Crystallization of Superfast-Spreading Oceanic Crust (ODP Hole 1256D, Pacific Ocean): Constraints From Zircon Geochronology
Crystallization of Superfast-Spreading Oceanic Crust (ODP Hole 1256D, Pacific Ocean): Constraints From Zircon Geochronology
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超快速扩张的海洋地壳的结晶（ODP 孔 1256D，太平洋）：来自锆石地质年代学的约束
DOI：
10.1029/2023gc010964
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发表时间：
2023
期刊：
影响因子：
--
通讯作者：
Lissenberg C
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作者：
Lissenberg C
海洋地壳覆盖了地球表面的很大一部分，对海洋地壳的研究为海洋中脊地壳增生过程的动力学提供了重要的见解。现在人们认识到，海洋地壳的性质随着扩张速度的变化而发生根本性的变化。Ocean Drilling Program (ODP) 1256D孔（东太平洋）是在高速扩张的地壳中钻出的，属于地壳端部。钻取了一段穿过熔岩和片状岩脉并进入深成层序的剖面，对这些层序的研究使我们对高速扩张的岩浆和热液过程有了丰富的认识。在这里，我们给出了1256D洞的锆石U - Pb年代，它限制了剖面的年龄，以及地壳增生的持续时间。发现深部岩体中锆石结晶的主脉冲发生在15.19 Ma，与地磁异常一致，持续了数万年。在这一时期，主要的深部岩体侵入，片状岩脉底部的部分熔体结晶。其中一个样本似乎比这一事件晚了0.25 Myr，可能是离轴入侵。总的来说，地壳增生的持续时间为数十年至数十万年，与快速扩张的东太平洋隆起和缓慢扩张的中大西洋洋脊相似。这表明沿慢速至超快扩张脊的地壳增生发生在相似的时间尺度上，而在以厚岩石圈为特征的超低扩张脊上发生的地壳增生周期要长得多。
Studies of oceanic crust, which covers a large proportion of the Earth's surface, have provided significant insight into the dynamics of crustal accretion processes at mid‐ocean ridges. It is now recognized that the nature of oceanic crust varies fundamentally as a function of spreading rate. Ocean Drilling Program (ODP) Hole 1256D (eastern Pacific Ocean) was drilled into the crust formed at a superfast spreading rate, and hence represents a crustal end member. Drilling recovered a section through lava and sheeted dykes and into the plutonic sequence, the study of which has yielded abundant insight into magmatic and hydrothermal processes operating at high spreading rates. Here, we present zircon U‐Pb dates for Hole 1256D, which constrain the age of the section, as well as the duration of crustal accretion. We find that the main pulse of zircon crystallization within plutonic rocks occurred at 15.19 Ma, consistent with magnetic anomalies, and lasted tens of thousands of years. During this episode, the main plutonic body intruded, and partial melts of the base of the sheeted dykes crystallized. One sample appears to postdate this episode by up to 0.25 Myr, and may be an off‐axis intrusion. Overall, the duration of crustal accretion was tens to several hundreds of thousands of years, similar to that found at the fast‐spreading East Pacific Rise and the slow‐spreading Mid‐Atlantic Ridge. This indicates that crustal accretion along slow‐ to superfast‐spreading ridges occurs over similar time scales, with substantially longer periods of accretion occurring at ultraslow‐spreading ridges characterized by thick lithosphere.