科研之友
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摘要
Alternations between fluvial incision and aggradation, in response to switches between uplift and subsidence and occurring over timescales of many hundreds of thousands of years, have been documented in many regions worldwide, contrasting markedly with the monotonic histories of uplift or subsidence evident elsewhere. It has been noted that this pattern of reversals in vertical crustal motion is only observed in regions where the mobile lower-crustal layer is thin, %26lt;= 6 km thick, suggesting a cause-and-effect connection with the physical properties of the underlying continental lithosphere. It is proposed that these reversals result from the interplay between the isostatic responses to erosional unloading by lower-crustal flow and by mantle lithosphere relaxation. Estimates of the characteristic timescale for relaxation of the continental mantle lithosphere range from several hundred thousand years in regions of %26apos;cold%26apos; crust, with a thin mobile lower-crustal layer, to a few tens of thousands of years in regions of %26apos;hot%26apos; crust, where the mobile lower-crustal layer is thicker. In regions of hot crust, relaxation of the mantle lithosphere requires a shorter characteristic timescale than flow within the lower crust. The complex interaction between these processes means that isostatic compensation of crustal thickening in regions of hot crust will typically involve surface uplift, the development of a lower-crustal %26apos;root%26apos;, and thinning of the mantle lithosphere. The observation of alternations between uplift and subsidence in long-timescale fluvial sequences and the proposed physical interpretation demonstrate the importance of fluvial records for providing unique, high-resolution control on deformation of the continental lithosphere and for constraining its layered rheology.
- 出版日期2012-9-1
