Low-temperature thermochronometric ages in fold-and-thrust belts
Low-temperature thermochronometric ages in fold-and-thrust belts
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DOI：
10.1016/j.tecto.2008.03.007
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发表时间：
2008-08
期刊：
影响因子：
2.9
通讯作者：
J. Lock;S. Willett
中科院分区：
文献类型：
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作者：
J. Lock;S. Willett
为了更好地理解由冷却年龄记录的逆冲推覆速率和时间，我们利用二维热运动学逆冲断层模型生成了褶皱冲断带中的低温热计时年龄。我们的模型将运动学结构模型2DMove与有限元平流-扩散热模型联系起来，以跟踪逆冲断裂和断层弯曲褶皱过程中被侵蚀剥离的物质的冷却历史。我们用冷却历史来模拟裂变径迹的退火和氦保留，并预测了锆石和磷灰石裂变径迹和磷灰石(U-Th)/He的热年龄。我们模拟了沿单个和多个正向传播的逆冲断层运动过程中产生的温度计时年龄模式，并探索了断层滑移率和断层几何形状的影响。我们所有的模型都沿着垂直于断层的横断面生成了一个特征的U型温度计时年龄模式。这种模式是由重置、未重置和部分重置的温度计时年龄的分布形成的。在推力斜坡上方，重置物质形成了一个年轻的温度计时年龄区。部分重置和未重置的材料位于这一年轻年龄带的两侧。虽然由我们的断层-弯曲-褶皱模型预测的一些温度计时年龄与用一维热模型预测的年龄相似，但年龄模式明显不同。在单个逆冲断裂和多个逆冲断裂模型中都出现了光滑的U型格局。在前陆传播的多断层模型中，各个逆冲断层的年龄没有明显的变化。在这些多断层模型中，温度年龄模式随逆冲断层间距的变化而变化。根据断层间距和沿每条断层的滑移量，可以在逆冲带的腹地或前陆记录到早期断层作用。
We use a 2-dimensional thermal-kinematic thrust fault model to generate low-temperature thermochronometric ages in a fold-and-thrust belt to understand better the rates and timing of thrust-deformation recorded by cooling ages. Our model links the kinematic structural model 2DMove to a finite-element advection–diffusion thermal model to track the cooling history of material exhumed by erosion during thrust faulting and fault bend folding. We use the cooling histories to model fission track annealing and He retention and predict zircon and apatite fission track and apatite (U–Th)/He thermochronometric ages. We model thermochronometric age patterns generated during motion along individual and multiple forward-propagating thrust faults, and explore the effects of fault slip rate and fault geometry. All our models generate a characteristic U-shaped thermochronometric age pattern along a transect perpendicular to the fault. This pattern is formed by the distribution of reset, unreset, and partially-reset thermochronometric ages. Above the thrust ramp, reset material forms a zone of young thermochronometric ages. Partially reset and unreset material lies on either side of this zone of young ages. Although some thermochronometric ages predicted by our fault-bend-fold model are similar to those predicted using a 1-d thermal model, the patterns of ages are markedly different. The smooth U-shaped pattern is generated in both the individual thrust fault and multiple thrust-fault models. In the foreland-propagating, multiple-fault models, there are no distinct changes in age across individual thrust faults. In these multiple fault models the thermochronometric age pattern changes with thrust-fault spacing. Depending on the fault spacing and amount of slip along each fault, early faulting can be recorded either in the hinterland or foreland of the thrust-belt.