Volatiles in submarine basaltic glasses from the Ontong Java Plateau (ODP Leg 192): implications for magmatic processes and source region compositions
Volatiles in submarine basaltic glasses from the Ontong Java Plateau (ODP Leg 192): implications for magmatic processes and source region compositions
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翁通爪哇高原海底玄武岩玻璃中的挥发物（ODP Leg 192）：对岩浆过程和源区成分的影响
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
P. Wallace
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作者：
J. Roberge;R. White;P. Wallace
摘要对翁东爪哇高原（OJP）五个相距甚远的海底玄武岩玻璃进行了主量元素和挥发性元素（H2O、CO2、S、Cl）的分析。在其中四个地点（1183、1185、1186、1187），玻璃来自枕状玄武岩边缘，而在1184号地点，玻璃以非泡状玻璃碎片的形式出现在火山岩中。与1183、1184和1186号站点的玻璃和1185号站点的下组流的7.2-8.0 wt% MgO值相比，1187号站点的玻璃枕状边缘和1185号站点的上组流具有8.3-9.3 wt% MgO。低MgO玻璃的H2O含量（平均0.22重量% H2O）略高于高MgO玻璃（平均0.19重量%），但1184号站点除外，其中低MgO玻璃的H2O含量较低（平均0.16重量%）。高MgO玻璃的平均S浓度为910 ± 60 ppm，低MgO玻璃的平均S浓度为1030 ± 60 ppm。当与大洋中脊玄武岩（MORB）相比，OJP玻璃具有较低的S在可比的FeOT。这表明，OJP玄武岩浆不饱和不混溶的硫化物液体在结晶过程中，但小的减少S/K2 O和S/TiO 2减少MgO需要一些硫化物分馏。在玻璃中的SK α峰的波长的测量表明，与MORB值相比，氧逸度低。与MORB相比，玻璃的氯含量非常高，并且所有玻璃的Cl/K比都相对较高（>0.7）。这个比例是敏感的同化热液蚀变物质，所以高值表示同化过程中的浅层次结晶的OJP岩浆。H_2O与Ce的比值比大多数亏损和富集的MORB都高，它们之间具有相似的不相容性。然而，这些高H2O/Ce值也可能是由相同的同化过程，导致高氯。污染前的高氧化镁岩浆的水含量估计约为0.07重量% H2O，对应于H2O/Ce为135的OJP玄武岩，在低端的太平洋MORB的范围内的值。没有证据表明高H2O含量会显著增加OJP下地幔熔融的程度，OJP地幔源区的估计H2O含量（170 ± 30 ppm H2O）与亏损MORB源区的H2O含量（140 ± 40 ppm H2O）相似。相反，大范围的熔融下的OJP一定是由一个相对较高的地幔位温，热地幔柱上涌一致。
Abstract 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 FeOT. 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 Kα 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.