Lawsonite: an exceptional geochemical archive in HP/LT rocks

硬钠石：HP/LT 岩石中特殊的地球化学档案

• 批准号: 1949895
• 负责人: Donna Whitney
• 金额: $ 31.95万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-02-01 至 2025-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1949895&HistoricalAwards=false
• 关键词: Lawsonite; exceptional; geochemical; archive; HP

Water and other chemical substances that are essential for life circulate from the Earth’s surface to the deep interior of the planet and back again in a cycle over many millions of years. Water is carried to great depths within mineral crystals in tectonic plates that dive (subduct) into the subsurface. One of the most important minerals in this cycle is lawsonite, which forms only under the characteristic high-pressure and relatively low-temperature conditions in the upper layer of subducting plates. Lawsonite is important because it contains a substantial amount of water and also contains trace amounts of other elements, such as uranium, lead, and rare earth elements. Although common in subducting plates, lawsonite rarely survives to be preserved in the rock record, particularly in the highest-pressure rocks of ancient subduction zones. This project uses the composition of rare, fresh lawsonite from a global suite of twelve subduction complexes as an archive of element-cycling processes in subduction zones. Lawsonite composition and zoning are exceptional recorders of fluid-rock interaction in subduction zones. Compositional and textural data illuminate the role of lawsonite and associated minerals in volatile and element cycling at the interface of the subducted oceanic crust and overlying mantle before major devolatilization at subarc depths. This research involves the first determination of oxygen isotope values in lawsonite and comprehensive characterization of the trace-element composition, zoning, and microstructures of lawsonite and associated minerals. Preliminary data indicate that oxygen isotope abundance in lawsonite is a sensitive indicator of the source(s) of fluids in subducted slabs, such as serpentinites (lower d18O) or oceanic sediments (higher d18O), and show that fluid sources in mélange vs. more structurally-coherent subduction complexes may be distinct. The sample suite consists of lawsonite eclogites and blueschists as well as lawsonite-bearing metasedimentary (carbonate, quartzite) and metasomatic rocks and veins, and includes prograde, peak, and retrograde generations of lawsonite. Owing to its high modal abundance and composition (12 wt% H2O, 1-2 wt% Fe2O3), lawsonite may be a significant factor in mantle redox conditions and H2O content since at least the Neoproterozoic.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

水和其他对生命至关重要的化学物质在数百万年的循环中从地球表面循环到地球深处，然后再循环回来。水在构造板块中的矿物晶体中被带到很深的地方，潜入(潜入)地下。在这个旋回中最重要的矿物之一是劳钠铝石，它只在俯冲板块上层特有的高压和相对低温的条件下形成。硬钠铝石很重要，因为它含有大量的水，还含有微量的其他元素，如铀、铅和稀土元素。虽然在俯冲板块中很常见，但在岩石记录中，特别是在古代俯冲带的最高压力岩石中，硬钠铝石很少幸存下来。该项目使用来自全球12个俯冲杂岩的稀有、新鲜的劳钠铝石组成，作为俯冲带元素循环过程的档案。水钠铝石的成分和分带是俯冲带流体-岩石相互作用的特殊记录。成分和结构数据表明，在弧下深度主要挥发分释放之前，钠铝石及其伴生矿物在俯冲洋壳和上地幔界面的挥发分和元素循环中所起的作用。这项研究首先测定了劳钠铝石中的氧同位素值，并对其微量元素组成、分带和显微结构进行了综合表征。初步数据表明，钠钠铝石中的氧同位素丰度是俯冲板块中流体来源(S)的灵敏指标，如蛇纹岩(d18O较低)或海洋沉积物(d18O较高)，并表明混杂岩类和结构上更一致的俯冲杂岩中的流体来源可能是不同的。样品套由硬钠铝石榴辉岩和蓝片岩以及含硬钠铝石的变质沉积岩(碳酸盐、石英岩)和交代岩石和脉体组成，包括前行、高峰和逆行世代的硬钠铝石。由于其高的模式丰度和组成(12wt%H2O，1-2wt%Fe2O3)，劳钠铝石可能是至少在新元古代以来地幔氧化还原条件和H2O含量的一个重要因素。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Controls on development of different mineral assemblages in gabbro and basalt during subduction metamorphism

• DOI: 10.1007/s00410-020-01753-6
• 发表时间: 2020-11
• 期刊: Contributions to Mineralogy and Petrology
• 影响因子: 3.5
• 作者: P. Kang;K. Fornash;D. Whitney

Lawsonite composition and zoning as tracers of subduction processes: A global review

• DOI: 10.1016/j.lithos.2020.105636
• 发表时间: 2020-10
• 期刊: Lithos
• 影响因子: 3.5
• 作者: D. Whitney;K. Fornash;P. Kang;E. Ghent;L. Martin;A. Okay;A. V. Brovarone

Trace and Rare Earth Element Compositions of Lawsonite as a Chemical Tracer of Metamorphic Processes in Subduction Zones

硬铝石矿的痕量和稀土元素组成作为俯冲带变质过程的化学示踪剂

• DOI: 10.1093/petrology/egac065
• 发表时间: 2022
• 期刊: Journal of Petrology
• 影响因子: 3.9
• 作者: Kang, Patricia;Whitney, Donna L;Martin, Laure A;Fornash, Katherine F
• 通讯作者: Fornash, Katherine F

How the Earth Recycles

地球如何循环利用

• DOI: 10.3389/frym.2021.599596
• 发表时间: 2021
• 期刊: Frontiers for Young Minds
• 作者: Newville, Christine;Whitney, Donna L.;Kang, Patricia;Raia, Natalie H.;Fornash, Katherine F.
• 通讯作者: Fornash, Katherine F.

Serpentinites of Different Tectonic Origin in an Exhumed Subduction Complex (New Caledonia, SW Pacific)

• DOI: 10.1029/2022gc010395
• 发表时间: 2022-07
• 期刊: Geochemistry
• 影响因子: 3.7
• 作者: Natalie H. Raia;D. Whitney;C. Teyssier;S. Lesimple