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Stakes, Debra S; Mével, Catherine; Cannat, Mathilde; Chaput, Teresa (1991): Chemistry of gabbroic rocks from ODP Hole 118-735B [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.757682, Supplement to: Stakes, DS et al. (1991): Metamorphic stratigraphy of Hole 735B. In: Von Herzen, RP; Robinson, PT; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 118, 153-180, https://doi.org/10.2973/odp.proc.sr.118.127.1991

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Abstract:
Gabbroic rocks and their late differentiates recovered at Site 735 represent 500 m of oceanic layer 3. The original cooling of a mid-ocean ridge magma chamber, its penetration by ductile shear zones and late intrusives, and the subsequent penetration of seawater through a network of cracks and into highly permeable magmatic hydrofracture horizons are recorded in the metamorphic stratigraphy of the core. Ductile shear zones are characterized by extensive dynamic recrystallization of primary phases, beginning in the granulite facies and continuing into the lower amphibolite facies. Increasing availability of seawater during dynamic recrystallization is reflected in depletions in 18O, increasing abundance of amphibole of variable composition and metamorphic plagioclase of intermediate composition, and more complete coronitic or pseudomorphous static replacement of magmatic minerals. Downcore correlation of synkinematic assemblages, bulk-rock oxygen isotopic compositions, and vein abundance suggest that seawater is introduced into the crust by way of small cracks and veins that mark the end of the ductile phase of deformation. This "deformation-enhanced" metamorphism dominates the upper 180 and the lower 100 m of the core.
In the lower 300 m of the core, mineral assemblages of greenschist and zeolite facies are abundant within or adjacent to brecciated zones. Leucocratic veins found in these zones and adjacent host rock contain diopside, sodic plagioclase, epidote, chlorite, analcime, thomsonite, natrolite, albite, quartz, actinolite, sphene, brookite, and sulfides. The presence of zircon, Cl-apatite, sodic plagioclase, sulfides, and diopside in leucocratic veins having local magmatic textures suggests that some of the veins originated from late magmas or from hydrothermal fluids exsolved from such magmas that were subsequently replaced by (seawater-derived) hydrothermal assemblages. The frequent association of these late magmatic intrusive rocks within the brecciated zones suggests that they are both artifacts of magmatic hydrofracture. Such catastrophic fracture and hydrothermal circulation could produce episodic venting of hydrothermal fluids as well as the incorporation of a magmatically derived hydrothermal component. The enhanced permeability of the brecciated zones produced lower temperature assemblages because of larger volumes of seawater that penetrated the crust. The last fractures were sealed either by these hydrothermal minerals or by late carbonate-smectite veins, resulting in the observed low permeability of the core.
Project(s):
Ocean Drilling Program (ODP)
Coverage:
Latitude: -32.724000 * Longitude: 57.266200
Date/Time Start: 1987-12-06T04:45:00 * Date/Time End: 1987-12-11T01:00:00
Event(s):
118-735B * Latitude: -32.724000 * Longitude: 57.266200 * Date/Time Start: 1987-12-06T04:45:00 * Date/Time End: 1987-12-11T01:00:00 * Elevation: -731.0 m * Penetration: 500.7 m * Recovery: 434.81 m * Location: South Indian Ridge, South Indian Ocean * Campaign: Leg118 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 88 cores; 500.7 m cored; 0 m drilled; 86.8 % recovery
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
9 datasets

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Datasets listed in this publication series

  1. Stakes, DS; Mével, C; Cannat, M et al. (1991): (Table 6) Representative amphibole compositions from metagabbros and late magmatic intrusives from ODP Hole 118-735B. https://doi.org/10.1594/PANGAEA.757678
  2. Stakes, DS; Mével, C; Cannat, M et al. (1991): (Table 1) Oxygen isotope ratios of whole rock and minerals of ODP Hole 118-735B. https://doi.org/10.1594/PANGAEA.757672
  3. Stakes, DS; Mével, C; Cannat, M et al. (1991): (Table 7) Mica, chlorite, and talc compositions from metamorphosed gabbros and late magmatic intrusions of ODP Hole 118-735B. https://doi.org/10.1594/PANGAEA.757679
  4. Stakes, DS; Mével, C; Cannat, M et al. (1991): (Table 9) Representative olivine analyses from metagabbros from ODP Hole 118-735B. https://doi.org/10.1594/PANGAEA.757681
  5. Stakes, DS; Mével, C; Cannat, M et al. (1991): (Table 5) Representative plagioclase compositions from metagabbroic rocks and late magmatic intrusives of ODP Hole 118-735B. https://doi.org/10.1594/PANGAEA.757677
  6. Stakes, DS; Mével, C; Cannat, M et al. (1991): (Table 2) Pyroxene prophyroclasts and neoblasts from deformed gabbros and magmatic pyroxenes from the late magmatic intrusives of ODP Hole 118-735B. https://doi.org/10.1594/PANGAEA.757673
  7. Stakes, DS; Mével, C; Cannat, M et al. (1991): (Table 3) Pyroxene compositions from breccias and veins of ODP Hole 118-735B. https://doi.org/10.1594/PANGAEA.757674
  8. Stakes, DS; Mével, C; Cannat, M et al. (1991): (Table 4) Pyroxene compositions for temperature calculations of granulite grade metamorphism associated with ductile deformation of ODP Hole 118-735B. https://doi.org/10.1594/PANGAEA.757675
  9. Stakes, DS; Mével, C; Cannat, M et al. (1991): (Table 8) Representative analyses of zeolithes and epidotes from ODP Hole 118-735B. https://doi.org/10.1594/PANGAEA.757680