ALBERT

Description: Carbonate was micro-sampled from representative listvenite and serpentinite core sections of Hole BT1B for carbonate stable isotope analysis (δ13C, δ18O) and clumped isotope thermometry. This sample subset includes matrix and vein magnesite, vein dolomite from the Upper Serpentinite (BT1B 43–02 and 44–03) and listvenite. The majority of listvenite carbonate samples are from the Lower Listvenite, comprising green, light red and dark red listvenite, plus one additional light red listvenite from the Upper Listvenite. Listvenite matrix carbonate is mainly magnesite except for matrix dolomite from core sections BT1B 72–04 and BT1B 77–03. Listvenite vein dolomite was sampled from the Upper Listvenite (BT1B 32–02) and Lower Listvenite (BT1B 67–04). Carbonate was sampled by using a micro drill with 3.8 mm inner diameter and a handheld Dremel tool from thin-section billets at sites selected based on the petrography. The relatively large diameter of the drill compared to the typical grain size and vein diameter, required sampling of the most homogeneous matrix areas and veins that were macroscopically devoid of crosscutting relationships. Carbonate samples were further crushed to a fine powder using an agate mortar and pestle prior to the analysis. Stable isotope analyses were performed at the GeoLab, Utrecht University, The Netherlands. Before isotope analysis, the mineralogy of each sample powder was constrained by XRD. The duration of acid digestion was adjusted to either dolomite or magnesite according to the dominant carbonate species in the sample powder. Dolomite samples were digested in 103% phosphoric acid at 70°C for 20 minutes and the released CO2 was continuously collected in a liquid nitrogen trap using a Kiel IV carbonate device, coupled to a 253 Plus isotope ratio mass spectrometer (both instruments from Thermo Scientific) and analyzed in Long-Integration Dual-Inlet mode (Müller et al., 2017a, doi: 10.1002/rcm.7878; with 600 seconds integration time per aliquot). The weight of individual aliquots of reference materials and unknown samples ranged between 75–95 µg. Magnesite samples were digested offline, using 10–20 mg solid powder and 1–2 ml 103% phosphoric acid at 100°C for 15–16 hours in individual, sealed vials using a custom-built vacuum line containing a cold trap with liquid nitrogen acetone slush (-96°C) to remove H2O trace quantities from the CO2 gas. The analyses were conducted using the Dual Inlet of a Thermo Fisher Scientific MAT 253 in the traditional way by 8 alternating reference gas-sample gas cycles (208 seconds sample gas integration time per measurement). All analyses were carried out in sequences with intermittent analyses of the carbonate (calcite) reference materials ETH-1, ETH-2, ETH-3. Each unknown sample was analyzed 4 to 14 times. A separate dataset contains the complete summary of all individual analyses of unknown samples and reference materials (Beinlich et al., 2019; doi:10.1594/PANGAEA.908649).

Description: The presented serpentine and fuchsite (Cr-muscovite) data were derived from representative carbonate-bearing serpentinite and listvenite samples from Hole BT1B, OmanDP. Electron microprobe analysis was conducted using the JEOL 8530F FE electron microprobe at Centre for Microscopy, Characterization and Analysis (CMCA), The University of Western Australia, using an acceleration voltage of 15 keV and a fully focused beam. The general analytical procedure and application of reference materials follow the method described in Beinlich et al. (2018; doi:10.1038/s41467-018-03039-9).

Description: Analysis of an in situ fault zone within the Atlantis Massif oceanic core complex (Mid-Atlantic Ridge) provides clues to the relevant deformation mechanisms and their temporal evolution within oceanic crust. IODP EXP304/305 drilled a succession of gabbroic lithologies to a final depth of 1415 m below the sea floor (mbsf), with very high recovery rates of up to 100% (generally ~80%). We identified an intra-crustal fault zone between 720 and 780 mbsf in a section of massive gabbro, olivine gabbro, oxide gabbro units, and minor diabase intrusions. Of particular interest is the section between 744 and 750 mbsf, which unfortunately was marked by low recovery rates (17%). Electrical borehole-wall images show a 1-m-thick zone of east-dipping fractures within this interval, which is otherwise dominated by N-S dipping structures. Despite the high fracture density in this section, the hole walls are smooth, with rare breakouts, suggesting that the low recovery rate was due to a change in lithology rather than well conditions. The recovered rocks include ultracataclasite and possibly incohesive fault gouge that formed in the upper amphibolite regime, with mostly amphibole infill. Logging data suggest that the gabbroic rocks in this interval are rich in hydrous phases, consistent with increased amounts of amphibole found in the core. Equilibration temperature conditions of about 640 °C were obtained for plagioclase clasts and aluminous actinolite, assuming a pressure of 200 MPa. The permeability of the fault zone is in the range of 10**-19 to 10**-17 m**2. Although the permeability appears to be high within the fault zone relative to other parts of the section, it is no higher than that in typical lower crustal material. As a consequence, because brittle failure occurred at high temperatures, the fault zone was subsequently completely sealed by hydrous minerals, thereby preventing further fluid circulation and preserving water in the crust.

Description: Carbonate separates from listvenite core BT1B, Oman Drilling Project, were analyzed for their stable oxygen and carbon isotope ratios and clumped isotope distribution to constrain the conditions of carbonate mineralization. This data set summarizes all individual measurement results of the reference materials used and of the unknown samples.

Description: The presented carbonate electron microprobe data were derived from representative carbonate-bearing serpentinite and listvenite samples in Hole BT1B, OmanDP. The analyzed carbonate grains are chemically zoned and the data represents averages for compositionally and texturally comparable zones, e.g. matrix magnesite in 44-03 is always the core as the rim is dolomite. Electron microprobe analysis was conducted using the JEOL 8530F FE electron microprobe at Centre for Microscopy, Characterization and Analysis (CMCA), The University of Western Australia, using an acceleration voltage of 15 keV and a 5 µm defocused beam. The general analytical procedure and application of reference materials follow the method described in Beinlich et al. (2018; doi:10.1038/s41467-018-03039-9).

Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nguyen, D. K., Morishita, T., Soda, Y., Tamura, A., Ghosh, B., Harigane, Y., France, L., Liu, C., Natland, J. H., Sanfilippo, A., MacLeod, C. J., Blum, P., & Dick, H. J. B. (2018). Occurrence of felsic rocks in oceanic gabbros from IODP hole U1473A: Implications for evolved melt migration in the lower oceanic crust. Minerals, 8(12), 583, doi:10.3390/min8120583.

Description: Felsic rocks are minor in abundance but occur ubiquitously in International Ocean Discovery Program Hole U1473A, Southwest Indian Ridge. The trace element abundances of high-Ti brown amphibole, plagioclase, and zircon in veins, as well as the presence of myrmekitic texture in the studied felsic rocks support crystallization origin from highly-evolved melts, probably controlled by fractional crystallization. Based on geochemical criteria and texture of the mineral assemblage in felsic rocks and their relationship with host gabbros, they can be divided into three types: (1) Felsic rock with sharp boundaries is formed when felsic melt intrudes into fractures of host gabbros, resulting in minimal interaction between the melt and the wall minerals. (2) Replacive felsic rock, which is characterized by a pseudomorphic replacement of minerals in the host gabbro. This vein type is caused by the replacement of the host mineralogy by minerals in equilibrium with the felsic melts. (3) Felsic rock with diffused boundaries is formed either by infiltration of felsic melt into the solidifying gabbro body or crystallization of interstitial melts. Infiltration modes of felsic melts are likely controlled by the temperature condition of the cooling host gabbros.

Description: This contribution is part of Du Khac Nguyen’s Ph.D. coursework at Kanazawa University with the funding provided by the Ministry of Education and Training of Vietnam (MOET) under grant number 950/Q -BGD T and Kanazawa University of Japan. This work was supported by Kanazawa University SAKIGAKE project and J-DESC post-cruise support funding.

Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 8 (2017): 1870, doi:10.1038/s41467-017-01610-4.

Description: Peridotite carbonation represents a critical step within the long-term carbon cycle by sequestering volatile CO2 in solid carbonate. This has been proposed as one potential pathway to mitigate the effects of greenhouse gas release. Most of our current understanding of reaction mechanisms is based on hand specimen and laboratory-scale analyses. Linking laboratory-scale observations to field scale processes remains challenging. Here we present the first geophysical characterization of serpentinite carbonation across scales ranging from km to sub-mm by combining aeromagnetic observations, outcrop- and thin section-scale magnetic mapping. At all scales, magnetic anomalies coherently change across reaction fronts separating assemblages indicative of incipient, intermittent, and final reaction progress. The abundance of magnetic minerals correlates with reaction progress, causing amplitude and wavelength variations in associated magnetic anomalies. This correlation represents a foundation for characterizing the extent and degree of in situ ultramafic rock carbonation in space and time.

Description: This project was supported by the Woods Hole Oceanographic Institution Independent Study Award (Tivey and Tominaga) and by NASA Astrobiology Institute NNA15BB02A (Tominaga). M.T. and A.B. are grateful to B. Jamtveit and H. Austrheim (University of Oslo) for their support during the 2011 and 2013 field campaigns. B.W. and E.A.L. thank the National Science Foundation grant DMS-1521765 and Thomas F. Peterson, Jr for generous support.

Description: Magmatic processes during the earliest stage of subduction initiation are still not well understood. We examined peridotites recovered from an exhumed crust-mantle section exposed along the landward slopes of the northern Izu-Bonin Trench using the Japan Agency for Marine-Earth Science and Technology's remotely operated vehicle KAIKO7000II. Based on the Cr# [Cr/(Cr + Al) atomic ratio] of spinel, two distinctive groups, (1) high-Cr# (〉0.8) dunite and (2) medium-Cr# (0.4-0.6) dunite, occur close to each other and are associated with refractory harzburgite. Two distinctive melts were in equilibrium with these dunites: a boninitic melt for the high-Cr# dunite and a mid-oceanic ridge basalt (MORB)-like melt for the medium-Cr# dunite. The TiO2 content of the latter melt is lower than typical MORB compositions. We suggest that the medium-Cr# dunite was a melt conduit for a basalt recently reported from the Mariana forearc that was erupted at the inception of subduction. The wide range of variation in the Cr#s of spinels in dunites from the Izu-Bonin-Mariana forearc probably reflects changing melt compositions from MORB-like melts to boninitic melts in the forearc setting due to an increase of slab-derived hydrous fluids and/or melts during subduction initiation.