科研之友
微信
新浪微博
Facebook
分享链接
摘要
The shortening and depth to detachment are two fundamental parameters for the construction, balancing, and restoration of geological cross-sections across fold and thrust systems. The principle of mass conservation requires both parameters to scale as the excess (uplifted) area above the original depositional level. In many occasions, however, the excess area appears to be less than the displaced (contracted) area, a phenomenon that is thought to be the product of bulk area loss, and layer thickening. We present a derivation of Chamberlin's relation of detachment folds in which the excess area equals shortening multiplied by the depth to detachment by means of a local area-balance approach. We work out corrections for changes in bed thickness and layer-parallel compaction. Our corrections indicate the missing linear shortening scales as the wavelength of the fold. Thus, larger folds should display larger strain deficits than smaller ones. Additionally, we demonstrate that the missing strain scales as the transported area as well given rocks are compressible materials. Consequently, Chamberlin's classical relationship only holds for low-strain, relatively small detachment folds. Under this condition layer parallel compaction, and changes in bed thickness are negligible. We further analyze and work out corrections for the case in which sedimentary layers gradually narrow with horizontal distance; we find the stratal geometry has a strong effect on the area balance of detachment folds. Our results are in agreement with previous works, and suggests a more accurate approximation to estimate the shortening is by means of a best fit model in which the response variable is the excess area and the regressor is the average layer thickness.
- 出版日期2016-12
