Meso-Cenozoic morphotectonic evolution of southern Norway: Neogene domal uplift inferred from apatite fission track thermochronology
Meso-Cenozoic morphotectonic evolution of southern Norway: Neogene domal uplift inferred from apatite fission track thermochronology
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挪威南部中新生代形态构造演化：从磷灰石裂变径迹热年代学推断的新近纪穹窿隆起
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发表时间：
1995
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通讯作者：
S. Cloetingh
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作者：
M. Rohrman;P. Beek;P. Andriessen;S. Cloetingh
挪威南部前寒武纪和古生代基底样品的磷灰石裂变径迹（AFT）热年代学揭示了一个后古生代的折返历史，与海上中生代和新生代伸展盆地的发展。这些数据表明，快速挖掘有两个主要阶段。第一个中生代阶段开始于三叠纪（1220 Ma）在东部和南部的研究领域和迁移到西部的侏罗纪（160 Ma）的折返年龄占主导地位。第二个事件是由AFT年龄和轨道长度分布的热历史模拟表明。它被推断为新第三纪的年龄，开始在大约30马，它产生了一个圆顶模式的AFT等时线，遵循今天的地形高程。最年轻的AFT年龄（~ 100 Ma）是在海平面附近的地形最高的地区内峡湾，年龄增加径向向外的山峰和海岸线。年龄-海拔模式的正演模拟表明，中生代的地热梯度比目前的20°C/km高10-15°C/km。在三叠纪和侏罗纪期间，从研究区域总共移除了1.3-3.5公里的覆盖层，假设该时期的地热梯度为30°C/公里。我们认为这是由于侵蚀基准面下降和侧翼隆起的裂谷边缘侵蚀，证明了厚的大陆碎屑岩序列沉积在三叠纪-侏罗纪半地堑在北海盆地。我们认为，晚第三纪1.5- 2.5km的折返是晚期穹隆隆升的结果。这是由挪威南部周围盆地的盆地内倾斜的前新近纪地层和含有各种内部不整合面的1至2公里厚的新近纪沉积楔的填充物所支持的。穹状隆起可能开始于渐新世晚期，上新世可能有所扩大，并被上新世-更新世冰川侵蚀所覆盖。最大的新近纪构造隆起估计约为1-1.5公里，径向向外减小到海岸线附近的值<500米。新近纪穹状隆起与北大西洋渐新世和上新世板块重组一致;在挪威-格陵兰海周围发现了类似的新近纪穹状隆起（即，挪威北方斯瓦尔巴特群岛和巴伦支海，格陵兰岛东部），这表明一个区域构造原因。晚第三纪隆起的开始比主要的火山活动和大陆裂解晚2.25亿年。早于上新世-更新世冰期其成因可能是诱发地幔对流，导致岩石圈的热侵蚀，板内应力的作用。
Apatite fission track (AFT) thermochronology of Precambrian and Paleozoic basement samples from southern Norway reveals a post-Paleozoic exhumation history, related to offshore Mesozoic and Cenozoic extensional basin development. The data indicate two major phases of rapid exhumation. A first Mesozoic phase started in the Triassic (∼220 Ma) in the east and south of the study area and migrated to the west where Jurassic (∼160 Ma) ages of exhumation predominate. A second event is indicated by thermal history modeling of AFT ages and track length distributions. It is inferred to be Neogene in age, initiated at about 30 Ma, and it produced a domal pattern of AFT isochrons which follow present-day topographic elevation. Youngest AFT ages (∼100 Ma) are encountered at sealevel in the inner fjords near the areas of highest topography; ages increase radially outward to the mountain peaks and the coastlines. Forward modeling of age-elevation patterns suggests that Mesozoic geothermal gradients were 10–15°C/km higher than the present value of 20°C/km. During the Triassic and Jurassic, a total of 1.3–3.5 km of overburden was removed from the study area, assuming a 30°C/km geothermal gradient for that period. We attribute this to rift margin erosion as a result of erosional base level lowering and flank uplift, as evidenced by thick continental clastic sequences deposited in Triassic-Jurassic half grabens in the North Sea basins. We propose that 1.5–2.5 km of Neogene exhumation were a result of late stage domal uplift. This is supported by basinward dipping pre-Neogene strata in the basins surrounding southern Norway and the infill of a 1- to 2-km-thick Neogene sediment wedge containing various internal unconformities. Domal uplift probably started in the Late Oligocene, may have been amplified in the Pliocene, and was overprinted by Plio-Pleistocene glacial erosion. Maximum Neogene tectonic uplift is estimated at approximately 1–1.5 km, radially decreasing outward to a value <500 m near the shoreline. Neogene domal uplift is coincident with Oligocene and Pliocene plate reorganizations in the North Atlantic; similar Neogene domes are found around the Norwegian-Greenland Sea (i.e., Svalbard and the Barents Sea, northern Norway, east Greenland), suggesting a regional tectonic cause. The onset of Neogene uplift postdates major volcanism and continental breakup by ∼25 m.y. and predates Plio-Pleistocene glaciations. Its origin is possibly a combination of induced mantle convection, resulting in thermal erosion of the lithosphere, and the operation of intraplate stresses.