New insights into the age and origin of two small Cretaceous seamount chains proximal to the Northwestern Hawaiian Ridge Geosphere

The Northwestern Hawaiian Ridge is an age-progressive volcanic chain sourced from the Hawaiian mantle plume. Proximal to the Northwestern Hawaiian Ridge are several clusters of smaller seamounts and ridges with limited age constraints and unknown geodynamic origins. This study presents new bathymetric data and 40Ar/39Ar age determinations from lava flow samples recovered by remotely operated vehicle (ROV) from two east–west-trending chains of seamounts that lie north of the Pūhāhonu and Mokumanamana volcanoes. The previously unexplored Naifeh Chain (28°48′N,167°48′W) and Plumeria Chain (25°36′N, 164°35′W) contain five volcanic structures each, including three guyots in the Naifeh Chain. New 40Ar/39Ar age determinations indicate that the Naifeh Chain formed ca. 88 Ma and the Plumeria Chain ca. 85 Ma. The Cretaceous ages, coupled with a perpendicular orientation of the seamounts relative to absolute Pacific plate motion at that time, eliminate either a Miocene Hawaiian volcanic arch or Cretaceous mantle-plume origin. The seamounts lie on oceanic crust that is modeled to be 10–15 Ma older than the corresponding seamounts. Here, two models are put forth to explain the origin of these enigmatic seamount chains as well as the similar nearby Mendelssohn Seamounts. (1) Diffuse lithospheric extension results in the formation of these seamounts until the initiation of the Kula-Pacific spreading center in the north at 84–79 Ma, which alleviates the tension. (2) Shear-driven upwelling of enriched mantle material beneath young oceanic lithosphere results in an age-progressive seamount track that is approximately perpendicular to the spreading ridge. Here we show that all sampled seamounts proximal to the Northwestern Hawaiian Ridge are intraplate in nature, but their formations can be attributed to both plume and plate processes. Grant no. NA17OAR0110336

西北夏威夷海岭（Northwestern Hawaiian Ridge）是一条源自夏威夷地幔柱的年龄递进型火山链。其周边分布着数个小型海山与海岭簇，相关年龄约束有限且地球动力学成因未知。本研究获取了两组东西走向海山链的新水深数据与熔岩流样品的40Ar/39Ar测年结果，这些样品由遥控水下机器人（remotely operated vehicle, ROV）采自普哈霍努火山（Pūhāhonu）与莫库马纳马纳火山（Mokumanamana）以北区域。此前未被勘探的奈夫海山链（Naifeh Chain，北纬28°48′、西经167°48′W）与素馨海山链（Plumeria Chain，北纬25°36′、西经164°35′W）各包含5处火山构造，其中奈夫海山链内有3座平顶海山（guyots）。新获得的40Ar/39Ar测年结果显示，奈夫海山链形成于约88 Ma，素馨海山链形成于约85 Ma。结合该时期太平洋板块绝对运动方向与海山链走向近乎垂直的特征，这些白垩纪年代数据排除了中新世夏威夷火山弧或白垩纪地幔柱起源的可能性。本次研究的海山所在的大洋地壳经估算比对应海山自身老10~15 Ma。本文提出两种模型以解释这些成因不明的海山链，以及附近相似的门德尔松海山群（Mendelssohn Seamounts）：(1) 弥散式岩石圈伸展作用造就了这些海山，直至北部库拉-太平洋扩张脊（Kula-Pacific spreading center）于84~79 Ma启动，从而缓解了区域张力；(2) 年轻大洋岩石圈下方富集地幔物质经剪切驱动上涌，形成了与扩张脊近乎垂直的年龄递进式海山链。本研究证实，所有紧邻西北夏威夷海岭的采样海山均属板内（intraplate）构造，但其成因可同时归因于地幔柱与板块运动过程。本研究受资助编号NA17OAR0110336。