DOCSLIB.ORG

A Magnetotelluric Transect of the Jacobsville Sandstone in Northern Michigan

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A Magnetotelluric Transect of the Jacobsville Sandstone in Northern Michigan A magnetotelluric transect of the Jacobsville Sandstone in northern Michigan CHARLES T. YOUNG I Department of Geology and Geological Engineering, Michigan Technological University, Houghton, Michigan 49931 TED R. REPASKY* ABSTRACT at Sturgeon River Falls about 30 km south of the MT survey line. Com- Eight magnetotelluric soundings were conducted across a basin plex structure within the Jacobsville Sandstone is indicated by highly of the Jacobsville Sandstone along a northwest-southeast line, begin- contorted gravity contours in some areas, and by folded, faulted, and tilted ning north of Toivola, Michigan, northwest of the Keweenaw fault beds at Limestone Mountain (the letter "A" in Fig. IB) (Bacon, 1966; and ending near the village of Keweenaw Bay in Michigan's Upper Kalliokoski, 1982). Peninsula. The soundings have provided an estimate of the thickness Meshref and Hinze (1970) interpreted cross sections of the western and resistivity of structures in the Jacobsville Sandstone as well as the Upper Peninsula of Michigan on the basis of aeromagnetic data. One resistivity, stratigraphy, and structure of the underlying strata. One- profile lies a few kilometres southwest of the MT profiles and is approxi- and two-dimensional models indicate a northwestward thickening of mately parallel to it. They estimate a thickness of about 2 km for the the Jacobsville Sandstone, a faulted basement uplift, the Keweenaw Jacobsville Sandstone near the Keweenaw fault and interpret a reversely fault, and a deep conductor at the southeast end of the profile. faulted anticline in the underlying basalt basement southeast of the Ke- weenaw fault. This fault and anticline intersect the magnetotelluric (MT) GEOLOGICAL AND GEOPHYSICAL SETTING profile as shown in Figure IB, and we used their model as a reference for our interpretation. The study area is a sedimentary basin southeast of the Keweenaw PRINCIPLES OF THE MAGNETOTELLURIC METHOD fault in northern Michigan, as shown in Figures 1A and IB. It is one of several basins flanking the Midcontinent (Keweenaw) Rift System. Explo- Here we present a qualitative description of the MT method to illus- ration for petroleum has been conducted in some of these basins in recent trate the significance of the survey data. The mathematical and physical years. The Jacobsville Sandstone was deposited in Proterozoic time on a formulation of MT has been given by Kaufmann and Keller (1981). basement of unknown nature and later faulted against the Portage Lake Summaries of MT principles and examples of surveys to evaluate a sedi- Volcanics. The Portage Lake Lavas (PLL), Copper Harbor Conglomerate mentary basin are given by Stanley and others (1985) and Vozoff (1972). (CHC), and Freda Sandstone (FSS) lie to the northwest of the fault; the The method utilizes natural transient electric and magnetic fields to Jacobsville Sandstone (JSS) and the Michigamme Formation (MF) lie to determine the surface electromagnetic impedance of the Earth. These fields the southeast. Early studies summarized in Heiland (1968, p. 661 and 662) are due to the flow of charged particles in the ionosphere and to distant reported resistivities of 120 to 44,000 ohm-m for the lavas and 35 to 120 lightning storms. The electromagnetic impedance expresses an assumed ohm-m for the Jacobsville Sandstone (originally termed "Eastern Sand- linear relationship between the applied magnetic field and the resulting stone"); thus it is likely that resistivity measurements can detect contacts electric field. The observation depth of a given measurement is dependent between these dominant rock types. upon the frequency of the detected signal and upon the subsurface resistiv- Various geophysical methods such as gravity (Bacon, 1966), aero- ity. Low-frequency electromagnetic waves penetrate more deeply than do magnetics (Meshref and Hinze, 1970), seismic-reflection (Aho, 1969), and high-frequency waves. Waves of a given frequency penetrate deeper into seismic surface-wave studies (Van Horn, 1980) have been used to estimate resistive rocks than into conductive rocks. The impedance is expressed as the thickness of the sandstone. Kalliokoski (1982) compiled geophysical apparent resistivity and plotted versus frequency (Fig. 2, for example). and borehole measurements which indicate that the sandstone may be as These plots resemble a highly smoothed electrical log with an axis of thick as 3,000 m near the Keweenaw fault and that it tapers to a thin edge frequency rather than depth. The structures giving rise to these curves are to the southeast. determined by comparison of the data with synthetic data computed from Gravity and magnetic data, as well as a few outcrops, indicate com- models. plex structures within and beneath the Jacobsville Sandstone. Gravity data MT equipment normally records two horizontal components of elec- suggest (1) major faulting generally parallel to the Keweenaw fault. Minor tric field and three orthogonal components of magnetic field. The cross-faulting (Fig. IB) and magnetic data suggest extensive buried basalt horizontal electric and magnetic fields are used to determine the imped- flows in a band parallel to the Portage Lake Lavas about 30 km southeast ance tensor, which is usually mathematically rotated to the principal axis. of the Keweenaw fault. This interpretation is confirmed by basalt outcrops The direction of principal axis (impedance maximum) and the ratios of the maximum to minimum impedance express the electrical fabric at the 'Present address: Mobil Exploration and Production Service, Inc., P.O. Box measurement site. 900, Dallas, Texas 75221. The vertical component of the magnetic field is used to define the Geological Society of America Bulletin, v. 97, p. 711 - 716,6 figs., June 1986. 711 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/97/6/711/3445109/i0016-7606-97-6-711.pdf by guest on 26 September 2021 712 YOUNG AND REPASKY -r 90 88 Figure 1A. Regional geologic map from Kalliokoski (1982). The location of the detailed map below is indicated by the heavy rectangle. PALEOZOIC UPPER PROTEROZOIC Jacobsville Sandstone MIDDLE AND UPPER PROT. [Wq Lavas; sediments £ ^ I* ' • J P. Powder Mill Gp. LOWER PROTEROZOIC | 1 Metased metavolc. I I rocks ARCHEAN —I X X Granite, gneiss, r x it X greenstone o 50 Km 88 45 88 30 88 15 88 00 "tipper," which is also used to reveal the electrical fabric of the area. If the Earth consisted only of flat layers, there would be only uniform cunents, but if there is more complicated structure, electric current will concentrate in conductors. The magnetic field of concentrated current curls around the current, as described by the right-hand rule, and thus a horizontal corrent concentration will have a vertical magnetic field component on either side of it. The ratio of the vertical magnetic field to horizontal magnetic field is known as the "tipper magnitude," and the tipper direction is the direction of the horizontal projection of the total magnetic field. The tipper is directed at right angles to the current concentration causing it, and it points away from the concentration. Tipper vectors are presented in the next section to supplement the impedance orientation data. EXPERIMENTAL PROCEDURE AND SURVEY RESULTS The MT profile transected the Jacobsville Sandstone at -90° to the Keweenaw fault (Fig. 1) and was located where the structure would be as nearly two dimensional as possible, several kilometres northeast of the complex magnetic and gravity anomalies associated with the faulting and the buried basalts. Detailed site selection depended on land access and on minimizing powerline and pipeline interference. The data quality lor the survey was generally good, except for occasional problems caused when high winds vibrated the ground in which the magnetometers were buried. Figure IB. Detailed geologic setting and location of MT stations. A sample plot of apparent resistivity versus frequency is shewn in The interpreted faults and anticline are from Meshref and Hinze Figure 2. The depth scale given by the diagonal lines is strictly valid only (1970) and Bacon (1966). Limestone Mountain is indicated by the bold for a two-layer earth. Apparent resistivities over a perfectly conducting face A near the liottom of the map. Key to rock types: FSS, Freda layer buried at a depth, h, will have asymptotic values that plot on these "h Sandstone; CHC, Copper Harbor Conglomerate; PLL, Portage Lake lines" at very low frequencies (Berdachevsky and Dmitriev, 1976, p. 174). Lavas; JSS, Jacobsville Sandstone; MF, Michigamme Formation. For preliminary interpretation, one assumes that the depth to a given Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/97/6/711/3445109/i0016-7606-97-6-711.pdf by guest on 26 September 2021 MAGNETOTELLURIC TRANSECT OF JACOBSVILLE SANDSTONE, MICHIGAN 713 SITE 3 datum is equal to the h line upon which it falls. The lowest apparent resistivities left of center therefore represent depths of 500 to 1,000 m. The Rho xy = c Rho yx = ] h lines also indicate proximity of the MT station to significant resistivity > 10,000 > contrasts (edge effects). The splitting of pxy and pyx that begins at about .3 Hz thus is due to structures about 3,000 m from the station and is probably due to the Keweenaw fault. These approximate distances and depths are iÖS 1000 helpful in formulating a starting model to be tested by more accurate CO • computations. LUS OCX \ The fact that pxy and pyx are very nearly identical at high frequencies hO 100 indicates that the Earth is nearly isotropic in the upper 2 to 5 km and may S3 S \ s t 3 ' be modeled locally with flat layers. The divergence of the curves at lower S* \<'i.c frequencies indicates the need for a two- or three-dimensional model there. o<c 1 \ \ 1 10 c The gravity and magnetic data indicate an absence of significant three- a. * t it J\ Ì \ <Q. \ dimensional structure, suggesting that two-dimensional modeling is proba- \ bly adequate for our data set.
Load more

Recommended publications
  • Regional Gravity Investigation of the Eastern Portion of the Northern Peninsula of Michigan
    REGIONAL GRAVITY INVESTIGATION OF THE EASTERN PORTION OF THE NORTHERN PENINSULA OF MICHIGAN By Erdogan Oray A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Geology 1971 PLEASE NOTE: Some pages may have indistinct print. Filmed as received. University Microfilms, A Xerox Education Company ABSTRACT REGIONAL GRAVITY INVESTIGATION OF THE EASTERN PORTION OF THE NORTHERN PENINSULA OF MICHIGAN By Erdogan Oray A regional gravity investigation was conducted to delineate the Precambrian features of the eastern portion of the Northern Peninsula of Michigan in relation to the tectonic framework of the Lake Superior region and the Southern Peninsula of Michigan. During the survey, an area of 12,000 square miles in the Northern Peninsula of Michigan was covered by a total of 1,003 gravity stations. An additional 851 gravity stations previously observed in the Southern Peninsula of Michigan, Beaver Island, northern Lake Huron, northern Lake Michigan and Sault Ste. Marie area of Canada were used to establish the regional gravity pattern. The Bouguer Gravity Anomaly Map with the aid of a Double Fourier Series Residual Gravity Map indicates that the eastern portion of the Northern Peninsula is associated with two major linear positive gra­ vity anomalies. One of these anomalies trends south from Whitefish Point on the south shore of Lake Superior and is associated with ba­ salts upthrown into a horst within the eastern limb of the Lake Sup­ erior syncline. This anomaly is correlated with the Middle Keweenawan Erdogan Oray volcanics outcropping on Mamainse Point, Ontario.
    [Show full text]
  • The End of Midcontinent Rift Magmatism and the Paleogeography of Laurentia
    THEMED ISSUE: Tectonics at the Micro- to Macroscale: Contributions in Honor of the University of Michigan Structure-Tectonics Research Group of Ben van der Pluijm and Rob Van der Voo The end of Midcontinent Rift magmatism and the paleogeography of Laurentia Luke M. Fairchild1, Nicholas L. Swanson-Hysell1, Jahandar Ramezani2, Courtney J. Sprain1, and Samuel A. Bowring2 1DEPARTMENT OF EARTH AND PLANETARY SCIENCE, UNIVERSITY OF CALIFORNIA, BERKELEY, CALIFORNIA 94720, USA 2DEPARTMENT OF EARTH, ATMOSPHERIC AND PLANETARY SCIENCES, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASSACHUSETTS 02139, USA ABSTRACT Paleomagnetism of the North American Midcontinent Rift provides a robust paleogeographic record of Laurentia (cratonic North America) from ca. 1110 to 1070 Ma, revealing rapid equatorward motion of the continent throughout rift magmatism. Existing age and paleomagnetic constraints on the youngest rift volcanic and sedimentary rocks have been interpreted to record a slowdown of this motion as rifting waned. We present new paleomagnetic and geochronologic data from the ca. 1090–1083 Ma “late-stage” rift volcanic rocks exposed as the Lake Shore Traps (Michigan), the Schroeder-Lutsen basalts (Minnesota), and the Michipicoten Island Formation (Ontario). The paleomagnetic data allow for the development of paleomagnetic poles for the Schroeder-Lutsen basalts (187.8°E, 27.1°N; A95 = 3.0°, N = 50) and the Michipicoten Island Formation (174.7°E, 17.0°N; A95 = 4.4°, N = 23). Temporal constraints on late-stage paleomagnetic poles are provided by high-precision, 206Pb-238U zircon dates from a Lake Shore Traps andesite (1085.57 ± 0.25 Ma; 2σ internal errors), a Michipicoten Island Formation tuff (1084.35 ± 0.20 Ma) and rhyolite (1083.52 ± 0.23 Ma), and a Silver Bay aplitic dike from the Beaver Bay Complex (1091.61 ± 0.14 Ma), which is overlain by the Schroeder-Lutsen basalt flows.
    [Show full text]
  • MIDCONTINENT RIFT SYSTEM BIBLIOGRAPHY by Steven A
    MIDCONTINENT RIFT SYSTEM BIBLIOGRAPHY By Steven A. Hauck December 1995 Technical Report NRRI/TR-95/33 Funded by the Natural Resources Research Institute In Preparation for the 1995 International Geological Correlation Program Project 336 Field Conference in Duluth, MN Natural Resources Research Institute University of Minnesota, Duluth 5013 Miller Trunk Highway Duluth, MN 55811-1442 TABLE OF CONTENTS INTRODUCTION ................................................... 1 THE DATABASE .............................................. 1 Use of the PAPYRUS Retriever Program (Diskette) .............. 3 Updates, Questions, Comments, Etc. ......................... 3 ACKNOWLEDGEMENTS ....................................... 4 MIDCONTINENT RIFT SYSTEM BIBLIOGRAPHY ......................... 5 AUTHOR INDEX ................................................. 191 KEYWORD INDEX ................................................ 216 i This page left blank intentionally. ii INTRODUCTION The co-chairs of the IGCP Project 336 field conference on the Midcontinent Rift System felt that a comprehensive bibliography of articles relating to a wide variety of subjects would be beneficial to individuals interested in, or working on, the Midcontinent Rift System. There are 2,543 references (>4.2 MB) included on the diskette at the back of this volume. PAPYRUS Bibliography System software by Research Software Design of Portland, Oregon, USA, was used in compiling the database. A retriever program (v. 7.0.011) for the database was provided by Research Software Design for use with the database. The retriever program allows the user to use the database without altering the contents of the database. However, the database can be used, changed, or augmented with a complete version of the program (ordering information can be found in the readme file). The retriever program allows the user to search the database and print from the database. The diskette contains compressed data files.
    [Show full text]
  • Western Upper Peninsula Planning & Development Regional Commission
    Western Upper Peninsula Planning & Development Regional Commission th 400 Quincy St., 8 Floor, Hancock, MI 49930 906-482-7205 [email protected] News Release Release Date: September 30, 2020 Media Contact: Rachael Pressley, Assistant Regional Planner 906.482.7205 ext. 116 [email protected] Keweenaw County Hazard Mitigation Plan available for review The Keweenaw County Office of Emergency Measures and the Western Upper Peninsula Planning and Development Region (WUPPDR) have recently made updates to the Keweenaw County Hazard Mitigation Plan. Hazard mitigation is any action taken before, during or after a disaster to eliminate or reduce the risk to human life and property from natural, technological, or human-related hazards. The plan’s purpose is to identify hazard risks throughout the county and to become better prepared for them. The draft of the Keweenaw County 2020-2025 Hazard Mitigation Plan Update will be available through October 30, 2020 for public review and comment prior to plan adoption by all local governments at regular meetings. A formal public hearing will also be held at a County Board meeting to be announced. Copies of the plan draft will be available at WUPPDR (400 Quincy St.) in Hancock and at the Keweenaw County Clerk’s Office (5095 4th St.) in Eagle River, and; online at www.wuppdr.org. Written comments will be considered by WUPPDR in cooperation with Keweenaw County and local governments, as appropriate. Comments must be received by October 30, 2020 and may be mailed to WUPPDR, 400 Quincy St., 8th Floor, Hancock, MI 49930 or emailed to Rachael Pressley, Assistant Regional Planner, at [email protected].
    [Show full text]
  • Geologic Map of the Keweenaw Peninsula and Adjacent Area, Michigan
    U.S. DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP I-2696 U.S. GEOLOGICAL SURVEY GEOLOGIC MAP OF THE KEWEENAW PENINSULA AND ADJACENT AREA, MICHIGAN By William F. Cannon and Suzanne W. Nicholson INTRODUCTION Early Proterozoic rocks The area of this map includes the classic geology and Early Proterozoic metasedimentary rocks of the mineral deposits of the Keweenaw Peninsula in northern Michigamme Formation are exposed in the southeastern Michigan, renowned for the occurrence of great volumes part of the map area. They consist of a thick sequence of of Middle Proterozoic flood basalts and the world's largest graywacke and slate, commonly in graded bedded turbidite concentration of native copper. Native copper was mined layers. Black pyritic slate is locally predominant, mostly in there continuously from the 1840's to the 1960's. For the the north and lower in the stratigraphic section. The rocks earlier part of that period the Keweenawan native copper are part of the Baraga Group, which constitutes the upper district was the principal source of copper for the United part of the Marquette Range Supergroup. In the map area, States. This map is intended to summarize and update a however, older representatives of the Marquette Range wealth of very detailed geologic maps of the region. This Supergroup are absent, and the Baraga Group lies direct­ 1: 100,000-scale map is part of a set of maps portraying ly on Late Archean crystalline rocks. the regional geology of the Midcontinent rift on the south­ The Michigamme strata were deposited, mostly as tur­ ern shore of Lake Superior.
    [Show full text]
  • The Cambrian Sandstones of Northern Michigan
    General Features .......................................................12 Interpretation..............................................................15 Lenticular Sandstone Facies ................................. 15 General Features .......................................................15 Sedimentary Structures..............................................15 Bedding..................................................................15 Channel Structures ................................................15 Cross-Bedding .......................................................16 Other Structures.....................................................18 Interpretation..............................................................18 Massive Sandstone Facies.................................... 19 General Features .......................................................19 Sedimentary Structures..............................................19 Bedding..................................................................19 Ripple Marks ..........................................................19 Interpretation..............................................................19 Frontispiece. The Munising formation exposed in the cliffs of Pictured Rocks. Red Siltstone Facies.............................................. 19 The Pre-Jacobsville Erosional Surface ........................20 STATE OF MICHIGAN Paleogeography ...........................................................21 DEPARTMENT OF CONSERVATION Location of the Source Area.................................
    [Show full text]
  • Copper Isotope Constraints on the Genesis of the Keweenaw Peninsula Native Copper District, Michigan, USA
    minerals Article Copper Isotope Constraints on the Genesis of the Keweenaw Peninsula Native Copper District, Michigan, USA Theodore J. Bornhorst 1,* ID and Ryan Mathur 2 1 A. E. Seaman Mineral Museum and Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, MI 49931, USA 2 Department of Geology, Juniata College, Huntingdon, PA 16652, USA; [email protected] * Correspondence: [email protected]; Tel.: +1-906-487-2721 Received: 22 August 2017; Accepted: 20 September 2017; Published: 30 September 2017 Abstract: The Keweenaw Peninsula native copper district of Michigan, USA is the largest concentration of native copper in the world. The copper isotopic composition of native copper was measured from stratabound and vein deposits, hosted by multiple rift-filling basalt-dominated stratigraphic horizons over 110 km of strike length. The δ65Cu of the native copper has an overall mean of +0.28‰ and a range of −0.32‰ to +0.80‰ (excluding one anomalous value). The data appear to be normally distributed and unimodal with no substantial differences between the native copper isotopic composition from the wide spread of deposits studied here. This suggests a common regional and relatively uniform process of derivation and precipitation of the copper in these deposits. Several published studies indicate that the ore-forming hydrothermal fluids carried copper as Cu1+, which is reduced to Cu0 during the precipitation of native copper. The δ65Cu of copper in the ore-forming fluids is thereby constrained to +0.80‰ or higher in order to yield the measured native copper values by reductive precipitation. The currently accepted hypothesis for the genesis of native copper relies on the leaching of copper from the rift-filling basalt-dominated stratigraphic section at a depth below the deposits during burial metamorphism.
    [Show full text]
  • Fractures in the Jacobsville Sandstone and the Precambrian Â
    Western Michigan University ScholarWorks at WMU Master's Theses Graduate College 8-1991 Fractures in the Jacobsville Sandstone and the Precambrian “W” Rocks in Eastern Marquette County, Michigan Leonard Paul Belliveau Follow this and additional works at: https://scholarworks.wmich.edu/masters_theses Part of the Geology Commons, and the Hydrology Commons Recommended Citation Belliveau, Leonard Paul, "Fractures in the Jacobsville Sandstone and the Precambrian “W” Rocks in Eastern Marquette County, Michigan" (1991). Master's Theses. 944. https://scholarworks.wmich.edu/masters_theses/944 This Masters Thesis-Open Access is brought to you for free and open access by the Graduate College at ScholarWorks at WMU. It has been accepted for inclusion in Master's Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact [email protected]. FRACTURES IN THE JACOBSVILLE SANDSTONE AND THE PRECAMBRIAN "W" ROCKS IN EASTERN MARQUETTE COUNTY, MICHIGAN by Leonard Paul Belliveau A Thesis Submitted to the Faculty of The Graduate College in partial fulfillment of the requirements for the Degree of Master of Science Department of Geology Western Michigan University Kalamazoo, Michigan August 1991 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. FRACTURES IN THE JACOBSVILLE SANDSTONE AND THE PRECAMBRIAN "W" ROCKS IN EASTERN MARQUETTE COUNTY, MICHIGAN Leonard Paul Belliveau, M.S. Western Michigan University, 1991 The major fracture systems in the Jacobsville sandstone likely originated by reverse faulting on the Keweenaw fault and by glacial­ ly produced thrusting. Fracture orientations, apertures, and spac- ings are uniform in the Jacobsville sandstone and Lighthouse Point member of the Mona Schist, and are variable in the Lower member of the Mona schist and Compeau Creek gneiss.
    [Show full text]
  • Geoheritage of the Keweenaw Peninsula
    Michigan Technological University Digital Commons @ Michigan Tech Dissertations, Master's Theses and Master's Reports 2016 Geoheritage of the Keweenaw Peninsula Erika Vye Michigan Technological University, [email protected] Copyright 2016 Erika Vye Recommended Citation Vye, Erika, "Geoheritage of the Keweenaw Peninsula", Open Access Dissertation, Michigan Technological University, 2016. https://doi.org/10.37099/mtu.dc.etdr/301 Follow this and additional works at: https://digitalcommons.mtu.edu/etdr Part of the Other Education Commons, and the Other Teacher Education and Professional Development Commons GEOHERITAGE OF THE KEWEENAW PENINSULA By Erika C. Vye A DISSERTATION Submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY In Geology MICHIGAN TECHNOLOGICAL UNIVERSITY 2016 ©2016 Erika C. Vye This dissertation has been approved in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY in Geology. Department of Geological/Mining Engineering and Sciences Dissertation Advisor: William I. Rose Committee Member: John S. Gierke Committee Member: Carol MacLennan Committee Member: Benjamin van Wyk de Vries Department Chair: John S. Gierke Dedication To all who marvel at the wisdom and magnificence of the talking rocks of the Keweenaw Peninsula. Table of Contents Preface ................................................................................................................................. viii Acknowledgments ..................................................................................................................
    [Show full text]
  • Midcontinent Rift
    North America’s Midcontinent Rift: When Rift Met LIP Seth Stein1, Carol Stein2, Jonas Kley3, Randy Keller4, Trevor Bollman1, Emily Wolin1, Hao Zhang1, Andrew Frederiksen5, Kunle Ola5, Michael Wysession6, Douglas Wiens6, Ghassan Al-Equabi6, Greg Waite7, Eunice Blavascunas8, Carol Engelmann7, Lucy Flesch9, Jake Crane9, Tyrone Rooney10, Robert Moucha11, Eric Brown12 1Northwestern Univ., 2Univ. of Illinois at Chicago, 3Georg-August-Universität Göngen, 4Univ. of Oklahoma, 5Univ. of Manitoba, 6Washington Univ., 7Michigan EarthScope Tech, 8Whitman College, 9Purdue Univ., video 10Michigan State Univ., 11Syracuse Univ., 12Aarhus Univ. EarthScope is catalyzing a new generaon of studies of North American geology Its large-scale nature encourages a synopc view EUS targets are large buried structures formed in distant past How & why did they form? Combine new & exisng geophysical data with insights from analogous younger & beEer understood structures elsewhere USArray Integrate with geological, 1/2012 petrological/geochemical data; kinemac & dynamic models Midcontinent Rift Prominent on (MCR) gravity & magnetic anomaly maps Long arms of buried dense & highly magnetized 1.1 Ga igneous rocks ~ 3000 km long ~ 2 x 106 km3 magma Outcrops near Lake Superior Broader Impact: MCR gave rise to Lake Superior, the basis of the surrounding area’s water-based history and economy, copper and building stone deposits that shaped the area’s selement and growth, and today’s tourism (place–based E&O opportunity). Pictured Rocks Naonal Apostle Islands Lakeshore, MI Naonal
    [Show full text]
  • Insights from North America's Failed Midcontinent Rift Into the Evolution of ☆ Continental Rifts and Passive Continental Margins T ⁎ Seth Steina, , Carol A
    Tectonophysics 744 (2018) 403–421 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Insights from North America's failed Midcontinent Rift into the evolution of ☆ continental rifts and passive continental margins T ⁎ Seth Steina, , Carol A. Steinb, Reece Ellinga, Jonas Kleyc, G. Randy Kellerd, Michael Wysessione, Tyrone Rooneyf, Andrew Frederikseng, Robert Mouchah a Northwestern University, United States of America b University of Illinois at Chicago, United States of America c Georg-August-Universität Göttingen, Germany d University of Oklahoma, United States of America e Washington University, United States of America f Michigan State University, United States of America g University of Manitoba, Canada h Syracuse University, United States of America ARTICLE INFO ABSTRACT Keywords: Continental rifts evolve along two possible paths. In one, a rift successfully evolves into seafloor spreading, Continental rifting leaving the rift structures buried beneath thick sedimentary and volcanic rocks at a passive continental margin. Volcanic passive margins Alternatively, the rift fails and remains as a fossil feature within a continent. We consider insights into these Midcontinent Rift processes from studies of North America's Midcontinent Rift (MCR). The MCR combines the linear geometry of a rift formed at a plate boundary and the huge igneous rock volume of a Large Igneous Province. The rift is a fault bounded basin filled with volcanics and sediments, which record a history of extension, volcanism, sedi- mentation, subsidence, and inversion. The MCR came close to evolving into an oceanic spreading center, but it instead failed and thus records a late stage of rifting. It thus preserves a snapshot of a stage of the process by which actively extending rifts, characterized by upwelling mantle and negative gravity anomalies, evolve either into failed and often inverted rifts without upwelling mantle and positive gravity anomalies or into passive continental margins.
    [Show full text]
  • Paleomagnetic Investigation of Igneous Rocks Deformed by the Keweenaw Fault in the Northwestern Keweenaw Peninsula
    Michigan Technological University Digital Commons @ Michigan Tech Dissertations, Master's Theses and Master's Reports 2019 PALEOMAGNETIC INVESTIGATION OF IGNEOUS ROCKS DEFORMED BY THE KEWEENAW FAULT IN THE NORTHWESTERN KEWEENAW PENINSULA. Daniel Trekas Michigan Technological University, [email protected] Copyright 2019 Daniel Trekas Recommended Citation Trekas, Daniel, "PALEOMAGNETIC INVESTIGATION OF IGNEOUS ROCKS DEFORMED BY THE KEWEENAW FAULT IN THE NORTHWESTERN KEWEENAW PENINSULA.", Open Access Master's Thesis, Michigan Technological University, 2019. https://doi.org/10.37099/mtu.dc.etdr/939 Follow this and additional works at: https://digitalcommons.mtu.edu/etdr Part of the Geology Commons, and the Geophysics and Seismology Commons PALEOMAGNETIC INVESTIGATION OF IGNEOUS ROCKS DEFORMED BY THE KEWEENAW FAULT IN THE NORTHWESTERN KEWEENAW PENINSULA. By Daniel B. Trekas A THESIS Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE In Geophysics MICHIGAN TECHNOLOGICAL UNIVERSITY 2019 © 2019 Daniel B. Trekas This thesis has been approved in partial fulfillment of the requirements for the Degree of MASTER OF SCIENCE in Geophysics. Department of Geological and Mining Engineering and Sciences Thesis Advisor: Aleksey Smirnov Committee Member: Chad Deering Committee Member: James DeGraff Department Chair: John Gierke Table of Contents 1.0 Introduction ..................................................................................................................1 1.1 Midcontinent Rift System .....................................................................................................
    [Show full text]