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Title: Southern Juan De Fuca Ridge and Escanaba Trough, Gorda Ridge: Comparison of hydrothermal deposits in sediment-free and sediment-covered ridge settings

Abstract

Southern Juan De Fuca Ridge (SJDF) is a low-relief, sediment-starved ridge axis that has a total opening rate of 6 cm/year and is characterized by lobate and brecciated sheet flows and pillows of MORB composition. Sulfide deposits form at {approximately}2,200 m water depth and are concentrated within a narrow graben centered within the ridge axial valley. Solitary and coalesced chimneys (0.25 to 12 m high) rise directly from the basalt basement and are composed predominantly of Zn sulfide accompanied by Fe and Cu-Fe sulfide and traces of Pb sulfide. Anhydrite occurs as a minor phase in some chimneys. Sulfide chimneys were formed by rapid-venting of high temperature ({approximately}285{degree}C) fluids. These acidic fluids (pH {approximately}3.5) are enriched in Cl, Na, and Ca and are depleted in Cu and Zn. In contrast to SJDF, Escanaba Trough (ET) is spreading at {approximately}2.3 cm/year and has the high relief and axial graben morphology typical of the slow-spreading Mid-Atlantic Ridge. The floor of the axial valley is buried by up to 500 m of clay and terrigenous silt. Rare basement exposures reveal unbrecciated sheet flows and pillow basalts of MORB composition. Large chimney-topped sulfide mounds up to 20 m high and hundreds of meters inmore » extent occur at {approximately}3,250 m water depth at the base of sediment hills; sulfide veins, small chimneys, and clastic deposits occur on, and within, the sediment between hills. Two distinct sulfide types occur at ET. Pyrrhotite-rich sulfide is enriched in Fe, Cu, and As and is associated with low-velocity venting of warm (<220{degree} C) alkaline (pH {approximately}5.4) fluids that are currently depositing anhydrite and barite sinter deposits on top of the sulfide mounds.« less

Authors:
; ; ;  [1]
  1. Geological Survey, Menlo Park, CA (USA)
Publication Date:
OSTI Identifier:
6317651
Report Number(s):
CONF-900702-
Journal ID: ISSN 0149-1423; CODEN: AABUD
Resource Type:
Conference
Journal Name:
AAPG Bulletin (American Association of Petroleum Geologists); (USA)
Additional Journal Information:
Journal Volume: 74:6; Conference: 5. Circum-Pacific energy and mineral resources conference, Honolulu, HI (USA), 29 Jul - 3 Aug 1990; Journal ID: ISSN 0149-1423
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; SEA BED; GEOLOGIC DEPOSITS; ANHYDRITE; ANTIMONY; ARSENIC; BISMUTH; CALCIUM; COPPER; IRON; PH VALUE; PYRRHOTITE; SODIUM; SULFIDE MINERALS; TIN; ZINC; ALKALI METALS; ALKALINE EARTH METAL COMPOUNDS; ALKALINE EARTH METALS; CALCIUM COMPOUNDS; CALCIUM SULFATES; CHALCOGENIDES; ELEMENTS; IRON COMPOUNDS; IRON SULFIDES; METALS; MINERALS; OXYGEN COMPOUNDS; SEMIMETALS; SULFATE MINERALS; SULFATES; SULFIDES; SULFUR COMPOUNDS; TRANSITION ELEMENT COMPOUNDS; TRANSITION ELEMENTS; 580000* - Geosciences

Citation Formats

Benninger, L M, Randolph, M, Koski, A, and Zierenberg, R A. Southern Juan De Fuca Ridge and Escanaba Trough, Gorda Ridge: Comparison of hydrothermal deposits in sediment-free and sediment-covered ridge settings. United States: N. p., 1990. Web.
Benninger, L M, Randolph, M, Koski, A, & Zierenberg, R A. Southern Juan De Fuca Ridge and Escanaba Trough, Gorda Ridge: Comparison of hydrothermal deposits in sediment-free and sediment-covered ridge settings. United States.
Benninger, L M, Randolph, M, Koski, A, and Zierenberg, R A. 1990. "Southern Juan De Fuca Ridge and Escanaba Trough, Gorda Ridge: Comparison of hydrothermal deposits in sediment-free and sediment-covered ridge settings". United States.
@article{osti_6317651,
title = {Southern Juan De Fuca Ridge and Escanaba Trough, Gorda Ridge: Comparison of hydrothermal deposits in sediment-free and sediment-covered ridge settings},
author = {Benninger, L M and Randolph, M and Koski, A and Zierenberg, R A},
abstractNote = {Southern Juan De Fuca Ridge (SJDF) is a low-relief, sediment-starved ridge axis that has a total opening rate of 6 cm/year and is characterized by lobate and brecciated sheet flows and pillows of MORB composition. Sulfide deposits form at {approximately}2,200 m water depth and are concentrated within a narrow graben centered within the ridge axial valley. Solitary and coalesced chimneys (0.25 to 12 m high) rise directly from the basalt basement and are composed predominantly of Zn sulfide accompanied by Fe and Cu-Fe sulfide and traces of Pb sulfide. Anhydrite occurs as a minor phase in some chimneys. Sulfide chimneys were formed by rapid-venting of high temperature ({approximately}285{degree}C) fluids. These acidic fluids (pH {approximately}3.5) are enriched in Cl, Na, and Ca and are depleted in Cu and Zn. In contrast to SJDF, Escanaba Trough (ET) is spreading at {approximately}2.3 cm/year and has the high relief and axial graben morphology typical of the slow-spreading Mid-Atlantic Ridge. The floor of the axial valley is buried by up to 500 m of clay and terrigenous silt. Rare basement exposures reveal unbrecciated sheet flows and pillow basalts of MORB composition. Large chimney-topped sulfide mounds up to 20 m high and hundreds of meters in extent occur at {approximately}3,250 m water depth at the base of sediment hills; sulfide veins, small chimneys, and clastic deposits occur on, and within, the sediment between hills. Two distinct sulfide types occur at ET. Pyrrhotite-rich sulfide is enriched in Fe, Cu, and As and is associated with low-velocity venting of warm (<220{degree} C) alkaline (pH {approximately}5.4) fluids that are currently depositing anhydrite and barite sinter deposits on top of the sulfide mounds.},
doi = {},
url = {https://www.osti.gov/biblio/6317651}, journal = {AAPG Bulletin (American Association of Petroleum Geologists); (USA)},
issn = {0149-1423},
number = ,
volume = 74:6,
place = {United States},
year = {Fri Jun 01 00:00:00 EDT 1990},
month = {Fri Jun 01 00:00:00 EDT 1990}
}

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