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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挤压引起了地震和火山活动等自然灾害，这在太平洋“火环”沿线可以观察到。这种运动代表了地球的热损失在地幔对流中的表面表现。因此，板块运动的历史为了解地球的内部运作提供了基础。由于地球磁场极性的变化，伸展脊两侧的磁等时线可以被识别出来，并用于推断两个或多个板块之间的相对运动。有了一个磁镐数据库和对俯冲带收敛的额外限制，科学家们已经重建了全球板块运动，时间可以追溯到2亿多年前。然而，洋脊扩张和俯冲收敛的观测结果只限制了与深部地幔无关的相对板块运动（RPM）。事实上，推动构造板块的深层地幔力和减缓构造板块的岩石圈下变形，在绝对板块运动（APM）的背景下得到了最好的理解。大多数确定APM的方法都是沿着线性岛屿和海山链观测年龄的变化，这些岛屿和海山链是由深层地幔柱将热物质带到地表而产生的。如果这些羽流在地幔中保持固定，那么就有可能直接求解出APM。然而，越来越多的证据表明，羽流本身也在运动，因此并不代表期望的固定参考框架。我们发现了一种可以同时求解绝对板块和地幔柱运动的新方法，本项目将发展这种新方法，并使用最全面的海山链几何形状、年龄、古地磁纬度等数据集对其进行校准。提高对APMs的了解对地球的其他研究有广泛的好处。它确定了一个将地表与地幔联系起来的框架，从而使地球化学和地震学等其他地球科学数据得以联系起来。该项目将训练学生在板块运动学和数据分析。除了数据和软件产品，合作机构还将提供一个联合板块构造研讨会，邀请远程嘉宾发言，并将录音以视频播客的形式发布在YouTube上。观测到的被解释为羽流漂移的古地磁异常使APM的建模具有挑战性，因为缺乏羽流漂移的直接观测。利用地幔环流模型的羽流漂移预测，在很大程度上满足观测到的古纬度，是迄今为止推导移动热点APM的最佳方法。然而，由于地幔流变学、温度和初始条件的不确定性，这些模型并不独特。一种新的方法（发现羽毛）已经被发现来解决这个未解决的问题。结果表明，沿太平洋热点轨迹的年龄进展对允许的羽流运动提供了强有力的约束，使得仅从这些数据就可以推导出相对羽流漂移的模型。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，但这些距离缺乏固定的参考点和方位方向。夏威夷和路易斯维尔的插值古纬度历史进一步限制了羽流运动，但有一个参数仍未解决：太平洋板块下所有羽流共有的经度历史。因此，有可能只解决热点相对于一个未知的纵向位移的运动。因此，根据欧拉定理，解决的APM旋转因此被围绕北极的相应旋转所破坏。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。其中一种方法是脊点定位，这是一种使用RPM模型来检查APM模型可行性的技术。脊斑重建了80 Ma以来的太平洋-法拉隆脊，暗示了脊向北迁移和单调的顺时针旋转。一些APM模式暗示脊系统有大的旋转，并表现出间歇性的不稳定行为。这些特性表明脊状点和羽状点相结合可能产生最佳的数据驱动APM。新的羽流和脊线定位方法将被开发出来，以处理板块运动数据的不一致性和不确定性，并用于导出羽流和板块运动的数据驱动模型。建立热点径迹年龄进展，发布带置信限的热点间年龄距离曲线；这些数据和古纬度将用于羽斑反演。古纬度的不确定性、真极漂移和替代古地磁解释将在贝叶斯反演框架中考虑。APM模型将通过脊点法测试与RPM模型的兼容性。其他考虑因素，如板块和地幔柱速度的地球动力学限制、岩石圈净旋转、地幔柱与LLSVP边缘和板块边界的接近程度，以及整体模型的平滑度，将进一步限制产生太平洋板块和地幔柱绝对运动的独特模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。