[S-CG51] Hard-Rock Drilling Science: Continental and Deep-Sea Drilling, and Ophiolite

[SCG51-06] Assessing the quality of measurement data for different forms of onboard physical property measurements of hard rock samples in IODP Exp 399

*Natsue Abe^1,2, Kristin Dickerson ³, Jeremy R. Deans ⁴, Susan Q Lang⁵, Andrew M McCaig⁶, Peter Blum⁷, Scientists Exp.399 IODP⁷ (1.Japan Agency for Marine-Earth Science and Technology , 2.Graduate School of Natural Science& Technology, Kanazawa University, 3.University of California Santa Cruz, 4.University of South Mississippi, 5.Woods Hole Oceanographic Institution, 6.University of Leeds, 7.Texas A&M University International Ocean Discovery Program)

Keywords:IODP Exp. 399, Serpentine drilling, Atlantis Massif, physical properties, Oceanic Core Complex

IODP Expedition 399 (2023/4/12-6/12) was conducted by D/V JOIDES Resolution aiming to elucidate the formation process of the oceanic core complex, explore reaction processes between the oceanic crust, upper mantle, and seawater, investigate non-biological reactions between water and rock representing ancient systems predating life on Earth, and evaluate sub-seafloor life activity. At the serpentine site, a new hole (U1601C) was drilled to 1267.8 mbsf, becoming the fifth deepest hard rock hole in IODP history. Hole U1601C comprises serpentinized peridotite with minor gabbroic intrusions. Continuous borehole measurements of temperature, density, porosity, and seismic velocity were taken.
Precise mini-cube (8 cm^3) samples are usually cut from representative core sections for both moisture and density (MAD) and compressional wave (P-wave) velocity measurements for physical property measurements in hard rock expeditions. However, in Hole U1601C, mini-cube samples could not be taken from many cores on board due to special circumstances. To take continuous data sets in the hole, the next two different types of discrete samples were used for physical properties measurements: 1) Irregular shape samples cutting off from microbiological samples (MBIO) used for MAD measurements on cores. 2) Half-section core pieces were selected for elastic wave velocity measurements on cores partly shared with thermal conductivity (TC) measurements.
To verify whether the quality of the onboard MAD and elastic wave measurement results using these irregular samples is maintained compared to the onboard routine measurements using mini-cube samples, several mini-cube samples from the same interval were sampled as post-disembarkation samples, and measurements were carried out. There was also some overlap between the mini-cube samples and the irregular samples mentioned above on board. The results of these measurements were compared and found to agree within an error of approximately 5% for elastic wave velocity, but the error for density and porosity was greater. This may be because the on-board sample (MBIO) used for density and porosity measurements and the sample used for validation were from different intervals. More detailed verification is required.