Metabasalts, axial hot springs, and the structure of hydrothermal systems at mid-ocean ridges

Abstract

Research Article| February 01, 1983 Metabasalts, axial hot springs, and the structure of hydrothermal systems at mid-ocean ridges MICHAEL J. MOTTL MICHAEL J. MOTTL 1Department of Chemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar Author and Article Information MICHAEL J. MOTTL 1Department of Chemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1983) 94 (2): 161–180. https://doi.org/10.1130/0016-7606(1983)94<161:MAHSAT>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation MICHAEL J. MOTTL; Metabasalts, axial hot springs, and the structure of hydrothermal systems at mid-ocean ridges. GSA Bulletin 1983;; 94 (2): 161–180. doi: https://doi.org/10.1130/0016-7606(1983)94<161:MAHSAT>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid-ocean ridge. Studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the Mid-Atlantic Ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy, mineral abundances, and mineral compositions, especially for chlorite. These relationships can be interpreted in terms of the distribution of alteration with respect to time, temperature, and water/rock ratio in young crust. Assemblages of chl-ab-ep-act, chl-ab-ep-act-qtz, chl-ab-qtz, and chl-qtz are produced at successively higher effective sea-water to rock ratios within the temperature range of the greenschist facies (−250 to 450 °C). Toward higher ratios, chlorites tend to become more Mg-rich. Pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending, rather than the ascending, limb of a convection system; this type of alteration, which reflects moderately high water/rock ratios, may characteristically occur above a still partially molten magma chamber. As the magma chamber solidifies and is then penetrated, more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water/rock ratios, producing solutions such as those recovered from springs on the Galapagos Rift and the East Pacific Rise at 21°N. Localized upwelling limbs of the convection system can produce veins filled with quartz, sulfides, and Fe-rich chlorite. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.