Geology and_Geochronology of Precambrian Rocks in the Central Interior Region of the United States
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1241-C Geology and Geochronology of Precambrian Rocks in the Central Interior Region of the United States
By RODGER E. DENISON, E. G. LIDIAK, M. E. BICKFORD, and EVA B. KISV ARSANYI
CORRELATION OF PRECAMBRIAN ROCKS OF THE UNITED STATES AND MEXICO
Edited by JACK E. HARRISON and ZELL E. PETERMAN
GEOLOGICAL SURVEY PROFESSIONAL PAPER 1241-C
Lithology, distribution, correlation, and isotope ages of Precambrian terrane for five subareas between the Appalachians and the Rocky Mountains
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1984 DEPARTMENT OF THE INTERIOR
WILLIAM P. CLARK, Secretary
U.S. GEOLOGICAL SURVEY
Dallas L. Peck, Director
Library of Congress Cataloging in Publication Data Main entry under title: Geology and geochronology of Precambrian rocks in the central interior region of the United States. (Geological Survey Professional Paper; 1241-C) Includes bibliographic references. Supt. of Docs. No.: I 19.16:1241-C 1. Geology, Stratigraphic-Precambrian. 2. Stratigraphic correlation. 3. Geology-United States. I. Denison, Rodger E. II. Series. QE653.G476 1984 551.7'1'0973 8:wi00332
For sale by the Branch of Distribution U.S. Geological Survey 604 South Pickett Street Alexandria, VA 22304 CONTENTS
Page Page Abstract ...... C1 Area III- Southern Missouri, Southern Kansas, Oklahoma, and Introduction . . . . . · 1 Northwestern Arkansas ...... C8 Aclrnowledgrnents 2 Proterozoic time (interval occurring 900-1,600 m.y. ago) . 8 Area I-North and South Dakota 2 Formation of rhyolitic to dacitic volcanic rocks and as Archean time . 2 sociated epizonal plutons 1,485 to 1,350 m.y. ago . 8 Gneiss ...... 2 Mesozonal granite rocks along the Nemaha Ridge in Greenstone ...... 4 Kansas and Oklahoma, and in the eastern Arbuckle Granite and granodiorite 4 Mountains, Oklahoma ...... 10 Proterozoic time (interval occurring 1,600-2,500 m.y. ago) 4 Phanerozoic time (Paleozoic Era, Cambrian Period) . . . 11 Metamorphic rocks . . 4 Area IV-Texas and Eastern New Mexico ...... 11 Granites ...... 4 Proterozoic time (interval occurring 1,600-2,500 m.y. ago) . 11 Silicic volcanic rocks ...... 5 Torrance metamorphic terrane and "older granitic Proterozoic time (interval occurring 900-1,600 m.y. ago) . 5 gneisses" ...... 11 Granite ...... 5 Proterozoic time (interval occurring 900-1,600 m.y. ago) . 11 Mafic and ultramafic rocks ...... 5 Rocks formed 1,200 to 1,400 m.y. ago ...... 11 Sioux Quartzite ...... 5 Rocks formed 1,000 to 1,200 m.y. ago ...... 13 Area 11-Nebraska, Iowa, Northern Missouri, Northern Kan Proterozoic time (interval occurring 600-900 m.y. ago) . 14 sas, and Eastern Colorado ...... 5 Metarhyolite of Devils River uplift ...... 14 Archean time ...... 5 The Van Horn Sandstone ...... 14 Proterozoic time (interval occurring 1,600-2,500 m.y. ago) 5 Phanerozoic time (Paleozoic Era, Cambrian Period) . 14 Metavolcanic, metasedimentary, and foliated granitic rocks formed 1,650-1,800 m.y. ago ...... 7 Area V-Eastern Midcontinent ...... 14 Proterozoic time (interval occurring 900-1,600 m.y. ago) . 14 Proterozoic time (interval occurring 900-1,600 m.y. ago) . 7 Anorogenic plutonic rocks. formed about 1,450-1,480 Granite-rhyolite terrane 14 m.y. ago ...... 7 Sedimentary rocks ...... 16 Anorthosites in southwestern Nebraska ...... 7 Basaltic rift zones ...... 16 Mafic volcanic and hypabyssal rocks and related arkosic Rift-related sedimentary rocks 16 sedimentary rocks associated with the Central North Subsurface Grenville province 16 American rift system 8 Metallogenic significance of the Precambrian basement 17 Metamorphism ...... 8 References cited ...... 18
ILLUSTRATIONS
Page PLATE 1. Correlation chart for Precambrian rocks of the Central Interior region, United States. In pocket FIGURES 1-5. Sketch maps showing geology of basementrocks in: 1. North and South Dakota ...... C3 2. Nebraska, Iowa, and parts of Missouri, Kansas, and Colorado. 6 3. Oklahoma and parts of Kansas, Missouri, and Arkansas . 9 4. Texas and eastern New Mexico ...... 12 5. Central Interior region east of the Mississippi River . . 15
III CORRELATION OF PRECAMBRIAN ROCKS OF THE UNITED STATES AND MEXICO
·GEOLOGY AND GEOCHRONOLOGY OF PRECAMBRIAN ROCKS IN THE CENTRAL INTERIOR REGION OF THE UNITED STATES
By RODGER E. DENISON! E. G. LIDIAK,2 M. E. BICKFORD,3 and EVA B. KISVARSANYI4
ABSTRACT INTRODUCTION Rocks of the buried Precambrian crust in the Central Interior re gion range from more than 2,700 to less than 1,000 million years Our understanding of the Precambrian in the Central in age and from granite and granulitic gneiss to gabbro and basalt Interior region is based upon widely separated outcrop in rock type. The oldest rocks occur in the Dakotas and clearly are areas and samples from irregularly distributed but buried portions of the Canadian Shield; they are mostly older than 2,700 million years, and some may be as old as 3,600 million years. numerous wells drilled largely in search of oil and gas. The central part of this region, including Nebraska, northern Mis Flawn (1956) showed that it was possible .to make a souri, and northern Kansas, is underlain by diverse igneous and map of the buried Precambrian terrane based on drill metamorphic rocks whose ages are mostly 1,600 to 1,800 million hole samples, and the larger scale study of Muehlberger years; scattered anorogenic granitic plutons whose ages are about and others (1967) led to publication of the basement 1,~1,500 million years are also known in this terrane. The most distinctive feature of the Continental Interior is the great rock map of the United States (Bayley and terrane of felsic igneous rocks that makes up the basement from Ohio Muehl berger, 1968). These works remain the founda and Wisconsin across southern Missouri and Kansas and into the tion of our present understanding. The geology and Texas Panhandle and far western Texas. These rocks, which include geochronology of the scattered surface exposures are abundant rhyolite and mesozonal and epizonal granitic bodies, range now better known, but the geochronology of the sub in age from 1,500 to 1,200 million years, and the general tendency ~ for ages to decrease from northeast to southwest; older rocks are surface has received little attention, and the basic re not known anywhere within this terrane. Toward the east in Ohio, ference work is the series of reports by Goldich and eastern· Kentucky, and eastern Tennessee, and toward the south in his coworkers (1966). central Texas, the basement terrane consists of medium-grade The rocks in the Central Interior region are here di metamorphic rocks and associated granitic plutons that formed vided into four general types: (1) deep-seated granitic mainly 1.000-1.100 million years ago. A belt of basalt, interflow arkosic sandstone and siltstone, and re and metamorphic rocks similar to those exposed in the lated mafic intrusive rocks can be traced with the aid of geophysical shield areas; (2) anorogenic mesozonal and epizonal data from the Lake Superior region southw~ into central Kansas. granite; (3) rhyolite and epizonal granite; and (4) basalt This feature, the Central North American rift system, is widely be and gabbro of "rift" type. lieved to be an abortive continental rift that formed about 1,100 mil The first type is typical of rocks exposed in the Pre lion years ago. Geophysical data suggest that other areas in the east em part of the interior are also underlain by rift basalts and related cambrian shields. These are diverse and strongly de rocks. formed rocks together with undeformed massive plu The Central Interior region was dominated by eugeosynclinal tons that are characteristically older than about 1,600 sedimentation and orogenic tectonics prior to about 1,600 million m.y. (million years). The marked density and magnetic years ago. After that time the region apparently stabilized, and the contrasts of these rocks allow extrapolation by sedimentation was characterized by the deposition of sheets of quartzose sandstone about 1,600 million years ago. Subsequent igne geophysical methods in areas where drill control is lack ous activity, sedimentation, and tectonics have been dominantly ing. About 18 percent of the Central Interior region anorogenic except along the margins of the stable interior. is underlain by rocks of this type.
10De EDeJV Square, Dallu, TX 76008. The second type is characterized by anorogenic meso IJ>epertment of GeolORY aDd P1aDetary Seleneee, Univendty or PlttabUJ'Ih, Pittsburgh, zonal to epizonal granitic plutons, formed 1,300 to 1,500 PA Ilia). 'Department of GeolCJRY, Univendty or KaMu, Lawnmee, KS 66CM6. m.y. ago, and associated with relatively minor 4Miuouri Department or Natural Reeoun!ee, Rolla, MO 66401. metasedimentary and metaigneous rocks. Silver and Cl C2 CORRELATION OF PRECAMBRIAN ROCKS OF THE UNITED STATES AND MEXICO others (1977) and Emslie (1978) have discussed the im Precambrian rocks of the Central Interior region is the portance of these rocks, which form a discontinuous great preponderance of granite and related volcanic band from northeastern New Mexico to central Mis rocks. These rocks, which generally have petrographic souri and probably eastward to the Grenville Front in features indicating that they were emplaced at shallow the Central Interior region. We estimate that 13 per to intermediate crustal levels, make up about two cent of the Continental Interior is underlain by these thirds of the Continental Interior. Mafic rocks occwr rocks. mostly along the Central North American rift system. The third type is characterized by large tracts of Igneous rocks of intermediate composition are excep rhyolite and associated epizonal granite. After these tionally rare. The greenstone belts that so characterize tracts were recognized in the subsurface (Muehlberger the older shield areas are confined to the buried exten and others, 1966; Muehlberger and others, 1967), addi sions of the shield in Area I, and thus make up only tional drilling showed that much of the area east of about 1 percent of the Central Interior region. the Mississippi River and west of the southward exten Sedimentary rocks are also notably rare. Shelf-type sion of the Grenville province is underlain by similar sedimentation evidently began about 1, 700 m.y. ago, rocks. Although the origin of the epizonal granite-rhyo but the major deposits were of clean sandstone. Car lite terrane remains unclear, certain conclusions may bonate rocks are virtually unknown, and all the sedi be drawn from our present understanding: mentary rocks make up only an estimated 7 percent (1) The rocks are preserved in structural depressions; of this great region. surrounding rocks represent deeper crustal levels of ACKNOWLEDGMENTS emplacement. (2) The rhyolites are invariably associated with The cooperation of the various State geological sur· coeval hypersolvus granites that commonly display veys, mining companies, and oil companies in providing micrographic quartz-perthite intergrowths. access to samples has been essential to this report. (3) The rhyolites are not known to be associated with James D. Hansink of Rocky Mountain Energy provided any significant volume of other volcanic or sedimentary an opportunity for Denison and Lidiak to review the rocks. basement of the Continental Interior in 1976, and this (4) The rhyolites are essentially undeformed and only work has been an important base for the results pre locally recrystallized. sented here. W. R. Muehlberger and W. R. Van (5) The several tracts of rhyolite-granite are similar Schmus reviewed the manuscript and gave many help but not the same in age; the ages show no simple pat ful comments. Financial support was provided by the tern of variation. U.S. Geological Survey and the U.S. Department of The rhyolite-epizonal granite association underlies an Energy. Lidiak is pleased to acknowledge support from estimated 52 percent of the Continental Interior, al NASA grant NSG--5270. though much of this area is east of the Mississippi River where drill-hole control is poor. The abundance AREA I-NORTH AND SOUTH DAKOTA of these rocks is the major difference between the buried Precambrian of the Continental Interior and the Characterization of the buried basement complex in. exposed shield areas. Gravity and magnetic observa North and South Dakota is based on gravity and mag-· tions are of limited value in extrapolating these rocks netic anomalies and on lithologic study of several into areas where drill control is poor. hundred basement well samples (Muehlberger and. The extension of Keweenawan basaltic and gabbroic others, 1967). Lithology and ages of rock units are rocks from the Lake Superior region into the Central shown on plate 1. These data indicate that the eastern Interior region along the Central North American rift Dakotas are mainly part of the subsurface extension system has yielded the fourth major rock association. of Archean rocks of the Canadian Shield. The western Basaltic rocks and related arkose can be traced as far Dakotas are a continuation of mainly Proterozoic rocks as east-central Kansas on the basis of scattered well of the Canadian Shield. samples and gravity and magnetic data. That smaller areas east of the Mississippi River are also underlain ARCHEAN TIME by similar mafic igneous rocks can be inferred from GNEISS geophysical measurements. These rocks are possibly time correlative with the Keweenawan associations. We Gneiss of Archean age is apparently widespread in estimate that about 10 percent of the interior is under eastern North and South Dakota. The oldest rocks (fig. lain by rocks of this type. 1) are granitic and granulitic gneisses that crop out in Perhaps the single most significant feature of the the Minnesota River valley (Goldich and others, 1961; GEOLOGY AND GEOCHRONOLOGY OF PRECAMBRIAN ROCKS C3
EXPLANATION
PROTEROZOIC
e.~.:;_~·~:t<~~~ SIOUX QUARTZITE !'<-;':_. GRANITE '..-'):'' : ).:~-~~:{ SILICIC VOLCANIC ROCKS
}~{:}~{:} METAMORPHIC BELTS
ARCHEAN
GRANITES AND GRANODIORITIES
GREENSTONE BELTS
GRANITIC AND GRANULITIC GNEISSES .
---- CONTACT OR INFERRED BASEMENT CONTACT ----FAULT OR INFERRED FAULT
AREA OF EXPOSED ROCKS
100 200 KILOMETERS
FIGURE 1.-Sketch geologic map of basement rocks in North and South Dakota. Unpatterned areas have no control.
Goldich and others, 1970) and extend along a series of highs; five wells to basement encountered granitic and prominent gravity and magnetic anomalies from near gneissic rocks. In North Dakota the gravity anomalies Duluth, Minn., west-southwestward to east-central are less distinct, but 22 wells to basement demonstrate South Dakota (Lidiak, 1971; Morey and Sims, 1976). the granitic and gneissic character of the terrane. Min Detailed radiometric studies of the Minnesota River eral assemblages in the gneisses indicate widespread valley rocks (Goldich and others, 1970; Goldich and metamorphism to the amphibolite facies. Hedge, 1974) have shown that they are at least 3,500 Sparse radiometric data indicate that the gneisses m.y. old and that one phase appears to be 3,700 m.y. are of probable Archean age (Burwash and others, old. Metamorphism and granite emplacement about 1962). A further indication of age is the continuation 2,700 m.y. ago and a thennal event about 1,800 m.y. of geophysical anomalies associated with Archean ago have partly obliterated the earlier geologic history gneisses of the Canadian Shield into the eastern of the gneisses. Dakotas. The higher grade of metamorphism in the Granitic gneiss is shown on figure 1 as the predomi gneisses compared to Archean greenstones suggests nant rock type in five other areas of northeastern South that at least some of the gneisses predate the 2, 700- Dakota and in a large area of northeastern North m.y.-old Algoman orogeny. Dakota. The belts in South Dakota are associated with Rocks of Archean age are also present in the Black west-southwest-trending gravity lows and magnetic Hills (Zartman and Stern. 1967; Ratte and Zartman, C4 COKRELATION OF PRECAMBRIAN ROCKS OF THE UNITED STATES AND MEXICO
1970; Kleinkopf and Redden, 1975). Two granulites IP'ffi.(Q>'lrJE.ffi.(Q>fl(Q>II SILICIC VOLCANIC ROCKS layers of rhyolite and quartz sandstone (Beyer, 1893). Similar silicic volcanic\,rocks in South Dakota yield ages Silicic volcanic rocks are present in eastern South of 1,680-1,700 m.y.; the Baraboo Quartzite of Wiscon Dakota. These rocks are essentially unmetamorphosed sin, often considered to be correlative with the Sioux and apparently overlie the older plutonic complex. Quartzite, rests upon rhyolite whose U-Pb zircon age Three determinations yield ages of 1,680-1,700 m.y. . is 1,760± 10 m.y. (Van Schmus, 1978). · (Goldich and others, 1966). Petrographically similar rhyolitic volcanic rocks occur in adjacent northwestern Iowa (included in undifferentiated felsic rocks on fig. 2). AREA II-NEBRASKA, IOWA, NORTHERN MISSOURI, NORTHERN PROTEROZOIC TIME (INTERVAL OCCURRING KANSAS, AND EASTERN COLORADO 900-1,600 M.Y. AGO) Basement rocks in Area II include a variety of igne- ous, metamorphic, and sedimentary rocks whose ages GRANITE range from at least 1,800 m.y. to about 1,000 m.y. The Four Rb-Sr whole rock or feldspar ages on granite distribution and petrography of these rocks have been from southern South Dakota and adjacent Nebraska are determined primarily from study of cuttings and cores in the range 1,480-1,510 m.y. (Goldich and others, from deep drilling, but geophysical data have also been 1966). These rocks are probably related to the used to extend terranes mapped on the basis of well anorogenic granites ·discussed in the following sectio11 samples. Large numbers of well samples are available on Nebraska, Iowa, and surrounding area. in Nebraska and Kansas because ofoil and gas explora tion; these have been studied by Lidiak (1972) in N e braska and by Scott (1966) and Bickford and others MAFIC AND ULTRAMAFIC ROCKS . (1979) in Kansas. The Missouri basement is reasonably Diabase, diorite, gabbro, and pyroxenite occur in well known beeause of drilling for minerals and has scattered wells in North and South Dakota. Except for been studied by Kisvarsanyi (1974, 1975). Relatively lit deuteric alteration in the diabases, the rocks are unal tle is known about the Precambrian rocks of Iowa and tered and thus intrusive into the plutonic complex. eastern Colorado, because a smaller number of wells Their age is unknown, but they probably reflect several have penetrated the basement there. intrusive episodes. They are tentatively regarded as postdating regional metamorphism and thus being less ARCHEAN TIME than 1, 750 m.y. old. No rocks of Archean age are known in Area II, al though we infer such rocks to underlie parts of north SIOUX QUARTZITE em Iowa because of the proximity of. the ancient rocks The Sioux Quartzite is a uniform, mildly folded, sub that are exposed in the Minnesota River valley (Goldich horizontal formation that is nonconformable on the un and others, 1970; Goldich and Hedge, 1974). derlying plutonic complex. It is extensively developed in the surface and subsurface of southeastern South PROTEROZOIC TIME (INTERVAL OCCURRING Dakota and extends into adjacent Minnesota, Iowa, and 1,600-2,500 M. Y. AGO) Nebraska. The formation is composed mainly of silicified quartz sandstone that is conglomeratic near Only one radiometric age greater than 1,800 m.y. has the base, and minor thin beds of red shale and argillite. been reported for any rocks from Area II, and most The presence in the essentially l.mdeformed quartzite are 1,700 m.y. or less (Goldich and others, 1966). We of diaspore plus quartz and pyrophyllite plus quartz have, however, indicated on the chronometric chart (pl. (Berg, 1938) suggests hydrothermal or burial meta 1) that both sedimentary and volcanic rocks may have morphism under static conditions. formed as early as 2,000 m.y. ago. This speculation is Pebbles of iron-formatio~ in the Sioux Quartzite indi based upon the presence of silicic metavolcanic rocks cate that the unit may be no older than about 1~900 and various metasedimentary rocks (schists, quartzites) m.y. (Goldich, 1973), and· a Rb-Sr age determination in the basement of both Kansas and Nebraska. These on a rhyolite from Sioux County, ·Iowa, suggests that are associated spatially with gneissoid granitic rocks it may be at least 1,520 m.y. old (Lidiak, 1971). A that have yielded ages of about 1,700 m.y. If nearby well is reported to have penetrated alternating metamorphism occurred later than 1,700 m.y. ago, it 0 0':1 0 0 ~ ~ ,../ tzj t'-4 I ~' r ( 1 •• ~ ' -0z ( 0 "%j ~ ~ tzj • ~ ----- ~-~~) 0 ~ ·~·,,~ t::d ~ ·:. 40"~ ~ ~~~,~"'~"""~ >z ~ -..... ,,., MISSOUR~ 0 ,,,, 0 COLORADO @ I 0 ,, ... ,, "%j ,,,, ~ ,,, ~ '''" tzj :.:_:.:·:·::.:: l"' ;J~]~ c::z ~ -tzj ._,,·. .. t:::l : t""j o" r:n 0 100 200 KILOMETERS -,;~,~ 0 I ~ ;5 r:n EXPLANATION z> t:::l ---- CONTACT OR INFERRED BASEMENT =~J a= FELSIC ROCKS UNDIFFERENTIATED r...... ;..... METAMORPHIC ROCKS CONTACT tzj =·:·=·==·:·:·==···:·:·:· Mostly metasedimentary; >< grade variable, mostly --?--FAULT OR INFERRED FAULT GRANITE 0 low to medium Queried where extension uncertain 0- RHYOLITE SIOUX QUARTZITE } Sedimentary :~¥[~\~Vi~! GABBRO KEWEENAWAN ro cks 7 • AGE ROCKS >· " : : ~ I BASALT v 7.., (" .,. ._J ' FIGURE 2.--Sketch geologic map of basement rocks in Nebraska, Iowa, and parts of Missouri, Kansas, and Colorado. Unpatterned areas have no well control. CNARS, Central North American rift system. GEOLOGY AND GEOCHRONOLOGY OF PRECAMBRIAN ROCKS C7 did not result- in lowering of Rb-Sr whole-rock or feld facies in parts of the area, affected all these rocks, or spar ages of at least some of .the gneissoid rocks, and whether the· metasedimentary and metavolcanic rocks we consider it more likely that metamorphism either were formed by a metamorphic episode earlier than the preceded or accompanied the synkinematic emplace period of shearing and cataclasis that affected the ment of the granitic rocks about 1,700 m.y. ago. This granitic rocks. event would thus be correlative with the Boulder Creek event, which has been well documented in the northern PROTEROZOIC TIME (INTERVAL OCCURRING Front Range of Colorado (Peterman and Hedge, 1968; 900-1,600 M.Y. AGO) Stern and others, 1971). ANOROGENIC PLUTONIC ROCKS FORMED ABOUT METAVOLCANIC, METASEDIMENTARY, AND FOUATED 1,450-1,480 M.Y. AGO GRANmC ROCKS FORMED 1,650-1,800 M.Y AGO Granitic to tonalitic plutons having ages ip the range Much of Area II is underlain by the gneissoid granitic 1,450-1,480 m.y. are known in Nebraska, northern rocks (fig. 2) mentioned in the preceding section. Some Kansas, and northern Missouri. These rocks are gener of these rocks have been ~etermined to be 1,600 to ally not foliated and thus presumably were intruded 1,800 m.y. old by either Rb-Sr or U-Pb (uranium-lead; into the older terrane after the pervasive shearing zircon) methods (Goldich and others, 1966; Bickford and event. Because these rocks are not accompanied by as others, 1981).' These rocks are commonly granitic to sociated volcanic rocks in this region, and because they granodioritic il}/ composition and' are characterized by are not deformed, they are assumed to have been slightly to moderately developed foliation caused by emplaced anorogenically. These rocks are evidently a pervasive shearing and cataclasis. Metasedimentary part of the great belt of anorogenic plutons of this age and metavolcanic rocks are distributed throughout the which are known from Labrador to California (Silver area either in fairly well defined belts or in small and oth~rs, 1977; Emslie, 1978). Where they have been patches only a few kilometers in diameter. Metavol well studied at the surface-for example, the Wolf canic rocks that were evidently originally rhyolitic to River batholith, Wisconsin (Van Schmus and others, dacitic are known in western Kansas, north-centraJ 1975; Anderson and Cullers, 1978) and the St. Francois Missouri, and in northern and southwestern Nebraska, Mountains batholith, Missouri (Bickford and Mose, but they are not as widely distributed as metasedimen 1975)--they .a.r~ seen to be characterized by rapakivi tary rocks. ;Metamorphic rocks include fairly abundant texture and silicic-alkalic che_mistry. . muscovite and biotite schist, minor amphibolite, and In Nebraska the age of these plutons is known abundant quartzite; t~e quartzite forms prominent mainly from Rb-Sr measurements of total rock samples, basement-surface highs in southwestern Nebraska but zircons separated from a core from southwestern (Lidiak, 1972), to the south on the Central Kansas up Nebraska yielded a U-Pb age of 1,445± 15 m.y., re lift (Walters, 1946), and on the Central Missouri high ported by Harrower (1977). Harrower also determined (Kisvarsanyi, 1974). The Sioux Quartzite-(age and ex- · a similar age for zircons from a core in north-central te~t discussed previously) extends as far south as ex Kansas. treme northern Nebraska in the· subsurface. It is As will be seen in the discussion of Area III, plutons known to rest nonconformably upon the underlying of the anorogenic type occur to the south in southern igneous-metamorphic complex, but it is not known Kansas, southern Missouri, and Oklahoma in associa whether the patches of metavolcanic and metasedimen tion with extensive rhyolitic volcanic rocks. There, tary rocks that are known elsewhere throughout Area however, the age of the plutons is about 1,380 m.y., II lie upon the 1,~1,800-m.y.-old granitic rocks or except in southeastern Missouri, where plutons and vol are older pendants and inclusions within them. canic rocks are about 1,480 m.y. old (Bickford and It seems clear that a widespread period of pervasive Mose, 1975). shearing and cataclasis occurred between 1,800 m.y. ago (the age of the oldest rocks dated) and about 1,480 ANORTHOSITES IN SOUTHWESTERN NEBRASKA m.y. ago, the oldest age determined from a widespread suite of norifoliated anorogenic plutons that· occur with A· complex of anorthositic rocks occupies an area of in the older terrane (Goldich and others, 1966; Har about 400 km2 in southwestern Nebraska (gabbro on rower, 1977; Bickford and others, 1981). Because the fig. 2). The rocks, ranging in composition froin anortho age of the metavolcanic and metasedimentary rocks rel site to anorthositic gabbro, have been subjected to ative to that of the foliated granitic rocksJs not known, cataclasis and to mcipient greenschist facies meta it cannot be determined whether a single period of per morphism. No direct radiometric age measurement is vasive regional metamorphism, reaching amphibolite available for these rocks, but Lidiak (1972) has inferred C8 CORRELATION OF PRECAMBRIAN ROCKS OF THE UNITED STATES AND MEXICO that they aR"e you.ngeJr than schlists in the a1rea because Lidliak (].972) also obseJrVed low-gnde meta.mo1rphic they lack metamorcphism of amphibolite fades that may mineJral assemblages in the basaltic ll"OCks of the Centnl have oocWI'l:1'18d about ])}00 m.y. ago~ and that they a1re North American rift system. These Msemblages~ in- oAdeJr than a perioo of cataclasis and gJreenschlst facies cluding p-qmpellyite~ laumontite~ epidote~ and chlorite, metamorcphism t]}w.t is mfenerll to have ooc'W'lr'erll· about aR"e indlicative of metamolr]phlsm undlell" conmtions com- 1~200 m.y. ago. monly attributed to simple burial metamolr]phlsm. MJill'll FIGURE 3.--Sketch geologic map of basement rocks in Oklahoma and parts of Kansas, Missouri, and ArkansaB. 0 e.o C10 CORRELATION OF PRECAMBRIAN ROCKS OF THE UNITED STATES AND MEXICO and a complex of subvolcanic and epizonal plutons. MESOZONAL GRANITE ROCKS ALONG THE NEMAHA Plutonic rocks are exposed principally in the northeast RIDGE IN KANSAS AND OKLAHOMA, AND IN THE em part of the area, whereas to the southwest, volcanic EASTERN ARBUCKLE MOUNTAINS, OKLAHOMA rocks are exposed, suggesting that some plutons are tilted to the southwest (Bickford and others, 1977). Contacts between the plutons and the volcanic roof, as A terrane of mesozonal granitic rocks is known in well as chemical, mineralogical, and textural variations southern Kansas along the northeast-southwest trend within the plutons, indicate that some of them are of the Nemaha Ridge (Bickford and others, 1979), and sheetlike. Some plutons, however, are cylindrical and it extends southwesterly into Oklahoma at least as far like a cone-sheet in form, as suggested by subsurface as Oklahoma City (Denison, 1966). The age of these and geophysical data (E. B. Kisvarsanyi, unpub. data, rocks is not well known, but their mesozonal character 1981). This terrane has clearly not been subjected to and their occurrence along the Nemaha Ridge suggest penetrative deformation. that they are somewhat deeper portions of the conti The exposed rocks of the St. Francois terrane have nental crust that were brought up by fault movements been dated by Rb-Sr whole-rock and by U-Pb (ziroon) on the Nemaha structure and exposed by erosion prior methods by Bickford and Mose (1975). The Rb-Sr sys to Late Cambrian sedimentation. tem has evidently been disturbed, for the ages reported The only other place in Area III where more deep range from about 1,380 m.y. to as low as 1,200 m.y., seated igneous rocks are known is in the eastern Ar and the age data and field relations sometimes con buckle Mountains of southeastern Oklahoma (Ham and tradict each other. U-Pb measurements on zircons, others, 1964). There, four extensive plutons are ex however, yield consistent ages of about 1,485 m.y. for posed in the core of the Tishomingo-Belton anticline four major plutons and for one of the major volcanic (Denison, 1973). Rocks exposed include an unnamed units; one small sill or stock, the Munger Granite Por granodiorite, the Troy Granite, the Tishomingo Gran phyry, yields a U-Pb zircon age of about 1,385 m.y., ite, and the gneiss of Blue River, an informal name. which may indicate a younger igneous event in this The Troy Granite intrudes the unnamed granodiorite area. A granite core from a buried part of the St. Fran and is intruded by the Tishomingo Granite; the Blue cois terrane also yields a U-Pb age of 1,485 m.y. River gneiss is intruded by the Tishomingo Granite,. (Bickford and others, 1981). but its age relationships with the Troy Granite and the Rocks entirely similar to those of the St. Francois unnamed granodiorite are not known because the terrane extend in the subsurface across southern Mis Tishomingo Granite separates it from those rock souri and northern Arkansas into southern Kansas, Ok bodies. All these rocks are medium to coarse grained· lahoma, and the Texas Panhandle. Studies of these and have petrographic features suggesting mesozonal rocks, mainly from cuttings and cores returned from emplacement. Bickford and Lewis (1979) have deter deep drilling, include those of Denison (1966) in north mined the U -Ph ages of zircons from the Tishomingo eastern Oklahoma,- southeastern Kansas, and south Granite (1,374± 15 m.y.), the Troy Granite (1,399±95 western Missouri; Muehlberger and others (1967) over m.y.), and the gneiss of Blue River (1,396±40 m.y.). a large region including parts of Texas and New Mexico The rocks are therefore the mesozonal age equivalents as well as the region considered here; Kisvarsanyi of the epizonal granophyres and rhyolites in southern· (1974) in Missouri; and Bickford and others (1979) in Kansas and northeastern Oklahoma. Kansas. The ages of these rocks have been studied in north Several types of dikes intrude the granitic rocks of eastern Oklahoma and southwestern Missouri by the eastern Arbuckle Mountains. The most common Muehlberger and others (1966), Denison and others dikes are diabasic, whereas dikes of micrograni~ por (1969), and Bickford and Lewis (1979), and in the Kan phyry, granite, and rhyolite porphyry are less common. sas basement by Bickford and others (1981). Zircons On the basis of unpublished age determinations, it ap from the Spavinaw Granite, which is exposed in north pears that some of the diabase dikes and the granite eastern Oklahoma, and from a granite in the subsurface and microgranite porphyry dikes are approximately the in southeastern Kansas (Bickford and others, 1981) same age as their granitic host rocks, about 1,3~1,400 yield U-Ph age determinations indicating that they are m.y.; the rhyolite porphyry dikes and the other diabase 1,375 m.y. old. These ages are in reasonable agreement dikes are of Cambrian age. All the dikes have a with the Rb-Sr isochron age of about 1,300 m.y. deter strongly developed preferred strike direction near N. mined by Denison and others (1969) from subsurface 60° W., which is parallel to the major Pennsylvanian samples in northeastern Oklahoma. deformational axes. GEOLOGY AND GEOCHRONOLOGY OF PRECAMBRIAN ROCKS C11 PHANEROZOIC TIME (PALEOZOIC ERA, PROTEROZOIC TIME (INTERVAL OCCURRING CAMBRIAN PERIOD) 1,600-2,500 M.Y. AGO) The igneous rocks of the Wichita Mountains consist TORRANCE METAMORPHIC TERRANE AND of a bimodal suite of silicic and gabbroic rocks. The "OLDER GRANmC GNEISSES" silicic rocks, consisting of epizonal granite plutons and The oldest isotopic ages from the area shown on fig rhyolite, and some of the gabbroic rocks have yielded ure 4 have been reported from eastern New Mexico ages in the range 510 to 530 m.y. (Tilton and others, where Muehlberger and others (1966) determined Rb 1962; Muehlberger and others, 1966). Paleomagnetic Sr ages in excess of 1,600 m.y. for a whole-rock sample data (Roggenthen and others, 1976) and geologic con and for a feldspar from granitic gneisses. Micas from siderations (Powell and Phelps, 1977) have suggested both of the rock samples studied yielded metamorphic that the oldest rock unit, the layered series of the ages of about 1,350 m.y. The granitic gneisses are as Raggedy Mountain Gabbro, is of Precambrian age. The sociated with metasedimentary and metavolcanic rocks K-Ar ages of these rocks, however, suggest a Cambrian that are probably equivalent to the sequence found in age (Burke and others, 1969), and the age must be con outcrop along the Los Piiios-Manzano trend (Stark and sidered uncertain. The Raggedy Mountain Gabbro is Dapples, 1946; Stark, 1956). Long (1972, p. 3425) re the only large layered gabbroic mass exposed in the ported ages of "about 1,600 m.y. or older'' for metavol Continental Interior. canic rocks northward along this trend. The relation Th.e geologic relations and structural framework for ship between gneisses and the supracrustal rocks can southern Oklahoma that were outlined by Ham and not be determined on the basis of the available informa others (1964) appear to be essentially correct. How tion, but the mature character of the metasedimentary ever, the rhyolite terrane in extreme southwestern Ok rocks suggests that they were originally shelf deposits lahoma, which was considered to be of Cambrian age . upon sialic crust. These two units (the Torrance by Ham and others, is now thought to be an outlier metamorphic terrane, and the "older granitic gneisses" of the Panhandle rhyolites of Precambrian age (see dis of Muehlberger and others, 1967) have been extended cussion of Area IV) on the basis of unpublished age by us with considerable trepidation in the subsurface determinations. The Tillman Metasedimentary Group is on the basis of petrography. most probably Precambrian, as suggested by Muehlberger and others (1967), although parts of this unit may indeed be of Cambrian age as argued by Ham PROTEROZOIC TIME (INTERVAL OCCURRING and others. 900-1,600 M.Y. AGO) ROCKS FORMED l,ZOO TO 1,400 M.Y. AGO Granitic gneisses, found through much of southeast AREAIV-TEXASANDEASTERN em New Mexico, were grouped into the Chaves grani NEW MEXICO tic terrane by Muehlberger and others (1967). It now seems desirable to extend this unit into the Texas This area, shown on figure 4, was the subject of the Panhandle on the basis of scattered unpublished age first successful study of the buried basement rocks of determinations (by Mobil Research and Development a large region. Flawn (1956) was able to show that con Corp.) and petrographic similarities of rocks encoun sistently mappable units could be recognized over large tered. These rocks have yielded ages in the. 1,400 m.y. areas by the petrographic study of well samples. Virtu range, the oldest ages known in Texas. Some of the ally no isotopic ages were available at that time, and ages measured reflect periods of metamorphism, but the sequence of events and relative ages of the units others are probably close to the time of original intru were later modified when ages became available. The sion. Differentiation of rock units within the area is not dating of both surfac~ and subsurface samples by Was justified on the basis of the available data. serburg and 9thers (1962) and Muehlberger ~d others The Sierra Grande terrane of northeastern New (1966) made possible the determination of the sequence Mexico and the Texas Panhandle (Muehlberger and of events. Later, largely unpublished geochronological others, 1967) is the oldest of the large areas underlain work on well samples has refined this timing of igneous by anorogenic granite. These rocks are distinguished and metamorphic activity, but no major modifications from older units by the absence of metamorphic fea of the published data are justified at this time. tures and by their more silicic chemical composition. C12 CORRELATION OF PRECAMBRIAN ROCKS OF THE UNITED STATES AND MEXICO OKLAHOMA 100 200 KILOM ETERS f_r...... ____.,.. ~ r( EXPLANATION 1100-- ~ 1400 m.y. (some . RAGGEDY MOUNTAIN 1350 m.y. RED RIVER UPLIFT - TILLMAN possibly older) CHAVES' GRANITE AND GABBRO METAMORPHIC GROUP GRANITI C GN EISS TORRANCE1 750 (7) m.y. DEVILS RIVER UPLIFT 1200m.y.• PANHANDLE' 1600m.y . ~ 0 METAMORPHIC ROCKS METARHYOLITE RHYOLITES ~ 1000m . y .~ FRANKLIN MOUNTAINS 1200m.y.• AMARILLO' AND 1600 m.y. GRANITIC GNEISS IGNEOUS ROCKS RELATED GRANITES 1000-- ~ DEBACA-SWISHER 1 1250(?)m.y.• CARRIZO MOUNTAIN GROUP --- INFERRED BASEMENT 1100m.y. METASEDIMENTARY METAMORPHIC ROCKS CONTACT - Dashed AND BASALTIC ROCKS where questionable 1300m.y.• SIERRA GRANDE1 1050-- ~ LLANO PROVINCE AND RELATED AREA OF EXPOSED ROCKS 1200 m.y. ROCKS ANOROGENIC GRANITES 1Names of terranes FIGURE 4.~ketch geologic map of basement rocks in Texas and eastern New Mexico. Unpattemed areas have no control. Well control essentially that of Bayley and Muehlberger (1968). GEOLOGY AND GEOCHRONOLOGY OF PRECAMBRIAN ROCKS C13 Rb-Sr data from several published and unpublished de The oldest of two metamorphic units is the Valley terminations of whole rocks, ·feldspars, and micas form Spring Gneiss. It is overlain by the Packsaddle Schist, an isochron indicating an age of about 1,300 m.y. Ap which has a measured thickness of 7,330 m and is com parent ages on some rhyolites that are petrographically po&ed of hornblende, graphite, biotite, muscovite, and ·and geographically inseparable from the younger actinolite schists; marble anc;l various leptites also make Panhandle volcanic terrane indicate that volcanism also up a substantial part of the Packsaddle section. These occurred during this period. two units form the country rock for the third unit, The metamorphic rocks called the Red River mobile which is composed of a variety of granitic intrusions. belt by Flawn (1956) and the Tillman Metasedimentary The Valley Spring Gneiss has yielded an age of about Group by Ham and others (1964) remain an unresolved 1,160±30 m.y. (Zartman, 1965). Foliated granitic intru problem. Rocks grouped under these names have sive rocks (Big Branch Gneiss and Red Mountain yielded metamorphic ages from 1,380 m.y. to about Gneiss) that cut the Valley Spring and lower Packsad 1,000 m.y. (Wasserburg and others, 1962; and R. E. dle have yielded a Rb-Sr isochron age of 1,167 ± 12 m.y. Denison, unpub. data, 1981). The rocks around the (Garrison and others, 1978; Garrison and others, 1979). Muenster arch are now believed to be related in time These· results suggest that the Packsaddle Schist was of metamorphism to those in the'Llano province. Rocks deposited during the relatively narrow time span be to the west, along the Red River uplift, are older, but tween 1,190 and 1,155 m.y. ago. All these older rocks their relationship to surrounding rocks is not known. were intruded by massive plutonic granites such as the Town Mountain Granite about 1,060 m.y. ago, near the ROCKS FORMED 1,000 TO 1,200 M.Y. AGO end of an episode of regional metamorphism (Zartman, 1964). A sequence of rhyolites and comagmatic granites was The Van Hom area of western Texas is underlain extruded and emplaced over much of the Texas by a wide variety of metaigneous and metase4imentary Panhandle and far eastern New Mexico about 1,180±20 rocks (King and Flawn, 1953; King, 1965)-. Dating of m.y. ago. The age of this extensive rhyolite field, the these rocks, the Carrizo Mountain Group, indicates a Panhandle volcanic terrane, is known from Rb-Sr period of regional metamorphism ~bout 1,000 m.y. ago whole-rock isochron studies. It covers more than 52,000 with the development of pegmatites (Denison and 2 km despite considerable diminution by erosion and others, 1971). The age of deposition of the Carrizo partial covering by younger rocks. Many of the rhyo Mountain Group has not been clearly defined. The lites preserve delicate ignimbritic features. The as metarhyolites in the Van Hom area :rru;Ly not be as old sociated granites, grouped into the Amarillo granite as the calculated Rb-Sr age of about 1,280 m.y. (Deni terrane, are typical hypersolvus epizonal intrusives; son and Hetherington, 1969), but they appear to be dis micrographic textures are common. The rocks are tinguishably older than the rhyolites in the Franklin leucocratic and are composed almost entirely of quartz Mountains, on the basis of comparative Rb-Sr and and perthite. 207Pbfl00Pb ages. (See also W asserburg and others, A wide variety of Precambrian metamorphic and 1962.) igneous rocks is exposed in the Llano uplift of central The DeBaca terrane and the Swisher diabasic terrane Texas. These rocks and their subsurface equivalents appear to be isochronous. Muehlberger and others are here called the Llano· province. This suite of rocks (1967) and Denison and Hetherington (1969) have re can be traced in the subsurface with some degree of viewed previous information and correlations from the confidence nearly 300 km north of the uplift. The outcrop into the subsurface. Outcrops of these boundary to the west is difficult to define because of metasedimentary and basaltic rocks are found in the sparse control and other complications. To the south northern Van Hom area,. the Franklin Mountains, and and east the Precambrian is buried beneath thick Paleo in small outcrop areas in southeastern New Mexico. In zoic rocks of the Ouachita foldbelt. The geology of the far western Texas the metasedimentary rocks are in Precambrian rocks in the Llano uplift has been sum part demonstrably of marine origin. Northward into the marized by Clabaugh and McGehee (1962) and Garrison subsurface the rocks become increasingly arkosic and and others (1978). The geochronology of certain of the are probably nonmarine. Basaltic rocks associated with rock units has been studied by Zartman (1964, 1965), the metasedimentary units are more common north Delong and Long (1976), and Garrison and others ward. (1979). The time of sedimentation has not been strictly de Three major rock units constitute the Llano province. termined. In the Franklin Mountains metasedimentary C14 CORRE.LATION OF PRECAMBRIAN ROCKS OF THE UNITED STATES AND MEXICO rocks are conformably overlain by rhyolites and in Texas. McGowan and Groat (1971) have shown that the truded by granites that have ages near 1,000 m.y. It unit was deposited as an alluvial fan upon strongly seems probable that the original sedimentary rocks folded, faulted, and dissected Precambrian rocks that were deposited just prior to the extrusion of the rhyo were metamorphosed about 1,000 m.y. ago. The Van lites, perhaps in the interval between 1,100 and 1,000 Hom Sandstone is overlain by the Bliss Sandstone, m.y. ago. which is of Ordovician age in this area. Thus the Van The Franklin Mountains have some exceptionally fine Hom must have been deposited between about 1,000 exposures of Precambrian igneous and metamorphic and 480 m.y. ago. The available data do not permit rocks (Harbour, 1972). Nearly 460 m of rhyolite flows extension of this unit into the subsurface. overlies metasedimentary rocks of the DeBaca terrane and is in turn intruded by diverse granitic stocks and PHANEROZOIC TIME (PALEOZOIC ERA, sills. CAMBRIAN PERIOD) The ages of rhyolites and granites in the Franklin Mountains all fall into a rather narrow range around Areas underlain by the subsurface extension of the 1,000 m.y. (Denison and Hetherington, 1969). These Wichita province igneous rocks (see discussion of Area ages indicate that this is the youngest of the Precam Ill) are found in adjacent parts of the Texas Panhan brian rhyolite-epizonal granite associations. These igne-. dle. Muehlberger and others (1966) reported a rhyolite ous rocks appear to be rather limited in areal extent. yielding an apparent Cambrian age in the central Texas Small isolated outcrops are found about 100 km to the Panhandle, well away from the principal exposures and east and some 150 km to the north of the Franklin subsurface extent in southern Oklahoma. Mountains. This igneous activity evidently did not cover as great an area as the older rhyolite fields. Perhaps a smaller volume of magma erupted; but the AREA V-EASTERN MIDCONTINENT rocks may also have been removed by erosion, or they Area V (fig. 5) is underlain by two widespread base may extend to the south into north-central Mexico ment rock terranes. In the ·eastern part of the area where no information is available. is the subsurface extension of the Grenville province of Canada. To the west of the Grenville province is PROTEROZOIC TIME (INTERVAL OCCURRING a terrane that consists predominantly of granite, rhyo 600-900 M.Y. AGO) lite, trachyte, basalt, and related rocks of middle and late Proterozoic age. METARHYOUTE OF DEVILS RIVER UPUFT A few wells along the Devils River uplift southwest PROTEROZOIC TIME (INTERVAL OCCURRING of the Llano uplift in Texas have penetrated metarhyo 90~1,600 M.Y. AGO) lite. The few isotopic measurements available from these rocks suggest late Precambrian or Early Cambri GRANITE-RHYOUTE TERRANE an ages (Nicholas and Rozendal, 1975; Denison and others, 1977). The rhyolites are underlain in part by Southern Wisconsin, Illinois, Indiana, and the west massive granitic rocks about 1,250 m.y. old that have em parts of Ohio, Kentucky, and Tennessee are under been penetrated in only one well. lain by a vast terrane of essentially unmetamorphosed The best interpretation of the isotopic data is that rhyolitic and trachytic volcanic rocks and epizonal the rhyolites were extruded not less than 725 m.y. ago. granitic rocks. These rocks represent an apparent con The extent of this unit and its significance are not tinuation of the anorogenic terrane to the north in cen known because of sparse control from drill holes; it tral Wisconsin. Van Schmus (1978) found that the Pre would appear to be the youngest Precambrian igneous cambrian basement in central Wisconsin consists in part rock found in the area. Micas from the metarhyolites of 1, 78()....1,800-m.y.-old rhyolitic ignimbrites, grano yield mid to late Paleozoic ages, indicating that they phyric granites, and porphyritic· granites intruded by have been strongly affected by younger metamorphism. 1,500-m.y.-old rapakivi-t~ granites. The anorogenic terrane is extensively developed in the eastern and south-central midcontinent. It :appar THE VAN HORN SANDSTONE ently extends from central Wisconsin southwestward to This sedimentary rock unit may be late Precambrian northern New Mexico and Arizona (Bass, 1960; Zietz or earliest Paleozoic in age. It is geographically re and others, 1966; Muehlberger and others, 1967; stricted to an area north of Van Hom in far western Bickford and Mose, 1975; and others). GEOLOGY AND GEOCHRONOLOGY OF PRECAMBRIAN ROCKS C15 100 200 KILO METER S EXPLANATION SUBSURFACE GRENVILLE PROVINCE ~ FELSIC ROCKS (Undifferentiated) SEDIMENTARY ROCKS INFERRED BASEMENT CONTACT FAULT ZONE MAFIC tGNEOUS ROCKS ---HIGH-ANGLE FAULT BASALTIC RIFT ZONE ---?--- INFERRED BASEMENT FAULT- Queries indicate possible extension GRANITE-RHYOLITE PROVINCE ...... _ ....~ .... ·- THRUST FAULT- Sawteeth on upthrown side FIGURE 5. Sketch geologic map of basement rocks in the Central Interior region east of the Mississippi River. Unpatterned areas have no control. C16 CORRELATION OF PRECAMBRIAN ROCKS OF THE UNITED STATES AND MEXICO The granite-rhyolite terrane of the eastern midconti The best documented of these inferred rifts occurs nent is characterized by an overall homogeneity and in the Michigan Basin. Hinze and others (1975) made relatively subdued magnetic anomaly pattern, suggest a detailed study of the linear gravity and magnetic ing that the area forms a distinct crustal unit of essen anomalies and concluded that they represent a middle tially undeformed volcanic rocks and mainly epizonal Keweenawan rift zone. A recent deep test drilled near granitic rocks. The western boundary of the terrane the center of the basin encountered mafic igneous rocks is drawn near the Iowa-Illinois State line along a dis beneath a thick section of red clastic sedimentary rocks tinct change in magnetic anomaly pattern (Zietz and (Bradley and Hinze, 1976; Van Der Voo and Watts, others, 1966). 1976), thus supporting the rift zone interpretation. The apparent age and petrographic character of the The linear gravity high in eastern Indiana and west granite-rhyolite terrane were described by Lidiak and ern Ohio is also regarded as indicating a rift zone. others (1966). Granitic igneous activity appears to have Three of the six wells to basement along this structure occurred between 1,200 and 1,500 m.y. ago. Most of bottomed in basalt; the other three bottomed in felsi<: the available age determinations, however, are Rb-Sr igneous rocks. Immediately to the south of the rift, two and K-Ar dates on micas, and thus they may be mini micrographic granites have Rb-Sr ages on feldspars of mum ages that have been reduced by later igneous or about 1,125 m.y. The relation of these felsic rocks to metamorphic activity. An unpublished Rb-Sr measure the basalts is not established, but the ages suggest that ment on a micrographic granite from Fulton County. felsic igneous activity also occurred during the develop northern Indiana, yielded an apparent age of 1,480±40 ment of the rift zones in middle Keweenawan time. m.y. This age corresponds to the age of the Wolf River Northwest-trending gravity and magnetic highs out batholith of central Wisconsin (Van Schmus and others, line an inferred belt of basalt or gabbroic igneous rocks 1975) and suggests that granitic igneous activity was in eastern Illinois. Rudman and others (1972) recog widespread at this time. The age of the volcanism is nized an area of magnetic and gravity highs im also uncertain. Apparent ages from rhyolite and mediately to the south in southwestern Indiana and trachyte are between 1,250 and 1,350 m.y. (Lidiak and concluded that the area is underlain by basalt. No base others, 1966). However, the volcanism may be older: ment well control presently exists for this proposed it may date from 1,500 m.y. to possibly 1, 760 ± 10 m.y. structure in Illinois or for its possible extension into ago. Indiana. SEDIMENTARY ROCKS The inferred north-trending rift zone in Kentucky, Tennessee, and Alabama also coincides with gravity U nmetamorphosed to slightly metamorphosed sedi and magnetic highs. The geophysical anomalies suggest mentary rocks of pre-Late Cambrian age occur in the presence of a thick sequence of mafic igneous rocks. widely spaced wells in the eastern midcontinent. At least some of the rocks are of middle Proterozoic age. For example, the Baraboo Quartzite and related rocks RIFI'-RELATED SEDIMENTARY ROCKS of south-central Wisconsin (Dott and Dalziel, 1972) were deposited later than 1,760 m.y. ago. The Baraboo Unmetamorphosed sedimentary rocks that are appar Quartzite and the previously described Sioux Quartzite ently associated with the basaltic rift zones have been of South Dakota are probably correlative and represent encountered in the Michigan Basin (Bradley and Hinze, widespread sedimentation. Similarly, the quartzites an~ 1976), western Ohio, and northern Kentucky. These slates in the subsurface of southern Wisconsin rocks occur beneath Upper Cambrian strata and are (Thwaites, 1931) may have been deposited during this of probable late Proterozoic age. They are inferred to period of time. have been deposited during formation of the rift zone. BASALTIC RIFI' ZONES Other sedimentary rocks. of pre-Late Cambrian age are also present in western Tennessee and Kentucky A series of north- to northwest-trending basement and in southern Illinois near the center of the Illinois rift zones occurs in the granite:;.rhyolite terrane (fig. 5). Basin. They are apparently not a:ssociated with basalts The rifts, which are probably underlain by mafic igne and may be as old as latest Proterozoic. ous rocks, are delineated mainly by linear gravity and magnetic anomalies and by sparse basement well con SUBSURFACE GRENVILLE PROVINCE trol. None of these rocks have been dated, but they are tentatively assigned a middle Keweenawan age The Grenville province of C~a extends ~to the (1,000-1,200 m.y.) because of their general similarities subsurface of the United States near the west end of to rocks of the Central North American rift system. Lake Erie along a series .of prominent south-trending GEOLOGY AND GEOCHRONOLOGY OF PRECAMBRIAN ROCKS C17 gravity and magnetic highs. These anomalies appear to METALLOGENIC SIGNIFICANCE cut and thus postdate the northwest-trending anomalies OF THE .PRECAMBRIAN BASEMENT associated with the rift zone In the Michigan Basin (Hinze and others, 1975). The south-trending anomalies Better understanding of the Precambrian geology of continue into Ohio and form a sharp gradient, separat the Central Interior region is a key to understanding the ev~lution and distribution of its resource systems. ing a series of positive magnetic ~d gravity highs on the east from broader, less intense anomalies on the The shallow volcanic-plutonic complexes. are potentially west (Zietz and .others, 1966). the most important tectonic and metallogenic units of the region. The St. Francois terrane of southeastern Petrographic study and age determinations (Lidiak Missouri constitutes an iron metallogenic province and and others, 1966) show that this sharp gradient coin has in. fact been the source of iron production for more cides with the boundary between a granite-metamor than 150 years. Kiruna-type iron (apatite) and iron-cop phic complex on the east and an older, less deformed terrane on the west. East of the boundary in eastern per deposits, some of them rare-earth enriched, are as Ohio and West Virginia, the basement rocks consist s~ated with the silicic volcanic rocks of the terrane. mainly of mica and hornblende schist and gneiss, two Marginal manganese miner8.lization has occurred in the feldspar granite, and less commonly marble and calc volcanic rocks; hypo-xenothermal veins of W-P~Ag silicate rock. Most of the metamorphic rocks are of am Sn occur in at least one of the plutonic bodies; and late phibolite grade. stage two-mica granites of the terrane are among the most uraniferous granites of North America (Malan Age determinations on micas from gneiss, schist, and 1972). ' granite in parts of Michigan, Ohio, Pennsylvania, and The metallogenesis of the volcanic-plutonic com West Virginia are in the range 800-1,000 m.y. These plexes, as suggested by observations in the St. Fran ages are in good agreement with mica ages determined cois terrane, is intimately related to the complex mag from the Grenville province in Canada. Most of the matic-tectonic processes that produced this extensive ~ca ages do not date the main period of orogeny, but mstead reflect later tectonic or thermal disturbance and anorogenic suite of rocks. Two lines of metallogenic probably deep burial and subsequent uplift. The last evolution are indicated and have the potential for en maip period of metamorphism occurred about 1,100 richments in ore deposits: (1) the ferrous metals, re m.y. ago. (Compare Lidiak and others, 1966.) More re lated to alkaline intermediate magmatism, and (2) W, cent studies by Krogh and Davis (1969) indieate that Ag, Sn, Pb, U, Th, and Fin the late granites (Kisvar regional metamorphism and formation of paragneiss in sanyi, 1976). the northwest Grenville area occurred between 1,500 The metallogenesis of the older metamorphic base and 1,900 m.y. ago. Other periods of Grenville regional ment is not known because of lack of outcrops and no metamorphism occurred about 1,300 and 1,100 m.y. proven ore bodies. By analogies with .Canadian Shield ago. · provinces, however, it may contain complex and varied mineral deposits. The resource potential in the base The Grenville ·Front extends southward into Ken ment complex of Missouri has recently been evaluated tucky and Tennessee (Lidiak and Zietz, 1976). The pre on the basis of drill-hole data (Kisvarsanyi and Kisvar dominant rock types east of the front are granite sanyi, 1977). Among the most interesting possibilities gn~iss, two-feldspar granite, medium:..grade metamor are the layered mafic intrusions, which have a potential phic rock, and anorthosite. Trachyte, rhyolite, basalt, for Fe-Ni-Cu-Co and Pt- Cr-Ti mineralization. The Cen and weakly metamorphosed sedimentary rocks are the tral North American rift system is a favorable site for characteristic rocks west of the front. Locally felsic vol rift-related metallogeny. canic rocks also occur immediately east of the front. _Another important metallogenic aspect of the Pre The Grenville Front is tentatively shown extending into cambrian basement is its tectono-morphologic control Alabama on figure 5. on the emplacement and localization of ore bodies in The only available isotopic age detenninations on the the overlying sedimentary rocks. Major mineral dis subsurface rocks of the Grenville province are the pre tricts in Missouri, Oklahoma, Kansas, and Illinois are viously mentioned K-Ar and Rb-Sr ages on micas. Con located over Precambrian topographic and structural sequently, the period or periods of sedimentation, anor highs and ancient fracture zones (Snyder, 1970; Kisvar thosite intrusion, and granitic plutonism that are shown sanyi, 1977). Although the metals may have been de on the chronometric chart have been inferred. They are rived from multiple sources, at least some of the metals based mainly on regional correlations and extrapola .may have been recycled from a Precambrian source and ~ions from outcrops. redistributed into f18.nking sedimentary basins. Cl8 CORRELATION OF PRECAMBRIAN ROCKS OF THE UNITED STATES AND MEXICO As neaJr-su..riace resowrces aJre depleted, the vast :re Cla.baugh, S. E., and McGehee, R. V., 1SS2, Precambrian :rocks of sowrce potential inherent in the bwried basement rocks Llano region in Geology of the Gulf Coast and central Texas becomes of increasingliy grreater interest, particuJaJrly and guidebook of excursions: Houston Geological Soeiety, p. 82- 78. where depth to basement is not prohibitive to mining. DeLong, S. E., and Long, L. E."', 1M8, Petrology and Rb/Sr age of Precambrian rhyolitic dikes, Llano County, Texas: Geological ~iet;v of AmP.ri,.a Bulletin, v. 87, p. 27&-200. Denison, R. E., ·1sss, Basement :rocks in adjoining parts of Ok lahoma, Kansas, Missouri, and Arkarums: Austin, T~xas, Univ~r Anderson, J. L., and Culler, R. L., 1M8, Geeehemistry and evolution sity of Texas at Austin, Ph. D. thesis, 328 p. of the Wolf River Batholith, a. Late Precambrian rapakivi massif --lm, Basement roclm in the Arbuckle Mountains: Geological in north Wisconsin, U.S.A.: Precambrian Research, v. 7, p. 287- ~iety of America Guidebook 5, Oklahoma Geological Survey, 324. p.~. 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G., 1966, Crustal ages from the Wichita and Arbuckle Mountains, Oklahoma, and study of a continental strip from the Atlantic Ocean to the Rocky the St. Francois Mountains, Missouri: Journal of Geophysical Re- Mountains: Geological Society of America Bulletin, v.. 77, p. search, v. 67, .P· 4011-4020. - 1427-1448. -{.{ US. GOVERNMENT PRINTING OFFICE: 1984-576-049/29,003 REGION NO. 8 Denison and others-GEOLOGY AND GEOCHRONOLOGY OF PRECAMBRIAN ROCKS, CENTRAL INTERIOR UNITED STATES--Geological Survey Professional Paper 1241--C