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: 1561882
• 负责人: Ethan Baxter
• 金额: $ 9.22万
• 依托单位: Boston College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1561882&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.

从俯冲岩石中释放水（和其他挥发物）代表了全球地质水（和CO2）周期的重要组成部分。 更具体地说，这是弧形火山，地震性和产生矿石液体的关键触发过程。 对俯冲岩石的主要脱水通量以及该释放的定时和位置（例如深度和温度范围）的了解对于理解这种广泛的构造过程至关重要，但是目前对流体产生的速度却一般不足。 拟议的研究将采用新型方法来重建来自现已在地表的4500万年历史的俯冲配合物中重建脱水通量，并在希腊Syros和Sifnos岛上保存良好的蓝石岩和叶绿石岩石。 有了这些独特的信息，将测试和完善俯冲带脱水过程的地球动力学模型预测。一个关键问题是，俯冲岩石的主要脱水通量是连续还是脉冲。 尽管过去的许多预测表明，从降落的岩石中相对连续释放水，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在迅速释放水的短暂爆发中发生。 在俯冲带脱水过程中生长的浓缩分区石榴石晶体将与samarium-neodymium衰减系统一样像树环一样。 至关重要的是，约会分辨率足以解决小石榴石生长速率（即豆类）的变化。 热力学分析将对石榴石生长的特定深度和温度间隔提供限制，这将直接与每个岩石的伴随水释放链接。 热力学分析的约束将与分区石榴石地质学的直接率和年龄信息集成，以提供独特的脱水时间。 这些新颖的方法和结果数据集将为科学家提供一个新的窗口，进入地球内部深处发生的俯冲带过程。