Explanatory Notes by Philippe Bouysse Geological Map of the World • At the scale of 1: 50 000 000 (2009) Sheet 1: Physiography, volcanoes, astroblemes - 1st edition Sheet 2: Geology, structure - 3rd edition • At the scale of 1: 25 000 000 (2010) Geology, structure - 3rd edition COMMISSION DE LA CARTE GÉOLOGIQUE DU MONDE COMMISSION FOR THE GEOLOGICAL MAP OF THE WORLD «Ce qui est simple est toujours faux. Ce qui ne l’est pas est inutilisable». Paul Valéry (Mauvaises pensées et autres, 1942) COMMISSION FOR THE GEOLOGICAL MAP OF THE WORLD Geological Map of the World at 1: 50 000 000 (ird edition) 2009 EXPLANATORY NOTES By Philippe BOUYSSE (CGMW) Translation by Philippe Bouysse & Clara Cardenas (CGMW), reviewed by Peter Miles (CGMW) and Françoise Cadet (University Paris VI). SUMMARY • Geological Map of the World at 1: 50 000 000 (2009) Foreword, p. 4 INTRODUCTION, p. 4 SHEET 1: PHYSIOGRAPHY, VOLCANOES, ASTROBLEMES I.1 - Physiography, p. 5 I.2 - Volcanoes, p. 5 I.3 - Astroblemes, p. 5 I.4 - Additional information, p. 5 SHEET 2: GEOLOGY, STRUCTURE II.1 - ONSHORE AREAS, p. 6 II.1.1 - Chronostratigraphic units, p. 6 II.1.2 - Ophiolites, p. 6 II.1.3 - Large Igneous Provinces : traps, p. 6 II.1.4 - Glaciers, inlandsis, p. 7 II.1.5 - Structural features, p. 7 II.1.6 - e Iceland case, p. 8 II.2 - OFFSFORE AREAS, p. 8 II.2.1 - Continental margin, p. 8 II.2.1.1 - Continent/Ocean Boundary (COB) , p. 8 II.2.1.2 - Microcontinent, p. 8 II.2.1.3 - Island arcs, p. 8 II.2.1.4 - Continental shelf, p. 8 II.2.1.5 - Continental slope, p. 9 II.2.1.6 - Antarctic margin, p. 9 II.2.1.7 - Ice shelf, p. 9 II.2.2 - OCEANIC BASINS, p. 9 II.2.2.1 - Age of the oceanic crust, p. 9 II.2.2.2 - Abyssal plains, p. 9 II.2.2.3 - Mid-oceanic ridges, p. 10 II.2.2.4 - Axis of mid-oceanic ridges, p. 10 II.2.2.5 - Transform faults and fracture zones, p. 10 II.2.2.6 - Subduction zones, subduction trenches and other trenches, p. 11 II.2.2.7 - "Anomalous" submarine features (seamounts, oceanic plateaus, hotspot tracks) , p. 12 II.2.2.8 - Distributed or diuse plate boundaries, p. 13 II.2.2.9 - Submarine volcanism and the opening of the North Atlantic Ocean, p. 13 II.2.2.10 - SDR's related to the opening of the South Atlantic Ocean, p. 13 II.3 - HOTSPOTS, p. 13 By way of conclusion…, p. 14 • Geological Map of the World at 1: 25 000 000 (2010) SINGLE SHEET: GEOLOGY, STRUCTURE (in 3 parts) ADDITIONAL NOTE, p. 16 The Geological Map of the World at 1: 50 000 000 (2009) Explanatory Notes by Philippe BOUYSSE (CGMW) Foreword ese Notes presented in a somewhat heterogeneous manner, combine regular peer-reviewed information dedicated to geoscience professionals – normal users of geological maps – with more basic information intended for the wider public including high school and college students who constituted a large section of the users of the former editions of this map. It was not possible to address in these notes all the geologic, structural or geodynamic aspects that may be raised by the careful examination of the Map. e text, consisting mainly of comments on the legends, is aimed at shedding some light on a selection of examples that are, in our view, illustrative of each element of the Map. It should be noted that, in this new edition, a particular attention was given to the oceanic areas, the large magmatic events, and to the geodynamics. INTRODUCTION is third edition of the Geological Map of the World at the and 72°S for Sheet 2 (instead of 78°N and 65°S for the former scale of 1:50,000,000 (1:50 M) follows the rst and second two editions), and at 72°N and 70°S for Sheet 1. As a conse- editions published by the CGMW respectively in 1990 and quence, a large extent of the Antarctic continental coastline 2000. is bilingual document (English-French) is the is visible, with a better delimitation of the southern result of a highly synthetic compilation given both the small ocean. As for Greenland, only its southern half is visible. scale of the map and its educational purpose. It is a tenta- On the other hand, the Taymir peninsula has been tive and (very) simplied representation of the entire solid severed from the far north of the Eurasian continent. surface of our planet and includes both continental and e circum-polar projections extend to the 60°N and oceanic domains. 60°S parallels (instead of 70°N and 60°S for the previous editions), Greenland is now displayed in its entirety and is new edition is a completely revised concept compared the 2 circum-polar areas have the same surface area. to the map issued in 2000 and takes into account the state of eir scale was slightly enlarged to 1:46 M. the geologic knowledge at the turn of the century. For the rst time, the Map is designed in two sheets of the same For practical reasons and marketing policy, this 3rd size: edition at the scale of 1:50 M (for the Mercator projec- tion) precedes the publication at 1:25 M (original scale of – Sheet 1 (Physiography, Volcanoes, Astroblemes) revea- the dra). An interactive digital version of the Map is ling the ne-grained texture of the totality of the Earth scheduled for the end of 2010. surface when removing the water of the oceans. In the previous editions at 1:25 M scale, the Mercator – Sheet 2 (Geology, Structure) showing the distribution projection was printed in two parts (20°W-170°W; of the main chronostratigraphic units and the main 170°W-20°W) that allowed adjusting the center of the structural features that make up the mosaic of the Map either on the Atlantic (opening of an ocean and t of present-day surface of our planet, the result of 4.56 the conjugated continents), or on the Pacic billion years of unremitting "resurfacing". Sheet 2 is the (subductions and hotspots tracks). In this new edition, equivalent of the single sheet of the second edition, the single 1:50 M sheet forced us to make a choice for the notably reworked and extended. centering. In order to overcome these inconveniences, we decided to center Sheet 1 (Physiography) on the Each sheet consists of a main map in Mercator projection, Pacic (meridian 0° for E and W sides) and Sheet 2 with the 2 polar areas in polar stereographic projections. (Geology) on the Atlantic (180° meridian for both sides). e dras have been carried out at the 1:25,000,000 scale is enables the reader to visualize both options of (1:25 M). assemblage. e Mercator projection has only a true scale representa- Scales and projections being identical, it is easy to super- tion along the equator but allows an optimal visualization pose the morphological features of the oshore areas that does not favour the continents at the expenses of the (Sheet 1) with the geological structures mapped on Sheet oceans or vice-versa, unlike many other projections used 2 using an illuminated table. for world maps. e main drawback of Mercator comes from the deformation that increases with the latitude to Nota: In the text that follows, words typed in bold become innite at the poles. For this reason, in this edition, characters correspond to the dierent items of the the "upper" and "lower" latitude limits have been set at 72°N legends. 1 e abbreviation for billion years (10 years) is Ga (from giga-annum, ocial designation of international geological bodies). e author wonders why the accusative form "annum" was chosen instead of the nominative one "annus". 4 SHEET - 1: PHYSIOGRAPHY, VOLCANOES, ASTROBLEMES I.1- PHYSIOGRAPHY Data acquisition dates back to April 2006. e sources are: Published for the rst time by the CGMW, this Map 1/ Planetary And Space Science Centre of New Brunswick displays all of the Earth’s morphology and, in particular, the University (John Spray & Jason Hines, web site: lesser known domains of the submarine areas that represent www.unb.ca/passc/Impact.Database) with 174 structures; nearly 71% of its surface. Colour palettes are used to repre- 2/ Jarmo Moilanen, Finland: Impact structures of the sent the land topography and, ocean bathymetry, the latter World with 21 structures; including ne black lines to indicate depth contours (site : www.somerikko.net/old/geo/imp/impacts.htm); (isobaths) at every 1000 m. In order to avoid blurring of the physiographic perception of mountain chains, the equiva- 3/ NASA/Goddard Space Flight Center Scientic Visualiza- lent for the subaerial areas (isohypses) were not plotted, tion Studio for the Araona/Iturralde crater (Bolivia), not except for the Greenland and Artarctica ice caps. validated yet; e topography was generated from a digital database of 4/ Wade S. et al., in Lunar and PlanetaryScience, 2002, land and sea-oor elevation (EOTPO2) on a 2-minute XXXIII, for the Velingara crater (Senegal); latitute/longitude grid resolution. Seaoor data are from 5/ Paillou Ph. et al., in C. R. Géoscience, 2004, v. 336, for the work of W. Smith & D. Sandwell (1997). ese data were the Gilf Kebir structure (Égypte). derived from satellite altimetry observations combined with carefully quality-assured shipboard echo-sounding Even though it is not an impact crater stricto sensu, the measurements. Land data were primarily from 30-second location of the Tunguska (Central Siberia) airblast of an gridded data collected from various sources by the National asteroid (a comet?) in 1908 was identied with a red circle.