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Archean and Early Proterozoic Tectonic Framework of North-Central United States and Adjacent Canada

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Archean and Early Proterozoic Tectonic Framework of North-Central United States and Adjacent Canada Archean and Early Proterozoic Tectonic Framework of North-Central United States and Adjacent Canada U.S. GEOLOGICAL SURVEY BULLETIN 1904-T Chapter T Archean and Early Proterozoic Tectonic Framework of North-Central United States and Adjacent Canada By P.K. SIMS U.S. GEOLOGICAL SURVEY BULLETIN 1904 CONTRIBUTIONS TO PRECAMBRIAN GEOLOGY OF LAKE SUPERIOR REGION P.K. SIMS and L.M.H. CARTER, Editors U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U. S. Government. UNITED STATES GOVERNMENT PRINTING OFFICE: 1995 For sale by U.S. Geological Survey, Information Services Box 25286, Federal Center Denver, CO 80225 Library of Congress Cataloging-in-Publication Data Sims, P.K. (Paul Kibler), 1918- Archean and early Proterozoic tectonic framework of North-Central United States and adjacent Canada / by P.K. Sims. p. cm. (U.S. Geological Survey bulletin ; 1904-T) (Contributions to Precambrian geology of Lake Superior region ; ch. T.) Includes bibliographical references. Supt.ofDocs.no.: I19.3:B1904T 1. Geology, Stratigraphic Precambrian. 2. Geology, Structural Middle West. 3. Geology, Structural Canada. I. Series. II. Series: Contributions to Precambrian geology of Lake Superior region ; ch. T. QE75.B9 no. 1904-T [QE653] 557.3 s dc20 [551.8'2'0977] 94-39033 CIP CONTENTS Abstract Tl Introduction T2 Archean cratons T2 Superior province T2 Wyoming province T3 Early Proterozoic collisional orogens T4 Penokean orogen T4 Trans-Hudson orogen T5 Central Plains orogen T8 Probable compound nature of the south margin of the Wyoming province T8 Regional correlations of Early Proterozoic margin sequences T9 References cited T10 PLATE [In pocket] 1. Geologic-tectonic maps of Precambrian rocks, showing basement rocks of north-central United States and adjacent Canada, and rocks exposed in Laramide uplifts, southeast Wyoming. FIGURES 1. Sketch map showing Sm-Nd model ages of Precambrian felsic rocks, north-central United States and adjacent Canada T3 2. Diagram showing stratigraphic succession of metasedimentary rocks of the Medicine Bow Mountains, southeastern Wyoming T9 Contents III CONTRIBUTIONS TO PRECAMBRIAN GEOLOGY OF LAKE SUPERIOR REGION Archean and Early Proterozoic Tectonic Framework of North-Central United States and Adjacent Canada tfyP.K. Sims Abstract with accreted juvenile arc rocks of the Wisconsin magmatic terranes. The suture is the north-verging Niagara fault (or shear) The southern part of the Canadian Shield and the subsur­ zone. The arc rocks formed during the interval 1.9-1.845 Ga. face of the southern interior platform comprise two Archean Collision occurred at = 1.85 Ga. In the Lake Huron area, an cratons and three Early Proterozoic collisional orogens. The older asymmetric succession (Huron Supergroup; 2.5-2.2 Ga) Middle Proterozoic Midcontinent rift system transects the older of dominantly metasedimentary rocks lies on the continental rocks in the eastern part of the area. Middle Proterozoic rhyo- margin; this sequence was deformed and metamorphosed prior lite-granite complexes overlap these terranes to the south. Ano- to 2.2 Ga and again, during the Penokean orogeny, at 1.85 Ga. rogenic granite (~ 1.45 Ga) bodies of the Transcontinental The Trans-Hudson orogen is composed mainly of Early Proterozoic province intrude older rocks in a belt extending Proterozoic arc-related rocks but includes substantial amounts from Wyoming northeastward to Lake Huron. of Archean basement rocks. In the main outcrop area in north­ The two Archean cratons, the Superior and Wyoming ern Saskatchewan, the principal igneous and metamorphic provinces, are welded by the Early Proterozoic Trans-Hudson events occurred between 1,910 and 1,830 Ma, approximately orogen. Sm-Nd data together with differences in lithotypes, contemporaneously with rock-forming events within the structure, and geophysical characteristics demonstrate that the Penokean orogen. Seismic reflection profiling at latitude two Archean provinces are not correlative as might be 48°30' N. suggests that both the east and west boundaries of expected by simple lateral extension across the Trans-Hudson the orogen dip beneath the respective Archean cratons, sug­ orogen. The Superior province consists mainly of alternating gesting subduction beneath the two Archean cratons. Outcrop greenstone-granite and metasedimentary gneiss terranes (sub- data in the Hartville uplift, southeastern Wyoming, however, provinces) formed = 2.7 Ga that are separated from generally suggest that the west margin of the orogen here is a probable older Archean gneiss to the south by the Great Lakes tectonic thrust to the west over the Wyoming craton. zone, a major paleosuture. The Wyoming province, on the The Central Plains orogen, the eastern subsurface exten­ other hand, consists of Early to Middle Archean crust that sion of the Early Proterozoic foldbelt exposed in the Laramide formed between 3.8 and 2.8 Ga. Distinct subprovinces such as basement uplifts of Colorado and southeastern Wyoming, is an are present in the Superior province have not yet been identi­ arcuate belt (convex to north) of arc-related metamorphic and fied in the Wyoming province. igneous rocks (1.8-1.63 Ga) that truncates the Wyoming and The three Early Proterozoic collisional orogens are (1) the Superior Archean cratons and the Early Proterozoic Trans-Hud­ Penokean, which extends from the Lake Superior region son and Penokean orogens on the south. Its northwest margin through the Lake Huron region and in the subsurface from the (suture) is the north-verging Cheyenne belt, exposed in the Lake Superior region to Nebraska, (2) the north-trending Trans- Medicine Bow Mountains, which formed between 1.78 Ga Hudson, and (3) the Central Plains, which truncates the two and 1.75 Ga. Phanerozoic sedimentary rocks cover the north Archean cratons and the Trans-Hudson and Penokean orogens and east margins of the Central Plains orogen. to the south. The Penokean in the type area (Lake Superior The south margin of the Wyoming province is a com­ region) consists of a deformed, south-facing, passive continen­ pound passive margin comparable to the compound margin in tal margin prism (~ 2.2-1.85 Ga), including foredeep deposits, the Lake Huron region. An older sequence (2.5-2.1 Ga) of overlying Archean basement that is juxtaposed to the south dominantly siliciclastic rocks was deformed prior to deposition Tectonic Framework, North-Central United States and Adjacent Canada T1 of an outboard younger sequence, which in turn was deformed The Early Proterozoic orogens referred to herein are at ~ 1.78 Ga by collision along the Cheyenne belt. collisional erogenic belts active between 2.0 and 1.75 Ga that welded older cratonic elements. Several authors have suggested that the dominantly silici- clastic rocks on the south, passive margin of the Wyoming era- ton are correlative with those on the Lake Huron segment of the ARCHEAN CRATONS Superior province. Although the proposed correlation is appealing because of similarities in lithology and order of suc­ cession, the assemblages are homotaxial because they were Whether the two Archean cratons (pi. 1, view A) are formed on different cratonic margins and are not necessarily related temporally and physicochemically has been a matter contemporaneous. In the same way, correlation of the younger of uncertainty until recently. Abundant new Sm-Nd data strata on the Wyoming passive margin with parts of the Mar- (Peterman and Futa, 1988; Frost, 1993) together with differ­ quette Range Supergroup (Early Proterozoic) in Michigan is ences in lithotypes, structure, and geophysical characteristics questionable; these assemblages are also homotaxial because have clearly demonstrated that the Superior and Wyoming provinces are not correlative as might be expected by simple they were deposited on different continental margins and are lateral extension across the Trans-Hudson orogen (Sims and not necessarily contemporaneous. others, 1991). In addition, the Wyoming province has a higher heat flow than the Superior province (Drury, 1988), INTRODUCTION indicating that it has a more radiogenic crust. Thus, the Wyoming province is not a rifted segment off the Superior Integration of geologic, geophysical, and geochemical province that was emplaced in its present position during data for the southern part of the Canadian Shield and the closure of the Trans-Hudson ocean; instead, it is exotic crust subsurface of the southern interior platform provides a relative to the Superior province. coherent framework for determining the Precambrian tec­ tonic history of the region. This report describes the regional tectonic elements of the north-central United States and their Superior Province assembly in the Early Proterozoic. The two Archean cratons in the region, the Superior and Wyoming provinces, are The Superior province is the largest and perhaps most welded by the north-trending Trans-Hudson orogen. The thoroughly studied Archean craton in the world (Card, Superior craton is bordered on the south by the northeast- 1990). It is made up of east-northeast-trending belts of con­ trending Penokean orogen. The arc rocks of both orogens trasting lithotypes, metamorphic grade, and age, some of developed nearly contemporaneously during the approxi­ which are bounded by major high-angle faults (Southwick, mate interval, 1,910-1,830 Ma. The two Early Proterozoic in press). The belts comprise four lithostratigraphic rock orogens and the intervening Archean cratons are truncated assemblages: (1) volcanic-plutonic terranes, which resemble to the south by the younger Central Plains orogen (1.8-1.63 Holocene island arcs, (2) metasedimentary belts, (3) plutonic Ga), which was accreted to the North American craton about complexes, and (4) high-grade gneiss complexes. Three 1.78 Ga. The Middle Proterozoic Midcontinent rift system juvenile terranes extend from Canada into the United States (=1.1 Ga) transects the Superior province, the Penokean orogen, and the Central Plains orogen. The Archean and segment of the province.
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