(Tables T1, T2) Major element content in alteration categories of ODP Site 193-1188 and Hole 193-1189A, PACMANUS field@en

In the Ocean Drilling Program's only foray to an active seafloor hydrothermal system hosted by felsic volcanic rocks at a convergent plate margin, deep penetrations were achieved at two contrasted sites within the PACMANUS field (Manus backarc basin, Papua New Guinea). Just 1.0 km apart, these sites are characterized, respectively, by diffuse low-temperature venting at the seabed (Site 1188, Snowcap site; 1650 meters below sea level [mbsl]) and focused high-temperature venting (Site 1189, Roman Ruins; 1700 mbsl). Shallow holes at a background location remote from known hydrothermal activity (Site 1190) and at a second high-temperature chimney field (Site 1191, Satanic Mills) failed to drill beyond unaltered felsic lavas which at Sites 1188 and 1189 form an impervious cap (as thick as 35 m) to an underlying, pervasively altered lava sequence with occasional volcaniclastic horizons. […]