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Fine‐grained, Ti‐poor titanomagnetite in the ~12.7 Ma Tiva Canyon (TC) Tuff systematically increases in grain size from superparamagnetic (SP) at the flow base to single domain (SD) at a few meters height. This allows us to examine the role of grain‐size variation on paleointensity, within the transition from SP to stable SD. We present magnetic properties from two previously unreported sections of the TC Tuff, as well as Thellier‐type paleointensity estimates from the lowermost ~7.0 m of the flow. Magnetic hysteresis, frequency‐dependent susceptibility, and thermomagnetic data show that sample grain‐size distribution is dominated by SP in the lower ~3.6 m, transitioning upwards to mostly stable SD. Paleointensity results are closely tied to stratigraphic height and to magnetic properties linked to domain state. SD samples have consistent absolute paleointensity values of 28.5 ± 1.94 μT (VADM of 51.3 ZAm²) and behaved ideally during paleointensity experiments. The samples including a significant SP fraction have consistently higher paleointensities and less ideal behavior but would likely pass many traditional quality‐control tests. We interpret the SD remanence to be a primary thermal remanent magnetization but discuss the possibility of a partial thermal‐chemical remanent magnetization if microcrystal growth continued at T < T_cand/or the section is affected by post‐emplacement vapor‐phase alteration. The link between paleointensity and domain state is stronger than correlations with water content or other evidence of alteration and suggests that the presence of a significant SP population may adversely impact paleointensity results, even in the presence of a stable SD fraction.

 

International Ocean Discovery Program (IODP) Expedition 362T was part of the transit from the April–June 2016 tie up in Cape Town, South Africa, to the IODP Expedition 362 port call in Colombo, Sri Lanka, (4 July–6 August 2016). Hole U1473A remedi- ation operations, approved in March 2016 by the JOIDES Resolution Facility Board (JRFB), took place 12–21 July 2016. The objectives of the Expedition 362T remedial operations were to remove the me- chanical bit release retainer sleeve (MBR-RS) left at the bottom of Hole U1473A at the end of IODP Expedition 360, cement multiple fault zone intervals to stabilize them, obtain a borehole temperature log across the fault zones (at the beginning of operations), and deepen the hole by coring an interval of no more than ~20 m. The planned temperature logging run at the beginning of opera- tions was only partially successful because the logging tool could not be lowered below a ledge at 277 m wireline log depth below sea- floor (WSF). Subsequent reaming using two tricone bit runs estab- lished a clean hole free of debris to the total depth of 789.7 m drilling depth below seafloor (DSF) established during Expedition 360. The fishing run with the reverse circulation junk basket (RCJB) yielded a surprise: it deepened Hole U1473A by 0.5 m and no junk was present at the bottom of the hole (i.e., the MBR-RS must have been removed with the last RCJB run during Expedition 360 and fallen to the seafloor without leaving any operational evidence). Next, four coring intervals deepened Hole U1473A by another 19.2 m, recovering 16.55 m (86%). The last task, cementing four fault zones identified in cores and mapped precisely based on Expedition 360 wireline logs, was partly successful. We completely cemented the lowermost fault zone (584–500 m DSF) and partly cemented the second lowest and most intense fault zone (489–443 m DSF). The upper two, less severe fault zones were not cemented at all. 

This is the site description for U1473 at Atlantis Bank 

During the 11 day transit from Colombo, Sri Lanka, to International Ocean Discovery Program (IODP) Site U1473 at Atlantis Bank, the Expedition 360 science party reexamined cores drilled during Ocean Drilling Program (ODP) Leg 179 in Hole 1105A (Pettigrew, Casey, Miller, et al., 1999; Casey et al., 2007). This activity involved rigorously describing the cores and many of the accompanying thin sections with the primary purpose of familiarizing the science party with the material likely to be encountered at the new Site U1473, situated 1.4 km to the north. The science party developed templates for description of the igneous, metamorphic, and structural features of the cores and analyzed thin sections made during Leg 179 to establish core description protocols for the new Site U1473 cores. An additional benefit of redescribing Hole 1105A cores is that the data generated are in a format directly comparable with those for Hole U1473A. In general, our findings were very similar to those produced by the Leg 179 scientists; however, with a larger science party to work on the cores, some of the information collected is new. We include this information in this chapter, as a basis for direct comparison with the results of drilling at Site U1473. In addition, we were able to make certain physical properties measurements on Hole 1105A cores, including magnetic susceptibility measurements of core section halves, that had not been possible during Leg 179. It is important to note here that the observations made on Hole 1105A cores by the Expedition 360 science party augment rather than replace those made by the Leg 179 scientists.