DOCSLIB.ORG

Tectonic Versus Magmatic Extension in the Presence of Core Complexes at Slow-Spreading Ridges from a Visualization of Faulted Seafl Oor Topography

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Tectonic Versus Magmatic Extension in the Presence of Core Complexes at Slow-Spreading Ridges from a Visualization of Faulted Seafl Oor Topography Tectonic versus magmatic extension in the presence of core complexes at slow-spreading ridges from a visualization of faulted seafl oor topography Hans Schouten1, Deborah K. Smith1, Johnson R. Cann2, and Javier Escartín3 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA 2School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK 3Groupe de Geosciences Marines, CNRS–IPGP, F-75252 Paris, France ABSTRACT assume symmetrical spreading. Taking a simple We develop a forward model of the generation of faulted seafl oor topography (visualiza- model that each dike is rooted in a magma body, tion) to estimate the relative roles of tectonic and magmatic extension in the presence of core we examine how gabbro would be partitioned to complexes at slow-spreading ridges. The visualization assumes fl exural rotation of 60° normal both sides of the axis as M varies through time. faults, a constant effective elastic thickness, Te, of young lithosphere, and a continuous infi ll of Our visualization of the 13°20′N topography pre- the depressed hanging wall by lava fl owing from the spreading axis. We obtain a new estimate dicts a high probability of fi nding gabbro beneath of Te = 0.5–1 km from the shapes of the toes of 6 well-documented oceanic core complexes. the surface of the 13°20′N core complex. We model an 80-km-long bathymetric profi le in the equatorial Atlantic across a core complex and the ridge axis at 13°20′N and estimate the variation in tectonic extension, which yields the OCEANIC CORE COMPLEX variation in the fraction of upper crust extension, M, by magmatic diking at the ridge axis. CURVATURE AND ESTIMATION OF Te Core complex formation appears to be stable for all values of M < 0.5. The visualization shows The locations of six core complexes are how gabbro emplaced at the base of the lithosphere during extension by magmatic diking is shown in Figure 1A; their profi les taken parallel partitioned to each side of the spreading axis, and predicts a high probability of fi nding gab- to the spreading direction are displayed in Fig- bros in the domes of core complexes. ure 1B. Four of the core complexes (13°30′N, 13°20′N, TAG [Trans-Atlantic Geotraverse], INTRODUCTION faulted seafl oor topography on both sides of and 22°30′N) intersect the seafl oor (termina- Over the past 10 years it has been recognized the spreading axis of the Mid-Atlantic Ridge tion) at the edge of the median valley fl oor, and that fault extension at slow-spreading ridges is at 13°20′N, which includes the 13°20′N core their association with high rates of seismicity much more important than previously thought, complex (Smith et al., 2006, 2008; MacLeod et suggests that they are active (deMartin et al., and that large offset faults involving signifi cant al., 2009), and estimate the variation in tectonic 2007; Escartin et al., 2008; Smith et al., 2008). rotation and the formation of core complexes extension at the axis over the past 3.2 m.y. We The extinct Kane megamullion core complex are common, accounting for >50% extension take the remainder of the extension to arise by at 23°33′N formed at the intersection of the along large sections of the ridge (e.g., Cannat et diking, and hence calculate the variation in the Mid-Atlantic Ridge and the Kane transform al., 2006; Escartin et al., 2008; Garcés and Gee, fraction of upper crust extension by diking at fault ca. 3.3 Ma (Dick et al., 2008; Tucholke 2007; Smith et al., 2006, 2008; Tucholke et al., the axis (M). Magnetic anomalies are poor in et al., 1998). An extinct core complex in the 1998). The outward rotation of normal faults with this area (Smith et al., 2008) so for simplicity we Eastern Atlantic that formed at the Mid-Atlan- increasing extension, from small offset faults to core complexes, has been described using mod- els of fault fl exure (e.g., Buck, 1988). Numerical b Te = 1 km V.E. = 1 models of core complex formation (e.g., Buck B r C 0.25 km 2240N a 0.5 km et al., 2005; Behn and Ito, 2008; Tucholke et t b al., 2008) require an input of M (0–1), the frac- A r 40˚N EATL 1 km tion of upper crust extension accommodated by t EATL r r b magmatic diking, and output a synthetic bathy- MAR 2 km r 2 km TAG TAG t KMM a metric profi le together with a tectonic cross sec- 22 40 20˚N 4 km r tion. Here we derive an alternative type of model 13 30 Africa b KMM t r based on fault fl exure that we term a visualiza- 13 20 8 km 0˚ r b 1330N tion, which uses a bathymetric profi le as input t 16 km 60˚W 30˚W a r and outputs a tectonic cross section as well as the b 1320N 32 km variation of M as a function of time. a t V.E. = 3 20 km The fault fl exure model requires an estimate -10 0 10 20 30 of the effective elastic thickness of the litho- Distance from axis (km) sphere, Te, specifying the fl exural wavelength. Smith et al. (2008) obtained an estimate of Te in Figure 1. A: Location map. B: Topographic profi les of six North Atlantic core complexes in A. See text for references. Active core complexes at 13°20′N, 13°30′N, TAG (Trans-Atlantic Geo- the range 0.5–1.0 km, from the outward slopes traverse), and 22°40′N are plotted against distance from spreading axis. Inactive core com- of what were assumed to be outward rotated plexes KMM (Kane megamullion) and EATL (Eastern Atlantic) are aligned on terminations, t, fault blocks. Here we obtain a more robust but of active core complexes. MAR—Mid-Atlantic Ridge. Bold lines—exposed detachment sur- similar estimate of Te from the curvature of six face. Gray lines—third-order polynomial fi t to exposed detachment surfaces between break- away b and termination t. r—rafted blocks. C: Primary fault model for fl exural rotation of well-documented core complexes. 60° normal fault developing into core complex at larger offsets. V.E.—vertical exaggeration. We use the fl exural rotation of 60° normal 11 2 ρ Model parameters: Young’s modulus = 10 N/m ; Poisson’s ratio = 0.5; tcrust = 6.0 km; water = 3 ρ 3 ρ 3 faults (e.g., Buck, 1988) and Te = 1 km to model 1030 kg/m ; crust = 2700 kg/m ; mantle = 3300 kg/m ; effective elastic thickness Te = 1.0 km. © 2010 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. GEOLOGY,Geology, July July 2010; 2010 v. 38; no. 7; p. 615–618; doi: 10.1130/G30803.1; 4 fi gures. 615 tic Ridge during the Cretaceous (ca. 130 Ma) A decoupling of stresses across the axis. Except (Ranero and Reston, 1999), is based on multi- Termination 2240N for infi lling of the depressed hanging wall, no channel seismic data. In Figure 1B, the profi les 2 km morphologic effects of volcanism are included EATL of the six core complexes were aligned at their (Thatcher and Hill, 1995). inferred terminations. A map of seafl oor centered on the Mid-Atlan- TAG Figure 1C shows a model for the fl exural tic Ridge at 13°20′N is shown in Figure 3A. Lin- rotation of a 60° normal fault developing into a KMM ear ridges, taken to be the crests of fault scarps, core complex (Buck, 1988). The exposed fault are marked with thin black lines. On the east (detachment) between the initiation (break- 1330N side of the axis the morphology suggests numer- away) and termination exhibits a characteristic ous steep normal faults. The 13°20′N core com- curvature. To emphasize the similarity between 1320N plex is immediately west of the axis. West of the profi les and the fault model in Figure 1C, V.E.= 2 that there are several distinctive linear ridges. we added a third-order polynomial fi t (gray B We interpret the breakaway of the 13°20′N line) to the exposed detachment surfaces (bold core complex to be marked by the linear ridge 10 line) between breakaway and termination in along 45°04′W, ~25 km from the spreading axis Figure 1B. The polynomials isolate what we 0.5 (Smith et al., 2008). If this is the case, the linear interpret as rafted blocks atop the primary 0 0.25 ridges along 44°59′W would be rafted blocks fault. Rafted blocks are sections of hanging resting on the long-lived primary fault. 1.0 wall (median valley fl oor) that are chopped Dots above the bathymetric profi le in Fig- off by successive normal faults that root in −10 ure 3B match the dots in Figure 3A at the inter- the same primary fault (Buck, 1988). They are section of the east-west profi le and the crests of Slope (deg) uplifted with the footwall, rotated, and carried −20 identifi ed fault scarps. Dotted lines in Figure 3B away from the axis (Smith et al., 2008; Ranero Te = 2.0 km that dip 60° toward the axis symbolically indi- and Reston, 1999). We use the similarity in cate the faults. We digitize fault locations and wavelength and surface curvature of the six −30 shift their across-axis distance from the axis to 0 10 20 core complexes to obtain a new estimate of Te the nearest multiple of 100 m.
Load more

Recommended publications
  • Geophysical Signatures of Oceanic Core Complexes
    Geophys. J. Int. (2009) 178, 593–613 doi: 10.1111/j.1365-246X.2009.04184.x REVIEW ARTICLE Geophysical signatures of oceanic core complexes Donna K. Blackman,1 J. Pablo Canales2 and Alistair Harding1 1Scripps Institution of Oceanography, UCSD La Jolla, CA, USA. E-mail: [email protected] 2Woods Hole Oceanographic Institution, Woods Hole, MA, USA Accepted 2009 March 16. Received 2009 February 15; in original form 2008 July 25 SUMMARY Oceanic core complexes (OCCs) provide access to intrusive and ultramafic sections of young lithosphere and their structure and evolution contain clues about how the balance between mag- matism and faulting controls the style of rifting that may dominate in a portion of a spreading centre for Myr timescales. Initial models of the development of OCCs depended strongly on insights available from continental core complexes and from seafloor mapping. While these frameworks have been useful in guiding a broader scope of studies and determining the extent GJI Geodesy, potential field and applied geophysics of OCC formation along slow spreading ridges, as we summarize herein, results from the past decade highlight the need to reassess the hypothesis that reduced magma supply is a driver of long-lived detachment faulting. The aim of this paper is to review the available geophysical constraints on OCC structure and to look at what aspects of current models are constrained or required by the data. We consider sonar data (morphology and backscatter), gravity, magnetics, borehole geophysics and seismic reflection. Additional emphasis is placed on seismic velocity results (refraction) since this is where deviations from normal crustal accretion should be most readily quantified.
    [Show full text]
  • Enhanced Mantle Upwelling/Melting Caused Segment Propagation, Oceanic Across the Ridge Crest of the TAMMAR Segment
    PUBLICATIONS Journal of Geophysical Research: Solid Earth RESEARCH ARTICLE Enhanced Mantle Upwelling/Melting Caused Segment 10.1002/2017JB014273 Propagation, Oceanic Core Complex Die Off, Key Points: and the Death of a Transform Fault: • Seismic data confirm ridge propagation induced by increased The Mid-Atlantic Ridge at 21.5°N melt supply due to increased fertility or upwelling of the asthenosphere A. Dannowski1 , J. P. Morgan2, I. Grevemeyer1 , and C. R. Ranero3,4 • Source of melt supply is migrating, ended a transform fault, and possibly 1GEOMAR/Helmholtz-Centre for Ocean Research Kiel, Kiel, Germany, 2Earth Sciences Department, Royal Holloway stopped OCC formation 3 • The growth direction of the enhanced University of London, London, UK, Barcelona Centre for Subsurface Imaging, Institut de Ciencias del Mar, Barcelona, Spain, 4 melt supply region is influenced by ICREA, Barcelona, Spain the distance to “colder” mantle zones Abstract Crustal structure provides the key to understand the interplay of magmatism and tectonism, while oceanic crust is constructed at Mid-Ocean Ridges (MORs). At slow spreading rates, magmatic Correspondence to: A. Dannowski, processes dominate central areas of MOR segments, whereas segment ends are highly tectonized. The [email protected] TAMMAR segment at the Mid-Atlantic Ridge (MAR) between 21°250N and 22°N is a magmatically active segment. At ~4.5 Ma this segment started to propagate south, causing the termination of the transform fault Citation: at 21°400N. This stopped long-lived detachment faulting and caused the migration of the ridge offset to the Dannowski, A., Morgan, J. P., south. Here a segment center with a high magmatic budget has replaced a transform fault region with Grevemeyer, I., & Ranero, C.
    [Show full text]
  • Role of Late Jurassic Intra-Oceanic Structural Inheritance in the Alpine Tectonic Evolution of the Monviso Meta-Ophiolite Complex (Western Alps)
    Geol. Mag. 155 (2), 2018, pp. 233–249. c Cambridge University Press 2017 233 doi:10.1017/S0016756817000553 Role of Late Jurassic intra-oceanic structural inheritance in the Alpine tectonic evolution of the Monviso meta-ophiolite Complex (Western Alps) ∗ ∗ ∗ GIANNI BALESTRO , ANDREA FESTA †, ALESSANDRO BORGHI , ∗ ∗ DANIELE CASTELLI , MARCO GATTIGLIO & PAOLA TARTAROTTI‡ ∗ Dipartimento di Scienze della Terra, Università di Torino, Via Valperga Caluso, 35, 10125 – Torino, Italy ‡Dipartimento di Scienze della Terra, Università di Milano, Via Mangiagalli, 34, 20133 – Milano, Italy (Received 31 October 2016; accepted 2 June 2017; first published online 17 July 2017) Abstract – The eclogite-facies Monviso meta-ophiolite Complex in the Western Alps represents a well-preserved fragment of oceanic lithosphere and related Upper Jurassic – Lower Cretaceous sed- imentary covers. This meta-ophiolite sequence records the evolution of an oceanic core complex formed by mantle exhumation along an intra-oceanic detachment fault (the Baracun Shear Zone), re- lated to the opening of the Ligurian–Piedmont oceanic basin (Alpine Tethys). On the basis of detailed geological mapping, and structural, stratigraphic and petrological observations, we propose a new interpretation for the tectonostratigraphic architecture of the Monviso meta-ophiolite Complex, and discuss the role played by structural inheritance in its formation. We document that subduction- and exhumation-related Alpine tectonics were strongly influenced by the inherited Jurassic intra-oceanic tectonosedimentary physiography. The latter, although strongly deformed during a major Alpine stage of non-cylindrical W-verging folding and faulting along exhumation-related Alpine shear zones (i.e. the Granero–Casteldelfino and Villanova–Armoine shear zones), was not completely dismembered into different tectonic units or subduction-related mélanges as suggested in previous interpretations.
    [Show full text]
  • Fluid Evolution in an Oceanic Core Complex: a Fluid Inclusion Study from IODP Hole U1309 D - Atlantis Massif, 30°N, Mid-Atlantic Ridge
    This is a repository copy of Fluid evolution in an Oceanic Core Complex: a fluid inclusion study from IODP hole U1309 D - Atlantis Massif, 30°N, Mid-Atlantic Ridge. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/80181/ Version: Published Version Article: Castelain, T, McCaig, AM and Cliff, RA (2014) Fluid evolution in an Oceanic Core Complex: a fluid inclusion study from IODP hole U1309 D - Atlantis Massif, 30°N, Mid-Atlantic Ridge. Geochemistry, Geophysics, Geosystems, 15 (4). 1193 - 1214. ISSN 1525-2027 https://doi.org/10.1002/2013GC004975 Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version - refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher’s website. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ PUBLICATIONS Geochemistry, Geophysics, Geosystems RESEARCH ARTICLE Fluid evolution in an Oceanic Core Complex: A fluid inclusion 10.1002/2013GC004975 study from IODP hole U1309 D—Atlantis Massif, 30N, Key Points: Mid-Atlantic Ridge The TAG model is a good analog for fluid evolution at Atlantis Massif Teddy Castelain1, Andrew M.
    [Show full text]
  • Fossil Oceanic Core Complexes in the Alps. New Field, Geochemical And
    Decrausaz et al. Swiss J Geosci (2021) 114:3 https://doi.org/10.1186/s00015-020-00380-4 Swiss Journal of Geosciences ORIGINAL PAPER Open Access Fossil oceanic core complexes in the Alps. New feld, geochemical and isotopic constraints from the Tethyan Aiguilles Rouges Ophiolite (Val d’Hérens, Western Alps, Switzerland) Thierry Decrausaz1,2* , Othmar Müntener1, Paola Manzotti3, Romain Lafay2 and Carl Spandler4 Abstract Exhumation of basement rocks on the seafoor is a worldwide feature along passive continental margins and (ultra-) slow-spreading environments, documented by dredging, drilling or direct observations by diving expeditions. Com- plementary observations from exhumed ophiolites in the Alps allow for a better understanding of the underlying processes. The Aiguilles Rouges ophiolitic units (Val d’Hérens, Switzerland) are composed of kilometre-scale remnants of laterally segmented oceanic lithosphere only weakly afected by Alpine metamorphism (greenschist facies, Raman thermometry on graphite: 370–380 °C) and deformation. Geometries and basement-cover sequences comparable to the ones recognized in actual (ultra-) slow-spreading environments were observed, involving exhumed serpentinized and carbonatized peridotites, gabbros, pillow basalts and tectono-sedimentary cover rocks. One remarkable feature is the presence of a kilometric gabbroic complex displaying preserved magmatic minerals, textures and crosscutting relationships between the host gabbro and intruding diabase, hornblende-bearing dikelets or plagiogranite. The bulk major and trace element chemistry of mafc rocks is typical of N-MORB magmatism (Ce N/YbN: 0.42–1.15). This is supported by in-situ isotopic signatures of magmatic zircons (εHf 13 0.6) and apatites (εNd 8.5 0.8), determined for gabbros and plagiogranites.
    [Show full text]
  • Integrated Ocean Drilling Program Expedition 312 Preliminary Report (Including Expedition 309 Accomplishments)
    Integrated Ocean Drilling Program Expedition 312 Preliminary Report (including Expedition 309 accomplishments) Superfast Spreading Rate Crust 3 A complete in situ section of upper oceanic crust formed at a superfast spreading rate 28 October–28 December 2005 Expedition 309 and 312 Scientists PUBLISHER’S NOTES Material in this publication may be copied without restraint for library, abstract service, educational, or personal research purposes; however, this source should be appropriately acknowledged. Citation: Expedition 309 and 312 Scientists, 2006. Superfast spreading rate crust 3: a complete in situ section of upper oceanic crust formed at a superfast spreading rate. IODP Prel. Rept., 312. doi:10:2204/ iodp.pr.312.2006 Distribution: Electronic copies of this series may be obtained from the Integrated Ocean Drilling Program (IODP) Publication Services homepage on the World Wide Web at iodp.tamu.edu/publications. This publication was prepared by the Integrated Ocean Drilling Program U.S. Implementing Organization (IODP-USIO): Joint Oceanographic Institutions, Inc., Lamont-Doherty Earth Observatory of Columbia University, and Texas A&M University, as an account of work performed under the international Integrated Ocean Drilling Program, which is managed by IODP Management International (IODP-MI), Inc. Funding for the program is provided by the following agencies: European Consortium for Ocean Research Drilling (ECORD) Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan Ministry of Science and Technology (MOST), People’s Republic of China U.S. National Science Foundation (NSF) DISCLAIMER Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the participating agencies, IODP Management International, Inc., Joint Oceanographic Institutions, Inc., Lamont-Doherty Earth Observatory of Columbia University, Texas A&M University, or Texas A&M Research Foundation.
    [Show full text]
  • Implications for the Rheological Behavior of Oceanic Detachment Faults
    Article Volume 14, Number 8 28 August 2013 doi: 10.1002/ggge.20184 ISSN: 1525-2027 Mylonitic deformation at the Kane oceanic core complex: Implications for the rheological behavior of oceanic detachment faults Lars N. Hansen Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, California, 94305, USA ([email protected]) Michael J. Cheadle, Barbara E. John, and Susan M. Swapp Department of Geology and Geophysics, University of Wyoming, Wyoming, USA Henry J. B. Dick, Brian E. Tucholke, and Maurice A. Tivey Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA [1] The depth extent, strength, and composition of oceanic detachment faults remain poorly understood because the grade of deformation-related fabrics varies widely among sampled oceanic core complexes (OCCs). We address this issue by analyzing fault rocks collected from the Kane oceanic core complex at 23300N on the Mid-Atlantic Ridge. A portion of the sample suite was collected from a younger fault scarp that cuts the detachment surface and exposes the interior of the most prominent dome. The style of deformation was assessed as a function of proximity to the detachment surface, revealing a 450 m thick zone of high-temperature mylonitization overprinted by a 200 m thick zone of brittle deformation. Geothermometry of deformed gabbros demonstrates that crystal-plastic deformation occurred at temperatures >700C. Analysis of the morphology of the complex in conjunction with recent thermochronology suggests that deformation initiated at depths of 7 km. Thus we suggest the detachment system extended into or below the brittle-plastic transition (BPT).
    [Show full text]
  • Drilling the Crust at Mid-Ocean Ridges
    or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of Th e Oceanography Society. Send all correspondence to: [email protected] or Th eOceanography PO Box 1931, Rockville, USA.Society, MD 20849-1931, or e to: [email protected] Oceanography correspondence all Society. Send of Th approval portionthe ofwith any articlepermitted only photocopy by is of machine, reposting, this means or collective or other redistirbution articleis has been published in Th SPECIAL ISSUE FEATURE Oceanography Drilling the Crust Threproduction, Republication, systemmatic research. for this and teaching article copy to use in reserved. e is rights granted All OceanographyPermission Society. by 2007 eCopyright Oceanography Society. journal of Th 20, Number 1, a quarterly , Volume at Mid-Ocean Ridges An “in Depth” perspective BY BENOÎT ILDEFONSE, PETER A. RONA, AND DONNA BLACKMAN In April 1961, 13.5 m of basalts were drilled off Guadalupe In the early 1970s, almost 15 years after the fi rst Mohole Island about 240 km west of Mexico’s Baja California, to- attempt, attendees of a Penrose fi eld conference (Confer- gether with a few hundred meters of Miocene sediments, in ence Participants, 1972) formulated the concept of a layered about 3500 m of water. This fi rst-time exploit, reported by oceanic crust composed of lavas, underlain by sheeted dikes, John Steinbeck for Life magazine, aimed to be the test phase then gabbros (corresponding to the seismic layers 2A, 2B, for the considerably more ambitious Mohole project, whose and 3, respectively), which themselves overlay mantle perido- objective was to drill through the oceanic crust down to tites.
    [Show full text]
  • IODP Expedition 305 Preliminary Report
    Integrated Ocean Drilling Program Expedition 305 Preliminary Report Oceanic Core Complex Formation, Atlantis Massif Oceanic core complex formation, Atlantis Massif, Mid-Atlantic Ridge: drilling into the footwall and hanging wall of a tectonic exposure of deep, young oceanic lithosphere to study deformation, alteration, and melt generation 8 January–2 March 2005 Expedition Scientific Party PUBLISHER’S NOTES Material in this publication may be copied without restraint for library, abstract service, educational, or personal research purposes; however, this source should be appropriately acknowledged. Citation: Expedition Scientific Party, 2005. Oceanic core complex formation, Atlantis Massif—oceanic core complex formation, Atlantis Massif, Mid-Atlantic Ridge: drilling into the footwall and hanging wall of a tectonic exposure of deep, young oceanic lithosphere to study deformation, alteration, and melt generation. IODP Prel. Rept., 305. http://iodp.tamu.edu/publications/PR/305PR/305PR.PDF. Distribution: Electronic copies of this series may be obtained from the Integrated Ocean Drilling Program (IODP) Publication Services homepage on the World Wide Web at iodp.tamu.edu/publications. This publication was prepared by the Integrated Ocean Drilling Program U.S. Implementing Organization (IODP-USIO): Joint Oceanographic Institutions, Inc., Lamont-Doherty Earth Observatory of Columbia University, and Texas A&M University, as an account of work performed under the international Integrated Ocean Drilling Program, which is managed by IODP Management International (IODP-MI), Inc. Funding for the program is provided by the following agencies: European Consortium for Ocean Research Drilling (ECORD) Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan Ministry of Science and Technology (MOST), People’s Republic of China U.S.
    [Show full text]
  • Slow Spreading Ridges of the Indian Ocean: an Overview of Marine Geophysical Investigations K
    J. Ind. Geophys.Slow Union Spreading ( April Ridges 2015 of the ) Indian Ocean: An Overview of Marine Geophysical Investigations v.19, no.2, pp:137-159 Slow Spreading Ridges of the Indian Ocean: An Overview of Marine Geophysical Investigations K. A. Kamesh Raju*, Abhay V. Mudholkar, Kiranmai Samudrala CSIR-National Institute of Oceanography, Dona Paula, Goa – 403004, India *Corresponding author: [email protected] ABSTRACT Sparse and non-availability of high resolution geophysical data hindered the delineation of accurate morphology, structural configuration, tectonism and spreading history of Carlsberg Ridge (CR) and Central Indian Ridges (CIR) in the Indian Ocean between Owen fracture zone at about 10oN, and the Rodriguez Triple Junction at ~25oS. Analysis of available multibeam bathymetry, magnetic, gravity, seabed sampling on the ridge crest, and selected water column data suggest that even with similar slow spreading history the segmentation significantly differ over the CR and CIR ridge systems. Topography, magnetic and gravity signatures indicate non-transform discontinuity over CR and suggest that it has relatively slower spreading history than CIR. Magmatic and less magmatic events characterize CR and CIR respectively and well defined oceanic core complex (OCC) are confined only to segments of the CIR. The mantle Bouguer anomaly signatures over the ridges suggest crustal accretion and pattern of localized magnetic anomalies indicate zones of high magnetization coinciding with the axial volcanic ridges. Geophysical investigations /
    [Show full text]
  • Mantle Rock Exposures at Oceanic Core Complexes Along Mid-Ocean Ridges
    Geologos 21, 4 (2015): 207–231 doi: 10.1515/logos-2015-0017 Mantle rock exposures at oceanic core complexes along mid-ocean ridges Jakub Ciazela1,2*, Juergen Koepke2, Henry J.B. Dick3 & Andrzej Muszynski1 1Institute of Geology, Adam Mickiewicz University, Institute of Geology, Maków polnych 16, 61-606 Poznań, Poland 2Institut für Mineralogie, Leibniz Universität Hannover, Callinstrasse 3, 30167 Hannover, Germany 3Department of Geology and Geophysics, Woods Hole Oceanographic Institution, MS #8, McLean Laboratory, Woods Hole MA 02543-1539, USA * corresponding author, e-mail: [email protected] Abstract The mantle is the most voluminous part of the Earth. However, mantle petrologists usually have to rely on indirect geophysical methods or on material found ex situ. In this review paper, we point out the in-situ existence of oceanic core complexes (OCCs), which provide large exposures of mantle and lower crustal rocks on the seafloor on detachment fault footwalls at slow-spreading ridges. OCCs are a common structure in oceanic crust architecture of slow-spreading ridges. At least 172 OCCs have been identified so far and we can expect to discover hundreds of new OCCs as more detailed mapping takes place. Thirty-two of the thirty-nine OCCs that have been sampled to date contain peridotites. Moreover, peridotites dominate in the plutonic footwall of 77% of OCCs. Massive OCC peridotites come from the very top of the melting column beneath ocean ridges. They are typically spinel harzburgites and show 11.3–18.3% partial melting, generally representing a maximum degree of melting along a segment. Another key feature is the lower frequency of plagioclase-bearing peridotites in the mantle rocks and the lower abundance of plagioclase in the plagioclase-bearing peridotites in comparison to transform peridotites.
    [Show full text]
  • Oceanic Detachment Faults Generate Compression in Extension
    Oceanic detachment faults generate compression in extension R. Parnell-Turner1, R.A. Sohn1, C. Peirce2, T.J. Reston3, C.J. MacLeod4, R.C. Searle2, and N.M. Simão2. 1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA 2Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE, UK 3School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK 4School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK ABSTRACT and sampled oceanic core complexes located In extensional geologic systems such as mid-ocean ridges, deformation is typically accom- at 13°20′N and 13°30′N (Smith et al., 2006; modated by slip on normal faults, where material is pulled apart under tension and stress MacLeod et al., 2009; Mallows and Searle, 2012; is released by rupture during earthquakes and magmatic accretion. However, at slowly Escartín et al., 2017). Both core complexes have spreading mid-ocean ridges where the tectonic plates move apart at rates <80 km m.y.–1, well-developed, domed, corrugated surfaces and these normal faults may roll over to form long-lived, low-angled detachments that exhume are accompanied by a high level of hydroacous- mantle rocks and form corrugated domes on the seabed. Here we present the results of a local tically recorded seismicity, suggesting that they micro-earthquake study over an active detachment at 13°20′N on the Mid-Atlantic Ridge are currently active or have been in the recent to show that these features can give rise to reverse-faulting earthquakes in response to plate geological past (Smith et al., 2008; MacLeod et bending.
    [Show full text]