Absolute Motion of Plumes and Plates

地球构造板块在板块边界的碰撞引发了自然灾害，如沿太平洋“火环”观察到的地震和火山喷发。这一运动代表了地幔对流造成的地球热损失的表面表现。因此，板块运动的历史提供了对地球内部运行的基本洞察。由于地球磁场的极性变化，可以识别扩张脊两侧的磁等时线，并用它来推断两个或更多板块之间的相对运动。有了磁选的数据库和俯冲带收敛的额外限制，科学家们已经重建了2亿多年前的全球板块运动。然而，对海脊扩展和俯冲会聚的观测只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，最好地理解推动构造板块的深部地幔力量和减缓它们的岩石圈下变形。大多数确定APM的方法是利用观测到的沿线性岛屿和海山链的年龄演化，这些链是由深部地幔热柱将热物质带到地表所产生的。如果这些羽流仍然固定在地幔中，那么就有可能直接求解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照系。已经发现了一种可以同时解决绝对板块运动和羽流运动的新方法，该项目将开发这种新方法，并使用关于海山链几何形状、年龄、古地磁纬度等最全面的数据集对其进行校准。对APM的更好理解对地球的其他研究具有广泛的益处。它确定了一个将地表与地幔联系起来的框架，这使得其他地球科学数据，如地球化学和地震学，得以联系起来。该项目将培训一名学生进行板块运动学和数据分析。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提供联合板块构造研讨会，并在YouTube上以视频播客的形式提供录音。观察到的解释为烟柱漂移的古地磁异常使APM的建模具有挑战性，因为缺乏对烟柱漂移的直接观测。到目前为止，使用大体上满足观测到的古纬度的地幔环流模式的羽流漂移预测是在移动的热点地区推算APM的最佳方法。然而，地幔流变性、温度和初始条件的不确定性使这些模型不是独一无二的。已经发现了一种新的方法(烟羽斑点)来解决这个悬而未决的问题。结果表明，沿着太平洋热点轨迹的年龄进程对允许的羽流运动具有很强的制约作用，这使得仅从这些数据就可以推导出相对羽流漂移的模式。相对羽流漂移是根据年龄进程得出的热点间距离来估计的，但这些距离缺乏固定的参照点和方位角。夏威夷和路易斯维尔的插补古纬度历史增加了对羽流运动的进一步限制，但有一个参数仍然没有解决：太平洋板块下所有羽流共享的经度历史。因此，可以仅解决热点相对于未知纵向移位的运动。因此，根据欧拉定理，解析的APM自转因此被围绕北极的相应自转所破坏。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。其中一种方法是脊斑法，这是一种使用RPM模型来检查APM模型的可行性的技术。80 Ma以来，海脊斑点法重建了太平洋-法拉隆海脊，反映了海脊的北移和单调顺时针旋转。一些APM模型暗示了脊线系统的大旋转，并表现出间歇性的不稳定行为。这些特性表明，脊线和羽流斑点相结合可能会产生最佳的数据驱动的APM。将开发新的羽流和脊点方法来处理板块运动数据的不一致性和不确定性，并用于推导数据驱动的羽流和板块运动模型。将开发热点追踪年龄级数，发布具有置信度的热点间年龄-距离曲线；这些数据和古纬度将用于烟羽斑点反演。将在贝叶斯反演框架中考虑古纬度不确定性、真正的极地漂移和可供选择的古地磁解释。APM模型将通过脊斑点法测试与RPM模型的兼容性。其他考虑因素，如板块和羽流速度的地球动力学限制，岩石圈净自转，羽流与LLSVP边缘和板块边界的接近程度，以及总体模型平稳性，将进一步增加限制，以产生一个独特的太平洋绝对板块和羽流运动模型。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影响审查标准进行评估，被认为值得支持。

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.