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首页> 外文期刊>South African Journal of Geology: Being the Transaction of the Geological Society of South African: Syndie die Verhandelinge van die Geologiese Vereniging van Suid-Afrika >Initial results from wide-angle seismic refraction lines in the southern Cape
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Initial results from wide-angle seismic refraction lines in the southern Cape

机译：南开普省广角地震折射线的初步结果

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摘要

One of the projects within the framework of Inkaba yeAfrica, an earth system science initiative between German and South African research communities, is the Agulhas-Karoo transect. This 800 km north-south off-onshore transect runs from the offshore Agulhas Plateau onto the South African coast, across the Cape Fold Belt, Beattie Magnetic Anomaly, the Karoo Basin, the Great Escarpment and into the Kaapvaal Craton. Among the number of geophysical measurements taken along the transect are two wide-angle on-shore seismic lines collected in April and May 2005. The lines run roughly parallel to each other approximately 200 km apart, starting at Mossel Bay and St. Francis, and running about 200 km north to Fraserburg and Graaf Reinet, respectively. At each line 48 seismic receivers were used to record data from 13 shots. The profiles cross a wide variety of geological terrains, such as the siliciclastic sequences of the Paleozoic - Mesozoic Karoo and Oudtshoorn basins, the lower Paleozoic Cape Fold Belt, and the Eocambrian Kango and Kaaimans inliers. They also cross the Beattie Magnetic Anomaly, a large east-west orientated crustal feature within the upper crust, anti more than 1000 km long, first reported almost a century ago, but still not fully understood. The overall quality of seismic data is very good. First (P-wave) arrivals were manually picked on the available traces, and tomographic inversion was done using these travel times. The ray coverage made it possible to create the P-wave velocity model to depths of up to 25 km. We find excellent correlation of the shallow features with surface rock type. Deeper down we can identify both stratigraphic and tectonic contacts between geological groups. These include an inferred possible blind Paleozoic thrust fault, and the unconformity between the Cape Supergroup and the Namaqua-Natal Metamorphic Complex. The normal listric geometry of the Kango and Gamtoos Faults is clearly seen to a minimum depth of 15 km. We also observe a high velocity anomaly within the NNMC at similar to 10 km depth that we relate to the source of the Beattie Magnetic Anomaly.
机译：Agulhas-Karoo样带是Inkaba yeAfrica（德国和南非研究团体之间的地球系统科学计划）框架内的项目之一。这条南北向北的800公里陆上样带从离岸的阿格哈斯高原（Agulhas Plateau）延伸到南非海岸，穿过海角褶皱带，比蒂磁异常，卡鲁盆地，大悬崖和Kaapvaal克拉通。沿着该断面进行的地球物理测量包括2005年4月和2005年5月收集的两条广角陆上地震线。这两条线相互平行，相距约200 km，从Mossel湾和St.Francis开始，分别向北延伸至Fraserburg和Graaf Reinet 200公里。在每条生产线上，使用了48个地震接收器来记录13个镜头的数据。这些剖面跨越各种地质地形，例如古生代-中生代卡鲁和奥兹颂盆地的硅质碎屑层序，下古生代海角褶皱带，以及Eucambrian Kango和Kaaimans矿床。他们还穿越了比蒂磁异常区，该地层是上地壳内东西向的大型地壳特征，反地长超过1000公里，大约一个世纪前就首次报道，但至今仍未完全了解。地震数据的整体质量非常好。首先在可用迹线上手动选择（P波）到达，然后使用这些行进时间进行层析成像反演。射线覆盖范围使创建P波速度模型的深度达到25 km成为可能。我们发现浅层特征与表层岩石类型之间具有极好的相关性。在更深的层次上，我们可以识别地质群体之间的地层和构造接触。其中包括推断可能的古生代逆冲断层，以及海角超群和纳马夸-纳塔尔变质复合体之间的不整合。从最小深度15 km可以清楚地看到Kango断层和Gamtoos断层的正常List几何形状。我们还观察到NNMC内的一个高速异常，其深度大约为10 km，这与Beattie磁异常的来源有关。

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