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Absolute Motion of Plumes and Plates

羽流和板块的绝对运动

基本信息

批准号：
1953499
负责人：
Garrett Apuzen-Ito
金额：
$ 27.7万
依托单位：
University of Hawaii
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：
2020-07-01 至 2024-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1953499&HistoricalAwards=false
关键词：
Absolute Motion Plumes Plates

项目摘要

The jostling of Earth’s tectonic plates at plate boundaries give rise to natural hazards such as earthquakes and volcanism as observed along the Pacific “Ring of Fire”. This motion represents the surface expression of the Earth’s heat loss by convection currents in the mantle. Thus, the history of plate motions provides fundamental insight into the internal operations of the planet. As a consequence of the changing polarity of the Earth’s magnetic field, magnetic isochrons on either side of spreading ridges can be identified and used to infer relative motions between two or more plates. Armed with a database of magnetic picks and additional constraints on convergence at subduction zones, scientists have produced reconstructions of global plate motions extending back over 200 million years. Yet, observations of ridge spreading and subduction convergence only constrain relative plate motions (RPM) not linked to the deep mantle. In fact, deep mantle forces that propel tectonic plates and the sub-lithospheric deformation that slows them are best understood within the context of absolute plate motions (APM). Most methods for determining APM use observed age progressions along linear island and seamount chains produced by a deep-seated mantle plume bringing hot materials to the surface. If these plumes remain fixed in the mantle then it is possible to directly solve for the APM. However, evidence is mounting that the plumes themselves are also moving and thus do not represent the desired fixed reference frame. A new method has been discovered that may solve for both absolute plate and plume motions simultaneously, and this project will develop this new method and calibrate it with the most comprehensive datasets on seamount chain geometry, age, paleomagnetic latitude, and more. An improved understanding of APMs has broad benefits for other studies of the Earth. It determines a framework for relating the surface to the mantle, which allows other geoscience data, such as geochemistry and seismology, to be linked. The project will train a student in plate kinematics and data analysis. Besides data and software products, the collaborating institutions will offer a joint plate tectonic seminar using remote guest speakers, with recordings made available as video podcasts on YouTube.Observed paleomagnetic anomalies interpreted as plume drift make modeling of APM challenging as direct observations of plume drift are lacking. Using plume drift predictions from mantle circulation models that broadly satisfy observed paleolatitudes has so far been the best approach for deriving APM over moving hotspots. Yet, uncertainties in mantle rheology, temperature, and initial conditions make such models nonunique. A new approach (plume-spotting) has been discovered to address this unresolved problem. It is demonstrated that age progressions along Pacific hotspot trails provide strong constraints on allowable plume motions, making it possible to derive models for relative plume drift from these data alone. Relative plume drifts are estimated from inter-hotspot distances derived from age progressions, but these lack a fixed reference point and azimuthal orientation. Interpolated paleolatitude histories for Hawaii and Louisville add further constraints on plume motion, yet one parameter remains unresolved: a longitude history shared by all plumes beneath the Pacific plate. Thus, it is possible to only resolve the motion of hotspots relative to an unknown longitudinal shift. Consequently, and per Euler’s theorem, resolved APM rotations are therefore corrupted by a corresponding rotation about the north pole. Yet, such APM models still satisfy the data, forcing the use of methods involving RPM as new constraints. One such method is ridge-spotting, a technique that uses RPM models to examine the viability of APM models. Ridge-spotting has reconstructed the Pacific-Farallon ridge since 80 Ma and implies northward migration and monotonic clockwise rotation of the ridge. Some APM models imply large rotations of the ridge system and exhibit intermittent erratic behaviors. These properties suggest ridge- and plume-spotting combined may yield an optimal data-driven APM. The new plume- and ridge-spotting methods will be developed to handle the inconsistencies and uncertainties of plate kinematic data and used to derive data-driven models of plume and plate motions. Hotspot trail age-progressions will be developed and inter-hotspot age-distance curves with confidence limits will be published; these data and paleolatitudes will be used in the plume-spotting inversion. Paleolatitudes uncertainties, true polar wander, and alternative paleomagnetic interpretations will be considered in a Bayesian inversion framework. APM models will be tested for compatibility with RPM models via the ridge-spotting method. Additional considerations, such as geodynamic limits on both plate and plume speeds, net lithospheric rotation, the proximity of plumes to LLSVP edges and plate boundaries, and overall model smoothness will add further constraints to produce a unique model of Pacific absolute plate and plume motions.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.

地球构造板块在板块边界处的碰撞会引发自然灾害，例如沿着太平洋“火环”观察到的地震和火山活动。这种运动代表了地幔对流造成的地球热量损失的表面表现。因此，板块运动的历史提供了对地球内部运作的基本了解。由于地球磁场极性的变化，可以识别扩张脊两侧的磁等时线，并用于推断两个或多个板块之间的相对运动。借助磁镐数据库和俯冲带收敛的额外限制，科学家们重建了 2 亿多年前的全球板块运动。然而，对山脊扩张和俯冲汇聚的观察仅限制了与深部地幔无关的相对板块运动（RPM）。事实上，在绝对板块运动（APM）的背景下，可以最好地理解推动构造板块的深层地幔力和减缓构造板块的亚岩石圈变形。大多数确定 APM 的方法都使用观察到的沿线性岛和海山链的年龄进展，这些岛链和海山链是由深层地幔羽流将热物质带到地表而产生的。如果这些羽流保持固定在地幔中，那么就可以直接求解 APM。然而，越来越多的证据表明，羽流本身也在移动，因此并不代表所需的固定参考系。已经发现了一种可以同时求解绝对板块和羽流运动的新方法，该项目将开发这种新方法，并使用有关海山链几何形状、年龄、古地磁纬度等最全面的数据集对其进行校准。加深对 APM 的了解对于地球的其他研究具有广泛的好处。它确定了将地表与地幔联系起来的框架，从而可以将地球化学和地震学等其他地球科学数据联系起来。该项目将对一名学生进行板运动学和数据分析方面的培训。除了数据和软件产品外，合作机构还将利用远程客座演讲者举办联合板块构造研讨会，其录音可在 YouTube 上以视频播客的形式提供。由于缺乏对羽流漂移的直接观测，观测到的古地磁异常被解释为羽流漂移，这使得 APM 建模具有挑战性。迄今为止，使用广泛满足观测到的古纬度的地幔循环模型进行的羽流漂移预测是推导移动热点上空 APM 的最佳方法。然而，地幔流变学、温度和初始条件的不确定性使得此类模型并不独特。人们发现了一种新方法（羽流识别）来解决这个未解决的问题。事实证明，沿着太平洋热点轨迹的年龄进程对允许的羽流运动提供了强有力的约束，使得仅从这些数据导出相对羽流漂移的模型成为可能。相对羽流漂移是根据年龄进展得出的热点间距离来估计的，但这些缺乏固定的参考点和方位角方向。夏威夷和路易斯维尔的插值古纬度历史进一步增加了对羽流运动的限制，但有一个参数仍未解决：太平洋板块下方所有羽流共享的经度历史。因此，可以仅解析热点相对于未知纵向位移的运动。因此，根据欧拉定理，解析的 APM 旋转会被绕北极的相应旋转破坏。然而，这样的 APM 模型仍然满足数据，迫使使用涉及 RPM 的方法作为新的约束。其中一种方法是脊线定位，这是一种使用 RPM 模型来检查 APM 模型可行性的技术。自80Ma以来，脊观测重建了太平洋-法拉隆脊，并暗示了脊的向北迁移和单调顺时针旋转。一些 APM 模型意味着山脊系统的大幅旋转，并表现出间歇性的不稳定行为。这些特性表明，山脊和羽流定位的结合可能会产生最佳的数据驱动 APM。将开发新的羽流和山脊定位方法来处理板块运动学数据的不一致和不确定性，并用于导出羽流和板块运动的数据驱动模型。将开发热点轨迹年龄进展，并发布具有置信限度的热点间年龄距离曲线；这些数据和古纬度将用于羽流观测反演。古纬度的不确定性、真正的极地漂移和替代的古地磁解释将在贝叶斯反演框架中考虑。 APM 模型将通过山脊定位方法测试与 RPM 模型的兼容性。其他考虑因素，例如板块和羽流速度的地球动力学限制、净岩石圈旋转、羽流与 LLSVP 边缘和板块边界的接近度以及整体模型平滑度，将进一步增加约束，以生成太平洋绝对板块和羽流运动的独特模型。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优势和更广泛的评估进行评估，被认为值得支持。影响审查标准。