An alternative early opening scenario for the Central Atlantic Ocean
An alternative early opening scenario for the Central Atlantic Ocean
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DOI：
10.1016/j.epsl.2010.06.024
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发表时间：
2009-12
影响因子：
5.3
通讯作者：
Cinthia Labails;J. Olivet;D. Aslanian;W. Roest
中科院分区：
文献类型：
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作者：
Cinthia Labails;J. Olivet;D. Aslanian;W. Roest
将北美与非洲西北部分开的中大西洋盆地的开放有很好的记录，并假定在晚侏罗纪开始。然而，泛大陆的早期演化和最初的解体历史仍然存在争议：大多数现有的模型都是基于中侏罗世的一次或多次脊跳跃，在东海岸磁异常（ECMA）和布莱克支线磁异常（BSMA）之间的美国一侧留下最古老的地壳。根据这些假设，BSMA代表了初始盆地的边界和脊跳跃之后的足迹。因此，非洲西北部边缘的演化与美国东北部边缘有很大的不同。然而，这一设定与现有的观察结果相矛盾。在本文中，我们提出了一个替代方案的大陆分裂和中生代扩张的历史中大西洋。新模型是基于对地球物理数据的分析（包括新的地震测线、对新编制的磁测数据的解释和卫星重力测量）和最近发表的结果表明，中大西洋的开放已经开始于晚Sinemurian（190 Ma），基于对ECMA的非洲共轭物的新识别以及摩洛哥和新斯科舍省的盐区范围。非洲布莱克支线磁异常（ABSMA）的非洲共轭磁异常的识别，以及基底地形的重大变化，与最初的重建非常一致。中大西洋的早期开放历史被描述为四个不同的阶段。在最初解体后的前2000万年（190- 170 Ma，从Sinemurian晚期到Bajocian早期），海洋吸积非常缓慢（约0.8cm/y）。在布莱克凸起（170 Ma，巴约纪早期），板块相对运动方向（从NNW-SSE到NW-SE）和扩张速率（增加到1.7cm/y）都发生了剧烈变化。在Chron M25（约154 Ma，Kimmeridgian）和Chron M22（约150 Ma，Tithonian）之间有一个小的增长之后，扩张速率减慢到约1.3cm/y，并保持相当稳定，直到Chron M0（约125 Ma，Barremian-Aptian边界）。此外，运动学重建说明了一个显着的扩展不对称的早期历史中的大西洋;吸积率较高的美洲一侧，并导致更多的海洋地壳的形成在这个板块。我们推断，这种不对称性可能与这样一个事实，即负责显着的岩浆活动的中大西洋岩浆省（CAMP）的热异常优先位于非洲板块下方。
The opening of the Central Atlantic Ocean basin that separated North America from northwest Africa is well documented and assumed to have started during the Late Jurassic. However, the early evolution and the initial breakup history of Pangaea are still debated: most of the existing models are based on one or multiple ridge jumps at the Middle Jurassic leaving the oldest crust on the American side, between the East Coast Magnetic Anomaly (ECMA) and the Blake Spur Magnetic Anomaly (BSMA). According to these hypotheses, the BSMA represents the limit of the initial basin and the footprint subsequent to the ridge jump. Consequently, the evolution of the northwest African margin is widely different from the northeast American margin. However, this setting is in contradiction with the existing observations. In this paper, we propose an alternative scenario for the continental breakup and the Mesozoic spreading history of the Central Atlantic Ocean. The new model is based on an analysis of geophysical data (including new seismic lines, an interpretation of the newly compiled magnetic data, and satellite derived gravimetry) and recently published results which demonstrate that the opening of the Central Atlantic Ocean started already during the Late Sinemurian (190Ma), based on a new identification of the African conjugate to the ECMA and on the extent of salt provinces off Morocco and Nova Scotia. The identification of an African conjugate magnetic anomaly to BSMA, the African Blake Spur Magnetic Anomaly (ABSMA), together with the significant change in basement topography, are in good agreement with that initial reconstruction. The early opening history for the Central Atlantic Ocean is described in four distinct phases. During the first 20Myr after the initial breakup (190–170Ma, from Late Sinemurian to early Bajocian), oceanic accretion was extremely slow (∼0.8cm/y). At the time of Blake Spur (170Ma, early Bajocian), a drastic change occurred both in the relative plate motion direction (from NNW–SSE to NW–SE) and in the spreading rate (an increase to ∼1.7cm/y). After a small increase between Chron M25 (∼154Ma, Kimmeridgian) and Chron M22 (∼150Ma, Tithonian), the spreading rate slowed down to about 1.3cm/y and remained fairly constant until Chron M0 (125Ma, Barremian–Aptian boundary). In addition, kinematic reconstructions illustrate a significant spreading asymmetry during the early history of the Central Atlantic Ocean; the accretion rates were higher on the American side and led to the formation of more oceanic crust on this plate. We infer that this asymmetry could be related to the fact that the thermal anomaly responsible for the significant magmatism of the Central Atlantic Magmatic Province (CAMP) was preferentially located below the African plate.