Collaborative Research: Field-Based Quantification of Dehyration Flux from Subducting Lithologies, Syros and Sifnos, Greece

来自俯冲岩石的水(和其他挥发物)的释放是全球地质水(和二氧化碳)循环的重要组成部分。更具体地说，它是弧火山活动、地震活动和成矿流体产生的关键触发过程。了解俯冲岩石的初级脱水通量以及释放的时间和位置(如深度和温度范围)是理解这种广泛构造过程的基础，但目前对流体产生速率的了解普遍较少。这项拟议的研究将使用新的方法来重建4500万年前的俯冲杂岩的脱水通量，这些俯冲杂岩现在暴露在希腊锡罗斯和西夫诺斯岛上保存完好的蓝片岩和榴辉岩中。有了这一独特的信息，俯冲带脱水过程的地球动力学模型预测将得到检验和完善。一个关键问题是，俯冲岩石的初级脱水通量是连续的还是脉冲的。虽然过去的许多预测表明，水从下降的岩石中相对持续地释放出来，但最近的工作(包括Sifnos的初步工作)表明，俯冲过程中的变质反应可能会以短暂的爆发形式发生，迅速释放水。在俯冲带脱水过程中生长的同心带状石榴石晶体，将用Sm-Ne衰变系统测定树轮的年龄。至关重要的是，测年分辨率将足以解决石榴石生长速度(即脉冲)在短短数十万年内的变化。热力学分析将提供石榴石生长的特定深度和温度区间的限制，这将直接与每块岩石伴随的水分释放有关。热力学分析的约束条件将与来自分区石榴石地质年代学的直接速率和年龄信息相结合，以提供独特的脱水年代学。这些新的方法和产生的数据集将为科学家提供一个新的窗口，了解地球深处发生的俯冲带过程。

The release of water (and other volatiles) from subducted rocks represents an important part of the global geological water (and CO2) cycle. More specifically, it is a crucial triggering process for arc volcanism, seismicity, and the generation of ore forming fluids. Knowledge of the primary dehydration flux from subducted rocks as well as the timing and location (e.g. depth and temperature range) of this release is fundamental to understanding such broad tectonic processes, but rates of fluid production are currently generally poorly understood. The proposed research will employ novel methods to reconstruct dehydration fluxes from a 45 million year old subduction complex now exposed at the surface as well-preserved blueschist and eclogite rocks on the islands of Syros and Sifnos, Greece. With this unique information, geodynamic model predictions of subduction zone dehydration processes will be tested and refined.A key question is whether the primary dehydration flux from subducted rocks is continuous or pulsed. While many past predictions suggest relatively continuous release of water from descending rocks, recent work (including preliminary work on Sifnos) has suggested that metamorphic reactions during subduction can occur in brief bursts that rapidly liberate water. Concentrically zoned garnet crystals, which grow during subduction zone dehydration, will be dated like tree rings with the Samarium-Neodymium decay system. Crucially, the dating resolution will be sufficient to resolve changes in the rate of garnet growth (i.e. pulses) as short as a few hundred thousand years. Thermodynamic analysis will provide constraints on the specific depth and temperature interval of garnet growth, which will be linked directly to concomitant water release for each rock. Constraints from thermodynamic analysis will be integrated with direct rate & age information from zoned garnet geochronology to provide a unique dehydration chronology. These novel methods and resulting datasets will provide scientists a new window into subduction zone processes occurring deep within the Earth.