Trace elements in ocean ridge basalt glasses - Implications for fractionations during mantle evolution and petrogenesis
Trace elements in ocean ridge basalt glasses - Implications for fractionations during mantle evolution and petrogenesis
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DOI：
10.1016/0016-7037(80)90209-4
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发表时间：
1980-12
影响因子：
5
通讯作者：
J. Hertogen;M. Janssens;H. Palme
中科院分区：
文献类型：
--
作者：
J. Hertogen;M. Janssens;H. Palme
用中子活化法对7个海底玄武岩枕状样品进行了Ag、Au、Bi、Br、Cd、Cs、Ge、In、Ir、Ni、Os、Pd、Rb、Re、Sb、Se、Te、Tl、U和Zn的分析。这些样本来自印度洋和大西洋的活跃扩张中心。来自DSDP第24航段，站点238（印度洋）的玻璃有一个有点奇特的微量元素模式，但这被认为反映了在浅深度的次级过程，而不是地幔中的异常源区。我们的数据表明，地幔中的不均匀性仅限于高度不相容的亲石元素。根据原始橄榄岩上地幔结核的文献数据，讨论了拉斑玄武岩成岩过程中的化学分馏。(Ir Os）、Au、Pd、Ni和Re在岩浆作用过程中相互强烈分馏，未分馏地幔模式对地幔演化模式形成了严格的制约。潜在的亲硫元素银，镉，在和锌不表现出不同的亲石元素的相同的化合价和可比的离子半径。残余硫化物不足以有效地控制这些元素在玄武岩成岩过程中的分配。然而，在洋底玄武岩中的铊的Rb和U的一致性差，可以指向保留的铊的残留硫化物在耗尽的MORB源区。锑强烈亏损的洋中脊玄武岩的源区，最有可能的是，它是作为一个高度不兼容的Sb 5+阳离子。有限的Rb/Cs分馏大洋拉斑玄武岩，而不是大陆拉斑玄武岩和酸性岩石，似乎反映了低丰度的挥发性成分和含水硅酸盐在正常的洋脊玄武岩。
Seven well-documented and fresh glassy selvages from ocean floor basalt pillows were analyzed by radiochemical neutron activation analysis for Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Ni, Os, Pd, Rb, Re, Sb, Se, Te, Tl, U and Zn. The samples came from active spreading centers in the Indian and Atlantic Ocean. Glasses from DSDP Leg 24, site 238 (Indian Ocean) have a somewhat peculiar trace element pattern, but this is thought to reflect secondary processes operating at shallow depth, not an anomalous source region in the mantle. Our data rather indicate that heterogeneities in the mantle are confined to the highly incompatible lithophile elements.Chemical fractionations during petrogenesis of tholeiitic basalts are discussed in the light of literature data for primitive peridotitic upper mantle nodules. (Ir, Os), Au, Pd, Ni and Re are strongly fractionated from each other in igneous processes; the unfractionated chondritic mantle pattern thus imposes firm constraints on mantle evolution models. The potentially chalcophile elements Ag, Cd, In and Zn do not behave differently from lithophile elements of the same valency and comparable ionic radius. Residual sulfides are not abundant enough to efficiently control the partitioning of these elements during basalt petrogenesis. However, the poor coherence of Tl to Rb and U in ocean floor basalts could point to retention of Tl by residual sulfides during depletion of the MORB source regions. Sb is strongly depleted in the source regions of ocean ridge basalts; most likely, it was present as a highly incompatible Sb5+cation. The limited Rb/Cs fractionation in oceanic tholeiites, as opposed to continental tholeiites and acidic rocks, appears to reflect the low abundance of volatile constituents and hydrous silicates in normal ocean ridge basalts.