins. Maximum sediment thickness is 32 m. The sedimentary section is nearly transparent witp few internal reflectors. Pelagic sediment at least several hundred meters thick laps up on the lower south flank. The water depth to abyssal sediment is about 400 m deeper on the north flank than on the south flank. Lines 4 through 9 total 241 km and cross North and South Laanmqjanjan Seamounts (Figs. 22-32), which are elongated in a northsouth direction. Hie summit of South Laanmqjanjan is about 7 km westnorthwest of its position on the Chase and Menard (1973) base map. Little or no sediment occurs on the summit or upper flanks of these generally very rugged seamounts (see Line 6; Figs. 26, 27). The shallowest water depth, 1090 m, was recorded at the end of line 9 (Pigs. 31, 32), which ended at the summit of North Laanmojanjan. Upper and lower slope angles vary from 9 to 17° and from 9 to 25°, respectively. The w...
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