Paleomagnetism of the Atlantic, Tethys and Iapetus Oceans: The opening of the Atlantic Ocean
Paleomagnetism of the Atlantic, Tethys and Iapetus Oceans: The opening of the Atlantic Ocean
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DOI：
10.1017/cbo9780511524936.007
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发表时间：
1993-03
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影响因子：
--
通讯作者：
R. Voo
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作者：
R. Voo
早侏罗纪之后，大西洋中部开始在冈瓦纳西部和劳鲁西亚之间扩张，而欧洲和北美之间的扩张则始于白垩纪。中大西洋最古老的海底估计约为175 Ma（Klitgord和Schouten，1986年）。然而，目前尚不清楚这两个大陆板块在此之前已经移动到何种程度（通过大陆地壳变薄而没有海底形成）。晚三叠世至早侏罗世的岩墙群和北美东部的沉积物填充地堑（例如，纽瓦克盆地）和西非的研究表明，裂谷作用早在175 Ma之前就开始了，但两个大陆之间与裂谷有关的伸展量却知之甚少。然而，从古地磁学的角度来看，早侏罗世劳鲁西亚和西冈瓦纳古极点之间并不存在严重的不一致（第5章，表5.10和5.11），因此只有在175 Ma之后，才需要将古极点与考虑海洋扩张的旋转参数进行比较。当然，大西洋今天仍在扩大。过去十年的技术发展已经允许精确测量这种宽度的增加。利用大地测量技术（例如，甚长基线干涉测量（VLBI），瑞典翁萨拉和美国马萨诸塞州韦斯特福德之间的距离每年增加13.4 ± 0.7毫米，也就是说，在八年的测量期间，大约增加10厘米（图6.1，来自B。O. Ronnang，pers. comm.，1990年）。类似的测量记录了太平洋板块的更高速度。
After Early Jurassic time the Central Atlantic Ocean began opening between West Gondwana and Laurussia, whereas between Europe and North America the spreading began in the Cretaceous. The oldest seafloor in the Central Atlantic is estimated to be about 175 Ma (Klitgord & Schouten, 1986). However, it is not clear to what extent the two continental landmasses already had been moving apart before that time (through thinning of the continental crust without ocean floor formation). The Late Triassic to Early Jurassic dike swarms and sediment-filled grabens of eastern North America (e.g., Newark Basin) and in West Africa suggest that rifting began well before 175 Ma, but the amount of rift-related extension between the two continents is poorly known. From a paleomagnetic viewpoint, however, there is no serious discordance between the Early Jurassic Laurussia and West Gondwana paleopoles (Chapter 5, Tables 5.10 and 5.11), so only after 175 Ma do the paleopoles need to be compared with rotation parameters that take the ocean spreading into account. The Atlantic Ocean is, of course, still widening today. Technological developments in the last decade have allowed precise measurements of this increase in width. Using geodetic techniques (e.g., Very Long Baseline Interferometry or VLBI) the distance between Onsala, Sweden and Westford, Massachusetts, USA is seen to be increasing by 13.4 ± 0.7 mm per year, that is, about 10 cm during the eight-year duration of the measurements (Figure 6.1, from B. O. Ronnang, pers. comm., 1990). Similar measurements have documented higher plate velocities in the Pacific Ocean.