DOCSLIB.ORG

Southern Louisiana Salt Dome Xenoliths: First Glimpse of Jurassic (Ca. 160 Ma) Gulf of Mexico Crust

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Southern Louisiana Salt Dome Xenoliths: First Glimpse of Jurassic (Ca. 160 Ma) Gulf of Mexico Crust Southern Louisiana salt dome xenoliths: First glimpse of Jurassic (ca. 160 Ma) Gulf of Mexico crust Robert J. Stern1*, Elizabeth Y. Anthony2, Minghua Ren2, Brian E. Lock3, Ian Norton4, Jun-Ichi Kimura5, Takashi Miyazaki5, Takeshi Hanyu5, Qing Chang5, and Yuka Hirahara5 1Geosciences Department, University of Texas at Dallas, Richardson, Texas 75083-0688, USA 2Department of Geological Sciences, University of Texas at El Paso, El Paso, Texas 79968, USA 3Department of Geology, Box 44530, University of Louisiana, Lafayette, Louisiana 70504, USA 4Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78758, USA 5Institute for Research on Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka 237-0061, Japan ABSTRACT Salt that was deposited on top of the Late Juras- No direct information about the age and composition of rift-related igneous activity associ- sic crust, occasionally bring up samples of igne- ated with the Late Jurassic opening of the Gulf of Mexico exists because the igneous rocks are ous rocks (Lock and Duex, 1996; Ren et al., deeply buried beneath sediments. Three salt diapirs from southern Louisiana exhume samples 2009). The Five Islands of southern Louisiana of alkalic igneous rocks; these salt domes rise from the base of the sedimentary pile and overlie are part of seven uniformly spaced salt diapirs an isolated magnetic high, which may mark the position of an ancient volcano. Three samples that defi ne a linear northwest trend (Fig. 1). The from two domes were studied; they are altered but preserve relict igneous minerals including Five Islands trend overlies transitional crust strongly zoned clinopyroxene (diopside to Ti-augite) and Cr-rich spinel rimmed with titanite. thought to have formed during Gulf of Mexico 40Ar/39Ar ages of 158.6 ± 0.2 Ma and 160.1 ± 0.7 Ma for Ti-rich biotite and kaersutite from two opening (Dobson and Buffl er, 1997; Harry and different salt domes are interpreted to represent the time the igneous rock solidifi ed. Trace Londono, 2004). The diapirs containing mafi c element compositions are strongly enriched in incompatible trace elements, indicating that the igneous rocks (Jefferson, Avery, and Weeks) igneous rocks are low-degree melts of metasomatized upper mantle. Isotopic compositions of rise over a magnetic high (Fig. 1), as might be Nd and Hf indicate derivation from depleted mantle. This information supports the idea that expected from a signifi cant volume of buried crust beneath southern Louisiana formed as a magma-starved rifted margin on the northern mafi c igneous rocks. Salt mine exposures reveal fl ank of the Gulf of Mexico ca. 160 Ma. These results also confi rm that some magnetic highs highly deformed bedding defi ned by interlay- mark accumulations of mafi c igneous rocks buried beneath thick sediments around the Gulf ered halite and anhydrite with inclusions of of Mexico margins. Oligocene sandstone, shale, and igneous rocks, as well as pockets of water, oil, and gas (Lock INTRODUCTION lack of correlatable, spreading-related magnetic and Duex, 1996). Structure in the salt domes The Gulf of Mexico opened as the western- anomalies. Indirect evidence indicates opening is essentially vertical, with multiphase isocli- most arm of Tethys, related to breakup of Pangea between ca. 165 and 139 Ma (Late Jurassic) and nal folding. The original stratigraphic position and synchronous with opening of the Central that the transitional crust ranges from a narrow, of the igneous samples is not known, but must Atlantic (Pindell, 1985). In spite of this general magma-rich volcanic rifted margin beneath the have been immediately beneath, interbedded understanding about when and how it opened, Texas coast to a broader, magma-poor rifted with, and/or intruded into or above the salt the Gulf of Mexico is a rare example where the passive margin beneath Louisiana (Mickus et (Fig. 2). The age of the Louann Salt is bracketed origin of a sizable oceanic basin at low latitudes al., 2009; Stern and Dickinson, 2010). We have on stratigraphic grounds (Salvador, 1991) as is unclear, due largely to thick blanketing sedi- no direct way to sample and study this Jurassic post–Early Jurassic to pre–late Oxfordian, prob- ments (to 16 km; Muehlberger, 1992) and the seafl oor, but salt diapirs, sourced from Louann ably mostly Callovian (165–161 Ma; Walker and Geissman, 2009). We report here mineral chemical, whole-rock chemical, Nd and Hf iso- Figure 1. Magnetic anom- topic compositions, and radiometric ages for Mississippi aly map of Louisiana Ala (United States) and en- Avery to Weeks ~12 km Louisiana virons. Red is magnetic 32°N high, blue is magnetic Texas low. Seven black dots are Cenozoic sediments Av salt domes of Five Islands Fl trend. Note that three salt J W domes containing mafi c 30°N xenoliths (J—Jefferson, Late Jurassic and Cretaceous 2. Alkalic mafics Av—Avery, W—Weeks) sediments intruded into salt? 3 . Lava lt? are above magnetic high s plucked above sa interpreted to mark pres- Louann Salt (176–158 Ma) ence of buried mafi c lavas. Magnetic anoma- 1. Alkalic mafics plucked from beneath salt? 28°N Gulf of Mexico lies are from Maus et al. (2007). Fl—Florida, Ala— Figure 2. Possible relationship between salt Alabama. 94°W 92° 90° 88° and alkalic mafi c rocks. Mafi c rocks could be plucked by rising salt from underneath or above, or could have intruded. Note distance *E-mail: [email protected]. between two salt domes containing xenoliths. © 2011 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. GEOLOGY,Geology, April April 2011; 2011 v. 39; no. 4; p. 315–318; doi: 10.1130/G31635.1; 4 fi gures; 1 table; Data Repository item 2011108. 315 three samples of igneous rocks entrained in two (Fig. DR3). Diopside also exhibits core-over- 1 of these salt bodies. A third salt dome, Jeffer- growth textures with two distinct core composi- A 2EO kaersutitic amphibole son Island (Fig. 1), also contains altered mafi c tions: one with a high Cr, Si and a second with K/Ca I xenoliths (Balk, 1953), but samples of this were low Cr, Si (Fig. DR1). Rims for both core types 200 0.1 not available for study. This is the fi rst time that exhibit titanopyroxene (MgSi2 = TiAl2) and Ca- such information has been presented for igneous tschermaks (MgSi = AlviAliv) substitution and 180 Q rocks that formed when the Gulf of Mexico is are identical to matrix diopside, indicating that 160.1 ± 0.7 Ma (MSWD = 2.37) thought to have opened, in Jurassic time. We use the rim compositions were in equilibrium with 160 N P this information to further our understanding of the fi nal melt. The diopside cores and chromite LM O Gulf of Mexico formation. are probably xenocrysts and have compositions Apparent age (Ma) 140 similar to minerals in mantle rocks, e.g., abys- Integrated Age = 167.1 ± 0.8 Ma RESULTS sal peridotites from the Vulcan Fracture Zone 120 Methods are summarized in the GSA Data (Dick, 1989) or Samoan xenoliths (Wright, 100 Repository1 (Ar results and chemical and iso- 1987; Hauri and Hart, 1994). Kaersutitic amphi- 10 K/Ca topic analytical procedures). Three samples of bole occurs as small grains in W26 and as large B W26 biotitte porphyritic igneous rocks from two salt domes phenocrysts in 2EO (Fig. DR4). Similar min- 200 1 were studied. Sample 2EO is from the 1000′ eral associations have been reported for alkalic (~304 m) level of the Weeks Island dome, and magmas from the Jasper (Gee et al., 1991) and 180 W26 is from the 1300′ (~395 m) level and W25 Line Island seamounts (Natland, 1976). Ti- 158.6 ± 0.2 Ma (MSWD = 1.49) is from the 1600′ (~486 m) level of the Avery rich (~5%–7% TiO ) biotite is intergrown with 160 2 F K C E G H I J Island dome. The samples are altered, as is magnetite and quartz. Magnetite has substantial D obvious from petrographic examination, which jacobsite (Mn) and ulvospinel (Ti) components, Apparent age (Ma) 140 B reveals that primary igneous minerals such as typically (Mn0.5Fe1.1)(Fe0.9Ti0.5)O4. Relict igne- Integrated Age = 158.1 ± 0.3 Ma clinopyroxene are replaced by secondary quartz, ous feldspar was not found. This mineral assem- 120 vermiculite, calcite, hematite, and K-feldspar blage, i.e., mantle-like diopside and Cr-spinel 0 20 40 60 80 100 39 (Figs. DR2, DR8, and DR9 in the Data Reposi- with Ti-rich rims and Ti-rich hydrous phases of Cumulative % Ar Released tory). The K-feldspar assemblage is similar to biotite and amphibole, indicates involvement Figure 3. 40Ar/39Ar age and K/Ca spectra. A: Deep Sea Drilling Project Site 453 samples of moderately depleted mantle, overprinted by Weeks Island kaersutitic amphibole (sample described by Natland (1982). Intergrown with water-rich alkaline melts, probably low-degree 2EO). B: Avery Island biotite (sample W26). calcite is mcgillite, a manganous hydroxychol- partial melts. These melts were strongly alka- MSWD—mean square of weighted deviates. orosilicate (Stevenson et al., 1984). Because a line, most likely undersaturated basanite or oliv- signifi cant component of this alteration involves ine nephelinite (Anthony et al., 1989; Panina carbonate and water-rich vermiculite, a simple and Usoltseva, 2008). strength elements (HFSE, e.g., Ti, Zr, Hf, Nb, way to quantify alteration is with measured loss Biotite (W26) and kaersutitic amphibole Y; Fig. 4A). This interpretation is confi rmed on ignition (Table DR1 in the Data Repository) (2EO) with primary, igneous morphologies by elevated abundances of immobile incom- for whole-rock samples.
Load more

Recommended publications
  • Middle Eocene Claiborne Group, United States Part of the Gulf of Mexico Basin
    Geologic Assessment of Undiscovered Conventional Oil and Gas Resources —Middle Eocene Claiborne Group, United States Part of the Gulf of Mexico Basin By Paul C. Hackley U.S. Geological Survey Open-File Report 2012–1144 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia 2012 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Suggested citation: Hackley, P.C., 2012, Geologic assessment of undiscovered conventional oil and gas resources—Middle Eocene Claiborne Group, United States part of the Gulf of Mexico Basin: U.S. Geological Survey Open–File Report 2012–1144, 87 p., available only at http://pubs.usgs.gov/of/2012/1144/. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted material contained within this report. ii Contents Abstract ......................................................................................................................................................................... 1 Acknowledgments
    [Show full text]
  • University of California, San Diego
    UNIVERSITY OF CALIFORNIA, SAN DIEGO Petrogenesis of Intraplate Lavas from Isolated Volcanoes in the Pacific: Implications for the Origin of the Enriched Mantle Source of OIB A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Earth Sciences by Liyan Tian Committee in charge: Professor Paterno Castillo, Chair Professor David Hilton Professor James Hawkins Professor Mark Thiemens Professor Peter Lonsdale 2011 Copyright Liyan Tian, 2011 All rights reserved. The Dissertation of Liyan Tian is approved, and it is acceptable in quality and form for publication on microfilm and electronically: Chair University of California, San Diego 2011 iii This dissertation is dedicated to my parents, You Tian and Xiufen Jiang, who taught me to value education. iv TABLE OF CONTENTS SIGNATURE PAGE………………………………………………………………….iii DEDICATION………………………………………………………………………...iv TABLE OF CONTENTS……………………………………………………………...v LIST OF FIGURES………………………………………………………………….vii LIST OF TABLES…………………………………………………………………..viii ACKNOWLEDGEMENTS…………………………………………………………..ix VITA AND PUBLICATIONS………………………………………………………..xii ABSTRACT………………………………………………………………………….xv CHAPTER 1: Introduction…………………………………………………………….1 1.1. Scientific background and objectives of this dissertation………………………...1 1.2. Contents of the dissertation……………………………………………………….4 1.2.1. Chapter 2………………………………………………………………………..4 1.2.2. Chapter 3 and 4…………………………………………………………………6 1.2.3. Chapter 5………………………………………………………………………..7 1.3. Conclusions……………………………………………………………………….8 References……………………………………………………………………………12
    [Show full text]
  • What Is a Salt Dome? How Do They Form? 3/2/18, 4:06 PM What Is a Salt Dome?
    What is a Salt Dome? How do they form? 3/2/18, 4:06 PM What is a Salt Dome? » » Salt Domes Columns of salt that intrude through overlying sediment units. Middle Jurassic salt: This cross-section shows rocks of the East Texas Basin between the Oklahoma-Texas border (on the left) and the Gulf of Mexico coastline (on the right). The purple rock unit is the Middle Jurassic salt, a rock unit that has the ability to flow under pressure. The salt is overlain by thousands of feet of sediment which place enormous pressure on the surface of the salt and cause it to flow. At numerous locations the salt has intruded upwards into overlying sediments. This has produced small mounds or towering columns of salt that can be thousands of feet tall. The salt columns and smaller mounds are called "salt domes." USGS image [1]. https://geology.com/stories/13/salt-domes/ Page 1 of 12 What is a Salt Dome? How do they form? 3/2/18, 4:06 PM Salt Dome: Cartoon of a salt dome showing piercement through two rock units and deformation of the rock unit immediately above. Growth of the dome is accomplished by migration of salt into the dome from surrounding areas. The salt migrates into the dome because it is compressed by the weight of overlying sediments. What is a Salt Dome? A salt dome is a mound or column of salt that has intruded upwards into overlying sediments. Salt domes can form in a sedimentary basin where a thick layer of salt is overlain by younger sediments of significant thickness.
    [Show full text]
  • A Geophysical and Geologic Study of Nagata Seamount, Northern Line Islands*
    J. Geomag. Geoelectr., 34, 283-305, 1982 A Geophysical and Geologic Study of Nagata Seamount, Northern Line Islands* W. W. SAGER, G. T. DAMS, B. H. KEATING, and J. A. PHILPOTTS Hawaii Institute of Geophysics, University of Hawaii, 2525 Correa Road, Honolulu, Hawaii, U. S. A. (Rece25 Correa Road, Honolulu, Hawaii, U. S. A. Nagata Seamount, located in the northern Line Islands at 12.5N, 167.0W, was surveyed and dredged by the Hawaii Institute of Geophysics in the fall of 1979. The seamount is 3.7 km in height, approximately 45 km at maximum width, and has an estimatedvolume of 590 km3 Analysisof dredgerocks indicatesthat the seamount consists of alkali basalts and hyaloclastitebreccias. Both acoustic reflectionrecords and magnetic modelingstudies indicate that the seamount is draped with a large volume of volcaniclastic debris about its base. At sometime in its history Nagata Seamountmay have been at or near sea level. The bulk of the seamount is made up of lavas of normal magnetic polarity; however, the uppermost 1,000 m consists of reverselypolarized rock. The virtual geomagneticpole determined from the seamount falls at 61.6N, 4.0E not far from the averageCretaceous Pacific seamount pole. Rock magnetism studies of the dredged basalts indicate a stable magnetization. Three dimensional gravity modeling determined an average density of 2.5 g/cm3 for the seamount. This value of the density agrees with other similar data from Pacific and Atlantic seamounts; although, unlike some other seamounts studied gravi- tationally, no large density variations were revealed on Nagata Seamount. K/Ar radiometricages of 70 Ma and 86 Ma wereobtained from the dredged basaltsin agreementwith the paleomagneticpole.
    [Show full text]
  • 33. Rock Magnetic Studies of Serpentinite Seamounts in the Mariana and Izu-Bonin Regions1
    Fryer, P., Pearce, J. A., Stokking, L. B., et al., 1992 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 125 33. ROCK MAGNETIC STUDIES OF SERPENTINITE SEAMOUNTS IN THE MARIANA AND IZU-BONIN REGIONS1 L. B. Stokking,2 D. L. Merrill,2 R. B. Haston,3 J. R. Ali,4 and K. L. Saboda5 ABSTRACT During Leg 125, scientists drilled two serpentinite seamounts: Conical Seamount in the Mariana forearc and Torishima Forearc Seamount in the Izu-Bonin forearc. Grain densities of the serpentinized peridotites range from 2.44 to 3.02 g/cm3. The NRM intensity of the serpentinized peridotites ranges from 0.01 to 0.59 A/m and that of serpentine sediments ranges from 0.01 to 0.43 A/m. Volume susceptibilities of serpentinized peridotites range from 0.05 × I0"3 S1 to 9.78 × I0"3 S1 and from 0.12 × I0"3 to 4.34 × 10~3 S1 in the sediments. Koenigsberger ratios, a measure of the relative contributions of remanent vs. induced magnetization to the magnetic anomaly, vary from 0.09 to 80.93 in the serpentinites and from 0.06 to 4.74 in the sediments. The AF demagnetization behavior of the serpentinized peridotites shows that a single component of remanence (probably a chemical remanence carried by secondary magnetite) can be isolated in many samples that have a median destructive field less than 9.5 mT. Multiple remanence components are observed in other samples. Serpentine sediments exhibit similar behavior. Comparison of the AF demagnetization of saturation isothermal remanence and NRM suggests that the serpentinized peridotites contain both single-domain and multidomain magnetite particles.
    [Show full text]
  • A Review of the Effects of Seamounts on Biological Processes
    A REVIEW OF THE EFFECTS OF SEAMOUNTS ON BIOLOGICAL PROCESSES George W. Boehlert Southwest Fisheries Center Honolulu Laboratory, National Marine Fisheries Service. NOAA. 2570 Dole St., Honolulu, HI 96822-2396 Amatzia Genin Scripps Institution of Oceanography, A-008, University of California, La Jolla, CA 92093 Abstract. Seamounts interacting with oceanic continental shelf or slope counterparts at similar currents create flow complexities which depend water depths [Hubbs, 19591. In the open ocean, upon current speed, stratification. latitude, and seamounts interact with ocean currents and create seamount morphology. Seamount effects. which variability in the physical flow field. Several include internal wave generation. eddy formation. studies have described these effects on the Gulf local upwelling. and closed circulation patterns Stream [Vastano and Warren, 19761 and the Kuroshio called Taylor columns. have important effects upon [Roden et al.. 1982; Roden. 19871. The physical pelagic and benthic ecosystems over seamounts. effects include local small- and mesosca7.e phe- The biological effects of these current-topography nomena including the shedding of mesoscale eddies interactions are poorly understood. Flow accel- which alter flow patterns for significant dis- eration on upper flanks of seamounts may lead to tances downstream of the seamounts [Royer. 19781. low sedimentation but areas of high standing Biological effects of these physical complexities stocks of benthic fauna, particularly filter feed- are not well understood [Genin and Boehlert 1985; ers. Other effects extend into the water column: Boehlert, 19861. Discovery of seamount fishery nutrient enrichment and enhanced primary produc- [Uchida and Tagami. 19841 and mineral resources tivity occur over some seamounts. Longer observa- [Manheim, 19861, however, has caused increased tional periods will be necessary to understand the interest in seamount oceanography and its effects time-varying nature of such enhanced productivity on biota [Darnitsky et al.
    [Show full text]
  • Spotlight 2Jasper Seamount
    or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The approval portionthe ofwith any articlepermitted only photocopy by is of machine, reposting, this means or collective or other redistirbution This article has This been published in MOUNTAINS IN THE SEA Jasper Seamount SPOTLIGHT 2 30°26.40'N, 122°44.40'W Oceanography By Jasper G. Konter, Hubert Staudigel, and Jeffrey Gee , Volume 23, Number 1, a quarterly journal of The 23, Number 1, a quarterly , Volume Jasper Seamount is a submarine volcano D1 Dredge OBS -500 -1500 -2700 -3900 in the Fieberling-Guadalupe seamount -900 -2100 -3300 mbsl trail, located off the coast of Baja California, Mexico. It rises from the 4000-m-deep seafloor to a summit depth of 700 m (Figure 1). Detailed geophys- 30°30'N ical, geochemical, and geological studies D1 O there provide an in-depth geological D9 D2 ceanography understanding of a seamount that D14 D15 D11 00 0 approaches our knowledge of subaerial S -1 ociety. ociety. volcanoes. Active-source seismic experi- D12 D3 D18 © D4 00 ments at Jasper Seamount resulted in 30°25'N 0 The 2010 by D6 -2 00 the first seismic velocity models of an 0 D13 -3 intraplate seamount (Hammer et al., D19 O 1994). Marine gravity and magnetics D5 ceanography surveys, combined with analyses of D8 O ceanography ceanography the physical properties, geochemistry, S ociety. ociety. and geochronology of dredge samples, A enabled scientists to develop a detailed 122°45'W 122°40'W reproduction, systemmatic Republication, article for use and research.
    [Show full text]
  • Implications for Seamount Paleopoles Jeff Gee, Hubert Staudigel, Lisa Tauxe, Thomas Pick
    Magnetization of the La Palma Seamount Series: Implications for Seamount Paleopoles Jeff Gee, Hubert Staudigel, Lisa Tauxe, Thomas Pick To cite this version: Jeff Gee, Hubert Staudigel, Lisa Tauxe, Thomas Pick. Magnetization of the La Palma Seamount Series: Implications for Seamount Paleopoles. Journal of Geophysical Research, American Geophysical Union, 1993, 98767, pp.11743-11754. 10.1029/93JB00932. insu-01864349 HAL Id: insu-01864349 https://hal-insu.archives-ouvertes.fr/insu-01864349 Submitted on 29 Aug 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 98, NO. B7, PAGES 11,743-11,767, JULY 10, 1993 Magnetizationof the La Palma SeamountSeries: Implicationsfor SeamountPaleopoles JEFFGF_11,1 HtmERT STAUDIGI•L, 2 LISA TAUX•, 3 AND THOMAS PICK ScrippsImtitutlon of Oceanography,La Jolla, California YVES GALLET Institutde Physiquedu G?obede Paris Paleopolesdetermined from seamountmagnetic anomalies constitute the major data sourcefor the Pacific apparentpolar wander path, but relatively little is known about the processesof remanence acquisitionin seamounts.Since magneticanomalies reflect both natural remanence(NRM) and the inducedfield, it is importantfirst to assesswhether the NRM is likely to representan original field directionand secondto constrainthe magnitudeof the inducedcomponent.
    [Show full text]
  • Magnetic Petrology and Magnetic Properties of Western Pacific Guyots; Implications for Seamount Paleopoles
    Haggerty, J.A., Premoli Silva, I., Rack, F., and McNutt, M.K. (Eds.), 1995 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 144 36. MAGNETIC PETROLOGY AND MAGNETIC PROPERTIES OF WESTERN PACIFIC GUYOTS: IMPLICATIONS FOR SEAMOUNT PALEOPOLES1 Jeff Gee2 and Masao Nakanishi3 ABSTRACT Despite the importance of seamount paleopoles in reconstructing past tectonic motions of the Pacific Plate, few data exist on the magnetic properties and processes of remanence acquisition in seamounts. We present a basic magnetic characterization and a detailed petrographic and microprobe study of the oxide minerals in mildly to strongly alkalic lavas recovered from five western Pacific guyots sampled during Ocean Drilling Program Leg 144. The Ti-rich chrome spinel compositions and Al- and Mg-enrich- ment in titanomagnetites reflect the alkalic nature of the lavas. The alteration history of these samples is diverse, ranging from low-temperature oxidation to highly oxidizing conditions resulting in an assemblage of magnesioferrite + titanohematite. The natural remanent magnetization (NRM) intensities for all five guyots are quite similar, yielding a combined arithmetic mean NRM intensity of 3.53 A/m, similar to previously reported values from dredged and drilled seamount material. The mean Königsberger ratio (9.8) implies an approximate 10% contribution of induced magnetization. Systematic discrepancies between the observed inclinations and inclinations derived from the magnetic anomaly data for Lo-En, MIT, and Takuyo-Daisan guyots are compatible with a significant bias from viscous and induced magnetization in these Cretaceous guyots. INTRODUCTION interval of opposite polarity to that of the original thermal remanence (Gee et al., 1993). In this paper, we present a petrographic and Paleopoles derived from seamount magnetic anomalies constitute microprobe characterization of the oxide mineralogy and alteration in a major source of data for reconstructing the past motions of the lavas from western Pacific guyots.
    [Show full text]
  • Sources Used in Compilation of the Geologic Map of North America
    GSA Data Repository #2005019 Sources Used in Compilation of the Geologic Map of North America This document lists the sources used in the compilation of the Decade of North American Geology Geologic map of North America. Sources used by Reed and Wheeler in the compilation of the on-land geology are listed together and are arranged by political entities or geographic regions, generally from north to south and from west to east. In Canada references are listed by type (general references, regional references, and provincial maps). In the conterminous United States references are listed by regions (Eastern States, Central States, Rocky Mountain states, and Great Basin and Pacific Coast states) and then by groups of states within each region. Sources used by Tucholke in compilation of the seafloor geology are listed separately , and are arranged by map quarter, beginning in the southerastern quarter and proceeding counterclockwise to the southwestern quarter. In each quarter the published sources and the sunpublished sources are listed separately. References that apply to more than one quarter are duplicated in the lists for all of the quarters to which they apply. ON-LAND GEOLOGY General References Fullerton, D. J., Bush, C. A., and Pennell, J. N., Map of surficial deposits and materials in the eastern and central United States: U. S. Geological Survey Geologic Investigations Map I-2789, scale 1:2,500,000 Global volcanism program, Smithsonian Institution, 1998, List of Holocene volcanoes; available at www.volcano.si.edu. King, P.B. and Edmonston, G.J., 1972, Generallized tectonic map of North America: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-688, scale 1:5,000,000.
    [Show full text]
  • Deep Sea Drilling Project Initial Reports Volume 10
    29. REGIONAL ASPECTS OF DEEP SEA DRILLING IN THE GULF OF MEXICO LEG 10 J. Lamar Worzel, Earth and Planetary Sciences, Marine Biomedical Institute, University of Texas at Galveston, Texas and William R. Bryant, Texas A&M University, College Station, Texas INTRODUCTION creasing amounts of gases. Beacon failure, causing loss of Leg 10 extended the drilling information in the Gulf of ability to properly control position while drilling, caused Mexico begun on Leg 1. The summary of results for Leg termination of Site 96 because there was only one effec- 1 in the Gulf of Mexico is reported by Ewing, Worzel, and tive beacon left, and it was deemed more important to drill Burk, (1969, p. 624). Figure 1 (reproduced from that re- Site 97 than to continue Site 96. Site 97 was most difficult port) shows the most important physiographic features of because of beacon troubles and the strong currents, no the Gulf including the known regions of salt domes and doubt associated with the Gulf Stream. Although the cur- the three holes drilled in the Gulf of Mexico during Leg rent charts indicated we should expect strong currents 1. As a short resume, Site 1, drilled to a subbottom depth from the northwest, we experienced 4- to 5-knot currents of 770.5 meters near the foot of the Sigsbee Scarp, encoun- from the southwest for the 2.5 days we were on station. tered only Pleistocene and Holocene sediments with abun- The thrusters were not adequate to keep the ship on sta- dant evidence that most, if not all, of the section drilled tion, so the computer program for position keeping had to was slump material.
    [Show full text]
  • Geochemistry of Juan Fernandez Lavas Reveal Variable Contributions from a High-3He/4He Mantle Plume
    Chemical Geology 476 (2018) 280–291 Contents lists available at ScienceDirect Chemical Geology journal homepage: www.elsevier.com/locate/chemgeo The trace element and Sr-Nd-Pb isotope geochemistry of Juan Fernandez T lavas reveal variable contributions from a high-3He/4He mantle plume ⁎ Thi B. Truong1, Paterno R. Castillo , David R. Hilton, James M.D. Day Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0212, USA ARTICLE INFO ABSTRACT Editor: Catherine Chauvel The Juan Fernandez Islands in the southeastern Pacific are an atypical linear volcanic chain that exhibits a 3 4 3 4 Keywords: considerable range in He/ He ratios (8 to 18 RA, where RA is the He/ He ratio of air), but limited ranges of 87 86 143 144 Juan Fernandez Sr/ Sr and Nd/ Nd. Here we report new trace element abundance data and Sr-Nd-Pb isotope data for 3He/4He mafic lavas previously analyzed for their 3He/4He and He contents from the two main islands of Robinson Crusoe Mantle plume and Alexander Selkirk. Lavas from these islands have been previously grouped based on geochemical and pet- Sr-Nd-Pb isotopes rological classification into Group I and III basalts, and Group II basanites. In general, samples have overlapping Isotope decoupling Sr-Nd-Pb isotope compositions that suggest a common, albeit slightly heterogeneous mantle source. In detail, the FOZO Group I and III tholeiitic and alkalic basalts have nearly identical incompatible trace element patterns, whereas the Group II basanites show elevated incompatible trace element abundances. Major and incompatible trace 3 4 element modeling indicates that Group III basalts ( He/ He = 7.8–9.5 RA) from younger Alexander Selkirk Island were produced by the highest degree of partial melting (> 10%) of a common mantle source, followed by Group I basalts (13.6–18.0 RA) and Group II basanites (11.2–12.5 RA) from older Robinson Crusoe Island.
    [Show full text]