DOCSLIB.ORG

Geochemistry and Geochronology of Tethyan-Arc Related Igneous Rocks, NE Iraq Sarmad Asi Ali University of Wollongong

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Geochemistry and Geochronology of Tethyan-Arc Related Igneous Rocks, NE Iraq Sarmad Asi Ali University of Wollongong University of Wollongong Research Online University of Wollongong Thesis Collection University of Wollongong Thesis Collections 2012 Geochemistry and geochronology of Tethyan-arc related igneous rocks, NE Iraq Sarmad Asi Ali University of Wollongong Recommended Citation Ali, Sarmad Asi, Geochemistry and geochronology of Tethyan-arc related igneous rocks, NE Iraq, Doctor of Philosophy thesis, School of Earth and Environmental Sciences, University of Wollongong, 2012. http://ro.uow.edu.au/theses/3478 Research Online is the open access institutional repository for the University of Wollongong. For further information contact Manager Repository Services: [email protected]. Geochemistry and geochronology of Tethyan-arc related igneous rocks, NE Iraq A thesis submitted in fulfilment of the requirements for the award of the degree Doctor of Philosophy from UNIVERSITY OF WOLLONGONG by SARMAD ASI ALI Master of Science School of Earth and Environmental Sciences 2012 CERTIFICATION I, Sarmad A. Ali, declare that this thesis, submitted in fulfilment of the requirements for the award of Doctor of Philosophy, in the School of Earth and Environmental Sciences, University of Wollongong, is wholly my own work unless otherwise referenced or acknowledged. The document has not been submitted for qualifications at any other academic institution. Sarmad Asi Ali January 2012. ﺑِ ﺴۡ ﻢِ ٱ ﷲِ ٱ ﻟ ﺮﱠ ﺣۡ ﻤَ ـٰ ﻦِ ٱ ﻟ ﺮﱠ ﺣِ ﻴ ﻢِ ﻭَ ﺗَ ﺮَ ﻯ ٱ ﻟۡ ﺠِ ﺒَ ﺎ ﻝَ ﺗَ ﺤۡ ﺴَ ﺒُ ﮩَ ﺎ ﺟَ ﺎ ﻣِ ﺪَ ﺓ ً۬ ﻭَ ﻫِ ﻰَ ﺗَ ﻤُ ﺮﱡ ﻣَ ﺮﱠ ٱ ﻟ ﺴﱠ ﺤَ ﺎ ﺏِ ۚ ﺻُ ﻨۡ ﻊَ ٱ ﻟ ﻠﱠ ﻪِ ٱ ﻟﱠ ﺬِ ﻯٓ ﺃﺗﻘﻦ ﻛُ ﻞﱠ ﺷَ ﻰۡ ءٍ ۚ ﺇِ ﻧﱠ ﻪُ ۥ ﺧَ ﺒِ ﻴ ﺮ ُۢ ﺑِ ﻤَ ﺎ ﺗَ ﻔۡ ﻌَ ﻠُ ﻮ ﻥَ (٨٨) ﺻﺪﻕ ﺍﷲ ﺍﻟﻌﻈﻴﻢ In the name of Allah, the Beneficent, the Merciful And thou seest the hills thou deemest solid flying with the flight of clouds: the doing of Allah Who perfecteth all things. Lo! He is informed of what ye do. (88) I dedicate this thesis to my grandmother's spirit of pure, To my parents…….. To my family …….. ABSTRACT The Hasanbag Arc Complex (HAC) is situated near Sidekan, 100 km northeast of Erbil city, Kurdistan region, within the Iraqi Zagros Suture Zone (IZSZ). It forms part of an ophiolite bearing terrane referred to as the ‘Upper Allochthon’ or Gemo-Qandil Group. The igneous complex is comprised of volcanic rocks of arc affinity cross-cut by dolerite and diorite dykes. The HAC consists predominantly of calc-alkaline basaltic andesites to andesites, which in the past have been interpreted as a part of the Eocene Walash volcanics. However, Ar-Ar dating of magmatic hornblende from the Hasanbag volcanic rocks indicate an Albian – Turonian age (106-92 Ma). The discovery of Late Cretaceous arc volcanism reveals an as yet unidentified episode of Late Cretaceous, Neo-Tethyan ophiolite-arc complex in the Iraqi Zagros Thrust Zone that may well represent lateral equivalents of the ophiolite-arc sequences in Oman-Neyriz and Cyprus. The petrography and mineral chemistry of the HAC shows that plagioclase, pyroxene, amphibole and iron oxides are the main phenocrysts. Albite forms the main composition of the subhedral laths and microlites in the matrix but primary oligoclase (An27) is also observed. All clinopyroxene samples are augite (Wo44.46-En46.43-Fs9.1) and amphibole is Ti-rich hornblende (kaersutite). Iron oxides are mostly ilmenite, magnetite and hematomagnetite, while apatite, sphene and zircon occur as accessory minerals. Arc spatial-chemical relationships indicate magmatic evolution of a calc-alkaline, island-arc suite with low-K characteristics. The geochemical variation in the rocks can be explained by fractionation of common mineral phases such as plagioclase, clinopyroxene, hornblende, magnetite and apatite. The subduction signature of volcanic and subvolcanic rocks of the HAC is confirmed by the Nb/Yb-Th/Yb diagram, which shows that all the samples fall within the compositional field of arc-related rocks, and above the field of the MORB-OIB mantle array. Their Nb/Yb > 3 suggests their mantle source had considerable subduction influence and the resulting magmas were affected by a significant contamination of lithospheric material from the pre-existing crustal component.They are generated from the mantle wedge within a supra-subduction zone setting and are influenced by slab-derived components. HAC samples show enrichment relative to N-MORB in the large-ion lithophile elements and depletion in the high field- strength elements with characteristic Nb troughs, confirming a subduction influence. The HAC shows similar geochemical trends to arc rocks from Neyriz in south western i Iran. We interpret the HAC as a remnant of Late Cretaceous ophiolite/arc rocks that developed within the Neo-Tethys Ocean and were subsequently accreted to the Arabian Plate during the Late Cretaceous to Paleocene. This is the first time that Late Cretaceous ophiolite-arc complexes have been identified in the Iraqi Zagros collision zone and unequivocally separates the HAC from the similar, but younger, Eocene - Oligocene Walash-Naopurdan arc-backarc complex. A comprehensive petrographic, geochronological, and geochemical study of a group of samples from the Walash-Naopurdan volcanic and subvolcanic rocks in four provinces, Mawat, Galalah-Choman, Leren (Sidekan) and Qalander-Sheikhan was carried out. The study area is within a lower allochthonous thrust sheet that occupies part of the Iraqi Zagros Suture Zone (IZSZ), northeast Iraq.. 40Ar-39Ar dates on three magmatic feldspar separates, one from Walash and two from Naopurdan volcanic rocks, indicate an Eocene-Oligocene age (43.01 ± 0.15 to 24.31 ± 0.60 Ma). The petrographic study shows the disappearance of some original textural and mineralogical characteristics, due to the superimposed conditions that prevailed during ocean-floor and subsequent hydrothermal alteration. This led to the appearance of secondary minerals that partially or completely replaced the original ones in both the Walash and Naopurdan volcanic rocks. The petrography and mineral chemistry confirm that all Walash-Naopurdan rocks are mafic to intermediate and show that plagioclase, pyroxene, and iron oxides are the main phenocrysts, whereas, apatite, sphene and zircon occur as accessory minerals. Variation of the less mobile elements (such as Ti, Zr, P, Y, Nb and REE) conforms that the majority of the rocks are basic in composition with basalt to andesitic basalt for Naopurdan samples and basalt to basaltic andesite, alkali basalt to trachytic andesite for Walash samples, and that they have subalkaline (tholeiite for Naopurdan and calc- alkaline to alkaline for Walash) affinities. Also these elements show that the studied rocks represent assemblage of island-arc tholeiite affinity (IAT) for Naopurdan and calc-alkaline to alkaline affinity (CAB-AK) for Walash. These rocks can be related to different degrees of partial melting. The magma of Walash alkaline and calc-alkaline rocks was generated by <5% and about 10-20% partial melting of a slightly enriched upper mantle source (spinel lherzolite), followed by fractional crystallization during the ascending of magma to the surface, while, Naopurdan samples are fractionated from a mostly more than 20% partial melting of a depleted mantle source. It is evident from ii the, field, age, petrographic and tectonomagmatic evidence that the Walash and Naopurdan rocks formed in back-arc and arc environments, respectively. The tectonic model proposed opening of the Neo-Tethys and separation of the Sanandaj-Sirjan microplate from the Arabian plate in the Permian to Triassic. During the Early Cretaceous a supra-subduction zone ophiolite/arc complex, represented by the Hasanbag rocks (106-92 Ma), developed in the Neo-Tethys Ocean and was subsequently obducted onto the Arabian continental margin during the Late Cretaceous to Paleocene. This collision initiated a new intra-oceanic subduction system in the Neo- Tethyan Ocean. The Walash Group includes calc-alkaline volcanic rocks with a distinct backarc geochemical signature (enrichments in highly incompatible elements relative to less incompatible elements (i.e. LREE/HREE and high Th/Nb, Nb/Zr), which commenced in the Eocene (43-34 Ma). The Naopurdan and limited Walash volcanic rocks are characterized by alkaline magmatism and were erupted during the final stage of intra Neo-Tethys oceanic subduction (33-24 Ma), before the final closure of Neo- Tethys. Development of the Walash-Naopurdan arc – back-arc system up until 33-24 million years ago indicates that arc collision with the Arabian continental passive margin must have occurred after the youngest age of volcanism, probably during the Early Miocene (23-16? Ma). Final continent-continent collision between the Iranian- Turkish and Arabian continents occurred when the final remnants of the Neo-Tethys were subducted beneath the Iranian-Turkish continent resulting in collision with the Arabian continent, probably during the Middle? Miocene. iii ACKNOWLEDGEMENTS First of all, I would like to thank God for providing me with the skills, patience and comfort needed to complete my studies. It would not have been possible to write this doctoral thesis without the help and support of the following individuals and organizations: The financial support for the PhD scholarship was provided by the Ministry of Higher Education and Scientific Research in Iraq and is gratefully acknowledged. I would like to also acknowledge the financial, academic and technical support of the University of Wollongong in providing laboratory and office facilities and conference funding. I would like to express my deep and sincere gratitude to my supervisors, Associate Professor Brian Jones, Dr Solomon Buckman, and Professor Sabah Ismail (University of Kirkuk, Iraq). Their understanding, encouragement and personal guidance have provided a good basis for the present thesis. I am deeply grateful for their detailed and constructive comments, and their important support throughout this work. Some key people in the development of publication from this study have been Professor Khalid Jalal Aswad from the University of Mosul, Iraq, and Associate Professor Allen Nutman of the University of Wollongong.
Load more

Recommended publications
  • Coastal and Marine Ecological Classification Standard (2012)
    FGDC-STD-018-2012 Coastal and Marine Ecological Classification Standard Marine and Coastal Spatial Data Subcommittee Federal Geographic Data Committee June, 2012 Federal Geographic Data Committee FGDC-STD-018-2012 Coastal and Marine Ecological Classification Standard, June 2012 ______________________________________________________________________________________ CONTENTS PAGE 1. Introduction ..................................................................................................................... 1 1.1 Objectives ................................................................................................................ 1 1.2 Need ......................................................................................................................... 2 1.3 Scope ........................................................................................................................ 2 1.4 Application ............................................................................................................... 3 1.5 Relationship to Previous FGDC Standards .............................................................. 4 1.6 Development Procedures ......................................................................................... 5 1.7 Guiding Principles ................................................................................................... 7 1.7.1 Build a Scientifically Sound Ecological Classification .................................... 7 1.7.2 Meet the Needs of a Wide Range of Users ......................................................
    [Show full text]
  • Articles Ranging in Resents Both Gravitational Acceleration and the Effect of Bed Size from Tens of Meters to a Few Centimeters in Diameter
    Nat. Hazards Earth Syst. Sci., 6, 671–685, 2006 www.nat-hazards-earth-syst-sci.net/6/671/2006/ Natural Hazards © Author(s) 2006. This work is licensed and Earth under a Creative Commons License. System Sciences Numerical simulation of tsunami generation by cold volcanic mass flows at Augustine Volcano, Alaska C. F. Waythomas1, P. Watts2, and J. S. Walder3 1U.S. Geological Survey, Alaska Volcano Observatory, Anchorage, AK, USA 2Applied Fluids Engineering Inc., Long Beach, CA, USA 3U.S. Geological Survey, Cascades Volcano Observatory, Vancouver, WA, USA Received: 18 April 2006 – Revised: 22 June 2006 – Accepted: 22 June 2006 – Published: 26 July 2006 Abstract. Many of the world’s active volcanoes are situated 1 Introduction on or near coastlines. During eruptions, diverse geophysical mass flows, including pyroclastic flows, debris avalanches, Many of the world’s active volcanoes are located within a and lahars, can deliver large volumes of unconsolidated de- few tens of kilometers of the sea or other large bodies of wa- bris to the ocean in a short period of time and thereby gen- ter. During eruptions, large volumes of volcaniclastic debris erate tsunamis. Deposits of both hot and cold volcanic mass may enter nearby water bodies, and under certain conditions, flows produced by eruptions of Aleutian arc volcanoes are this process may initiate tsunamis (Tinti et al., 1999; Tinti exposed at many locations along the coastlines of the Bering et al., 2003). Worldwide, tsunamis caused by volcanic erup- Sea, North Pacific Ocean, and Cook Inlet, indicating that tions are somewhat infrequent (Latter, 1981); however, doc- the flows entered the sea and in some cases may have ini- umented historical cases illustrate that loss of life and prop- tiated tsunamis.
    [Show full text]
  • Geologic Map of the Piedmont in the Savage and Relay Quadrangles, Howard, Baltimore, and Anne Arundel Counties, Maryland
    U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Geologic Map of the Piedmont in the Savage and Relay Quadrangles, Howard, Baltimore, and Anne Arundel Counties, Maryland By Avery Ala Drake, Jr.1 Open-File Report 98-757 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 'Reston, VA 1998 GEOLOGIC MAP OF THE PIEDMONT IN THE SAVAGE AND RELAY QUADRANGLES, HOWARD, BALTIMORE, AND ANNE ARUNDEL COUNTIES, MARYLAND by Avery Ala Drake, Jr. INTRODUCTION The Piedmont in the Savage and Relay quadrangles (fig. 1) is largely in Howard County, Maryland. The northeasternmost part is in Baltimore County, Maryland and about 0.03 square miles is in Anne Arundel County. Most of the area is suburban and almost all outcrops are restricted to the Patapsco, Middle Patuxent, Little Patuxent, and other stream valleys. Crystalline rocks of the central Appalachian Piedmont within these quadrangles are overlain in many places by Coastal Plain deposits of Cretaceous age. Alluvium occurs along most streams. The geology of adjacent quadrangles on the west and south has been mapped by Drake (in press, unpublished data, 1991-1997) and J.N. Roen and A.A. Drake, Jr. (in press), and that to the north and east by Crowley (1976). The tectonics of the area were interpreted by Crowley (1976) and Drake (1995). Aeromagnetic and gravity surveys of the area were interpreted by Bromery (1968).
    [Show full text]
  • Exploring Submarine Arc Volcanoes Steven Carey University of Rhode Island, [email protected]
    University of Rhode Island DigitalCommons@URI Graduate School of Oceanography Faculty Graduate School of Oceanography Publications 2007 Exploring Submarine Arc Volcanoes Steven Carey University of Rhode Island, [email protected] Haraldur Sigurdsson University of Rhode Island Follow this and additional works at: https://digitalcommons.uri.edu/gsofacpubs Terms of Use All rights reserved under copyright. Citation/Publisher Attribution Carey, S., and H. Sigurdsson. 2007. Exploring submarine arc volcanoes. Oceanography 20(4):80–89, https://doi.org/10.5670/ oceanog.2007.08. Available at: https://doi.org/10.5670/oceanog.2007.08 This Article is brought to you for free and open access by the Graduate School of Oceanography at DigitalCommons@URI. It has been accepted for inclusion in Graduate School of Oceanography Faculty Publications by an authorized administrator of DigitalCommons@URI. For more information, please contact [email protected]. This article has This been published in 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 permitted articleonly photocopy by is of machine, reposting, this means or collective or other redistirbution SP ec I A L Iss U E On Ocean E X P L O R ATIO N Oceanography , Volume 20, Number 4, a quarterly journal of The 20, Number 4, a quarterly , Volume O ceanography Society. Copyright 2007 by The 2007 by Copyright Society. ceanography Exploring O ceanography Society. All rights All reserved. Society. ceanography O Submarine Arc Volcanoes or Th e [email protected] Send Society. ceanography to: correspondence all B Y S T even C A R E Y an D H A R A LDUR SIGURD ss O N Three quarters of Earth’s volcanic activ- although a significant part of arc volca- tion of tsunamis (Latter, 1981).
    [Show full text]
  • Active Continental Margin
    Encyclopedia of Marine Geosciences DOI 10.1007/978-94-007-6644-0_102-2 # Springer Science+Business Media Dordrecht 2014 Active Continental Margin Serge Lallemand* Géosciences Montpellier, University of Montpellier, Montpellier, France Synonyms Convergent boundary; Convergent margin; Destructive margin; Ocean-continent subduction; Oceanic subduction zone; Subduction zone Definition An active continental margin refers to the submerged edge of a continent overriding an oceanic lithosphere at a convergent plate boundary by opposition with a passive continental margin which is the remaining scar at the edge of a continent following continental break-up. The term “active” stresses the importance of the tectonic activity (seismicity, volcanism, mountain building) associated with plate convergence along that boundary. Today, people typically refer to a “subduction zone” rather than an “active margin.” Generalities Active continental margins, i.e., when an oceanic plate subducts beneath a continent, represent about two-thirds of the modern convergent margins. Their cumulated length has been estimated to 45,000 km (Lallemand et al., 2005). Most of them are located in the circum-Pacific (Japan, Kurils, Aleutians, and North, Middle, and South America), Southeast Asia (Ryukyus, Philippines, New Guinea), Indian Ocean (Java, Sumatra, Andaman, Makran), Mediterranean region (Aegea, Cala- bria), or Antilles. They are generally “active” over tens (Tonga, Mariana) or hundreds (Japan, South America) of millions of years. This longevity has consequences on their internal structure, especially in terms of continental growth by tectonic accretion of oceanic terranes, or by arc magmatism, but also sometimes in terms of continental consumption by tectonic erosion. Morphology A continental margin generally extends from the coast down to the abyssal plain (see Fig.
    [Show full text]
  • Petrology and Chemistry of Some Exotic Rock Fragments from Jabal Sanam, Basrah, Iraq
    Iraqi Bulletin of Geology and Mining Vol.7, No.1, 2011 p 39 −−− 53 PETROLOGY AND CHEMISTRY OF SOME EXOTIC ROCK FRAGMENTS FROM JABAL SANAM, BASRAH, IRAQ Khaldoun S. Al-Bassam * Received: 26 / 08/ 20 10 , Accepted: 29 / 12 / 20 10 Key words: Hormuz Series, Sanam, Salt plug, Iraq ABSTRACT Petrologic and chemical analyses of 16 exotic rock samples collected from Sanam salt plug in southern Iraq showed igneous and sedimentary rocks of various types and origins. Highly magnesian igneous rock samples with forsterite composition of (Fo 90 – 92 ) mole% are the only igneous rock type found in this study. They are highly serpentinized and the alteration minerals are antigorite and talc. This is a mantle-derived subvolcanic rock, fragmented and brought to surface with the rising salt diapir. Dark gray dolomite with possible stromatolitic structures is one of the common rock types at the Sanam plug. It is fine crystalline and partly silicified. It was probably precipitated in reducing environment on the flanks of the salt basin. Some pure recrystallized calcitic limestones were also recognized and seem to be of chemogenic origin; as parts of vein fillings. Shale, with illite, as dominant clay mineral, and quartz with minor kaolinite and montmorillonite may represent ancient fluvial deposits. One sample was identified as silicified ferruginous mudstone with peculiar mineral composition of orthoclase, quartz, illite, hematite, goethite, gypsum and jarosite. The origin of this rock may be volcanic and include initial mud rich in feldspar, which was indurated and altered by microbial Fe precipitation and enrichment via colloidal state, gypsum cement was introduced later and silicification followed.
    [Show full text]
  • Archean Subduction Or Not? Evidence from Volcanic Geochemistry
    Archean Subduction or Not? Evidence from Volcanic Geochemistry Julian Pearce (Cardiff, UK) including collaboration with Hugh Smithies and David Peate Plan Part 1: Theory: Fingerprinting Subduction Volcanism Part 2: Life Cycles of Volcanic Arcs Part 3: Identification of Subduction Volcanism in the Palaeoproterozoic Part 4: Identification of Subduction Volcanism in the Middle to Late Archean Part 5: Identification of Subduction Volcanism in the Early Archean Plan Part 1: Theory: Fingerprinting Subduction Volcanism Part 2: Life Cycles of Volcanic Arcs Part 3: Identification of Subduction Volcanism in the Palaeoproterozoic Part 4: Identification of Subduction Volcanism in the Middle to Late Archean Part 5: Identification of Subduction Volcanism in the Early Archean Arc-aeology: Fingerprinting Arc Lavas in the Geological Record 1. Selective element mantle depletion by episodic enrichment In the mantle melt extraction towards arc front wedge. volcanic back-arc rear-arc intraplate arc ridge seamount volcano 2. Distinctive mantle flow pattern constrained by the F lithosphere B’ A’ subducting slab. C LT a sthenosphere HT B 3. Effects of high water UHT content on melting of the mantle wedge A 3. Effects of high water content in magmas on crystallization history and vesicularity/explosivity Arc-aeology: Fingerprinting Arc Lavas in the Geological Record 1. Selective element mantle depletion by episodic enrichment In the mantle melt extraction towards arc front wedge. volcanic back-arc rear-arc intraplate arc ridge seamount volcano 2. Distinctive mantle flow pattern constrained by the F lithosphere B’ A’ subducting slab. C LT a sthenosphere HT B 3. Effects of high water UHT content on melting of the mantle wedge A 3.
    [Show full text]
  • Subduction Zones
    AccessScience from McGraw-Hill Education Page 1 of 11 www.accessscience.com Subduction zones Contributed by: R. J. Stern, S. H. Bloomer Publication year: 2019 Regions where portions of the Earth’s tectonic plates sink beneath other plates, into the Earth’s interior. Subduction zones are defined by deep oceanic trenches, lines of volcanoes parallel to the trenches and zones of large earthquakes that extend from the trenches landward. Plate tectonic theory recognizes that the Earth’s solid surface is composed of a mosaic of interacting lithospheric plates, with the lithosphere consisting of the crust (continental or oceanic) and associated underlying mantle, for a total thickness that varies with age but that is typically about 100 km (60 mi). Oceanic lithosphere is created by seafloor spreading at mid-ocean ridges (divergent, or accretionary, plate boundaries) and destroyed at subduction zones (at convergent, or destructive, plate boundaries). At subduction zones, the oceanic lithosphere dives beneath another plate, which may be either oceanic or continental. Part of the material on the subducted plate is recycled back to the surface (by being scraped off the subducting plate and accreted to the overriding plate, or by melting and rising as magma) and the remainder is mixed back into the Earth’s deeper mantle. This process balances the creation of lithosphere that occurs at the mid-ocean ridge system. The convergence of two plates occurs at rates of 1–10 cm∕yr (0.4–4 in.∕yr) or 10–100 km (6–60 mi) per million years (Fig. 1). During subduction, stress and phase changes in the upper part of the cold descending plate produce earthquakes in the upper portion of the plate, in a narrow band called the Wadati-Benioff zone (named after the Japanese and U.S.
    [Show full text]
  • 19860010298.Pdf
    o ARCHEAN FORELAND BASIN TECTONICS IN THE WITWATERSRAND, SOUTH AFRICA Kevin Burke Lunar and Planetary Institute 3303 NASA Road One MAR1986 Houston, Texas 77058 BEOIMEB W.S.F. Kidd and T.M. Kusky Department of Geological Sciences State University of New York at Albany 1400 Washington Avenue Albany, New York 12222 JNAS&-CR-176561) ARCHBAN FORELAND BASIN N86-19769 TECTONICS IN THE HITiATEHSBASE, SOOTH AFRICA (Luuar and Planetary lust.) 62 p HC AOV«F A01 CSC1 08G Onclas G3/46 04607 o o Page 2 f ABSTRACT The Witwatersrand Basin of j>r South Africa is the best-known of Archean sedimentary basins and contains some of the largest gold reserves in the world. Sediments in the basin include a lower flysch-type sequence and an upper molassic facies, both of which contain abundant silicic volcanic detritus. The strata are thicker and more proximal on the northwestern side of the basin which is, at least locally, bound by thrust faults. These features indicate that the Witwatersrand strata may have been deposited in a foreland basin and a regional geologic synthesis suggests that this basin developed initially on the cratonward side of an Andean-type arc. Remarkably similar Phanerozoic basins may be found in the southern Andes above zones of shallow subduction. We suggest that the continental collision between the Kaapvaal and Zimbabwe Cratons at about 2.7 Ga caused further subsidence and deposition in the Witwatersrand Basin. Regional uplift during this later phase of development placed the basin on the cratonward edge of a collision-related plateau, now represented by the Limpopo Province.
    [Show full text]
  • Volcanic Tsunami Generating Source Mechanisms in the Eastern Caribbean Region
    VOLCANIC TSUNAMI GENERATING SOURCE MECHANISMS IN THE EASTERN CARIBBEAN REGION George Pararas-Carayannis Honolulu, Hawaii, USA ABSTRACT Earthquakes, volcanic eruptions, volcanic island flank failures and underwater slides have generated numerous destructive tsunamis in the Caribbean region. Convergent, compressional and collisional tectonic activity caused primarily from the eastward movement of the Caribbean Plate in relation to the North American, Atlantic and South American Plates, is responsible for zones of subduction in the region, the formation of island arcs and the evolution of particular volcanic centers on the overlying plate. The inter-plate tectonic interaction and deformation along these marginal boundaries result in moderate seismic and volcanic events that can generate tsunamis by a number of different mechanisms. The active geo-dynamic processes have created the Lesser Antilles, an arc of small islands with volcanoes characterized by both effusive and explosive activity. Eruption mechanisms of these Caribbean volcanoes are complex and often anomalous. Collapses of lava domes often precede major eruptions, which may vary in intensity from Strombolian to Plinian. Locally catastrophic, short-period tsunami-like waves can be generated directly by lateral, direct or channelized volcanic blast episodes, or in combination with collateral air pressure perturbations, nuéss ardentes, pyroclastic flows, lahars, or cascading debris avalanches. Submarine volcanic caldera collapses can also generate locally destructive tsunami waves. Volcanoes in the Eastern Caribbean Region have unstable flanks. Destructive local tsunamis may be generated from aerial and submarine volcanic edifice mass edifice flank failures, which may be triggered by volcanic episodes, lava dome collapses, or simply by gravitational instabilities. The present report evaluates volcanic mechanisms, resulting flank failure processes and their potential for tsunami generation.
    [Show full text]
  • Geology of the Wadi Ash Shu'bah Quadrangle, Sheet 26E Kingdom of Saudi Arabia
    DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Geology of the Wadi Ash Shu'bah Quadrangle, sheet 26E Kingdom of Saudi Arabia by I/ I/ James E. Quick and Jeff L. Doebrich Open-File Report 87-501 Report prepared by the U.S. Geological Survey in cooperation with the Deputy Ministry for Mineral Resources, Saudi Arabia This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature, I/ USGS Mission Saudi Arabia 1987 CONTENTS ABSTRACT ............................................... 1 INTRODUCTION ........................................... 2 Geographic setting ................................. 2 Previous investigations ............................ 2 Present investigations ............................. 5 Acknowledgments .................................... 6 GEOLOGIC OVERVIEW ...................................... 7 PRECAMBRIAN VOLCANIC AND SEDIMENTARY ROCKS ............. 9 Hulayfah group ..................................... 9 Banana formation .............................. 9 Sufran formation .............................. 10 Afna format ion ................................. 10 Limestone and marble member .............. 11 Sedimentary and volcanic member .......... 11 Medium-grade metamorphic rock.................. 11 Age and thickness ............................. 11 Maraghan formation ................................. 11 Hadn formation ..................................... 12 Sandstone and conglomerate member ............. 13 Age and thickness ............................
    [Show full text]
  • SKI Report 94:10 Geological Documentation of the Norrköping
    SKI Report 94:10 Geological Documentation of the Norrköping - Oskarshamn Region in South-eastern Sweden Discussion of Factors Relevant to Siting Sören Scherman April 1994 ISSN 1104-1374 ISRN SKI-R--94/10--SE SK! Report 94:10 Geological Documentation of the Norrköping - Oskarshamn Region in South-eastern Sweden Discussion of Factors Relevant to Siting Sören Scherman Svensk Ingenjörstjänst AB Körsbärsvägen 7, 741 31 Knivsta April 1994 This report concerns a study which has been conducted for the Swedish Nuclear Power Inspectorate (SKI). The conclusions and viewpoints presented in the report are those of the author(s) and dc not necessarily coincide with those of the SKI. The geological maps in this report are published with permission from the Geological Survey of Sweden. SI MM ARV ! r.:s study comprises a compilation of data from two tectonic regions in southeastern Sweden and a presentation of geological factors judged to be of importance for the regional- scale suing or a high level nuclear waste repository.The study areas were selected to complement earlier investigations in that part of Sweden and to allow for an analysis of the transition zone between the Svecofennian subprovince and the Transcandinavian Igneous Be!: i TIB). The study started with a literature survey and map studies. Reconaissance work of the regions (Norrköping - Västervik and Oskarshamn - Västervik) was initially done to get an overall picture of the bedrock geology. Finally a field excursion was carried out in order to iiiustrate geological and structural characteristics of the areas. Experiences from earlier studies in Swedish underground constructions have to some extent been used as a basis for the conclusions in the report.
    [Show full text]