Collaborative Research: Study of Relationship of Crustal Extension to Mantle Dynamics: Paleobotanical Constraints on the Eocene History of Mean Elevations in Pacivic NW

9725807摩尔纳正断层和水平地壳伸展，而不仅仅是侵蚀，最终摧毁了大多数主要的山脉带。由于大多数这样的带是通过地壳缩短和增厚而形成的，因此必须在区域地球动力学中发生一些变化，才能导致从水平挤压到伸展的这种变化。一种可能性是，在挤压阶段增厚的地幔岩石圈下部变得不稳定，并下沉到山脉下方的地幔中。当这种情况发生时，范围会上升，这给了它驱动正常断层的势能。为了验证这一想法，需要在正常断层开始之前和之后测量古海拔。P.I.计划使用化石叶子形态进行测量，化石叶子形态已经根据现代气候(以及海拔高度)进行了校准，从现代森林中收集了大量这样的叶子形态。太平洋西北部是进行这种分析的理想地点，因为该地区在中生代经历了地壳缩短，在新生代经历了地壳伸展，而且在靠近海平面和内陆的地方都有大量的化石叶子，那里曾经是一条高山带。***

9725807 Molnar Normal faulting and horizontal crustal extension, not just erosion, ultimately destroy most major mountain belts. Because most such belts have been built by crustal shortening and thickening, some change in the regional geodynamics must occur to cause such a change from horizontal compression to extension. One possibility is that the lower part of the mantle lithosphere, thickened during the phase of compression, becomes unstable and sinks into the mantle beneath the range. When this happens, the range rises, giving it potential energy to drive normal faulting. To test such an idea requires that paleo-altitudes are measured before and after the normal faulting begins. The P.I.s plan to make such measurements using fossil leaf morphology, which has been calibrated to modern climates (and hence altitudes) with an extensive collection of such leaf morphology from modern forests. The Pacific Northwest is an ideal locality for such analysis because the region underwent crustal shortening in Mesozoic time and crustal extension in Cenozoic time and because there are numerous fossil leaf localities, both near sea level and inland where a high mountain belt once lay. ***