Testing the effects of cooling history and rheology on oceanic plateau accretion and their role in tectonic modification of convergent margins

海洋高原是在海洋盆地中形成的又宽又厚的火山大厦。俯冲是一种构造过程，海洋地壳被拉回到地球内部，有时会导致这些高原与大陆碰撞。这些碰撞的影响仍然知之甚少，取决于各种因素，包括海洋高原的年龄。年轻的高原保持温暖，浮力和脆弱，抵抗被拉入地球内部，而较老的高原寒冷，致密，坚固，更容易被拉入地幔。研究员将通过对同一海洋高原在不同时间与北美碰撞的两个碎片进行跨学科研究，调查和比较海洋高原碰撞的影响。这一比较将为海洋高原的年龄与碰撞过程的关系提供新的见解。该提案将支持一名女博士生，几名本科生研究人员和两名早期职业教师。它将包括一个实地考察华盛顿州的美洲原住民本科生，旨在连接地球科学的重要问题，以美洲原住民社区。这种联系是获得学生兴趣，招募和培训下一代美洲原住民地球科学家的重要一步。为了实现拟议的研究目标，研究人员将对海洋高原吸积的两个自然例子进行多学科研究：始新世西勒齐亚向华盛顿、俄勒冈州和温哥华岛的增生，以及雅库特地体与阿拉斯加南部碰撞的最新渐新世。 这些高原被认为是一个单一的高原，可能具有相同的地壳结构。然而，Siletzia在高原形成的过程中不断增长，而Yakutat Eye在与阿拉斯加南部最终碰撞之前又冷却了3000万年。这两次碰撞分别提供了涉及“年轻、热、弱和浮力”高原的碰撞和涉及“较冷、较老、较强、浮力较小”高原的碰撞的例子。 为了更好地了解每次碰撞如何改变会聚边缘，PI将研究覆盖在两个断层上的同碰撞和后碰撞沉积地层。这项工作将包括利用铀-铅锆石ID-TIMS（同位素稀释-热电离质谱法）地质年代学从层间凝灰岩中建立精确的年代地层学，并结合详细的相变研究，以更好地了解每次碰撞期间和之后沉积体系的演变。PI还将在其年代地层学的背景下整合目标碎屑锆石种群的（U-Th）/He（铀-钍/氦）锆石热年代学，以评估每次碰撞期间弧前侵蚀的持续时间和强度。最后，研究人员将利用高原俯冲的热力学模型，通过系统地改变高原年龄和厚度等参数来帮助推广结果。这个多学科的方法将提供一个更完整的了解如何海洋高原与俯冲带的相互作用，以及它们在收敛边缘的修改作用。这个奖项反映了NSF的法定使命，并已被认为是值得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的支持。

Ocean plateaus are broad and thick volcanic edifices that form in ocean basins. Subduction, the tectonic process in which oceanic crust is pulled back into the Earth’s interior, sometimes causes these plateaus to collide with the continents. The effects of these collisions remain poorly understood and depend on a variety of factors, including the oceanic plateau’s age. Younger plateaus remain warm, buoyant, and weak and resist being pulled into the Earth’s interior, whereas older plateaus are cold, dense, and strong and can more easily be pulled into the Earth’s mantle. The PIs will investigate and compare the effects of ocean plateau collision through an interdisciplinary study of two fragments of the same oceanic plateau that collided with North America at different times. This comparison will provide insights into how the age of an oceanic plateau relates to the collisional process. The proposal will support a female PhD student, several undergraduate researchers, and two early career faculty. It will include a fieldtrip to Washington State for Native American undergraduate students that is designed to connect Earth Science to issues important to Native American communities. This connection is an important step in gaining student interest, recruiting, and training the next generation of Native American Earth scientists.To accomplish the proposed research goals, the researchers will undertake a multi-disciplinary study of two natural examples of oceanic plateau accretion: the Eocene accretion of Siletzia to Washington, Oregon, and Vancouver Island, and the latest Oligocene to present collision of the Yakutat terrane with southern Alaska. The terranes are proposed to have formed as a single plateau and likely have the same crustal structure. However, Siletzia accreted as the plateau was being built while the Yakutat terrane cooled for an additional 30 million years prior to its final collision with southern Alaska. These two collisions provide examples of a collision involving a ‘young, hot, weak, and buoyant’ plateau and one involving a ‘colder, older, stronger, less buoyant’ plateau, respectively. To better understand how each collision modified the convergent margin the PIs will study the syn- and post-collisional sedimentary strata overlying both terranes. This effort will include constructing a precise chronostratigraphy using uranium-lead zircon ID-TIMS (isotope dilution-thermal ionization mass spectrometry) geochronology from interbedded tuffs combined with detailed study of facies changes to better understand how depositional systems evolved during and after each collision. The PIs will also integrate (U-Th)/He (uranium-thorium/helium) zircon thermochronology on targeted detrital zircon populations within the context of their chronostratigraphy to assess the duration and intensity of forearc erosion during each collision. Finally, the investigators will utilize thermo-mechanical models of plateau subduction to help generalize results by systematically varying parameters such as plateau age and thickness. This multidisciplinary approach will provide a more complete understanding of how oceanic plateaus interact with subduction zones, and their role in the modification of convergent margins.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.