Geochemical and experimental study of the genesis of magmas of Reunion Island, Indian Ocean
Geochemical and experimental study of the genesis of magmas of Reunion Island, Indian Ocean
复制标题
印度洋留尼汪岛岩浆成因地球化学与实验研究
DOI：
10.1029/jb093ib05p04933
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发表时间：
1988
影响因子：
--
通讯作者：
W. White
中科院分区：
文献类型：
--
作者：
M. Fisk;B. Upton;C. Ford;W. White
对留尼汪岛Piton des Neiges和Piton de la Fourneise火山的熔岩和侵入岩进行了常量元素、微量元素和锶、钕同位素组成的测定。通过熔融重结晶实验测定了6个玄武岩样品在1-atm~2000 Mpa压力下的矿物相出现温度。用电子探针分析了原始玄武岩和实验运行产物中的矿物组成，并进行了对比，确定了玄武岩中矿物的形成温度和深度。两个火山玄武岩样品的锶、钕同位素和高度不相容的微量元素比值基本相同，表明岩浆的地幔来源在时间和空间上都是化学均一的。活火山的熔岩(Piton De La Fourneise)和晚阶段分异的Piton des Neiges系列的熔岩比Piton des Neiges的原始屏蔽熔岩略富碱。碱的富集可能是年轻喷发时地幔部分熔融程度较低的结果，但不符合这一模式。另一种解释是，碱的富集性是由于岩浆与熔岩堆的低熔点成分混杂而成的。熔融实验和最小二乘模拟表明，辉石是一个重要的分馏相，橄榄石+辉石的分馏至少发生在5公里深处。该深度岩浆房的温度在1200~1300℃之间，留尼汪岛的母岩浆成分为15~17%的MgO，所有的Piton des Neiges岩浆都可以在5~15公里深处通过分离结晶获得。Piton de la Fourneise岩浆可以从这一母岩浆中衍生出来，如果它们也通过一个独立的过程富含碱性元素。
Major element, trace element, and Sr and Nd isotopic compositions were determined on a suite of lavas and intrusives from Piton des Neiges and Piton de la Fournaise volcanoes of Reunion Island. The temperatures of appearance of mineral phases in six basalt samples were determined by melting and recrystallization experiments at pressures from 1-atm to 2000 MPa. The compositions of minerals, both in the starting basalts and in the experimental run products, were analyzed by electron microprobe and compared to determine the temperature and depth of their formation in the basalts. The Sr and Nd isotopes and ratios of highly incompatible trace elements of basalt samples from both volcanoes are virtually identical, indicating that the mantle source for the magmas is chemically homogeneous, both in time and space. The lavas of the active volcano (Piton de la Fournaise) and the late stage Differentiated Series of Piton des Neiges are slightly more alkali-rich than the primitive shield lavas of Piton des Neiges. The alkali enrichment could be the result of lower degrees of partial melting of the mantle for the young eruptions, but Zr and the rare earths do not fit this model. An alternative explanation is that the alkali enrichment resulted from contamination of a Piton des Neiges-type magma with the low-melting component of the lava pile. The melting experiments and least squares modeling indicate that augite was an important fractionating phase and that the fractionation of olivine plus augite occurred at depths of at least 5 km. The temperature of the magma chamber at this depth was between 1200° and 1300°C. The parent magma composition for Reunion had between 15 and 17% MgO, and all Piton des Neiges magmas can be derived from it by fractional crystallization at 5 to 15 km depth. Piton de la Fournaise magmas can be derived from this parent magma if they are also enriched with alkali elements by an independent process.
影响因子：
3.5
作者：
J. Pearce;M. Norry
通讯作者：
J. Pearce;M. Norry