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504B钻孔位于加拉帕戈斯扩张中心科斯塔里卡裂谷南部山峰,是D.S.D.P.(即深海钻探计划,下同)布置在典型大洋中脊部位的钻孔中第一个见到含绿片岩相次生矿物的热液蚀变岩石的钻孔。在海底以下890米深度上,打到了高温下海水与岩石相互作用的蚀变岩石。根据次生矿物、细脉分布和微量元素的含量,可把岩心分为三带:1带(274—890米),岩石仍然是新鲜的,或部分蚀变为次生矿物(蒙脱石和皂石等);2带(890—1050米)和3带(1050—1350米)出现浊沸石、绿泥石、绿帘石、石英和阳起石。2带中细脉比3带更为频繁,2带的一些样品富集Mn和Zn。根据阳起石的化学组成、全岩组成和S_r同位素资料,2带和3带的一部分被认为是热液对水体系中的排放带。 2带和3带之间估测的蚀变温度变化很突然。1带温度低于100℃,而2、3带的温度高于200℃。这一差距与热液蚀变和其它地球物理特征的突变对应。解释这种间隔形成的最有道理的机制是时间的滞后,当洋壳在裂谷中形成的时候蚀变最强烈。2带和3带岩石上还覆盖了另一次熔岩流。
The 504B is located in the southern tip of the Costa Rica rift in the Galapagos Dilatation Center and is the first of the boreholes to be found in the mid-ocean ridges of the DSDP (Deep Sea Drilling Program) Secondary hydrothermal alteration of rocks by rock drilling. At an altitude of 890 meters below the seafloor, altered rocks were found that interact with seawater and rocks at high temperatures. According to secondary minerals, veins and trace elements content, the core can be divided into three zones: 1 zone (274-890 m), the rock is still fresh, or partially altered into secondary minerals (montmorillonite and soap Stone, etc.); 2 lanes (890-1050 m) and 3 belts (1050-1350 m) appear laumontite, chlorite, epidote, quartz and actinolite. 2 in the veinlets more frequently than the 3 bands, some of the 2 bands are enriched in Mn and Zn. Based on the chemical composition, total rock composition and S_r isotopic data of the actinolite, some of the 2 and 3 belts are considered as discharge zones in the hydrothermal system. The estimated change in temperature between Zone 2 and Zone 3 varies abruptly. 1 with a temperature below 100 ° C and 2,3 with a temperature above 200 ° C. This difference corresponds to abrupt changes in hydrothermal alteration and other geophysical features. The most plausible mechanism explaining the formation of this interval is the lag of time, with the highest alteration when the oceanic crust is formed in the rift. 2 and 3 with another lava flow covered rock.