DOCSLIB.ORG

Comparing Petrographic Signatures of Bioalteration in Recent to Mesoarchean Pillow Lavas: Tracing Subsurface Life in Oceanic Igneous Rocks Harald Furnes A,∗, Neil R

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Comparing Petrographic Signatures of Bioalteration in Recent to Mesoarchean Pillow Lavas: Tracing Subsurface Life in Oceanic Igneous Rocks Harald Furnes A,∗, Neil R Precambrian Research 158 (2007) 156–176 Comparing petrographic signatures of bioalteration in recent to Mesoarchean pillow lavas: Tracing subsurface life in oceanic igneous rocks Harald Furnes a,∗, Neil R. Banerjee b, Hubert Staudigel c, Karlis Muehlenbachs d, Nicola McLoughlin a, Maarten de Wit e, Martin Van Kranendonk f a Centre for Geobiology and Department of Earth Science, University of Bergen, Allegt. 41, 5007 Bergen, Norway b Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada N6A 5B7 c Scripps Institution of Oceanography, University of California, La Jolla, CA 92093-0225, USA d Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E3 e AEON and Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa f Geological Survey of Western Australia, 100 Plain St. East Perth, Western Australia 6004, Australia Received 31 October 2006; received in revised form 12 March 2007; accepted 28 April 2007 Abstract Bioalteration of basaltic glass in pillow lava rims and glassy volcanic breccias (hyaloclastites) produces several distinctive traces including conspicuous petrographic textures. These biologically generated textures include granular and tubular morphologies that form during glass dissolution by microbes and subsequent precipitation of amorphous material. Such bioalteration textures have been described from upper, in situ oceanic crust spanning the youngest to the oldest oceanic basins (0–170 Ma). The granular type consists of individual and/or coalescing spherical bodies with diameters typically around 0.4 ␮m. These are by far the most abundant, having been traced up to ∼550 m depths in the oceanic crust. The tubular type is defined by distinct, straight to irregular tubes with diameters most commonly around 1–2 ␮m and lengths exceeding 100 ␮m. The tubes are most abundant between ∼50 m and 250 m into the volcanic basement. We advance a model for the production of these bioalteration textures and propose criteria for testing the biogenicity and antiquity of ancient examples. Similar bioalteration textures have also been found in hyaloclastites and well-preserved pillow lava margins of Phanerozoic to Proterozoic ophiolites and Archean greenstone belts. The latter include pillow lavas and hyaloclastites from the Mesoarchean Barberton Greenstone Belt of South Africa and the East Pilbara Terrane of the Pilbara Craton, Western Australia, where conspicuous titanite-mineralized tubes, have been found. Petrographic relationships and age data confirm that these structures developed in the Archean. Thus, these biologically generated textures may provide an important tool for mapping the deep oceanic biosphere and for tracing some of the earliest biological processes on Earth and perhaps other planetary surfaces. © 2007 Elsevier B.V. All rights reserved. Keywords: Bioalteration textures; Volcanic glass; Oceanic crust; Ophiolites; Greenstone belts; Evidence for early life 1. Introduction Life on Earth may have evolved well before the old- est preserved rocks, prior to 3.8 Ga, and most likely in ∗ Corresponding author. Tel.: +47 5558 3530; fax: +47 5558 3660. the vicinity of hydrothermal vents in the oceanic crust E-mail address: [email protected] (H. Furnes). (Nisbet and Sleep, 2001; Canfield et al., 2006). Evidence 0301-9268/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.precamres.2007.04.012 H. Furnes et al. / Precambrian Research 158 (2007) 156–176 157 for the earliest (∼3.8 Ga) purported life on Earth is solely et al., 1998; Furnes and Staudigel, 1999; Banerjee geochemical and consists of isotopically light carbon and Muehlenbachs, 2003). Furthermore, Furnes and in graphite contained within amphibolite- to granulite- Staudigel (1999) have demonstrated that the bioalter- grade supracrustal rocks in the Itsaq Gneiss Complex ation process can be traced as deep as ∼550 m into the of the North Atlantic Craton in southwest Greenland oceanic crust and that these biotic alteration processes (Schidlowski, 1988, 2001; Mojzsis et al., 1996; Rosing, dominate in the upper ∼350 m of the volcanic crust. 1999), but this evidence has been controversial (van Thus, a large body of evidence collected over the last Zuilen et al., 2002; Lepland et al., 2005). The earliest decade has convincingly demonstrated that the upper candidate fossilized microorganisms, on the other hand, volcanic part of the in situ oceanic crust is a habitat for are found in rocks ∼3.5 Ga from the Pilbara Craton in microbial life. Moreover, the bioalteration of pillow lava Australia (Walter et al., 1980; Schopf, 1993; Hoffman et glass is a widespread and common process that may have al., 1999; Ueno et al., 2001; Van Kranendonk et al., 2003; a profound effect on the chemical reactions, fluxes and Allwood et al., 2006) and the Barberton Greenstone products of seawater–rock interactions (e.g. Staudigel Belt in South Africa (Muir and Grant, 1976; Knoll and and Furnes, 2004; Staudigel et al., 2004). Barghoorn, 1977; Walsh and Lowe, 1985; Walsh, 1992; Textural studies of pillow lavas from in situ oceanic Westall et al., 2001, 2006), but many of these claims have crust can only record bio-interaction with pillow lavas likewise proved controversial (e.g. Lowe, 1994; Brasier dating back to the oldest intact example of ∼170 Ma et al., 2002, 2005; Garcia-Ruiz et al., 2003). (Fisk et al., 1999). This represents only a small fraction of Until recently, only sediments were considered to Earth’s history and to extend the record of bioalteration provide habitats for microbial activity, leaving volcanic further back in Earth’s history, it is therefore necessary rocks largely unexplored by biogeoscience research. to investigate pillow lavas of former oceanic crust repre- Recent studies have shown that submarine glassy basaltic sented by ophiolites and greenstone belts. These studies rocks also provide habitats for microbial life, first con- have so far confirmed that similar microbe-rock interac- vincingly shown by Thorseth et al. (1992). Moreover, tions have taken place within formerly glassy volcanic it has been suggested that soon after eruption, when rocks since the Mesoarchean (Furnes and Muehlenbachs, the ambient temperature (<113 ◦C) is tolerable for life 2003; Furnes et al., 2004, 2005; Banerjee et al., 2006a). to exist (Stetter et al., 1990; Stetter, 2006), coloniza- Thus bioalteration textures provide a new search tool for tion of the glassy rim of pillow lavas by microorganisms the earliest signs of life on Earth and other planetary sur- occurs contemporaneously wherever seawater has access faces (e.g. Banerjee et al., 2004a,b, 2006b; McLoughlin (Thorseth et al., 2001). et al., 2007). Microbial colonization of the glassy selvages of pil- In this paper, we first describe the range of alteration low lavas is most commonly observed along fractures, textures that are found within the glassy rims of pillow leaving behind several traces of their former presence. lavas from in situ oceanic crust. We then present a model The most ubiquitous are microscopic alteration tex- for the biotic alteration of oceanic pillow lavas and pro- tures found within the fresh glass at the interface with posed criteria for testing the antiquity and biogenicity of altered glass. These are empty or mineral-filled pits and these bioalteration textures. We then proceed to demon- channels with sizes and shapes that are comparable to strate that similar bioalteration textures are preserved in modern microbes. Furthermore, samples with these pet- ancient pillow lavas from ophiolites and greenstone belts rographic alteration textures commonly show very low back to 3.5 billion years ago. We outline the petrographic δ13C values (e.g. Furnes et al., 1999, 2001a; Banerjee and characteristics of mineralised bioalteration structures in Muehlenbachs, 2003), elevated concentrations of ele- ancient pillow lava rims and hyaloclastites and review ments such as C, N, P, K and S (e.g. Furnes et al., 2001b; what is currently known about how these biostructures Banerjee and Muehlenbachs, 2003), and in younger sam- are preserved. Lastly, we explore how bioalteration tex- ples the presence of DNA (e.g. Torsvik et al., 1998; tures found in terrestrial pillow lavas may be sought in Furnes et al., 2001a; Banerjee and Muehlenbachs, 2003), extraterrestrial rocks. all of which are strongly suggestive of a biogenic origin. Several studies have documented alteration textures, 2. Alteration textures in pillow lava of the element distributions and carbon isotope compositions modern oceanic crust of pillow lavas from in situ oceanic crust world-wide that are indicative of microbial alteration processes There are two fundamentally different modes of alter- (Thorseth et al., 1995a, 2001, 2003; Furnes et al., ation of basaltic glass in modern seafloor setting, i.e. 1996, 1999, 2001a,b; Fisk et al., 1998, 2003; Torsvik abiotic and biotic alteration. The abiotic alteration results 158 H. Furnes et al. / Precambrian Research 158 (2007) 156–176 in the formation of the long-recognized, but enigmatic as palagonite. It appears as banded material of approx- material termed palagonite. The other alteration mode imately equal thickness on both sides of fractures, with is the more recently-recognized biotic etching gener- smooth alteration fronts between the fresh and altered ated by the microbial colonization of rock surfaces. glass that are symmetric with respect to the fracture. The two alteration processes may be
Load more

Recommended publications
  • Volcanology and Mineral Deposits
    THESE TERMS GOVERN YOUR USE OF THIS DOCUMENT Your use of this Ontario Geological Survey document (the “Content”) is governed by the terms set out on this page (“Terms of Use”). By downloading this Content, you (the “User”) have accepted, and have agreed to be bound by, the Terms of Use. Content: This Content is offered by the Province of Ontario’s Ministry of Northern Development and Mines (MNDM) as a public service, on an “as-is” basis. Recommendations and statements of opinion expressed in the Content are those of the author or authors and are not to be construed as statement of government policy. You are solely responsible for your use of the Content. You should not rely on the Content for legal advice nor as authoritative in your particular circumstances. Users should verify the accuracy and applicability of any Content before acting on it. MNDM does not guarantee, or make any warranty express or implied, that the Content is current, accurate, complete or reliable. MNDM is not responsible for any damage however caused, which results, directly or indirectly, from your use of the Content. MNDM assumes no legal liability or responsibility for the Content whatsoever. Links to Other Web Sites: This Content may contain links, to Web sites that are not operated by MNDM. Linked Web sites may not be available in French. MNDM neither endorses nor assumes any responsibility for the safety, accuracy or availability of linked Web sites or the information contained on them. The linked Web sites, their operation and content are the responsibility of the person or entity for which they were created or maintained (the “Owner”).
    [Show full text]
  • Geochemical Heterogeneity Within Mid-Ocean Ridge Lava £Ows: Insights Into Eruption, Emplacement and Global Variations in Magma Generation
    Earth and Planetary Science Letters 188 (2001) 349^367 www.elsevier.com/locate/epsl Geochemical heterogeneity within mid-ocean ridge lava £ows: insights into eruption, emplacement and global variations in magma generation K.H. Rubin a;*, M.C. Smith a, E.C. Bergmanis a, M.R. Per¢t b, J.M. Sinton a, R. Batiza a;c a b c Received 5 September 2000; accepted 28 March 2001 Abstract Compositional heterogeneity in mid-ocean ridge (MOR) lava flows is a powerful yet presently under-utilized volcanological and petrological tracer. Here, it is demonstrated that variations in pre- and syn-eruptive magmatic conditions throughout the global ridge system can be constrained with intra-flow compositional heterogeneity among 10 discrete MOR flows. Geographical distribution of chemical heterogeneity within flows is also used along with mapped physical features to help decipher the range of conditions that apply to seafloor eruptions (i.e. inferred vent locations and whether there were single or multiple eruptive episodes). Although low-pressure equilibrium fractional crystallization can account for much of the observed intra-flow compositional heterogeneity, some cases require multiple parent magmas and/or more complex crystallization conditions. Globally, the extent of within-flow compositional heterogeneity is well correlated (positively) with estimated erupted volume for flows from the northern East Pacific Rise (EPR), and the Mid Atlantic, Juan de Fuca and Gorda Ridges; however, some lavas from the superfast spreading southern EPR fall below this trend. Compositional heterogeneity is also inversely correlated with spreading rate. The more homogeneous compositions of lavas from faster spreading ridges likely reflect the relative thermal stability and longevity of sub-ridge crustal magma bodies, and possibly higher eruption frequencies.
    [Show full text]
  • Timeline of Natural History
    Timeline of natural history This timeline of natural history summarizes significant geological and Life timeline Ice Ages biological events from the formation of the 0 — Primates Quater nary Flowers ←Earliest apes Earth to the arrival of modern humans. P Birds h Mammals – Plants Dinosaurs Times are listed in millions of years, or Karo o a n ← Andean Tetrapoda megaanni (Ma). -50 0 — e Arthropods Molluscs r ←Cambrian explosion o ← Cryoge nian Ediacara biota – z ←Earliest animals o ←Earliest plants i Multicellular -1000 — c Contents life ←Sexual reproduction Dating of the Geologic record – P r The earliest Solar System -1500 — o t Precambrian Supereon – e r Eukaryotes Hadean Eon o -2000 — z o Archean Eon i Huron ian – c Eoarchean Era ←Oxygen crisis Paleoarchean Era -2500 — ←Atmospheric oxygen Mesoarchean Era – Photosynthesis Neoarchean Era Pong ola Proterozoic Eon -3000 — A r Paleoproterozoic Era c – h Siderian Period e a Rhyacian Period -3500 — n ←Earliest oxygen Orosirian Period Single-celled – life Statherian Period -4000 — ←Earliest life Mesoproterozoic Era H Calymmian Period a water – d e Ectasian Period a ←Earliest water Stenian Period -4500 — n ←Earth (−4540) (million years ago) Clickable Neoproterozoic Era ( Tonian Period Cryogenian Period Ediacaran Period Phanerozoic Eon Paleozoic Era Cambrian Period Ordovician Period Silurian Period Devonian Period Carboniferous Period Permian Period Mesozoic Era Triassic Period Jurassic Period Cretaceous Period Cenozoic Era Paleogene Period Neogene Period Quaternary Period Etymology of period names References See also External links Dating of the Geologic record The Geologic record is the strata (layers) of rock in the planet's crust and the science of geology is much concerned with the age and origin of all rocks to determine the history and formation of Earth and to understand the forces that have acted upon it.
    [Show full text]
  • A Community Effort Towards an Improved Geological Time Scale
    A community effort towards an improved geological time scale 1 This manuscript is a preprint of a paper that was submitted for publication in Journal 2 of the Geological Society. Please note that the manuscript is now formally accepted 3 for publication in JGS and has the doi number: 4 5 https://doi.org/10.1144/jgs2020-222 6 7 The final version of this manuscript will be available via the ‘Peer reviewed Publication 8 DOI’ link on the right-hand side of this webpage. Please feel free to contact any of the 9 authors. We welcome feedback on this community effort to produce a framework for 10 future rock record-based subdivision of the pre-Cryogenian geological timescale. 11 1 A community effort towards an improved geological time scale 12 Towards a new geological time scale: A template for improved rock-based subdivision of 13 pre-Cryogenian time 14 15 Graham A. Shields1*, Robin A. Strachan2, Susannah M. Porter3, Galen P. Halverson4, Francis A. 16 Macdonald3, Kenneth A. Plumb5, Carlos J. de Alvarenga6, Dhiraj M. Banerjee7, Andrey Bekker8, 17 Wouter Bleeker9, Alexander Brasier10, Partha P. Chakraborty7, Alan S. Collins11, Kent Condie12, 18 Kaushik Das13, Evans, D.A.D.14, Richard Ernst15, Anthony E. Fallick16, Hartwig Frimmel17, Reinhardt 19 Fuck6, Paul F. Hoffman18, Balz S. Kamber19, Anton Kuznetsov20, Ross Mitchell21, Daniel G. Poiré22, 20 Simon W. Poulton23, Robert Riding24, Mukund Sharma25, Craig Storey2, Eva Stueeken26, Rosalie 21 Tostevin27, Elizabeth Turner28, Shuhai Xiao29, Shuanhong Zhang30, Ying Zhou1, Maoyan Zhu31 22 23 1Department
    [Show full text]
  • Gawler Craton: Half a Billion Years Older Than Previously Thought!
    ISSUE 92 Dec 2008 Foundations of South Australia discovered Gawler Craton: half a billion years older than previously thought! Geoff Fraser, Chris Foudoulis, Narelle Neumann, Keith Sircombe (Geoscience Australia) Stacey McAvaney, Anthony Reid, Michael Szpunar (Primary Industries and Resources South Australia) Recent geochronology results obtained using Geoscience Australia’s a billion years older than the Sensitive High Resolution Ion Microprobe (SHRIMP) have identified oldest previously-dated rock from Mesoarchean rocks (about 3150 million years old) in the eastern South Australia, making these Gawler Craton, South Australia. These rocks are approximately half the oldest rocks yet discovered in 136° 137° Australia outside the Pilbara and Port Augusta Yilgarn Craton areas of Western 08GA-G01 Australia. A series of seismic transects are being collected across selected regions of the Australian 33° See Inset below Whyalla continent as part of Geoscience Kimba Australia’s Onshore Energy SOUTH Security Program. One of these AUSTRALIA seismic transects, collected in June 2008, traverses the northern Cowell Eyre Peninsula of South Australia Iron Monarch (figure 1). When processed, the seismic data will provide an east– 23 Mile Wallaroo west cross-section of the eastern 34° margin of the Gawler Craton. Spencer Moonta Gulf This region hosts significant CUMMINS uranium, geothermal, copper- Iron Baron/ TUMBY BAY Iron Prince gold, gold and iron resources. Maitland To assist the interpretation of 08-3449-1 0 50 km the seismic data and the current geological mapping program of Mesoarchean granite NT QLD Primary Industries and Resources WA Seismic survey route SA Road South Australia, a program of NSW VIC Railway geochronology is underway to Mineral occurence TAS Town/locality determine the ages of major rock units crossed by the seismic line.
    [Show full text]
  • Earth: Atmospheric Evolution of a Habitable Planet
    Earth: Atmospheric Evolution of a Habitable Planet Stephanie L. Olson1,2*, Edward W. Schwieterman1,2, Christopher T. Reinhard1,3, Timothy W. Lyons1,2 1NASA Astrobiology Institute Alternative Earth’s Team 2Department of Earth Sciences, University of California, Riverside 3School of Earth and Atmospheric Science, Georgia Institute of Technology *Correspondence: [email protected] Table of Contents 1. Introduction ............................................................................................................................ 2 2. Oxygen and biological innovation .................................................................................... 3 2.1. Oxygenic photosynthesis on the early Earth .......................................................... 4 2.2. The Great Oxidation Event ......................................................................................... 6 2.3. Oxygen during Earth’s middle chapter ..................................................................... 7 2.4. Neoproterozoic oxygen dynamics and the rise of animals .................................. 9 2.5. Continued oxygen evolution in the Phanerozoic.................................................. 11 3. Carbon dioxide, climate regulation, and enduring habitability ................................. 12 3.1. The faint young Sun paradox ................................................................................... 12 3.2. The silicate weathering thermostat ......................................................................... 12 3.3. Geological
    [Show full text]
  • Subglacial and Submarine Volcanism in Iceland
    Mars Polar Science 2000 4078.pdf SUBGLACIAL AND SUBMARINE VOLCANISM IN ICELAND. S. P. Jakobsson, Icelandic Inst. of Natural His- tory, P. O. Box 5320, 125 Reykjavik, Iceland Introduction: Iceland is the largest landmass ex- mounds, ridges and tuyas [5]. The thickness of basal posed along the Mid-Ocean Ridge System. It has been basaltic pillow lava piles often exceeds 60-80 meters constructed over the past 16 Ma by basaltic to silicic and a 300 m thick section has been reported. Pillow volcanic activity occurring at the Mid-Atlantic Ridge, lavas may also form lenses or pods at a higher level in and is topographically elevated because of the abundant the volcanoes. igneous material produced in association with the Ice- It has been suggested that at a water depth less than land hot spot, the center of which is thought to be lo- approximately 100-150 m, basaltic phreatic explosions cated beneath Vatnajokull glacier [1]. The axial rift produce hydroclastites. It appears feasible to subdivide zones which run through Iceland from southwest to the hyaloclastites of the Icelandic ridges and tuyas, ge- northeast are in direct continuation of the crestal zones netically into two main types. A substantial part of the of the Mid Atlantic Ridge and are among the most ac- base of the submarine Surtsey tuya is poorly bedded, tive volcanic zones on Earth. unsorted, hydroclastite, which probably was quenched Subglacial Volcanism: Volcanic accumulations of and rapidly accumulated below the seawater level with- hyaloclastites which are deposits formed by the intru- out penetrating the surface [6]. Only 1-2 % of the vol- sion of lava beneath water or ice and the consequent ume of extruded material in the 1996 Gjalp eruption fell shattering into small angular vitric particles, combined as air-fall tephra, the bulk piled up below the ice [4].
    [Show full text]
  • High-Silica Lava Morphology at Ocean Spreading Ridges: Machine-Learning Seafloor Classification at Alarcon Rise
    Article High-Silica Lava Morphology at Ocean Spreading Ridges: Machine-Learning Seafloor Classification at Alarcon Rise Christina H. Maschmeyer 1,†, Scott M. White 1,*, Brian M. Dreyer 2 and David A. Clague 3 1 School of the Earth, Ocean and Environment, University of South Carolina, Columbia, SC 29208, USA; [email protected] 2 Institute of Marine Sciences, University of California, Santa Cruz, CA 95064, USA; [email protected] 3 Monterey Bay Aquarium Research Institute, Moss Landing, CA 95039, USA; [email protected] † Now at: Fugro USA Marine, Inc. Geoconsulting Exploration, 6100 Hillcroft Ave, Houston, TX 77081, USA * Correspondence: [email protected] Received 31 March 2019; Accepted 28 May 2019; Published: 1 June 2019 Abstract: The oceanic crust consists mostly of basalt, but more evolved compositions may be far more common than previously thought. To aid in distinguishing rhyolite from basaltic lava and help guide sampling and understand spatial distribution, we constructed a classifier using neural networks and fuzzy inference to recognize rhyolite from its lava morphology in sonar data. The Alarcon Rise is ideal to study the relationship between lava flow morphology and composition, because it exhibits a full range of lava compositions in a well‐mapped ocean ridge segment. This study shows that the most dramatic geomorphic threshold in submarine lava separates rhyolitic lava from lower‐silica compositions. Extremely viscous rhyolite erupts as jagged lobes and lava branches in submarine environments. An automated classification of sonar data is a useful first‐order tool to differentiate submarine rhyolite flows from widespread basalts, yielding insights into eruption, emplacement, and architecture of the ocean crust.
    [Show full text]
  • Open Kosei.Pdf
    The Pennsylvania State University The Graduate School Department of Geosciences GEOCHEMISTRY OF ARCHEAN–PALEOPROTEROZOIC BLACK SHALES: THE EARLY EVOLUTION OF THE ATMOSPHERE, OCEANS, AND BIOSPHERE A Thesis in Geosciences by Kosei Yamaguchi Copyright 2002 Kosei Yamaguchi Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy May 2002 We approve the thesis of Kosei Yamaguchi Date of Signature ____________________________________ _______________________ Hiroshi Ohmoto Professor of Geochemistry Thesis Advisor Chair of Committee ____________________________________ _______________________ Michael A. Arthur Professor of Geosciences ____________________________________ _______________________ Lee R. Kump Professor of Geosciences ____________________________________ _______________________ Raymond G. Najjar Associate Professor of Meteorology ____________________________________ _______________________ Peter Deines Professor of Geochemistry Associate Head for Graduate Program and Research in Geosciences iii ABSTRACT When did the Earth's surface environment become oxic? The timing and mechanism of the rise of atmospheric pO2 level in the early Precambrian have been long debated but no consensus has been reached. The oxygenation of the atmosphere and oceans has significant impacts on the evolution of the biosphere and the geochemical cycles of redox-sensitive elements. In order to constrain the evolution of the atmosphere, oceans, biosphere, and geochemical cycles of elements, a systematic and multidisciplinary
    [Show full text]
  • Drilling for the Archean Roots of Life and Tectonic Earth in the Barberton Mountains
    Progress Reports Drilling for the Archean Roots of Life and Tectonic Earth in the Barberton Mountains by Eugene G. Grosch, Nicola McLoughlin, Maarten de Wit, and Harald Furnes doi:10.2204/iodp.sd.8.03.2009 Introduction phase of drilling yielded three boreholes with a total of 800 m of core with 99% core recovery in the early Archean Barberton In the Barberton Scientific Drilling Program (BSDP) we Greenstone Belt (BGB), South Africa. Five decades of scien- successfully completed three drill holes in 2008 across tific research on the 3.5–3.1-Ba-old BGB has established the strategically selected rock formations in the early Archean mountain ranges of Barberton as a world heritage site and a Barberton Greenstone Belt, South Africa. This collaborative focus for international scientists interested in early Earth project’s goal is to advance understanding of geodynamic processes. The rocks around Barberton are unique in that and biogeochemical processes of the young Earth. The they represent relatively intact and undisturbed remnants of program aims to better define and characterize Earth’s preserved ancient seafloor and continental crust that have earliest preserved ocean crust shear zones and microbial largely escaped tectonometamorphic reworking since the borings in Archean basaltic glass, and to identify biogeo- time they formed (Schoene et al., 2008). chemical fingerprints of ancient ecological niches recorded in rocks. The state-of-the-art analytical and imaging work Outstanding questions about early Earth—as well as will address the question of earliest plate tectonics in the Earth systems and linkages between physical, chemical, and Archean, the δ18O composition, the redox state and biological processes operating within and on the early temperature of Archean seawater, and the origin of life Earth—include the following areas of interest: question.
    [Show full text]
  • The Archean Geology of Montana
    THE ARCHEAN GEOLOGY OF MONTANA David W. Mogk,1 Paul A. Mueller,2 and Darrell J. Henry3 1Department of Earth Sciences, Montana State University, Bozeman, Montana 2Department of Geological Sciences, University of Florida, Gainesville, Florida 3Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana ABSTRACT in a subduction tectonic setting. Jackson (2005) char- acterized cratons as areas of thick, stable continental The Archean rocks in the northern Wyoming crust that have experienced little deformation over Province of Montana provide fundamental evidence long (Ga) periods of time. In the Wyoming Province, related to the evolution of the early Earth. This exten- the process of cratonization included the establishment sive record provides insight into some of the major, of a thick tectosphere (subcontinental mantle litho- unanswered questions of Earth history and Earth-sys- sphere). The thick, stable crust–lithosphere system tem processes: Crustal genesis—when and how did permitted deposition of mature, passive-margin-type the continental crust separate from the mantle? Crustal sediments immediately prior to and during a period of evolution—to what extent are Earth materials cycled tectonic quiescence from 3.1 to 2.9 Ga. These compo- from mantle to crust and back again? Continental sitionally mature sediments, together with subordinate growth—how do continents grow, vertically through mafi c rocks that could have been basaltic fl ows, char- magmatic accretion of plutons and volcanic rocks, acterize this period. A second major magmatic event laterally through tectonic accretion of crustal blocks generated the Beartooth–Bighorn magmatic zone assembled at continental margins, or both? Structural at ~2.9–2.8 Ga.
    [Show full text]
  • Glaciovolcanic Megapillows of Undirhlíđar, Reykjanes Peninsula, Southwestern Iceland
    GLACIOVOLCANIC MEGAPILLOWS OF UNDIRHLÍĐAR, REYKJANES PENINSULA, SOUTHWESTERN ICELAND Rachel Heineman Honors Research in Geology Dr. F. Zeb Page, Thesis Advisor Oberlin College 2016-2017 ABSTRACT At Undirhlíðar tindar on the Reykjanes Peninsula, southwestern Iceland, megapillows are among the features formed during a series of ridge-building glaciovolcanic eruptions. Mapping of the northeastern 3 km of the ridge and petrographic and geochemical analysis of the megapillow outcrops occurring throughout this area demonstrate their role in the multi-stage construction of the ridge modeled by Pollock et al. (2014). The outcrops exhibit radial jointing, bands of vesicles and glassy rims; they occur in high relief surrounded by basalt breccia resembling pillow rubble, and are composed of plagioclase-phyric olivine basalt with plagioclase-rich groundmass. They occur in multiple pillow lava units formed from two distinct magma batches. Two groups of outcrops are represented that are petrographically, geochemically and geographically distinct; the first group is near to and consistent with the pillow units of Undirhlíðar quarry described by Pollock et al. (2014), and the second group, located near the tephra cone, is derived from a more evolved unit of the same magma. Megapillows show significant plagioclase accumulation with variable phenocryst zoning, indicating the movement of multiple pulses of magma through the megapillows. Megapillows at Undirhlíðar may represent a significant mechanism, demonstrated elsewhere at a marine ​ megapillow by Goto and McPhie (2004), for magmatic distribution: feeding and then overrunning pillows which propagate and are fed from their basal margins at the eruptive front. INTRODUCTION Pillow lavas are among the most common lava morphologies on Earth, yet the construction of pillow-dominated volcanoes is not widely understood due to the relative inaccessibility of the submarine environments in which they form.
    [Show full text]