UMR Journal -- V. H. McNutt Colloquium Series Volume 1 Article 5 April 1968 Tectonic History of Midcontinental United States Frank G. Snyder Follow this and additional works at: https://scholarsmine.mst.edu/umr-journal Part of the Geology Commons Recommended Citation Snyder, Frank G. (1968) "Tectonic History of Midcontinental United States," UMR Journal -- V. H. McNutt Colloquium Series: Vol. 1 , Article 5. Available at: https://scholarsmine.mst.edu/umr-journal/vol1/iss1/5 This Article - Journal is brought to you for free and open access by Scholars' Mine. It has been accepted for inclusion in UMR Journal -- V. H. McNutt Colloquium Series by an authorized administrator of Scholars' Mine. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. UMR Journal, No. 1 (April 1968) 65 Tectonic History of Midcontinental United States F r a n k G. Sn y d er * ABSTRACT Metasediments of Middle Precambrian, and possibly some of earlier age, form an arcuate trending belt across Missouri, Kansas, and Nebraska. These were intruded by granites of several ages that appear to be part of a continuous wave of Late Precambrfan igneous activity. Late Precambrian events that can be delineated include, besides the igneous activity and formation of iron deposits, development of a Keweenawan basin that extended from Lake Superior into eastern Kansas; igneous activity and meta­ morphism of Grenville age in the eastern Midcontinent; development of a major fault lineament extend­ ing northeastward from northeast Arkansas into the Canadian shield outcrop area and separating base­ ment rocks of two distinct ages; and a long period of uplift and erosion during which sediments were deposited in interior and fringing basins. A belt of volcanic rock, partly preserved as an erosional remnant, extended from Ohio into New Mexico and formed a continental divide during Late Precambrian and Early and Middle Cambrian time. Higher peaks in this belt form the present St. Francois, Eminence, and Spavinaw outcrop areas. This area of high volcanic rock is termed the “Ancestral Ozarks.” Paleozoic time was a transition from a positive to a negative to a stable area. It began with broad submergence followed by development of domes, arches, and basins. Continued development of lesser arches fragmented the Midcontinent into numerous small basins and highs. The final stage of activity, oscillation and accompanying cyclical sedimentation, was succeeded by stability. Numerous cryptoexplosion structures are known in the Midcontinent. Some are associated with intrusive and extrusive igneous activity. Nearly all of them lie on a preexisting structural axis. INTRODUCTION The Midcontinent, which embraces the re­ gion from the Appalachians to the Rockies, is largely an area of subdued topography and flat-lying beds. In the field of structural ge­ ology, its history is summed up— and fre­ quently dismissed— as the stable interior. The low-lying surface and flat beds conceal, however, a long and complex history in which only the major elements can be outlined. Age dating of basement rocks indicates that the foundations of the Midcontinent came into ex­ istence far back in Precambrian time. The older rocks were intruded and largely engulfed by later periods of igneous activity. For half a billion years, erosion and denudation reduced the face of the continent; the area became the Fig. 1. Central stable region and Canadian Shield. stable platform (Fig. 1) upon which a veneer of Paleozoic sediments (thin over positive plateau, the Cincinnati arch with its branches, areas, thick in locally subsiding basins) was the Ozark uplift, the Sioux and Nemaha up­ deposited. lifts, the Michigan, Illinois, and Forest City Objectives and Tools of basins, and the several western basins and Structural Geology intervening arches. The development of these Structural geology seeks to decipher the features is the story of the Paleozoic era. character of the present geological situation, Folds and faults, the obvious and often spec­ to define the events that led to development tacular features of structural geology, are the of that situation, and to integrate those events culmination of a long series of events, each into a coherent tectonic history. related to and influenced by preceding events. The character of the present conditions is The keys to deciphering these events are the well known and can be adequately portrayed sedimentary record and the dated ages of on maps (Fig. 2). igneous and metamorphic episodes. The major elements include the Appalachian The sedimentary record reveals activity of *ConsuItinK Geologist, Wheaton, Illinois. both the source area and the depositional 66 Frank G. Snyder BASINS U P L I F T S A. Michigan 1. N ashville 7 . Nemaha B . Illinois 2. Lexington 8. Ozark C . Forest City 3, Findlay 9 . Cambridge D . Sallna 4. Kankakee 10. Central Kansas E . Anadarko 5. W iscon sin 11. Las Animas F . Cherokee 6. Sioux 12. Amarillo G . Arkansas — H . Appalachlan Fault trend — Fig. 2. Major structural features of the Midcontinent. basin. Coarseness and composition of clastic methods are subject to errors in measurement sediments reflect periods of uplift and the and interpretation. They provide the only type of rock which provided the sediments. basis, however, for defining Precambrian oro­ Carbonates indicate inactive land areas and genies and for relating subsurface areas to stable conditions; the sediments are those those orogenies. generated within the depositional basins. For An orogenic cycle begins with the develop­ Paleozoic and younger formations, the sedi­ ment of a geosyncline and deposition of sedi­ mentary record indicates times of subsidence ments. After a long period of sedimentation, and uplift, patterns of warping which gave the cycle culminates in a period of folding, rise to arches and basins, and nearly continu­ usually, although not always, accompanied by ous deposition in some areas and intermittent igneous intrusion. Age dating of metasedi­ subsidence and erosion in others. ments deposited during the geosynclinal stage Deciphering Precambrian history is a far would reveal the time of metamorphism and more complex task because only the remnants intrusion, not the time of deposition. Because of formations are preserved or known from of limitations in age dating methods and the drillhole records, and a great deal of interpre­ long span of time involved in a period of tation must be based on limited data. In Mis­ igneous activity, the age given for an orogeny souri, for instance, age determinations from may represent a time span of up to 200 mil­ only 15 localities are available (Muehlberger lion yea,rs. Older rocks involved in a later met­ and others, 1966). These data suffice to draw amorphic event would show the age of the only the broad outline of the history of an younger event or, more likely, an age between immensely long period of time. Age dating the younger event and their true age. UMR Journal, No. 1 (April 1968) Tectonic History of Midcontinental United States 6 7 Of particular importance to understanding Table 2 Precambrian history is the recognition that Precambrian Geochronology petrographically similar granites in the Mid­ (adapted from Goldich and others, 1961; Stockwell and others, continent may be considerably different in age 1965) (Muehlberger and others, 1966). Approx, age, PRECAMBRIAN Epoch Series Orogeny m.y. Classification and Geochronolgy During the period from 1840 to 1900, a sub­ Late Keweenawan Grenville 1,100 division of the Precambrian, based on rock types with age connotations for each, was de­ 1,700 veloped. This classic “chronology”, with pe­ Middle Huronian Penokean riodic refinement, was accepted and used by most geologists. Age dating of orogenies and geologic provinces in the past decade (Goldich Timiskaming Algoman 2,500 and others, 1961; Engel, 1963; Stockwell, Early 1964) has provided time points on the geologic Keewatin Laurentian ? calendar. The older terminology continues to be useful, however, in terms of type of sedi­ ment and depositional history (Table 1). correlates with Keweenawan igneous activity. Much of the eastern part of the Midcontinent Table 1 was involved in this orogeny (Lidiak and Subdivision of the Precambrian others, 1966). 2) Beginning in Late Precam­ brian time, but earlier than the Grenville orogeny, the Midcontinent experienced a wave Series Types of Rock of igneous activity that became progressively younger southward and culminated in the Upper Clastic Llano (Grenville) orogeny in central Texas (Muehlberger and others, 1966). 3) Although Keweenawan Middle Basic volcanic and intrusive most of the recorded dates from the western Lower Clastic part of the Midcontinent fit an early Late Precambrian time of igneous activity, scat­ Upper Eugeosynclinal and volcanic tered remnants of older rocks are present (Goldich and others, 1966b; Muehlberger and Huronian Middle Miogeosynclinal and shelf others, 1966). Age dating indicates that the St. Francois-Spavinaw-Nemaha type granites Lower Miogeossoiclinal and shelf intruded a terrane of older granites which, in turn, had intruded and metamorphosed still Timiskaming Clastic older sedimentary rocks. Keewatin Eugeosynclinal and basic The presently accepted geochronology, based volcanic on detailed stratigraphy (James, 1958) and age dating (Goldich and others, 1961), pro­ vides a threefold division of the Precambrian