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  • 1
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    Palaeomagnetism and Tectonics of the Mediterranean Region (1996)
    London : The Geological Society
    Details
    Keywords: Mittelmeerraum ; Paläomagnetismus ; Tektonik ; Cenozoic ; Geodynamics ; Geologia estrutural ; Geology, Stratigraphic ; Geology, Structural ; Mediterranean Region ; Mesozoic ; Paleomagnetism ; Paleomagnetismo ; Plate tectonics
    Description / Table of Contents: A. Morris and D. H. Tarling: Palaeomagnetism and tectonics of the Mediterranean region: an introduction / Geological Society, London, Special Publications, 105:1-18, doi:10.1144/GSL.SP.1996.105.01.01 --- Western Mediterranean --- A. Kirker and E. McClelland: Application of net tectonic rotations and inclination analysis to a high-resolution palaeomagnetic study in the Betic Cordillera / Geological Society, London, Special Publications, 105:19-32, doi:10.1144/GSL.SP.1996.105.01.02 --- J. J. Villalaín, M. L. Osete, R. Vegas, V. García-Dueñas, and F. Heller: The Neogene remagnetization in the western Betics: a brief comment on the reliability of palaeomagnetic directions / Geological Society, London, Special Publications, 105:33-41, doi:10.1144/GSL.SP.1996.105.01.03 --- H. Feinberg, O. Saddiqi, and A. Michard: New constraints on the bending of the Gibraltar Arc from palaeomagnetism of the Ronda peridotites (Betic Cordilleras, Spain) / Geological Society, London, Special Publications, 105:43-52, doi:10.1144/GSL.SP.1996.105.01.04 --- D. Khattach, D. Najid, N. Hamoumi, and D. H. Tarling: Palaeomagnetic studies in Morocco: tectonic implications for the Meseta and Anti-Atlas since the Permian / Geological Society, London, Special Publications, 105:53-57, doi:10.1144/GSL.SP.1996.105.01.05 --- D. Rey, P. Turner, and A. Ramos: Palaeomagnetism and magnetostratigraphy of the Middle Triassic in the Iberian Ranges (Central Spain) / Geological Society, London, Special Publications, 105:59-82, doi:10.1144/GSL.SP.1996.105.01.06 --- M. T. Juárez, M. L. Osete, R. Vegas, C. G. Langereis, and G. Meléndez: Palaeomagnetic study of Jurassic limestones from the Iberian Range (Spain): tectonic implications / Geological Society, London, Special Publications, 105:83-90, doi:10.1144/GSL.SP.1996.105.01.07 --- M. Garcés, J. M. Parés, and L. Cabrera: Inclination error linked to sedimentary facies in Miocene detrital sequences from the Vallès-Penedès Basin (NE Spain) / Geological Society, London, Special Publications, 105:91-99, doi:10.1144/GSL.SP.1996.105.01.08 --- P. Keller and U. Gehring: Consequences of post-collisional deformation on the reconstruction of the East Pyrenees / Geological Society, London, Special Publications, 105:101-109, doi:10.1144/GSL.SP.1996.105.01.09 --- J. L. Pereira, A. Rapalini, D. H. Tarling, and J. Fonseca: Palaeomagnetic dating and determination of tectonic tilting: a study of Mesozoic-Cenozoic igneous rocks in central West Portugal / Geological Society, London, Special Publications, 105:111-117, doi:10.1144/GSL.SP.1996.105.01.10 --- Central Mediterranean and Carpathians --- J. E. T. Channell: Palaeomagnetism and palaeogeography of Adria / Geological Society, London, Special Publications, 105:119-132, doi:10.1144/GSL.SP.1996.105.01.11 --- M. Iorio, G. Nardi, D. Pierattini, and D. H. Tarling: Palaeomagnetic evidence of block rotations in the Matese Mountains, Southern Apennines, Italy / Geological Society, London, Special Publications, 105:133-139, doi:10.1144/GSL.SP.1996.105.01.12 --- M. Mattei, C. Kissel, L. Sagnotti, R. Funiciello, and C. Faccenna: Lack of Late Miocene to Present rotation in the Northern Tyrrhenian margin (Italy): a constraint on geodynamic evolution / Geological Society, London, Special Publications, 105:141-146, doi:10.1144/GSL.SP.1996.105.01.13 --- M. Fedi, G. Florio, and A. Rapolla: The pattern of crustal block rotations in the Italian region deduced from aeromagnetic anomalies / Geological Society, London, Special Publications, 105:147-152, doi:10.1144/GSL.SP.1996.105.01.14 --- Emő Márton and Péter Márton: Large scale rotations in North Hungary during the Neogene as indicated by palaeomagnetic data / Geological Society, London, Special Publications, 105:153-173, doi:10.1144/GSL.SP.1996.105.01.15 --- Miroslav Krs, Marta Krsová, and Petr Pruner: Palaeomagnetism and palaeogeography of the Western Carpathians from the Permian to the Neogene / Geological Society, London, Special Publications, 105:175-184, doi:10.1144/GSL.SP.1996.105.01.16 --- Václav Houša, Miroslav Krs, Marta Krsová, and Petr Pruner: Magnetostratigraphy of Jurassic-Cretaceous limestones in the Western Carpathians / Geological Society, London, Special Publications, 105:185-194, doi:10.1144/GSL.SP.1996.105.01.17 --- M. Iorio, D. H. Tarling, B. D’argenio, and G. Nardi: Ultra-fine magnetostratigraphy of Cretaceous shallow water carbonates, Monte Raggeto, southern Italy / Geological Society, London, Special Publications, 105:195-203, doi:10.1144/GSL.SP.1996.105.01.18 --- E. McClelland, B. Finegan, and R. W. H. Butler: A magnetostratigraphic study of the onset of the Mediterranean Messinian salility crisis; Caltanissetta Basin, Sicily / Geological Society, London, Special Publications, 105:205-217, doi:10.1144/GSL.SP.1996.105.01.19 --- F. Florindo and L. Sagnotti: Revised magnetostratigraphy and rock magnetism of Pliocene sediments from Valle Ricca (Rome, Italy) / Geological Society, London, Special Publications, 105:219-223, doi:10.1144/GSL.SP.1996.105.01.20 --- Giancarlo Scalera, Paolo Favali, and Fabio Florindo: Palaeomagnetic database: the effect of quality filtering for geodynamic studies / Geological Society, London, Special Publications, 105:225-237, doi:10.1144/GSL.SP.1996.105.01.21 --- Eastern Mediterranean --- A. H. F. Robertson, J. E. Dixon, S. Brown, A. Collins, A. Morris, E. Pickett, I. Sharp, and T. Ustaömer: Alternative tectonic models for the Late Palaeozoic-Early Tertiary development of Tethys in the Eastern Mediterranean region / Geological Society, London, Special Publications, 105:239-263, doi:10.1144/GSL.SP.1996.105.01.22 --- H. J. Mauritsch, R. Scholger, S. L. Bushati, and A. Xhomo: Palaeomagnetic investigations in Northern Albania and their significance for the geodynamic evolution of the Adriatic-Aegean realm / Geological Society, London, Special Publications, 105:265-275, doi:10.1144/GSL.SP.1996.105.01.23 --- D. Kondopoulou, A. Atzemoglou, and S. Pavlides: Palaeomagnetism as a tool for testing geodynamic models in the North Aegean: convergences, controversies and a further hypothesis / Geological Society, London, Special Publications, 105:277-288, doi:10.1144/GSL.SP.1996.105.01.24 --- H. Feinberg, B. Edel, D. Kondopoulou, and A. Michard: Implications of ophiolite palaeomagnetism for the interpretation of the geodynamics of Northern Greece / Geological Society, London, Special Publications, 105:289-298, doi:10.1144/GSL.SP.1996.105.01.25 --- J. D. A. Piper, Joanna M. Moore, O. Tatar, H. Gursoy, and R. G. Park: Palaeomagnetic study of crustal deformation across an intracontinental transform: the North Anatolian Fault Zone in Northern Turkey / Geological Society, London, Special Publications, 105:299-310, doi:10.1144/GSL.SP.1996.105.01.26 --- Antony Morris: A review of palaeomagnetic research in the Troodos ophiolite, Cyprus / Geological Society, London, Special Publications, 105:311-324, doi:10.1144/GSL.SP.1996.105.01.27 --- A. M. Kafafy, D. H. Tarling, M. M. El Gamili, H. H. Hamama, and E. H. Ibrahim: Palaeomagnetism of some Cretaceous Nubian Sandstones, Northern Sinai, Egypt / Geological Society, London, Special Publications, 105:325-332, doi:10.1144/GSL.SP.1996.105.01.28 --- A. L. Abdeldayem and D. H. Tarling: Palaeomagnetism of some Tertiary sedimentary rocks, southwest Sinai, Egypt, in the tectonic framework of the SE Mediterranean / Geological Society, London, Special Publications, 105:333-343, doi:10.1144/GSL.SP.1996.105.01.29 --- Applications in Volcanology --- Leon Bardot, Rick Thomas, and Elizabeth McClelland: Emplacement temperatures of pyroclastic deposits on Santorini deduced from palaeomagnetic measurements: constraints on eruption mechanisms / Geological Society, London, Special Publications, 105:345-357, doi:10.1144/GSL.SP.1996.105.01.30 --- Maurizio De’ Gennaro, Paola R. Gialanella, Alberto Incoronato, Giuseppe Mastrolorenzo, and Debora Naimo: Palaeomagnetic controls on the emplacement of the Neapolitan Yellow Tuff (Campi Flegrei, Southern Italy) / Geological Society, London, Special Publications, 105:359-365, doi:10.1144/GSL.SP.1996.105.01.31 --- Alberto Incoronato: Magnetic stratigraphy procedures in volcanic areas: the experience at Vesuvius / Geological Society, London, Special Publications, 105:367-371, doi:10.1144/GSL.SP.1996.105.01.32 --- Archaeomagnetism --- M. E. Evans: Archaeomagnetic results from the Mediterranean region: an overview / Geological Society, London, Special Publications, 105:373-384, doi:10.1144/GSL.SP.1996.105.01.33 --- P. Márton: Archaeomagnetic directions: the Hungarian calibration curve / Geological Society, London, Special Publications, 105:385-399, doi:10.1144/GSL.SP.1996.105.01.34 --- A. Morris: Glossary of basic palaeomagnetic and rock magnetic terms / Geological Society, London, Special Publications, 105:401-415, doi:10.1144/GSL.SP.1996.105.01.35
    Pages: Online-Ressource (422 Seiten) , Diagramme, Karten
    ISBN: 1897799551
    URL: http://sp.lyellcollection.org/content/105/1
    Language: English
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  • 2
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    (Table 1) Paleomagnetic of reoriented core pieces of IODP Hole 304-U1309D
    PANGAEA
    In:  Supplement to: Morris, Antony; Gee, Jeff S; Pressling, Nicola; John, Barbara E; MacLeod, Christopher J; Grimes, Craig B; Searle, R C (2009): Footwall rotation in an oceanic core complex quantified using reoriented Integrated Ocean Drilling Program core samples. Earth and Planetary Science Letters, 287(1-2), 217-228, https://doi.org/10.1016/j.epsl.2009.08.007
    Details
    Publication Date: 2023-06-27
    Description: Oceanic core complexes expose lower crustal and upper mantle rocks on the seafloor by tectonic unroofing in the footwalls of large-slip detachment faults. The common occurrence of these structures in slow and ultra-slow spread oceanic crust suggests that they accommodate a significant component of plate divergence. However, the subsurface geometry of detachment faults in oceanic core complexes remains unclear. Competing models involve either: (a) displacement on planar, low-angle faults with little tectonic rotation; or (b) progressive shallowing by rotation of initially steeply dipping faults as a result of flexural unloading (the "rolling-hinge" model). We address this debate using palaeomagnetic remanences as markers for tectonic rotation within a unique 1.4 km long footwall section of gabbroic rocks recovered by Integrated Ocean Drilling Program (IODP) sampling at Atlantis Massif oceanic core complex on the Mid-Atlantic Ridge (MAR). These rocks contain a complex record of multipolarity magnetizations that are unrelated to alteration and igneous stratigraphy in the sampled section and are inferred to result from progressive cooling of the footwall section over geomagnetic polarity chrons C1r.2r, C1r.1n (Jaramillo) and C1r.1r. For the first time we have independently reoriented drill-core samples of lower crustal gabbros, that were initially azimuthally unconstrained, to a true geographic reference frame by correlating structures in individual core pieces with those identified from oriented imagery of the borehole wall. This allows reorientation of the palaeomagnetic data, placing far more rigorous constraints on the tectonic history than those possible using only palaeomagnetic inclination data. Analysis of the reoriented high temperature reversed component of magnetization indicates a 46° ± 6° anticlockwise rotation of the footwall around a MAR-parallel horizontal axis trending 011° ± 6°. Reoriented lower temperature components of normal and reversed polarity suggest that much of this rotation occurred after the end of the Jaramillo chron (0.99 Ma). The data provide unequivocal confirmation of the key prediction of flexural, rolling-hinge models for oceanic core complexes, whereby oceanic detachment faults initiate at higher dips and rotate to their present day low-angle geometries as displacement increases.
    Keywords: 304-U1309D; Angle; Comment; DEPTH, sediment/rock; DRILL; Drilling/drill rig; Exp304; Integrated Ocean Drilling Program / International Ocean Discovery Program; IODP; Joides Resolution; Maximum angular deviation; NRM, Declination; NRM, Inclination; Number of points; Oceanic Core Complex Formation, Atlantis Massive 1; Sample code/label
    Type: Dataset
    Format: text/tab-separated-values, 800 data points
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  • 3
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    Pleistocene depositional environments and links to cryosphere-ocean interactions on the eastern Ross Sea continental slope, Antarctica (IODP Hole U1525A) (2022)
    In:  EPIC3Marine Geology, 443, pp. 106674, ISSN: 00253227
    Details
    Publication Date: 2022-04-12
    Description: The repeated proximity of West Antarctic Ice Sheet (WAIS) ice to the eastern Ross Sea continental shelf break during past ice age cycles has been inferred to directly influence sedimentary processes occurring on the continental slope, such as turbidity current and debris flow activity; thus, the records of these processes can be used to study the past history of the WAIS. Ross Sea slope sediments may additionally provide an archive on the history and interplay of density-driven or geostrophic oceanic bottom currents with ice-sheet-driven depositional mechanisms. We investigate the upper 121 m of Hole U1525A, collected during International Ocean Discovery Program (IODP) Expedition 374 in 2018. Hole U1525A is located on the southwestern external levee of the Hillary Canyon (Ross Sea, Antarctica) and the depositional lobe of the nearby trough-mouth fan. Using core descriptions, grain size analysis, and physical properties datasets, we develop a lithofacies scheme that allows construction of a detailed depositional model and environmental history of past ice sheet-ocean interactions at the eastern Ross Sea continental shelf break/slope since ~2.4 Ma. The earliest Pleistocene interval (~2.4- ~ 1.4 Ma) represents a hemipelagic environment dominated by ice-rafting and reworking/deposition by relatively persistent bottom current activity. Finely interlaminated silty muds with ice-rafted debris (IRD) layers are interpreted as contourites. Between ~1.4 and ~0.8 Ma, geostrophic bottom current activity was weaker and turbiditic processes more common, likely related to the increased proximity of grounded ice at the shelf edge. Silty, normally-graded laminations with sharp bases may be the result of flow-stripped turbidity currents overbanking the canyon levee during periods when ice was grounded at or proximal to the shelf edge. A sandy, IRD- and foraminifera-bearing interval dated to ~1.18 Ma potentially reflects warmer oceanographic conditions and a period of stronger Antarctic Slope Current flow. This may have enhanced upwelling of warm Circumpolar Deep Water onto the shelf, leading to large-scale glacial retreat at that time. The thickest interval of turbidite interlamination was deposited after ~1 Ma, following the onset of the Mid-Pleistocene Transition, interpreted as a time when most ice sheets grew and glacial periods were longer and more extreme. Sedimentation after ~0.8 Ma was dominated by glacigenic debris flow deposition, as the trough mouth fan that dominates the eastern Ross Sea continental slope prograded and expanded over the site. These findings will help to improve estimations of WAIS ice extent in future Ross Sea shelf-based modelling studies, and provide a basis for more detailed analysis of the inception and growth of the WAIS under distinct oceanographic conditions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Drilling constraints on lithospheric accretion and evolution at Atlantis Massif, Mid-Atlantic Ridge 30°N (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): B07103, doi:10.1029/2010JB007931.
    Description: Expeditions 304 and 305 of the Integrated Ocean Drilling Program cored and logged a 1.4 km section of the domal core of Atlantis Massif. Postdrilling research results summarized here constrain the structure and lithology of the Central Dome of this oceanic core complex. The dominantly gabbroic sequence recovered contrasts with predrilling predictions; application of the ground truth in subsequent geophysical processing has produced self-consistent models for the Central Dome. The presence of many thin interfingered petrologic units indicates that the intrusions forming the domal core were emplaced over a minimum of 100–220 kyr, and not as a single magma pulse. Isotopic and mineralogical alteration is intense in the upper 100 m but decreases in intensity with depth. Below 800 m, alteration is restricted to narrow zones surrounding faults, veins, igneous contacts, and to an interval of locally intense serpentinization in olivine-rich troctolite. Hydration of the lithosphere occurred over the complete range of temperature conditions from granulite to zeolite facies, but was predominantly in the amphibolite and greenschist range. Deformation of the sequence was remarkably localized, despite paleomagnetic indications that the dome has undergone at least 45° rotation, presumably during unroofing via detachment faulting. Both the deformation pattern and the lithology contrast with what is known from seafloor studies on the adjacent Southern Ridge of the massif. There, the detachment capping the domal core deformed a 100 m thick zone and serpentinized peridotite comprises ∼70% of recovered samples. We develop a working model of the evolution of Atlantis Massif over the past 2 Myr, outlining several stages that could explain the observed similarities and differences between the Central Dome and the Southern Ridge.
    Keywords: Atlantis Massif ; Integrated Ocean Drilling Program ; Oceanic Core Complex
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    Characterization of the in situ magnetic architecture of oceanic crust (Hess Deep) using near-source vector magnetic data (2016)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Solid Earth 121 (2016): 4130–4146, doi:10.1002/2015JB012783.
    Description: Marine magnetic anomalies are a powerful tool for detecting geomagnetic polarity reversals, lithological boundaries, topographic contrasts, and alteration fronts in the oceanic lithosphere. Our aim here is to detect lithological contacts in fast-spreading lower crust and shallow mantle by characterizing magnetic anomalies and investigating their origins. We conducted a high-resolution, near-bottom, vector magnetic survey of crust exposed in the Hess Deep “tectonic window” using the remotely operated vehicle (ROV) Isis during RRS James Cook cruise JC21 in 2008. Hess Deep is located at the western tip of the propagating rift of the Cocos-Nazca plate boundary near the East Pacific Rise (EPR) (2°15′N, 101°30′W). ROV Isis collected high-resolution bathymetry and near-bottom magnetic data as well as seafloor samples to determine the in situ lithostratigraphy and internal structure of a section of EPR lower crust and mantle exposed on the steep (~20°dipping) south facing slope just north of the Hess Deep nadir. Ten magnetic profiles were collected up the slope using a three-axis fluxgate magnetometer mounted on ROV Isis. We develop and extend the vertical magnetic profile (VMP) approach of Tivey (1996) by incorporating, for the first time, a three-dimensional vector analysis, leading to what we here termed as “vector vertical magnetic profiling” approach. We calculate the source magnetization distribution, the deviation from two dimensionality, and the strike of magnetic boundaries using both the total field Fourier-transform inversion approach and a modified differential vector magnetic analysis. Overall, coherent, long-wavelength total field anomalies are present with a strong magnetization contrast between the upper and lower parts of the slope. The total field anomalies indicate a coherently magnetized source at depth. The upper part of the slope is weakly magnetized and magnetic structure follows the underlying slope morphology, including a “bench” and lobe-shaped steps, imaged by microbathymetry. The lower part of the slope is strongly magnetized, with a gradual reduction in amplitude from east to west across the slope. Surface morphology and recent drilling results indicate that the slope has been affected by mass wasting, but the observation of internally coherent magnetization distributions within the upper and lower slopes suggest that the disturbance is surficial. We attribute the spatial differences in magnetization distribution to the combination of changes in in situ lithology and depth to the source. These survey lines document the first magnetic profiles that capture the gabbro-ultramafic and possibly dike-gabbro boundaries in fast-spreading lower crust.
    Description: NERC Grant Number: NERC509023/1; IODP-USSSP; Woods Hole Oceanographic Institution Postdoctoral Scholarship
    Keywords: Marine magnetics ; Lower crust ; Upper mantle
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Magnetic anisotropy reveals Acadian transpressional fabrics in an Appalachian ophiolite (Thetford Mines, Canada) (2021)
    Oxford University press - RAS
    Details
    Publication Date: 2021-11-26
    Description: This article has been accepted for publication in Geophysical Journal International ©: 2020, Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
    Description: Magnetic anisotropy has proved effective in characterizing primary, spreading-related magmatic fabrics in Mesozoic (Tethyan) ophiolites, for example in documenting lower oceanic crustal flow. The potential for preservation of primary magnetic fabrics has not been tested, however, in older Palaeozoic ophiolites, where anisotropy may record regional strain during polyphase deformation. Here, we present anisotropy of magnetic susceptibility results from the Ordovician Thetford Mines ophiolite (Canada) that experienced two major phases of postaccretion deformation, during the Taconian and Acadian orogenic events. Magnetic fabrics consistent with modal layering in gabbros are observed at one locality, suggesting that primary fabrics may survive deformation locally in low strain zones. However, at remaining sites rocks with different magmatic origins have consistent magnetic fabrics, reflecting structurally controlled shape preferred orientations of iron-rich phases. Subhorizontal NW-SE-oriented minimum principal susceptibility axes correlate with poles to cleavage observed in overlying post-obduction, pre-Acadian sedimentary formations, indicating that the magnetic foliation in the ophiolite formed during regionalNW-SE Acadian shortening. Maximum principal susceptibility axes plunging steeply to the NE are orthogonal to the orientation of regional Acadian fold axes, and are consistent with subvertical tectonic stretching. This magnetic lineation is parallel to the shape preferred orientation of secondary amphibole crystals and is interpreted to reflect grain growth during Acadian dextral transpression. This structural style has been widely reported along the Appalachian orogen, but the magnetic fabric data presented here provide the first evidence for transpression recorded in an Appalachian ophiolite.
    Description: Published
    Description: 1034–1045
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Keywords: Magnetic properties; North America; Magnetic fabrics and anisotropy; Folds and folding
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 7
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    Magnetic mineral populations in lower oceanic crustal gabbros (Atlantis Bank, SW Indian Ridge): implications for marine magnetic anomalies (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 21(3), (2020): e2019GC008847, doi:10.1029/2019GC008847.
    Description: To learn more about magnetic properties of the lower ocean crust and its contributions to marine magnetic anomalies, gabbro samples were collected from International Ocean Discovery Program Hole U1473A at Atlantis Bank on the Southwest Indian Ridge. Detailed magnetic property work links certain magnetic behaviors and domain states to specific magnetic mineral populations. Measurements on whole rocks and mineral separates included magnetic hysteresis, first‐order reversal curves, low‐temperature remanence measurements, thermomagnetic analysis, and magnetic force microscopy. Characteristics of the thermomagnetic data indicate that the upper ~500 m of the hole has undergone hydrothermal alteration. The thermomagnetic and natural remanent magnetization data are consistent with earlier observations from Hole 735B that show remanence arises from low‐Ti magnetite and that natural remanent magnetizations are up to 25 A m−1 in evolved Fe‐Ti oxide gabbros, but are mostly 〈1 A m−1. Magnetite is present in at least three forms. Primary magnetite is associated with coarse‐grained oxides that are more frequent in the upper part of the hole. This magnetic population is linked to dominantly “pseudo‐single‐domain” behavior that arises from fine‐scale lamellar intergrowths within the large oxides. Deeper in the hole the magnetic signal is more commonly dominated by an interacting single‐domain assemblage most likely found along crystal discontinuities in olivine and/or pyroxene. A third contribution is from noninteracting single‐domain inclusions within plagioclase. Because the concentration of the highly magnetic, oxide‐rich gabbros is greatest toward the surface, the signal from coarse oxides will likely dominate the near‐bottom magnetic anomaly signal at Atlantis Bank.
    Description: This work used samples and data provided by the International Ocean Discovery Program. Funding was provided by the U.S. Science Support Program (J.B.). I.L. has benefited from a Smithsonian Edward and Helen Hintz Secretarial Scholarship. We thank the members of the IODP Expedition 360 Science Party, and the captain and crew of the JOIDES Resolution. Part of this work was done as a Visiting Fellow at the Institute for Rock Magnetism (IRM) at the University of Minnesota. The IRM is made possible through the Instrumentation and Facilities program of the National Science Foundation, Earth Sciences Division, and by funding from the University of Minnesota. We would like to thank IRM staff M. Jackson, P. Solheid, and D. Bilardello for their generous assistance. Many thanks to A. Butula, K. Vernon, and J. Marquardt for their assistance with rock magnetic measurements at UWM and to L. McHenry for assistance with XRD. We also thank two anonymous reviewers for their thoughtful comments that improved the manuscript. Magnetic data associated with this manuscript are available in the Magnetics Information Consortium (MagIC) database at https://www.earthref.org/MagIC/doi/10.1029/2019GC008847. XRD data are available at https://zenodo.org/record/3611642.
    Description: 2020-08-28
    Keywords: Marine magnetic anomalies ; Ocean crust magnetization ; Magnetic mineralogy ; IODP ; Expedition 360 ; JOIDES Resolution
    Repository Name: Woods Hole Open Access Server
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  • 8
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    Dynamic accretion beneath a slow-spreading ridge segment: IODP hole 1473A and the Atlantis Bank oceanic core complex (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Solid Earth 124(12), (2019): 12631-12659, doi:10.1029/2018JB016858.
    Description: 809 deep IODP Hole U1473A at Atlantis Bank, SWIR, is 2.2 km from 1,508‐m Hole 735B and 1.4 from 158‐m Hole 1105A. With mapping, it provides the first 3‐D view of the upper levels of a 660‐km2 lower crustal batholith. It is laterally and vertically zoned, representing a complex interplay of cyclic intrusion, and ongoing deformation, with kilometer‐scale upward and lateral migration of interstial melt. Transform wall dives over the gabbro‐peridotite contact found only evolved gabbro intruded directly into the mantle near the transform. There was no high‐level melt lens, rather the gabbros crystallized at depth, and then emplaced into the zone of diking by diapiric rise of a crystal mush followed by crystal‐plastic deformation and faulting. The residues to mass balance the crust to a parent melt composition lie at depth below the center of the massif—likely near the crust‐mantle boundary. Thus, basalts erupted to the seafloor from 〉1,550 mbsf. By contrast, the Mid‐Atlantic Ridge lower crust drilled at 23°N and at Atlantis Massif experienced little high‐temperature deformation and limited late‐stage melt transport. They contain primitive cumulates and represent direct intrusion, storage, and crystallization of parental MORB in thinner crust below the dike‐gabbro transition. The strong asymmetric spreading of the SWIR to the south was due to fault capture, with the northern rift valley wall faults cutoff by a detachment fault that extended across most of the zone of intrusion. This caused rapid migration of the plate boundary to the north, while the large majority of the lower crust to spread south unroofing Atlantis Bank and uplifting it into the rift mountains.
    Description: The first author wishes to also recognize grants OCE1434452 and OCE1637130 from The National Science Foundation (NSF) for synthesis of the Atlantis Bank site survey data and post‐cruise rock analysis and for analysis of Expedition 360 and 362T cores and data. Additional support was also gratefully received from The Investment in Science Fund at WHOI.
    Description: 2020-05-07
    Keywords: Lower ocean crust ; Crustal accretion ; SW Indian Ridge ; Crust‐mantle boundary ; Ocean core complex ; Ocean drilling
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 9
    Electronic Resource
    Electronic Resource
    Rotational deformation during Palaeogene thrusting and basin closure in eastern central Greece: palaeomagnetic evidence from Mesozoic carbonates (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 121 (1995), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Palaeomagnetic studies in Greece have concentrated upon Neogene sequences, with Mesozoic rocks of mainland Greece receiving little attention. The Neogene data base is now sufficiently extensive, however, to allow meaningful interpretation of older units. This paper presents new palaeomagnetic data from Mesozoic and Tertiary sequences of eastern central Greece, which document a pre-Neogene phase of rotational deformation.Mesozoic carbonates have been sampled within the classic Pelagonian Zone in the Argolis Peninsula, Beotia and Evvia. Pelagonian sequences record the development, drowning and subsequent re-establishment of a carbonate platform separating two strands of the Neotethys Ocean (the Pindos and Vardar basins). Most platformal facies are too weakly magnetized for palaeomagnetic analysis. However, pelagic horizons consisting of pink condensed limestones have been deposited periodically in response to platform subsidence. These Middle-Late Triassic, Jurassic and Upper Cretaceous sequences yield high-quality palaeomagnetic data, which reveal a consistent clockwise rotation of about 94°. The constancy of rotation angle deduced from the Mesozoic rocks suggests that the total Tertiary rotation is uniform throughout the area studied. This implies that observed variations in declination within the Neogene sequences result from sampling of rocks of different ages deposited during a period of rapid overall rotation. Removal of the largest Neogene rotation (45°) from the Mesozoic data set reveals a pre-Middle Miocene. post-Late Cretaceous clockwise rotation of the southern Pelagonian Zone of 50°. The major tectonic event during this time period was the closure of the Pindos Ocean during the Eocene. A large carbonate platform within the Pindos basin, now preserved in the Parnassos Zone, presented a major obstacle to the advancing Pelagonian nappes during SW-directed thrusting (present coordinates). Impingement of the nappes on to the Parnassos platform resulted in pinning and subsequent clockwise rotation of thrust units around the south-eastern margin of the platform. The southernmost tip of the Pelagonian Zone (southern Argolis) was detached along a pre-existing line of weakness along the present Migdhalitsa Graben, and experienced a different rotation history.Additional palaeomagnetic data from the Pindos nappes in the eastern Peloponnesos also provide evidence for significant rotation of thrust sheets during Eocene basin closure. The Pindos sequences formed by pelagic sedimentation within the Pindos Ocean. An overall anti-clockwise rotation with respect to the underlying Gavrovo-Tripolitza autochthon is implied by the data. This probably reflects oblique emplacement of the Pindos thrust sheets on to the adjacent platform. Variations in rotation angle probably result from variations in footwall topography.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1995.tb06442.x
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  • 10
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    Unknown
    The puzzle of axis-normal magnetic lineations in folded low-grade sediments (Bude Formation, SW England) (2007)
    In:  Geological Society Special Publication 238: 175-190.
    Details
    Publication Date: 2007-10-08
    Description: A single upright, open anticline from sub-greenschist facies sedimentary rocks of the Bude Formation (Cornwall, UK) was sampled in order to investigate the kinematic relationships between fold development and anisotropy of magnetic susceptibility (AMS). The mean magnetic susceptibility of these samples is 0.25 x 10-3 SI, suggesting low concentrations of ferromagnetic phases. AMS ellipsoids have a mean corrected anisotropy degree of 1.03 and a mean shape parameter of -0.54 (prolate). Kmin and Kint define a girdle distribution striking sub-parallel to the fold axial plane, with Kmin tending to cluster around the fold axis. Kmax axes from both limbs of the fold define a cluster with a mean azimuth perpendicular to the fold axis. This arrangement of Kmax and Kmin could represent an inverse magnetic fabric of composite primary/tectonic origin. This is discounted, however, on the basis of broad correlation between the orientation of AMS and AIRM (anisotropy of isothermal remanence) ellipsoids. The prolate shapes and axis-normal orientation of Kmax axes contrast markedly with the widely observed relationship of AMS ellipsoids in folds, which are typically oblate and have Kmax parallel to the fold axis. This relationship is interpreted to represent progressive overprinting of primary depositional/compactional fabrics (Kmin perpendicular to bedding) by a tectonic fabric (Kmin perpendicular to cleavage). Consistency of Kmax orientations irrespective of position within the fold clearly points to a fabric of tectonic origin. Prolate ellipsoids with long axes perpendicular to the fold hinge line are indicative of superimposed sub-horizontal stretching at a late stage or post-dating fold formation. Such a situation is not inconsistent with superimposed southward-directed thrusting simple shear that has been suggested in this area to account for variations in fold attitude on a regional scale. It is more likely, however, that the fabric reflects post-orogenic extension, with the fold occupying a position in the immediate hanging-wall of a major northward dipping normal fault. In either case, the AMS fabrics around the fold record only the last increments of deformation in this area, with earlier primary and fold-related fabrics being entirely obliterated.
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