Evaluating the Role of Fluid and Melts in Mediating Element Recycling and Exhumation During Retrograde Metamorphism Following UHP Metamorphism

评估流体和熔体在超高压变质作用后逆行变质过程中介导元素回收和折返中的作用

• 批准号: 1624546
• 负责人: Stacia Gordon
• 金额: $ 32.82万
• 依托单位: Board of Regents, NSHE, obo University of Nevada, Reno
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1624546&HistoricalAwards=false
• 关键词: Evaluating; Role; Fluid; Melts; Mediating

Nontechnical AbstractPlate tectonics introduces a feedback loop in which subduction of crustal material at convergent plate margins continually injects less dense rocks formed at the surface back into Earth's dense mantle. As this crustal material is subducted, it interacts with the mantle, exchanges elements, and continuously drives the geochemical evolution of Earth. In order to determine the effect of element recycling during the exhumation of subducted rocks, it is necessary to investigate the chemical reactions that occur during the exhumation of crustal rocks back to Earth's surface. Ultrahigh-pressure (UHP) terranes contain rocks that were carried down to mantle depths via subduction and then returned to the surface. Some of the rocks within UHP terranes preserve "pristine" mineral assemblages that equilibrated at mantle depths. Typically the outermost rind of these rocks contain new or "retrogressed" mineral assemblages that formed as the rocks were being exhumed to the surface. By comparing the chemistry of the "fresh" to the "retrogressed" UHP rocks, the chemical changes that are triggered by exhumation will be examined and their impact upon the geochemical evolution of Earth will be assessed.Technical AbstractMass transfer within subduction zones remains poorly understood. In particular, there is limited knowledge of the P-T conditions at which elemental recycling occurs and of what transporting agents drive the elemental-recycling processes. Many field-based studies have focused upon exhumed high-pressure and ultrahigh-pressure (UHP) terranes to better understand the devolatilization reactions and products that occur along the prograde path as crustal rocks are subducted deep within Earth. In contrast, the retrograde reactions that transpire during the exhumation of these deeply subducted rocks have largely been ignored despite the fact that peak temperatures generally occur along the retrograde path and devolatilization and melting reactions are common. Retrograde metamorphic reactions and associated mass transfer may thus have a great influence on elemental-recycling processes in subduction zones and may also dictate the nature of the exhumation processes that bring crustal material from UHP depths to the surface. This integrated field and laboratory study of the Western Gneiss Region will reveal whether large-scale elemental recycling occurs during retrogression of UHP crustal rocks and whether these processes influence the rates and mechanisms by which UHP terranes are exhumed back to Earth's surface.

非技术抽象板构造引入了一个反馈回路，在这种反馈环上，在收敛板缘处的地壳材料的俯冲不断地注入较少的地表中形成的密度较小的岩石，回到地球浓密的地幔中。由于这种地壳材料被俯冲，它与地幔相互作用，交换元素，并不断驱动地球的地球化学演化。为了确定俯冲岩石发掘过程中元素回收的影响，有必要研究在地壳岩石回到地球表面期间发生的化学反应。超高压（UHP）地层包含岩石，这些岩石通过俯冲将其延伸到地幔深度，然后返回表面。 UHP地层内的一些岩石保留了在地幔深度平衡的“原始”矿物组合。通常，这些岩石的最外层包含新的或“翻转”的矿物组合物，这些矿物组合是在岩石被挖掘成表面的。通过将“新鲜”的化学与“翻转”的UHP岩石进行比较，将检查由挖掘触发的化学变化，并将评估它们对地球地球化学演化的影响。俯冲Zones中的技术抽象转移仍然不足。特别是，对发生元素回收的P-T条件的了解有限，并且传输剂驱动元素回收过程的情况有限。许多基于野外的研究集中在发掘的高压和超高压（UHP）地层上，以更好地了解沿着甲壳岩石在地球深处俯冲，沿着前岩石沿着前路径发生的脱脂反应和产物。相反，尽管峰值温度通常沿着逆行路径，而脱水和融化反应很常见，但在这些深俯冲岩石挖掘过程中逐渐爆发的逆行反应在很大程度上被忽略了。因此，逆行变质反应和相关的传质可能会对俯冲带中的元素回收过程产生很大的影响，并且还可能决定将挖掘过程的性质从UHP深度带到表面。西部片麻岩区域的这项综合田间和实验室研究将揭示在UHP地壳岩石倒流期间是否发生大规模元素回收，以及这些过程是否影响将UHP Terranes挖回地球表面的速率和机制。

项目成果

Deformation-enhanced recrystallization of titanite drives decoupling between U-Pb and trace elements

钛矿的形变强化再结晶驱动 U-Pb 与微量元素之间的解耦

• DOI: 10.1016/j.epsl2021.116810
• 发表时间: 2021
• 期刊: Earth and planetary science letters
• 影响因子: 5.3
• 作者: Gordon, S.M.;Kirkland, C.L.;Reddy, S.M.;Blatchford, H.J.;Whitney, D.L.;Teyssier, C.;Evans, N.J.;McDonald, B.J.
• 通讯作者: McDonald, B.J.