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| Format: | Dataset Open Access |
| Language: | en |
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PANGAEA
1982
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| Online Access: | https://doi.org/10.1594/PANGAEA.820025 |
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| _version_ | 1867170963435552768 |
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| author | Schmincke, Hans-Ulrich |
| author_facet | Schmincke, Hans-Ulrich |
| collection | Datos científicos de ciencias marinas y ambientales |
| contents | Precisely determined refractive indices of glass shards from 32 ash-rich, volcaniclastic sediments, mostly turbidites interbedded with nonvolcanic sediments in the Mariana Trough, range from 1.480 to 1.585 (corresponding to SiO2 ca. 75 to 49%), with most in the range 1.500 to 1.540 (SiO2 ca. 70-62%) and a second, smaller mode between ca. 1.560 and 1.585 (57 to 49% SiO2). Shards are almost exclusively colorless from 1.480 to ca. 1.530, light brown with minor colorless and green tones between 1.530 and 1.560, and dominantly brown at higher refractive indices. Tubular pumice shards are more common at higher silica percentages and non- to poorly-vesicular cuniform shards at low SiO2 values, but there is no clear correlation between shape and composition of shards. About half of the samples have bimodal shard populations with silica differences ranging up to 20 percent; unimodal layers have a range of up to about 7 percent SiO2. Of 21 samples in which one type of shard dominates, seven have the main mode in the rhyolitic composition (>69% SiO2), eight in the intermediate range (56 to 69% SiO2), and five in mafic composition (SiO2 <53%). These unusually abundant mafic shards occur mainly in site survey piston cores, SP-IA and 4E, and in Holes 454, 456, 458, and 459B. These are the sites closest to the present arc. Hole 453, containing by far the most vitric tuff turbidites, shows a gradual increase in silica content of ash layers upward to the hole from Cores 36 to 19 (about 4.6 to 3.0 Ma). A drastic decrease in ash-rich beds in the younger (Pleistocene) part of this hole was noted by the shipboard party (see site chapter, Site 453) and was interpreted by them as indicating increasing distance from the arc volcanoes as the trough opened. The increase in silica in ashes from the early to the late Pliocene at Site 453 could be interpreted in the same way and might indicate that the trough started to open in early Pliocene time. |
| format | Dataset Open Access |
| id | pangaea_https___doi_org_10_1594_PANGAEA_820025 |
| institution | PANGAEA |
| language | en |
| publishDate | 1982 |
| publisher | PANGAEA |
| record_format | pangaea |
| spellingShingle | (Table 1) Stratigraphic position, abundance, shape, color, and refractive indices of glass shards of selected samples from DSDP Leg 60 Holes vitric muds Schmincke, Hans-Ulrich 60-453; 60-454; 60-455; 60-456; 60-458; 60-459B; Compounds; Deep Sea Drilling Project; Description; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Elevation of event; Event label; Glomar Challenger; Insoluble residue; Latitude of event; Leg60; Longitude of event; North Pacific/BASIN; North Pacific/SEDIMENT POND; North Pacific/TRENCH; Refractive index; Sample code/label; Sample mass; see reference(s); Wet sieving Precisely determined refractive indices of glass shards from 32 ash-rich, volcaniclastic sediments, mostly turbidites interbedded with nonvolcanic sediments in the Mariana Trough, range from 1.480 to 1.585 (corresponding to SiO2 ca. 75 to 49%), with most in the range 1.500 to 1.540 (SiO2 ca. 70-62%) and a second, smaller mode between ca. 1.560 and 1.585 (57 to 49% SiO2). Shards are almost exclusively colorless from 1.480 to ca. 1.530, light brown with minor colorless and green tones between 1.530 and 1.560, and dominantly brown at higher refractive indices. Tubular pumice shards are more common at higher silica percentages and non- to poorly-vesicular cuniform shards at low SiO2 values, but there is no clear correlation between shape and composition of shards. About half of the samples have bimodal shard populations with silica differences ranging up to 20 percent; unimodal layers have a range of up to about 7 percent SiO2. Of 21 samples in which one type of shard dominates, seven have the main mode in the rhyolitic composition (>69% SiO2), eight in the intermediate range (56 to 69% SiO2), and five in mafic composition (SiO2 <53%). These unusually abundant mafic shards occur mainly in site survey piston cores, SP-IA and 4E, and in Holes 454, 456, 458, and 459B. These are the sites closest to the present arc. Hole 453, containing by far the most vitric tuff turbidites, shows a gradual increase in silica content of ash layers upward to the hole from Cores 36 to 19 (about 4.6 to 3.0 Ma). A drastic decrease in ash-rich beds in the younger (Pleistocene) part of this hole was noted by the shipboard party (see site chapter, Site 453) and was interpreted by them as indicating increasing distance from the arc volcanoes as the trough opened. The increase in silica in ashes from the early to the late Pliocene at Site 453 could be interpreted in the same way and might indicate that the trough started to open in early Pliocene time. |
| title | (Table 1) Stratigraphic position, abundance, shape, color, and refractive indices of glass shards of selected samples from DSDP Leg 60 Holes vitric muds |
| topic | 60-453; 60-454; 60-455; 60-456; 60-458; 60-459B; Compounds; Deep Sea Drilling Project; Description; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Elevation of event; Event label; Glomar Challenger; Insoluble residue; Latitude of event; Leg60; Longitude of event; North Pacific/BASIN; North Pacific/SEDIMENT POND; North Pacific/TRENCH; Refractive index; Sample code/label; Sample mass; see reference(s); Wet sieving |
| url | https://doi.org/10.1594/PANGAEA.820025 |