• ODP Hole 1256D;
  • Integrated Ocean Drilling Program;
  • upper oceanic crust;
  • boron;
  • chlorine;
  • prompt gamma neutron activation analysis

[1] Boron, Cl, Ti, K, Sm, and Gd concentrations of oceanic crust samples were determined by prompt gamma neutron activation analysis. The samples include 63 basalts and 5 gabbros obtained at various depths (369–1503 m below seafloor) from Hole 1256D during Ocean Drilling Program Leg 206 and Integrated Ocean Drilling Program Expedition 309 and 312. The results show stepwise downhole variations, B content and B/K decrease, and Cl content and Cl/K increase with increasing depth. High B content (>1.5 ppm) in shallower rocks (extrusive lavas) is probably achieved by low-temperature seawater alteration, and high Cl contents (up to 1400 ppm) in the deeper rocks (plutonic section) would show result of high-temperature hydrothermal alteration. Average B and Cl values for the upper oceanic crust in Hole 1256D are 1.5 ppm and 334 ppm, respectively.