DOCSLIB.ORG

Metamorphic Evolution of the Middle Seve Nappe in the Snasahögarna Area, Scandinavian Caledonides

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Metamorphic Evolution of the Middle Seve Nappe in the Snasahögarna Area, Scandinavian Caledonides Examensarbete vid Institutionen för geovetenskaper Metamorphic Evolution of the Middle Seve Nappe in the Snasahögarna area, Scandinavian ISSN 1650-6553 Nr 277 Caledonides Åke Rosén Metamorphic Evolution of the In the Snasahögarna area, situated in the central Scandinavian Middle Seve Nappe in the Caledonides, the Middle Seve Nappe Complex mainly consist of pelitic Snasahögarna area, Scandinavian gneisses. Within these garnet and kyanite bearing gneisses the first Caledonides discovery of metamorphogenic diamond in Sweden has been confirmed by micro raman spectroscopy. The garnet hosted diamond together with associated carbonate and fluid inclusions were deposited by carbon saturated fluids at a pressures exceeding 3.1 GPa. The peak mineral assemblage, Phg Mgs-Sid Grt Ky Jd Rt Coe (Dia), is constrained by Åke Rosén microscopic observations and thermodynamic phase equilibrium modeling. Modeled garnet cores equilibrated at c. 750oC and 1.3 GPa together with phengite rims. This early exhumation stage was followed by heating reaching a peak temperature of 880-910oC at 1.05-1.18 GPa. Partial melting following the increased temperature is confirmed by anatectic segregations and microscopic melt related textures in the paragneiss. A fluid restricted environment at the late high temperature stage is inferred from mineral textures, mineral chemistry and low bulk rock loss on ignition. This is in agreement with thermodynamic models. Uppsala universitet, Institutionen för geovetenskaper Examensarbete E1, 30 hp i Berggrundsgeologi ISSN 1650-6553 Nr 277 Tryckt hos Institutionen för geovetenskaper, Geotryckeriet, Uppsala universitet, Uppsala, 2014. Examensarbete vid Institutionen för geovetenskaper ISSN 1650-6553 Nr 277 Metamorphic Evolution of the Middle Seve Nappe in the Snasahögarna area, Scandinavian Caledonides Åke Rosén Supervisor: Jaroslaw Majka Copyright © ¯LF3PTÏO and the Department of Earth Sciences Uppsala University Published at Department of Earth Sciences, Geotryckeriet Uppsala University, Uppsala, 2014 Abstract In the Snasahögarna area, situated in the central Scandinavian Caledonides, the Middle Seve Nappe Complex mainly consist of pelitic gneisses. Within these garnet and kyanite bearing gneisses the first discovery of metamorphogenic diamond in Sweden has been confirmed by micro raman spectroscopy. The garnet hosted diamond together with associated carbonate and fluid inclusions were deposited by carbon saturated fluids at a pressures exceeding 3.1 GPa. The peak mineral assemblage, Phg Mgs-Sid Grt Ky Jd Rt Coe (Dia), is constrained by microscopic observations and thermodynamic phase equilibrium modeling. Modeled garnet cores equilibrated at c. 750oC and 1.3 GPa together with phengite rims. This early exhumation stage was followed by heating reaching a peak temperature of 880-910oC at 1.05-1.18 GPa. Partial melting following the increased temperature is confirmed by anatectic segregations and microscopic melt related textures in the paragneiss. A fluid restricted environment at the late high temperature stage is inferred from mineral textures, mineral chemistry and low bulk rock loss on ignition. This is in agreement with thermodynamic models. Sammanfattning Den mellersta Seveskållan i området kring Snasahögarna i Jämtland domineras av granat- och kyanitförande paragnejser. I dessa har metamorfogena diamanter identifierats med hjälp av ramanspektroskopi. Diamanterna återfinns som inneslutningar i granat tillsammans med associerade karbonater samt vätskeinneslutningar. Dessa avsattes från kolmättade vätskor vid tryck överstigande 3.1 GPa. Mineralsammansättningen vid maximalt tryck, Phg Mgs-Sid Grt Ky Jd Rt Coe (Dia), har härletts från mikroskopobservationer samt termodynamisk fasmodellering. Jämvikt för anomala granatsammansättningar inneslutna i senare homogeniserad granat uppnåddes nära 750oC och 1.3 GPa. Efterföljande tryckavlastning medförde värmeökning till 880-910oC vid 1.05-1.18 GPa. Anatektisk textur samt smältrelaterade mikrostrukturer tyder på partiell uppsmältning till följd av ökad temperatur och minskat tryck. Mineraltexturer, mineralkemi och en låg viktförlust vid upphettning av prov indikerar låg vätsketillgång vid den sena högtemperatursfasen. Detta bekräftas av termodynamisk fasmodellering. Contents 1. Introduction ..................................................................................................................... 1 2. Background ..................................................................................................................... 1 2.1. Pre-Caledonian Baltica ................................................................................................ 1 2.2. Caledonian orogeny ..................................................................................................... 3 2.3. Scandinavian Caledonides ........................................................................................... 4 2.4. The Snasahögarna area and surroundings .................................................................... 9 3. Previous studies ............................................................................................................. 11 3.1. Geothermobarometry ................................................................................................. 11 3.2. Geochronology ........................................................................................................... 12 4. Methods ......................................................................................................................... 13 4.1. Thin sections .............................................................................................................. 13 4.2. Microprobe analysis ................................................................................................... 13 4.3. Raman spectroscopy .................................................................................................. 14 4.4. Whole rock chemistry ................................................................................................ 14 4.5. Geothermometry ........................................................................................................ 14 4.6. PT Pseudosections & Isopleths (thermodynamic modeling) ..................................... 14 5. Results ........................................................................................................................... 15 5.1. Petrography ................................................................................................................ 15 5.2. Raman spectroscopy .................................................................................................. 35 6. Geothermometry ............................................................................................................ 42 6.1. Garnet-Biotite thermometer ....................................................................................... 42 7. Thermodynamic phase equilibrium modeling ............................................................... 44 7.1. Model 1 ...................................................................................................................... 44 7.2. Model 2 ...................................................................................................................... 45 7.3. Exhumation PT path .................................................................................................. 45 8. Discussion ..................................................................................................................... 50 1 8.1. Ultrahigh pressure metamorphism (UHP) ............................................................. 50 8.2. Metamorphogenic diamond ................................................................................... 51 8.3. Metamorphic evolution .......................................................................................... 52 8.4. Exhumation processes ............................................................................................ 54 8.5. Timing of subduction ............................................................................................. 54 9. Conclusions ................................................................................................................... 55 Acknowledgements .............................................................................................................. 56 References ............................................................................................................................ 57 2 1. Introduction The Scandinavian Caledonides is a continent-continent collisional style orogen in many aspects well suited for studying the effects of orogenic processes. It was recognized several decades before the notion of plate tectonics that the nappes of the Scandes must have been vastly laterally displaced from where they had originally been deposited (Törnebohm 1888). It is now generally accepted that allochthonous units of the Scandinavian Caledonides were originally derived from as far away as the Laurentian margin (Gee et al. 2008). Given the age of the Scandes, through uplifting and erosional processes it is possible to study rocks and structures whose analogues are hidden deep below the ground surface in younger orogens. The evolution of the mountain chain and the timing of its different stages along with the proposed mechanisms of nappe emplacement and exhumation of subducted units is still not fully understood. This study focuses on the metamorphic evolution
Load more

Recommended publications
  • 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]
  • From the Early Paleozoic Platforms of Baltica and Laurentia to the Caledonide Orogen of Scandinavia and Greenland
    44 by David G. Gee1, Haakon Fossen2, Niels Henriksen3, and Anthony K. Higgins3 From the Early Paleozoic Platforms of Baltica and Laurentia to the Caledonide Orogen of Scandinavia and Greenland 1 Department of Earth Sciences, Uppsala University, Villavagen Villavägen 16, Uppsala, SE-752 36, Sweden. E-mail: [email protected] 2 Department of Earth Science, University of Bergen, Allégaten 41, N-5007, Bergen, Norway. E-mail: [email protected] 3 The Geological Survey of Denmark and Greenland, Øster Voldgade 10, Dk 1350 Copenhagen, Denmark. E-mail: [email protected], [email protected] The Caledonide Orogen in the Nordic countries is exposed in Norway, western Sweden, westernmost Fin- Introduction land, on Svalbard and in northeast Greenland. In the The Caledonide Orogen is preserved on both sides of the North mountains of western Scandinavia, the structure is dom- Atlantic Ocean, in the mountains of western Scandinavia and north- inated by E-vergent thrusts with allochthons derived eastern Greenland; it continues northwards from northern Norway, across the Barents Shelf and Svalbard to the edge of the Eurasian from the Baltoscandian platform and margin, from out- Basin (Figure 1). The orogen is notable for its thrust systems, board oceanic (Iapetus) terranes and with the highest E-vergent in Scandinavia and W-vergent in Greenland. The width of the orogen, prior to Cenozoic opening of the North Atlantic, was in thrust sheets having Laurentian affinities. The other the order of at least 700–800 km, the deformation fronts on both side of this bivergent orogen is well exposed in north- sides of the orogen being defined by thrusts that, in the Devonian, eastern Greenland, where W-vergent thrust sheets probably reached substantially further onto the foreland platforms than they do today.
    [Show full text]
  • The Terrane Concept and the Scandinavian Caledonides: a Synthesis
    The terrane concept and the Scandinavian Caledonides: a synthesis DAVID ROBERTS Roberts , D. 1988: The terrane concept and the Scandinavian Caledonides: a synthesis. Nor. geol . unders . Bull. 413. 93-99. A revised terrane map is presented for the Scandinavian Caledcnldes. and an outline is given of the principal suspect and exot ic terranes and terrane-complexe s identified outboa rd from the Baltoscand ian miogeocline. The outermost part of the Baltoscandian continental margin is itself suspect , in the terrane sense. since the true palaeogeographical location s of rocks now represented in the Seve and serey-seuano Nappes, while inferred, are not known. The orogen -internal exotic terranes embrace the oceanic/eugeoclinal elements of the Caledonides, represented by the mag­ matosed imentary assemblages of the Koli Nappes, including ophiolite fragments and island arc products. Even more exot ic terranes occur in the highest parts of the tectonostratigraphy, inclu­ ding units which are thought possibly to derive from the Laurentian side of lapetus . D. Roberts. Norges geologiske uruierseketse, Postboks 3006. Lade, N-7002 Trondbeim , Norway . Introduction Project 233 has been to prepare a preliminary Earlier in this decade much of the research terrane map' at 1:5 M scale (Roberts et al. effort in the Caledonides of Scandinavia was 1986) for a larger, circum-Atlantic compilation. channelled through the highly successfu l IGCP This map, much simplified, is really one of Project 27 The Caledonide Orogen ' (Gee & palaeo-environments (marginal basins, vol­ Sturt 1985). An important aspect of the collabo­ canic arc comp lexes, overstep sequences , rative work in this project was that of map etc.), and not of terranes in the true sense.
    [Show full text]
  • Nd Isotope Mapping of the Grenvillian Allochthon Boundary Thrust in Algonquin Park, Ontario
    Canadian Journal of Earth Sciences Nd isotope mapping of the Grenvillian Allochthon Boundary Thrust in Algonquin Park, Ontario Journal: Canadian Journal of Earth Sciences Manuscript ID cjes-2018-0142.R1 Manuscript Type: Article Date Submitted by the 26-Sep-2018 Author: Complete List of Authors: Dickin, Alan; School of Geography and Geology Strong, Jacob; School of Geography and Geology Keyword: Nd isotopes,Draft Model ages, Grenville Province Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? : https://mc06.manuscriptcentral.com/cjes-pubs Page 1 of 34 Canadian Journal of Earth Sciences 1 Nd isotope mapping of the Grenvillian Allochthon Boundary Thrust in Algonquin Park, 2 Ontario 3 4 A.P. Dickin and J.W.D. Strong 5 School of Geography and Earth Sciences, McMaster University, Hamilton ON, Canada 6 7 Abstract 8 Over fifty new Nd isotope analyses are presented for high-grade orthogneisses from 9 Algonquin Park and surrounding region in order to map major Grenvillian thrust boundaries. Nd 10 model ages display a consistent geographical pattern that allows detailed mapping of the 11 boundary between the Algonquin and MuskokaDraft domains, here interpreted as the local trajectory 12 of the Ottawan-age Allochthon Boundary Thrust (ABT). The ABT is underlain by a domain with 13 Paleoproterozoic Nd model ages, interpreted as a tectonic duplex entrained onto the base of the 14 main allochthon. The boundaries determined using Nd isotope mapping are consistent with field 15 mapping and with remotely sensed aeromagnetic and digital elevation data. The precise location 16 of the ABT can be observed in a road-cut on Highway 60, on the north shore of the Lake of Two 17 Rivers in the centre of Algonquin Park.
    [Show full text]
  • New Siberian Islands Archipelago)
    Detrital zircon ages and provenance of the Upper Paleozoic successions of Kotel’ny Island (New Siberian Islands archipelago) Victoria B. Ershova1,*, Andrei V. Prokopiev2, Andrei K. Khudoley1, Nikolay N. Sobolev3, and Eugeny O. Petrov3 1INSTITUTE OF EARTH SCIENCE, ST. PETERSBURG STATE UNIVERSITY, UNIVERSITETSKAYA NAB. 7/9, ST. PETERSBURG 199034, RUSSIA 2DIAMOND AND PRECIOUS METAL GEOLOGY INSTITUTE, SIBERIAN BRANCH, RUSSIAN ACADEMY OF SCIENCES, LENIN PROSPECT 39, YAKUTSK 677980, RUSSIA 3RUSSIAN GEOLOGICAL RESEARCH INSTITUTE (VSEGEI), SREDNIY PROSPECT 74, ST. PETERSBURG 199106, RUSSIA ABSTRACT Plate-tectonic models for the Paleozoic evolution of the Arctic are numerous and diverse. Our detrital zircon provenance study of Upper Paleozoic sandstones from Kotel’ny Island (New Siberian Island archipelago) provides new data on the provenance of clastic sediments and crustal affinity of the New Siberian Islands. Upper Devonian–Lower Carboniferous deposits yield detrital zircon populations that are consistent with the age of magmatic and metamorphic rocks within the Grenvillian-Sveconorwegian, Timanian, and Caledonian orogenic belts, but not with the Siberian craton. The Kolmogorov-Smirnov test reveals a strong similarity between detrital zircon populations within Devonian–Permian clastics of the New Siberian Islands, Wrangel Island (and possibly Chukotka), and the Severnaya Zemlya Archipelago. These results suggest that the New Siberian Islands, along with Wrangel Island and the Severnaya Zemlya Archipelago, were located along the northern margin of Laurentia-Baltica in the Late Devonian–Mississippian and possibly made up a single tectonic block. Detrital zircon populations from the Permian clastics record a dramatic shift to a Uralian provenance. The data and results presented here provide vital information to aid Paleozoic tectonic reconstructions of the Arctic region prior to opening of the Mesozoic oceanic basins.
    [Show full text]
  • Plate Tectonic Regulation of Global Marine Animal Diversity
    Plate tectonic regulation of global marine animal diversity Andrew Zaffosa,1, Seth Finneganb, and Shanan E. Petersa aDepartment of Geoscience, University of Wisconsin–Madison, Madison, WI 53706; and bDepartment of Integrative Biology, University of California, Berkeley, CA 94720 Edited by Neil H. Shubin, The University of Chicago, Chicago, IL, and approved April 13, 2017 (received for review February 13, 2017) Valentine and Moores [Valentine JW, Moores EM (1970) Nature which may be complicated by spatial and temporal inequities in 228:657–659] hypothesized that plate tectonics regulates global the quantity or quality of samples (11–18). Nevertheless, many biodiversity by changing the geographic arrangement of conti- major features in the fossil record of biodiversity are consis- nental crust, but the data required to fully test the hypothesis tently reproducible, although not all have universally accepted were not available. Here, we use a global database of marine explanations. In particular, the reasons for a long Paleozoic animal fossil occurrences and a paleogeographic reconstruction plateau in marine richness and a steady rise in biodiversity dur- model to test the hypothesis that temporal patterns of continen- ing the Late Mesozoic–Cenozoic remain contentious (11, 12, tal fragmentation have impacted global Phanerozoic biodiversity. 14, 19–22). We find a positive correlation between global marine inverte- Here, we explicitly test the plate tectonic regulation hypothesis brate genus richness and an independently derived quantitative articulated by Valentine and Moores (1) by measuring the extent index describing the fragmentation of continental crust during to which the fragmentation of continental crust covaries with supercontinental coalescence–breakup cycles. The observed posi- global genus-level richness among skeletonized marine inverte- tive correlation between global biodiversity and continental frag- brates.
    [Show full text]
  • Technical Report 08-05 Skb-Tr-98-05
    SE9900011 TECHNICAL REPORT 08-05 SKB-TR-98-05 The Very Deep Hole Concept - Geoscientific appraisal of conditions at great depth C Juhlin1, T Wallroth2, J Smellie3, T Eliasson4, C Ljunggren5, B Leijon3, J Beswick6 1 Christopher Juhlin Consulting 2 Bergab Consulting Geologists 3 ConterraAB 4 Geological Survey of Sweden 5 Vattenfall Hydropower AB 6 EDECO Petroleum Services Ltd June 1998 30- 07 SVENSK KARNBRANSLEHANTERING AB SWEDISH NUCLEAR FUEL AND WASTE MANAGEMENT CO P.O.BOX 5864 S-102 40 STOCKHOLM SWEDEN PHONE +46 8 459 84 00 FAX+46 8 661 57 19 THE VERY DEEP HOLE CONCEPT • GEOSCIENTIFIC APPRAISAL OF CONDITIONS AT GREAT DEPTH CJuhlin1, T Wai froth2, J Smeflie3, TEIiasson4, C Ljunggren5, B Leijon3, J Beswick6 1 Christopher Juhlin Consulting 2 Bergab Consulting Geologists 3 Conterra AB 4 Geological Survey of Sweden 5 Vattenfall Hydropower AB 6 EDECO Petroleum Services Ltd. June 1998 This report concerns a study which was conducted for SKB. The conclusions and viewpoints presented in the report are those of the author(s) and do not necessarily coincide with those of the client. Information on SKB technical reports froml 977-1978 (TR 121), 1979 (TR 79-28), 1980 (TR 80-26), 1981 (TR 81-17), 1982 (TR 82-28), 1983 (TR 83-77), 1984 (TR 85-01), 1985 (TR 85-20), 1986 (TR 86-31), 1987 (TR 87-33), 1988 (TR 88-32), 1989 (TR 89-40), 1990 (TR 90-46), 1991 (TR 91-64), 1992 (TR 92-46), 1993 (TR 93-34), 1994 (TR 94-33), 1995 (TR 95-37) and 1996 (TR 96-25) is available through SKB.
    [Show full text]
  • Teixeira Et Al Paleoproterozoic Record.Pdf
    2019 ASGBC 2019 Annual Symposium on Geology of Brazil and China The Paleoproterozoic record of the São Francisco Craton Paleocontinent and Late Paleoproterozoic to Neoproterozoic covers Field Workshop Brazil, 13-25 August, 2019 W. Teixeira (IGc-USP), F. Chemale Jr. (PPGEO- UNISINOS), E. P. Oliveira (IG-UNICAMP) (Organizers) São Paulo, August - 2019 2019 ASGBC 2019 Annual Symposium on Geology of Brazil and China Institutional support: 2019 ASGBC 2019 Annual Symposium on Geology of Brazil and China Field trip 1 – The Mineiro belt and the Quadrilátero Ferrífero, Southern São Francisco Craton by W. Teixeira, E. Oliveira, F. Alkmim, L. Seixas Field workshop 1 Brazil, 13-18 August, 2019 2019 ASGBC 2019 Annual Symposium on Geology of Brazil and China 1. Introduction The field workshop on the Paleoproterozoic record of the São Francisco craton (SFC) has been designed to provide a view on the aspects of the Paleoproterozoic geology with emphasis on the Mineiro belt and the Minas Supergroup in Minas Gerais state, and thus afford the opportunity to discuss outcrop evidence for the issues such as: i) Significance of the Paleoproterozoic orogenic domains of the SFC; ii) Supercontinent assembly in the context of the Columbia Supercontinent; iii) Paleoproterozoic orogenic architecture as a transition between Archean tectonic styles; iv) Differential response of the Paleoproterozoic lithosphere to extensional tectonism. The first part of field trip traverses the Paleoproterozoic orogenic domain of the southern portion of the SFC in Minas Gerais state, emphasizing its most representative rock assemblages, geochronological and geochemical constraints and tectonic features of the Mineiro belt. This part of the field workshop ends in the mining district of the Quadrilátero Ferrífero where it traverses the Minas Supergroup, which corresponds to the foreland domain of the Paleoproterozoic Mineiro belt.
    [Show full text]
  • Tectonic Regimes in the Baltic Shield During the Last 1200 Ma • a Review
    Tectonic regimes in the Baltic Shield during the last 1200 Ma • A review Sven Åke Larsson ' ', Bva-L^na Tuliborq- 1 Department of Geology Chalmers University of Technology/Göteborij U^vjrsivy 2 Terralogica AB November 1993 TECTONIC REGIMES IN THE BALTIC SHIELD DURING THE LAST 1200 Ma - A REVIEW Sven Åke Larsson12, Eva-Lena Tullborg2 1 Department of Geology, Chalmers University of Technology/Göteborg University 2 Terralogica AB November 1993 This report concerns a study which was conducted for SKB. The conclusions and viewpoints presented in the report are those of the author(s) and do not necessarily coincide with those of the client. Information on SKB technical reports from 1977-1978 (TR 121), 1979 (TR 79-28), 1980 (TR 80-26), 1981 (TR 81-17), 1982 (TR 82-28), 1983 (TR 83-77), 1984 (TR 85-01), 1985 (TR 85-20), 1986 (TR 86-31), 1987 (TR 87-33), 1988 (TR 88-32),. 1989 (TR 89-40), 1990 (TR 90-46), 1991 (TR 91-64) and 1992 (TR 92-46) is available through SKB. ) TECTONIC REGIMES IN THE BALTIC SHIELD DURING THE LAST 1200 Ma - A REVIEW by Sven Åke Larson and Eva-Lena Tullborg Department of Geology, Chalmers University of Technology / Göteborg University & Terralogica AB Gråbo, November, 1993 Keywords: Baltic shield, Tectonicregimes. Upper Protero/.oic, Phanerozoic, Mag- matism. Sedimentation. Erosion. Metamorphism, Continental drift. Stress regimes. , ABSTRACT 1 his report is a review about tectonic regimes in the Baltic (Fennoscandian) Shield from the Sveeonorwegian (1.2 Ga ago) to the present. It also covers what is known about palaeostress during this period, which was chosen to include both orogenic and anorogenic events.
    [Show full text]
  • The High Pressure Belt in the Grenville Province: 75 Architecture, Timing, and Exhumation1
    100 867 100 95 95 75 The High Pressure belt in the Grenville Province: 75 architecture, timing, and exhumation1 25 25 Toby Rivers, John Ketchum, Aphrodite Indares, and Andrew Hynes 5 5 0 0 Abstract: We propose that the Grenvillian allochthonous terranes may be grouped into High Pressure (HP) and Low Pressure (LP) belts and examine the HP belt in detail in the western and central Grenville Province. The HP belt is developed in Paleo- and Mesoproterozoic rocks of the pre-Grenvillian Laurentian margin and characterized by Grenvillian eclogite and co-facial HP granulite in mafic rocks. Pressure–temperature (P–T) estimates for eclogite-facies conditions in well-preserved assemblages are about 1800 MPa and 850°C. In the central Grenville Province, HP rocks formed at -1060–1040 Ma and underwent a single stage of unroofing with transport into the upper crust by -1020 Ma, whereas farther west they underwent two stages of unroofing separated by penetrative mid-crustal recrystallization before transport to the upper crust at -1020 Ma. Unroofing processes were comparable in the two areas, involving both thrusting and extensional faulting in an orogen propagating into its foreland by understacking. In detail, thrusting episodes preceded extension in the western Grenville Province, whereas in the central Grenville Province, they were coeval, resulting in unroofing by tectonic extrusion. In the central Grenville Province, the footwall ramp is well preserved, but any former ramp in the western Grenville Province was obliterated by later lower crustal extensional flow. Continuation of the HP belt into the eastern Grenville Province is not established, but likely on geological grounds.
    [Show full text]
  • Crespi, Cooper Boemmels, and Robinson Geology of The
    CRESPI, COOPER BOEMMELS, AND ROBINSON C2-1 GEOLOGY OF THE NORTHERN TACONIC ALLOCHTHON: STRAIN VARIATION IN THRUST SHEETS, BRITTLE FAULTS, AND POSTRIFT DIKE EMPLACEMENT by Jean Crespi, Jennifer Cooper Boemmels, and Jessica Robinson Geosciences, University of Connecticut, Storrs, CT 06269 INTRODUCTION This field trip has three purposes: (1) to present a synthesis of structural and strain data for the Taconic slate belt, which lies in the northern part of the Giddings Brook thrust sheet in the Taconic allochthon, (2) to present an analysis of fault-slip data for postcleavage faults in the region, and (3) to present the results of work on mafic dikes in the Taconic lobe of the New England–Québec igneous province. The stops have been selected to illustrate the along-strike variation in structure and strain, to show representative postcleavage faults, and to include dikes in a variety of orientations. The data presented at the stops cover a region that extends for about 60 km along strike in the Giddings Brook thrust sheet, from Hubbardton, Vermont, in the north to Salem, New York, in the south (Figs. 1 and 2). Emplacement of the Taconic allochthon took place during the Early to Late Ordovician Taconic orogeny. In the northeastern United States, the Taconic orogeny has traditionally been interpreted as resulting from the collision of a west-facing volcanic arc with the eastern margin of Laurentia (Bird and Dewey, 1970; Rowley and Kidd, 1981; Stanley and Ratcliffe, 1985). In this interpretation, emplacement of the Taconic allochthon occurred in a proforeland setting. New geochronological data, however, indicate that the orogeny involved several phases (Karabinos et al., 1998, 2017; Macdonald et al., 2014, 2017).
    [Show full text]
  • GONDWANA I11 Du Toit
    GONDWANA 503 i11 du Toit < Gondwana, Samfrau > ... the really important point is not so much to disprove Wegener’s particular views as to decide from the relevant evidence whether or not continental drift is a genuine variety of earth movement. —Holmes, 1944.1 A geologist who looked for geological evidence to test Wegener’s hypothesis of continental drift was Alexander Logie du Toit (1878-1948). As a field geologist for the Geological Survey of South Africa he became familiar with the regional geology of that country. Curious to see firsthand how well, if at all, the geology either side of the Atlantic matched, he applied for and upon receiving a generous grant from the Carnegie Institution of Washington in 1923 he spent five months in South America familiarizing himself with the geology of Argentina, Paraguay and Brazil. His seminal paper, A Geological Comparison of South America with South Africa, was published in 1927. He wrote, “The concordance between the opposed shores, incidentally pointed out and discussed by others long before Wegener, has consistently been extended by each fresh geological observation until at present the amount of agreement is 5 In his book, Our Wandering Continents nothing short of marvellous.” Persuasive of a former (1937)2 is the statement: “from the proximity of the two continents are the discoverable linkages mid-Palaeozoic onwards the lands must have that “cross from coast to coast, not only directly but crept northwards for thousands of kilometers diagonally as well, and are furthermore of widely different to account for their deduced climatic ages.” In the map to illustrate this tectonic and phasal (lateral vicissitudes.
    [Show full text]