A Geomorphic Framework for Interpreting Continental Interior Mountain Belt Exhumation: The Laramide Example

摘要：解释大陆内部山带发掘的地貌框架：以Laramide为例在大约80至50万年前，Laramide造山运动抬升了一系列逆冲断层为界的高山山脉，形成了大陆内部一些最引人注目的山地景观。这些山脉和中间的沉积盆地横跨怀俄明州、科罗拉多州、蒙大拿州、犹他州和南达科他州的大部分地区。对整个美国西部的构造和气候历史的解释取决于对拉拉米德地貌演变的假设，然而这种演变仍然不为人所知。争论集中在两次地貌事件的意义、时间和原因上，证据记录在一系列独特的拉腊米地貌中。在Laramide山脉的大部分地区，被狭窄的基岩脊覆盖的低局部起伏的广泛的高海拔表面记录了一个局部起伏下降的时期。随后一段时期的区域侵蚀在山脉中形成了峡谷，在盆地填充物中形成了又宽又深的洼地，其间点缀着无数的河流阶地。以前的研究人员试图将这些地貌的发展与区域性的构造或气候强迫联系起来。然而，Laramide地貌显然不是以一种简单的方式反映外部强迫，因为有限的年代测定表明它们在年龄上是不同的。这一发现阻碍了区域连贯地质历史的构建，迄今为止还没有提出基于过程的模型来解释它。这项研究将探讨在整个内陆山地景观的不同时期可能引发侵蚀活动的地貌机制。pi的假设是，即使是一个简单的强迫事件也会产生复杂的侵蚀模式，考虑到一组由综合排水网络连接的连锁山脉和盆地。他们将定量地解决这一假设，重点关注在晚新生代形成Laramide景观的发掘事件。他们的方法将包括：1)通过使用宇宙成因放射性核素来确定盆地内地貌和河流成因沉积物的年代，从而改善Laramide盆地发掘时间的限制；2)通过描述花岗岩山脉的地貌特征，改善了对挖掘前山脉形态的限制，他们认为花岗岩山脉与其他Laramide山脉的古代条件具有现代相似性；3)建立区域和山脉尺度景观演变的数值模型，为数据解释提供机制框架。

ABSTRACTA Geomorphic Framework for Interpreting Continental Interior Mountain Belt Exhumation: The Laramide ExampleRobert Anderson and Elizabeth Safran EAR-0003604Between about 80 and 50 Myr ago, the Laramide orogeny uplifted a series of high, thrust fault-bounded mountain ranges that form some of the most dramatic mountain landscapes of the continental interior. These ranges and the intervening sedimentary basins stretch across much of Wyoming, Colorado, Montana, Utah, and South Dakota. Interpretations of the tectonic and climatic history of the entire western U. S. hinge on assumptions about Laramide landscape evolution, and yet this evolution remains ill-understood. The debate centers on the significance, timing, and cause of two geomorphic episodes, evidence for which is recorded in a suite of distinctive Laramide landforms. Widespread, high-elevation surfaces of low local relief capped by narrow bedrock spines record a period of declining local relief in most of the Laramide ranges. A subsequent period of regional erosion produced canyons in the ranges and broad, deep depressions in the basin fills, punctuated by numerous river terraces. Previous researchers have tried to correlate the development of these landforms with regional episodes of tectonic or climatic forcing. However, the Laramide landforms apparently do not reflect external forcing in a simple way, because limited dating suggests that they vary in age. This finding has hindered the construction of a regionally coherent geologic history, and to date no process-based model has been put forth to explain it.This study will address geomorphic mechanisms by which erosional activity might have been triggered at different times throughout this interior mountain landscape. PIs hypothesize that even a simple forcing event would produce complex erosional patterns, given a set of interlocking ranges and basins linked by an integrated drainage network. They will quantitatively address this hypothesis, focusing on the exhumational episode that shaped the Laramide landscape during the late Cenozoic. Their approach will involve: 1) improving constraints on the timing of Laramide basin exhumation by using cosmogenic radionuclides to date landforms and deposits of fluvial origin within the basins; 2) improving constraints on pre-exhumation range morphology by characterizing the geomorphology of the Granite Mountains, which they view as a modern analogue to the ancient condition of other Laramide ranges; and 3) developing numerical models of both regional and mountain range-scale landscape evolution to provide a mechanistic framework for data interpretation.