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[SiO,, in weight percent. Total REE, in parts per million. La,/Yb,, ratio of the chondrite-normalized abundance of lanthanum to that of ytterbium; Eu/Eu%, ratio of determined europium abundance to europium abundance interpolated from the abundances of samarium and gadolinium; Dispersion, standard deviation of L abundance divided by average La abundance; —, no data] Neoproterozoic (Stoeser and Elliott, 1980). Many of the 1.48 to 1.45 Ga igneous intrusions in the St. Francois Mountains terrane have been depicted as roughly circular masses (Kis- varsanyi, 1981) that accordingly are consistent with intraplat« anorogenic magmatism. extend north along the Rocky Mountains throughout New Mexico, Colorado, and southern Wyoming, and form isolated outcrops in north-central Idaho (du Bray and others, 2015). This distribution is inconsistent with these rocks being related to subduction-related magmatism, because it requires that all of these areas, dispersed across the Laurentian craton, were sites of coeval arc magmatism. A geometry that requires coeval subduction-related magmatism at each of these disparate and irregularly oriented locales is implausible. Therefore, the spatial characteristics and distribution of 1.4 Ga igneous rocks through- out the conterminous United States, including those in the St. Francois Mountains terrane, are inconsistent with an arc magmatism genesis.

Table 23 [SiO,, in weight percent. Total REE, in parts per million. La,/Yb,, ratio of the chondrite-normalized abundance of lanthanum to that of ytterbium; Eu/Eu%, ratio of determined europium abundance to europium abundance interpolated from the abundances of samarium and gadolinium; Dispersion, standard deviation of L abundance divided by average La abundance; —, no data] Neoproterozoic (Stoeser and Elliott, 1980). Many of the 1.48 to 1.45 Ga igneous intrusions in the St. Francois Mountains terrane have been depicted as roughly circular masses (Kis- varsanyi, 1981) that accordingly are consistent with intraplat« anorogenic magmatism. extend north along the Rocky Mountains throughout New Mexico, Colorado, and southern Wyoming, and form isolated outcrops in north-central Idaho (du Bray and others, 2015). This distribution is inconsistent with these rocks being related to subduction-related magmatism, because it requires that all of these areas, dispersed across the Laurentian craton, were sites of coeval arc magmatism. A geometry that requires coeval subduction-related magmatism at each of these disparate and irregularly oriented locales is implausible. Therefore, the spatial characteristics and distribution of 1.4 Ga igneous rocks through- out the conterminous United States, including those in the St. Francois Mountains terrane, are inconsistent with an arc magmatism genesis.

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Professional Paper 1866 -etrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks n the St. Francois Mountains Terrane, Southeast Missouri
Professional Paper 1866 -etrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks n the St. Francois Mountains Terrane, Southeast Missouri
Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: U.S. customary units to International System of Units
Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: U.S. customary units to International System of Units
International System of Units to U.S. customary units Conversion Factors
International System of Units to U.S. customary units Conversion Factors
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri Figure 1. Map showing the spatial distribution of Mesoproterozoic igneous rocks in the St. Francois Mountains terrane, southeast Missouri. A, Geochemical and geochronologic sample sites. B, Locations and names of mines and prospects. [Ga, giga-annum (billion year old)]
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri Figure 1. Map showing the spatial distribution of Mesoproterozoic igneous rocks in the St. Francois Mountains terrane, southeast Missouri. A, Geochemical and geochronologic sample sites. B, Locations and names of mines and prospects. [Ga, giga-annum (billion year old)]
Table 1. Relative abundances, delineated from geologic maps of 1.48 to 1.45 Ga igneous rock types in the St. Francois Mountains terrane, southeast Missouri and corresponding sample abundances aggregated by geochemical composition; all data in percent.
Table 1. Relative abundances, delineated from geologic maps of 1.48 to 1.45 Ga igneous rock types in the St. Francois Mountains terrane, southeast Missouri and corresponding sample abundances aggregated by geochemical composition; all data in percent.
[Aleinikoff (2021) presents SHRIMP U-Pb geochronologic data for the analyzed samples]
[Aleinikoff (2021) presents SHRIMP U-Pb geochronologic data for the analyzed samples]
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/Pb ages. [Ma, million years; Ga, billion years] Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/Pb ages. [Ma, million years; Ga, billion years] Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued etrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missour
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued etrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missour
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/2Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/2Pb ages. [Ma, million years; Ga, billion years]|—Continued
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/2Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/2Pb ages. [Ma, million years; Ga, billion years]|—Continued
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missour'
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missour'
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/Pb ages. [Ma, million years; Ga, billion years]|—Continued
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
Figure 2. Representative cathodoluminescence images of zircon and backscattered electron images of titanite from igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Zircon uranium-lead isotope data are plotted on Wetherill (1956) concordia curves, whereas titanite uranium-lead isotope data are plotted on Tera-Wasserburg (1972) concordia curves. Insets show weighted means of selected “’Pb/*Pb ages. [Ma, million years; Ga, billion years]|—Continued
[Errors are | sigma unless otherwise specified. Struckthrough data are omitted from the weighted mean based on percent common Pb. Pb* denotes radiogenic lead. *“Pb/*°*Pb, ratio of the abundances of the mass 204 isotope of lead to that of the mass 206 isotope of lead; %, percent; ?°’Pb/**°Pb, ratio of the abundances of the mass 207 isotope of lead to that of the mass 206 isotope of lead; 7°*Pb/?°°Pb, ratio of the abundances of the mass 208 isotope of lead to that of the mass 206 isotope of lead; °°Pb/?*U, ratio of the abundances of the mass 206 isotope of lead to that of the mass 238 isotope of uranium; *°’Pb, mass 20’ isotope of lead; 7°°Pb, mass 206 isotope of lead; U ppm, uranium abundance in parts per million; Th ppm, thorium abundance in parts per million; ?’Th/?*8U, ratio of the abundances of the mass 232 isotope of thorium to that of the mass 238 isotope of uranium; Ma, million years; *U/?"Pb, ratio of the abundances of the mass 238 isotope of uranium to that of the mass 206 isotope of lead; ?°’Pb/**U, ratio of the abundances of the mass 207 isotope of lead to that of the mass 235 isotope of uranium]
[Errors are | sigma unless otherwise specified. Struckthrough data are omitted from the weighted mean based on percent common Pb. Pb* denotes radiogenic lead. *“Pb/*°*Pb, ratio of the abundances of the mass 204 isotope of lead to that of the mass 206 isotope of lead; %, percent; ?°’Pb/**°Pb, ratio of the abundances of the mass 207 isotope of lead to that of the mass 206 isotope of lead; 7°*Pb/?°°Pb, ratio of the abundances of the mass 208 isotope of lead to that of the mass 206 isotope of lead; °°Pb/?*U, ratio of the abundances of the mass 206 isotope of lead to that of the mass 238 isotope of uranium; *°’Pb, mass 20’ isotope of lead; 7°°Pb, mass 206 isotope of lead; U ppm, uranium abundance in parts per million; Th ppm, thorium abundance in parts per million; ?’Th/?*8U, ratio of the abundances of the mass 232 isotope of thorium to that of the mass 238 isotope of uranium; Ma, million years; *U/?"Pb, ratio of the abundances of the mass 238 isotope of uranium to that of the mass 206 isotope of lead; ?°’Pb/**U, ratio of the abundances of the mass 207 isotope of lead to that of the mass 235 isotope of uranium]
[Errors are | sigma unless otherwise specified. Struckthrough data are omitted from the weighted mean based on percent common Pb. Pb* denotes radiogenic lead. ?*Pb/?"°Pb, ratio of the abundances of the mass 204 isotope of lead to that of the mass 206 isotope of lead; %, percent; 7°’Pb/?Pb, ratio of the abundances of the mass 207 isotope of lead to that of the mass 206 isotope of lead; *°SPb/*°*Pb, ratio of the abundances of the mass 208 isotope of lead to that of the mass 206 isotope of lead; *°°Pb/?*U, ratio of the abundances of the mass 206 isotope of lead to that of the mass 238 isotope of uranium; *°’Pb, mass 2( isotope of lead; 7°°Pb, mass 206 isotope of lead; U ppm, uranium abundance in parts per million; Th ppm, thorium abundance in parts per million; *°Th/?*8U, ratio of the abundances of the mass 232 isotope of thorium to that of the mass 238 isotope of uranium; Ma, million years; *U/°"°Pb, ratio of the abundances of the mass 238 isotope of uranium to that of the mass 206 isotope of lead; ?°’Pb/*°U, ratio of the abundances of the mass 207 isotope of lead to that of the mass 235 isotope of uranium]
[Errors are | sigma unless otherwise specified. Struckthrough data are omitted from the weighted mean based on percent common Pb. Pb* denotes radiogenic lead. ?*Pb/?"°Pb, ratio of the abundances of the mass 204 isotope of lead to that of the mass 206 isotope of lead; %, percent; 7°’Pb/?Pb, ratio of the abundances of the mass 207 isotope of lead to that of the mass 206 isotope of lead; *°SPb/*°*Pb, ratio of the abundances of the mass 208 isotope of lead to that of the mass 206 isotope of lead; *°°Pb/?*U, ratio of the abundances of the mass 206 isotope of lead to that of the mass 238 isotope of uranium; *°’Pb, mass 2( isotope of lead; 7°°Pb, mass 206 isotope of lead; U ppm, uranium abundance in parts per million; Th ppm, thorium abundance in parts per million; *°Th/?*8U, ratio of the abundances of the mass 232 isotope of thorium to that of the mass 238 isotope of uranium; Ma, million years; *U/°"°Pb, ratio of the abundances of the mass 238 isotope of uranium to that of the mass 206 isotope of lead; ?°’Pb/*°U, ratio of the abundances of the mass 207 isotope of lead to that of the mass 235 isotope of uranium]
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri Figure 3. CA-ID-TIMS and SHRIMP-RG zircon Pb/Pb weighted mean and U/Pb concordia plots for two samples of Mesoproterozoic igneous rock from the St. Francois Mountains terrane, southeast Missouri. Preferred dates shown in bold type. [CA-ID-TIMS, chemical abrasion-isotope dilution-thermal ionization mass spectrometry; SHRIMP-RG, sensitive high resolution ion microprobe-reverse geometry; Pb, lead; U, uranium]
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri Figure 3. CA-ID-TIMS and SHRIMP-RG zircon Pb/Pb weighted mean and U/Pb concordia plots for two samples of Mesoproterozoic igneous rock from the St. Francois Mountains terrane, southeast Missouri. Preferred dates shown in bold type. [CA-ID-TIMS, chemical abrasion-isotope dilution-thermal ionization mass spectrometry; SHRIMP-RG, sensitive high resolution ion microprobe-reverse geometry; Pb, lead; U, uranium]
EXPLANATION
EXPLANATION
[U ppm, uranium in parts per million; Th ppm, thorium in parts per million; Th/U, ratio of thorium and uranium abundances; **U/?Pb, ratio of the abundances of the mass 238 isotope of uranium to that of the mass 206 isotope of lead; +/- 2SE, two standard errors; 7°’Pb/?"Pb, ratio of the abundances of the mass 207 isotope of lead to that of the mass 206 isotope of lead; Rho, correlation coefficient between “*U/Pb and 7°’Pb/?*Pb. Values in italics are outliers not used in age calculations]
[U ppm, uranium in parts per million; Th ppm, thorium in parts per million; Th/U, ratio of thorium and uranium abundances; **U/?Pb, ratio of the abundances of the mass 238 isotope of uranium to that of the mass 206 isotope of lead; +/- 2SE, two standard errors; 7°’Pb/?"Pb, ratio of the abundances of the mass 207 isotope of lead to that of the mass 206 isotope of lead; Rho, correlation coefficient between “*U/Pb and 7°’Pb/?*Pb. Values in italics are outliers not used in age calculations]
' Time-resolved analysis (TRA) session number. Correction factor (F) value is given with +2SE uncertainty 2 U/Pb ratio corrected for instrumental mass-bias using BLR-| titanite standard (see text for details). > Ratio corrected for Pb-isotope fractionation using NIST 610 glass standard. [U ppm, uranium in parts per million; Th ppm, thorium in parts per million; Th/U, ratio of thorium and uranium abundances; 7*U/?*Pb, ratio of the abundances of the mass 238 isotope of uranium to that of the mass 206 isotope of lead; +/- 2SE, two standard errors; *°’Pb/*Pb, ratio of the abundances of the mass 207 isotope of lead to that of the mass 206 isotope of lead; Rho, correlation coefficient between *8U/"°Pb and 7"’Pb/*Pb. Values in italics are outliers not used in age calculations]
' Time-resolved analysis (TRA) session number. Correction factor (F) value is given with +2SE uncertainty 2 U/Pb ratio corrected for instrumental mass-bias using BLR-| titanite standard (see text for details). > Ratio corrected for Pb-isotope fractionation using NIST 610 glass standard. [U ppm, uranium in parts per million; Th ppm, thorium in parts per million; Th/U, ratio of thorium and uranium abundances; 7*U/?*Pb, ratio of the abundances of the mass 238 isotope of uranium to that of the mass 206 isotope of lead; +/- 2SE, two standard errors; *°’Pb/*Pb, ratio of the abundances of the mass 207 isotope of lead to that of the mass 206 isotope of lead; Rho, correlation coefficient between *8U/"°Pb and 7"’Pb/*Pb. Values in italics are outliers not used in age calculations]
' Corrected for initial Th/U disequilibrium using radiogenic ***Pb and Th/U[magma] = 4.0. * Isotopic dates calculated using A7°U = 1.55125E-10 (Jaffey and others, 1971) and 4?°U = 9.8485E-10 (Jaffey and others, 1971). > Corrected for initial Pa/U disequilibrium using initial fraction activity ratio [?*'Pa]/[?°U] = 1.1. ‘Th contents calculated from radiogenic 7°*Pb and °Th-corrected ?°°Pb/?*U date of the sample, assuming concordance between U-Pb Th-Pb system > Total mass of radiogenic Pb. ° Total mass of common Pb. 7 Ratio of radiogenic Pb (including ?°*Pb) to common Pb. 8 Measured ratio corrected for fractionation and spike contribution only. 9 Meacired ratings corrected for fractionation tracer and blank [°°Pb/?8U <Th> age, Ma, age in millions of years indicated by the ratio of the abundances of the mass 206 isotope of lead to that of the mass 238 isotope of uranium corrected for initial Th/U disequilibrium; +20, plus or minus 2-sigma age uncertainty, millions of years; *°’Pb/?°U age, Ma, age in millions of years indicated by the ratio of the abundances of the mass 207 isotope of lead to that of the mass 235 isotop of uranium; *°’Pb/*°°U <ThPa> age, Ma, age indicated by the ratio of the abundances of the mass 207 isotope of lead to that of the mass 206 isotope of lead corrected for initial Pa/U disequilibrium; Th/U, ratio of the abundances of thorium and uranium; Pb*, radiogenic lead; Pb*/Pb, ratio of the abundance of radiogenic lead to that of common lead; ?°°Pb/*“Pb, ratio of the abundances of the mass 206 isotope of lead t that of the mass 204 isotope of lead; ?°°Pb/**8U, ratio of the abundances of the mass 206 isotope of lead to that of the mass 238 isotope of uranium; %, percent; ?°’Pb/**°U, ratio of the abundances of the mass 20 isotope of lead to that of the mass 235 isotope of uranium; *°’Pb/***Pb, ratio of the abundances of the mass 207 isotope of lead to that of the mass 206 isotope of lead]
' Corrected for initial Th/U disequilibrium using radiogenic ***Pb and Th/U[magma] = 4.0. * Isotopic dates calculated using A7°U = 1.55125E-10 (Jaffey and others, 1971) and 4?°U = 9.8485E-10 (Jaffey and others, 1971). > Corrected for initial Pa/U disequilibrium using initial fraction activity ratio [?*'Pa]/[?°U] = 1.1. ‘Th contents calculated from radiogenic 7°*Pb and °Th-corrected ?°°Pb/?*U date of the sample, assuming concordance between U-Pb Th-Pb system > Total mass of radiogenic Pb. ° Total mass of common Pb. 7 Ratio of radiogenic Pb (including ?°*Pb) to common Pb. 8 Measured ratio corrected for fractionation and spike contribution only. 9 Meacired ratings corrected for fractionation tracer and blank [°°Pb/?8U <Th> age, Ma, age in millions of years indicated by the ratio of the abundances of the mass 206 isotope of lead to that of the mass 238 isotope of uranium corrected for initial Th/U disequilibrium; +20, plus or minus 2-sigma age uncertainty, millions of years; *°’Pb/?°U age, Ma, age in millions of years indicated by the ratio of the abundances of the mass 207 isotope of lead to that of the mass 235 isotop of uranium; *°’Pb/*°°U <ThPa> age, Ma, age indicated by the ratio of the abundances of the mass 207 isotope of lead to that of the mass 206 isotope of lead corrected for initial Pa/U disequilibrium; Th/U, ratio of the abundances of thorium and uranium; Pb*, radiogenic lead; Pb*/Pb, ratio of the abundance of radiogenic lead to that of common lead; ?°°Pb/*“Pb, ratio of the abundances of the mass 206 isotope of lead t that of the mass 204 isotope of lead; ?°°Pb/**8U, ratio of the abundances of the mass 206 isotope of lead to that of the mass 238 isotope of uranium; %, percent; ?°’Pb/**°U, ratio of the abundances of the mass 20 isotope of lead to that of the mass 235 isotope of uranium; *°’Pb/***Pb, ratio of the abundances of the mass 207 isotope of lead to that of the mass 206 isotope of lead]
Table 7. Summary of stratigraphic relations and new U-Pb ages for Mesoproterozoic igneous rocks in the St. Francois Mountains terrane, southeast Missouri.
Table 7. Summary of stratigraphic relations and new U-Pb ages for Mesoproterozoic igneous rocks in the St. Francois Mountains terrane, southeast Missouri.
'Van Schmus and others (1996) list samples from cores according to the drill hole name. Although we used a similar naming convention, it is not known if the same units were sampled within the drill core. Thus, age comparisons are made only on samples collected at outcrops. [TIMS, thermal ionization mass spectrometry; CA-TIMS, chemical abrasion-thermal ionization mass spectrometry]
'Van Schmus and others (1996) list samples from cores according to the drill hole name. Although we used a similar naming convention, it is not known if the same units were sampled within the drill core. Thus, age comparisons are made only on samples collected at outcrops. [TIMS, thermal ionization mass spectrometry; CA-TIMS, chemical abrasion-thermal ionization mass spectrometry]
Figure 4. Compilation of age data for Mesoproterozoic igneous rocks in the St. Francois Mountains terrane, southeast Missouri. A, Relative probability plot of all high precision ages displaying two major episodes of magmatism (Harrison and others, 2000; Lowell and Ram, 1999; Ramo and others, 1994; Thomas and others, 2012; this study). B, Comparison of ages (+ 2-sigma errors) for samples of approximately 1400 Ma extrusive and intrusive rocks, each shown in chronologic order. Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missour'
Figure 4. Compilation of age data for Mesoproterozoic igneous rocks in the St. Francois Mountains terrane, southeast Missouri. A, Relative probability plot of all high precision ages displaying two major episodes of magmatism (Harrison and others, 2000; Lowell and Ram, 1999; Ramo and others, 1994; Thomas and others, 2012; this study). B, Comparison of ages (+ 2-sigma errors) for samples of approximately 1400 Ma extrusive and intrusive rocks, each shown in chronologic order. Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missour'
[N, number of samples; Pl, plagioclase; AFS, alkali feldspar; Qtz, quartz; Hbl, hornblende; Cpx, clinopyroxene; Bt, biotite; Opq, opaque Fe-Ti oxides; — species not present]
[N, number of samples; Pl, plagioclase; AFS, alkali feldspar; Qtz, quartz; Hbl, hornblende; Cpx, clinopyroxene; Bt, biotite; Opq, opaque Fe-Ti oxides; — species not present]
Table 10. Identification and characteristics of igneous rock samples from the St. Francois Mountains terrane, southeast Missouri for which representative geochemical analyses are presented by du Bray and others (2018b) and Granitto and others (2018).—Continued
Table 10. Identification and characteristics of igneous rock samples from the St. Francois Mountains terrane, southeast Missouri for which representative geochemical analyses are presented by du Bray and others (2018b) and Granitto and others (2018).—Continued
Figure 5. Quartz-alkali feldspar-plagioclase ternary diagram showing modal compositions of 1.48 to 1.45 billion year old granitoid intrusions in the St. Francois Mountains terrane, southeast Missouri. Data from Bickford and others (1981) and Kisvarsanyi (1972). Classification grid and rock names are from Streckeisen (1976) Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missour
Figure 5. Quartz-alkali feldspar-plagioclase ternary diagram showing modal compositions of 1.48 to 1.45 billion year old granitoid intrusions in the St. Francois Mountains terrane, southeast Missouri. Data from Bickford and others (1981) and Kisvarsanyi (1972). Classification grid and rock names are from Streckeisen (1976) Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missour
Figure 6. Total alkali-silica variation diagrams showing compositions of 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Alkaline-subalkaline dividing line from Irvine and Baragar (1971). Extrusive rock classification grid from Le Maitre (1989). Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 6. Total alkali-silica variation diagrams showing compositions of 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Alkaline-subalkaline dividing line from Irvine and Baragar (1971). Extrusive rock classification grid from Le Maitre (1989). Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 7. Variation diagrams showing molar major-oxide compositions of 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri as a function of relative alumina and alkali saturation. Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 7. Variation diagrams showing molar major-oxide compositions of 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri as a function of relative alumina and alkali saturation. Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 8. Na,0 + K,0 —Ca0 relative to SiO, variation diagram showing the compositions of 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri relative to boundaries between alkalic, alkali-calcic, calc-alkalic, and calcic rock series. Boundaries between various rock series from Frost and others (2001). Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 8. Na,0 + K,0 —Ca0 relative to SiO, variation diagram showing the compositions of 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri relative to boundaries between alkalic, alkali-calcic, calc-alkalic, and calcic rock series. Boundaries between various rock series from Frost and others (2001). Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
[Units with compositions transitional between more than one category are listed in each appropriate category. Entries in parentheses represent reclassification of unit compositions based on the data of du Bray and others (2018b) and the classification schema of Le Maitre (1989)]
[Units with compositions transitional between more than one category are listed in each appropriate category. Entries in parentheses represent reclassification of unit compositions based on the data of du Bray and others (2018b) and the classification schema of Le Maitre (1989)]
[Units with compositions transitional between more than one category are listed in each appropriate category. Entries in parentheses represent reclassification of unit compositions based on the data of du Bray and others (2018b) and the classification schema of Le Maitre (1989)]
[Units with compositions transitional between more than one category are listed in each appropriate category. Entries in parentheses represent reclassification of unit compositions based on the data of du Bray and others (2018b) and the classification schema of Le Maitre (1989)]
Figure 9. FeQ*/(FeO* + MgO) variation diagram showing the composition of 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri relative to boundaries between ferroan and magnesian rocks as well as between tholeiitic and calc-alkaline rocks. Ferroan-magnesian boundary from Frost and others (2001); tholeiitic-calc-alkaline boundary from Miyashiro (1974). Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 9. FeQ*/(FeO* + MgO) variation diagram showing the composition of 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri relative to boundaries between ferroan and magnesian rocks as well as between tholeiitic and calc-alkaline rocks. Ferroan-magnesian boundary from Frost and others (2001); tholeiitic-calc-alkaline boundary from Miyashiro (1974). Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 10. Ternary AFM (Na,0+K,0—Fe0*—MgQ) diagram showing compositions of 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Calc-alkaline and tholeiitic trend lines from Irvine and Baragar (1971). A. Extrusive and hypabyssal intrusive rocks
Figure 10. Ternary AFM (Na,0+K,0—Fe0*—MgQ) diagram showing compositions of 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Calc-alkaline and tholeiitic trend lines from Irvine and Baragar (1971). A. Extrusive and hypabyssal intrusive rocks
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri Figure 11. Variation diagrams showing abundances of major oxides (weight percent) in 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Field boundaries on K,0 relative to SiO, diagram from Le Maitre (1989); high-potassium shoshonitic dividing line from Ewart (1982). For comparison, dashed green lines delineate the compositional fields defined by Mesoproterozoic intrusive rocks of the conterminous United States (du Bray and others, 2018a).—Continued
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri Figure 11. Variation diagrams showing abundances of major oxides (weight percent) in 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Field boundaries on K,0 relative to SiO, diagram from Le Maitre (1989); high-potassium shoshonitic dividing line from Ewart (1982). For comparison, dashed green lines delineate the compositional fields defined by Mesoproterozoic intrusive rocks of the conterminous United States (du Bray and others, 2018a).—Continued
[SiO,, in weight percent. Total REE, in parts per million. La,/Yb,, ratio of the chondrite-normalized abundance of lanthanum to that of ytterbium; Eu/Eu’, rati of determined europium abundance to europium abundance interpolated from the abundances of samarium and gadolinium; Dispersion, standard deviation of I abundance divided by average La abundance; —, no data]
[SiO,, in weight percent. Total REE, in parts per million. La,/Yb,, ratio of the chondrite-normalized abundance of lanthanum to that of ytterbium; Eu/Eu’, rati of determined europium abundance to europium abundance interpolated from the abundances of samarium and gadolinium; Dispersion, standard deviation of I abundance divided by average La abundance; —, no data]
Figure 12. Representative chondrite-normalized rare earth element patterns for 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Chondrite abundances from Anders and Ebihara (1982). Truncated pattern segments indicate missing data.—Continued Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 12. Representative chondrite-normalized rare earth element patterns for 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Chondrite abundances from Anders and Ebihara (1982). Truncated pattern segments indicate missing data.—Continued Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 13. Comparison of representative chondrite-normalized rare earth element patterns for 1.48 to 1.45 billion year old extrusive and hypabyssal intrusive rocks in the St. Francois Mountains terrane, southeast Missouri, compiled from all data for these rocks (fig. 12). Chondrite abundances from Anders and Ebihara (1982). Discontinuous patterns indicate missing data.
Figure 13. Comparison of representative chondrite-normalized rare earth element patterns for 1.48 to 1.45 billion year old extrusive and hypabyssal intrusive rocks in the St. Francois Mountains terrane, southeast Missouri, compiled from all data for these rocks (fig. 12). Chondrite abundances from Anders and Ebihara (1982). Discontinuous patterns indicate missing data.
Figure 14. Representative primitive-mantle-normalized (Sun and McDonough, 1989) trace element diagrams for igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Discontinuous patterns indicate missing data. Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 14. Representative primitive-mantle-normalized (Sun and McDonough, 1989) trace element diagrams for igneous rocks in the St. Francois Mountains terrane, southeast Missouri. Discontinuous patterns indicate missing data. Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri
Figure 15. Comparison of representative primitive-mantle-normalized (Sun and McDonough, 1989) trace element patterns for 1.48 to 1.45 billion year old extrusive and hypabyssal intrusive rocks in the St. Francois Mountains terrane, southeast Missouri. Discontinuous patterns indicate missing data.
Figure 15. Comparison of representative primitive-mantle-normalized (Sun and McDonough, 1989) trace element patterns for 1.48 to 1.45 billion year old extrusive and hypabyssal intrusive rocks in the St. Francois Mountains terrane, southeast Missouri. Discontinuous patterns indicate missing data.
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri Figure 17. Variation diagrams showing that compositions of igneous rocks in the St. Francois Mountains terrane, southeast Missouri are consistent with primary magmas being variably contaminated by crustal assimilants. A, P,0,/K,0 relative to SiO, for extrusive and hypabyssal intrusive rocks. B, P,0,/K,0 relative to SiO, for phaneritic intrusive rocks. C, CaO/AlI,O, relative to SiO, for extrusive and hypabyssal intrusive rocks. D, CaO/AI,0, relative to Si0,. for phaneritic intrusive rocks. [P,0,, phosphorous pentoxide; K,0, potassium oxide; Sid, silicon dioxide; CaO, calcium oxide; Al,0,, aluminum oxide] BF
Petrology and Geochronology of 1.48 to 1.45 Ga Igneous Rocks in the St. Francois Mountains Terrane, Southeast Missouri Figure 17. Variation diagrams showing that compositions of igneous rocks in the St. Francois Mountains terrane, southeast Missouri are consistent with primary magmas being variably contaminated by crustal assimilants. A, P,0,/K,0 relative to SiO, for extrusive and hypabyssal intrusive rocks. B, P,0,/K,0 relative to SiO, for phaneritic intrusive rocks. C, CaO/AlI,O, relative to SiO, for extrusive and hypabyssal intrusive rocks. D, CaO/AI,0, relative to Si0,. for phaneritic intrusive rocks. [P,0,, phosphorous pentoxide; K,0, potassium oxide; Sid, silicon dioxide; CaO, calcium oxide; Al,0,, aluminum oxide] BF
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