Major element oxides and 40Ar/39Ar plateau and isochron ages of ODP Hole 165-1001A

40Ar-39Ar incremental heating experiments and electron microprobe analyses were performed on basaltic rocks recovered from Site 1001 during Ocean Drilling Program Leg 165. The lower Nicaraguan Rise, on which Site 1001 lies, appears to be part of a larger Caribbean oceanic plateau that makes up the core of the Caribbean plate. Our results indicate an eruption age of 81 ± 1 Ma. A single flow-rim glass is tholeiitic and almost identical to the shipboard X-ray fluorescence analyses of the whole rock. The slightly porphyritic basalts have at least two populations of plagioclase, groundmass, and glomerocrystic plagioclase laths that appear to be in equilibrium with the surrounding melt and corroded tabular phenocrysts that have a higher An content (An84-86).

本研究针对大洋钻探计划（Ocean Drilling Program）第165航次自1001站位采获的玄武岩样品，开展了⁴⁰Ar-³⁹Ar阶段加热实验与电子探针分析（electron microprobe analyses）。1001站位坐落的尼加拉瓜海隆下段，应为构成加勒比板块核心的大型加勒比洋高原的组成部分。本研究结果显示该玄武岩的喷发年龄为81 ± 1 Ma。单颗熔岩流边缘玻璃质具有拉斑玄武质成分，其全岩组分与船上开展的全岩X射线荧光分析（X-ray fluorescence analyses）结果几乎一致。该斑状玄武岩至少包含两类斜长石组分：一类为与周围熔体处于平衡状态的基质斜长石与聚斑斜长石板晶，另一类为钙长石分子占比更高（An₈₄-₈₆）的溶蚀板状斑晶。