DOCSLIB.ORG

Deep-Tow Studies of the Structure of the Mid-Atlantic Ridge Crest Near Lat 37°N

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Deep-Tow Studies of the Structure of the Mid-Atlantic Ridge Crest Near Lat 37°N Deep-tow studies of the structure of the Mid-Atlantic Ridge crest near lat 37°N KEN C. MACDONALD* Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, La Jolla, California 92093 BRUCE P. LUYENDYK Department of Geological Sciences, University of California, Santa Barbara, California 93106 This article is one of a series appearing in the April and May issues of the Geological Society of America Bulletin on the scientific results of Project FAMOUS. These studies were undertaken in the axial area of the Mid-Atlantic Ridge between approximately 36°30' and 37°N latitudes. ABSTRACT large faulted blocks toward nearby fracture Le Pichon, 1974). We discuss here the de- zones suggests that spreading-center tec- tailed structure and evolution of the rift val- A detailed study of the structure of the tonics is affected by fracture-zone tectonics leys between fracture zones A and B (rift Mid-Atlantic Ridge median valley and rift throughout the length of the rift in the valley 2) and B and C (rift valley 3) and the mountains near lat 37°N (FAMOUS) was FAMOUS area. Both the crustal accretion rift mountains in these areas. Fine-scale conducted using a deep-tow instrument zone and transform fault zone are narrow, deep-tow studies of the inner floor of rift package. The median valley may have either only 1 to 2 km wide, over short periods of valley 2 are discussed by Luyendyk and a very narrow inner floor (1 to 4 km) and time. In the course of millions of years, how- Macdonald (1977). Studies of near-bottom well-developed terraces or a wide inner floor ever, they apparently migrate over a zone 10 magnetic anomalies and a tectonic synthesis (10 to 14 km) and narrow or no terraces. to 20 km wide. of rift valleys 2 and 3 are presented by The terraces appear to be non-steady-state Macdonald (1977). features of the rift valley. The entire depth OBJECTIVES and gross morphology of the median valley SETTING may be accounted for by normal faulting, Recently, several detailed surveys have while volcanic relief contributes to the been made on the Mid-Atlantic Ridge (at lat The FAMOUS area lies south of the short-wavelength topography (<2 km). 45°N, Aumento and others, 1971; at lat Azores triple junction on the North Most faults dip toward the valley axis an 37°N, Needham and Francheteau, 1974; American-African plate boundary (Fig. average of 50°, and the blocks are tilted back and at lat 26°N, McGregor and Rona, 1A). Rotation of magnetic anomalies about 2° to 3°. Fault dip is asymmetric about the 1975). However, the limitations of wide- the North America-Africa pole of opening valley axis. Active crustal extension in the beam echo sounders and other conventional and absence of a distinct median valley in- inner floor and inner walls has the same geophysical tools have made it difficult to dicate that the ridge crest is influenced by sense of asymmetry as the local spreading investigate the fine-scale structure and tec- triple-junction tectonics as far south as lat rates, reaching a maximum of 18 percent. tonics of the median valley and rift moun- 38°N (J. D. Phillips and H. S. Fleming, in Thus, asymmetric spreading appears to be tains. Several fundamental problems have prep.). South of lat 38°N, however, the me- accomplished by asymmetric crustal exten- remained unsolved: (1) the width and mor- dian valley is well defined, and magnetic sion on a fine scale as well as by asymmetric phologic expression of the crustal accretion anomalies 2' prime and 5 overlap properly crustal accretion. Spreading is 17° oblique to zone within the median valley, (2) the roles when rotated back about the pole of open- the transform faults and shows no indication of volcanism and faulting in creating relief ing. The part of the ridge studied consists of of readjusting to an orthogonal system, even in the median valley and in the rift moun- two segments, each 40 km long, trending on a fine scale. Eighty percent of the decay or tains, (3) the morphologic and structural N17°E (Figs. 1A, IB). Fracture zones A, B, transformation of median-valley relief into expression of asymmetric and oblique and C each right-laterally offset the valley rift-mountain topography is accomplished spreading, (4) the degree of horizontal ex- about 20 km and trend east. Spreading is by normal faults that dip away from the tension of crust within the plate-boundary currently 17° oblique, and detailed studies valley axis. Most of the outward-facing zone, (5) the tectonic interaction between of the tectonic and magnetic trends in the faulting occurs near the median-valley- transform faults and spreading centers, (6) inner floor of the rift suggest that the rift-mountain boundary. Tilting of crustal the relationship between microearthquakes spreading is stably oblique—that is, the blocks accounts for only 20 percent of the and the fine-scale structure of ridge crests, ridge is not readjusting to an orthogonal decay of median-valley relief. Most long- and (7) the evolution of the median valley configuration (Macdonald, 1977; Luyen- wavelength topography in the rift moun- into the relief of the rift mountains. dyk and Macdonald, 1977). Oblique tains has a faulted origin. As in the median To address these problems, a near- spreading may have been stable here for at valley, volcanic relief is short wavelength bottom geophysical study of the Mid- least 6 m.y., even through a change in (<2 km) and appears to be fossil, originating Atlantic Ridge near lat 37°N was conducted spreading direction (Macdonald, 1977). In in the median-valley inner floor. Bending of from the R/V Knorr (cruise 31) of the addition, spreading is highly asymmetric in Woods Hole Oceanographic Institution, rift valley 2, with rates of 7.0 mm/yr to the using the deep-tow instrument package of west and 13.4 mm/yr to the east. At 1.7 the Marine Physical Laboratory (Scripps m.y. B.P., the sense of asymmetry reversed, * Present address: Marine Physical Laboratory and with rates of 13.3 mm/yr to the west and Geological Research Division, Scripps Institution of Institution of Oceanography). This effort is Oceanography, La Jolla, California 92093. part of the FAMOUS project (Heirtzler and 10.8 mm/yr to the east (Macdonald, 1977). Geological Society of America Bulletin, v. 88, p. 621-636, 16 figs., May 1977, Doc. no. 70502. 621 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/88/5/621/3418363/i0016-7606-88-5-621.pdf by guest on 23 September 2021 622 MACDONALD AND LUYENDYK 38°W Figure 1A. Regional setting and plate boundaries in FAMOUS area (unpub. U. S. Navy bathymetric chart, courtesy of J. Phillips and W. Perry). E-E'" is long deep-tow traverse into eastern rift mountains. FZ=Fracture zone. Spreading is only slightly asymmetric in rift tains is discussed here first. Rift valley 3, looking sonar has a range of 400 to 700 m valley 3, with rates of 9.8 mm/yr to the west which has a much wider inner floor than rift to either side, resulting in an effective search and 10.6 mm/yr to the east (Macdonald, valley 2, is discussed for comparison. path approximately 1 km wide. The side- 1977). looking sonar is particularly effective in Most of the FAMOUS investigations, in- DATA INTERPRETATION mapping linear scarps on a small scale and cluding use of manned submersibles, have is useful in determining the linearity of fea- focused on rift valley 2 (Fig. IB) (Reid and The structural studies are based on in- tures. We (Luyendyk and Macdonald, Macdonald, 1973; Needham and Fran- terpretation of three types of deep-tow 1977) discuss photographic data, and cheteau, 1974; Macdonald and others, sonar records: high-frequency (40 kHz) (Macdonald, 1977) discusses near-bottom 1975; Laughton and Rusby, 1975; Bel- narrow-beam sonar for depth, low- magnetic data. laiche and others, 1974; Moore and others, frequency (4.0 kHz) sonar for sediment Within the outer walls of the median val- 1974; ARCYANA, 1975; Ballard and penetration, and left and right side-looking ley the fish was navigated using bottom- others, 1975; Ballard and van Andel, 1977; sonar (110 kHz) (Spiess and Tyce, 1973). moored acoustic transponders (Spiess and Bryan and Moore, 1977; Luyendyk and When the fish is towed at normal heights Tyce, 1973). Relative accuracy is 10 to 50 Macdonald, 1977; Macdonald, 1977). Rift above bottom (50 to 150 m), the 40-kHz m. Outside the transponder net the fish was valley 3 has also been studied but in some- sonar can track slopes greater than 70°, as tracked using satellite navigation and a what less detail (Laughton and Rusby, verified by submersible observations of the cable trajectory program by Ivers and 1975; Macdonald, 1977; Ramberg and van same scarps (FAMOUS dive team, 1975, Mudie (1973), for which accuracy is 500 to Andel, 1977; J. D. Phillips and H. S. Flem- personal commun.). The 4.0-kHz sonar re- 1,000 m. Location relative to latitude and ing, in prep.). The deep-tow studies concen- liably penetrates and detects sediment longitude was determined by comparing trating on rift valley 2 and the rift moun- thicknesses from 5 to 100 m. The side- some 40 satellite fixes with transponder- Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/88/5/621/3418363/i0016-7606-88-5-621.pdf by guest on 23 September 2021 STRUCTURE OF MID-ATLANTIC RIDGE CREST 623 Inner Walls The inner floor is bounded by the inner walls (Figs.
Load more

Recommended publications
  • 38. Effect of Axial Magma Chambers Beneath Spreading Centers on the Compositions of Basaltic Rocks
    38. EFFECT OF AXIAL MAGMA CHAMBERS BENEATH SPREADING CENTERS ON THE COMPOSITIONS OF BASALTIC ROCKS James H. Natland, Scripps Institution of Oceanography, La Jolla, California ABSTRACT Ferrobasalts are among a range of basalt types erupted over large, shallow, axial magma chambers beneath the East Pacific Rise crest near 9°N, and the Galapagos Rift near 86°W. Geological and geo- chemical evidence indicates that they evolve in small, isolated magma bodies either in conduit systems over the chambers, or in the solidify- ing walls of the magma chamber flanks away from the loci of fissure eruptions. The chambers act mainly as buffers in which efficient mix- ing ensures that a uniform average, moderately fractionated parent is supplied to the range of magma types erupted at the sea floor. For- mation of ferrobasalts in isolated magma bodies prevents them from mixing directly with primitive olivine tholeiite supplied to the base of the East Pacific Rise magma chamber at 9°N. Rises with abundant ferrobasalts may have magma chambers with broad, flat tops over which eruptions occur in wide, probably struc- turally unstable rift zones. Rises without ferrobasalts may have magma chambers with tapered tops which persistently constrain eruptions to narrow fissure zones, preventing formation of isolated shallow magma bodies where ferrobasalts can evolve. Formation of a flat-topped, rather than a tapered, magma chamber may reflect a high rate of magma supply relative to spreading rate. Steady-state compositions can be approached in magma cham- bers, probably approximating the least-fractionated typical lavas erupted above them. On this basis, the bulk magma composition in the chamber beneath the Galapagos Rift has become more iron-rich through time, a consequence of magma migration eastward down the rift as it shoaled to the west under the influence of the Galapagos Island hot spot.
    [Show full text]
  • Ocean-Bottom Seismograph Observations on the Mid-Atlantic Ridge Near Lat 37°N
    Ocean-bottom seismograph observations on the Mid-Atlantic Ridge near lat 37°N T.J.G. FRANCIS* Cooperative Institute for Research in Environmental Sciences, University of ColoradolNOAA, Boulder, Col- orado 80309 I. T. PORTER Institute of Oceanographic Sciences, Blacknest, Brimpton, Reading, RG7 4TJ England J. R. McGRATH U.S. Naval Research Laboratory, Washington, D.C. 20390 This article is one of a series appearing in the April and May issues of the Geological Society of America Bulletin on the scientific results of Project FAMOUS. These studies were undertaken in the axial area of the Mid-Atlantic Ridge between approximately 36°30' and 37°N latitudes. ABSTRACT 200 Hz. The tape speed of the recording system used by the ocean-bottom seismographs set an upper limit of about 40 Hz to Ocean-bottom seismographs were deployed twice in the FA- the frequencies recorded. It was decided to retain the original hyd- MOUS area in 1973. Few earthquakes were observed on the first rophones of the seismographs as well to be able to compare the per- occasion, but 515 were recorded on the second with magnitudes formance of the two systems. Since only four data channels can be ranging from 0 to 2.5. These occurred both in the median valley recorded in each ocean-bottom seismograph, the H-58 hydrophone and in the fracture zone adjacent to the instruments. The latter was substituted for one of the horizontal seismometers. Thus dur- events have been interpreted as activity along a single Riedel frac- ing the October 1973 deployment, each instrument recorded the ture cutting obliquely across the trend of the fracture zone.
    [Show full text]
  • Spatial and Temporal Distribution of Seismicity Along the Northern Mid-Atlantic Ridge (15°–35°N) Deborah K
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. B3, 2167, doi:10.1029/2002JB001964, 2003 Spatial and temporal distribution of seismicity along the northern Mid-Atlantic Ridge (15°–35°N) Deborah K. Smith,1 Javier Escartin,2 Mathilde Cannat,2 Maya Tolstoy,3 Christopher G. Fox,4 DelWayne R. Bohnenstiehl,3 and Sara Bazin2 Received 8 May 2002; revised 16 September 2002; accepted 8 November 2002; published 25 March 2003. [1] A detailed investigation of the relationship between the spatial and temporal patterns of the seismic activity recorded by six autonomous hydrophones and the structure of the northern Mid-Atlantic Ridge between 15° and 35°N is presented. Two years of monitoring yielded a total of 3485 hydroacoustically detected events within the array recorded by four or more hydrophones. The seismically active zone extends 20 km to either side of the ridge axis, consistent with earlier results from studies of fault morphology. Along the axis, hydrophone-recorded activity shows important variations. Areas with intense and persistent seismic activity (stripes) stand in sharp contrast to areas that lack seismicity (gaps). The regions of persistent activity are a new observation at mid-ocean ridges. In general, the patterns of seismically active/inactive regions are also recognized in the 28-year teleseismic record, implying that these patterns are maintained at timescales between a few years and a few decades. We find no simple relationship between individual segment variables (e.g., length or trend of the segment, maximum offset of discontinuities, or along-axis change in mantle Bouguer anomaly (MBA) and water depths) and number of hydrophone-recorded events.
    [Show full text]
  • WOODS HOLE OCEANOGRAPHIC INSTITUTION Deep-Diving
    NEWSLETTER WOODS HOLE OCEANOGRAPHIC INSTITUTION AUGUST-SEPTEMBER 1995 Deep-Diving Submersible ALVIN WHOI Names Paul Clemente Sets Another Dive Record Chief Financial Officer The nation's first research submarine, the Deep Submergence Paul CI~mente, Jr., a resident of Hingham Vehicle (DSV) Alvin. passed another milestone in its long career and former Associate Vice President for September 20 when it made its 3,OOOth dive to the ocean floor, a Financial Affairs at Boston University, as· record no other deep-diving sub has achieved. Alvin is one of only sumed his duties as Associate Director for seven deep-diving (10,000 feet or more) manned submersibles in the Finance and Administration at WHOI on world and is considered by far the most active of the group, making October 2. between 150 and 200 dives to depths up to nearly 15,000 feet each In his new position Clemente is respon· year for scientific and engineering research . sible for directing all business and financial The 23-1001, three-person submersible has been operated by operations of the Institution, with specifIC Woods Hole Oceanographic Institution since 1964 for the U.S. ocean resp:>nsibility for accounting and finance, research community. It is owned by the OffICe of Naval Research facilities, human resources, commercial and supported by the Navy. the National Science Foundation and the affairs and procurement operations. WHOI, National Oceanic and Atmospheric Administration (NOAA). Alvin the largest private non· profit marine research and its support vessel, the 21 0-100t Research Vessel Atlantis II, are organization in the U.S., has an annual on an extended voyage in the Pacific which began in January 1995 operating budget of nearly $90 million and a with departure from Woods Hole.
    [Show full text]
  • Petrogenetic Study of the Porcupine Lake Mafic Intrusive Complex, Trinity Terrane, Northern California
    UNLV Retrospective Theses & Dissertations 1-1-2000 Petrogenetic study of the Porcupine Lake mafic intrusive complex, Trinity terrane, northern California Edward Robert Muller University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/rtds Repository Citation Muller, Edward Robert, "Petrogenetic study of the Porcupine Lake mafic intrusive complex, Trinity terrane, northern California" (2000). UNLV Retrospective Theses & Dissertations. 1171. http://dx.doi.org/10.25669/tnq4-ppc2 This Thesis is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Thesis has been accepted for inclusion in UNLV Retrospective Theses & Dissertations by an authorized administrator of Digital Scholarship@UNLV. For more information, please contact [email protected]. INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter ^ ce , while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy subm itted. Broken or irxlistnct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction.
    [Show full text]
  • Trailblazer in the Ocean Depths Alvin Celebrates 50 Years of Pioneering Accomplishments by Kate Madin and Lonny Lippsett
    The History Trailblazer in the Ocean Depths ALVIN CELEBRATES 50 YEARS OF PIONEERING ACCOMPLISHMENTS by Kate Madin and Lonny Lippsett Jan Hahn/WHOI Draped in bunting and with a Navy brass band playing, the new research submersible Alvin was commissioned at the Woods Hole Oceanographic Institution dock on June 5, 1964. his years marks the 50th anniversary of two of America’s WHOI dock. Over its first half century, it responded to nation- most iconic, cutting-edge vehicles: the Ford Mustang, and al crises, recovered a lost hydrogen bomb and investigated the another vehicle that was hardly sleek or stylish and didn’t impacts of the Deepwater Horizon oil spill. It helped document have a bold, jazzy name. Three years after President John the world’s most famous shipwreck. It revealed seafloor terrain F. Kennedy committed the nation to the goal of “land- that scientists never imagined. It discovered unexpected deep- ing a man on the moon and returning him safely to the sea life thriving without sunlight, revolutionizing our under- Earth”—andT five years before we did so—a stubby white sub- standing of where and how life could exist on Earth and other mersible was built with the goal of taking people to the bottom planetary bodies. It inspired the development of new genera- of the ocean and returning them safely to the surface: Alvin. tions of deep-submergence technology and vehicles, as well as Owned by the Navy and operated by Woods Hole Oceano- generations of future scientists, engineers, and explorers. graphic Institution (WHOI), Alvin was officially commissioned Much has already been written about Alvin, but a brief retelling June 5, 1964, in a ceremony attended by hundreds at the of its story seems appropriate to celebrate the sub’s 50th birthday.
    [Show full text]
  • This Dynamic Earth in January of 1992
    View of the planet Earth from the Apollo spacecraft. The Red Sea, which separates Saudi Arabia from the continent of Africa, is clearly visible at the top. (Photograph courtesy of NASA.) Contents Preface Historical perspective Developing the theory Understanding plate motions "Hotspots": Mantle Some unanswered questions Plate tectonics and people Endnotes thermal plumes 1 of 77 2002-01-01 11:52 This pdf-version was edited by Peter Lindeberg in December 2001. Any deviation from the original text is non-intentional. This book was originally published in paper form in February 1996 (design and coordination by Martha Kiger; illustrations and production by Jane Russell). It is for sale for $7 from: U.S. Government Printing Office Superintendent of Documents, Mail Stop SSOP Washington, DC 20402-9328 or it can be ordered directly from the U.S. Geological Survey: Call toll-free 1-888-ASK-USGS Or write to USGS Information Services Box 25286, Building 810 Denver Federal Center Denver, CO 80225 303-202-4700; Fax 303-202-4693 ISBN 0-16-048220-8 Version 1.08 The online edition contains all text from the original book in its entirety. Some figures have been modified to enhance legibility at screen resolutions. Many of the images in this book are available in high resolution from the USGS Media for Science page. USGS Home Page URL: http://pubs.usgs.gov/publications/text/dynamic.html Last updated: 01.29.01 Contact: [email protected] 2 of 77 2002-01-01 11:52 In the early 1960s, the emergence of the theory of plate tectonics started a revolution in the earth sciences.
    [Show full text]
  • 98-031 Oceanus F/W 97 Final
    Emory Kristoff, © National Geographic Society Geographic © National Emory Kristoff, Tanya Atwater (right) and R/V Knorr shipmate look over mid-ocean ridge rocks. The Women of FAMOUS Remembrance of Times Past Kathryn D. Sullivan President & CEO, Center of Science & Industry (COSI), Columbus, Ohio visited the research vessel Knorr during a Woods Hole commonplace in the early 1970s. Knorr’s scientific rosters port call in May 1997, twenty-three years almost to the show that 38 people sailed as members of the scientific I day since Paul Johnson (now at the University of Wash- parties during the various FAMOUS voyages. The eight ington) and I had first gone aboard the ship to install women among them probably represent the first significant paleomagnetics equipment that Dalhousie University had female participation at sea in a large oceanographic pro- committed to Project FAMOUS (French-American Mid- gram. We were quite a diverse group. All of us had been to Ocean Undersea Study). Knorr has been stretched since sea before, but our experience level varied from that of se- then, and is no longer propelled by cycloids, but the labs nior technical staff (like Helen Hays and Rosamund Corr) to and passageways were still familiar enough to bring back very junior graduate students (Margaret Leinen, Pat vivid memories. McGraw, and Kathy Sullivan). Our jobs included surveying, My FAMOUS story begins during my first year in graduate coring and dredging, data and sample logging, subsampling, school at Dalhousie University in Nova Scotia. I was develop- and initial analysis. I’m sure we all dreamt of diving in Alvin, ing a thesis proposal to study the but that was not to be.
    [Show full text]
  • Volume 31, Number 4, Winter 1988/89
    Volume 31, Number 4, Winter 1988/89 mm Oceanus" ISSN 0029-8182 The International Magazine of Marine Science and Policy Volume 31, Number 4, Winter 1988/89 Frederic Golden, Acting Editor T. M. Hawley, Assistant Editor Sara L. Ellis, Editorial Assistant Plummy K. Tucker, Intern Editorial Advisory Board 1930 James M. Broadus, Director, Marine Policy Center, Woods Hole Oceanographic Institution Henry Charnock, Professor of Physical Oceanography, University of Southampton, England Gotthilf Hempel, Director of the Alfred Wegener Institute for Polar Research, West Germany Charles D. Hollister, Dean of Graduate Studies, Woods Hole Oceanographic Institution John Imbrie, Henry L. Doherty Professor of Oceanography, Brown University John A. Knauss, Professor of Oceanography, University of Rhode Island Arthur E. Maxwell, Director of the Institute for Geophysics, University of Texas Timothy R. Parsons, Professor, Institute of Oceanography, University of British Columbia, Canada Allan R. Robinson, Gordon McKay Professor of Geophysical Fluid Dynamics, Harvard University David A. Ross, Chairman, Department of Geology and Geophysics, and Sea Grant Coordinator, Woods Hole Oceanographic Institution Permission to photocopy for internal or personal use or the internal or personal use of the Hole Institution Published by Woods Oceanographic specific clients is granted by Oceanus magazine to libraries and other users registered Guy W. Nichols, Chairman, Board of Trustees with the Copyright Clearance James S. Coles, President of the Associates Center (CCC), provided that the base fee of $2.00 per copy of the article, plus .05 per page is paid directly to CCC, John H. Steele, President of the Corporation 21 Congress Street, Salem, MA and Director of the Institution 01970.
    [Show full text]
  • RAINBOW to LUCKY STRIKE an Integrated Studies Site Proposal For
    MID-ATLANTIC RIDGE 36° 10'N – 37° 50'N: RAINBOW TO LUCKY STRIKE An Integrated Studies Site Proposal for the Ridge 2000 Program This proposal was considered along with several other MAR ISS proposals at the start of the U.S. National Science Foundation Ridge 2000 Program. It was written by a group of proponents and reflects their vision. This ISS proposal was not endorsed for one of the 3 initial R2K ISS, however work by InterRidge researchers (including some US investigators, but dominantly French) did proceed at a modest rate and has increased since 2005. The summary contained here of R2K objectives that might be pursued in the MoMAR region provides a useful overview, and the synthesis of work (up to the year 2000) may be useful to some researchers beginning to consider work in the area. MID-ATLANTIC RIDGE 36° 10'N – 37° 50'N: RAINBOW TO LUCKY STRIKE An Integrated Studies Site Proposal Interested Investigators: Paul Asimow Caltech Javier Escartin University of Paris Elizabeth Gier LDEO Susan Humprhis WHOI Charles Langmuir LDEO Jian Lin WHOI Cindy Van Dover College of William and Mary Ken Macdonald UC Santa Barbara INTRODUCTION The challenge of selection of an integrated study site on a slow-spreading ridge is to find an area that is limited enough in extent to allow coupled studies from mantle to water column to be pursued in a single region, while at the same time having enough variability to encompass a significant range of accretionary variables. Established hydrothermal vents and associated biological activity are also essential in order to plan and carry out the integrated studies and to include all the disciplines involved.
    [Show full text]
  • The Magmatic Evolution of Krafla, NE Iceland
    The Magmatic Evolution of Krafla, NE Iceland. Hugh Nicholson Thesis submitted for the degree of Doctor of Philosophy University of Edinburgh DECLARATION I declare that this thesis is my own work except where otherwise stated. Hugh Nicholson ABSTRACT Krafla is an active central volcano in the NE axial rift zone of Iceland associated with a fissure swarm which trends NNE-SSW. Lava/hyaloclastite samples were collected from the volcanic system, covering the last 4 interglacial and 3 glacial periods. A siratigraphic framework for the volcanic system has been established by use of the Hekla tephra layers and the distinctive volcanic products of glacial and interglacial periods. Recent volcanic activity has shown that there is a shallow magma reservoir beneath the central volcano, which supplies magma laterally to the fissure swarms forming dykes and to the surface directly for eruption. The Krafla rocks contain the following phenocryst assemblages: ol + plag, ol + plag + cpx, plag + cpx ± ol, plag + cpx + opx + FeTi oxides, plag + FeTi oxides ± cpx ± fayalitic ol. These distinct assemblages suggest that the Krafla suite evolves predominantly by fractional crystallisation. They are also similar to the assemblages - found in other mid-ocean ridge basalt (MORB) suites. Most samples, excluding rhyolites, contain plagioclase xenocrysts, implying that there has been at least 2 stages of magma mixing prior to eruption. The absence of plagioclase xenocrysts in the rhyolites suggests that they formed in isolation from the most primitive magmas, with or without crustal assimilation. Fractional crystallisation using the observed phenocryst assemblage explains many aspects of the major-element compositions of the suite. Least-squares modelling confirms this observation, although it also suggests that the rhyolites contain higher concentrations of K 20 than would be predicted by closed-system fractional crystallisation.
    [Show full text]
  • Fall 2019 (Pdf)
    UC Santa Barbara Earth Science Chair’s Letter: Andy Wyss IN THIS ISSUE | FALL 2019 Alumni & Friends, News from the Field: With solstice near, it’s time for an update on the Summer Field 2 department. My hope is to convey a sense of the energy Santa Cruz Island 3 and excitement coursing through Webb Hall and beyond, by providing you glimpses of recent events. We cannot be Distinguished Alumni: prouder to announce that Professor Emerita Tanya Atwater Joe Acaba 4 was awarded the Penrose Medal by the Geological Society of America, its Susan Hubbard 4 highest scholarly distinction. Art Sylvester’s poignant citation (p. 5), beautifully Faculty Awards encapsulates her paradigm-shifting career. We recognize two talented current Tanya Atwater 5 graduate students (p. 8–9), the accomplishments of Distinguished Alumni Susan Hubbard and Joe Acaba (p. 4), and the distinguished career of Professor Francis Macdonald 5 Bruce Luyendyk (p. 11). Wishing you a healthy and gratifying 2020. Robin Matoza 6 Susannah Porter 10 In the trenches Giving & Donors: We Wish For … 6 UCSB-led research team uncovers a previously unrecognized active With Appreciation 7 fault in British Columbia, Canada Graduate Student Spotlight: by Kristin Morell Kaelynn Rose 8 Jiong Wang 9 Faculty in the Field: Montecito Debris Flow 10 Emeritus Spotlight: Bruce Luyendyk 11 During the summer of 2019, a UCSB- exciting, as Holocene activity of this led research team found evidence fault has important implications for for at least five Holocene ruptures how strain is accumulating in the on the Beaufort Range Fault, a major northern portion of the Cascadia A free annual publication of: 100-km-long fault in southwestern subduction zone.
    [Show full text]