Chlorine in submarine volcanic glasses from the eastern manus basin
Chlorine in submarine volcanic glasses from the eastern manus basin
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DOI：
10.1016/j.gca.2006.12.003
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发表时间：
2007-03
影响因子：
5
通讯作者：
Weidong Sun;R. Binns;A. Fan;Vadim Kamenetsky;R. Wysoczanski;G. Wei;Yanhua Hu;R. Arculus
中科院分区：
文献类型：
--
作者：
Weidong Sun;R. Binns;A. Fan;Vadim Kamenetsky;R. Wysoczanski;G. Wei;Yanhua Hu;R. Arculus
巴布亚新几内亚东部马努斯盆地的海底火山玻璃，从玄武岩到流纹石，阐明了弧型岩浆中Cl的地球化学行为。对于马努斯样品，Cl与非挥发性高度不相容的微量元素有很好的相关性，表明它不是高度挥发性的，并排除了明显的海水污染。Cl分配系数接近但略低于Nb和K2O的分配系数，与洋中脊玄武岩（MORB）和洋岛玄武岩（OIB）相似。Cl和Nb相似的不相容性表明，马努斯盆地东部玻璃的Cl/Nb值反映了其岩浆来源。对于其他西太平洋弧后盆地的玻璃，Cl/Nb、Ba/Nb和U/Nb向俯冲沟方向增加，表明富含Cl、Ba和U的组分的贡献增加，可能来自俯冲释放的板块流体。据估计，马努斯弧形玻璃中约80%的Cl是直接从俯冲的板岩衍生流体中添加的。我们还模拟了岩浆演化过程中Cl的一般行为。结果表明，岩浆中Cl的行为受压力、初始H2O含量和岩浆分馏程度的强烈影响。在岩浆演化早期，对于初始H2O含量<4.0wt%的岩浆，Cl在各种压力下都是高度不相容的。相比之下，对于中等高压和高H2O含量的更进化的岩浆，一旦达到H2O饱和，就可以从岩浆中提取出相当数量的Cl。因此，Cl在MORB和OIB中通常是高度不相容的，因为它们的H2O含量低，结晶程度相对较低。Cl在弧岩浆中的行为则更为复杂，根据岩浆室的水含量和深度的不同，Cl在弧岩浆中的行为可以从高度不相容到高度相容。马努斯盆地东部岩浆中Cl的表现与低H2O含量（1.1 ~ 1.7wt%）和低压（<0.1GPa）演化相一致。模拟结果还表明，由于所涉及的压力不同，Cl在侵入岩和火山岩中的表现也不同。这可能对这两个构造背景下的成矿机制产生强烈影响。
Submarine volcanic glasses from the eastern Manus Basin of Papua New Guinea, ranging from basalt to rhyodacite, clarify the geochemical behavior of Cl in arc-type magmas. For the Manus samples, Cl is well correlated with non-volatile highly incompatible trace elements, suggesting it was not highly volatile and discounting significant seawater contamination. The Cl partition coefficient is close to but slightly lower than that of Nb and K2O, a behavior similar to that in mid-ocean ridge basalts (MORB) and ocean island basalts (OIB). The similar incompatibilities of Cl and Nb imply that the Cl/Nb values of the eastern Manus Basin glasses reflect their magma source. For glasses from other west Pacific back-arc basins, Cl/Nb, Ba/Nb, and U/Nb increase towards the subduction trench, indicating increased contribution of a component enriched in Cl, Ba, and U, likely from subduction-released slab fluids. It is estimate that ∼80% of the Cl in the Manus arc-type glasses was added directly from subducted slab-derived fluids. We have also modeled Cl behavior during magma evolution in general. Our results show that the behavior of Cl in magma is strongly influenced by pressure, initial H2O content, and the degree of magmatic fractionation. At early stages of magmatic evolution, for magmas with initial H2O content of <4.0wt%, Cl is highly incompatible under all pressures. By contrast, for more evolved magmas at moderately high pressure and high H2O contents, considerable amounts of Cl can be extracted from the magma once H2O saturation is reached. Accordingly, Cl is usually highly incompatible in MORB and OIB because of their low H2O contents and relatively low degrees of fractional crystallization. The behavior of Cl in arc magmas is more complicated, ranging from highly incompatible to compatible depending on H2O content and depth of magma chambers. The behavior of Cl in the eastern Manus Basin magmas is consistent with low H2O contents (1.1–1.7wt%) and evolution at low pressures (<0.1GPa). Modeling results also indicate that Cl will behave differently in intrusive rocks compared to volcanic rocks because of the different pressures involved. This may have a strong influence on the mechanisms of ore genesis in these two tectonic settings.