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

合作研究：希腊锡罗斯岛和锡夫诺斯岛俯冲岩性脱水通量的现场定量

• 批准号: 1250497
• 负责人: Ethan Baxter
• 金额: $ 26.66万
• 依托单位: Trustees of Boston University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-01-01 至 2015-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1250497&HistoricalAwards=false
• 关键词: Collaborative; Research; Field; Based; Quantification

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.

水（和其他挥发性物质）从俯冲岩石中的释放是全球地质水（和CO2）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生成的关键触发过程。 了解俯冲岩石的主要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至关重要，但目前对流体生产率的了解普遍不足。 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，该复合体现在暴露在希腊锡罗斯岛和锡夫诺斯岛上保存完好的蓝片岩和榴辉岩表面。 有了这些独特的信息，俯冲带脱水过程的地球动力学模型预测将得到检验和改进。一个关键问题是俯冲带岩石的初始脱水通量是连续的还是脉冲的。 虽然许多过去的预测表明，相对连续的水从下降的岩石释放，最近的工作（包括对锡弗诺斯的初步工作）表明，俯冲过程中的变质反应可以发生在短暂的爆发，迅速释放水。 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-钕衰变系统进行年代测定。 至关重要的是，测年分辨率将足以解决石榴石生长速率（即脉冲）的变化，短至几十万年。 热力学分析将提供对石榴石生长的特定深度和温度区间的限制，这将直接与每种岩石伴随的水释放有关。 热力学分析的约束条件将与分区石榴石地质年代学的直接速率年龄信息相结合，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提供一个新的窗口，以了解地球深处发生的俯冲带过程。