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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Mantle thermal structure and active upwelling during continental breakup in the North Atlantic
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Mantle thermal structure and active upwelling during continental breakup in the North Atlantic

机译：北大西洋大陆破裂期间的地幔热结构和活跃的上升流

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摘要

Seismic reflection and refraction data acquired on four transects spanning the Southeast Greenland rifted margin and Greenland-Iceland Ridge (GIR) provide new constraints on mantle thermal structure and melting processes during continental breakup in the North Atlantic. Maximum igneous crustal thickness varies along the margin from >30 km in the near-hotspot zone (<500 km from the hotspot track) to ～18 km in the distal zone (500-1100 km). Magmatic productivity on summed conjugate margins of the North Atlantic decreases through time from 1800 ± 300 to 600 ± 50 km~3/km/Ma in the near-hotspot zone and from 700 ± 200 to 300 ± 50 km~3/km/Ma in the distal zone. Comparison of our data with the British/Faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist. Joint consideration of crustal thickness and mean crustal seismic velocity suggests that along-margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature. The thermal anomaly (ΔT) at breakup was modest (～100-125 ℃), varied little along the margin, and transient. Date along the GIR indicate that the potential temperature anomaly (125 ± 50 ℃) and upwelling ratio (～4 times passive) of the Iceland hotspot have remained roughly constant since 56 Ma. Our results are consistent with a plum-impact model, in which (1) a plume of radius ～300 km and ΔT of ～125 ℃ impacted the margin around 61 Ma and delivered warm material to distal portions of the margin; (2) at breakup (56 Ma), the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin; and (3) by 45 Ma, both the remaining plume head and the distal warm layer were exhausted, with excess magmatism thereafter largely confined to a narrow (<200 km radius) zone immediately above the Iceland plume stem. Alternatively, the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been a pre-existing thermal anomaly unrelated to the plume.
机译：在横跨东南格陵兰裂谷边缘和格陵兰-冰岛脊（GIR）的四个样条上获得的地震反射和折射数据为北大西洋大陆解体期间的地幔热结构和融化过程提供了新的约束。火成岩的最大厚度沿边缘变化，从近热点区的> 30 km（距热点轨迹<500 km）到远端区的〜18 km（500-1100 km）。北大西洋总共轭边缘的岩浆生产力随时间从近热点区的1800±300降低至600±50 km〜3 / km / Ma，从700±200降至300±50 km〜3 / km / Ma在远端区域。我们的数据与英国/法罗边缘的比较表明，对称和非对称共轭火山裂谷边缘都存在。地壳厚度和平均地壳地震速度的共同考虑表明，沿岩浆的边缘变化主要是由活动上升流的变化而不是地幔温度控制的。破裂时的温度异常（ΔT）中等（〜100-125℃），沿边缘的变化很小，并且是瞬态的。沿GIR的日期表明，自56 Ma以来，冰岛热点的潜在温度异常（125±50℃）和上升流率（〜4倍被动）保持大致恒定。我们的结果与李子冲击模型相吻合，其中（1）半径为〜300 km的羽流和ΔT为〜125℃的羽流影响了61 Ma附近的边缘，并向边缘的远端输送了温暖的物质; （2）破裂（56 Ma）时，羽状头的下半部分继续将上升的上地幔积极地注入边缘的近端部分; （3）到45 Ma时，剩余的羽状喷头和远端暖层都被耗尽，随后岩浆活动过多，基本上局限于冰岛羽状茎杆上方的狭窄区域（半径<200 km）。可替代地，在边缘的远侧部分馈入过多岩浆作用的温暖的上地幔层可能是与羽流无关的预先存在的热异常。

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