(Table DR1) Trace element contents in basalts from ODP Hole 33-317A

Numerous large igneous provinces formed in the Pacific Ocean during Early Cretaceous time, but their origins and relations are poorly understood. We present new geochronological and geochemical data on rocks from the Manihiki Plateau and compare these results to those for other Cretaceous Pacific plateaus. A dredged Manihiki basalt gives an 40Ar-39Ar age of 117.9+/-3.5 Ma (2 sigma), essentially contemporaneous with the Ontong Java Plateau ~2500 km to the west, and the possibly related Hikurangi Plateau ~3000 km to the south. Drilled Manihiki lavas are tholeiitic with incompatible trace element abundances similar to those of Ontong Java basalts. These lavas may result from high degrees of partial melting during the main eruptive phase of plateau formation. There are two categories of dredged lavas from the Danger Islands Troughs, which bisect the plateau. The first is alkalic lavas having strong enrichments in light rare earth and large-ion lithophile elements; these lavas may represent late-stage activity, as one sample yields an 40Ar-39Ar age of 99.5+/-0.7 Ma. The second category consists of tholeiitic basalts with U-shaped incompatible element patterns and unusually low abundances of several elements; these basalts record a mantle component not previously observed in Manihiki, Ontong Java, or Hikurangi lavas. Their trace element characteristics may result from extensive melting of depleted mantle wedge material mixed with small amounts of volcaniclastic sediment. We are unaware of comparable basalts elsewhere.

早白垩世时期，太平洋域内形成了多处大火成岩省（Large Igneous Provinces），但其成因与相互关联机制迄今尚未得到清晰阐释。本文针对马尼希基高原（Manihiki Plateau）的岩石样品，提供了全新的地质年代学与地球化学数据，并将该结果与其他白垩纪太平洋高原的相关数据进行对比。疏浚采得的马尼希基玄武岩的氩-40-氩-39（40Ar-39Ar）年龄为117.9±3.5 Ma（2σ，两倍标准偏差），其形成时间大致与西侧约2500千米处的翁通爪哇高原（Ontong Java Plateau）、南侧约3000千米处的疑似关联希库朗伊高原（Hikurangi Plateau）同期。钻探获取的马尼希基熔岩为拉斑玄武质岩石，其不相容微量元素丰度与翁通爪哇高原玄武岩相近，这类熔岩可能形成于高原形成主喷发阶段的高程度部分熔融过程中。分隔马尼希基高原的危险岛海槽（Danger Islands Troughs）所获疏浚熔岩可分为两类：第一类为碱性熔岩，其轻稀土元素与大离子亲石元素富集程度极高，其中一件样品的氩-40-氩-39年龄为99.5±0.7 Ma，该类熔岩可能代表了晚阶段的岩浆活动；第二类为拉斑玄武质玄武岩，其不相容元素配分模式呈U型，且多种元素的丰度异常偏低，这类玄武岩记录了此前在马尼希基、翁通爪哇及希库朗伊高原熔岩中未被观测到的地幔端元，其微量元素特征可能源于亏损地幔楔物质经历广泛熔融后混入了少量火山碎屑沉积物。目前我们尚未在其他区域发现与之类似的玄武岩。