Composition, volatile components, and trace elements in andesitic melts of the Kurile-Kamchatka region

详细信息   全文下载|推荐本文 |

• 出版年：2007
• 作者：M.L.Tolstykh；V.B.Naumov；A.D.Babansky
• 单位1：Vernadsky Institute of Geochemistry Analytical Chemistry,Russian Academy of Sciences，ul.Kosygina19
• 语种：英文
• 作者关键词：Fluid；Melt；Inclusion；Basalt；Andesite；Dacite；Rhyolite；Kamchatka
• 起始页：93
• 总页数：12
• 刊名：岩石学报
• 是否内版：否
• 刊频：月刊
• 创刊时间：1985
• 主办单位：中国矿物岩石地球化学学会；中国科学院地质与地球物理研究所
• 电子信箱：Ihzd@ public.tpt.tj.cn
• 卷：23
• 期：1
• 期刊索取号：P350.66357

摘要

Melt inclusions in minerals from some volcanoes of the Kurile-Kamchatka region were examined. The studied basalticandesites and andesites were sampled from volcanoes of the Central Kamchatka depression (Shiveluch and Bezymyannyi) , EastemKamchatka volcanic belt (Avachinskii and Karymskii), and Iturup Island, Southem Kuriles (Kudryavyi).Basalts of the 1996eruption of the Karymskii volcanic center and dacites of Dikii Greben' volcano, Southern Kamchatka were also studied. More than 260melt inclusions from 31 rock samples were homogenized, and quenched glasses were analyzed using electron and ion microprobes. Thecompositions of melt inclusions in andesitic phenocrysts vary in silica contents from 56 to 80wt%. Al₂O₃ , FeO, MgO, CaO decreaseand Na₂O and K₂O increase with increasing SiO₂. Many inclusions (about 80%) are dacitic or thyolitic. However, the compositions of silicic glasses ( ＞65wt% SiO₂) in andesites significantly differ in TiO₂, FeO, MgO, CaO, and K₂O contents from those in dacitesand thyolites. High-potassium melts (K₂O3.8～6.8wt%)with various SiO₂ from 51.4 t0 77.2wt% were found in minerals of allvolcanoes studied. This indicates a contribution of a component selectively enriched in potassium to magmas of the whole region. Agreat compositional diversity of melt inclusions in plagioclase phenocrysts from the Bezymyannyi andesites suggests a complex history ofplagioclase crystallization and magma evolution in the andesite formation. Melts from different volcanoes strongly vary in volatilecontents. The highest H**2O contents are found in the melts from Shiveluch (3.0～7.2wt%, 4.7wt% on average) and Avachinskii( 4.7～4.8wt%)；while those are lower in melts of Kudryavyi(0.1～2.6wt% ),Dikii Greben'(0.4～1.8wt%),and Bezymyannyi（＜1wt% ).Chlorine contents are also variable. The lowest values are found in the Bezymyannyi melts (0.09wt% on average), thehighest Cl contents are typical of melt inclusions in minerals from the Karymskii andesites (0.26wt% on average).The melts fromAvachinskii, Dikii Greben', Kudryavyi, and Shiveluch show intermediate Cl contents (0.13～0.20wt%).The pressure of 350～1600bar determined by CO₂ fluid inclusions in plagioclase from the Shiveluch andesites suggests a magma chamber at a depth of 1.5～6 km.Concentrations of 17 elements were determined in glasses of melt inclusions in plagioclases from five volcanoes (Avachinskii,Bezymyannyi, Dikii Greben', Kudryavyi, and Shiveluch). The studied melts show similar trace-element pattems with Nb and Timinima and B,K,Be,and Li maxima. The melts are close to typicalisland arc magmas by Sr/Y, La/Yb, K/Ti, and Ca/Sr ratios,and have some specific regional geochemical features. REE pattems sensitive to degree of magma differentiation indicate that Kudryavyimagmas are most primitive, while Shiveluch magmas are most evolved.