Wyoming on the Run—Toward Final Paleoproterozoic Assembly of Laurentia

Total Page:16

File Type:pdf, Size:1020Kb

Wyoming on the Run—Toward Final Paleoproterozoic Assembly of Laurentia Wyoming on the run—Toward final Paleoproterozoic assembly of Laurentia Taylor M. Kilian1*, Kevin R. Chamberlain2, David A.D. Evans1, Wouter Bleeker3, and Brian L. Cousens4 1Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, Connecticut 06511, USA 2Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071-3006, USA 3Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada 4Ottawa-Carleton Geoscience Centre, Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada ABSTRACT investigate their positions at a crucial time inter- Paleoproterozoic suture zones mark the formation of supercontinent Nuna and provide val, providing initial conditions for the subse- a record of North America’s assembly. Conspicuously young ages (ca. 1.715 Ga) associated quent series of collisions that stitched Laurentia with deformation in southeast Wyoming craton argue for a more protracted consolidation of together. Coupled to existing geochronologic Laurentia, long after peak metamorphism in the Trans-Hudson orogen. Using paleomagnetic constraints on suturing along Wyoming’s mar- data from the newly dated 1899 ± 5 Ma Sourdough mafic dike swarm (Wyoming craton), we gins, we present a novel kinematic model for the compare the relative positions of Wyoming, Superior, and Slave cratons before, during, and late stages of assembly of Laurentia. after peak metamorphism in the Trans-Hudson orogen. With these constraints, we refine a collisional model for Laurentia that incorporates Wyoming craton after Superior and Slave COLLISIONAL CONSTRAINTS cratons united, redefining the Paleoproterozoic sutures that bind southern Laurentia. The best exposures of Wyoming’s Paleopro- terozoic suture zones are found along the south- INTRODUCTION becoming a late addition to Laurentia (Chamber- eastern and northern margins of the craton. In Paleoproterozoic amalgamation of Lauren- lain et al., 2002; Dahl et al., 1999)? the south, the Medicine Bow orogeny and the tia’s Archean cratons likely involved closure of We present a precisely dated primary paleo- Cheyenne belt are well defined by metamorphic expansive oceans (Hoffman, 1988) born from magnetic pole for the ca. 1.899 Ga Sourdough and deformational pulses from 1.78 to 1.74 Ga fragmentation of Neoarchean supercratonic land- dikes, which represent a newly recognized (Chamberlain, 1998; Houston et al., 1989; Jones masses (Bleeker, 2003). One ancestral connec- swarm and a significant addition to the mafic et al., 2010) and have been interpreted to doc- tion, between Superior and Wyoming cratons, magmatic record of Wyoming craton. By com- ument accretion of the Yavapai arc terrane to is compatible with both stratigraphic (Roscoe paring this new paleomagnetic datum with Wyoming craton (Condie, 1992). The best age and Card, 1993) and paleomagnetic (Kilian et coeval data from Superior and Slave cratons, we constraints for sutures along Wyoming’s eastern al., 2015) records from both blocks, while their 2.1–2.0 Ga mafic dike swarms (Bowers and Figure 1. Geologic map Trans-Hudson Precambrian exposures Chamberlain, 2006; Cox et al., 2000; Mueller of Precambrian basement Orogen (THO) near Wyoming 110ºW (1.92-1.78 Ga) Sourdough dikes from central Laurentia with Inferred faults and lineaments et al., 2005) document their rifting and breakup. Taltson(2.0-1.9 Orogen Ga) Archean cratons (green) (Sims and Peterman, 1986) This breakup initiated a brief period of indepen- 52ºN Hearne Craton Inferred aeromag. lineaments and orogens labeled and (2.7-1.8 Ga) (Bankey et al., 2002) dent movement of Wyoming craton prior to its colored according to rock Cheyenne belt mag 1.740-1.715 Ga shortening dir- aero g. incorporation into Laurentia. Because the dates age. Dark gray area rep- an lo ections (Allard and Portis, 2013) lc w u of sutures surrounding Wyoming craton sug- resents 1.715 Ga suture (>2.6 Ga) V Lake Clearwater Superior discussed in this study. Medicine HatSGH gest multiple episodes of deformation, meta- B (3.3-2.8 Ga) s Superior lo LSC—Little Sand Creek ck Craton morphism, and arc collisions after development Great Fall LSC ctonicFTZ) zone (>2.5 Ga) xenoliths (Barnhart et te (G LBM n of the Trans-Hudson orogen (THO), especially Black Hills/ e al., 2012; Bolhar et al., g Big Sky Dakotan Orogens ro along the northwestern and eastern margins, 2007); SGH—Sweet Grass Orogen BT 1.715 Ga) O (1.8-1.76/ t f Highland i Hills xenoliths (Davis et R there is some question of when Wyoming craton Mtns. Black BGH t Tobacco Hills n n al., 1995); LBM—Little a e joined Laurentia and which pieces were contigu- Root Mtns. e n k i o t Belt Mountains; BT— Hartville n n Central Plai e o ous with Wyoming craton prior to its docking LM Uplift P Beartooth Mountains; Grouse -C Creek Wyoming Craton Orogen id (Fig. 1). Was Wyoming craton fused to the Medi- (1.8 ns M BGH—Bighorn Mountains; (>2.5 Ga) (>2.5 Ga) -1.7 cine Hat block (MHB) long before collision with LM—Laramie Mountains; Ga) Hearne craton (Boerner et al., 1998)? Was Wyo- aeromag.—aeromagen- ) ? tic. The Mid-Continent Yavapai ming craton connected with both the MHB and Mojave Rift System (ca. 1.1 Ga) is (2.0-1.7 Ga) (1.8-1.7 Ga Hearne craton before collision with Superior cra- stippled. Magnetic anoma- ton in the THO (Eglington et al., 2013)? Or was lies between Superior, Wyoming, and Hearne cratons may represent small crustal fragments Wyoming craton on its own (or with the MHB) (e.g., Sask) of Archean to early Proterozoic crust that were sutured into Trans-Hudson orogen during development of the THO, subsequently (THO) and Black Hills–Dakotan orogens. It is uncertain how far south THO extended and which fragments were connected before Wyoming craton arrived. Archean basement ages from drill cores in northeastern Wyoming and southeastern Montana (USA) likely derive from fragments within Dakotan orogen (Peterman, 1981). Boundaries of Great Falls tectonic zone are estimated *E-mail: [email protected] from Ross (2002). Other margins modified after Foster et al. (2006) and Worthington et al. (2016). GEOLOGY, October 2016; v. 44; no. 10; p. 863–866 | Data Repository item 2016283 | doi:10.1130/G38042.1 | Published online 31 August 2016 GEOLOGY© 2016 Geological | Volume Society 44 | ofNumber America. 10 For | www.gsapubs.orgpermission to copy, contact [email protected]. 863 margin come from syn-deformational pegma- emplacement of numerous mafic dike swarms. trace elements (Fig. 2). The slopes of the rare tites in northwest-vergent thrusts of the Hartville Most of these are older than 2.0 Ga (Kilian et earth element (REE) patterns for all samples (Fig. uplift directly dated at 1714 ± 2 Ma (U-Pb zir- al., 2015), but herein we document one younger 2C and 2D) are consistent, with only minor varia- con; Krugh, 1997) and late deformational fabrics swarm. We name this the Sourdough swarm and tion among mostly the light REEs. Collectively, superimposed on Cheyenne belt metamorphism present its paleomagnetic, trace element geo- the data suggest that all dikes represent the same in the eastern Laramie Mountains (Wyoming) at chemistry, and U-Pb age results. magmatic event, with minor geochemical dif- 1722 ± 6 Ma (207Pb/206Pb titanite; Allard, 2003). Field and laboratory methods are described in ferences being the product of interactions with The Black Hills region (South Dakota and the GSA Data Repository1. The Sourdough dikes different crustal rocks. Wyoming) experienced WSW-ENE shortening crop out in the central Bighorn and Beartooth All analyses of baddeleyite (U-Pb isotope (1.770–1.740 Ga; Allard and Portis, 2013; Dahl uplifts where Laramide tilting is negligible. Most dilution thermal ionization mass spectrometry et al., 1999), WNW-ESE compression (1.740– dikes have subophitic texture, dominated by pla- [ID-TIMS]) from dike BH10 are within 1.7% of 1.715 Ga; Allard and Portis, 2013; Dahl et al., gioclase, pyroxene, and magnetite (with minor the concordia curve (N = 3); one analysis is con- 2005), and thrust-related shear heating that pro- sericite), and typically have northwest-southeast cordant (Fig. 2B; see also the Data Repository). duced the Harney Peak granite (Dahl et al., 1999; trends (335°–290°) and widths ranging from A linear regression of the data yields an upper Nabelek and Liu, 1999) at 1.715 Ga (Redden et 0.3 m to ~30 m. The vast majority of samples intercept date of 1896 ± 3 Ma, with a weighted- al., 1990). This tectonic history contrasts greatly contain a single-component remanence held by mean 207Pb/206Pb date of 1899 ± 5 Ma. As the 2s with the timing of peak metamorphic conditions (titano)magnetite. Principal component analysis confidence intervals of each calculation method (ca. 1.81 Ga) for various locations of the THO (Fig. 2A) yielded notably steep northeast-down essentially overlap, we favor the more conserva- (Ansdell et al., 2005). (or southwest-up) directions that are confirmed tive weighted-mean 207Pb/206Pb date as the age On the northern margin of Wyoming cra- to record primary thermal remanence from the estimate for BH10, 1899 ± 5 Ma. This age is ton is the Great Falls tectonic zone (GFTZ), a time of initial cooling by two positive baked- applied to the primary magnetization of the Sour- broadly defined and poorly exposed orogenic contact tests into older mafic dikes (see the Data dough swarm; dike BH10 yielded typical paleo- belt that connects the MHB to Wyoming craton Repository). Geochemical analysis of 15 Sour- magnetic and geochemical results for the swarm. (Fig. 1; Boerner et al., 1998). The Little Belt dough dikes yielded similar concentrations of Mountains (Montana) host magmatic and defor- WYOMING’S RUN mational ages of ca. 1.87–1.86 Ga (Mueller et Incorporating the tectonic synthesis and new 1 GSA Data Repository item 2016283, supplemen- al., 2002), which are also prevalent in the Clear- tary text, nine figures, five tables, and references, is Sourdough swarm data presented above, we pro- water block in northern Idaho (Vervoort et al., available online at www.geosociety.org /pubs /ft2016 pose a novel hypothesis for the path of Wyo- 2016).
Recommended publications
  • Strike and Dip Refer to the Orientation Or Attitude of a Geologic Feature. The
    Name__________________________________ 89.325 – Geology for Engineers Faults, Folds, Outcrop Patterns and Geologic Maps I. Properties of Earth Materials When rocks are subjected to differential stress the resulting build-up in strain can cause deformation. Depending on the material properties the result can either be elastic deformation which can ultimately lead to the breaking of the rock material (faults) or ductile deformation which can lead to the development of folds. In this exercise we will look at the various types of deformation and how geologists use geologic maps to understand this deformation. II. Strike and Dip Strike and dip refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature, is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented parallel to the strike line. Strike (or strike angle) can be given as either a quadrant compass bearing of the strike line (N25°E for example) or in terms of east or west of true north or south, a single three digit number representing the azimuth, where the lower number is usually given (where the example of N25°E would simply be 025), or the azimuth number followed by the degree sign (example of N25°E would be 025°). The dip gives the steepest angle of descent of a tilted bed or feature relative to a horizontal plane, and is given by the number (0°-90°) as well as a letter (N, S, E, W) with rough direction in which the bed is dipping.
    [Show full text]
  • Taxonomic Overview of the Greater Fritillary Genus Speyeria Scudder
    INSECTA MUNDI A Journal of World Insect Systematics 0090 Taxonomic overview of the greater fritillary genus Speyeria Scudder and the atlantis hesperis species complexes, with species accounts, type images, and relevant literature (Lepidoptera: Nymphalidae) James C. Dunford McGuire Center for Lepidoptera and Biodiversity Florida Museum of Natural History, University of Florida PO Box 112710, Gainesville, FL 326112710, USA Date of Issue: September 26, 2009 CENTER FOR SYSTEMATIC ENTOMOLOGY, INC., Gainesville, FL James C. Dunford Taxonomic overview of the greater fritillary genus Speyeria Scudder and the atlantis hesperis species complexes, with species accounts, type images, and relevant literature (Lepidoptera: Nymphalidae) Insecta Mundi 0090: 174 Published in 2009 by Center for Systematic Entomology, Inc. P. O. Box 141874 Gainesville, FL 326141874 U. S. A. http://www.centerforsystematicentomology.org/ Insecta Mundi is a journal primarily devoted to insect systematics, but articles can be published on any nonmarine arthropod taxon. Manuscripts considered for publication include, but are not limited to, systematic or taxonomic studies, revisions, nomenclatural changes, faunal studies, book reviews, phylo genetic analyses, biological or behavioral studies, etc. Insecta Mundi is widely distributed, and refer- enced or abstracted by several sources including the Zoological Record, CAB Abstracts, etc. As of 2007, Insecta Mundi is published irregularly throughout the year, not as quarterly issues. As manuscripts are completed they are published and given an individual number. Manuscripts must be peer reviewed prior to submission, after which they are again reviewed by the editorial board to insure quality. One author of each submitted manuscript must be a current member of the Center for System- atic Entomology.
    [Show full text]
  • GEOL360 Structural Geology Problem Set #3: Apparent Dip, Angles And
    GEOL360 Structural Geology Name______________________ Date_______________________ Problem Set #3: Apparent Dip, Angles and Orientations Part 1. Apparent dip 1. In a mine, a tabular dike has an apparent dip of 14°, 270° in one tunnel and 25°, 169° in another tunnel (here we use azimuth directions). Using a stereonet, what is the attitude (strike and dip) of the dike? _____________________ 1. Along a vertical railroad cut a bed has an apparent dip of 20°, N62°W. The bed strikes N67°E. What is the true dip? _____________________ 1. Suppose a fault strikes N10°E and its apparent dip trends S26°E and plunges 35°. Using a stereonet, determine the true dip of the fault. _____________________ Part II. Angle between two lines 1. What is the angle between the following two lines? a. 35°, S10°E a. 15°, N23°W _____________________ 1. What is the angle between the following two lines? a. 12°, N8°E a. 40°, S19°W _____________________ 1. What is the angle between the following two lines? a. 70°, S38°E a. 49°, N15°E _____________________ Part III. Angle between two planes 1. What is the angle between the following two planes? a. N27°E, 85°SE a. N89°W, 7°NE _____________________ 2. What is the angle between the following two planes? a. 315°, 20°NE a. 165°, 24°SW _____________________ 3. What is the angle between the following two planes? a. 014°, 10°SE a. N18°W, 37°NE _____________________ Part IV. Orientation of the intersection of two planes: 1. Determine the orientation of the intersection of the following two planes: a.
    [Show full text]
  • 5-Year Review Short Form Summary
    5-Year Review Short Form Summary Species Reviewed: Preble’s meadow jumping mouse (Zapus hudsonius preblei) FR Notice Announcing Initiation of This Review: March 31, 2004. 90-Day Finding for a Petition to Delist the Preble’s Meadow Jumping Mouse in Colorado and Wyoming and Initiation of a 5-Year Review (69 FR 16944-16946). Lead Region/Field Office: Region 6, Seth Willey, Recovery Coordinator, 303-236-4257. Colorado Field Office, Susan Linner, Field Supervisor, 303-236-4773. Name of Reviewer: Peter Plage, Colorado Field Office, 303-236-4750. Cooperating Field Office: Wyoming Field Office, Brian Kelly, Field Supervisor, 307-772-2374. Current Classification: Threatened rangewide. Current Recovery Priority Number: 9c. This recovery priority number is indicative of a subspecies facing a moderate degree of threat, a high recovery potential, and whose recovery may be in conflict with construction or other development projects or other forms of economic activity. Methodology used to complete the review: The 5-year review for the Preble’s meadow jumping mouse (Preble’s) was accomplished through the petition and rulemaking process. On December 23, 2003, we received two nearly identical petitions from the State of Wyoming’s Office of the Governor and from Coloradans for Water Conservation and Development, seeking to remove the Preble’s from the Federal List of Endangered and Threatened Wildlife. Both petitions were similar and maintained that the Preble’s should be delisted based on the taxonomic revision, and based on new distribution, abundance, and trends data that suggested the Preble’s was no longer threatened. On March 31, 2004, we published a notice announcing a 90-day finding that the petitions presented substantial information indicating that the petitioned action may be warranted and initiated a 5-year review (69 FR 16944-16946).
    [Show full text]
  • Denudation History and Internal Structure of the Front Range and Wet Mountains, Colorado, Based on Apatite-Fission-Track Thermoc
    NEW MEXICO BUREAU OF GEOLOGY & MINERAL RESOURCES, BULLETIN 160, 2004 41 Denudation history and internal structure of the Front Range and Wet Mountains, Colorado, based on apatite­fission­track thermochronology 1 2 1Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM 87801Shari A. Kelley and Charles E. Chapin 2New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, NM 87801 Abstract An apatite fission­track (AFT) partial annealing zone (PAZ) that developed during Late Cretaceous time provides a structural datum for addressing questions concerning the timing and magnitude of denudation, as well as the structural style of Laramide deformation, in the Front Range and Wet Mountains of Colorado. AFT cooling ages are also used to estimate the magnitude and sense of dis­ placement across faults and to differentiate between exhumation and fault­generated topography. AFT ages at low elevationX along the eastern margin of the southern Front Range between Golden and Colorado Springs are from 100 to 270 Ma, and the mean track lengths are short (10–12.5 µm). Old AFT ages (> 100 Ma) are also found along the western margin of the Front Range along the Elkhorn thrust fault. In contrast AFT ages of 45–75 Ma and relatively long mean track lengths (12.5–14 µm) are common in the interior of the range. The AFT ages generally decrease across northwest­trending faults toward the center of the range. The base of a fossil PAZ, which separates AFT cooling ages of 45– 70 Ma at low elevations from AFT ages > 100 Ma at higher elevations, is exposed on the south side of Pikes Peak, on Mt.
    [Show full text]
  • GY 112 Lecture Notes D
    GY 112 Lecture Notes D. Haywick (2006) 1 GY 112 Lecture Notes Archean Geology Lecture Goals: A) Time frame (the Archean and earlier) B) Rocks and tectonic elements (shield/platform/craton) C) Tectonics and paleogeography Textbook reference: Levin 7th edition (2003), Chapter 6; Levin 8th edition (2006), Chapter 8 A) Time frame Up until comparatively recently (start of the 20th century), most geologists focused their discussion of geological time on two eons; the “Precambrian” and the Phanerozoic. We now officially recognize 4 eons and the Precambrian is just used as a come-all term for all time before the Phanerozoic: Eon Time Phanerozoic 550 MA to 0 MA Proterozoic 2.5 GA to 550 MA Archean 3.96 GA to 2.5 GA Hadean 4.6 GA to 3.96 GA The “youngest” of these two new eons, the Archean, was first introduced by field geologists working in areas where very old rocks cropped out. One of these geologists was Sir William Logan (pictured at left; ess.nrcan.gc.ca ) one of the most respected geologists working with the Geological Survey of Canada. His study area was the Canadian Shield. Logan was able to identify two major types of rocks; 1) layered sedimentary and volcanic rocks and 2) highly metamorphosed granitic gneisses (see image at the top of the next page from http://www.trailcanada.com/images/canadian-shield.jpg). Logan found evidence that the gneisses mostly underlayed the layered rocks and hence, they had to be older than the layered rocks. The layered rocks were known to be Proterozoic in age.
    [Show full text]
  • Dike Orientations, Faultblock Rotations, and the Construction of Slow
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL 103, NO. B1, PAGES 663-676, JANUARY 10, 1998 Dike orientations, fault-block rotations, and the constructionof slow spreading oceaniccrust at 22 ø40'N on the Mid-Atlantic Ridge R6isfn M. Lawrence and Jeffrey A. Karson Divisionof Earthand Ocean Sciences, Duke University,Durham, North Carolina StephenD. Hurst DepartmentofGeology, The University ofIllinois, Urbana, Illinois Abstract. The firstpalcomagnetic results from oriented dike samples collected on the Mid- AtlanticRidge shed new light on thecomplex interplay between magmatic accretion and mechanicalextension at a slowspreading ridge segment. An uppercrustal section about 1.5 km thickis exposed along a west-dippingnormal fault zone that defines the eastern median valley wall of thesouthern segment of theMid-Atlantic Ridge south of theKane fracture zone (MARK area). Twodistinct groups of dikesare differentiated onthe basis of orientationand palcomagnetic characteristics.One group, on the basis of thepalcomagnetic data, appears to bein itsoriginal intrusionorientation. This group includes both ridge-parallel, vertical dikes as well as dikes in otherorientations, calling into question assumptions about uniform dike orientations at oceanic spreadingcenters. The second group consists ofdikes that have palcomagnetic directions that are distinctfrom the predicted dipole direction, and we interpret them to have been tectonically rotated. Thesealso occur in manyorientations. The spatial relations between rotated and nonrotated dikes indicatethat intrusion, faulting, and block rotation were contemporaneous beneath the median valleyfloor. Nonrotated dikes exposed onthe eastern median valley wall indicate that there has beenno net rotation of thisupper crustal assemblage since magmatic construction ceased. Hence slipand associated uplift probably occurred inthe fault zones' present orientation. These results providethe basis for a generalmodel of mechanical extension anddike intrusion forthis segment ofthe Mid-Atlantic Ridge.
    [Show full text]
  • Northwestern Superior Craton Margin, Manitoba: an Overview of Archean
    GS-7 Northwestern Superior craton margin, Manitoba: an overview of Archean and Proterozoic episodes of crustal growth, erosion and orogenesis (parts of NTS 54D and 64A) by R.P. Hartlaub1, C.O. Böhm, L.M. Heaman2, and A. Simonetti2 Hartlaub, R.P., Böhm, C.O., Heaman, L.M. and Simonetti, A. 2005: Northwestern Superior craton margin, Manitoba: an overview of Archean and Proterozoic episodes of crustal growth, erosion, and orogenesis (parts of NTS 54D and 64A); in Report of Activities 2005, Manitoba Industry, Economic Development and Mines, Manitoba Geological Survey, p. 54–60. Summary xenocrystic zircon, and in the The northwestern margin of the Superior Province in isotopic signature of Neoarchean Manitoba represents a dynamic boundary zone with good granite bodies (Böhm et al., 2000; potential for magmatic, sedimentary-hosted, and structur- Hartlaub et al., in press). The ALCC extends along the ally controlled mineral deposits. The region has a history Superior margin for at least 50 km, and may have a com- that commences in the early Archean with the formation mon history with other early Archean crustal fragments of the Assean Lake Crustal Complex. This fragment of in northern Quebec and Greenland (Hartlaub et al., in early to middle Archean crust was likely accreted to the press). Superior Province between 2.7 and 2.6 Ga, a major period South of the ALCC, the Split Lake Block repre- of Superior Province amalgamation. Sediments derived sents a variably retrogressed and shear zone–bounded from this amalgamation process were deposited at granulite terrain that is dominated by plutonic rocks and numerous locations along the northwestern margin of mafic granulite (Hartlaub et al., 2003, 2004).
    [Show full text]
  • Magma Genesis and Arc Evolution at the Indochina Terrane Subduction
    feart-08-00271 July 13, 2020 Time: 10:29 # 1 ORIGINAL RESEARCH published: 14 July 2020 doi: 10.3389/feart.2020.00271 Magma Genesis and Arc Evolution at the Indochina Terrane Subduction: Petrological and Geochemical Constraints From the Volcanic Rocks in Wang Nam Khiao Area, Nakhon Ratchasima, Thailand Vanachawan Hunyek, Chakkaphan Sutthirat and Alongkot Fanka* Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok, Thailand Volcanic rocks and associated dikes have been exposed in Wang Nam Khiao area, Nakhon Ratchasima Province, northeastern Thailand where complex tectonic setting was reported. These volcanic rocks are classified as rhyolite, dacite, and andesite whereas dikes are also characterized by andesitic composition. These dikes clearly Edited by: cut into the volcanic rocks and Late Permian hornblende granite in the adjacent area. Basilios Tsikouras, Universiti Brunei Darussalam, Brunei Rhyolite and dacite are composed of abundant plagioclase and quartz whereas andesite Reviewed by: and andesitic dike contain mainly plagioclase and hornblende with minor quartz. The Toshiaki Tsunogae, volcanic rocks typically show plagioclase and hornblende phenocrysts embedded in University of Tsukuba, Japan fine-grained quartz and glass groundmass whereas dike rocks contain less glass matrix Gianluca Vignaroli, University of Bologna, Italy with more albitic laths. P–T conditions of crystallization are estimated, on the basis of Al- *Correspondence: in-hornblende geobarometry and hornblende geothermometry, at about 4.5–5.5 kbar, Alongkot Fanka 861–927◦C and 4.8–5.5 kbar, 873–890◦C for the magma intrusions that fed volcanic [email protected]; [email protected] rocks and andesitic dikes, respectively. Whole-rock geochemistry indicates that these rock suites are related to calc-alkaline hydrous magma.
    [Show full text]
  • Part 629 – Glossary of Landform and Geologic Terms
    Title 430 – National Soil Survey Handbook Part 629 – Glossary of Landform and Geologic Terms Subpart A – General Information 629.0 Definition and Purpose This glossary provides the NCSS soil survey program, soil scientists, and natural resource specialists with landform, geologic, and related terms and their definitions to— (1) Improve soil landscape description with a standard, single source landform and geologic glossary. (2) Enhance geomorphic content and clarity of soil map unit descriptions by use of accurate, defined terms. (3) Establish consistent geomorphic term usage in soil science and the National Cooperative Soil Survey (NCSS). (4) Provide standard geomorphic definitions for databases and soil survey technical publications. (5) Train soil scientists and related professionals in soils as landscape and geomorphic entities. 629.1 Responsibilities This glossary serves as the official NCSS reference for landform, geologic, and related terms. The staff of the National Soil Survey Center, located in Lincoln, NE, is responsible for maintaining and updating this glossary. Soil Science Division staff and NCSS participants are encouraged to propose additions and changes to the glossary for use in pedon descriptions, soil map unit descriptions, and soil survey publications. The Glossary of Geology (GG, 2005) serves as a major source for many glossary terms. The American Geologic Institute (AGI) granted the USDA Natural Resources Conservation Service (formerly the Soil Conservation Service) permission (in letters dated September 11, 1985, and September 22, 1993) to use existing definitions. Sources of, and modifications to, original definitions are explained immediately below. 629.2 Definitions A. Reference Codes Sources from which definitions were taken, whole or in part, are identified by a code (e.g., GG) following each definition.
    [Show full text]
  • Pan-African Orogeny 1
    Encyclopedia 0f Geology (2004), vol. 1, Elsevier, Amsterdam AFRICA/Pan-African Orogeny 1 Contents Pan-African Orogeny North African Phanerozoic Rift Valley Within the Pan-African domains, two broad types of Pan-African Orogeny orogenic or mobile belts can be distinguished. One type consists predominantly of Neoproterozoic supracrustal and magmatic assemblages, many of juvenile (mantle- A Kröner, Universität Mainz, Mainz, Germany R J Stern, University of Texas-Dallas, Richardson derived) origin, with structural and metamorphic his- TX, USA tories that are similar to those in Phanerozoic collision and accretion belts. These belts expose upper to middle O 2005, Elsevier Ltd. All Rights Reserved. crustal levels and contain diagnostic features such as ophiolites, subduction- or collision-related granitoids, lntroduction island-arc or passive continental margin assemblages as well as exotic terranes that permit reconstruction of The term 'Pan-African' was coined by WQ Kennedy in their evolution in Phanerozoic-style plate tectonic scen- 1964 on the basis of an assessment of available Rb-Sr arios. Such belts include the Arabian-Nubian shield of and K-Ar ages in Africa. The Pan-African was inter- Arabia and north-east Africa (Figure 2), the Damara- preted as a tectono-thermal event, some 500 Ma ago, Kaoko-Gariep Belt and Lufilian Arc of south-central during which a number of mobile belts formed, sur- and south-western Africa, the West Congo Belt of rounding older cratons. The concept was then extended Angola and Congo Republic, the Trans-Sahara Belt of to the Gondwana continents (Figure 1) although West Africa, and the Rokelide and Mauretanian belts regional names were proposed such as Brasiliano along the western Part of the West African Craton for South America, Adelaidean for Australia, and (Figure 1).
    [Show full text]
  • Timothy O. Nesheim
    Timothy O. Nesheim Introduction Superior Craton Kimberlites Beneath eastern North Dakota lays the Superior Craton and the To date, over a hundred kimberlites have been discovered across potential for continued diamond exploration as well as diamond the Superior Craton, more than half of which were discovered mine development. The Superior Craton is a large piece of Earth’s within the past 15 years. Most of these kimberlites occur as crust that has been tectonically stable for over 2.5 billion years. clusters within the Canadian provinces of Ontario and Quebec The long duration of tectonic stability has allowed the underlying (figs. 1 and 2). Moorhead et al. (2000) noted that the average mantle to cool enough to develop the necessary temperature and distance between kimberlite fields/clusters across the Canadian pressure conditions to form diamonds at depths of more than 50 Shield is similar to the typical global average distance of 250 miles miles below the surface. Diamonds are transported to the surface (400 km) between large kimberlite fields. Globally, only 14% through kimberlitic eruptions, which are volcanic eruptions that of kimberlites are diamondiferous (contain diamonds), most in originate tens of miles below the surface and typically erupt concentrations too low for commercial mining. The percentage along zones of weakness in Earth’s crust such as faults and of diamondiferous Superior kimberlites appears to be higher than fractures. The resulting eruption commonly forms a pipe-shaped the global average, including 1) the Attawapiskat cluster – 16 of 18 geologic feature called a kimberlite. Kimberlites typically occur kimberlites (89%) are diamondiferous and so far one kimberlite in groups referred to as either fields or clusters.
    [Show full text]