No abstract

No abstract

809 deep IODP Hole U1473A at Atlantis Bank, SWIR, is 2.2 km from 1,508‐m Hole 735B and 1.4 from 158‐m Hole 1105A. With mapping, it provides the first 3‐D view of the upper levels of a 660‐km2 lower crustal batholith. It is laterally and vertically zoned, representing a complex interplay of cyclic intrusion, and ongoing deformation, with kilometer‐scale upward and lateral migration of interstial melt. Transform wall dives over the gabbro‐peridotite contact found only evolved gabbro intruded directly into the mantle near the transform. There was no high‐level melt lens, rather the gabbros crystallized at depth, and then emplaced into the zone of diking by diapiric rise of a crystal mush followed by crystal‐plastic deformation and faulting. The residues to mass balance the crust to a parent melt composition lie at depth below the center of the massif—likely near the crust‐mantle boundary. Thus, basalts erupted to the seafloor from >1,550 mbsf. By contrast, the Mid‐Atlantic Ridge lower crust drilled at 23°N and at Atlantis Massif experienced little high‐temperature deformation and limited late‐stage melt transport. They contain primitive cumulates and represent direct intrusion, storage, and crystallization of parental MORB in thinner crust below the dike‐gabbro transition. The strong asymmetric spreading of the SWIR to the south was due to fault capture, with the northern rift valley wall faults cutoff by a detachment fault that extended across most of the zone of intrusion. This caused rapid migration of the plate boundary to the north, while the large majority of the lower crust to spread south unroofing Atlantis Bank and uplifting it into the rift mountains.

Two equations, a single exponential: Nt = No (1 − e‐kt) and a double exponential: Nt = No S (1 − e‐kt) + No (1 − S)(1 − e‐kt), were used to compare mineralization potentials of soils, where Nt is the N mineralized in time (t), No is the potentially mineralizable N, and S and (1 − S) are the fractions of the labile and recalcitrant organic N compounds decomposing at specific rates h and k, respectively. Data were obtained from the published and unpublished incubation studies of Stanford and Smith (MD), Smith et al. (WA), Deans et al. (MN), El‐Haris et al. (US), and Griffin and Laine (CT). The double exponential equation provided the “best fit” of the N mineralization‐time (Nt/t) curve as determined by the estimated mean square error (MSE). With long‐term (>84 d) incubations, Nt/t curves for the double exponential equation resulted in an avg MSE of 6 compared with the single exponential equation (avg MSE of 79) for CT, MN, and MD data sets (n = 20). For short‐term (≤84 d) incubations, Nt/t curves were better estimated by the double exponential (avg MSE = 4, n = 21) than by the single exponential (avg MSE = 12, n = 13) for WA, US, and MN data.

Introduction 14 Igneous petrology 18 Metamorphic petrology 21 Structural geology 26 Geochemistry 33 Microbiology 38 Paleomagnetism 40 Petrophysics 49 References 11 Sum up section recovered lengths and enter as total core recovered; compute percent recovery. 12 Select microbiology sample if appropriate. Designated scientist 13 Wash and space out pieces in split liners; mark "upward" orientation. 14 Reconstruct fractured pieces if possible; shrink-wrap fragile pieces. 15 Add spacers between pieces (no glue yet). 16 Check binning and draw splitting line on each piece; mark working half. Designated scientist 17 Permanently glue spacers in split liner; angle braces point upcore so top of piece is at top of bin. 18 Enter spacer offsets in registry for piece log. 19 Enter final "curated section lengths" in registry. 20 Optionally enter piece lengths in registry for piece log. Designated scientist 21 Image whole-round surface (0°, 90°, 180°, and 270° quarter images). Designated technicians, scientists 22 Prepare whole-round composite images. Imaging specialist 23 Measure gamma ray attenuation (GRA) and magnetic susceptibility loop sensor (MSL) with Whole-Round Multisensor Logger (WRMSL). 24 Measure natural gamma radiation (NGR) with Natural Gamma Radiation Logger (NGRL). 25 Split sections (i.e., split pieces along the lines indicated by designated scientists). 26 Label piece halves. 27 Image dry surface of archive halves with Section Half Imaging Logger (SHIL). 28 Measure reflectance spectroscopy and colorimetry (RSC) and point magnetic susceptibility (MSP) on archive halves with Section Half Multisensor Logger (SHMSL). 29 Macroscopic description of archive half (and working half if needed). 30 Measure paleomagnetic properties on archive halves. Paleomagnetists 31 Measure P-wave velocity on Section Half Measurement Gantry (SHMG). Physical properties specialists 32 Select and flag samples to be taken from working half for shipboard analysis. Designated scientist 33 Cut shipboard and shore-based samples from working-half pieces. Curatorial staff 34 Microscopic description of thin sections. Core describers 35 Inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), and carbon-hydrogen-nitrogen-sulfur (CHNS) analyses. Geochemists 36 Measure paleomagnetic and rock magnetic properties on cube samples. Paleomagnetists 37 Measure moisture and density (MAD) on cube samples. Physical properties specialists 38 Select and flag personal/group samples to be taken from working half for shore-based analysis. Scientists 39 Inspect and approve personal samples. Sample Allocation Committee 40 Cut shipboard and shore-based samples from working-half pieces. Curatorial staff 41 Place archive halves in D-tubes when description and paleomagnetic measurements are complete. Store in refrigerator until shipment to designated IODP core repository (i.e., Kochi Core Center). 42 Bag and pack personal/group samples in boxes for shipment to designated investigator addresses. Curatorial staff Drilling and coring Ship cr...