Lyell Collection

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Roberge, J. Articles by Wallace, P. J. Search for Related Content GeoRef GeoRef Citation

Volatiles in submarine basaltic glasses from the Ontong Java Plateau (ODP Leg 192): implications for magmatic processes and source region compositions

¹ Department of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403-1272, USA pwallace{at}darkwing.uoregon.edu
² Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK

Submarine basaltic glasses from five widely separated sites on the Ontong Java Plateau (OJP) were analysed for major and volatile elements (H₂O, CO₂, S, Cl). At four of the sites (1183, 1185, 1186, 1187) the glass is from pillow basalt rims, whereas at Site 1184 the glass occurs as non-vesicular glass shards in volcaniclastic rocks. Glassy pillow rims from Site 1187 and the upper group of flows at Site 1185 have 8.3–9.3 wt% MgO compared with values of 7.2–8.0 wt% MgO for glasses from Sites 1183, 1184 1186, and the lower group of flows at Site 1185. Low-MgO glasses have slightly higher H₂O contents (average 0.22 wt% H₂O) than high-MgO glasses (average 0.19 wt%), with the exception of Site 1184, where low-MgO glasses have lower H₂O (average 0.16 wt%). Average S concentrations are 910 ± 60 ppm for the high-MgO glasses v. 1030 ± 60 ppm for the low-MgO glasses. When compared with mid-ocean ridge basalt (MORB), the OJP glasses have lower S at comparable FeO^T. This suggests that OJP basaltic magmas were not saturated with immiscible sulphide liquid during crystallization, but small decreases in S/K₂O and S/TiO₂ with decreasing MgO require some sulphide fractionation. Measurements of the wavelength of the S K peak in the glasses indicate low oxygen fugacities comparable to MORB values. Chlorine contents of the glasses are very high compared with MORB, and Cl/K ratios for all glasses are relatively high (>0.7). This ratio is sensitive to assimilation of hydrothermally altered material, so the high values indicate assimilation during shallow-level crystallization of OJP magmas. Ratios of H₂O to Ce, which have similar incompatibility to each other, are higher than most depleted and enriched MORB. However, these high H₂O/Ce values are probably also caused by the same assimilation process that results in high Cl. The water content of the high MgO-magmas before contamination is estimated to be approximately 0.07 wt% H₂O, corresponding to H₂O/Ce of 135 for OJP basalts, a value at the low end of the range for Pacific MORB. There is no evidence for high H₂O contents that would have significantly increased extents of mantle melting beneath the OJP, and the estimated H₂O content of the OJP mantle source region (170 ± 30 ppm H₂O) is similar to that of the depleted MORB source (140 ± 40 ppm H₂O). Instead, large extents of melting beneath the OJP must have been caused by a relatively high mantle potential temperature, consistent with upwelling of a hot mantle plume.

This article has been cited by other articles:

				M. L. G. Tejada, J. J. Mahoney, P. R. Castillo, S. P. Ingle, H. C. Sheth, and D. Weis Pin-pricking the elephant: evidence on the origin of the Ontong Java Plateau from Pb-Sr-Hf-Nd isotopic characteristics of ODP Leg 192 basalts Geological Society, London, Special Publications, 2004; 229: 133 - 150. [Abstract] [PDF]

				J. G. Fitton and M. Godard Origin and evolution of magmas on the Ontong Java Plateau Geological Society, London, Special Publications, 2004; 229: 151 - 178. [Abstract] [PDF]

				T. Sano and S. Yamashita Experimental petrology of basement lavas from Ocean Drilling Program Leg 192: implications for differentiation processes in Ontong Java Plateau magmas Geological Society, London, Special Publications, 2004; 229: 185 - 218. [Abstract] [PDF]

				W. J. Chazey III and C. R. Neal Large igneous province magma petrogenesis from source to surface: platinum-group element evidence from Ontong Java Plateau basalts recovered during ODP Legs 130 and 192 Geological Society, London, Special Publications, 2004; 229: 219 - 238. [Abstract] [PDF]

				T. Thordarson Accretionary-lapilli-bearing pyroclastic rocks at ODP Leg 192 Site 1184: a record of subaerial phreatomagmatic eruptions on the Ontong Java Plateau Geological Society, London, Special Publications, 2004; 229: 275 - 306. [Abstract] [PDF]

				R. V. White, P. R. Castillo, C. R. Neal, J. G. Fitton, and M. Godard Phreatomagmatic eruptions on the Ontong Java Plateau: chemical and isotopic relationship to Ontong Java Plateau basalts Geological Society, London, Special Publications, 2004; 229: 307 - 323. [Abstract] [PDF]

				L. M. Chambers, M. S. Pringle, and J. G. Fitton Phreatomagmatic eruptions on the Ontong Java Plateau: an Aptian 40Ar/39Ar age for volcaniclastic rocks at ODP Site 1184 Geological Society, London, Special Publications, 2004; 229: 325 - 331. [Abstract] [PDF]

• Home  |  
• Current volume  |  
• Table of contents  |  
• Archive  |  
• Search  |  
• Feedback

• Copyright policy  |  
• Permissions request   |  
• Terms of use   |  
• Feedback   |  
• HighWire Press