DOCSLIB.ORG

40Ar/39Ar Mineral Dates from Retrogressed Eclogites Within the Baltoscandian Miogeocline: Implications for a Polyphase Caledonian Orogenic Evolution

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
40Ar/39Ar Mineral Dates from Retrogressed Eclogites Within the Baltoscandian Miogeocline: Implications for a Polyphase Caledonian Orogenic Evolution 40Ar/39Ar mineral dates from retrogressed eclogites within the Baltoscandian miogeocline: Implications for a polyphase Caledonian orogenic evolution R. D. DALLMEYER Department of Geology, University of Georgia, Athens, Georgia 30602 D. G. GEE Geological Survey of Sweden, Box 670, S-751 28 Uppsala, Sweden ABSTRACT Late Silurian to Early Devonian transport suggest that this tectonic activity occurred while onto the Baltoscandian Platform. Baltica and Laurentia were separated by a con- Late Proterozcic, rift-fades dolerite dikes siderable expanse of the Iapetus Ocean (Ilruton within Baltoscandian rocks of the Seve INTRODUCTION and Bockelie, 1980). Nappe Complex locally underwent eclogite A comprehensive geochronological program metamorphism during Caledonian orogen- Scandinavian portions of the Caledonian oro- is underway to more fully document the ;xtent esis. Hornblende from retrograde amphibo- gen are represented by a succession of far- and character of the pre-Scandian tectono- lite selvages developed around two eclogite traveled allochthons which were emplaced onto thermal record within the Scandinavian Cal- boudins exposed at Grapesvare, Norrbotten the Baltoscandian Platform during the early to edonides. This report presents new 40Ar/39Ar County, Sweden, record identical 40Ar/39Ar middle Paleozoic (Fig. 1). Medium- and high- data for hornblende in retrograde selvages plateau dates of 491 ± 8 Ma. Phengitic mus- grade Baltoscandian rocks of the Seve Nappe developed from eclogite assemblages within covite from host schists records plateau dates Complex constitute one of the major tectonic Seve rocks. These results bear directly ori both of 447 ± 7 Ma and 436 ± 7 Ma. Coexisting units in central parts of the orogen (Zachrisson, the chronology and nature of pre-Scandian oro- biotite yields plateau dates of 594 ± 10 Ma 1973). Seve structural units separate underlying genesis and also provide controls for understand- and 808 ± 13 Ma. allochthons of lower grade metasedimentary ing the early middle Paleozoic tectonothermal The biotite dates are interpreted to reflect rocks with Baltoscandian affinities from overly- evolution of the Baltoscandian miogeocline. the presence of extraneous argon compo- ing, variably metamorphosed tectonic units with nents. The hornblende and phengitic musco- oceanic and/or island arc affinities. The high- REGIONAL GEOLOGIC SETTING vite ages are interpreted to date times of grade metamorphism recorded within the Seve postmetamorphic cooling through argon re- Nappe Complex has been considered to be of Seve Nappe Complex tention temperatures. Together with previous Middle Silurian (early Scandian) age, and the 40Ar/39Ar mineral ages from Jamtland, result of attempted underthrusting of Laurentia The Seve Nappe Complex is a westward- Sweden, they confirm that a significant pre- by Baltica during elimination of the Iapetus thinning, internally imbricated allochthon which 40 39 Scandian tectonothermal event is recorded Ocean (Gee, 1975). Recent Ar/ Ar dating of is composed of amphibolite facies and higher regionally in allochthonous sequences which hornblende within the Seve Nappe Complex grade rocks (Gee and Zachrisson, 1979). Within originated within the Baltoscandian miogeo- (Dallmeyer and others, 1983, 1985) in western central portions of the orogen (Jamtland and cline. The eclogite assemblages are inter- Jamtland (Fig. 1), however, suggests that, at Vasterbotten Counties of Sweden), tectonic preted to have formed during westerly sub- least locally, Scandian metamorphic tempera- units of high-grade gneissic rocks are structurally duction of distal [tortions of the miogeocline tures did not exceed -500 °C. This indicates underlain and overlain by amphibolite-facies with attendant development of an accretion- that the high-grade Seve assemblages developed schists and amphibolites (Trouw, 1973; 2)wart, ary wedge. The latter was subsequently up- during an earlier tectonothermal event which af- 1974; Williams and Zwart, 1977). Contacts be- lifted and eroded, providing a source for fected outer portions of the Baltoscandian mio- tween these Seve Nappes are generally marked Middle Ordovician through Lower Silurian geocline. The thermal evolution reflected by by development of high-temperature, ductile 40 39 clastic successions which accumulated in both these Ar/ Ar dates suggests that ocean- shear zones (Trouw, 1973; Arnbom, 1980; Sjos- eastern and weste rn basins. These, together directed (westward) subduction was active out- trom, 1983). Both U-Pb zircon and Rb-Sr with previously metamorphosed older por- board of the Baltoscandian margin by the Late whole-rock dating suggest that some portions of tions of the miogeocline, were imbricated, Cambrian. Faunal characteristics of allochthons the gneissic terrane are of middle Proterozoic folded, and variably metamorphosed during structurally above the Seve Nappe Complex age (Reymer, 1979; Claesson, 1982). Figure 1. Simplified terrane map of the Scandinavian Caledonides. Subdivision of the tectonostratigraphy into Autochthon, Parautochthon, and the Lower, Middle, Upper, and Uppermost Allochthons is based on the Tectonostratigraphic Map of the Scandinavian Caledonides in Gee and Sturt (1985). Geological Society of America Bulletin, v. 97, p. 26-34, 4 figs., 2 tables, January 1986. 26 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/97/1/26/3445033/i0016-7606-97-1-26.pdf by guest on 30 September 2021 SCANDINAVIAN CALEDONIDES TERRANE MAP . * \ - ' \ I 01 100 200 "kr-.,' Scale in km NASAFJÄLL AREA (Fig.2) f PERMIAN DEVONIAN (Neoautoch.) LAURENTIAN MIOGEOCLINE (?) (Uppermost Allochthon) Koli Nappes EUGEOCLINAL (upper part of TCDDAMrc Upper Allochthon) Seve Nappes BALTOSCANDIAN (outermost part of miogeocline, lower units of Upper Allochthon) ulnrrnri imt Undifferentiated MIOGEOCLINE- (Middle and Lower Allochthon) PLATFORM Sedimentary Cover BALTOSCANDIAN (Autochthon - Parautochthon) Basement PLATFORM Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/97/1/26/3445033/i0016-7606-97-1-26.pdf by guest on 30 September 2021 28 DALLMEYER AND GEE Underlying Tectonic Units Allochthon has been recognized from southern Ryan and Sturt, 1985). Structurally higher por- of the Baltoscandian Margin Norway to northern Sweden (southern Vaster- tions of the Köli Nappe Complex exposed near botten County). Although similar lithologies Trondheim (Storen Nappe), contain variably Seve rocks teci:onically overlie various struc- overlie Cambrian black shales as far north as fragmented ophiolitic associations (Gale and tural units of the Middle Allochthon (Gee and Akkajaure in Norrbotten County, Sweden Roberts, 1974, Grenne and others, 1980; Fumes Sturt, 1985). The latter is composed mainly of (Fig. 1), there are no direct paleontologic age and others, 1980) which are overlain by Early late Proterozoic metasedimentary rocks which controls. No overlying Upper Ordovician or Ordovician metasedimentary rocks containing are in ductile tectonic contact with variably de- Lower Silurian sedimentary successions have faunas with North American affinities (Bruton formed, middle Proterozoic crystalline basement been recognized within the Lower Allochthon and Bockelie, 1980; Spjeldnaes, 1985). Thus at rocks of Baltic Sh ield affinity (Fig. 1). Metased- north of Jamtland County. In the Finnmark least some protoliths of the Köli Nappe Com- imentary rocks within the Middle Allochthon area of northernmost Norway (Fig. 1), metased- plex may have been derived from eugeoclinal ter- are represented by low-grade, fluviatile sand- imentary successions beneath the Middle Al- ranes more closely related to Laurentia than to stones which are overlain by dolomites, tillites, lochthon only extend into the Tremadoc. On the Baltica. and sandstones of probable Vendian age (Kum- basis of Rb-Sr and K-Ar isotopic age-determina- The highest tectonic units within the Scandi- pulainen, 1980). Locally, Cambrian and early tions, Sturt and others (1975, 1978) suggested navian Caledonides (Uppermost Allochthon; Fig. Middle Ordovician metasediments are present. that deposition along northernmost portions of 1) overlie eugeoclinal rocks of the Köli Nappe These late Proterozoic and early Paleozoic suc- the Baltoscandian miogeocline was interrupted Complex. The structurally high units are domi- cessions have been correlated with sequences in in the Early Ordovician by emplacement of pre- nated by a variety of gneissic rocks together with the structurally underlying Lower Allochthon viously metamorphosed nappes. ^Ar/^Ar min- platformal, metasedimentary cover sequences (Gee, 1975; Kumpulainen and Nystuen, 1985) eral ages from central Jamtland (Dallmeyer and which, at least in part, are thought to represent and are therefore thought to have originated in others, 1985), together with regional strati- components of the Laurentian miogeocline outboard (western) portions of the Baltoscan- graphic relations, support this interpretation and (Stephens and Gee, 1985). dian miogeocline. Higher tectonic units of the indicate that initial emplacement of allochthons Middle Allochthon are intruded by extensive onto the Baltoscandian Platform occurred GEOLOGY OF THE SAMPLE AREA swarms of rift-feicies, tholeiitic, dolerite dikes earlier in Finnmark than in more southerly (Stromberg, 1969; Solyom and others, 1979a) portions of the orogen. Retrogressed eclogites and host, polydeform- which record late Proterozoic radiometric ages ed schists within the Seve Nappe Complex were (Claesson, 1977; Claesson and Roddick,
Load more

Recommended publications
  • Tectonic Features of the Precambrian Belt Basin and Their Influence on Post-Belt Structures
    ... Tectonic Features of the .., Precambrian Belt Basin and Their Influence on Post-Belt Structures GEOLOGICAL SURVEY PROFESSIONAL PAPER 866 · Tectonic Features of the · Precambrian Belt Basin and Their Influence on Post-Belt Structures By JACK E. HARRISON, ALLAN B. GRIGGS, and JOHN D. WELLS GEOLOGICAL SURVEY PROFESSIONAL PAPER X66 U N IT ED STATES G 0 V ERN M EN T P R I NT I N G 0 F F I C E, \VAS H I N G T 0 N 19 7 4 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 74-600111 ) For sale by the Superintendent of Documents, U.S. GO\·ernment Printing Office 'Vashington, D.C. 20402 - Price 65 cents (paper cO\·er) Stock Number 2401-02554 CONTENTS Page Page Abstract................................................. 1 Phanerozoic events-Continued Introduction . 1 Late Mesozoic through early Tertiary-Continued Genesis and filling of the Belt basin . 1 Idaho batholith ................................. 7 Is the Belt basin an aulacogen? . 5 Boulder batholith ............................... 8 Precambrian Z events . 5 Northern Montana disturbed belt ................. 8 Phanerozoic events . 5 Tectonics along the Lewis and Clark line .............. 9 Paleozoic through early Mesozoic . 6 Late Cenozoic block faults ........................... 13 Late Mesozoic through early Tertiary . 6 Conclusions ............................................. 13 Kootenay arc and mobile belt . 6 References cited ......................................... 14 ILLUSTRATIONS Page FIGURES 1-4. Maps: 1. Principal basins of sedimentation along the U.S.-Canadian Cordillera during Precambrian Y time (1,600-800 m.y. ago) ............................................................................................... 2 2. Principal tectonic elements of the Belt basin reentrant as inferred from the sedimentation record ............
    [Show full text]
  • GSA TODAY North-Central, P
    Vol. 9, No. 10 October 1999 INSIDE • 1999 Honorary Fellows, p. 16 • Awards Nominations, p. 18, 20 • 2000 Section Meetings GSA TODAY North-Central, p. 27 A Publication of the Geological Society of America Rocky Mountain, p. 28 Cordilleran, p. 30 Refining Rodinia: Geologic Evidence for the Australia–Western U.S. connection in the Proterozoic Karl E. Karlstrom, [email protected], Stephen S. Harlan*, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 Michael L. Williams, Department of Geosciences, University of Massachusetts, Amherst, MA, 01003-5820, [email protected] James McLelland, Department of Geology, Colgate University, Hamilton, NY 13346, [email protected] John W. Geissman, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, [email protected] Karl-Inge Åhäll, Earth Sciences Centre, Göteborg University, Box 460, SE-405 30 Göteborg, Sweden, [email protected] ABSTRACT BALTICA Prior to the Grenvillian continent- continent collision at about 1.0 Ga, the southern margin of Laurentia was a long-lived convergent margin that SWEAT TRANSSCANDINAVIAN extended from Greenland to southern W. GOTHIAM California. The truncation of these 1.8–1.0 Ga orogenic belts in southwest- ern and northeastern Laurentia suggests KETILIDEAN that they once extended farther. We propose that Australia contains the con- tinuation of these belts to the southwest LABRADORIAN and that Baltica was the continuation to the northeast. The combined orogenic LAURENTIA system was comparable in
    [Show full text]
  • Strain Analysis on the Sub-Lay Dam Unconformity Near
    Alabama Geological Society 2012 Annual Field Trip COMBINED REFERENCES Abrams, C.E., and McConnell, K.I., 1981, Stratigraphy Bieler, D. B., 1993, Correlation of Emuckfaw Group of the area around the Austell-Frolona metagraywackes with the Wedowee Group, antiform, west-central Georgia, in Wigley, Southern Piedmont, Alabama: implications P.B., ed., Latest thinking on the stratigraphy for the interpretation of the Alexander City of selected areas in Georgia; Volume 1: fault, Geological Society of America Georgia Geological Survey Information Abstracts with Programs, v. 25, No. 4, p. 3-4. Circular, no. 54-A, p. 55-67. Bream, B.R., 2003, Tectonic implications of para- and Adams, G. I., 1926, The crystalline rocks, in Adams, ortho gneiss geochronology and G. I., Butts, C., Stephenson, L. W., and geochemistry from the Southern Cooke, C. W., eds., Geology of Alabama: Appalachian crystalline core [Ph.D. thesis]: Alabama Geological Survey Special Report Knoxville, University of Tennessee, 310 p. 14, p. 25-40. Butts, C., 1926, The Paleozoic rocks, in Adams, G.I., Allison, D.T., 1992, Structural evolution and et al., eds., Geology of Alabama: Alabama metamorphic petrogenesis of a Geological Survey Special Report, v. 14, p. metasediment and metaigneous complex, 40-223. Coosa County, Alabama, (Ph.D. Butts, C., 1940, Description of the Montevallo and dissertation): Tallahassee, Florida, Florida Columbiana Quadrangles: U.S. Geological State University, 378 p. Survey Atlas, Folio 226, p. 0–19. Alsop, G.I. and Holdsworth, R.E., Sheath folds as Carter, W.W., 1985, Geology of Cedar and Talladega discriminators of bulk strain type, Journal of Mountains, Clay County, Alabama [M.S.
    [Show full text]
  • Geology-Of-The-Appalachian
    2 3 GEOLOGY OF THE APPALACHIAN-CALEDONIAN OROGEN IN CANADA AND GREENLAND Geological Survey of Canada, Geology of Canada, No. 6 Edited by Harold Williams, 1995 Chapter 1 – Introduction (by Harold Williams) PREAMBLE AND DEFINITION The Canadian Appalachian region includes the provinces of insular Newfoundland, Nova Scotia, New Brunswick, Prince Edward Island, and the southern part of Quebec along the south side of the St. Lawrence River (Fig. 1.1). It has an area of approximately 500000 km2 and it is widest (600 km) at the Canada-United States International Boundary in New Brunswick and Nova Scotia. A larger unexposed area of Appalachian rocks and structures extends across the Gulf of St. Lawrence and seaward to the Atlantic continental edge. Because of its coastal setting and insular makeup, the region offers tremendous shoreline exposures along marine passages. The Appalachian region is a Paleozoic geological mountain belt or orogen. This means that its rocks have been affected by orogeny, the combined effects of folding, faulting, metamorphism, and plutonism. Paleozoic folds and faults of several generations trend northeastward. Regional metamorphic rocks occupy continuous belts in interior parts of the orogen, and granitic batholiths are common throughout its length (Maps 1 and 2). 4 5 The word "Appalachian" was first used in a geographic context for the morphological mountains in the southeast United States. It has displaced the word "Acadian" formerly applied to this region of eastern Canada. In the present context, the word "Appalachian" is used for the geological mountain belt without regard for its morphological expression. Like the Cordilleran and Innuitian orogens, the Appalachian Orogen occupies a position peripheral to the stable interior craton of North America (Fig.
    [Show full text]
  • U.S. DEPARTMENT of the INTERIOR U.S.GEOLOGICAL SURVEY ALK.BIB a Selected Bibliography of Alkaline Igneous Rocks and Related Mine
    U.S. DEPARTMENT OF THE INTERIOR U.S.GEOLOGICAL SURVEY ALK.BIB A selected bibliography of alkaline igneous rocks and related mineral deposits, with an emphasis on western North America compiled by Felix E. Mutschler, D. Chad Johnson, and Thomas C. Mooney Open-File Report 94-624 1994 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. INTRODUCTION This bibliography contains 3,406 references on alkaline igneous rocks and related mineral deposits compiled in conjunction with ongoing studies of alkaline igneous rocks, metallogeny, and tectonics in western North America. Much of the literature on these topics is not readily recovered by searches of current bibliographies and computerized reference systems. We hope that by making this bibliography available, it will help other workers to access this occasionally hard to find literature. The bibliography is available in two formats: (1) paper hardcopy and (2) Apple Macintosh computer-readable 3.5 inch double density diskette. The computer-readable version of the bibliography is a 725 KB WORD (version 5.0) document. Individual literature citations are arranged alphabetically by author(s) and the order of items in each citation follows the standard U.S. Geological Survey format. Version 3.4 1 February 1994 BIBLIOGRAPHY Abbott, J. G., Gordey, S. P., and Tempelman-Kluit, D. J., 1986, Setting of stratiform, sediment- hosted lead-zinc deposits in Yukon and northeastern British Columbia, in Morin, J.
    [Show full text]
  • GSA TODAY North-Central, P
    Vol. 9, No. 10 October 1999 INSIDE • 1999 Honorary Fellows, p. 16 • Awards Nominations, p. 18, 20 • 2000 Section Meetings GSA TODAY North-Central, p. 27 A Publication of the Geological Society of America Rocky Mountain, p. 28 Cordilleran, p. 30 Refining Rodinia: Geologic Evidence for the Australia–Western U.S. connection in the Proterozoic Karl E. Karlstrom, [email protected], Stephen S. Harlan*, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 Michael L. Williams, Department of Geosciences, University of Massachusetts, Amherst, MA, 01003-5820, [email protected] James McLelland, Department of Geology, Colgate University, Hamilton, NY 13346, [email protected] John W. Geissman, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, [email protected] Karl-Inge Åhäll, Earth Sciences Centre, Göteborg University, Box 460, SE-405 30 Göteborg, Sweden, [email protected] ABSTRACT BALTICA Prior to the Grenvillian continent- continent collision at about 1.0 Ga, the southern margin of Laurentia was a long-lived convergent margin that SWEAT TRANSSCANDINAVIAN extended from Greenland to southern W. GOTHIAM California. The truncation of these 1.8–1.0 Ga orogenic belts in southwest- ern and northeastern Laurentia suggests KETILIDEAN that they once extended farther. We propose that Australia contains the con- tinuation of these belts to the southwest LABRADORIAN and that Baltica was the continuation to the northeast. The combined orogenic LAURENTIA system was comparable in
    [Show full text]
  • Stratigraphic Trends in Detrital Zircon Geochronology of Upper
    Stratigraphic trends in detrital zircon geochronology of upper Neoproterozoic and Cambrian strata, Osgood Mountains, Nevada, and elsewhere in the Cordilleran miogeocline: Evidence for early Cambrian uplift of the Transcontinental Arch Gwen M. Linde1, Patricia H. Cashman1, James H. Trexler, Jr.1, and William R. Dickinson2 1Department of Geological Sciences and Engineering, University of Nevada, Reno, Nevada 89557, USA 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721-0077, USA ABSTRACT a funda mental feature of the lower Paleozoic strata that reflect initial rifting (e.g., Poole Laurentian craton. It was fi rst recognized from et al., 1992; Yonkee et al., 2014, and references U-Pb detrital zircon geochronology pro- broad structures and Phanerozoic sedimentation therein). These strata are mostly quartzite, with vides insight into the provenance of the patterns in the mid-continent (Fig. 1) (Keith, some siltstone, argillite, and phyllite; carbon- upper Neoproterozoic–lower Cambrian 1928). Sloss (1963, 1988) noted the deposition ate intervals are present in some locations (e.g., Osgood Mountain Quartzite and the upper of the middle and lowermost upper Cambrian Stewart, 1991; Poole et al., 1992). These units Cambrian–lower Ordovician Preble Forma- Sauk II sequence onlapping from the craton have been correlated across a broad region of tion in the Osgood Mountains of northern margin onto the Transcontinental Arch (Fig. 1). western North America (e.g., Poole et al., 1992). Nevada (USA). We analyzed 535 detrital zir- Carlson (1999) proposed, instead of a discrete Previous detrital zircon studies of upper Neo- con grains from six samples of quartz arenite arch, a platform, a discontinuous zone with proterozoic–lower Paleozoic passive margin by laser ablation–multicollector–inductively highs and lows and fl anking basins that give the strata record similar changes in detrital zircon coupled plasma–mass spectrometry.
    [Show full text]
  • Redalyc.Detrital Zircon Geochronology of Neoproterozoic to Middle Cambrian Miogeoclinal and Platformal Strata: Northwest Sonor
    Geofísica Internacional ISSN: 0016-7169 [email protected] Universidad Nacional Autónoma de México México Gross, Essa L.; Stewart, John H.; Gehrels, George E. Detrital zircon geochronology of Neoproterozoic to Middle Cambrian miogeoclinal and platformal strata: Northwest Sonora, Mexico Geofísica Internacional, vol. 39, núm. 4, october-december, 2000, pp. 295-308 Universidad Nacional Autónoma de México Distrito Federal, México Available in: http://www.redalyc.org/articulo.oa?id=56839401 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Geofísica Internacional (2000), Vol. 39, Num. 4, pp. 295-308 Detrital zircon geochronology of Neoproterozoic to Middle Cambrian miogeoclinal and platformal strata: Northwest Sonora, Mexico Essa L. Gross1, John H. Stewart2 and George E. Gehrels3 1 Department of Geosciences, University of Arizona, Tucson, Arizona, USA 2 United States Geological Survey, Menlo Park, California, USA 3 Department of Geosciences, University of Arizona, Tucson, Arizona, USA Received: May 28, 1999; accepted: May 09, 2000. RESUMEN Ochenta y cinco circones detritales provenientes de estratos sedimentarios del Mesoproterozoico y/o Neoproterozoico al Cámbrico Medio del noroeste de Sonora, México, han sido analizados para determinar los terrenos fuente y delimitar las edades de deposición de las unidades. Los conjuntos de circones de la Formación El Alamo y la unidad El Aguila del Mesoproterozoico y/o Neoproterozoico tienen edades entre 1.06 Ga y 2.67 Ga, con predominio de edades de 1.1 a 1.2 Ga.
    [Show full text]
  • Proterozoic Multistage (Ca. 1.1 and 0.8 Ga) Extension Recorded in The
    Proterozoic multistage (ca. 1.1 and 0.8 Ga) extension recorded in the Grand Canyon Supergroup and establishment of northwest- and north-trending tectonic grains in the southwestern United States J. Michael Timmons* Karl E. Karlstrom Carol M. Dehler John W. Geissman Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA Matthew T. Heizler New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801, USA ABSTRACT tures and ca. 800±700 Ma north-trending cord of intracratonic extensional tectonism extensional structures created regional and sedimentation inboard of the plate mar- The Grand Canyon Supergroup records fault networks that were tectonically in- gins. We recognize at least two discrete epi- at least two distinct periods of intracratonic verted during formation of the Ancestral sodes of Proterozoic extension in Grand Can- extension and sedimentation in the late Me- Rocky Mountains and Laramide contrac- yon, one at ca. 1100±900 Ma and another at soproterozoic and Neoproterozoic. New tion and reactivated during Tertiary 800±700 Ma. Two different structural trends 40Ar/39Ar age determinations indicate that extension. were associated with these two episodes of ex- the Mesoproterozoic Unkar Group was de- tension: northwest-striking faults are associ- posited between ca. 1.2 and 1.1 Ga. Basins Keywords: Chuar Group, Grand Canyon, ated with deposition and tilting of the Unkar in which the Unkar Group was deposited growth faults, intracratonic basins, Neopro- Group and north-striking faults were active and the related northwest-striking faults terozoic, Proterozoic rifting. during deposition of the Chuar Group (Fig.
    [Show full text]
  • Dickinson2004.Pdf
    7 Apr 2004 20:19 AR AR211-EA32-02.tex AR211-EA32-02.sgm LaTeX2e(2002/01/18) P1: GCE 10.1146/annurev.earth.32.101802.120257 Annu. Rev. Earth Planet. Sci. 2004. 32:13–45 doi: 10.1146/annurev.earth.32.101802.120257 Copyright c 2004 by Annual Reviews. All rights reserved First published online as a Review in Advance on November 10, 2003 EVOLUTION OF THE NORTH AMERICAN CORDILLERA William R. Dickinson Department of Geosciences, University of Arizona, Tucson, Arizona 85721; email: [email protected] Key Words continental margin, crustal genesis, geologic history, orogen, tectonics ■ Abstract The Cordilleran orogen of western North America is a segment of the Circum-Pacific orogenic belt where subduction of oceanic lithosphere has been under- way along a great circle of the globe since breakup of the supercontinent Pangea began in Triassic time. Early stages of Cordilleran evolution involved Neoproterozoic rifting of the supercontinent Rodinia to trigger miogeoclinal sedimentation along a passive continental margin until Late Devonian time, and overthrusting of oceanic allochthons across the miogeoclinal belt from Late Devonian to Early Triassic time. Subsequent evolution of the Cordilleran arc-trench system was punctuated by tectonic accretion of intraoceanic island arcs that further expanded the Cordilleran continental margin during mid-Mesozoic time, and later produced a Cretaceous batholith belt along the Cordilleran trend. Cenozoic interaction with intra-Pacific seafloor spreading systems fostered transform faulting along the Cordilleran continental margin and promoted incipient rupture of continental crust within the adjacent continental block. INTRODUCTION Geologic analysis of the Cordilleran orogen, forming the western mountain system of North America, raises the following questions: 1.
    [Show full text]
  • Early Mississippian Ocean Anoxia Triggering
    University of New Mexico UNM Digital Repository Earth and Planetary Sciences ETDs Electronic Theses and Dissertations Summer 7-10-2019 Early Mississippian ocean anoxia triggering organic carbon burial and enhancing Late Paleozoic Ice Age onset: evidence from uranium isotopes of marine limestones Keyi Cheng Earth and Planetary Sciences Follow this and additional works at: https://digitalrepository.unm.edu/eps_etds Part of the Geology Commons Recommended Citation Cheng, Keyi. "Early Mississippian ocean anoxia triggering organic carbon burial and enhancing Late Paleozoic Ice Age onset: evidence from uranium isotopes of marine limestones." (2019). https://digitalrepository.unm.edu/eps_etds/261 This Thesis is brought to you for free and open access by the Electronic Theses and Dissertations at UNM Digital Repository. It has been accepted for inclusion in Earth and Planetary Sciences ETDs by an authorized administrator of UNM Digital Repository. For more information, please contact [email protected]. Keyi Cheng Candidate Earth and Planetary Sciences Department This thesis is approved, and it is acceptable in quality and form for publication: Approved by the Thesis Committee: Dr. Maya Elrick, Earth and Planetary Sciences, Chairperson Dr. Stephen Romaniello, Arizona State University Dr. Peter Fawcett, Earth and Planetary Sciences i EARLY MISSISSIPPIAN OCEAN ANOXIA TRIGGERING ORGANIC CARBON BURIAL AND ENHANCING LATE PALEOZOIC ICE AGE ONSET: EVIDENCE FROM URANIUM ISOTOPES OF MARINE LIMESTONES by KEYI CHENG BACHELOR OF SCIENCE, GEOCHEMISTRY CHINA UNIVERSITY OF GEOSCIENCES (WUHAN), 2016 THESIS Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science Earth and Planetary Sciences The University of New Mexico Albuquerque, New Mexico July, 2019 ii ACKNOWLEDGMENTS I sincerely acknowledge my advisor and dissertation chair, Dr.
    [Show full text]
  • Construction of Tectonic Subsidence Curves for The
    Construction of tectonic subsidence curves for the early Paleozoic miogeocline, southern Canadian Rocky Mountains: Implications for subsidence mechanisms, age of breakup, and crustal thinning GERARD C. BOND Lamont-Doherty Geological Observatory of Columbia University, Palisades, New York 10964 MICHELLE A. KOMINZ ABSTRACT interpreted by Stewart (1971, 1972) and by sections in the thrust and fold belt of the south- Burchfiel and Davis (1972) as evidence that a ern Canadian Rockies, where the strata are ex- A quantitative procedure has been developed passive continental margin was initiated at some ceptionally well exposed and good stratigraphic for calculating tectonic subsidence in fully lithi- time in the late Precambrian along the western and structural controls have been established. fied strata and has been applied to stratigraphic edge of the North American craton. This inter- The results of the analysis are compared with sections in the early Paleozoic miogeocline of pretation was based on a comparison of the thermal-mechanical models of passive margins the southern Canadian Rocky Mountains. The geology of the miogeocline with the generalized to identify the mechanisms that controlled the results indicate that tectonic subsidence along and largely descriptive models of passive mar- subsidence and to obtain a new estimate for the inner edge of the miogeocline was controlled gins that were available at the time. the age of continental breakup and initiation of mainly by thermal contraction of heated litho- In recent years, new quantitative methods and the passive margin in the southern Canadian sphere. Comparison of a palinspastically restored geophysical models have been developed for Rockies cross section of the inner part of the miogeocline analyzing the evolution of modern passive mar- with a cross section constructed from a two- gins (Keen, 1982; Watts, 1981).
    [Show full text]