Laramide Orogenesis Driven by Late Cretaceous Weakening of the North American Lithosphere
Laramide Orogenesis Driven by Late Cretaceous Weakening of the North American Lithosphere
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DOI：
10.1029/2020jb019570
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发表时间：
2020-08
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影响因子：
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通讯作者：
J. Saylor;K. Rudolph;K. Sundell;J. Wijk
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作者：
J. Saylor;K. Rudolph;K. Sundell;J. Wijk
本文探讨了晚白垩世北美“Sevier”造山运动向“Laramide”造山运动转变的原因及北美岩石圈有效弹性厚度（EET）的时空演化。我们将蒙特卡罗弯曲模型应用于Laramide省的34个地层剖面和加拿大西部盆地的5个剖面，以估计模型参数，这些参数产生的弯曲剖面与观测到的沉积厚度相匹配。沉积物厚度来自新墨西哥至加拿大的cenomanian -始新世盆地，与Sevier和Laramide地壳负荷有关。弯曲模型显示，在分析的所有时间间隔中，EET在空间上从东向西递减。EET在空间上的减少可能与Sevier冲断带的弯曲应力有关，也可能与古大陆边缘与衰减大陆地壳的距离增加有关。在Laramide省（即~48°N以南），在cenomanian - sanantonian （~98 ~ 84 Ma）和Campanian-Maastrichtian （~77 ~ 66 Ma）之间，EET出现了一个同步的区域性减少，随后在Maastrichtian和古近纪之间出现了轻微的减少。然而，加拿大西部盆地（~48°N以北）的EET没有减少，这与Laramide - style变形或平坦俯冲的缺乏是一致的。我们认为，晚圣东—坎帕尼亚期区域岩石圈弱化的最好解释是北美岩石圈的水化作用被浅俯冲的法拉龙板块推平而变薄。岩石圈的减弱通过聚焦与扁平俯冲相关的端载应力，促进了拉腊酰胺收缩变形。拉腊酰胺变形反过来又可能通过削弱上地壳进一步降低EET。最后，Campanian - maastrichtian和古近系EET的估计与目前的估计相当，表明现代岩石圈强度分布是由Campanian对平坦俯冲的响应而实现的。
This paper investigates the causes of the Late Cretaceous transition from “Sevier” to “Laramide” orogenesis and the spatial and temporal evolution of effective elastic thickness (EET) of the North American lithosphere. We use a Monte Carlo flexural model applied to 34 stratigraphic profiles in the Laramide province and five profiles from the Western Canadian Basin to estimate model parameters which produce flexural profiles that match observed sedimentary thicknesses. Sediment thicknesses come from basins from New Mexico to Canada of Cenomanian–Eocene age that are related to both Sevier and Laramide crustal loads. Flexural models reveal an east‐to‐west spatial decrease in EET in all time intervals analyzed. This spatial decrease in EET may have been associated with either bending stresses associated with the Sevier thrust belt, or increased proximity to attenuated continental crust at the paleocontinental margin. In the Laramide province (i.e., south of ~48°N) there was a coeval, regional decrease in EET between the Cenomanian–Santonian (~98–84 Ma) and the Campanian–Maastrichtian (~77–66 Ma), followed by a minor decrease between the Maastrichtian and Paleogene. However, there was no decrease in EET in the Western Canada Basin (north of ~48°N), which is consistent with a lack of Laramide‐style deformation or flat subduction. We conclude that the regional lithospheric weakening in the late Santonian–Campanian is best explained by hydration of the North American lithosphere thinned by bulldozing by a shallowly subducting Farallon plate. The weakening of the lithosphere facilitated Laramide contractional deformation by focusing end‐loading stresses associated with flat subduction. Laramide deformation in turn may have further reduced EET by weakening the upper crust. Finally, estimates of Campanian–Maastrichtian and Paleogene EET are comparable to current estimates indicating that the modern distribution of lithospheric strength was achieved by the Campanian in response to flat subduction.