Expedition 360 methods

MacLeod, C. J.; Dick, H. J.; Blum, Peter; Abe, Natsue; Blackman, Donna K.; Bowles, J. A.; Cheadle, M. J.; Cho, K.; Ciążela, Jakub; Deans, J. R.; Edgcomb, Virginia P.; Ferrando, Carlotta; Ghosh, Biswajit; Ildefonse, Benoı̂t; Kendrick, Mark A.; Koepke, Juergen; Leong, James Andrew; Liu, C.; Ma, Qiang; Morishita, Tomoaki; Morris, A.; Natland, James H.; Nozaka, Toshio; Pluemper, O.; Sanfilippo, Alessio; Sylvan, Jason B.; Tivey, Maurice A.; Tribuzio, R.; Viegas, Luís

doi:10.14379/iodp.proc.360.102.2017

Cited by 21 publications

(22 citation statements)

References 66 publications

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“…Hole 735 B penetrated 1,508 mbsf, and the logged uppermost 500 m shows a mean Vp of 6,895 m/s and 7,036 m/s at 500 mbsf measured at 200 MPa (Iturrino et al., 2002). Hole U1473 A penetrated 808 mbsf, shows a mean Vp of 6.74 km/s measured under room/standard temperature and pressure (MacLeod et al., 2017), which are basically consistent with Hole 735B. Hole U1309D penetrated 1,415 mbsf, and shows a Vp of ∼5.1–6.8 km/s measured at 200 MPa.…”

Section: Results and Comparison With Previous Studiesmentioning

confidence: 52%

“…There are three successful drill holes penetrated into the gabbroic section of the OCC footwalls, ODP Hole 735B (Dick et al., 2000) and IODP Hole U1473 A (MacLeod et al., 2017) in Atlantis Bank OCC along the SWIR, and IODP Hole U1309D (Blackman et al., 2011) in the Central Dome of Atlantis Massif OCC along the MAR. Here we summarize previous reported characteristics of average Vp at these sites.…”

Section: Results and Comparison With Previous Studiesmentioning

confidence: 99%

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Seismic Imaging of Dante's Domes Oceanic Core Complex From Streamer Waveform Inversion and Reverse Time Migration

Zhang

et al. 2022

JGR Solid Earth

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Early arrival traveltime tomography and full waveform inversion were conducted on downward continued streamer seismic data at Dante's Domes oceanic core complex (OCC), providing unprecedented details of shallow P wave velocity structure. Together with reverse time migration images, seafloor morphology, in situ geological samples, magnetic and gravity data, the seismic constraints are used to infer the lithological distribution along the seismic profiles. Based on the striking similarity in velocity structure beneath the corrugated domes with other OCCs and drilling results from Atlantis Massif, we confidently reconfirmed the Southern Dome as dominantly gabbroic rocks, and the Northern Dome as serpentinized peridotites. A series of isolated gabbroic bodies embedded in the diabase and basaltic layers is observed in the breakaway zone, suggesting that the initiation of Dante's Domes OCC occurred over a long period during which there were several failed attempts to form a long‐lived detachment fault. This early development of the OCC probably occurred under a regime of alternating magma starvation and magma replenishment. The predominantly gabbroic section, beneath the Southern Dome and extending to termination, indicates the OCC has been created with relatively high magma flux. We also imaged distinct shallow subseafloor reflections which are also termed as D reflectors underneath the corrugated domes. The location of the D reflectors is similar to those in the Atlantis Massif, with depths well correlated with the top of exhumed gabbroic bodies and the discontinuities in the D reflectors between gabbroic bodies. Our findings contribute to the understanding of processes controlling the OCCs initiation and evolution at slow spreading ridges.

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Section: Results and Comparison With Previous Studiesmentioning

confidence: 52%

Section: Results and Comparison With Previous Studiesmentioning

confidence: 99%

Seismic Imaging of Dante's Domes Oceanic Core Complex From Streamer Waveform Inversion and Reverse Time Migration

Zhang

et al. 2022

JGR Solid Earth

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“…The common types of shear‐sense indicators under dextral shear sense are shown in Figure 3. The certainty of shear‐sense determination is based on the shipboard principle (MacLeod, et al, 2017b). Shear‐sense data obtained by Exp 360 shipboard macroscopic descriptions and those determined by our thin section observations (Table S2) are both included.…”

Section: Methodsmentioning

confidence: 99%

“…Moreover, four unveined reverse-sense foliated oxide gabbros and five undeformed oxide gabbronorites from below ~90 mbsf were also included, corresponding to a reverse-shear sense-dominated region in gabbro (Figure 2b). Most of the foliated gabbros have intensity rank ranging from Grade 3 (protomylonite) to Grade 5 (ultramylonite) on the IODP Expedition 360 textural deformation scale (MacLeod, et al, 2017b). The shear sense, true dip, and crystal-plastic fabrics (CPFs) intensities for the gabbros and felsic veins were mostly taken from the shipboard macroscopic descriptions, together with additional data from our personal sample sets.…”

Section: General Descriptions and Representative Structures In Hole U1473amentioning

confidence: 99%

Silica‐Rich Vein Formation in an Evolving Stress Field, Atlantis Bank Oceanic Core Complex

Dick

Urann

et al. 2020

Geochem Geophys Geosyst

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Drilling 809‐m Hole U1473A in the gabbro batholith at the Atlantis Bank Oceanic Core Complex (OCC) found two felsic vein generations: late magmatic fractionates, rich in deuteric water, hosted by oxide gabbros, and anatectic veins associated with dike intrusion and introduction of seawater‐derived volatiles. Microtextures show a change from compressional to tensional stress during vein formation. Temperatures and oxidation state were obtained from amphibole‐plagioclase and oxide pairs in the adjacent gabbros. Type I veins generally have reverse shear‐sense, with restricted ΔFMQ, high Mt/Ilm ratios, and low‐amphibole Cl/F indicating deuteric fluids. They formed during percolation and fractionation of Fe‐Ti‐rich melts into the primary olivine gabbro. Type II veins are usually hosted by olivine gabbro, occur at dike contacts and the margins of normal‐sense shear zones. They are undeformed or weakly deformed, with highly variable ΔFMQ, low Mt/Ilm ratios, and high‐amphibole Cl/F, indicating seawater‐derived fluids. The detachment fault on which the gabbro massif was emplaced rooted near the base of the dike‐gabbro transition beneath the rift valley. The ingress of seawater volatiles began at >800°C and penetrated at least ~590 m into the lower crust during extensional faulting in the rift valley and adjacent rift mountains. The sequence of the felsic vein formation likely reflects asymmetric diapiric flow, with a reversal of the stress regime, and a transition from juvenile to seawater‐derived volatiles. This, in turn, is consistent with fault capture leading to the large asymmetries in spreading rates during OCC formations and heat flow beneath the rift mountains.

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“…Serpentinization accompanied by magnetite formation occurs in the olivine-bearing gabbroic rocks that constitute the lower oceanic crust at temperatures similar to serpentinization of peridotites (e.g., Majumdar et al, 2020;Nakamura et al, 2009;Nozaka et al, 2017). However, in contrast to the wide distribution of serpentine + magnetite veins cutting olivine and mineral assemblages formed by alteration under a wide range of temperature (T) conditions from amphibolite to subgreenschist facies, the typical greenschist mineral assemblage found within mafic rocks, that is, epidote + chlorite + actinolite + albite, is rare or absent in olivine gabbros and troctolites of the lower oceanic crust (e.g., Blackman et al, 2006;Gillis et al, 2014;Kelemen et al, 2020;MacLeod et al, 2017). In particular, the occurrence of epidote, which is widespread in statically altered basalts and diabases of the upper oceanic crust (e.g., Nehlig & Juteau, 1988), is common in or near hydrothermal veins that fill fracture networks or in cataclastic zones in lower crustal gabbros (Bieseler et al, 2018;Blackman et al, 2006;Gillis et al, 2014;Greenberger et al, 2021;MacLeod et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Incompatibility between serpentinization and epidote formation in the lower oceanic crust: Evidence from the Oman Drilling Project

Nozaka

Tateishi

2023

Journal Metamorphic Geology

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It is a general tendency that epidote, which is a typical greenschist facies mineral, is scarce in the lower oceanic crust, in spite of the widespread occurrence of the other minerals indicative of similar temperature conditions such as chlorite, actinolite, prehnite and serpentine. To find the cause of this, we carried out petrological analyses of lower crustal rocks of the Oman ophiolite sampled by the Oman Drilling Project of the International Continental Scientific Drilling Program (ICDP). Petrographic observations revealed the tendency, as expected, that the amount of epidote formed by static alteration of plagioclase decreases with depth. Because mineral assemblages indicative of a wide range of temperature conditions from amphibolite to subgreenschist facies occur throughout the cores without systematic variations of abundance, the decrease of epidote amount cannot be explained by the difference of temperature condition of alteration. Petrographic observations also revealed that epidote is absent or rare in rocks containing serpentinized olivine in contrast to prehnite showing a close association with serpentinization of olivine. In an exceptional sample containing both epidote and serpentinized olivine, epidote occurs with chlorite that cuts or replaces plagioclase, mantles adjacent olivine and is connected with chlorite + lizardite veins cutting mesh‐forming serpentine veins. The distribution and mode of occurrence of epidote suggest decoupling of its formation with the main stage of serpentinization. Serpentine veins cutting olivine to form mesh texture are typically lizardite with magnetite ribbons at vein centres and have compositions of lizardite–cronstedtite solid solution at vein margins or in magnetite‐free veins, suggesting a chemical condition with low silica and low oxygen potentials at an early stage of serpentinization. Thermodynamic modelling for olivine and plagioclase alteration at greenschist facies conditions indicates that silica potential for plagioclase alteration to form prehnite + chlorite and epidote + chlorite could be higher than for olivine serpentinization. On the other hand, oxygen potential for the prehnite + chlorite formation is lower than for the epidote + chlorite formation and is comparable with that for olivine serpentinization. From the observations and analyses, it is concluded that epidote formation is inhibited by olivine serpentinization, which maintains a reducing condition for alteration in the lower oceanic crust.

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Expedition 360 methods

Cited by 21 publications

References 66 publications

Seismic Imaging of Dante's Domes Oceanic Core Complex From Streamer Waveform Inversion and Reverse Time Migration

Seismic Imaging of Dante's Domes Oceanic Core Complex From Streamer Waveform Inversion and Reverse Time Migration

Silica‐Rich Vein Formation in an Evolving Stress Field, Atlantis Bank Oceanic Core Complex

Incompatibility between serpentinization and epidote formation in the lower oceanic crust: Evidence from the Oman Drilling Project

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