Isotopic shifts in waters from geothermal and volcanic systems along convergent plate boundaries and their origin
Isotopic shifts in waters from geothermal and volcanic systems along convergent plate boundaries and their origin
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DOI：
10.1016/0012-821x(92)90127-h
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发表时间：
1992-11
影响因子：
5.3
通讯作者：
W. Giggenbach
中科院分区：
文献类型：
--
作者：
W. Giggenbach
由水排放的D和18 O含量所描绘的趋势，来自于太平洋周围沿着会聚板块边界的广泛的地热和火山系统，指出存在一种共同的岩浆成分，δ D值的范围很窄，为−20 ± 10‰。这些沃茨的δ D值通常与安山岩浆作用有关，远高于地幔水的−65 ± 15‰。这种“安山岩”水最有可能的来源是循环海水。它以孔隙水的形式进入俯冲系统，或作为积聚的海洋沉积物的粘土矿物中的水化水，并被带到俯冲板片顶部的弧岩浆源区。来自大陆和蚀变洋壳的贡献似乎很小，来自地幔的贡献非常小（< 1%）。大部分其他成分（CO2，N2和可能的Cl）在火山，并暗示，地热流体排放沿着会聚板块边界很可能也主要是俯冲的海洋起源。并非由于地壳内的水-岩石同位素交换，沿着会聚板块边界来自热系统的高温沃茨中18 O的变化可能在很大程度上反映了与富含D、18 O（+ 10 ± 2‰）的安山质沃茨不同程度的混合，因此同位素“预变化”。由于在形成条件和D含量方面与新西兰沉积盆地和增生棱柱体相关的“演化海水”相似，因此建议将俯冲沉积物产生的岩浆沃茨称为“演化海水”。
The trends delineated by D and18O contents of water discharges, from a wide range of geothermal and volcanic systems along convergent plate boundaries around the Pacific, point to the existence of a common magmatic component with a narrow range ofδDvalues of−20 ± 10‰. TheδDvalues for these waters, which are generally associated with andesitic magmatism, are well above those of−65 ± 15‰suggested for mantle water. The most likely source for this ‘andesitic’ water is recycled seawater. It enters the subduction system in the form of porewater, or as the water of hydration in the clay minerals of accumulated marine sediments and is carried to the source region of arc magmas on the top of the subducting slab. Contributions from the continental and altered oceanic crusts appear to be minor, those from the mantle very minor (< 1%). Large proportions of other components (CO2, N2and probably Cl) in volcanic and, by implication, geothermal fluid discharges along convergent plate boundaries are likely to be also of predominantly subducted marine origin. Rather than being due to water-rock isotope exchange within the crust,18O shifts in high-temperature waters from thermal systems along convergent plate boundaries may largely reflect varying degrees of mixing with, in addition to D,18O-enriched (+ 10 ± 2‰), and thus isotopically ‘pre-shifted’, andesitic waters. Because of similarities, in terms of their formation conditions and D contents, with ‘evolved seawaters’ associated with sedimentary basins and an accretionary prism in New Zealand, the term ‘devolved seawater’ is proposed for magmatic waters produced from subducted sediments.