Garnet zoning patterns record multiple processes of chemical transfer during subduction
Garnet zoning patterns record multiple processes of chemical transfer during subduction
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DOI：
10.1016/j.epsl.2024.118634
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发表时间：
2024-04
影响因子：
5.3
通讯作者：
Freya R. George;D. Viete;Janaína Ávila;G. Seward;George L. Guice;Mark B. Allen;Michael J. Harrower
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文献类型：
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作者：
Freya R. George;D. Viete;Janaína Ávila;G. Seward;George L. Guice;Mark B. Allen;Michael J. Harrower
俯冲是挥发物从地球表面转移到其内部的主要机制。在俯冲环境中形成的榴辉岩和蓝片岩的石榴石中，精细尺度的振荡元素分带是一个共同特征，有时被认为记录了前变质过程中开放系统的流体交换。我们提供了来自五个挖掘出的俯冲带复合体的具有这种分区的石榴石的氧同位素数据。元素和氧同位素分区（其本身在空间上解耦）的短尺度波动不能与所有样品中石榴石结晶过程中的开放系统流体交换联系起来；这些数据没有为元素振荡和流体流动之间的遗传关系提供证据。然而，来自一种环境的石榴石确实为元素和同位素缓冲流体的同步生长进入提供了明确的证据，这一过程与元素振荡的形成同时进行。我们的研究结果表明，在俯冲过程中，化学传递的多种机制在颗粒-岩石尺度上起作用，并且一些俯冲带岩石可能仅与外部顺流流体发生有限的相互作用。这些结果与俯冲过程中高度异质挥发物转移的情况一致，并表明在浅层继承的一定比例的流体库存可能转移到弧下深度。
Subduction is the principal mechanism by which volatiles are transferred from the Earth's surface to its interior. In garnets from eclogites and blueschists formed within the subduction setting, fine-scale, oscillatory elemental zoning is a common feature, sometimes considered to record open-system fluid exchange during prograde metamorphism. We present oxygen isotope data for garnets with such zoning from five exhumed subduction zone complexes. Short length scale fluctuations in elemental and oxygen isotope zoning (which are themselves spatially decoupled) cannot be linked to open-system fluid exchange during garnet crystallization in all samples; these data do not provide evidence for a genetic relationship between elemental oscillations and fluid fluxing. However, garnets from one setting do provide clear evidence for syn-growth ingress of elementally and isotopically buffering fluids, a process that operated simultaneously with the formation of elemental oscillations. Our findings indicate multiple mechanisms of chemical transfer operate at the grain–rock scale during subduction, and that some subduction zone rocks may experience only limited interaction with external prograde fluids. These results are consistent with a picture of highly heterogenous volatile transfer during subduction, and suggest that some proportion of the fluid inventory inherited at shallow depths may be transferred to sub-arc depths.