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深海钻探计划504B孔是大洋壳中最深的基底钻孔,它穿过571.5米的枕状岩段,209米的岩性过渡带,并进入席状岩墙段杂岩体295米。504站上部洋壳的氧同位素剖面与许多蛇绿岩杂岩体氧同位素剖面的情况类似,在那里,喷出岩段相对未受蚀变的玄武岩更富含~(18)O,而岩墙段的~(18)O可变动于亏损与富集之间。504站枕状岩段玄武岩中,虽然少量富含沸石样品的δ~(18)O可达12.7‰,但一般值从+6.1至+8.5‰SMOW(平均为+7.0‰)。在从100％的枕状岩至100％岩墙的岩性过渡带,基底之下的624米处,岩石突然出现~(18)O的亏损,这与岩石中出现绿片岩相矿物相吻合。全岩的δ~(18)O值可低至+3.6‰,但岩性过渡带与岩墙段的平均值分别为+5.8及+5.4‰。
Deep Hole Drilling Project 504B is the deepest basement borehole in the oceanic crust. It passes through a 571.5-meter pillow rock segment, a 209-meter lithological transition zone, and enters a 295-meter-long schistose wall complex. Oxygen isotope profiles of the upper oceanic crust at 504 are similar to those of the oxygen ophiolite profiles of many ophiolite complexes, where the eruptions are more enriched in ~ (18) O than the unaltered basalts, and the dikes The segment of (18) O can fluctuate between loss and enrichment. Although the δ 18 O values of a few zeolite-rich samples can reach 12.7 ‰, the typical values range from +6.1 to + 8.5 ‰ SMOW (averaging + 7.0 ‰) in the basalt of 504 pillow-beds. At a lithogenic transition from 100% of the pillow rock to 100% of the dyke, 618 meters below the basement, a sudden loss of ~ (18) O occurs in the rock, consistent with the presence of greenschist facies in the rock. The δ 18 O value of whole rock can be as low as + 3.6 ‰, but the mean value of lithology transition zone and rock wall segment is respectively +5.8 and + 5.4 ‰.