DOCSLIB.ORG

Chemical Variation in Hercynian Basalts Relative to Plate Tectonics

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Chemical Variation in Hercynian Basalts Relative to Plate Tectonics J. geol. Soc. London, Vol. 139, 1982, pp. 505-520, 7 figs., 2 tables. Printed in Northern Ireland. Chemical variation in Hercynian basalts relative to plate tectonics P. A. Floyd SUMMARY:The geochemistry of Hercynianbasalts is reviewed with special reference to SW England. Hercynian basalts have thefollowing chemical features: (1) relative enrichment in incompatible elements, (2) fractionated rare earth element (REE) patterns ranging from mild to strongly light-REE enriched, and(3) generally low large-ion-lithophile (L1L)ihigh field strength (HFS)element ratios. High and variable alkali contents and KiRb ratios are indicative of low-gradealteration. Basalts are predominantlytholeiites, although alkali basalts maybe developed on some trough margins. Basalts fromdifferent sedimentary troughs within the main Hercynian tectonic zones are characterized by specific incompatible element abundances and ratios. These variations are interpreted in terms of variable fractional crystallization, partial melting and mantle heterogeneity. Hercynian volcanism was typically bimodal with basic and acid products characterizing the Rheno-Hercynian and Saxo-Thuringian zones. Activity in the Moldanubian zone wasmore variable with a high proportion of calc-alkaliandesites. Two systematic chemical changes throughout the Devonian and Carboniferous have been recognized, with both lightiheavyREE and LIL/HFS element ratios increasing with time. These featuresmay relate to the introduction of LIL-enriched fluids derived by dehydration of subducted lithosphere that caused progressive metasomatism of the overlying mantle wedge. Chemical discrimination of tectonic setting demonstrates that most of the basalts typify the continental intra-plate environment, although early Devonian basalts produced in the initial stages of continent rifting have someof the chemical features of incompatible element enriched oceanic basalts. An ensialic back-arc basin model underlain by a shallow northward-dipping subduction zone provides a possible explanation for the spatial and temporal variation in the Hercynian volcanic rocks. The Hercynian fold belt has been subjected to many 1972) and also a Palaeozoic ocean (now represented different interpretations in termsof plate tectonics (for by theIle de Groix blueschists, Hanmer 1977) be- referencesand reviews see Ager 1975; Krebs 1976; tween Armorica and N Iberia (Lefort 1979). Windley 1977; Ziegler 1978; Anderton et al. 1979). The problem is compounded by the general lack of For someworkers the particular tectonic, metamor- magmatic plate margin characteristics such as typical phic and magmatic characters of this belt have led to ophiolite sequences, island arc or continental margin non-plate tectonic models involving lithospheric ther- volcanic rocks (in particular andesites) and voluminous maldisturbances (e.g. Krebs & Wachendorf1973; intermediate plutonics. This has led to other models Zwart & Dornsiepen1978). Much of theplate tec- involvingoblique collision or passive lateralsliding tonic argument has been concerned with the location betweenopposing continental masses (Badham & of former oceans and related subduction zones down Halls1975; Arthaud & Matte1977), although sub- which oceaniccrust disappeared prior to continent- duction and collision arestill involved at a late stage. continent collision. Interpretations generally fall into two main groups, either presented singly or in combi- nation, concerning the location of the suture relative Objectives. Thispaper outlines the chemical charac- to the Hercynian tectonic zones (Fig. 1): teristics. of basaltic lavas and high-level intrusives in (1)Within ornear the southern margin of the different Hercynian sedimentary troughs and tectonic Rheno-Hercynian (R-H) zone with either southward zones with regard to: (1) chemical variations in space (under continental Europe) or northward (under the and time, and (2) their tectonic settingby analogy with OldRed Sandstone continent) dipping subduction modern volcanic rocks. In general the chemical data zones-the vanished ocean (with the possible excep- lendsupport to ensialic rifting models with the de- tion of theLizard ophiolite, Kirby 1979) being the velopment of back-arcbasins (e.g. Reading1973; Mid-European ocean of Johnson (1973). Leeder1976; BCbien et al. 1977;Anderton et al. (2) S of theMoldanubian zone with a northward 1979), although the lack of suitable or sufficient trace dipping subduction zone under continental Europe- elementdata means that only a crude geochemical the subducted ocean being the proto-Tethys (Nicholas model can be presented. 0016-7649/82/0700-0505$02.00 @ 1982 The Geological Society Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/139/4/505/4887555/gsjgs.139.4.0505.pdf by guest on 02 October 2021 5 06 P. A. Floyd Si02 distribution RHENO-HERCYNIAN 1 SAX0 -THURINGIAN Vosges - Iberian Pyrite FIG. 1. Location of Upper Palaeozoic volcanic rocks within the Hercynian massifs and tectonic zones of Europe. Characteristic features of zones summarized by Read & Watson (1975). Numbers refer to localities mentioned in text.Distribution of magmatypes (AB =alkali basalt,TB = tholeiiticbasalt, CA = calc-alkali)and nature of volcanism (triangles = pre-orogenic bimodal; squares = pre-orogenic bimodal +synorogenic unimodal andesite- dominated; dots = synorogenic intermediateiacid-dominated) also indicated. Volcanic nature partly after Btbien et al. (1977). SiO, distribution: various sources and author (unpubl), except Vosges Meridionales from Btbien (1976) with b = pre-orogenic bimodal and a = synorogenic andesite-dominated. Chemical problems Y, Nb, rare earth elements, REE) are largely used to characterize the Hercynian magmatic suites. In thispaper the incompatible elements will be Chemical mobility during low-grade divided according to their respective ionic potential or metamorphism field strength (ionic charge/size ratio) into two groups All the volcanicrocks preserved in the Hercynian which show differential behaviour in destructive mar- troughs have been eithermildly metamorphosed in the gin settings (cf. Saunders et al. 1979): (1) Large-ion- very low-grade anchizone (based on illite crystallinity lithophile (LIL) elements (K, Rh, CS,Ba, Sr) together in sedimentary rocks, e.g. Weber 1972; Brazier et al. with the light REE (La, Ce, Nd) that have relatively 1979) or more commonly in the prehnite-pumpellyite low field strength and represent the least mobile ele- facies to greenschist facies of regional metamorphism mentsin this group. (2) High field strength(HFS) (based on meta-basaltassemblages). As low-grade elements (Ti, P, Zr, Nb, Hf, Ta) which are immobile metamorphism causes changes in the bulk chemistryof duringalteration. Owing to thelack of full REE basalts (e.g. Hart et al. 1974; Humphris &L Thompson analyses fractionation between light and heavy REE 1978) selected stable incompatible elements (Ti,P, Zr, will be demonstrated using the Ce/Y ratio (elements Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/139/4/505/4887555/gsjgs.139.4.0505.pdf by guest on 02 October 2021 Chemical variation in Hercynian basalts relative to platetectonics 5 07 determined by XRF) where Y has a similar behaviour have higher incompatible element contents (but lower to the heavy REE. LIL and HFS element decoupling Y),exhibit well fractionated REE patternswith will be indicated by changes in the La/Nb ratio. (Ce/Y),>4.5 and more restricted La/Nb ratios 21.0. Alkaline pillow lavas and intrusive suites may overlap compositionally, but are chemically unrelated by low- environment discrimination Tectonic pressure fractionation. Modernvolcanic rocks (in particularbasalts) with One major feature to emerge from a study of the specific chemical features characterize particular tec- chemicalcomposition of the volcanicrocks from tonic environments and as such form the basis for the different stratigraphic belts is that each geographically tectonic designation of ancient basalts (e.g. Pearce & separate volcanic centre has its own incompatible ele- Cann 1973; Wood et al. 1979). However, basalts with ment identity. Variation within each volcanic centreis a similar chemistry may be produced in different tec- governed by low-pressurecrystal fractionation as tonic regimes, since their compositions reflect the na- exemplified by the decrease in both Ni and Cr with ture of the particular mantle and the melting processes progressive fractionation, measured by the Zr content. operatingrather than the regime in which they are As seenin Fig. 2 incompatibleelement ratios (all found. This may often make the chemical designation relativeto Zr) remain constant over much of the of ancient basalts less certain. For example, in the Ti- compositional range for each volcanic centre and iden- Zr-Y diagram (Pearce & Cann 1973) certain incom- tify one magmatic suite relative to others with differ- patible element enriched oceanic basalts can also plot ent ratios. Variation in such ratios for trace elements in the intra-plate field, whereas primitive continental with low distribution coefficients (K,<< 1) can be ac- rift basalts may plot in the ocean-floor field. For the counted for by variable partial melting and/or, mantle Hercynianvolcanic rocks numbera of chemical source composition (Floyd, in press). criteria are used, which together with the geological environment, provide a reasonable, although specula- tive, interpretation of the tectonic situation throughout Compositional changes in space and time the Upper Palaeozoic. Fig.
Load more

Recommended publications
  • Geology of Cyprus and Eastern Mediterranean Department: Sciences and Engineering Host Institution: University of Nicosia, Nicosia, Cyprus
    Global Semesters Course Syllabus Course: GEOL 315 Geology of Cyprus and Eastern Mediterranean Department: Sciences and Engineering Host Institution: University of Nicosia, Nicosia, Cyprus Course Summary Course Code Course Title Recommended Credit Hours Geology of Cyprus and Eastern GEOL-315 3 Mediterranean Subject Contact Hours Prerequisites Geology 42-45 At least a 2nd year student Department Level of Course Language of Instruction Sciences & Engineering Upper-Division English Course Description The course introduces students to the science and the basics of geology, and studies the formation of Cyprus and the Mediterranean Basin and specially the unique geological formations of Cyprus. The Troodos mountain range, a unique place in the world for the understanding of an oceanic plate and the relevant geodynamic phenomena, will be of special focus. The course includes several site visits. The course can be taken by any science student. Prerequisites (if applicable) At least a 2nd year student Instructor Information Nicki Nicolaidou, [email protected]: Mrs.Nicki Nicolaidou received her Degree in Geology from the Aristotle University of Thessaloniki, Greece in 2007. Since 2010 she is working as a project geologist for the Canadian gold exploration company Northern Lion, in Cyprus. Previous work experience as a geologist includes geotechnical and environmental impact assessment studies. Ifigenia Gavriel, [email protected]: Mrs.Ifigenia Gavriel is a postgraduate student of the MSc Environmental Engineering of the Department of Civil and Environmental Engineering at the University of Cyprus. She received her Degree in Geology from the National and Kapodestrian University of Athens, Greece in 2009. From 2010 she is working as a project geologist for the Canadian gold exploration company Northern Lion, in Cyprus.
    [Show full text]
  • Study of the Geomorphology of Cyprus
    STUDY OF THE GEOMORPHOLOGY OF CYPRUS FINAL REPORT Unger and Kotshy (1865) – Geological Map of Cyprus PART 1/3 Main Report Metakron Consortium January 2010 TABLE OF CONTENTS PART 1/3 1 Introduction 1.1 Present Investigation 1-1 1.2 Previous Investigations 1-1 1.3 Project Approach and Scope of Work 1-15 1.4 Methodology 1-16 2 Physiographic Setting 2.1 Regions and Provinces 2-1 2.2 Ammochostos Region (Am) 2-3 2.3 Karpasia Region (Ka) 2-3 2.4 Keryneia Region (Ky) 2-4 2.5 Mesaoria Region (Me) 2-4 2.6 Troodos Region (Tr) 2-5 2.7 Pafos Region (Pa) 2-5 2.8 Lemesos Region (Le) 2-6 2.9 Larnaca Region (La) 2-6 3 Geological Framework 3.1 Introduction 3-1 3.2 Terranes 3-2 3.3 Stratigraphy 3-2 4 Environmental Setting 4.1 Paleoclimate 4-1 4.2 Hydrology 4-11 4.3 Discharge 4-30 5 Geomorphic Processes and Landforms 5.1 Introduction 5-1 6 Quaternary Geological Map Units 6.1 Introduction 6-1 6.2 Anthropogenic Units 6-4 6.3 Marine Units 6-6 6.4 Eolian Units 6-10 6.5 Fluvial Units 6-11 6.6 Gravitational Units 6-14 6.7 Mixed Units 6-15 6.8 Paludal Units 6-16 6.9 Residual Units 6-18 7. Geochronology 7.1 Outcomes and Results 7-1 7.2 Sidereal Methods 7-3 7.3 Isotopic Methods 7-3 7.4 Radiogenic Methods – Luminescence Geochronology 7-17 7.5 Chemical and Biological Methods 7-88 7.6 Geomorphic Methods 7-88 7.7 Correlational Methods 7-95 8 Quaternary History 8-1 9 Geoarchaeology 9.1 Introduction 9-1 9.2 Survey of Major Archaeological Sites 9-6 9.3 Landscapes of Major Archaeological Sites 9-10 10 Geomorphosites: Recognition and Legal Framework for their Protection 10.1
    [Show full text]
  • Tertiary Uplift History of the Troodos Massif, Cyprus
    Tertiary uplift history of the Troodos massif, Cyprus A.H.F. ROBERTSON* Department of Geology, University of Cambridge, Sedgwick Museum, Downing Street, Cambridge CB2 3EQ, England ABSTRACT INTRODUCTION Troodos massif that he took as an indica- tion of possible subaerial exposure. The detailed uplift history of a portion of In the recent debate about the mech- Subsequently, in Maastrichtian time, the Late Cretaceous Tethyan oceanic litho- anisms of formation and subsequent de- open oceanic stage in the evolution of the sphère is documented by in situ sedimentary formation of the Troodos massif of Cyprus, Troodos massif was terminated by major sequences around the Troodos massif of little account has been taken of the various tectonic movements that simultaneously af- Cyprus. The pre-uplift tectonic setting first in situ Upper Cretaceous and Tertiary fected the whole belt stretching from Greece involved genesis of the Troodos massif at a sedimentary sequences that are exposed through Cyprus to Oman and beyond spreading ocean ridge of Late Cretaceous around the perimeter of the Troodos mas- (Smith, 1971). In the south and southwest age, followed by deformation in Maas- sif. This paper has two main objectives. of Cyprus, substantial thrust sheets and trichtian time. Then, after a brief period of First, it outlines the sedimentary develop- mélange were emplaced directly over the latest Cretaceous deep-water pelagic ment of southern Cyprus in the Tertiary Troodos ocean floor. This deformation is sedimentation, much of the area was blan- Period, of interest to many working in the suggestive of subduction and a trench envi- keted in early Tertiary time by a wedge of East Mediterranean.
    [Show full text]
  • The Pre-Alpine Evolution of the Basement of the Pelagonian Zone and the Vardar Zone, Greece
    The Pre-Alpine Evolution of the Basement of the Pelagonian Zone and the Vardar Zone, Greece Dissertation zur Erlangung des Grades „Doktor der Naturwissenschaften“ am Fachbereich Chemie, Pharmazie und Geowissenschaften der Johannes Gutenberg-Universität Mainz Birte Anders Mainz, Juni 2005 Erklärung: Hiermit versichere ich, die vorliegende Arbeit selbstständig und nur unter Verwendung der angegebene Quellen und Hilfsmittel verfasst zu haben. Mainz, Juni 2005 Tag der mündlichen Prüfung: 27.07.2005 Summary iii Summary The Hellenides in Greece constitute an integral part of the Alpine-Himalayan mountain chain. They are traditionally divided into several subparallel, c. NNW-SSE trending tectono-stratigraphic zones. These zones are grouped into two large units, namely the External Hellenides (Hellenide foreland) in the west and the Internal Hellenides (Hellenide hinterland) in the east. The External Hellenides comprise the Paxon, Ionian and Gavrovo-Tripolis Zones, which are dominated by Mesozoic and Cainozoic cover rocks. The Pelagonian Zone, the Attico-Cycladic Massif, the Vardar Zone, the Serbo-Macedonian Massif and the Rhodope Massif (from west to east) form the Internal Hellenides. They are characterised by abundant occurrences of crystalline basement. The Pelagonian Zone and the Vardar Zone in Greece represent the western part of the Internal Hellenides. While the Pelagonian Zone comprises predominantly crystalline basement and sedimentary cover rocks, the Vardar Zone has long been regarded as an ophiolite-decorated suture zone separating the Pelagonian Zone from the Serbo-Macedonian Massif to the east. In order to identify the major crust-forming episodes and to improve the understanding of the evolutionary history of this region, felsic basement rocks from both the Pelagonian Zone and the Vardar Zone were dated, with the main focus being on the Pelagonian Zone.
    [Show full text]
  • The Mamonia Complex (SW Cyprus) Revisited: Remnant of Late Triassic Intra-Oceanic Volcanism Along the Tethyan Southwestern Passive Margin
    Geol. Mag. 144 (1), 2007, pp. 1–19. c 2006 Cambridge University Press 1 doi:10.1017/S0016756806002937 First published online 21 December 2006 Printed in the United Kingdom The Mamonia Complex (SW Cyprus) revisited: remnant of Late Triassic intra-oceanic volcanism along the Tethyan southwestern passive margin H. LAPIERRE∗, D. BOSCH‡, A. NARROS∗, G. H. MASCLE∗§, M. TARDY ¶ & A. DEMANT ∗Laboratoire Geodynamique´ des Chaˆınes Alpines, UMR-CNRS 5025, Universite´ J. Fourier, Maison des Geosciences,´ B. P. 53, F. 38041 Grenoble Cedex, France ‡Laboratoire de Tectonophysique, UMR-CNRS 5568, Institut des Sciences de la Terre, de l’Eau et de l’Espace de Montpellier, CC049, Universite´ de Montpellier II, Place Eugene` Bataillon, F. 34095 Montpellier Cedex 05, France ¶Laboratoire Geodynamique´ des Chaˆınes Alpines, UMR-CNRS 5025, Universite´ de Savoie, F. 73376 Le Bourget du Lac, France Laboratoire de Petrologie´ magmatique, Universite´ Paul Cezanne´ (Aix-Marseille), case courrier 441, F. 13397 Marseille Cedex 20, France (Received 21 June 2005; accepted 11 May 2006) Abstract – Upper Triassic volcanic and sedimentary rocks of the Mamonia Complex in southwestern Cyprus are exposed in erosional windows through the post-Cretaceous cover, where the Mamonia Complex is tectonically imbricated with the Troodos and Akamas ophiolitic suites. Most of these Upper Triassic volcanic rocks have been considered to represent remnants of Triassic oceanic crust and its associated seamounts. New Nd and Pb isotopic data show that the whole Mamonia volcanic suite exhibits features of oceanic island basalts (OIB). Four rock types have been distinguished on the basis of the petrology and chemistry of the rocks. Volcanism began with the eruption of depleted olivine tholeiites (Type 1) and oceanic island tholeiites (Type 2) associated with deep basin siliceous and/or calcareous sediments.
    [Show full text]
  • A Seismic Model for Moho and Crustal Structure in Europe, Greenland, and the North Atlantic Region☆
    Tectonophysics 609 (2013) 97–153 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Review Article EUNAseis: A seismic model for Moho and crustal structure in Europe, Greenland, and the North Atlantic region☆ Irina M. Artemieva ⁎, Hans Thybo IGN, University of Copenhagen, Denmark article info abstract Article history: We present a new digital crustal model for Moho depth and crustal structure in Europe, Greenland, Iceland, Received 27 November 2012 Svalbard, European Arctic shelf, and the North Atlantic Ocean (72W–62E, 30N–84N). Our compilation is based Received in revised form 18 July 2013 on digitization of original seismic profiles and Receiver Functions from ca. 650 publications which provides a Accepted 4 August 2013 dense regional data coverage. Exclusion of non-seismic data allows application of the database to potential Available online 15 August 2013 field modeling. EUNAseis model includes Vp velocity and thickness of five crustal layers, including the sedimen- tary cover, and Pn velocity. For each parameter we discuss uncertainties associated with theoretical limitations, Keywords: Moho regional data quality, and interpolation. Crustal thickness By analyzing regional trends in crustal structure and links to tectonic evolution illustrated by a new tectonic map, Crystalline crust we conclude that: (1) Each tectonic setting shows significant variation in depth to Moho and crustal structure, Sedimentary cover essentially controlled by the age of latest tectono-thermal processes; (2) Published global averages of crustal pa- Pn velocity rameters are outside of observed ranges for any tectonic setting in Europe; (3) Variation of Vp with depth in the Crustal evolution sedimentary cover does not follow commonly accepted trends; (4) The thickness ratio between upper-middle (Vp b 6.8 km/s) and lower (Vp N 6.8 km/s) crystalline crust is indicative of crustal origin: oceanic, transitional, platform, or extended crust; (5) Continental rifting generally thins the upper-middle crust significantly without changing Vp.
    [Show full text]
  • 43. Pleistocene Fanglomerate Deposition Related to Uplift of the Troodos Ophiolite, Cyprus1
    Robertson, A.H.F., Emeis, K.-C., Richter, C., and Camerlenghi, A. (Eds.), 1998 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 160 43. PLEISTOCENE FANGLOMERATE DEPOSITION RELATED TO UPLIFT OF THE TROODOS OPHIOLITE, CYPRUS1 Andrew Poole2 and Alastair Robertson3 ABSTRACT The Pleistocene Fanglomerate Group of the southern part of Cyprus exemplifies coarse alluvial clastic deposition within a zone of focused tectonic uplift, related to collision of African and Eurasian plates, as documented by Ocean Drilling Program Leg 160. During the Pleistocene, the Troodos ophiolite was progressively unroofed, resulting in a near-radial pattern of coarse clastic sedimentation. The Pleistocene Fanglomerate Group depositionally overlies Pliocene marine sediments. Along the southern margin of the Troodos Massif the contact is erosional, whereas along its northern margin a regressive fan-delta (Kakkaristra Fm.) intervenes. The Pleistocene Fanglomerate Group is subdivided into four units (termed F1−F4), each of which were formed at progres- sively lower topographic levels. A wide variety of alluvial units are recognized within these, representing mainly high-energy coarse alluvial fans, channel fans, braidstream, and floodplain environments. A near-radial sediment dispersal pattern away from Mt. Olympos is indicated by paleocurrent studies, based on clast imbrication. Provenance studies indicate relatively early unroofing of the ophiolite, but with only minor localized erosion of ultramafic rocks from the Mt. Olympos area. Clasts of erosionally resistant lithologies, notably ophiolitic diabase and Miocene reef- related limestone, are volumetrically over-represented, relative to friable basalt and early Tertiary pelagic carbonate sediments. The younger Fanglomerate Group units (F3 and F4) can be correlated with littoral marine terraces previously dated radio- metrically at about 185−219 ka and 116−134 ka, respectively.
    [Show full text]
  • Geological Correlation Between Northern Cyprus and Southern Anatolia
    Canadian Journal of Earth Sciences Geological Correlation Between Northern Cyprus And Southern Anatolia Journal: Canadian Journal of Earth Sciences Manuscript ID cjes-2020-0129.R3 Manuscript Type: Article Date Submitted by the 15-Jan-2021 Author: Complete List of Authors: Yilmaz, Yucel; Istanbul Teknik Universitesi, Geological Engineering Keyword: Geology, Cyprus, SE Anatolia, Correlation, Tectonics Is the invited manuscript for consideration in a Special Not applicableDraft (regular submission) Issue? : © The Author(s) or their Institution(s) Page 1 of 53 Canadian Journal of Earth Sciences 1 Geological Correlation Between Northern Cyprus And Southern Anatolia 2 Yücel Yılmaz 3 Istanbul Technical University, Faculty of Mines, Department of Geological Engineering 4 Sariyer, 34469, Istanbul, Turkey 5 [email protected] 6 7 Abstract 8 The island of Cyprus constitutes a fragment of southern Anatolia separated from the mainland 9 by left-oblique transtension in late Cenozoic time. However, a geological framework of offset 10 features of the south-central Anatolia, for comparison of Cyprus with a source region within 11 and west of the southeastern Anatolian Draftsuture zone, has not yet been developed. In this paper, 12 I enumerate, describe, and compare a full suite of potentially correlative spatial and temporal 13 elements exposed in both regions. Northern Cyprus and south-central Anatolia have identical 14 tectonostratigraphic units. At the base of both belts, crop out ophiolitic mélange-accretionary 15 complex generated during the northward subduction of the NeoTethyan Oceanic lithosphere 16 from the Late Cretaceous until the end of middle Eocene. The nappes of the Taurus carbonate 17 platform were thrust above this internally chaotic unit during late Eocene.
    [Show full text]
  • Tethyan Oceans
    Downloaded from http://sp.lyellcollection.org/ by guest on September 29, 2021 Tethyan oceans Gt~RARD M. STAMPFLI Institut de GOologie et Paldontologie, UniversitO de Lausanne, BFSH2-CH 1015 Lausanne, Switzerland (e-mail: [email protected]) Abstract: Diachronous subsidence patterns of Tethyan margins since the Early Palaeozoic provide constraints for paleocontinental reconstructions and the opening of disappeared oceans. Palaeotethys opening can be placed from Ordovician to Silurian times and corresponds to the detachment of a ribbon-like Hun Superterrane along the Gondwanan margin. Neotethys opening took place from Late Carboniferous to late Early Permian from Australia to the eastern Mediterranean area. This opening corresponds to the drifting of the Cimmerian superterrane and the final closing of Palaeotethys in Middle Triassic times. Northward subduction of Palaeotethys triggered the opening of back-arc oceans along the Eurasian margin from Austria to the Pamirs. The fate of these Permo-Triassic marginal basins is quite different from areas to area. Some closed during the Eocimmerian collisional event (Karakaya, Agh-Darband), others (Meliata) stayed open and their delayed subduc- tion induced the opening of younger back-arc oceans (Vardar, Black Sea). The subduction of the Neotethys mid-ocean ridge was certainly responsible for a major change in the Jurassic plate tectonics. The Central Atlantic ocean opened in Early Jurassic time and extended eastwards into the Alpine Tethys in an attempt to link up with the Eurasian back- arc oceans. When these marginal basins started to close the Atlantic system had to find another way, and started to open southwards and northwards, slowly replacing the Tethyan ocean by mountain belts.
    [Show full text]
  • Geology of Cyprus
    CYPRUS GEOLOGICAL SURVEY The geological structure of Cyprus AGE FORMATION / SEQUENCE Cyprus is divided into four geological zones: (a) the Pentadaktylos GEOLOGICAL MAP OF CYPRUS (Keryneia) Zone, (b) the Troodos Zone or Troodos Ophiolite, (c) the ALLUVIUM Mamonia Zone or Complex and (d) the Zone of the autochthonous Ministry of Agriculture, 0,011 MARINE DEPOSITS 35°30'N sedimentary rocks. Rural Development and Environment FANGLOMERATE Keryneia PLEIST. HOL. APALOS The Pentadaktylos (Keryneia) Zone is the northern-most geological 2,58 zone of Cyprus and is considered to be the southern-most portion of the Tauro-Diranide Alpine Zone. It has an arciform disposition with Lefkosia ENECOILP an east-west direction and is characterised by southward thrusting. Ammochostos NICOSIA The base of the Zone is mostly composed of a series of allochthonous massive and recrystallised limestones, dolomites and marbles of 35°0'N Permian-Carboniferous to Lower Cretaceous age (350-135 Ma). These Larnaka are stratigraphically followed by younger autochthonous sedimentary SKCORYRATNEMIDES SUONOHTHCOTUA SKCORYRATNEMIDES 5,33 rocks of Upper Cretaceous to Middle Miocene age (67-15 Ma), on which KALAVASOS the older allochthonous formations have been thrust southward. Pafos SRAEYNOILLIM )aM( ENECOIM Lemesos The Troodos Zone or the Troodos Ophiolite dominates the central part PACHNA of the island, constitutes the geological core of Cyprus, appears in two regions (main mass of the Troodos mountain range and in the Limassol 32°30'E 33°0'E 33°30'E 34°0'E 34°30'E and Akapnou Forests south of the range) and has a characteristic L E G E N D elongated dome structure.
    [Show full text]
  • A Model for the Plate Tectonic Evolution of the Eastern Mediterranean Region That Emphasizes the Role of Transform (Strike-Slip) Structures RICHARD W
    1st WSEAS International Conference on ENVIRONMENTAL and GEOLOGICAL SCIENCE and ENGINEERING (EG'08) Malta, September 11-13, 2008 A Model for the Plate Tectonic Evolution of the Eastern Mediterranean Region that Emphasizes the Role of Transform (Strike-Slip) Structures RICHARD W. HARRISON U.S. Geological Survey MS926A National Center 12201 Sunrise Valley Drive Reston, VA 20192 USA Abstract: - A model for the tectonic evolution of the Eastern Mediterranean region from Mesozoic to Present is developed from geological, geophysical, and seismological data on and surrounding the island of Cyprus. This model emphasizes the role of major transform structures in accommodating horizontal plate motions, driven from the west by spreading along the Atlantic-Arctic mid-ocean-ridge system and from the east by escape tectonics related to the movement of the Arabian plate. In particular, this model interprets the African-Anatolian plate boundary as a system of left-lateral transform structures, >75 km wide, that has been active since the early Mesozoic. In this model, Neotethys spreading and closure (subduction and obduction) occurred north of the transform system. Geophysical data indicates that the Troodos ophiolite dips northward; suggesting that subduction was to the north beneath the Anatolian plate. Southward obduction of the Troodos ophiolite was facilitated by contemporaneous left-lateral horizontal shear. The northward sequence of 1) a wide zone of shear containing ophiolites; 2) contracted trench and accretionary prism rocks; and 3) a north-dipping subduction zone is similar to the sequence described across the Arabia-Anatolian plate boundary, indicating commonality in tectonic evolution. Key Words: Eastern Mediterranean, Plate tectonics, African plate, Mesozoic, Cenozoic, Cyprus, Troodos 1 Introduction portion of the collage and includes its margin with the Plate tectonics is one of the Earth’s most important African plate.
    [Show full text]
  • BGS Report, Single Column Layout
    New methodologies for volcanic- hosted copper sulphide mineralization on Cyprus: A GIS–prospectivity analysis-based approach Economic Minerals Programme Internal Report CR/06/129 BRITISH GEOLOGICAL SURVEY ECONOMIC MINERALS PROGRAMME INTERNAL REPORT CR/06/129 New methodologies for volcanic- hosted copper sulphide mineralization on Cyprus: A GIS–prospectivity analysis-based approach Keywords J Naden, RJ Herrington, SM Jowitt, FM McEvoy, JP Williamson, GIS, Cyprus, Volcanic massive AJ Monhemius sulphide. Front cover With contributions from Photograph looking east at the AG Gunn, L Bateson, KE Rollin, R Thomas, C White, R Osborn Alestos open cast pit that was mined at the end of the 1930s. Alestos hill rises to the north Bibliographical reference J NADEN, RJ HERRINGTON, SM JOWITT, FM MCEVOY, JP WILLIAMSON, AJ MONHEMIUS. 2006. New methodologies for volcanic-hosted copper sulphide mineralization on Cyprus: A GIS–prospectivity analysis-based approach. British Geological Survey Internal Report, CR/06/129. 242pp. Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail [email protected]. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract. Keyworth, Nottingham British Geological Survey 2006 BRITISH GEOLOGICAL SURVEY The full range of Survey publications is available from the BGS British Geological Survey offices Sales Desks at Nottingham, Edinburgh and London; see contact Keyworth, Nottingham NG12 5GG details below or shop online at www.geologyshop.com 0115-936 3241 Fax 0115-936 3488 The London Information Office also maintains a reference e-mail: [email protected] collection of BGS publications including maps for consultation.
    [Show full text]