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

从俯冲岩石中释放的水（和其他挥发物）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这种释放的时间和位置（例如深度和温度范围）对于理解这种广泛的构造过程是至关重要的，但目前对流体生产速率的了解通常很少。拟议的研究将采用新的方法来重建一个4500万年前的俯冲复合体的脱水通量，该复合体现在以保存完好的蓝片岩和榴辉岩的形式暴露在希腊锡罗斯岛和锡弗诺斯岛上。有了这些独特的信息，对俯冲带脱水过程的地球动力学模型预测将进行测试和改进。一个关键的问题是，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连续地释放出来，但最近的研究（包括对西弗诺斯的初步研究）表明，在俯冲过程中，变质反应可能发生在短暂的爆发中，迅速释放出水。在俯冲带脱水过程中生长的同心带石榴石晶体将像树木年轮一样用钐-钕衰变系统测定年代。至关重要的是，测年分辨率将足以解决短短几十万年里石榴石生长速率（即脉冲）的变化。热力学分析将提供石榴石生长的具体深度和温度区间的限制，这将直接与每块岩石的伴随水释放有关。来自热力学分析的限制将与来自带状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。这些新方法和由此产生的数据集将为科学家研究地球深处发生的俯冲带过程提供一个新的窗口。

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.