BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL.. 43. PP. 965-992:14 FIGS. DECEMBER 30. 1932 INTRUSIVE RELATIONSHIP OP THE GRANITE TO THE RHYOLITE (PORPHYRY) OF SOUTHEASTERN MISSOURI * BY W. A. TARR (Bead before the Geological Society December 81,1931) CONTENTS Page Introduction ................................................................................................................ 965 General geology .......................................................................................................... 968 Distribution of granites and porphyries............................................................... 974 Intrusive relationship of the granite to the porphyry....................................... 974 General statement ............................................................................................ 974 Localities where sharp contacts are found................................................... 975 General statement...................................................................................... 975 Knoblick M ountain.................................................................................... 976 Graniteville ................................................................................................ 980 Cornwall ....................................................................................................... 981 Matthews Mountain ................................................................................... 983 Areas of probable intrusive contacts ........................................................... 987 Cedar Creek ................................................................................................. 987 Mount Devon ............................................................................................... 987 Buckner Mountain...................'................................................................. 987 Cold water, Wayne County ....................................................................... 987 Contacts in and around the large central area of granite......................... 987 General discussion ..................................................................................... 987 Evans Mountain and hill to the w e s t..................................................... 988 Skrainka Hill, Bald Mountain, and Fizzell Branch....................... 989 Stouts Creek south of Roselle ................................................................ 990 Stono Mountain .......................................................................................... 990 Stouts Creek “shut-in” ............................................................................. 990 Summary ..................................................................................................................... 991 I ntroduction Although the general distribution of the igneous rocks of southeastern Missouri has been known since the publication of Schoolcraft’s report, “Lead Mines of Missouri,” in 1819, they were first studied and mapped in detail by Erasmus Haworth about 70 years later. In one of his papers, * Manuscript received by the Secretary of the Society December 31, 1931. (965) Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/43/4/965/3415045/BUL43_4-0965.pdf by guest on 02 October 2021 966 W . A. TAKE----RELATIONSHIP OF GRANITE TO RHYOLITE published in 1888,1 he states that “a comparative study of the porphyries and granites of this district reveals the fact that there is no sharp division line between the two, at least, so far as can be judged from the hand specimens.” He further raised the question as to whether these rocks in Missouri illustrated “the gradual transition from a holocrystalline, coarse­ grained rock through the fine-grained ones to those which originally were vitrophyres.'” He concluded, tentatively at that time, that such a grada­ tion existed. Haworth’s next contribution was a paper2 in which he presented the arguments in favor of an Archean age and an igneous origin for these crystalline rocks. The Missouri State Report on the Iron Mountain Quadrangle was published in January, 1894, in which Haworth briefly discussed (pp. 15-27) the igneous rocks of the quadrangle. He concluded (pp. 24-25) that the granites and porphyries are gradational in their relationship, and that they have different textures in different parts of the same magma because of different conditions during solidification. He says: “There are literally hundreds of places where the phenomenon 3 can be observed, with only here and there one in the whole Missouri Archean which bears evidence of the granite having been forced up through the porphyry.” He cites various localities where gradation is found. The final summary of Haworth’s work, which extended over several years and, in considerable part, at least, was done independently, appeared in 1895.4 Since then, no important contributions to the igneous history of the State have been made; only a few brief notes have appeared in miscellaneous reports, most of which have incorporated material from Haworth’s work on the crystalline rocks. Although the entire trend of Haworth’s thought in his last paper is in favor of a gradational relationship between these two groups of rocks and he devotes considerable space in all to proving it, he cites one locality, 2 miles south of Cornwall in Madison County, in which he thinks the granite is intrusive. Also, he suggests, but does not state positively, that three small granite outcrops on Black River in Reynolds County might “represent independent eruptions which took place after the surround- 1 Erasmus Haworth: A contribution to the Archean geology of Missouri, University Press, State University of Minnesota, 1888, pp. 1-40. See also : Am. Geol., vol. 1, 1888, pp. 280-297, 363-382 ; Johns Hopkins Univ. Circ., vol. 7, 1888, pp. 70-71. 2 Erasmus Haworth : The age and origin of the crystalline rocks of Missouri. Mis­ souri Geol. Survey Bull. no. 5, 1891, pp. 5-42. 8 1, e., gradation. * Erasmus Haworth : Crystalline rocks of Missouri. Missouri Geol. Survey, vol. 8, 1895, pp. 81-224, pis. 1-30, with map of the area. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/43/4/965/3415045/BUL43_4-0965.pdf by guest on 02 October 2021 INTRODUCTION 967 ing masses 5 were formed/’6 a conclusion in which Dake 7 concurs. On pages 209-219 of his paper, he goes into detail as to localities where grada­ tion may be seen. To make Haworth’s interpretation of the relationship clear the following quotations are needed: “Early in the course of field work, it was decided to advance as a working hypothesis the idea that the granites and the porphyries belong practically to the same general period of eruption, and that in many cases, from a particular magma a granite was produced in one portion and a porphyry in another.8 It was not thought that this was true in every case of contact between the two rocks, but that it probably was in a majority of cases. Since it was produced the hypothesis has been strengthened by many observations, and it is now offered as the most probable explanation for the intimate relations of the two kinds of rocks.” 9 On page 218 of the same report, after stating that some granites may be intrusive, as indicated above, the following statement occurs: “It is not to be understood that all the granites in the big area were brought to the surface at once; but rather that the granites and the porphyries were formed simultaneously and came from the same general magma, and conse­ quently are of the same geological age. It is therefore useless to attempt to decide which is the older, the granite or the porphyry.10 This view is placed in contrast with the one that the two types of rocks are of two different periods, and possibly of different origins.” In the next quotation, however, which represents the closing sentences of the paragraph quoted above, Haworth recognizes that there were prob­ ably different eruptions of both porphyries and granites which, if true, could mean only that certain of the igneous rocks are younger than others and thus that they are of different ages. “From statements already made, it will be seen that there are good reasons for believing that many of the prominent porphyry hills are the result of dif­ ferent individual outbursts. In a similar way, different granite areas may also have resulted from a number of different eruptions.” There can be no doubt after reading Haworth’s account of the occur­ rence of these igneous rocks that he fully believed their relationship throughout the area to be dominantly gradational, yet there is also the 5 I. e., the porphyries. 6 Idem, p. 180. 7 €. L. Dake: Potosi and Edgehill Quadrangles, Missouri Bur. Geol. and Mines, vol. 23, series II, 1930, p. 38. 8 Italics are the present writer’s. 9 Erasmus Haworth: Crystalline rocks of Missouri. Missouri Geol. Survey, vol. 8, 1895, p. 209. 10 The italics are the present writer s. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/43/4/965/3415045/BUL43_4-0965.pdf by guest on 02 October 2021 968 W . A. TARR---- RELATIONSHIP OF GRANITE TO RHYOLITE evident attempt to leave open the possibility of another explanation while maintaining his gradational hypothesis. It seems probable that Haworth’s use of textural terms as general rock names has led to some confusion on His part. For example, many of his “granite porphyries,” such as the one found at the Graniteville quarries, would undoubtedly be called