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Alt, Jeffrey C; France-Lanord, Christian; Floyd, Peter A; Castillo, Paterno R; Galy, Albert (1992): Chemistry of low-temperature hydrothermal altered basement of ODP Site 129-801 [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.779207, Supplement to: Alt, JC et al. (1992): Low-temperature hydrothermal alteration of Jurassic ocean crust, Site 801. In: Larson, RL; Lancelot, Y; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 129, 415-427, https://doi.org/10.2973/odp.proc.sr.129.132.1992

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Abstract:
Low-temperature hydrothermal alteration of basement from Site 801 was studied through analyses of the mineralogy, chemistry, and oxygen isotopic compositions of the rocks. The more than 100-m section of 170-Ma basement consists of 60 m of tholeiitic basalt separated from the overlying 60 m of alkalic basalts by a >3-m-thick Fe-Si hydrothermal deposit. Four alteration types were distinguished in the basalts: (1) saponite-type (Mg-smectite) rocks are generally slightly altered, exhibiting small increases in H2O, d18O, and oxidation; (2) celadonite-type rocks are also slightly altered, but exhibit uptake of alkalis in addition to hydration and oxidation, reflecting somewhat greater seawater/rock ratios than the saponite type; (3) Al-saponite-type alteration resulted in oxidation, hydration, and alkali and 18O uptake and losses of Ca and Na due to the breakdown of plagioclase and clinopyroxene; and (4) blue-green rocks exhibit the greatest chemical changes, including oxidation, hydration, alkali uptake, and loss of Ca, Na, and Mg due to the complete breakdown of plagioclase and olivine to K-feldspar and phyllosilicates.
Saponite- and celadonite-type alteration of the tholeiite section occurred at a normal mid-ocean ridge basalt spreading center at temperatures <20°C. Near- or off-axis intrusion of an alkali basalt magma at depth reinitiated hydrothermal circulation, and the Fe-Si hydrothermal deposit formed from cool (<60°C) distal hydrothermal fluids. Focusing of fluid flow in the rocks immediately underlying the deposit resulted in the extensive alteration of the blue-green rocks at similar temperatures. Al-saponite alteration of the subsequent alkali basalts overlying the deposit occurred at relatively high water/rock ratios as part of the same low-temperature circulation system that formed the hydrothermal deposit. Abundant calcite formed in the rocks during progressive "aging" of the crust during its long history away from the spreading center.
Project(s):
Ocean Drilling Program (ODP)
Coverage:
Median Latitude: 18.642250 * Median Longitude: 156.359783 * South-bound Latitude: 18.642000 * West-bound Longitude: 156.359700 * North-bound Latitude: 18.642300 * East-bound Longitude: 156.359800
Date/Time Start: 1989-12-09T17:00:00 * Date/Time End: 1990-01-16T07:15:00
Event(s):
129-801B * Latitude: 18.642000 * Longitude: 156.359700 * Date/Time Start: 1989-12-09T17:00:00 * Date/Time End: 1989-12-17T01:15:00 * Elevation: -5685.0 m * Penetration: 511.2 m * Recovery: 59.17 m * Location: North Pacific Ocean * Campaign: Leg129 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 44 cores; 317.2 m cored; 0 m drilled; 18.7 % recovery
129-801C * Latitude: 18.642300 * Longitude: 156.359800 * Date/Time Start: 1990-01-06T11:48:00 * Date/Time End: 1990-01-16T07:15:00 * Elevation: -5685.0 m * Penetration: 594.3 m * Recovery: 60.6 m * Location: North Pacific Ocean * Campaign: Leg129 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 12 cores; 100.6 m cored; 0 m drilled; 60.2 % recovery
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
3 datasets

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Datasets listed in this publication series

  1. Alt, JC; France-Lanord, C; Floyd, PA et al. (1992): (Table 3) Oxygen and carbon isotopic composition of carbonates and silicates of ODP Site 129-801. https://doi.org/10.1594/PANGAEA.779206
  2. Alt, JC; France-Lanord, C; Floyd, PA et al. (1992): (Table 2) Chemical analyses of the hydrothermal deposit and interpillow material from ODP Hole 129-801C. https://doi.org/10.1594/PANGAEA.779204
  3. Alt, JC; France-Lanord, C; Floyd, PA et al. (1992): (Table 1) Chemistry of secondary phyllosilicates in ODP Hole 129-801C basement. https://doi.org/10.1594/PANGAEA.779202