Limits to reconstructing paleotopography from thermochronometer data
Limits to reconstructing paleotopography from thermochronometer data
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DOI：
10.1029/2011jf001985
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发表时间：
2012-03
影响因子：
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通讯作者：
Stephanie Olen;T. Ehlers;Mathew S. Densmore
中科院分区：
文献类型：
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作者：
Stephanie Olen;T. Ehlers;Mathew S. Densmore
[1]最近的研究表明，造山带可以达到地形稳定状态，从而达到平衡之间的构造和侵蚀。然而，在许多经历气候或构造大变化的造山带中，稳定状态的地形可能不是常态，这可能产生地形瞬变。在地质时间尺度上的瞬态地形的量化需要重建古地形，但这在许多情况下已被证明是困难的。本研究探讨利用基岩热时计资料重建百万年时间尺度的造山带古地形。磷灰石（U-Th）/He和裂变径迹年龄集成与热动力学模型的单参数反演古地形。一个迭代的计划，最大限度地减少预测和观察到的冷却年龄之间的失配，以确定范围内的paleotopographies，可以产生样品的不确定性内观察到的年龄。考虑两种方法。首先，合成的2-D地形被用来测试的方法的鲁棒性。考虑了以下地形演变情景：（1）侧脊迁移，（2）地形起伏变化，（3）冰川作用导致的河谷加宽和加深。第二，该方法适用于现有的数据从海岸山脉的不列颠哥伦比亚省，加拿大的三维。两种模型的应用结果表明：（1）古地形重建通常会低估地形变化的幅度，特别是地形变化的幅度;（2）在长波长地形中，侧脊迁移后的古地形重建最成功;（3）重建了不列颠哥伦比亚省海岸山脉的古地形，这表明，冰川侵蚀可能有可能消除排水分水岭和横向移动地形山脊和山峰。
[1] Recent studies suggest that orogens can achieve a topographic steady state whereby equilibrium is reached between tectonics and erosion. However, steady state topography may not be the norm in many orogens experiencing large changes in climate or tectonics, which can produce topographic transients. The quantification of transient topography over geologic timescales requires reconstructing paleotopography, but this has proven difficult in many cases. This study investigates the utility of bedrock thermochronometer data to reconstruct orogen paleotopography over million year timescales. Apatite (U-Th)/He and fission track ages are integrated with a thermokinematic model for a single-parameter inversion of paleotopography. An iterative scheme is used that minimizes the misfit between predicted and observed cooling ages to identify the range of paleotopographies that could produce observed ages within sample uncertainty. Two approaches are considered. First, synthetic 2-D topographies are used to test the robustness of the approach. The following topographic evolution scenarios are considered: (1) lateral ridge migration, (2) topographic relief change, and (3) valley widening and deepening from glaciation. Second, the method is applied in three dimensions to existing data from the Coast Mountains of British Columbia, Canada. Results from both applications of the model suggest that (1) paleotopographic reconstruction will typically underpredict the magnitude of topographic change, especially relief change; (2) paleotopography is most successfully reconstructed after lateral ridge migration in long-wavelength topographies; and (3) reconstructed paleotopography from the Coast Mountains, British Columbia, suggests that glacial erosion may have the potential to remove drainage divides and laterally shift topographic ridges and peaks.