Retrograde Metamorphism in the Greek Cycladic Islands as a Window into Exhumation Mechanisms of High Pressure Terranes

希腊基克拉迪群岛的逆变质作用是了解高压地体折返机制的窗口

• 批准号: 1725110
• 负责人: Jaime Barnes
• 金额: $ 33.48万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-07-01 至 2022-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1725110&HistoricalAwards=false
• 关键词: Retrograde; Metamorphism; Greek; Cycladic; Islands

Subduction zones carry oceanic and continental lithosphere to depths of arc magma genesis and beyond. However, not all subducted material reaches these depths and rocks are often returned to Earth's surface and preserved as exhumed high-pressure and ultra-high-pressure terranes in orogenic belts. The mechanism(s) by which these rocks return to the surface remains enigmatic. Knowledge of exhumation mechanisms is fundamental for a complete understanding of subduction zone dynamics. Although the research focus is on a particular part of the Aegean, the results will have implications for the general tectonic and geochemical processes operative in other exhumed subduction complexes as well as modern and ancient subduction zones. For example, modern observations of subduction zones reveal a spectrum of deformational and seismic behaviors along the subduction interface that are a function of interface effective width, rheological and metamorphic heterogeneities, and fluid distribution. The exhumed rock record on Syros and Tinos samples this subduction interface allowing us to better understand the linkage among mass transport, fluids, deformation and seismic behavior during the return-flow of material. In addition to the intellectual impacts of improved understanding of material transfer in subductions zone, the broader impacts consist of two key components: 1) international collaboration with colleagues at the University of Athens and 2) minority student support/outreach via training of two Ph.D. students (one minority and one female) and support for a minority undergraduate summer internship program for students from the University of Puerto Rico.It is commonly accepted that metamorphic rocks on Syros and Tinos record prograde metamorphism due to subduction during the Eocene (~ 50 Ma), followed by exhumation from mid-crustal levels during Miocene (~25 Ma) extensional detachment faulting. However, the processes responsible for exhuming these rocks from mantle depths to the middle crust during substantial window of time (~25 m.y.) between subduction and core-complex-capture remain enigmatic and the pressure and temperature conditions are poorly constrained. In addition, there are several cryptic phases of retrograde metamorphism that are likely associated with this time gap, and that record different mineral assemblages, deformation fabrics, and degrees of fluid infiltration and fluid sources. THe researchers will determine the pressure-temperature-time-deformation-fluid-source paths for several outcrops on Syros and Tinos, in order to decipher the exhumation mechanisms responsible for the early retrograde history and provide a high resolution snapshot of the Eo-Oligocene exhumation history of the Cycladic Blueschist Unit. The researchers will use a multi-disciplinary suite of approaches, including field structural geology, petrology, geochronology, and geochemistry, to decipher the early exhumation mechanisms of high pressure metamorphic rocks on Syros and Tinos. Field structural geology will focus on establishing deformation stages, strain distributions and kinematics; petrology, thermobarometry and microstructural analysis will be used to link particular fabrics identified in outcrop to their pressure-temperature conditions of deformation; in-situ and multi-mineral-isochron geochronology will provide constraints on the timing of development of particular retrograde fabrics; and stable isotope geochemistry will allow us to decipher the fluid sources that facilitated the retrogression process.

俯冲带将大洋和大陆岩石圈带到弧岩浆成因的深处和更远的地方。然而，并不是所有的俯冲物质都能到达这些深度，岩石经常被带回地球表面，并作为造山带中的高压和超高压地体保存下来。这些岩石返回地表的机制(S)仍然是个谜。对折返机制的了解是全面了解俯冲带动力学的基础。尽管研究的重点是爱琴海的一个特定部分，但研究结果将对其他出土的俯冲杂岩以及现代和古代俯冲带的一般构造和地球化学过程产生影响。例如，对俯冲带的现代观察揭示了沿俯冲界面的一系列变形和地震行为，这些行为是界面有效宽度、流变性和变质非均质性以及流体分布的函数。Syros和Tinos上出土的岩石记录采样了这一俯冲界面，使我们能够更好地了解物质返回流动过程中质量传输、流体、变形和地震行为之间的联系。除了对俯冲带物质转移认识的提高带来的智力影响外，更广泛的影响还包括两个关键组成部分：1)与雅典大学的同事进行国际合作；2)通过培训两名博士生(一名少数民族和一名女性)和支持波多黎各大学少数民族本科生暑期实习计划来支持/推广少数民族学生。人们普遍认为，Syros和Tinos上的变质岩记录了始新世(~50 Ma)俯冲作用导致的进行性变质作用，随后在中新世(~25 Ma)伸展拆离断层期间从地壳中层折返。然而，在相当长的一段时间内(约25英里)，负责将这些岩石从地幔深处挖出到中地壳的过程。俯冲和核杂岩俘获之间的关系仍然是个谜，压力和温度条件的约束很差。此外，有几个隐蔽的退变质阶段可能与这个时间间隔有关，它们记录了不同的矿物组合、变形组构、流体渗透程度和流体来源。研究人员将确定Syros和Tinos上几个露头的pressure-temperature-time-deformation-fluid-source路径，以破译导致早期退行性历史的折返机制，并提供Cycldic蓝片岩单元始始渐新世折返历史的高分辨率快照。研究人员将使用一套多学科的方法，包括野外构造地质学、岩石学、地质年代学和地球化学，以破译赛罗斯和蒂诺斯高压变质岩的早期折返机制。野外构造地质学将侧重于确定变形阶段、应变分布和运动学；岩石学、温压测量和显微构造分析将被用于将露头发现的特定组构与其变形的压力-温度条件联系起来；原位和多矿物等时线年代学将提供特定退变组构发育时间的限制；稳定同位素地球化学将使我们能够破译促成退缩过程的流体来源。

项目成果

Evaluation and application of the quartz-inclusions-in-epidote mineral barometer

• DOI: 10.2138/am-2020-7379
• 发表时间: 2020-08
• 期刊: American Mineralogist
• 影响因子: 3.1
• 作者: M. Cisneros;K. Ashley;R. Bodnar

Insights from elastic thermobarometry into exhumation of high-pressure metamorphic rocks from Syros, Greece

• DOI: 10.5194/se-12-1335-2021
• 发表时间: 2020-09
• 期刊: Solid Earth
• 影响因子: 3.4
• 作者: Miguel Cisneros;Jaime D. Barnes;W. Behr;A. Kotowski;D. Stockli;K. Soukis

Applications and Limitations of Elastic Thermobarometry: Insights From Elastic Modeling of Inclusion‐Host Pairs and Example Case Studies

• DOI: 10.1029/2020gc009231
• 发表时间: 2020-09
• 期刊: Geochemistry
• 影响因子: 3.7
• 作者: M. Cisneros;K. Befus

Zircon U-Pb and geochemical signatures in high-pressure, low-temperature metamorphic rocks as recorders of subduction zone processes, Sikinos and Ios islands, Greece

• DOI: 10.1016/j.chemgeo.2021.120447
• 发表时间: 2021-11
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: Eirini M. Poulaki;D. Stockli;Megan E. Flansburg;M. Gevedon;L. Stockli;J. Barnes;K. Soukis;K. Kitajima;J. Valley

Subduction, Underplating, and Return Flow Recorded in the Cycladic Blueschist Unit Exposed on Syros, Greece

希腊锡罗斯岛上基克拉迪蓝片岩单元记录的俯冲、底侵和回流

• DOI: 10.1029/2020tc006528
• 发表时间: 2022
• 期刊: Tectonics
• 影响因子: 4.2
• 作者: Kotowski, Alissa J.;Cisneros, Miguel;Behr, Whitney M.;Stockli, Daniel F.;Soukis, Konstantinos;Barnes, Jaime D.;Ortega‐Arroyo, Daniel
• 通讯作者: Ortega‐Arroyo, Daniel