Decrease in oceanic crustal thickness since the breakup of Pangaea
Decrease in oceanic crustal thickness since the breakup of Pangaea
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DOI：
10.1038/ngeo2849
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发表时间：
2017
影响因子：
18.3
通讯作者：
H. Avendonk;Joshua K. Davis;Jennifer L. Harding;L. Lawver
中科院分区：
文献类型：
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作者：
H. Avendonk;Joshua K. Davis;Jennifer L. Harding;L. Lawver
自25亿年前的侏罗纪以来，地球的地幔每1亿年冷却6-11 °C。在更近的时期，导致这种温度下降的表面热量损失可能由于板块构造过程而加剧，例如大陆分裂、大洋中脊不断形成大洋岩石圈以及深海海沟的俯冲。在这里，我们使用全球海洋盆地的海洋地震折射数据汇编来分析海洋地壳厚度随时间的变化。我们发现，大约1.7亿年前形成于中侏罗世的洋壳比沿着现今洋中脊系统形成的洋壳平均厚1.7公里。如果较高的地幔温度是侏罗纪海洋地壳较厚的原因，那么在这段时间内，上地幔可能每1亿年冷却15-20 °C。这与长期地幔冷却速率之间的差异确实表明，现代板块构造与更大的地幔热损失相吻合。我们还发现，与太平洋相比，印度洋和大西洋的洋壳厚度随板块年龄的增加更强。这一观测结果支持了侏罗纪上地幔温度在破碎的超大陆泛古陆之后由于大陆绝缘效应而升高的观点。
Earth’s mantle has cooled by 6–11 °C every 100 million years since the Archaean, 2.5 billion years ago. In more recent times, the surface heat loss that led to this temperature drop may have been enhanced by plate-tectonic processes, such as continental breakup, the continuous creation of oceanic lithosphere at mid-ocean ridges and subduction at deep-sea trenches. Here we use a compilation of marine seismic refraction data from ocean basins globally to analyse changes in the thickness of oceanic crust over time. We find that oceanic crust formed in the mid-Jurassic, about 170 million years ago, is 1.7 km thicker on average than crust produced along the present-day mid-ocean ridge system. If a higher mantle temperature is the cause of thicker Jurassic ocean crust, the upper mantle may have cooled by 15–20 °C per 100 million years over this time period. The difference between this and the long-term mantle cooling rate indeed suggests that modern plate tectonics coincide with greater mantle heat loss. We also find that the increase of ocean crustal thickness with plate age is stronger in the Indian and Atlantic oceans compared with the Pacific Ocean. This observation supports the idea that upper mantle temperature in the Jurassic was higher in the wake of the fragmented supercontinent Pangaea due to the effect of continental insulation.