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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Gravity anomalies of sedimentary basins and their mechanical implications: Application to the Ross Sea basins, West Antarctica
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Gravity anomalies of sedimentary basins and their mechanical implications: Application to the Ross Sea basins, West Antarctica

机译：沉积盆地重力异常及其力学意义：在南极西部罗斯海盆地的应用

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摘要

In general, sedimentary basins are characterized by negative free-air and Bouguer gravity anomalies. However, the extensional basins of the Ross Sea are paradoxical in that positive gravity anomalies overlay the Victoria Land Basin, Northern Basin, Central Trough and Northern Central Trough while basement highs are associated with negative gravity anomalies. Measured basement densities from DSDP basement cores give values between 2600-2800 kg/m(3) while bulk sediment densities range from 1210-2200 kg/m(3) indicating a normal density relationship between basement and sediment infill. In contrast, the relatively young and narrow Terror Rift is associated with negative free-air and Bouguer gravity anomalies, but has a different geological history as compared to the larger Ross Sea basins. Process-oriented gravity modeling indicates that magmatic underplating and crustal intrusions are inconsistent with the observed gravity and basement geometry of the Ross Sea basins. The magma volume necessary to account for the distribution and amplitude of the positive gravity anomaly of the Central Basin and be isostatically balanced would need to be comparable to the tholeiitic flood basalt volume of the Columbia River province-it is thus unlikely that the volume of Neogene volcanics of the Ross Sea region is sufficient to explain the observed gravity relationship by modifying the bulk density of the crust.We demonstrate that positive free-air and Bouguer gravity anomalies over extensional basins are the consequence of a relatively low flexural strength of the lithosphere during rifting being contrasted by higher flexural strengths later during sedimentation. As the difference between the rigidity of the lithosphere during sedimentation increases relative to the rigidity of the rifted lithosphere, the gravity over the basin becomes progressively more positive but only for a limited range of wavelengths. The narrow width of the Terror Rift precludes it from having a positive gravity anomaly while the opposite is true for the large Ross Sea basins. For the Ross Sea region, such a loading scenario requires a significant delay between extension and the timing of sediment infilling of the basins, consistent with the late Cretaceous extension of the Ross Sea region and the sedimentary succession being dominated by large-scale late Eocene-Neogene glaciogenic progradational sequences. Sediment source was presumably from the denudation of the Transantarctic Mountains, which commenced in the late Paleogene. The time delay between the late Cretaceous formation of the Transantarctic Mountains, late Paleogene exhumation, and the generation of significant Paleogene paleobathymetry requires either the Ross Sea region to be sub-aerial and sediment starved for most of the Paleogene and/or the Paleogene climate was ineffective in producing clastics until the onset of glaciation in the late Eocene-early Oligocene. (c) 2005 Elsevier B.V. All rights reserved.
机译：一般而言，沉积盆地的特征是负自由空气和布格重力异常。然而，罗斯海的伸展盆地是自相矛盾的，因为正重力异常覆盖了维多利亚陆地盆地，北部盆地，中央海槽和北部中央海槽，而基底高度与负重力异常有关。从DSDP地下室芯测得的地下室密度值介于2600-2800 kg / m（3），而整体沉积物密度范围为1210-2200 kg / m（3），表明地下室与沉积物填充物之间具有正常的密度关系。相比之下，相对较年轻且狭窄的Terror Rift与负自由空气和Bouguer重力异常相关，但与较大的Ross海盆相比，其地质历史不同。面向过程的重力模型表明，岩浆岩的底板作用和地壳侵入与所观测到的罗斯海盆地的重力和基底几何形状不一致。解释中央盆地正重力异常的分布和幅度并实现等静平衡所必需的岩浆量必须与哥伦比亚河省的黄潮型玄武岩量相当，因此，新近纪的量不太可能罗斯海地区的火山岩足以通过改变地壳的堆积密度来解释观测到的重力关系。我们证明了伸展盆地上的正向自由空气和布格重力异常是岩石圈相对弯曲强度较低的结果。在沉降过程中，裂口与较高的抗弯强度形成对比。随着沉积过程中岩石圈刚度之间的差异相对于裂谷岩石圈刚度之间的差异增加，盆地上的重力逐渐变正，但仅在有限的波长范围内。恐怖裂谷的狭窄宽度使其无法产生正重力异常，而罗斯大盆地则相反。对于罗斯海地区而言，这种加载方案要求在扩张和盆地沉积物充填时间之间有显着的延迟，这与罗斯海地区晚白垩世扩张和大规模晚始新世主导的沉积演替相一致。新近生冰生的渐进序列。沉积物的来源大概是始于古近纪晚期的跨南极山脉的剥蚀作用。在跨南极山脉的白垩纪晚期，古近纪发掘和重要古近纪古生物学的产生之间的时间延迟要求罗斯海地区为亚空中，大部分古近纪和/或古近纪气候都缺乏沉积物。直到晚始新世-早渐新世开始冰川化之前，在产生碎屑方面均无效。 （c）2005 Elsevier B.V.保留所有权利。

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