Collaborative Research: Investigating the Sedimentary Record of Differing Modes of Flat-Slab Subduction

合作研究：调查不同模式板片俯冲的沉积记录

• 批准号: 1419790
• 负责人: Eva Enkelmann
• 金额: $ 19万
• 依托单位: University of Cincinnati Main Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1419790&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigating; Sedimentary; Record

The paradigm of convergent margins involves an oceanic plate of uniform character that subducts at a relatively steep (30 to 45 degrees) angle. Oceanic plates are not uniform, however, and instead consist of broad (plateaus) and narrow (aseismic ridges) regions of thickened crust, as well as spreading ridges where molten mantle material comes to the surface and creates new crust. An increase in crustal thickness or heat flow associated with these features causes the plates to be more buoyant than typical oceanic plates and to subduct at shallower or nearly flat angles. Flat-slab subduction of buoyant oceanic plateaus and aseismic and spreading ridges occurs along some of the world?s major convergent margins. The response of sedimentary basins above a these zones of flat slab subduction is not well understood. This project investigates the response of the Cook Inlet basin in south central Alaska to changes in subduction angle with special focus on the transition from steep subduction to flat subduction. A significant impact of the proposed research will be to provide a better understanding of the response of the upper plate and the sedimentary record to flat slab subduction, results which inform future studies of potential flat slab localities. The project will advance desired societal outcomes through: 1) full participation of women in STEM through support of two early career female PIs and outreach to minority high school students; 2) increased public scientific literacy and public engagement with science and technology through public outreach; and 3) development of a diverse, globally competitive STEM workforce though activities at Cincinnati high school, a short course for students and professionals in Anchorage, and training of graduate and undergraduate students.The sequence, timing, and magnitude of upper plate processes related to flat-slab subduction are still poorly understood. Recognition of flat-slab subduction in the ancient geologic record is based primarily on changes in volcanic arc magmatism and less frequently on inboard migration of upper plate deformation, exhumation, and sedimentary basin evolution. However, very few studies have attempted to quantify the spatial and temporal patterns of surface uplift and erosion as it relates to subduction of a buoyant slab, and which result in changes to the types and locations of major sediment sources to adjacent basins. Here, a research team from the University of Iowa and University of Cincinnati will investigate the Late Cretaceous-Cenozoic sedimentary deposits of the Cook Inlet basin in south central Alaska, which constitute a complete sedimentary record of forearc basin strata deposited during three different modes of subduction. Normal subduction of oceanic crust in the Late Cretaceous was followed by flat-slab subduction of a spreading ridge (ca. 62-50 Ma), and later by subduction of an oceanic plateau (ca. 40-0 Ma). Two hypotheses are tested: (1) subduction of a spreading-ridge in late Paleocene?Eocene time resulted in a change in topography and a shift in sediment sources from the adjacent arc to the retroarc region; (2) flat-slab subduction of an oceanic plateau from Oligocene time to the present resulted in the creation of topography above the flat-slab region and an overall contraction of the forearc basin drainage area. The researchers investigate the sedimentary record of flat slab subduction in southern Alaska by examining Late Mesozoic and Cenozoic strata in core samples from the Cook Inlet forearc basin through traditional stratigraphic analysis combined with provenance and thermochronologic techniques of double-dating detrital zircons using uranium-lead and fission track dating, rare earth element analyses of mudstones, and sandstone petrography. The integration of these datasets enables the investigation of the patterns of regional exhumation, magmatism, and sediment transport across the area and interpretation these patterns in terms of regional tectonics and changes through time. This study will provide a foundation for new tectonic and provenance models of forearc basins that have been modified by flat-slab subduction processes.

会聚边缘的范例涉及一个性质一致的海洋板块，以相对陡的角度（30至45度）俯冲。然而，海洋板块并不均匀，而是由宽阔的（高原）和狭窄的（海隆脊）加厚地壳区域组成，以及熔融地幔物质到达地表并产生新地壳的扩张脊。与这些特征相关的地壳厚度或热流的增加导致板块比典型的大洋板块更有浮力，并以更浅或几乎平坦的角度俯冲。有浮力的海洋高原和海隆以及扩张脊的平板俯冲作用发生在世界上沿着一些？的主要收敛边缘。在这些板块俯冲带之上的沉积盆地的反应还不很清楚。本项目研究了阿拉斯加中南部库克湾盆地对俯冲角度变化的反应，特别关注从陡峭俯冲到平坦俯冲的过渡。拟议的研究的一个重大影响将是提供一个更好的理解的上层板块和沉积记录的平板俯冲的响应，结果通知未来的研究潜在的平板地点。该项目将通过以下方式推进预期的社会成果：1）通过支持两名职业女性初级研究员和向少数民族高中生开展外联活动，使妇女充分参与STEM; 2）通过公共外联活动，提高公众的科学素养和公众对科学技术的参与;和3）通过在辛辛那提高中的活动，为安克雷奇的学生和专业人士提供短期课程，培养多元化、具有全球竞争力的STEM劳动力，研究生和本科生的培训。与板块俯冲有关的上板块过程的顺序、时间和幅度仍然知之甚少。在古代地质记录中，对板块俯冲的认识主要是基于火山弧岩浆活动的变化，而较少基于上板块变形、折返和沉积盆地演化的向内迁移。然而，很少有研究试图量化的空间和时间模式的表面隆起和侵蚀，因为它涉及到俯冲的浮板，并导致改变的类型和位置的主要沉积物来源到邻近的盆地。在这里，来自爱荷华州大学和辛辛那提大学的一个研究小组将调查阿拉斯加中南部库克湾盆地的晚白垩世-新生代沉积矿床，这些矿床构成了三种不同俯冲模式期间沉积的弧前盆地地层的完整沉积记录。晚白垩世洋壳的正常俯冲之后，是扩张脊的平板俯冲（约100公里）。62-50 Ma），以及后来的大洋高原俯冲（约。40-0 Ma）。验证了两个假说：（1）古新世晚期扩张脊俯冲;始新世的时间导致了地形的变化和转移的沉积物来源，从相邻的弧弧后地区;（2）从渐新世到现在的海洋高原的平板俯冲，导致在平板地区和弧前盆地流域面积的整体收缩地形创建。研究人员通过检查库克湾弧前盆地岩芯样品中的晚中生代和新生代地层，调查阿拉斯加南部平板俯冲的沉积记录，通过传统的地层分析，结合使用铀铅和裂变径迹定年的双重定年碎屑锆石的起源和热年代学技术，泥岩的稀土元素分析和砂岩岩相学。这些数据集的整合，使区域折返，岩浆活动和沉积物运输的模式在整个地区的调查和解释这些模式的区域构造和随时间的变化。这一研究将为弧前盆地构造和物源模式提供基础，这些盆地已被板块俯冲过程所改变。