Composition of minerals and rocks from the Markov Deep, Central Atlantic

The paper presents materials on composition and texture of weakly serpentinized ultrabasic rocks from the western and eastern walls of the Markov Deep (5°30.6'-5°32.4'N) in the rift valley of the Mid-Atlantic Ridge. Predominant harzburgites with protogranular and porphyroclastic textures contain two major generations of minerals: the first generation composes the bulk of rocks and consists of Ol_89.8-90.4 + En_90.2-90.8 + Di_91.8 + Chr (Cr#32.3-36.6, Mg#67.2-70.0), while the second generation composes very thin branching veinlets and consists of PlAn_32-47 + Ol_74.3-77.1 + Opx_55.7-71.9 + Cpx_67.5 + Amph_53.7-74.2 + Ilm. Syndeformational olivine neoblasts in recrystallization zones are highly magnesian. Concentrations and covariations of major elements in harzburgites indicate that these rocks are depleted in mantle residues (high Mg# of minerals and whole-rock samples and low in CaO, Al2O3, and TiO2) that are significantly enriched in trace HFSE and REE (Zr, Hf, Y, LREE, and all REE). Mineralogy and geochemistry of harzburgites were formed by interaction of mantle residues with hydrous, strongly fractionated melts that impregnated them. Mineral composition of veinlets in harzburgites and mineralogical-geochemical characteristics of related plagiogranites and gabbronorites suggest that these plagiogranites were produced by melt residuals after crystallization of gabbronorites. Modern characteristics of harzburgites were shaped by the following processes: (i) partial melting of mantle material simultaneously with its subsolidus deformations, (ii) brittle-plastic deformations associated with cataclastic flow and recrystallization, and (iii) melt percolation along zones of maximal stress relief and interaction of this melt with magnesian mantle residue.

Faunal turnovers in the central Pacific benthic foraminifera during the Paleocene-Eocene thermal maximum

Although it is well known that the Paleocene/Eocene thermal maximum (PETM) coincided with a major benthic foraminiferal extinction event, the detailed pattern of the faunal turnover has not yet been clarified. Our high-resolution benthic foraminiferal and carbon isotope analyses at the low latitude Pacific Ocean Shatsky Rise have revealed the following record of major faunal transitions: (1) An initial turnover which involved the benthic foraminiferal extinction event (BFE). The BFE, marked by a sharp transition from Pre-extinction fauna to Disaster fauna represented by small-sized Bolivina gracilis, expresses the onset of the PETM and the abrupt extinction of about 30% of taxa. This faunal transition lasted about 45-74 kyr after the initiation of the PETM and was followed by: (2) the appearance of Opportunistic fauna represented by Quadrimorphina profunda, which existed for about 74-91 kyr after the initiation of the PETM. These two faunas, which appeared after the extinction event, are characterized by low diversity and dwarfism, possibly due to lowered oxygen condition and decreased surface productivity. The second pronounced turnover involved the gradual recovery from Opportunistic Fauna to the establishment of Recovery fauna, which coincided with the recovery about 83-91 kyr after its initiation.

High resolution bathymetry of the Red Sea Rift (1 arc-second) from POSEIDON cruise POS408 and PELAGIA cruises 64PE350 and 64PE351

Gridded multibeam bathymetry from Poseidon cruise 408 and Pelagia cruises 64PE350 and 64PE351 within the Jeddah Transect Project. The raw-data were post-processed and gridded at a resolution of 30 m with QPS Fledermaus Pro. For smaller file size and better handling 11 tiles were created with GlobalMapper (5 columns, 5 lines).

Description of manganese nodules and crust collected from the Hakurei Maru Cruise GH76-1, January-March, 1976, in the Central Pacific Basin

This report of the GH76-1 cruise mainly includes the results of the on-board observations in the survey area of the medial-eastern part of Central Pacific Basin (5 degree -10 degree N, 170 degree -175 degree W) and partly of analytical work at the on-shore laboratory. In addition, the results of some on-board optical and geophysical works along the tracks of Japan-Ogasawara-survey area-Hawaii, are described in appendices. The GH76-1 cruise of the R/V Hakurei-maru was carried out from the 10th January to the 9th March, 1976 as the second phase field work of the Geological Survey of Japan five-year research program of study on the manganese nodule deposits of the Central Pacific Basin and also as a part of the National Research Institute for Pollution and Resources research program of technological study on the exploitation of deep sea mineral resources. The GSJ research program (F.Y. 1974-F.Y. 1978) aims at providing basic information on the manganese nodule distribution and their origin on the deep sea floor of the Central Pacific Basin bounded by the Marshall Ridge to the west, the Christmas Ridge to the east, and the Mid-Pacific Mountains to the north. The first phase of investigation was carried out during the GH74-5 cruise in the eastern part of the area (6 degree -10 degree 30'W, 164 degree 30'-171 degree 30'N)(Mizuno and Chujo, eds., 1975), and the present second phase covered an areas of 5 degree square, just west of the GH74-5 area.