Prepared in cooperation with the State of Vermont, 

Vermont Geological Survey 

Provisional Zircon and Monazite Uranium-Lead

Geochronology for Selected Rocks From Vermont 

By John N. Aleinikoff, Nicholas M. Ratcliffe, and Gregory J. Walsh

Open-File Report 2011–1309

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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Suggested citation:

Aleinikoff, J.N., Ratcliffe, N.M., and Walsh, G.J., 2011, Provisional zircon and monazite uranium-lead 

geochronology for selected rocks from Vermont: U.S. Geological Survey Open-File Report 2011–1309, 

46 p., available only online at http://pubs.usgs.gov/of/2011/1309/. 

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endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.
ii

Contents

Introduction.................................................................................................................................................... 1

Geochronology .............................................................................................................................................. 1

Analytical Methods..................................................................................................................................... 1

Results....................................................................................................................................................... 2

References Cited........................................................................................................................................... 2

Figures

1. Conventional concordia plot of SHRIMP U-Pb data for zircon from hornblende diorite 

gneiss at South Londonderry, Vermont .......................................................................................... 23

2. Conventional concordia plot of SHRIMP U-Pb data for zircon from tonalitic gneiss at 

Baileys Mills, Vermont .................................................................................................................... 24

3. Conventional concordia plot of SHRIMP U-Pb data for zircon from Rawsonville 

trondhjemite gneiss at Bromley Mountain, Vermont ....................................................................... 25

4. Conventional concordia plot of SHRIMP U-Pb data for zircon from Felchville Gneiss

(aplite facies) from Cavendish Gorge, Vermont.............................................................................. 26

5. Conventional concordia plot of SHRIMP U-Pb data for zircon from Felchville Gneiss

(trondhjemite facies) from Felchville, Vermont................................................................................ 27

6. Conventional concordia plot of TIMS U-Pb data for zircon from Bondville metadacite at 

Winhall River bridge in Bondville, Vermont..................................................................................... 28

7. Conventional concordia plot of SHRIMP U-Pb data for zircon from Cole Pond tonalite 

gniess near Cole Pond, Vermont.................................................................................................... 29

8. Conventional concordia plot of SHRIMP U-Pb data for zircon from migmatite gneiss at 

Stratton Mountain, Vermont............................................................................................................ 30

9. Conventional concordia plot of SHRIMP U-Pb data for zircon from fine-grained granodiorite 

of the Ludlow Mountain granodiorite gneiss at Ludlow Mountain, Vermont.................................... 31

10. Conventional concordia plot of SHRIMP U-Pb data for detrital zircon from Okemo Quartzite 

at Ludlow Mountain, Vermont......................................................................................................... 32

11. Conventional concordia plot of TIMS U-Pb data for zircon from College Hill Granite Gneiss 

at Stratton Mountain, Vermont........................................................................................................ 33

12. Conventional concordia plot of TIMS U-Pb data for zircon from granitic gneiss ............................. 34

13. Conventional concordia plot of SHRIMP U-Pb data for zircon from megacrystic augen 

gneiss at Brandon Gap, Vermont ................................................................................................... 35

14. Conventional concordia plot of SHRIMP U-Pb data for zircon from migmatite gneiss in the 

Pine Hill slice, Vermont................................................................................................................... 36

15. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon from Newfane tonalite near 

South Newfane, Vermont................................................................................................................ 37

16. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon from trondhjemite in the 

Barnard Gneiss proper (of Richardson, 1924) north of Proctorsville, Vermont ............................... 38

17. Conventional concordia plot of TIMS U-Pb data for zircon from tonalite gneiss in the

North River Igneous Suite near Bartonsville, Vermont................................................................... 39

18. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon from felsic volcanic layer 

within mafic volcanic rocks in the Cram Hill Formation at Springfield, Vermont.............................. 40

19. Tera-Wasserburg concordia plot SHRIMP U-Pb data for zircon from granite in the Braintree 

Intrusive Complex, Vermont ........................................................................................................... 41
iii

20. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon from trondhjemite of 

the Newport Intrusive Complex, Vermont ....................................................................................... 42

21. Conventional concordia plot of SHRIMP U-Pb data for zircon from granite in the 

Chester dome, Vermont.................................................................................................................. 43

22. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon from Barre Granite, 

Rock of Ages quarry, Barre, Vermont............................................................................................. 44

23. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon and monazite from 

the Black Mountain pluton, Vermont............................................................................................... 45

24. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon from a granite dike near 

Plymouth, Vermont ......................................................................................................................... 46

Tables

1. Locations of zircon samples collected for U-Pb geochronology in support of the “Bedrock 

Geologic Map of Vermont” (Ratcliffe and others, in press) ............................................................... 5

2. Summary of analytical information and ages of samples from Vermont ........................................... 6

3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data 

for zircon and monazite from rocks of Vermont ................................................................................ 8

4. Thermal ionization mass spectrometry (TIMS) uranium-lead (U-Pb) data for zircon from 

rocks of Vermont ............................................................................................................................ 21

Conversion Factors

Multiply By To obtain

Length

micrometer (μm) 0.00003937 inch (in.)

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Volume

cubic meter (m3) 35.31 cubic foot (ft3)

Mass

milligram (mg) 0.00003527 ounce, avoirdupois (oz)

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound avoirdupois (lb)

Horizontal coordinate information is referenced to the World Geodetic System datum of 1984 (WGS 84).
1 

Provisional Zircon and Monazite Uranium-Lead 

Geochronology for Selected Rocks From Vermont

By John N. Aleinikoff, Nicholas M. Ratcliffe, and Gregory J. Walsh

Introduction

This report presents the results of zircon uranium-lead (U-Pb) geochronologic analyses of 

24 rock samples collected and analyzed in support of the “Bedrock Geologic Map of Vermont” 

by Ratcliffe and others (in press). The samples in this study were collected from mapped 

exposures identified while conducting either new, detailed (1:24,000-scale) geologic quadrangle 

mapping or reconnaissance mapping, both of which were used for compilation of the bedrock 

geologic map of Vermont. Nearly all of the collected samples were judged to be igneous rocks 

(either intrusive or extrusive) on the basis of field relations and geochemistry. The one exception 

is the Okemo Quartzite on Ludlow Mountain. Sampling rocks of uncertain origin was avoided as 

much as possible. 

These geochronologic data were used to supplement regional correlations between

igneous suites on the basis of similar geochemistry and geologic mapping. The locations of the 

sample sites and the assignment of the rocks to mapped igneous suites and their members are 

shown on the “Bedrock Geologic Map of Vermont.” The geographic coordinates specifying the 

location of each sample are approximate and were either digitized from point locations shown on 

the 1:100,000-scale geologic map or located in reference to cultural features visible on satellite 

imagery (Google Earth). The coordinates were not obtained by a global positioning system 

(GPS) receiver.

Geochronology

Analytical Methods

Rock samples weighing approximately 10 kilograms (kg) were collected from outcrops in 

Vermont. After the rocks were crushed and pulverized, the material was processed over a 

Wilfley table to concentrate heavy minerals. Further processing included separating the ironbearing minerals on a magnetic separator and concentrating those minerals with densities greater 

than about 3.3 g/cm3

 by sinking them in methylene iodide. Individual grains were handpicked 

using a binocular microscope, mounted in epoxy, ground to nearly half of their thickness to 

expose internal zones, and polished sequentially using 6-μm and 1-μm diamond suspension. All 

of the grains were imaged in transmitted and reflected light using a petrographic microscope and 

in cathodoluminescence (CL) using a scanning electron microscope (SEM). 

Before 1993, zircon samples from Vermont, including four in this study, were dated by 

thermal ionization mass spectrometry (TIMS). Beginning in 1993, Vermont zircon samples, 

including 20 in this study, were dated using the sensitive high resolution ion microprobe 
2 

(SHRIMP). This work was performed using the U.S. Geological Survey/Stanford University 

SHRIMP-reverse geometry (SHRIMP–RG), SHRIMP II at the Research School of Earth 

Sciences (Australian National University, Canberra), or SHRIMP II at the Geological Survey of 

Canada. 

The TIMS analytical procedures followed methods described in Aleinikoff and others 

(1996). The zircons were abraded (Krogh, 1982; Aleinikoff and others, 1990) to remove 

overgrowths and metamict areas. Next, the zircons were dissolved, and uranium and lead were 

extracted from the solution for isotopic analysis. In some cases, the material removed by 

abrasion (dust from an area referred to as the “rim” in the four TIMS concordia plots) was 

collected and analyzed separately in an attempt to determine the metamorphic age. Because 

subsequent CL imagery and SHRIMP analyses showed that many samples had multiple ages of 

metamorphic overgrowths, the TIMS analyses of this dust probably represented composite (or 

mixed) ages, which are likely to be geologically meaningless. Nonetheless, the data are shown 

for an historical perspective and to indicate that younger metamorphic rims were present in these 

samples. The data were reduced using the PBDAT program (Ludwig, 1991) and plotted using 

Isoplot 3 software (Ludwig, 2003). Three samples of zircon that were previously dated by TIMS 

(Ratcliffe and others, 1991) were subsequently re-analyzed by SHRIMP (tables 1, 2). 

The SHRIMP analytical procedures followed the methods described by Williams (1998). 

The locations of the analytical spot (about 25 to 35 μm in diameter and about 1 μm in depth) 

were determined using (1) CL images to distinguish igneous cores and metamorphic overgrowths 

and (2) transmitted light images to avoid imperfections, such as cracks and inclusions. The crater 

was excavated using a primary oxygen beam of about 4 to 6 nanoamps (nA). A magnet cycled 

through the mass stations five times per analysis. Raw data were reduced using the Squid 1 

program (Ludwig, 2001) or Squid 2 program (Kenneth R. Ludwig, Berkley Geochronology 

Laboratory, written commun., 2008) and plotted using Isoplot 3 software (Ludwig, 2003). The 

measured 206Pb/238U ages were referenced to zircon standard R33 (419±1 Ma; Black and others, 

2004). The uranium concentrations were considered to be accurate to ±20 percent. U-Pb data 

were plotted on concordia plots to visually identify coherent age groups. For Precambrian 

samples that might have suffered minor lead loss, ages were determined by calculating a 

weighted average of selected 207Pb/206Pb ages; for Paleozoic samples, ages were determined by 

calculating a weighted average of selected 206Pb/238U ages. Plots of weighted average 

calculations are shown as insets with concordia plots. In some cases, concordant data sets 

permitted calculation of a concordia age (Ludwig, 1980, 1998), as noted on the figures. 

Results

The U-Pb zircon geochronology results of 24 samples are presented chronologically from 

oldest to youngest. Information about the locations and lithologies of all samples is listed in table 

1. Ages are summarized in table 2 and plotted in figures 1 through 24. SHRIMP isotopic data are 

listed in table 3; TIMS isotopic data are listed in table 4. 

References Cited

Aleinikoff, J.N., Horton, J.W., Jr., and Walter, M., 1996, Middle Proterozoic age for the 

Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia: Geological Society of 

America Bulletin, v. 108, p. 1481–1491. 
3 

Aleinikoff, J.N., Schenck, W.S., Plank, M.O., Srogi, L., Fanning, C.M., Kamo, S.L., and 

Bosbyshell, H., 2006, Deciphering igneous and metamorphic events in high grade rocks of the 

Wilmington Complex, Delaware; Morphology, CL and BSE zoning, and SHRIMP U-Pb 

geochronology of zircon and monazite: Geological Society of America Bulletin, v. 118, p. 39–

64. 

Aleinikoff, J.N., Winegarden, D.L., and Walter, M., 1990, U-Pb ages of rims of zircons; A new 

analytical method using the air-abrasion technique: Chemical Geology (Isotope Geoscience 

Section), v. 80, p. 351–363. 

Black, L.P., Kamo, S.L., Allen, C.M., Davis, D.W., Aleinikoff, J.N., Valley, J.W., Mundil, R., 

Campbell, I.H., Korsuch, R.J., Williams, I.S., and Foudoulis, C., 2004, Improved 206Pb/238U 

microprobe geochronology by the monitoring of a trace-element-related matrix effect; 

SHRIMP, ID–TIMS, ELA–ICP–MS and oxygen isotope documentation for a series of zircon 

standards: Chemical Geology, v. 205, p. 115–140. 

Claoué-Long, J.C., Compston, W., Roberts, J., and Fanning, C.M., 1995, Two carboniferous 

ages; a comparison of SHRIMP zircon dating with conventional zircon ages and 40Ar/39Ar 

analysis, in Berggren, W.A., Kent, D.V., Aubrey, M.-P., and Hardenbol, J., eds., 

Geochronology time scales and global stratigraphic correlation: SEPM (Society for 

Sedimentary Geology) Special Publication 54, p. 3–21. 

Krogh, T.E., 1982, Improved accuracy of U-Pb zircon ages by the creation of more concordant 

systems using an air abrasion technique: Geochimica et Cosmochimica Acta, v. 46, p. 485–

494. 

Ludwig, K.R., 1980, Calculation of uncertainties of U-Pb isotope data: Earth and Planetary 

Science Letters, v. 46, p. 212–220. 

Ludwig, K.R., 1991, PBDAT—A computer program for processing Pb-U-Th isotope data, 

version 1.20: U.S. Geological Survey Open-File Report 88–542, 34 p. 

Ludwig, K.R., 1998, On the treatment of concordant uranium-lead ages: Geochimica et 

Cosmochimica Acta, v. 62, p. 665–676. 

Ludwig, K.R., 2001, Squid, version 1.05, A user’s manual: Berkeley Geochronology Center 

Special Publication 2, 16 p. 

Ludwig, K.R., 2003, Isoplot/Ex version 3.00, A geochronological toolkit for Microsoft Excel: 

Berkeley Geochronology Center Special Publication 4, 73 p. 

Paces, J.B., and Miller J.D., Jr., 1993, Precise U-Pb ages of Duluth Complex and related mafic 

intrusions, northeastern Minnesota; Geochronological insights to physical, petrogenetic, 

paleomagnetic, and tectonomagmatic processes associated with the 1.1 Ga Midcontinent Rift 

System: Journal of Geophysical Research, v. 98, p. 13,997–14,013. 

Ratcliffe, N.M., Aleinikoff, J.N., Burton, W.C., and Karabinos, P., 1991, Trondhjemitic, 1.35-

1.31 Ga gneisses of the Mount Holly Complex of Vermont; Evidence for an Elzevirian event 

in the Grenville basement of the United States Appalachians: Canadian Journal of Earth 

Sciences, v. 28, p. 77–93 

Ratcliffe, N.M., Stanley, R.S., Gale, M.H., Thompson, P.J., and Walsh, G.J., in press, Bedrock 

geologic map of Vermont: U.S. Geological Survey Scientific Investigations Map 3184, scale 

1:100,000. 

Richardson, C.H., 1924, The terranes of Bethel, Vermont, in Perkins, G.H., Fourteenth report of 

the State Geologist on the mineral industries and geology of Vermont, 1923–1924: Montpelier, 

Vt., Vermont Geological Survey, p. 77–103. 
4 

Stacey, J.S., and Kramers, J.D., 1975, Approximation of terrestrial lead isotope evolution by a 

two-stage model: Earth and Planetary Science Letters, v. 26, no. 2, p. 207–221. 

Steiger, R.H., and Jäger, E., 1977, Subcommission on geochronology; Convention on the use of 

decay constants in geo- and cosmochronology: Earth and Planetary Science Letters, v. 36, p. 

359–362. 

Williams, I.S., 1998, U-Th-Pb geochronology by ion microprobe, in McKibben, M.A., Shanks, 

W.C., III, and Ridley, W.I., eds., Applications of microanalytical techniques to understanding 

mineralizing processes: Reviews in Economic Geology, v. 7, p. 1–35. 

Williams, I.S., and Hergt, J.M., 2000, U-Pb dating of Tasmanian dolerites; a cautionary tale of 

SHRIMP analysis of high-U zircon, in Woodhead, J.D., Hergt, J.M., and Noble, W.P., eds., 

Beyond 2000; New frontiers in isotope geoscience, Abstracts and Proceedings, Lorne, 

Australia, January 30–February 4, 2000: Melbourne, Australia, University of Melbourne, p. 

185–188. 
5 

Table 1. Locations of zircon samples collected for U-Pb geochronology in support of the “Bedrock 

Geologic Map of Vermont” (Ratcliffe and others, in press).

Sample

number1 Field number

Map 

unit Map sheet2 Description

1 Lon–1–A Y1dg Southern Hornblende diorite gneiss at South Londonderry.

2 VT–CSTR–1 Y1bm Southern Baileys Mills tonalite gneiss in the Chester dome.

3 VT/Pe 1–88 (6327) Y1rt Southern Rawsonville trondhjemite gneiss at Bromley Mountain.

4 C718 Y1fga Southern Felchville Gneiss (aplite facies) at Cavendish Gorge.

5 C609 Y1fg Southern Felchville Gneiss (trondhjemite facies) at Felchville.

6B VT/Pe 2–88 (6329) Y2bv Southern Bondville metadacite at Winhall River bridge.

7 87Rat–1 (3016A) Y2cp Southern Cole Pond tonalite gneiss.

8 VT/Ja 1–88 Y2mig Southern Migmatite gneiss at Stratton Mountain.

9 VT/Lu 1-91 Y2lgg Southern Fine-grained granodiorite of the Ludlow Mountain 

granodiorite gneiss at Okemo Mountain.

10 VT/Lu 2–91 Y2lq Southern Okemo Quartzite—Detrital zircon.

11 87Rat–2 Y2ch Southern College Hill Granite Gneiss at Stratton Mountain, which

crosscuts older and deformed intrusive rocks and paragneiss.

12 VT/Lo 1–89 Y2gg Southern Granitic gneiss, which crosscuts older and deformed intrusive

rocks (suite ranging in age from 1.3 to 1.4 Ga) and paragneiss.

13 MC6000 Y3Amb Southern Megacrystic augen gneiss at Brandon Gap.

16 R2008 Y3Bp Southern Migmatite gneiss in Pine Hill slice.

22 VT/Br 2–89 Onnt Southern Newfane tonalite intrudes Cram Hill Formation near South 

Newfane.

23 L–18 Onb Southern Trondhjemite in Barnard Gneiss proper (of Richardson, 1924) 

north of Proctorsville.

24 SR3053 Ont Southern Tonalite gneiss in the North River Igneous Suite near 

Bartonsville.

25 SP450 Ochv Southern Felsic volcanic layer interlayered with mafic volcanic rocks in 

Cram Hill Formation at Springfield.

38 MC3432 Sbg Northern Granite in the Braintree Intrusive Complex.

39 VT–Nq–1–97 Snd Northern Trondhjemite of Newport Intrusive Complex.

46 VT–CSTR–2 Dg Southern Granite in the Chester dome.

47 Barre#2 Dbbg Northern Barre Granite.

48 VT/Br 1–89 Dbmg Southern Black Mountain pluton.

49 VT/Pl 2–91 Dg Southern Granite dike south of Plymouth.

1

The sample numbers correspond to numbers shown on the “Bedrock Geologic Map of Vermont” (Ratcliffe and 

others, in press).

2

The “Bedrock Geologic Map of Vermont" (Ratcliffe and others, in press) is divided into northern and southern map 

sheets at latitude 43°52′30′′N.
6 

Table 2. Summary of analytical information and ages of samples from Vermont.

[See table 1 for locations. Ma, millions of years (mega-annum); NA, not applicable; ≈, approximately]

Sample

number Field number Date analyzed Instrument1 Mineral standard2

Mount 

number

Age and 

error (2σ)

(Ma)

Method 

of age 

analysis3

1 Lon–1–A 1/4/2001 USGS–RG R33 A133 1,393±9 76

2 VT–CSTR–1 4/25/1998 RSES SII AS3 A105 1,383±13 76

3 VT/Pe 1–88 (6327) 10/11/1998 RSES SII AS3 A102 1,367±16 76

4 C718 4/28/2009 GSC SII R33 A342 1,372±11 76

5 C609 4/29/2009 GSC SII R33 A342 1,370±11 76

6B VT/Pe 2–88 (6329) 1989 TIMS NA NA ≈1,342 76

7 87Rat–1 (3016A) 10/11/1998 RSES SII AS3 A102 1,321±9 76

8 VT/Ja 1–88 11/11/1999 USGS–RG AS57 A117 1,326±4 76

9 VT/Lu 1–91 4/25/1996 RSES SII SL13 Z2548 1,309±6 76

10 VT/Lu 2–91 1/4/2001 USGS–RG R33 A133 1,261±62 

to 

1,359±32

dz

11 87Rat–2 1988 TIMS NA NA 1,244±8 76

12 VT/Lo 1–89 1988 TIMS NA NA 1,221±4 UI

13 MC6000 4/24/1998 RSES SII AS3 A112 1,149±8 CA

16 R2008 4/24/1998 RSES SII AS3 A105 1,037±6 CA

22 VT/Br 2–89 9/2/1999 USGS–RG AS57 A115 502±4 68

23 L–18 11/19/1996 RSES SII AS3 Z2727 496±8 68

24 SR3053 1996 TIMS NA NA 486±3 76

25 SP450 4/28/1997 RSES SII AS3 Z2848 483±3 68

38 MC3432 1/3/2001 USGS–RG R33 A133 421±7 CA

39 VT–Nq–1–97 3/22/2010 USGS–RG R33 A354 425±3 68

46 VT–CSTR–2 11/12/1999 USGS–RG AS57 A117 392±6 68

47 Barre#2 9/13/2000 USGS–RG R33 A119 368±4 68

48 VT/Br 1–89z 9/14/2000 USGS–RG R33 A119 364±4 68+76

48 VT/Br 1–89m 10/15/2011 USGS–RG 44069 A131 363±2 CA

49 VT/Pl 2–91 9/13/2000 USGS–RG R33 A119 365±5 68

1

Ion microprobe or other instrument used:

USGS–RG, U.S. Geological Survey/Stanford sensitive high resolution ion microprobe–reverse geometry 

(SHRIMP–RG). 

RSES SII, Research School of Earth Sciences, Australian National University sensitive high resolution ion 

microprobe II (SHRIMP II). 

GSC SII, Geological Survey of Canada SHRIMP II. 

TIMS, thermal ionization mass spectrometry. 
7 

Table 2. Summary of analytical information and ages of samples from Vermont.—Continued

2

Mineral standard used:

Zircon

R33, from monzodiorite of the Braintree Intrusive Complex, Vermont; 419±1 Ma (Black and others, 

2004). Used since September 2000.

AS57, from gabbroic anorthosite, Duluth Complex, Minnesota; presumed age of 1,099±1 Ma (Paces 

and Miller, 1993). Used from September 1999 to January 2000.

AS3, from gabbroic anorthosite, Duluth Complex, Minnesota; 1,099±1 Ma (Paces and Miller, 1993). 

Used from November 1996 to May 1999.

SL13, Neoproterozoic zircon megacryst from stream gravels, Sri Lanka; 572 Ma (Claoué-Long and 

others, 1995; and Black and others, 2004). Used from February 1993 to July 1996.

Monazite

44069, from Wissahickon Schist, Yorklyn, Delaware; 424.9±0.4Ma (Aleinikoff and others, 2006).

3

Age calculation method used:

76, weighted average of 207Pb/206Pb ages. 

UI, upper intercept age. 

CA, concordia age (Ludwig, 1980, 1998). 

68, weighted average of 206Pb/238U ages. 

dz, detrital zircon (individual grain ages only). 
8 

Table 3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data for zircon and monazite from rocks of Vermont.

[Abbreviations are as follows: Ma, millions of years (mega-annum); NA, not applicable; ppm, parts per million; —, measured 204Pb below detection limit; ρ, error correlation]

Analysis1 Measured 

204Pb/206Pb

Measured 

207Pb/206Pb

Percent 

common 

206Pb 

Uranium

(ppm) Th/U 206Pb/238U (Ma)2

Error 

(Ma)3

207Pb/206Pb 

(Ma)2

Error 

(Ma)3 207Pb/235U4 Error 

(percent)3 206Pb/238U4 Error (percent)3 ρ

Lon–1–A (Hornblende diorite gneiss at South Londonderry)

Lon–1–A–1 0.000017 .0896 0.03 383 0.71 1,327.0 13.3 1,413 15 2.83 1.3 .2296 1.0 .799

Lon–1–A–2 — .0848 0.00 399 0.62 1,274.9 12.8 1,311 15 2.56 1.3 .2191 1.0 .801

Lon–1–A–3 — .0886 0.00 391 0.76 1,413.8 14.2 1,395 14 2.99 1.3 .2450 1.0 .810

Lon–1–A–4 — .0890 0.00 592 0.82 1,386.9 13.7 1,404 12 2.95 1.2 .2403 1.0 .861

Lon–1–A–5 0.000008 .0887 0.01 712 1.07 1,394.6 13.7 1,396 10 2.95 1.2 .2415 1.0 .881

Lon–1–A–6 — .0879 0.00 840 1.22 1,162.7 12.8 1,381 12 2.42 1.3 .1998 1.1 .885

Lon–1–A–7 0.000331 .0884 0.55 94 0.25 1,249.9 14.4 1,287 58 2.48 3.2 .2144 1.2 .369

Lon–1–A–8 0.000075 .0889 0.12 108 0.31 1,345.5 15.1 1,380 30 2.82 1.9 .2325 1.2 .600

Lon–1–A–9 0.000038 .0896 0.06 180 0.36 1,432.9 15.1 1,405 22 3.05 1.6 .2485 1.1 .693

Lon–1–A–10 0.000032 .0876 0.05 471 0.70 1,318.2 13.1 1,363 17 2.73 1.4 .2274 1.0 .753

Lon–1–A–11 — .0890 0.00 721 1.34 1,405.4 13.9 1,405 10 2.99 1.2 .2436 1.0 .883

Lon–1–A–12 0.000007 .0882 0.01 825 1.49 1,411.6 13.8 1,385 10 2.97 1.1 .2444 1.0 .892

Lon–1–A–13 0.000055 .0901 0.09 502 1.39 1,387.1 13.8 1,411 13 2.96 1.2 .2404 1.0 .825

Lon–1–A–14 0.000017 .0875 0.03 372 0.57 1,362.4 13.7 1,366 15 2.83 1.3 .2354 1.0 .797

Lon–1–A–15 0.000068 .0891 0.11 255 0.33 1,393.8 14.6 1,387 22 2.93 1.6 .2413 1.1 .686

VT–CSTR–1 (Baileys Mill tonalitic gneiss in Chester dome)

VT–CSTR–1–1.1 0.000239 .0866 0.09 51 0.28 1,334.7 40.0 1,275 51 2.63 4.1 .2293 3.1 .767

VT–CSTR–1–1.2 0.000036 .0854 -0.01 426 0.08 1,328.2 27.9 1,314 12 2.68 2.3 .2286 2.2 .962

VT–CSTR–1–2.1 0.000022 .0890 -0.22 222 0.29 1,442.7 30.7 1,396 15 3.06 2.3 .2502 2.2 .939

VT–CSTR–1–2.2 0.000073 .0892 -0.41 87 0.28 1,482.5 33.0 1,386 24 3.13 2.6 .2572 2.3 .879

VT–CSTR–1–2.3 0.000062 .0787 -0.16 586 0.00 1,197.8 22.3 1,141 13 2.18 2.0 .2036 1.9 .944

VT–CSTR–1–3.1 -0.000040 .0885 -0.07 266 0.43 1,406.1 28.7 1,405 20 2.99 2.4 .2437 2.1 .895

VT–CSTR–1–4.1 0.000103 .0861 0.51 240 0.27 1,238.7 27.0 1,307 21 2.48 2.5 .2126 2.3 .902

VT–CSTR–1–4.2 -0.000016 .0820 0.19 616 0.05 1,206.8 25.5 1,250 16 2.34 2.3 .2063 2.2 .940

VT–CSTR–1–5.1 -0.000092 .0902 0.16 55 0.27 1,400.8 31.7 1,457 34 3.07 2.9 .2435 2.3 .798

VT–CSTR–1–5.2 0.000062 .0798 0.83 409 0.01 1,007.9 23.4 1,169 16 1.85 2.5 .1705 2.4 .946

VT–CSTR–1–6.1 0.000047 .0854 0.60 49 0.33 1,203.4 27.4 1,309 37 2.41 3.0 .2063 2.4 .775

VT–CSTR–1–6.2 0.000004 .0844 0.05 939 0.12 1,293.2 23.9 1,301 13 2.59 2.0 .2222 1.9 .940

VT–CSTR–1–6.3 -0.000085 .0873 0.27 131 0.28 1,315.7 26.4 1,393 29 2.77 2.6 .2273 2.1 .809

VT–CSTR–1–7.1 0.000044 .0764 0.51 859 0.02 992.2 23.6 1,090 12 1.75 2.5 .1671 2.5 .974

VT–CSTR–1–7.2 0.000060 .0881 -0.06 200 0.43 1,395.8 32.0 1,367 17 2.90 2.5 .2414 2.4 .939

VT–CSTR–1–8.1 0.006176 .2050 13.10 62 0.27 1,476.8 70.7 1,987 228 4.49 13.7 .2667 4.8 .348

VT–CSTR–1–8.2 -0.000263 .0915 0.62 61 0.53 1,343.0 32.8 1,531 60 3.07 4.1 .2341 2.5 .620

VT–CSTR–1–9.1 0.000857 .1002 1.74 80 0.33 1,323.3 28.0 1,387 90 2.78 5.2 .2286 2.2 .430
9 

Table 3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data for zircon and monazite from rocks of Vermont.—Continued

[Abbreviations are as follows: Ma, millions of years (mega-annum); NA, not applicable; ppm, parts per million; —, measured 204Pb below detection limit; ρ, error correlation]

Analysis1 Measured 

204Pb/206Pb

Measured 

207Pb/206Pb

Percent 

common 

206Pb 

Uranium

(ppm) Th/U 206Pb/238U (Ma)2

Error 

(Ma)3

207Pb/206Pb 

(Ma)2

Error 

(Ma)3 207Pb/235U4 Error 

(percent)3 206Pb/238U4 Error (percent)3 ρ

VT–CSTR–1 (Baileys Mill tonalitic gneiss in Chester dome)—Continued

VT–CSTR–1–9.2 -0.000053 .0885 -0.06 137 0.39 1,404.8 31.0 1,409 20 3.00 2.5 .2435 2.3 .907

VT–CSTR–1–10.1 0.000071 .0880 -0.15 334 0.31 1,411.2 27.2 1,361 14 2.93 2.1 .2441 2.0 .943

VT–CSTR–1–11.1 -0.000012 .0870 0.29 179 0.39 1,304.6 35.6 1,364 17 2.70 3.0 .2250 2.8 .952

VT–CSTR–1–12.1 0.000013 .0890 0.09 128 0.27 1,387.8 27.7 1,400 22 2.94 2.4 .2404 2.1 .873

VT–CSTR–1–12.2 0.000005 .0894 -0.06 237 0.22 1,422.3 33.1 1,410 16 3.04 2.6 .2467 2.4 .942

VT–CSTR–1–13.1 -0.000017 .0841 0.00 600 0.07 1,293.5 28.0 1,300 11 2.58 2.3 .2223 2.2 .969

VT–CSTR–1–14.1 0.000045 .0877 -0.06 100 0.28 1,388.3 32.6 1,363 26 2.88 2.8 .2400 2.4 .876

VT–CSTR–1–15.1 0.000006 .0754 0.08 842 0.03 1,062.2 21.2 1,077 11 1.86 2.1 .1792 2.1 .969

VT–CSTR–1–15.2 0.000281 .0865 0.44 40 0.45 1,264.1 35.6 1,259 66 2.47 4.5 .2166 2.9 .655

VT–CSTR–1–15.3 0.000046 .0892 -0.19 144 0.32 1,443.4 31.2 1,394 22 3.06 2.5 .2503 2.2 .886

VT–CSTR–1–16.1 -0.000020 .0865 -0.04 513 0.15 1,355.1 25.4 1,355 14 2.80 2.1 .2339 1.9 .935

VT–CSTR–1–16.2 -0.000196 .0895 0.00 61 0.34 1,414.7 31.1 1,472 37 3.13 3.0 .2462 2.3 .761

VT–CSTR–1–16.3 0.000043 .0893 0.01 660 0.16 1,408.3 34.3 1,397 28 2.98 2.9 .2440 2.5 .866

VT–CSTR–1–17.1 0.000008 .0846 0.33 1,542 0.11 1,239.6 27.9 1,303 28 2.48 2.7 .2127 2.3 .853

VT/Pe 1–88 (6327) (Rawsonville trondhjemite gneiss at Bromley Mountain)

VT/Pe–1–1.1 0.000043 .0876 0.07 111 0.22 1,392.8 19.6 1,361 13 2.89 1.6 .2408 1.5 .902

VT/Pe–1–2.1 0.000070 .0892 0.11 113 0.40 1,386.4 19.5 1,387 16 2.92 1.7 .2399 1.5 .874

VT/Pe–1–3.1 0.000112 .0889 0.18 206 0.36 1,398.4 19.2 1,367 19 2.91 1.7 .2418 1.4 .822

VT/Pe–1–4.1 0.000139 .0878 0.23 82 0.26 1,385.3 29.8 1,334 35 2.83 2.9 .2391 2.2 .773

VT/Pe–1–5.1 0.000056 .0877 0.09 179 0.34 1,406.3 19.6 1,358 22 2.91 1.8 .2431 1.4 .790

VT/Pe–1–6.1 0.000135 .0836 0.22 87 0.28 1,256.6 18.0 1,239 23 2.42 1.9 .2150 1.5 .789

C718 (Felchville Gneiss (aplite facies) at Cavendish Gorge)

C718–1.1 0.000064 .0887 0.104 130 0.34 1,342 22 1,378 17 2.81 1.9 0.232 1.7 0.89

C718–2.1 0.000103 .0893 0.169 113 0.32 1,378 25 1,379 23 2.89 2.2 0.238 1.9 0.84

C718–3.1 0.000060 .0897 0.098 209 0.45 1,404 24 1,402 17 2.98 2.0 0.243 1.7 0.89

C718–3.2 0.000879 .0762 1.543 362 0.02 1,080 17 725 79 1.57 4.1 0.180 1.7 0.42

C718–4.1 0.000135 .0882 0.223 94 0.24 1,368 26 1,345 28 2.81 2.5 0.236 2.0 0.81

C718–5.1 0.000066 .0876 0.109 110 0.29 1,414 25 1,353 21 2.92 2.2 0.244 1.9 0.86

C718–6.1 0.000079 .0884 0.130 199 0.29 1,370 22 1,368 16 2.85 1.9 0.237 1.7 0.90

C718–7.1 0.000103 .0893 0.168 88 0.36 1,410 27 1,379 25 2.96 2.4 0.244 2.0 0.83

C718–8.1 0.000021 .0842 0.035 321 0.06 1,266 19 1,291 11 2.52 1.7 0.217 1.6 0.94

C718–10.1 -0.000020 .0910 -0.032 101 0.36 1,353 25 1,452 20 2.95 2.2 0.235 1.9 0.88

C718–10.2 0.000016 .0750 0.027 1,731 0.00 980 14 1,062 6 1.70 1.5 0.165 1.4 0.98

C718–11.1 0.000065 .0875 0.107 88 0.23 1,369 25 1,351 21 2.82 2.2 0.236 1.9 0.86
10

Table 3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data for zircon and monazite from rocks of Vermont.—Continued

[Abbreviations are as follows: Ma, millions of years (mega-annum); NA, not applicable; ppm, parts per million; —, measured 204Pb below detection limit; ρ, error correlation]

Analysis1 Measured 

204Pb/206Pb

Measured 

207Pb/206Pb

Percent 

common 

206Pb 

Uranium

(ppm) Th/U 206Pb/238U (Ma)2

Error 

(Ma)3

207Pb/206Pb 

(Ma)2

Error 

(Ma)3 207Pb/235U4 Error 

(percent)3 206Pb/238U4 Error (percent)3 ρ

C718 (Felchville Gneiss (aplite facies) at Cavendish Gorge)—Continued

C718–12.1 0.000043 .0878 0.070 151 0.35 1,370 25 1,366 23 2.85 2.2 0.237 1.9 0.85

C718–13.1 0.000015 .0904 0.025 123 0.30 1,395 25 1,428 18 3.01 2.0 0.242 1.8 0.89

C718–14.1 0.000042 .0872 0.069 128 0.45 1,381 24 1,353 19 2.85 2.0 0.238 1.8 0.88

C718–15.1 0.000051 .0880 0.083 88 0.26 1,328 24 1,367 21 2.76 2.2 0.229 1.9 0.87

C718–16.1 0.000118 .0884 0.195 101 0.27 1,326 27 1,355 31 2.74 2.6 0.229 2.1 0.79

C718–1.2 0.000034 .0765 0.057 784 0.01 1,107 16 1,095 8 1.96 1.5 0.187 1.5 0.97

C718–16.2 0.000063 .0774 0.106 459 0.03 1,109 16 1,109 11 1.98 1.6 0.188 1.5 0.94

C718–17.1 0.000482 .0874 0.805 40 0.27 1,267 28 1,211 60 2.41 3.8 0.217 2.3 0.60

C718–17.2 0.000145 .0904 0.237 75 0.25 1,416 26 1,390 24 2.99 2.3 0.245 1.9 0.84

C718–18.1 0.000285 .0860 0.473 36 0.34 1,340 30 1,244 126 2.60 6.8 0.230 2.3 0.34

C718–18.2 -0.000024 .0903 -0.039 151 0.47 1,435 23 1,440 13 3.12 1.8 0.249 1.7 0.93

C609 (Felchville Gneiss (trondhjemite facies) at Felchville)

C609–1.1 0.000048 .0869 0.079 259 0.17 1,299 20 1,343 11 2.66 1.7 0.224 1.6 0.94

C609–2.1 0.000015 .0880 0.025 149 0.36 1,334 21 1,377 13 2.79 1.8 0.230 1.7 0.93

C609–3.1 0.000097 .0884 0.159 133 0.34 1,298 21 1,362 16 2.69 1.9 0.224 1.7 0.89

C609–4.1 0.000036 .0881 0.059 125 0.38 1,365 23 1,373 66 2.85 3.8 0.236 1.7 0.44

C609–5.1 0.000069 .0892 0.113 143 0.49 1,351 22 1,388 15 2.84 1.8 0.234 1.7 0.90

C609–6.2 0.000033 .0878 0.054 303 0.24 1,339 20 1,368 10 2.78 1.6 0.231 1.6 0.94

C609–7.1 0.000026 .0883 0.043 99 0.37 1,323 23 1,380 17 2.77 2.0 0.229 1.8 0.89

C609–8.1 0.000043 .0881 0.070 145 0.43 1,377 23 1,372 56 2.87 3.4 0.238 1.7 0.50

C609–9.2 0.000041 .0880 0.067 166 0.48 1,357 22 1,370 14 2.83 1.8 0.234 1.7 0.92

C609–10.1 -0.000009 .0894 -0.014 160 0.52 1,384 22 1,415 13 2.96 1.8 0.240 1.7 0.92

C609–11.1 0.000039 .0888 0.064 136 0.45 1,386 23 1,388 15 2.92 1.9 0.240 1.7 0.91

C609–12.1 0.000017 .0889 0.028 160 0.40 1,390 23 1,396 14 2.94 1.8 0.241 1.7 0.92

C609–13.1 0.000033 .0845 0.055 188 0.11 1,248 20 1,292 14 2.48 1.8 0.214 1.7 0.91

C609–14.1 0.000048 .0867 0.078 161 0.39 1,389 24 1,339 21 2.85 2.1 0.240 1.8 0.85

C609–15.1 0.000064 .0896 0.105 117 0.27 1,395 25 1,398 18 2.96 2.1 0.242 1.8 0.89

C609–16.1 0.000074 .0877 0.122 197 0.31 1,410 23 1,352 77 2.91 4.3 0.244 1.7 0.38

C609–17.1 0.000061 .0898 0.100 138 0.36 1,394 24 1,403 18 2.96 2.0 0.242 1.8 0.89

C609–6.1 0.002524 .0795 4.720 199 0.01 498 9 -222 424 0.46 17.0 0.079 2.0 0.12

C609–9.1 0.000064 .0658 0.111 1,051 0.03 694 10 770 11 1.02 1.6 0.114 1.5 0.94

C609–16.2 0.000270 .0785 0.458 399 0.02 1,006 15 1,060 19 1.74 1.8 0.169 1.5 0.85

C609–17.1 0.000069 .0863 0.114 163 0.40 1,310 21 1,323 16 2.65 1.9 0.225 1.7 0.90

C609–17.2 0.000052 .0877 0.086 204 0.19 1,328 21 1,360 14 2.75 1.8 0.229 1.6 0.92
11

Table 3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data for zircon and monazite from rocks of Vermont.—Continued

[Abbreviations are as follows: Ma, millions of years (mega-annum); NA, not applicable; ppm, parts per million; —, measured 204Pb below detection limit; ρ, error correlation]

Analysis1 Measured 

204Pb/206Pb

Measured 

207Pb/206Pb

Percent 

common 

206Pb 

Uranium

(ppm) Th/U 206Pb/238U (Ma)2

Error 

(Ma)3

207Pb/206Pb 

(Ma)2

Error 

(Ma)3 207Pb/235U4 Error 

(percent)3 206Pb/238U4 Error (percent)3 ρ

87Rat–1 (3016A) (Cole Pond tonalite gneiss)

87Rat–1–1.1 -0.000051 .0872 -0.08 104 0.70 1,255.5 17.8 1,380 15 2.62 1.7 .2164 1.5 .880

87Rat–1–1.2 0.000023 .0823 0.04 541 0.14 1,228.5 16.5 1,245 9 2.38 1.5 .2101 1.4 .948

87Rat–1–2.1 0.000158 .0851 0.26 112 0.61 1,301.3 18.4 1,266 21 2.55 1.8 .2233 1.5 .813

87Rat–1–2.2 0.000028 .0780 0.05 663 0.00 1,189.9 15.9 1,137 7 2.16 1.4 .2022 1.4 .972

87Rat–1–3.1 0.000076 .0869 0.12 125 0.76 1,309.3 18.4 1,335 19 2.67 1.8 .2255 1.5 .833

87Rat–1–4.1 0.000080 .0860 0.13 97 0.51 1,302.0 18.9 1,313 19 2.62 1.8 .2239 1.5 .842

87Rat–1–4.2 0.000153 .0871 0.25 376 0.35 1,329.4 17.9 1,314 9 2.68 1.5 .2288 1.4 .944

87Rat–1–5.1 0.000036 .0868 0.06 62 0.53 1,329.4 19.7 1,344 22 2.73 1.9 .2292 1.5 .798

87Rat–1–5.2 0.000034 .0859 0.06 285 0.34 1,299.1 17.6 1,325 8 2.63 1.5 .2236 1.4 .955

87Rat–1–1.3 0.003050 .1259 5.06 45 0.39 1,299.1 25.0 1,267 339 2.55 17.5 .2229 2.1 .118

87Rat–1–6.1 0.000105 .0861 0.17 76 0.42 1,320.4 19.2 1,306 27 2.65 2.1 .2272 1.5 .735

87Rat–1–6.2 0.000487 .0874 0.81 56 0.41 1,345.1 20.1 1,210 40 2.56 2.5 .2304 1.6 .612

87Rat–1–7.1 0.000335 .0891 0.55 113 0.73 1,299.8 18.5 1,302 24 2.60 1.9 .2234 1.5 .767

87Rat–1–7.2 0.000032 .0852 0.05 300 0.35 1,313.0 17.8 1,311 9 2.64 1.5 .2259 1.4 .947

87Rat–1–8.1 0.000051 .0862 0.08 94 0.71 1,329.7 19.0 1,326 19 2.70 1.8 .2290 1.5 .831

87Rat–1–8.2 0.000022 .0855 0.04 239 0.29 1,346.3 18.3 1,320 9 2.73 1.5 .2319 1.4 .951

87Rat–1–9.1 0.000010 .0862 0.02 102 0.40 1,330.1 18.9 1,340 13 2.72 1.6 .2293 1.5 .915

87Rat–1–9.2 0.000425 .0841 0.71 301 0.11 1,099.8 14.8 1,149 18 2.01 1.7 .1864 1.4 .837

87Rat–1–10.1 0.000272 .0881 0.45 46 0.40 1,313.1 20.1 1,300 53 2.62 3.2 .2258 1.6 .508

87Rat–1–11.1 0.000098 .0864 0.16 134 0.70 1,351.7 18.8 1,316 14 2.73 1.6 .2329 1.4 .890

87Rat–1–11.2 0.000062 .0871 0.10 61 0.38 1,309.1 19.8 1,343 23 2.68 2.0 .2256 1.6 .795

87Rat–1–12.1 0.000093 .0856 0.15 101 0.63 1,291.6 18.2 1,300 17 2.58 1.7 .2219 1.5 .861

87Rat–1–13.1 0.000065 .0872 0.11 54 0.44 1,336.7 19.8 1,344 22 2.74 1.9 .2305 1.5 .808

87Rat–1–13.2 0.000007 .0855 0.01 270 0.36 1,363.5 18.5 1,325 10 2.77 1.5 .2351 1.4 .935

87Rat–1–14.1 0.000017 .0846 0.03 201 0.34 1,299.7 17.8 1,300 10 2.60 1.5 .2234 1.4 .939

VT/Ja 1–88 (Migmatite gneiss at Stratton Mountain)

VT/Ja–1–1.1 0.000000 .0856 0.000 1,042 0.43 1,423.8 25.8 1,330 5 2.90 1.9 .2459 1.9 .990

VT/Ja–1–2.1 -0.000004 .0848 -0.007 1,180 0.38 1,430.9 26.2 1,312 10 2.89 2.0 .2470 1.9 .966

VT/Ja–1–3.1 -0.000008 .0852 -0.015 1,305 0.48 1,335.6 24.2 1,324 5 2.71 1.9 .2301 1.9 .989

VT/Ja–1–4.1 0.000000 .0856 -0.001 1,267 0.44 1,378.9 24.9 1,330 5 2.81 1.9 .2379 1.9 .991

VT/Ja–1–5.1 0.000000 .0838 0.000 1,505 0.40 1,402.7 25.4 1,289 8 2.79 1.9 .2416 1.9 .978

VT/Ja–1–6.1 0.000000 .0849 0.000 1,131 0.39 1,341.5 25.5 1,313 6 2.70 2.0 .2310 2.0 .987

VT/Ja–1–7.1 0.000000 .0853 0.000 1,204 0.42 1,340.4 24.3 1,321 5 2.71 1.9 .2309 1.9 .989

VT/Ja–1–8.1 0.000000 .0860 0.000 903 0.40 1,309.3 24.3 1,337 13 2.67 2.0 .2255 1.9 .947
12

Table 3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data for zircon and monazite from rocks of Vermont.—Continued

[Abbreviations are as follows: Ma, millions of years (mega-annum); NA, not applicable; ppm, parts per million; —, measured 204Pb below detection limit; ρ, error correlation]

Analysis1 Measured 

204Pb/206Pb

Measured 

207Pb/206Pb

Percent 

common 

206Pb 

Uranium

(ppm) Th/U 206Pb/238U (Ma)2

Error 

(Ma)3

207Pb/206Pb 

(Ma)2

Error 

(Ma)3 207Pb/235U4 Error 

(percent)3 206Pb/238U4 Error (percent)3 ρ

VT/Ja 1–88 (Migmatite gneiss at Stratton Mountain)—Continued

VT/Ja–1–9.1 0.000001 .0855 0.002 1,329 0.45 1,358.4 24.8 1,328 5 2.76 1.9 .2342 1.9 .991

VT/Ja–1–10.1 0.000001 .0856 0.001 1,116 0.44 1,372.1 25.3 1,330 6 2.79 1.9 .2367 1.9 .988

VT/Ja–1–11.1 0.000000 .0855 0.000 1,210 0.46 1,344.7 24.3 1,328 5 2.73 1.9 .2318 1.9 .990

VT/Lu 1–91 (Fine-grained granodiorite of the Ludlow Mountain granodiorite gneiss at Okemo Mountain)

VT/Lu–1–1.1 0.000016 .0854 0.03 190 0.43 1,259.7 11.0 1,320 12 2.54 1.1 .2165 0.9 .827

VT/Lu–1–2.1 0.000486 .1078 0.77 134 0.33 1,324.9 12.5 1,644 34 3.24 2.1 .2323 1.0 .475

VT/Lu–1–3.1 0.000035 .0850 0.06 215 0.39 1,233.1 13.3 1,305 13 2.47 1.3 .2116 1.1 .852

VT/Lu–1–4.1 0.000034 .0848 0.06 238 0.38 1,258.8 10.8 1,301 11 2.51 1.0 .2161 0.9 .855

VT/Lu–1–5.1 0.000021 .0854 0.03 299 0.42 1,297.3 11.0 1,318 9 2.62 1.0 .2231 0.9 .876

VT/Lu–1–6.1 -0.000009 .0801 -0.02 375 0.16 1,099.9 9.5 1,203 10 2.07 1.0 .1869 0.9 .875

VT/Lu–1–7.1 -0.000014 .0843 -0.02 271 0.31 1,251.6 10.8 1,305 10 2.50 1.0 .2149 0.9 .874

VT/Lu–1–8.1 0.000053 .0856 0.09 221 0.39 1,274.5 11.1 1,313 12 2.56 1.1 .2190 0.9 .819

VT/Lu–1–9.1 0.000131 .0852 0.22 206 0.33 1,158.7 10.2 1,277 17 2.28 1.3 .1980 0.9 .723

VT/Lu–1–10.1 -0.000004 .0850 -0.01 255 0.46 1,263.4 10.9 1,317 9 2.55 1.0 .2171 0.9 .882

VT/Lu–1–11.1 0.000029 .0854 0.05 399 0.40 1,291.5 10.8 1,316 8 2.60 1.0 .2221 0.9 .897

VT/Lu–1–12.1 0.000050 .0852 0.08 266 0.55 1,229.5 10.6 1,305 10 2.46 1.0 .2109 0.9 .859

VT/Lu–1–13.1 0.000094 .0871 0.16 141 0.43 1,198.9 11.1 1,334 19 2.43 1.4 .2058 1.0 .702

VT/Lu–1–14.1 -0.000061 .0854 -0.10 102 0.35 1,272.3 12.3 1,344 17 2.60 1.3 .2190 1.0 .746

VT/Lu–1–15.1 0.000061 .0854 0.10 269 0.40 1,246.3 10.7 1,306 12 2.49 1.1 .2139 0.9 .827

VT/Lu–1–16.1 0.000035 .0853 0.06 453 0.41 1,249.6 10.4 1,311 9 2.51 1.0 .2146 0.9 .881

VT/Lu–1–17.1 0.000039 .0854 0.06 280 0.48 1,250.7 11.6 1,313 11 2.51 1.1 .2148 1.0 .857

VT/Lu–1–18.1 -0.000027 .0861 -0.04 249 0.45 1,296.7 11.2 1,350 10 2.66 1.0 .2234 0.9 .869

VT/Lu–1–19.1 0.000044 .0808 0.07 1,265 0.23 1,247.5 10.1 1,202 6 2.36 0.9 .2130 0.8 .939

VT/Lu–1–20.1 0.000013 .0843 0.02 695 0.35 1,343.9 11.0 1,294 7 2.68 0.9 .2312 0.8 .927

VT/Lu 2–91(Okemo Quartzite–Detrital zircon)

VT/Lu–2–1 — .0855 0.00 213 0.48 1,181.8 12.4 1,327 22 2.39 1.6 .2027 1.1 .692

VT/Lu–2–2 — .0875 0.00 196 0.48 1,163.9 12.4 1,371 24 2.41 1.6 .1999 1.1 .668

VT/Lu–2–3 — .0864 0.00 113 0.78 1,239.8 13.9 1,348 29 2.54 1.9 .2132 1.2 .613

VT/Lu–2–4 — .0867 0.00 206 0.40 1,265.4 13.3 1,353 21 2.60 1.5 .2179 1.1 .706

VT/Lu–2–5 — .0869 0.00 351 0.48 1,270.4 13.0 1,359 16 2.62 1.4 .2188 1.1 .783

VT/Lu–2–6 — .0875 0.00 99 0.56 1,211.2 14.2 1,371 33 2.51 2.1 .2084 1.2 .577

VT/Lu–2–7 0.000049 .0852 0.08 205 0.58 1,364.8 14.4 1,303 22 2.74 1.6 .2350 1.1 .686

VT/Lu–2–8 0.000043 .0867 0.07 283 0.42 1,286.9 13.2 1,341 19 2.63 1.5 .2216 1.1 .725

VT/Lu–2–9 0.000076 .0832 0.13 111 0.51 1,143.0 13.1 1,249 48 2.21 2.7 .1950 1.2 .429
13

Table 3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data for zircon and monazite from rocks of Vermont.—Continued

[Abbreviations are as follows: Ma, millions of years (mega-annum); NA, not applicable; ppm, parts per million; —, measured 204Pb below detection limit; ρ, error correlation]

Analysis1 Measured 

204Pb/206Pb

Measured 

207Pb/206Pb

Percent 

common 

206Pb 

Uranium

(ppm) Th/U 206Pb/238U (Ma)2

Error 

(Ma)3

207Pb/206Pb 

(Ma)2

Error 

(Ma)3 207Pb/235U4 Error 

(percent)3 206Pb/238U4 Error (percent)3 ρ

VT/Lu 2–91(Okemo Quartzite–Detrital zircon)—Continued

VT/Lu–2–10 — .0798 0.00 340 0.19 964.1 10.3 1,192 26 1.79 1.7 .1630 1.1 .647

VT/Lu–2–11 — .0863 0.00 239 0.38 1,336.0 13.8 1,344 19 2.74 1.5 .2304 1.1 .733

VT/Lu–2–12 — .0854 0.00 137 0.83 1,338.3 14.6 1,324 26 2.71 1.7 .2306 1.1 .647

VT/Lu–2–13 0.000119 .0843 0.20 154 0.29 1,284.2 14.0 1,261 31 2.51 1.9 .2202 1.1 .579

VT/Lu–2–14 — .0855 0.00 296 0.21 1,386.5 14.4 1,328 19 2.82 1.5 .2392 1.1 .734

VT/Lu–2–15 — .0839 0.00 91 0.69 1,333.9 15.4 1,291 31 2.65 2.0 .2294 1.2 .594

VT/Lu–2–16 0.000046 .0857 0.08 94 0.54 1,366.7 15.7 1,318 31 2.76 2.0 .2356 1.2 .588

MC6000 (Megacrystic augen gneiss at Brandon Gap)

MC6000–1.1 0.000115 .0795 0.19 229 0.69 1,130.7 14.0 1,144 24 2.06 1.8 .1918 1.3 .723

MC6000–2.1 0.000141 .0791 0.24 150 0.49 1,134.7 12.2 1,124 31 2.05 1.9 .1924 1.1 .588

MC6000–2.2 0.000060 .0735 0.10 753 0.00 1,093.7 9.5 1,003 11 1.84 1.0 .1842 0.9 .868

MC6000–3.1 0.000682 .0796 1.17 29 0.48 1,162.1 20.8 924 146 1.88 7.4 .1955 1.9 .261

MC6000–4.1 0.000518 .0816 0.88 30 0.43 1,136.1 21.1 1,047 99 1.96 5.3 .1919 2.0 .370

MC6000–5.1 0.000217 .0791 0.37 123 0.47 1,173.2 13.3 1,096 40 2.08 2.3 .1989 1.2 .511

MC6000–6.1 0.000107 .0774 0.18 98 0.49 1,172.7 13.9 1,092 44 2.08 2.5 .1988 1.2 .489

MC6000–6.2 0.000127 .0791 0.21 178 0.25 1,133.1 15.4 1,129 26 2.05 1.9 .1921 1.4 .728

MC6000–7.1 0.000109 .0808 0.18 81 0.50 1,146.9 15.0 1,178 35 2.13 2.2 .1950 1.4 .611

MC6000–8.1 0.000132 .0802 0.22 194 0.32 1,161.7 12.2 1,154 25 2.13 1.7 .1974 1.1 .652

MC6000–9.1 -0.000054 .0791 -0.09 152 0.51 1,184.6 13.1 1,194 20 2.22 1.5 .2018 1.1 .746

MC6000–10.1 0.000203 .0784 0.34 137 0.49 1,138.4 12.9 1,082 37 2.01 2.2 .1926 1.2 .544

MC6000–11.1 0.000136 .0789 0.23 144 0.31 1,132.8 12.9 1,121 33 2.04 2.0 .1920 1.2 .584

MC6000–12.1 0.000096 .0786 0.16 171 0.41 1,169.9 12.8 1,128 29 2.12 1.9 .1986 1.1 .614

MC6000–13.1 -0.000019 .0790 -0.03 224 0.50 1,158.2 15.0 1,180 16 2.15 1.6 .1970 1.3 .850

MC6000–14.1 0.000096 .0789 0.16 127 0.62 1,155.1 15.7 1,136 29 2.10 2.0 .1961 1.4 .695

MC6000–14.2 0.000112 .0782 0.19 187 0.25 1,176.2 12.4 1,111 28 2.11 1.8 .1996 1.1 .615

MC6000–15.1 0.000033 .0789 0.05 654 0.24 1,194.0 10.7 1,157 10 2.20 1.1 .2031 0.9 .872

R2008 (Migmatite gneiss in Pine Hill slice)

R2008–1.1 -0.000003 .0732 -0.22 592 0.45 1,070.8 19.9 1,022 12 1.82 2.0 .1803 1.9 .956

R2008–2.1 -0.000015 .0735 -0.11 584 0.34 1,053.9 19.6 1,034 12 1.80 2.0 .1775 1.9 .953

R2008–3.1 0.000042 .0738 -0.01 573 0.26 1,038.7 19.4 1,019 19 1.76 2.1 .1747 1.9 .903

R2008–4.1 -0.000020 .0730 -0.11 407 0.30 1,040.4 19.6 1,023 15 1.77 2.1 .1750 2.0 .937

R2008–5.1 -0.000006 .0731 -0.19 610 0.34 1,059.8 19.7 1,018 12 1.80 2.0 .1784 1.9 .954

R2008–6.1 0.000042 .0737 -0.01 480 0.27 1,036.3 19.4 1,017 17 1.76 2.1 .1743 1.9 .919

R2008–7.1 0.000023 .0750 0.09 444 0.21 1,046.7 19.6 1,059 17 1.81 2.1 .1764 1.9 .918
14

Table 3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data for zircon and monazite from rocks of Vermont.—Continued

[Abbreviations are as follows: Ma, millions of years (mega-annum); NA, not applicable; ppm, parts per million; —, measured 204Pb below detection limit; ρ, error correlation]

Analysis1 Measured 

204Pb/206Pb

Measured 

207Pb/206Pb

Percent 

common 

206Pb 

Uranium

(ppm) Th/U 206Pb/238U (Ma)2

Error 

(Ma)3

207Pb/206Pb 

(Ma)2

Error 

(Ma)3 207Pb/235U4 Error 

(percent)3 206Pb/238U4 Error (percent)3 ρ

R2008 (Migmatite gneiss in Pine Hill slice)—Continued

R2008–8.1 -0.000033 .0745 0.47 452 0.16 945.0 17.7 1,066 16 1.64 2.1 .1587 1.9 .924

R2008–8.2 0.000021 .0743 0.03 582 0.47 1,042.8 19.4 1,042 15 1.79 2.1 .1756 1.9 .930

R2008–9.1 0.000018 .0737 -0.07 667 0.35 1,050.1 19.5 1,026 12 1.79 2.0 .1767 1.9 .955

R2008–10.1 -0.000086 .0721 -0.26 383 0.20 1,047.6 19.6 1,022 22 1.78 2.2 .1763 1.9 .877

R2008–10.2 -0.000059 .0744 -0.04 423 0.29 1,061.3 22.7 1,075 27 1.86 2.6 .1791 2.2 .858

R2008–11.1 -0.000101 .0739 0.27 424 0.18 976.2 19.4 1,079 23 1.71 2.3 .1642 2.1 .876

R2008R–1.1 -0.000003 .0743 0.18 1,138 0.13 1,006.8 19.5 1,049 11 1.73 2.1 .1693 2.0 .967

R2008R–1.2 — .0739 0.02 1,019 0.08 1,033.9 19.1 1,039 9 1.77 2.0 .1740 1.9 .972

R2008R–2.1 0.000029 .0737 -0.02 596 0.46 1,037.3 19.3 1,022 13 1.76 2.0 .1745 1.9 .947

R2008R–3.1 0.000038 .0744 0.06 541 0.34 1,038.9 19.8 1,038 15 1.78 2.1 .1749 2.0 .936

R2008R–3.2 0.000028 .0744 0.06 683 0.41 1,037.1 19.7 1,040 12 1.78 2.1 .1746 2.0 .957

R2008R–3.3 0.000029 .0750 0.07 396 0.30 1,051.5 52.4 1,057 38 1.82 5.5 .1772 5.2 .939

VT/Br 2–89 (Newfane tonalite intruding Cram Hill Formation near South Newfane)

VT/Br–2–1.1 0.000075 .0572 -0.15 100 0.71 543.7 8.1 NA NA 0.68 2.4 .0878 1.5 .643

VT/Br–2–2.1 0.000077 .0561 -0.23 154 0.73 530.9 7.8 NA NA 0.65 2.2 .0855 1.5 .680

VT/Br–2–3.1 — .0588 0.08 141 0.72 534.4 8.0 NA NA 0.70 2.2 .0865 1.5 .697

VT/Br–2–4.1 0.000040 .0574 0.01 207 0.82 505.2 7.4 NA NA 0.64 2.1 .0815 1.5 .716

VT/Br–2–5.1 0.000038 .0588 0.17 314 0.88 507.1 7.3 NA NA 0.66 1.9 .0819 1.5 .768

VT/Br–2–6.1 0.000213 .0547 -0.34 181 0.57 506.9 7.5 NA NA 0.58 4.3 .0812 1.5 .354

VT/Br–2–7.1 0.000069 .0567 -0.08 302 0.66 504.2 7.2 NA NA 0.62 2.2 .0812 1.5 .676

VT/Br–2–8.1 0.000017 .0914 -0.36 153 0.52 1,518.9 21.7 NA NA 3.33 1.6 .2647 1.5 .898

VT/Br–2–9.1 — .0573 -0.02 266 0.73 510.4 7.3 NA NA 0.65 1.8 .0824 1.5 .793

VT/Br–2–10.1 — .0566 -0.06 76 0.57 495.8 8.3 NA NA 0.62 2.9 .0799 1.7 .594

VT/Br–2–11.1 — .0561 -0.13 173 0.51 495.1 7.4 NA NA 0.62 2.4 .0797 1.5 .642

VT/Br–2–12.1 0.000149 .0619 0.06 147 1.68 652.9 9.7 NA NA 0.88 2.6 .1064 1.5 .588

VT/Br–2–13.1 0.000056 .0555 -0.22 178 0.62 504.4 7.5 NA NA 0.61 2.3 .0811 1.5 .663

VT/Br–2–14.1 — .0568 -0.04 218 0.69 497.1 7.3 NA NA 0.63 2.1 .0801 1.5 .726

VT/Br–2–15.1 — .0560 -0.15 82 0.64 501.0 9.3 NA NA 0.62 3.0 .0807 1.9 .634

VT/Br–2–16.1 0.000384 .0559 -0.24 83 0.55 524.2 8.5 NA NA 0.58 5.8 .0839 1.7 .285

VT/Br–2–17.1 0.000107 .0558 -0.19 195 0.37 505.7 7.5 NA NA 0.61 2.7 .0813 1.5 .559

VT/Br–2–18.1 0.000044 .0562 -0.12 547 0.76 499.5 7.1 NA NA 0.62 1.9 .0804 1.4 .779

VT/Br–2–19.1 — .0573 0.01 287 0.86 499.3 7.3 NA NA 0.64 2.0 .0805 1.5 .754
15

Table 3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data for zircon and monazite from rocks of Vermont.—Continued

[Abbreviations are as follows: Ma, millions of years (mega-annum); NA, not applicable; ppm, parts per million; —, measured 204Pb below detection limit; ρ, error correlation]

Analysis1 Measured 

204Pb/206Pb

Measured 

207Pb/206Pb

Percent 

common 

206Pb 

Uranium

(ppm) Th/U 206Pb/238U (Ma)2

Error 

(Ma)3

207Pb/206Pb 

(Ma)2

Error 

(Ma)3 207Pb/235U4 Error 

(percent)3 206Pb/238U4 Error (percent)3 ρ

VT/Br 2–89 (Newfane tonalite intruding Cram Hill Formation near South Newfane)—Continued

VT/Br–2–20.1 0.000139 .0575 0.02 82 0.60 504.4 10.0 NA NA 0.62 3.7 .0812 2.0 .542

VT/Br–2–21.1 — .0555 -0.25 229 0.58 512.5 7.5 NA NA 0.63 2.1 .0825 1.5 .725

VT/Br–2–7.2 0.000200 .0590 0.18 167 0.61 511.8 7.7 NA NA 0.64 3.1 .0825 1.5 .489

L–18 (Trondhjemite in Barnard Gneiss proper (of Richardson, 1924) north of Proctorsville)

L18–3.1 0.000013 .0571 0.00 1,580 1.22 494.3 7.1 NA NA 0.63 1.6 .0797 1.5 .925

L18–4.1 0.000175 .0570 -0.03 285 0.99 497.8 7.6 NA NA 0.60 2.6 .0800 1.6 .601

L18–5.1 0.000030 .0579 0.05 744 0.73 510.2 7.4 NA NA 0.65 1.8 .0824 1.5 .849

L18–6.1 0.000054 .0827 0.01 158 0.48 1,258.6 19.3 NA NA 2.43 1.9 .2154 1.6 .815

L18–7.1 -0.000017 .0575 0.09 163 0.48 484.6 8.5 NA NA 0.62 2.6 .0782 1.8 .697

L18–8.1 0.001953 .0755 2.15 110 0.55 528.8 12.2 NA NA 0.54 15.8 .0843 2.4 .152

L18–9.1 0.000238 .0563 -0.11 278 0.83 498.5 8.5 NA NA 0.58 3.5 .0800 1.8 .504

L18–10.1 0.000101 .0570 -0.01 339 0.62 494.5 7.6 NA NA 0.61 2.3 .0796 1.6 .674

L18–11.1 -0.000015 .0573 -0.02 920 0.48 508.6 7.4 NA NA 0.65 1.6 .0821 1.5 .902

SP450 (Felsic volcanic layer within Cram Hill Formation at Springfield)

SP450–1.1 -0.000101 .0568 -0.18 345 1.05 490.2 6.2 NA NA 0.64 2.2 .0791 1.3 .596

SP450–2.1 0.000204 .0573 0.37 187 0.54 481.4 6.7 NA NA 0.58 3.1 .0773 1.4 .465

SP450–3.1 0.000182 .0593 0.33 85 0.36 477.1 7.9 NA NA 0.60 5.8 .0768 1.7 .294

SP450–4.1 -0.000084 .0577 -0.15 197 0.40 487.2 6.7 NA NA 0.64 2.4 .0787 1.4 .592

SP450–5.1 0.000084 .0575 0.15 211 0.42 481.8 6.6 NA NA 0.60 3.0 .0776 1.4 .466

SP450–6.1 -0.000058 .0571 -0.10 137 0.43 475.1 7.1 NA NA 0.61 2.6 .0766 1.5 .592

SP450–7.1 0.000006 .0571 0.01 414 0.51 491.1 6.1 NA NA 0.62 1.7 .0792 1.3 .761

SP450–8.1 0.000074 .0590 0.13 151 0.49 478.5 7.0 NA NA 0.62 3.0 .0772 1.5 .497

SP450–9.1 -0.000077 .0572 -0.14 149 0.52 482.3 7.0 NA NA 0.63 3.0 .0778 1.5 .498

SP450–10.1 0.000031 .0554 0.05 291 0.74 488.7 6.6 NA NA 0.60 2.2 .0786 1.4 .630

SP450–11.1 0.000000 .0565 0.00 674 0.89 485.4 5.8 NA NA 0.61 1.5 .0782 1.2 .825

SP450–12.1 -0.000544 .0584 -0.98 79 0.37 476.3 8.4 NA NA 0.71 5.9 .0776 1.8 .308

SP450–13.1 0.000021 .0583 0.04 235 0.46 489.3 6.4 NA NA 0.63 1.9 .0790 1.3 .685

SP450–14.1 -0.000170 .0595 -0.30 75 0.39 475.7 7.7 NA NA 0.66 3.5 .0771 1.7 .472

SP450–15.1 0.000119 .0571 0.21 126 0.69 476.0 6.9 NA NA 0.58 3.2 .0765 1.5 .463

SP450–16.1 0.000019 .0583 0.03 223 0.44 482.5 6.4 NA NA 0.62 2.1 .0778 1.4 .653

SP450–17.1 -0.000149 .0575 -0.27 142 0.42 468.2 6.7 NA NA 0.62 4.4 .0756 1.5 .339

SP450–18.1 0.000080 .0574 0.14 257 0.62 477.4 6.2 NA NA 0.60 2.7 .0768 1.3 .497

SP450–19.1 -0.000002 .0564 0.00 249 0.43 475.5 6.2 NA NA 0.59 1.9 .0765 1.3 .695

SP450–20.1 0.000045 .0562 0.08 286 0.54 487.5 6.2 NA NA 0.60 2.2 .0784 1.3 .580
16

Table 3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data for zircon and monazite from rocks of Vermont.—Continued

[Abbreviations are as follows: Ma, millions of years (mega-annum); NA, not applicable; ppm, parts per million; —, measured 204Pb below detection limit; ρ, error correlation]

Analysis1 Measured 

204Pb/206Pb

Measured 

207Pb/206Pb

Percent 

common 

206Pb 

Uranium

(ppm) Th/U 206Pb/238U (Ma)2

Error 

(Ma)3

207Pb/206Pb 

(Ma)2

Error 

(Ma)3 207Pb/235U4 Error 

(percent)3 206Pb/238U4 Error (percent)3 ρ

MC3432 (Granite in the Braintree Intrusive Complex)

MC3432–1 0.000328 .0532 -0.21 136 0.65 407.9 8.5 NA NA 0.43 5.8 .0648 2.1 .372

MC3432–2 — .0582 0.43 153 0.38 401.9 8.4 NA NA 0.52 3.7 .0646 2.1 .575

MC3432–3 0.000125 .0569 0.21 267 0.52 420.8 8.4 NA NA 0.51 3.4 .0674 2.0 .593

MC3432–4 — .0566 0.19 444 0.83 417.0 8.1 NA NA 0.52 2.7 .0670 2.0 .741

MC3432–5 — .0560 0.06 234 0.53 432.5 8.7 NA NA 0.54 3.1 .0694 2.0 .661

MC3432–6 — .0551 0.05 674 0.37 402.1 7.8 NA NA 0.49 2.5 .0644 2.0 .785

MC3432–7 — .0545 -0.11 239 0.49 430.5 9.2 NA NA 0.52 3.2 .0690 2.2 .680

MC3432–8 0.000405 .0599 0.57 192 0.77 426.1 8.7 NA NA 0.51 5.2 .0682 2.1 .400

MC3432–9 0.000176 .0579 0.35 602 0.43 413.6 8.0 NA NA 0.51 2.9 .0663 2.0 .676

MC3432–10 — .0545 -0.04 148 0.83 406.8 8.5 NA NA 0.49 3.7 .0651 2.1 .579

MC3432–11 0.000148 .0557 0.00 371 0.52 438.5 8.6 NA NA 0.52 3.3 .0702 2.0 .614

MC3432–12 0.000087 .0542 -0.18 397 0.48 437.0 8.6 NA NA 0.51 3.1 .0699 2.0 .660

MC3432–13 — .0582 0.39 234 0.51 413.6 8.4 NA NA 0.53 3.2 .0665 2.1 .650

MC3432–14 — .0554 0.02 392 0.50 420.9 8.3 NA NA 0.52 2.7 .0675 2.0 .732

MC3432–15 — .0586 0.45 257 0.42 411.2 8.2 NA NA 0.53 3.0 .0662 2.0 .677

MC3432–16 0.000126 .0548 -0.09 317 0.56 433.4 8.5 NA NA 0.51 3.2 .0693 2.0 .618

VT–Nq–1–97 (Trondhjemite of the Newport Intrusive Complex)

VT–Nq–1–1.1 — .0563 0.12 1,105 0.37 425.2 3.3 NA NA 0.53 1.2 .0683 0.8 .637

VT–Nq–1–2.1 0.000018 .0543 -0.04 636 0.46 395.8 3.3 NA NA 0.47 1.6 .0633 0.8 .533

VT–Nq–1–3.1 0.000015 .0552 -0.02 980 0.25 428.0 3.4 NA NA 0.52 1.3 .0686 0.8 .615

VT–Nq–1–4.1 0.000016 .0552 0.02 1,177 0.35 414.0 3.3 NA NA 0.50 1.3 .0663 0.8 .610

VT–Nq–1–5.1 0.000255 .0593 0.63 1,010 0.52 378.9 3.1 NA NA 0.46 2.1 .0606 0.8 .393

VT–Nq–1–6.1 -0.000019 .0550 -0.05 768 0.34 427.1 3.4 NA NA 0.52 1.4 .0685 0.8 .598

VT–Nq–1–7.1 0.000040 .0555 0.04 700 0.29 422.7 3.5 NA NA 0.51 1.6 .0677 0.8 .538

VT–Nq–1–8.1 0.000044 .0554 0.01 986 0.35 425.9 3.4 NA NA 0.52 1.4 .0682 0.8 .571

VT–Nq–1–9.1 — .0562 0.17 1,142 0.32 403.9 3.2 NA NA 0.50 1.3 .0648 0.8 .612

VT–Nq–1–10.1 0.000697 .0636 1.10 1,718 0.71 399.5 3.1 NA NA 0.47 3.6 .0638 0.8 .220

VT–Nq–1–11.1 0.000148 .0571 0.23 1,105 0.46 422.3 3.3 NA NA 0.51 1.6 .0677 0.8 .510

VT–Nq–1–12.1 0.000863 .0672 1.61 876 1.13 379.0 3.1 NA NA 0.46 3.8 .0606 0.8 .220

VT–Nq–1–13.1 0.000020 .0563 0.12 1,008 0.42 424.1 3.3 NA NA 0.53 1.3 .0681 0.8 .619

VT–Nq–1–14.1 0.000006 .0559 -0.03 2,852 0.23 457.8 3.3 NA NA 0.57 0.9 .0736 0.7 .807

VT–CSTR–2 (Granite in Chester dome)

VT–CSTR–2–1.1 0.000114 .0561 0.06 524 0.06 438.4 4.9 NA NA 0.53 2.2 .0703 1.1 .532

VT–CSTR–2–2.1 0.000075 .0885 0.05 230 0.39 1,385.6 17.3 NA NA 2.89 1.6 .2396 1.3 .791

VT–CSTR–2–3.1 0.000022 .0546 -0.01 2,130 0.07 398.6 4.9 NA NA 0.48 1.5 .0637 1.3 .858
17

Table 3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data for zircon and monazite from rocks of Vermont.—Continued

[Abbreviations are as follows: Ma, millions of years (mega-annum); NA, not applicable; ppm, parts per million; —, measured 204Pb below detection limit; ρ, error correlation]

Analysis1 Measured 

204Pb/206Pb

Measured 

207Pb/206Pb

Percent 

common 

206Pb 

Uranium

(ppm) Th/U 206Pb/238U (Ma)2

Error 

(Ma)3

207Pb/206Pb 

(Ma)2

Error 

(Ma)3 207Pb/235U4 Error 

(percent)3 206Pb/238U4 Error (percent)3 ρ

VT–CSTR–2 (Granite in Chester dome)—Continued

VT–CSTR–2–4.1 0.000272 .0579 0.41 141 0.04 395.9 5.7 NA NA 0.47 5.5 .0633 1.5 .270

VT–CSTR–2–4.2 0.000731 .0628 1.01 40 0.01 394.5 8.3 NA NA 0.45 13.4 .0629 2.2 .164

VT–CSTR–2–3.2 — .0787 0.07 147 0.47 1,149.8 14.3 NA NA 2.12 1.9 .1954 1.3 .662

VT–CSTR–2–5.1 0.000114 .0580 0.43 604 0.01 390.7 4.4 NA NA 0.49 2.2 .0626 1.1 .513

VT–CSTR–2–6.1 0.000051 .0539 -0.05 795 0.04 384.8 4.2 NA NA 0.45 1.9 .0614 1.1 .597

VT–CSTR–2–7.1 0.000030 .0543 -0.09 1,417 0.10 411.2 4.4 NA NA 0.49 1.6 .0658 1.1 .697

VT–CSTR–2–8.1 — .0564 0.27 886 0.07 380.0 4.2 NA NA 0.47 2.3 .0609 1.1 .486

VT–CSTR–2–9.1 — .0543 -0.01 1,623 0.09 387.9 4.1 NA NA 0.46 1.4 .0620 1.1 .767

VT–CSTR–2–10.1 0.000012 .0546 -0.04 2,552 0.06 406.9 4.3 NA NA 0.49 1.3 .0651 1.1 .815

VT–CSTR–2–10.1 — .0837 0.06 136 0.39 1,274.0 16.1 NA NA 2.52 1.9 .2187 1.3 .686

VT–CSTR–2–11.1 0.000033 .0557 0.09 1,409 0.07 412.5 4.7 NA NA 0.50 1.9 .0661 1.2 .610

VT–CSTR–2–12.1 — .0551 0.08 1,634 0.12 390.6 6.4 NA NA 0.47 1.9 .0625 1.7 .878

VT–CSTR–2–13.1 0.000031 .0539 -0.08 2,743 0.08 393.3 4.4 NA NA 0.46 1.4 .0628 1.1 .784

VT–CSTR–2–14.1 0.000035 .0552 0.08 2,124 0.04 394.2 4.2 NA NA 0.48 1.4 .0631 1.1 .778

VT–CSTR–2–15.1 0.000015 .0541 -0.02 2,012 0.14 384.7 4.8 NA NA 0.46 1.8 .0615 1.3 .715

Barre#2 (Barre Granite)

BARRE–1.1 — .0537 -0.16 18,759 0.36 414.0 5.3 NA NA 0.49 1.3 .0662 1.3 .976

BARRE–2.1 — .0550 0.15 811 0.14 362.0 5.7 NA NA 0.44 2.1 .0578 1.6 .756

BARRE–3.1 0.000255 .0570 0.39 1,170 0.12 365.5 5.1 NA NA 0.43 2.5 .0583 1.4 .571

BARRE–4.1 0.000027 .0547 0.10 1,023 0.13 366.2 4.7 NA NA 0.44 1.8 .0585 1.3 .713

BARRE–5.1 0.000133 .0565 0.34 1,317 0.18 363.7 6.0 NA NA 0.44 2.2 .0581 1.7 .751

BARRE–6.1 0.000016 .0541 0.02 1,893 0.24 369.6 4.7 NA NA 0.44 1.6 .0590 1.3 .798

BARRE–7.1 0.000029 .0544 0.05 1,595 0.25 372.0 5.3 NA NA 0.44 2.0 .0594 1.4 .742

BARRE–8.1 — .0544 0.04 2,177 0.37 376.8 5.1 NA NA 0.45 1.6 .0602 1.4 .853

BARRE–9.1 — .0536 -0.05 1,191 0.15 368.9 4.9 NA NA 0.43 1.9 .0589 1.4 .726

BARRE–10.1 0.000036 .0560 0.22 910 0.21 379.2 4.9 NA NA 0.46 1.9 .0607 1.3 .696

BARRE–11.1 0.000021 .0551 0.17 1,630 0.21 360.4 4.6 NA NA 0.43 1.6 .0576 1.3 .803

BARRE–12.1 0.000012 .0535 -0.06 1,480 0.24 370.4 4.9 NA NA 0.43 1.7 .0591 1.3 .796

BARRE–13.1 0.000038 .0527 -0.14 1,260 0.17 365.5 4.7 NA NA 0.42 1.8 .0582 1.3 .714

BARRE–14.1 — .0553 0.15 2,060 0.29 374.1 4.8 NA NA 0.46 1.6 .0598 1.3 .831

BARRE–15.1 0.000042 .0544 0.06 935 0.14 367.9 4.8 NA NA 0.44 1.9 .0587 1.3 .698

VT/Br 1–89 (Black Mountain pluton)

VT/Br1–1.1 — .0526 -0.10 560 0.30 345.0 5.0 NA NA 0.40 2.4 .0549 1.5 .612

VT/Br1–2.1 — .0539 0.08 644 0.25 342.5 4.6 NA NA 0.41 3.1 .0546 1.4 .446
18

Table 3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data for zircon and monazite from rocks of Vermont.—Continued

[Abbreviations are as follows: Ma, millions of years (mega-annum); NA, not applicable; ppm, parts per million; —, measured 204Pb below detection limit; ρ, error correlation]

Analysis1 Measured 

204Pb/206Pb

Measured 

207Pb/206Pb

Percent 

common 

206Pb 

Uranium

(ppm) Th/U 206Pb/238U (Ma)2

Error 

(Ma)3

207Pb/206Pb 

(Ma)2

Error 

(Ma)3 207Pb/235U4 Error 

(percent)3 206Pb/238U4 Error (percent)3 ρ

VT/Br 1–89 (Black Mountain pluton)—Continued

VT/Br1–3.1 0.000059 .0533 0.03 452 0.24 331.3 8.1 NA NA 0.38 3.3 .0527 2.5 .748

VT/Br1–4.1 — .0551 0.20 682 0.25 350.4 6.7 NA NA 0.43 2.5 .0560 1.9 .769

VT/Br1–5.1 0.000128 .0532 -0.06 367 0.31 355.2 6.7 NA NA 0.40 3.4 .0565 1.9 .567

VT/Br1–5.2 0.000044 .0548 -0.10 28,188 0.02 434.4 5.4 NA NA 0.52 1.3 .0696 1.3 .974

VT/Br1–6.1 0.000102 .0554 0.10 233 0.27 395.5 7.4 NA NA 0.47 3.5 .0632 1.9 .546

VT/Br1–7.1 — .0506 -0.42 276 0.14 371.1 7.5 NA NA 0.41 3.1 .0590 2.0 .661

VT/Br1–8.1 — .0520 -0.24 560 0.34 369.2 6.8 NA NA 0.42 2.5 .0588 1.9 .752

VT/Br1–9.1 — .0533 -0.07 309 0.29 364.7 8.1 NA NA 0.43 3.1 .0582 2.3 .721

VT/Br1–10.1 — .0540 0.05 478 0.36 353.0 5.8 NA NA 0.42 2.4 .0563 1.7 .688

VT/Br1–11.1 — .0554 0.18 448 0.34 370.0 5.0 NA NA 0.45 2.2 .0592 1.4 .607

VT/Br1–12.1 0.000135 .0539 0.00 241 0.26 365.8 5.4 NA NA 0.42 3.9 .0582 1.5 .382

VT/Br1–13.1 — .0547 0.05 293 0.31 380.1 6.6 NA NA 0.46 3.0 .0608 1.7 .584

VT/Br1–14.1 0.000045 .0538 0.08 516 0.37 335.0 4.6 NA NA 0.39 2.4 .0533 1.4 .571

VT/Br1–15.1 0.000034 .0541 0.04 912 0.22 360.1 5.1 NA NA 0.42 2.0 .0574 1.4 .715

VT/Br1–16.1 — .0533 -0.06 479 0.19 361.1 8.7 NA NA 0.42 3.0 .0576 2.4 .799

VT/Br1–17.1 0.000112 .0516 -0.16 488 0.29 325.8 6.2 NA NA 0.36 3.0 .0517 1.9 .637

VT/Br1–18.1 — .0534 -0.02 483 0.19 351.7 4.7 NA NA 0.41 2.2 .0561 1.4 .608

VT/Br1–19.1 — .0544 0.08 324 0.15 360.3 12.3 NA NA 0.43 4.1 .0575 3.5 .850

VT/Br1–20.1 0.000436 .0586 0.59 863 0.20 363.2 8.2 NA NA 0.42 4.8 .0578 2.3 .484

VT/Br1–21.1 0.000100 .0552 -0.09 19,799 0.03 447.0 5.6 NA NA 0.53 1.3 .0716 1.3 .952

VT/Br1–22.1 0.000056 .0547 0.04 10,177 0.07 387.5 4.9 NA NA 0.46 1.4 .0619 1.3 .907

VT/Br1–23.1 0.000100 .0551 0.11 20,856 0.02 378.9 4.8 NA NA 0.45 1.3 .0605 1.3 .952

VT/Br1–24.1 0.000245 .0574 0.10 30,266 0.02 476.7 6.0 NA NA 0.57 1.3 .0765 1.3 .952

VT/Br1–25.1 0.000033 .0544 -0.02 9,736 0.16 393.3 5.0 NA NA 0.47 1.5 .0629 1.3 .831

mVT/Br11.2 0.000351 0.058 0.53 1,241 41.4 361.1 3.5 NA NA 0.42 4.4 .0576 1.0 .227

mVT/Br113.2 0.000233 0.054 0.02 1,298 32.1 364.9 3.5 NA NA 0.40 3.5 .0580 1.0 .277

mVT/Br13.1 0.000335 0.060 0.76 1,153 75.0 362.0 3.6 NA NA 0.44 4.2 .0578 1.0 .240

mVT/Br14.1 0.000105 0.057 0.39 1,533 40.5 359.3 3.2 NA NA 0.44 2.3 .0574 0.9 .399

mVT/Br114.1 0.000511 0.058 0.52 496 77.8 364.7 4.3 NA NA 0.40 7.2 .0580 1.2 .173

mVT/Br114.2 0.000125 0.056 0.30 1,042 34.2 364.5 3.6 NA NA 0.44 2.9 .0582 1.0 .340

mVT/Br15.1 0.000116 0.060 0.79 758 93.1 359.7 3.9 NA NA 0.47 3.1 .0577 1.1 .345

mVT/Br115.2 0.000206 0.056 0.24 1,823 30.2 354.3 3.2 NA NA 0.41 3.1 .0564 0.9 .300

mVT/Br115.1 0.000245 0.057 0.41 804 93.4 361.3 3.9 NA NA 0.43 4.3 .0576 1.1 .257

mVT/Br116.1 0.000192 0.055 0.08 617 33.0 367.4 3.9 NA NA 0.42 4.0 .0585 1.1 .272
19

Table 3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data for zircon and monazite from rocks of Vermont.—Continued

[Abbreviations are as follows: Ma, millions of years (mega-annum); NA, not applicable; ppm, parts per million; —, measured 204Pb below detection limit; ρ, error correlation]

Analysis1 Measured 

204Pb/206Pb

Measured 

207Pb/206Pb

Percent 

common 

206Pb 

Uranium

(ppm) Th/U 206Pb/238U (Ma)2

Error 

(Ma)3

207Pb/206Pb 

(Ma)2

Error 

(Ma)3 207Pb/235U4 Error 

(percent)3 206Pb/238U4 Error (percent)3 ρ

VT/Br 1–89 (Black Mountain pluton)—Continued

mVT/Br117.1 0.000856 0.066 1.50 1,649 29.7 355.6 3.3 NA NA 0.42 6.4 .0567 1.0 .150

mVT/Br117.2 0.000159 0.056 0.27 2,564 21.8 358.9 3.1 NA NA 0.42 2.3 .0572 0.9 .377

mVT/Br118.1 0.000153 0.057 0.41 791 77.2 366.7 3.7 NA NA 0.44 3.2 .0586 1.0 .322

mVT/Br119.1 0.000107 0.056 0.28 1,326 49.9 359.0 3.3 NA NA 0.43 2.5 .0573 0.9 .377

mVT/Br119.2 0.000063 0.056 0.27 1,811 21.9 363.9 3.2 NA NA 0.44 1.9 .0582 0.9 .452

mVT/Br120.1 0.000364 0.060 0.75 1,039 62.6 357.5 3.4 NA NA 0.43 4.2 .0571 1.0 .234

mVT/Br121.1 0.000227 0.057 0.35 668 38.7 365.5 3.8 NA NA 0.43 3.9 .0583 1.1 .268

mVT/Br122.1 0.000135 0.054 0.08 1,750 29.5 363.3 3.2 NA NA 0.42 3.0 .0579 0.9 .302

mVT/Br111.1 0.000045 0.054 0.08 3,079 10.3 364.2 3.0 NA NA 0.43 1.6 .0581 0.8 .535

mVT/Br123.1 0.000454 0.057 0.37 1,528 49.8 361.0 3.3 NA NA 0.40 4.5 .0573 1.0 .212

mVT/Br123.2 0.000752 0.068 1.81 568 62.7 355.5 4.0 NA NA 0.45 7.0 .0570 1.2 .172

mVT/Br110.1 0.000134 0.054 -0.02 987 45.8 372.7 3.6 NA NA 0.42 2.9 .0594 1.0 .341

mVT/Br124.1 0.000355 0.058 0.50 811 125.8 355.1 3.8 NA NA 0.41 5.4 .0565 1.1 .204

mVT/Br124.2 0.000093 0.056 0.24 1,573 28.8 363.9 3.3 NA NA 0.44 2.5 .0581 0.9 .369

mVT/Br16.1 0.000091 0.054 0.04 893 44.9 364.9 3.7 NA NA 0.42 2.9 .0582 1.0 .355

mVT/Br17.1 0.000393 0.058 0.53 666 73.1 364.4 3.7 NA NA 0.42 4.7 .0580 1.1 .225

mVT/Br18.1 0.000045 0.055 0.22 2,963 15.5 355.8 2.9 NA NA 0.43 1.5 .0568 0.8 .557

mVT/Br125.1 0.000273 0.055 0.13 1,310 47.8 364.9 3.3 NA NA 0.41 3.4 .0580 0.9 .271

mVT/Br125.2 0.001054 0.070 1.95 716 49.3 367.2 3.7 NA NA 0.44 7.9 .0586 1.1 .140

mVT/Br19.1 0.000921 0.061 0.85 302 117.8 377.6 4.7 NA NA 0.39 11.1 .0598 1.4 .124

VT/Pl 2–91 (Granite dike south of Plymouth)

VT/Pl1–1.1 0.000033 .0790 -0.11 315 0.38 1,195.4 24.8 NA NA 2.20 2.7 .2034 2.1 .782

VT/Pl1–2.1 — .0847 0.15 225 0.35 1,279.5 26.9 NA NA 2.57 2.5 .2199 2.2 .879

VT/Pl1–3.1 0.000096 .0860 0.26 155 0.39 1,288.5 27.8 NA NA 2.59 2.7 .2215 2.2 .823

VT/Pl1–4.1 — .0543 0.00 47 0.02 383.9 13.5 NA NA 0.46 6.9 .0614 3.6 .517

VT/Pl1–5.1 — .0575 0.31 288 0.04 411.0 9.0 NA NA 0.52 3.3 .0660 2.2 .667

VT/Pl1–5.2 — .0855 0.48 359 0.31 1,232.2 25.4 NA NA 2.50 2.3 .2117 2.1 .925

VT/Pl1–6.1 — .0759 -0.33 267 0.55 1,165.9 26.5 NA NA 2.07 2.6 .1976 2.4 .901

VT/Pl1–7.1 0.000102 .0549 0.06 527 0.01 387.1 8.2 NA NA 0.46 3.1 .0618 2.2 .699

VT/Pl1–8.1 — .0550 0.14 79 0.01 366.3 9.0 NA NA 0.44 7.1 .0586 2.5 .344

VT/Pl1–9.1 — .0740 0.13 197 0.03 1,010.6 21.3 NA NA 1.73 2.6 .1699 2.2 .843

VT/Pl1–10.1 — .0727 0.18 485 0.06 963.9 19.8 NA NA 1.62 2.3 .1616 2.1 .915

VT/Pl1–11.1 0.000271 .0594 0.63 3,187 0.23 384.4 7.9 NA NA 0.47 2.4 .0615 2.1 .858

VT/Pl1–12.1 0.001328 .0726 2.31 556 0.05 368.2 7.8 NA NA 0.43 6.7 .0587 2.2 .327
20

Table 3. Sensitive high resolution ion microprobe (SHRIMP) uranium-thorium-lead (U-Th-Pb) data for zircon and monazite from rocks of Vermont.—Continued

[Abbreviations are as follows: Ma, millions of years (mega-annum); NA, not applicable; ppm, parts per million; —, measured 204Pb below detection limit; ρ, error correlation]

Analysis1 Measured 

204Pb/206Pb

Measured 

207Pb/206Pb

Percent 

common 

206Pb 

Uranium

(ppm) Th/U 206Pb/238U (Ma)2

Error 

(Ma)3

207Pb/206Pb 

(Ma)2

Error 

(Ma)3 207Pb/235U4 Error 

(percent)3 206Pb/238U4 Error (percent)3 ρ

VT/Pl 2–91 (Granite dike south of Plymouth)—Continued

VT/Pl1–13.1 0.007440 .1525 12.18 3,609 0.25 379.0 12.5 NA NA 0.35 80.0 .0597 3.9 .048

VT/Pl1–14.1 0.001482 .0727 2.35 645 0.21 363.3 7.9 NA NA 0.41 13.7 .0578 2.3 .171

VT/Pl1–16.1 0.004493 .1171 7.82 214 0.02 371.7 9.8 NA NA 0.42 42.2 .0592 3.2 .076

VT/Pl1–17.1 — .0666 0.81 253 0.19 603.1 13.1 NA NA 0.91 3.0 .0989 2.2 .755

1

The prefix “m” for analyses of sample VT/Br 1–89 means monazite; all other samples are zircon; labels for individual analyses may be abbreviated.

2 206Pb/238U and 207Pb/206Pb ages are corrected for common lead using the 204Pb-correction method, which is based on a model by Stacey and Kramers (1975). Decay 

constants from Steiger and Jäger (1977).

3

1σ errors.

4

Radiogenic ratios, corrected for common lead using the 204Pb-correction method, which is based on the model by Stacey and Kramers (1975).
21

Table 4. Thermal ionization mass spectrometry (TIMS) uranium-lead (U-Pb) data for zircon from rocks of Vermont.

[Abbreviations: A, abraded; C, colorless; E, elongate; Ma, millions of years (mega-annum); mg, milligrams; Mg, magnetic; NMD, nonmagnetic, diamagnetic; 

Pb, lead; ppm, parts per million; U, uranium. The term “dust” refers to rim material removed by abrasion]

Fraction Weight 

(mg)

Concentrations 

(ppm) Ratios (percent error)2 Ages (Ma)3,4

U Pb 206Pb/204Pb1 206Pb/

238U 207Pb/235U 207Pb/206Pb

206Pb/ 

238U 

207Pb/ 

235U 

207Pb/ 

206Pb

VT/Pe 2–88 (Bondville metadacite at Winhall River bridge)

(-100+150) NMDA 0.42 148.6 33.07 1648.5 0.2197 (0.20) 2.573 (0.22) 0.0849 (0.10) 1280 1293 1314

(+100)NMDEA 0.21 221.3 49.81 1115.8 0.2295 (0.15) 2.738 (0.22) 0.0865 (0.14) 1332 1339 1350

(-100+150) NMDEA 0.69 286.9 54.63 3865.0 0.1902 (0.15) 2.171 (0.17) 0.0828 (0.07) 1122 1172 1264

(-100+150) NMDEA 0.51 179.9 40.08 1344.5 0.2176 (0.42) 2.576 (0.44) 0.0858 (0.12) 1269 1294 1335

(-100+150) NMDEA 0.41 219.3 49.17 1367.9 0.2207 (0.15) 2.593 (0.20) 0.0852 (0.12) 1285 1299 1320

(+100) Dust 0.61 170.0 30.73 438.3 0.1709 (0.15) 1.893 (0.25) 0.0803 (0.17) 1017 1079 1205

(-100+150) Dust 0.44 214.0 40.48 1055.3 0.1912 (0.15) 2.150 (0.23) 0.0815 (0.17) 1128 1165 1235

(-100+150) Dust 0.06 1990 80.44 185.24 0.1557 (0.36) 1.665 (0.81) 0.0776 (0.64) 933 995 1136

(-100+150) Dust 0.10 167.9 32.72 192.91 0.1787 (0.42) 1.928 (0.94) 0.0783 (0.75) 1060 1091 1153

(-100+150) Dust 0.10 124.8 20.05 106.98 0.1278 (0.77) 1.356 (01.8) 0.0770 (01.4) 775 870 1120

(-100+150) Dust 0.28 179.4 31.1 411.78 0.1696 (0.83) 1.831 (0.90) 0.0783 (0.31) 1010 1057 1155

87Rat–2 (College Hill Granite Gneiss at Stratton Mountain)

(-50+100) NMDA 1.15 221.1 49.43 433.76 0.2014 (0.48) 2.271 (0.49) 0.0818 (0.11) 1183 1203 1240

(-50+100) NMDAMg 0.87 217.6 39.25 626.87 0.1712 (0.54) 1.941 (0.54) 0.0823 (0.08) 1019 1095 1252

(-100+150) NMDA 0.92 205.0 43.48 226.99 0.2017 (0.66) 2.280 (0.65) 0.0820 (0.23) 1184 1206 1245

(-100+150) NMDAMg 0.90 220.2 46.85 214.97 0.2051 (0.70) 2.313 (0.69) 0.0818 (0.27) 1203 1216 1241

(-150+200) NMDA 1.93 303.8 61.55 1467.2 0.2001 (0.47) 2.215 (0.47) 0.0803 (0.06) 1176 1186 1205

(-150+200) NMDAMg 1.84 320.5 69.59 530.86 0.1988 (0.47) 2.201 (0.48) 0.0803 (0.10) 1169 1181 1204

(-200+250) NMD 4.10 329.5 65.14 1050.8 0.1924 (0.47) 2.098 (0.47) 0.0791 (0.06) 1135 1148 1174

(-400) 0.87 329.1 64.38 651.17 0.1869 (0.47) 2.022 (0.49) 0.0785 (0.13) 1105 1123 1159

(-50+100) Dust 0.24 183.9 30.40 339.2 0.1719 (0.58) 1.805 (0.61) 0.0761 (0.26) 1023 1047 1099

VT/Lo 1–89 (granitic gneiss)

(-100+150) NMDEA 0.65 156.7 31.97 3284.5 0.2038 (0.24) 2.271 (0.25) 0.0808 (0.08) 1196 1203 1217

(-100+150) NMDEA 0.72 174.9 35.38 4199.5 0.2025 (0.15) 2.249 (0.17) 0.0806 (0.07) 1187 1196 1211

(-150+200) NMDEA 0.37 201.8 42.60 3168.1 0.2132 (0.18) 2.377 (0.21) 0.0808 (0.09) 1246 1236 1218

(-150+200) NMDEA 0.47 197.3 40.18 2289.8 0.2055 (0.13) 2.278 (0.15) 0.0805 (0.08) 1205 1206 1208

(-150+200) NMDEA 0.34 187.2 37.91 3187.0 0.2045 (0.12) 2.277 (0.14) 0.0808 (0.07) 1200 1205 1216

(-100+150) Dust 0.17 137.8 31.19 176.92 0.1856 (0.31) 1.978 (0.68) 0.0773 (0.54) 1097 1108 1128
22

Table 4. Thermal ionization mass spectrometry (TIMS) uranium-lead (U-Pb) data for zircon from rocks of Vermont.—Continued

[Abbreviations: A, abraded; C, colorless; E, elongate; Ma, millions of years (mega-annum); mg, milligrams; Mg, magnetic; NMD, nonmagnetic, diamagnetic; 

Pb, lead; ppm, parts per million; U, uranium. The term “dust” refers to rim material removed by abrasion]

Fraction Weight 

(mg)

Concentrations 

(ppm) Ratios (percent error)2 Ages (Ma)3,4

U Pb 206Pb/204Pb1 206Pb/

238U 207Pb/235U 207Pb/206Pb

206Pb/ 

238U 

207Pb/ 

235U 

207Pb/ 

206Pb

SR3053 (Tonalite gneiss in the North River Igneous Suite)

(-100+150) ECA 0.011 294.8 31.00 237.79 0.0763 (0.55) 0.5975 (0.70) 0.0568 (0.42) 473.8 475.6 484.5

(-100+150) ECA 0.014 372.5 33.39 1020.5 0.0770 (0.26) 0.6034 (0.31) 0.0569 (0.16) 477.9 479.4 486.3

(-100+150) ECA 0.016 302.8 29.95 256.66 0.0792 (0.93) 0.6260 (1.1) 0.0573 (0.55) 491.3 493.6 504.2

(-100+150) ECA 0.026 278.1 25.17 514.9 0.0770 (0.68) 0.6033 (0.81) 0.0568 (0.42) 478.4 479.3 483.8

(-100+150) ECA 0.017 298.7 35.41 139.80 0.0772 (0.87) 0.6100 (1.15) 0.0573 (0.71) 479.4 483.5 503.4

(-100+150) ECA 0.011 381.8 34.99 472.60 0.0771 (0.58) 0.6041 (0.70) 0.0569 (0.38) 478.5 479.8 486.1

(-100+150) ECA 0.024 347.3 30.49 831.88 0.7677 (0.62) 0.6025 (0.73) 0.0569 (0.35) 476.8 478.9 488.7

(-100+150) ECA 0.010 433.1 47.48 164.51 0.7655 (1.05) 0.5995 (1.28) 0.0568 (0.71) 475.5 476.9 483.8

1

Measured ratio. 

2

2σ errors.

3

Corrected for common lead using appropriate values from Stacey and Kramers (1975).

4

Decay constants used for age calculation from Steiger and Jäger (1977).
23

Sample number: 1 

Description: Hornblende diorite gneiss at South Londonderry

Field number: Lon–1–A 

Method: SHRIMP

Age: 1,393±9 Ma

Sample location coordinates (WGS 84 datum): 43°11′06′′N., 72°48′09′′W. 

Sample location description: In bed of the West River, 0.7 km southeast of South Londonderry in the Londonderry 

quadrangle.

Figure 1. Conventional concordia plot of SHRIMP U-Pb data for zircon from hornblende diorite gneiss at South 

Londonderry, Vermont. White-filled error ellipses represent data from oscillatory-zoned cores used in the weighted 

average calculation of 207Pb/206Pb ages (see inset) for determining the time of emplacement of the igneous 

protolith. Gray error ellipse represents an analysis that overlapped an igneous core and metamorphic rim, yielding 

a geologically meaningless mixed age. Abbreviations are as follows: km, kilometers; Ma, millions of years (megaannum); MSWD, mean square of the weighted deviates; SHRIMP, sensitive high resolution ion microprobe; WGS 

84, World Geodetic System datum of 1984.
24

Sample number: 2 

Description: Baileys Mills tonalitic gneiss in the Chester dome

Field number: VT–CSTR–1 

Method: SHRIMP

Age: 1,383±13 Ma

Sample location coordinates (WGS 84 datum): 43°19′10′′N., 72°36′29′′W. 

Sample location description: Roadcut on the eastern side of Vermont Route 103, about 600 m south of the intersection with 

Vermont Route 10 in the Chester quadrangle. 

VT-CSTR-1 

Baileys Mills tonalitic gneiss

Figure 2. Conventional concordia plot of SHRIMP U-Pb data for zircon from tonalitic gneiss at Baileys Mills, 

Vermont. White-filled error ellipses represent data from oscillatory-zoned cores used in the weighted average 

calculation of 207Pb/

206Pb ages (see inset) for determining the time of emplacement of the igneous protolith. Gray 

error ellipses represent data from metamorphic rims (dark, unzoned in CL; approx. 1.05, 1.17–1.31 Ga). 

Horizontally ruled ellipses represent older ages (approx. 1.5 Ga) in cores from inherited zircon. Abbreviations are 

as follows: approx., approximately; CL, cathodoluminescence; Ga, billions of years (giga-annum); m, meters; Ma, 

millions of years (mega-annum); MSWD, mean square of the weighted deviates; SHRIMP, sensitive high resolution

ion microprobe; WGS 84, World Geodetic System datum of 1984.
25

Sample number: 3 

Description: Rawsonville trondhjemite gneiss at Bromley Mountain

Field number: VT/Pe 1–88 (6327)

Method: SHRIMP

Age: 1,367±16 Ma

Sample location coordinates (WGS 84 datum): 43°13′40′′N., 72°56′26′′W.

Sample location description: Sample collected near the top of Bromley Mountain in the Peru quadrangle, approximately 7 

m south of the top of the ski lift.

 

VT/Pe 1-88 (6327)

Rawsonville

Figure 3. Conventional concordia plot of SHRIMP U-Pb data for zircon from Rawsonville trondhjemite gneiss at 

Bromley Mountain, Vermont. White-filled error ellipses represent data from oscillatory-zoned cores used in the 

weighted average calculation of 207Pb/

206Pb ages (see inset) for determining the time of emplacement of the 

igneous protolith. Gray error ellipse represents an analysis of a damaged area (crack) within a core, resulting in 

lead loss; age probably is geologically meaningless. Previous discordant TIMS data (Ratcliffe and others, 1991) 

suggested an age of 1,356.5±2.7 Ma for this sample. Abbreviations are as follows: m, meters; Ma, millions of years 

(mega-annum); MSWD, mean square of the weighted deviates; SHRIMP, sensitive high resolution ion microprobe; 

TIMS, thermal ionization mass spectrometry; WGS 84, World Geodetic System datum of 1984.
26

Sample number: 4 

Description: Felchville Gneiss (aplite facies) at Cavendish Gorge

Field number: C718

Method: SHRIMP

Age: 1,372±11 Ma

Sample location coordinates (WGS 84 datum): 43°23′04′′N., 72°35′54′′W. 

Sample location description: Southern side of the power station at Cavendish Gorge in sharp contact with underlying 

dolomite marble of the Cavendish Formation in the Cavendish quadrangle. 

C718

Felchville Gneiss

Figure 4. Conventional concordia plot of SHRIMP U-Pb data for zircon from Felchville Gneiss (aplite facies) from 

Cavendish Gorge, Vermont. White-filled error ellipses represent data from oscillatory-zoned cores used in the 

weighted average calculation of 207Pb/

206Pb ages (see inset) for determining the time of emplacement of the 

igneous protolith. Gray error ellipses represent data from metamorphic rims (dark, unzoned in CL; approx. 1.06–

1.09, 1.21–1.29 Ga). Horizontally ruled ellipses represent older ages (approx. 1.45 Ga) in cores from inherited 

zircon. Abbreviations are as follows: approx., approximately; Ga, billions of years (giga-annum); Ma, millions of 

years (mega-annum); MSWD, mean square of the weighted deviates; SHRIMP, sensitive high resolution ion 

microprobe; WGS 84, World Geodetic System datum of 1984.
27

Sample number: 5 

Description: Felchville Gneiss (trondhjemite facies) at Felchville

Field number: C609

Method: SHRIMP 

Age: 1,370±11 Ma

Sample location coordinates (WGS 84 datum): 43°28′10′′N., 72°32′00′′W. 

Sample location description: Roadcut on the western side of Vermont Route 106, opposite its intersection with Vermont 

Route 44 in the Cavendish quadrangle. 

C609

Felchville Gneiss

Figure 5. Conventional concordia plot of SHRIMP U-Pb data for zircon from Felchville Gneiss (trondhjemite 

facies) from Felchville, Vermont. White-filled error ellipses represent data from oscillatory-zoned cores used in the 

weighted average calculation of 207Pb/

206Pb ages (see inset) for determining the time of emplacement of the 

igneous protolith. Gray error ellipses represent data from metamorphic rims (dark, unzoned in CL; approx. 1.06, 

1.29–1.31 Ga). One rim (not shown) has an age of about 500 Ma. Abbreviations are as follows: approx., 

approximately; CL, cathodoluminescence; Ga, billions of years (giga-annum); Ma, millions of years (mega-annum); 

MSWD, mean square of the weighted deviates; SHRIMP, sensitive high resolution ion microprobe; WGS 84, World 

Geodetic System datum of 1984.
28

Sample number: 6B

Description: Bondville metadacite at Winhall River bridge

Field number: VT/Pe 2–88 (6329)

Method: TIMS

Age: approx. 1,342 Ma

Sample location coordinates (WGS 84 datum): 43°08′40′′N., 72°52′34′′W. 

Sample location description: Winhall River bridge on Vermont Route 30, Bondville, Vt. Sample collected from a pavement 

outcrop exposed at the base of the eastern bridge abutment during construction. 

≈1342 Ma

Figure 6. Conventional concordia plot of TIMS U-Pb data for zircon from Bondville metadacite at Winhall River

bridge in Bondville, Vermont. White-filled circles represent data from cores (some of which were in Ratcliffe and 

others, 1991); black-filled diamonds represent material removed by abrasion. Because most of the data are 

discordant, the best estimate of the age of this rock is the 207Pb/206Pb age of the least discordant fraction (approx. 

1,342 Ma). Abbreviations are as follows: ≈, approximately; Ma, millions of years (mega-annum); TIMS, thermal 

ionization mass spectrometry; WGS 84, World Geodetic System datum of 1984.
29

Sample number: 7 

Description: Cole Pond tonalite gneiss

Field number: 87Rat–1 (3016A)

Method: SHRIMP

Age: 1,321±9 Ma

Sample location coordinates (WGS 84 datum): 43°08′37′′N., 72°48′38′′W. 

Sample location description: Roadcuts on the western side of Cole Pond Road, a dirt road leading to Cole Pond from 

Vermont Route 100, approximately 160 m southwest of Cole Pond in the Londonderry quadrangle. 

87RAT-1 (3016A)

Cole Pond

Figure 7. Conventional concordia plot of SHRIMP U-Pb data for zircon from Cole Pond tonalite gneiss near Cole 

Pond, Vermont. White-filled error ellipses represent data from oscillatory-zoned cores; gray error ellipses represent

data from metamorphic rims (dark, unzoned in CL). 207Pb/206Pb weighted average age is calculated from cores 

only. Close agreement of ages of cores and rims at about 1.31 Ga suggests synmetamorphic emplacement of the 

trondhjemite. Horizontally ruled ellipse represents an older age (approx. 1.38 Ga) from inherited zircon. Previous 

discordant TIMS data (Ratcliffe and others, 1991) suggested an age of 1,308±10 Ma for this sample. Abbreviations 

are as follows: approx., approximately; CL, cathodoluminescence; Ga, billions of years (giga-annum); m, meters; 

Ma, millions of years (mega-annum); MSWD, mean square of the weighted deviates; SHRIMP, sensitive high 

resolution ion microprobe; TIMS, thermal ionization mass spectrometry; WGS 84, World Geodetic System datum of 

1984.
30

Sample number: 8 

Description: Migmatite gneiss at Stratton Mountain

Field number: VT/Ja 1–88

Method: SHRIMP

Age: 1,326±4 Ma

Sample location coordinates (WGS 84 datum): 43°05′14′′N., 72°53′14′′W. 

Sample location description: Roadcut on Mountain Road about 0.5 km northwest of Forester Pond near the western border 

of the Jamaica quadrangle and south of 597.2-m benchmark. 

Figure 8. Conventional concordia plot of SHRIMP U-Pb data for zircon from migmatite gneiss at Stratton 

Mountain, Vermont. White-filled error ellipses represent data from oscillatory-zoned cores used in the weighted 

average calculation of 207Pb/206Pb ages (see inset) for determining the time of emplacement of the igneous 

protolith. Dashed outline of error ellipse represents reversely discordant data, possibly from damaged area of grain. 

Abbreviations are as follows: m, meters; Ma, millions of years (mega-annum); MSWD, mean square of the 

weighted deviates; SHRIMP, sensitive high resolution ion microprobe; WGS 84, World Geodetic System datum of 

1984.
31

Sample number: 9 

Description: Fine-grained granodiorite of the Ludlow Mountain granodiorite gneiss at Okemo Mountain

Field number: VT/Lu 1–91

Method: SHRIMP

Age: 1,309±6 Ma

Sample location coordinates (WGS 84 datum): 43°24′37′′N., 72°44′36′′W. 

Sample location description: Sample collected from blasted outcrop at the summit of Ludlow Mountain at the top of 

Okemo ski area, on a dirt road from the top descending to a ski lift, in the Ludlow quadrangle.

Figure 9. Conventional concordia plot of SHRIMP U-Pb data for zircon from fine-grained granodiorite of the 

Ludlow Mountain granodiorite gneiss at Ludlow Mountain, Vermont. No CL available at time of analyses 

(1996). White-filled error ellipses represent data from interiors of grains used in the weighted average 

calculation of 207Pb/

206Pb ages (see inset) for determining the time of emplacement of the igneous protolith. 

Gray error ellipses represent data from edges (metamorphic rims?) of grains (approx. 1.20 Ga). Horizontally

ruled ellipse represents older age (approx. 1.34 Ga) in interior of grain, probably from inherited zircon. One 

older grain (approx. 1.64 Ga) not shown. Abbreviations are as follows: approx., approximately; CL, 

cathodoluminescence; Ma, millions of years (mega-annum); MSWD, mean square of the weighted deviates; 

SHRIMP, sensitive high resolution ion microprobe; WGS 84, World Geodetic System datum of 1984.
32

Sample number: 10

Description: Okemo Quartzite—Detrital zircon

Field number: Vt/Lu 2–91

Method: SHRIMP 

Age: about 1,261 to 1,359 Ma

Sample location coordinates (WGS 84 datum): 43°24′55′′N., 72°44′29′′W. 

Sample location description: Sample collected at a small roadcut about 1.6 km north of the Ludlow Mountain summit at 

Okemo ski area, on the paved summit road, in the Ludlow quadrangle.

Figure 10. Conventional concordia plot of SHRIMP U-Pb data for detrital zircon from Okemo Quartzite at 

Ludlow Mountain, Vermont. All analyses from oscillatory-zoned cores. White-filled error ellipses represent

concordant or less than 10 percent discordant analyses. Gray error ellipses represent discordant data.

Abbreviations are as follows: km, kilometers; Ma, millions of years (mega-annum); SHRIMP, sensitive high 

resolution ion microprobe; WGS 84, World Geodetic System datum of 1984.
33

Sample number: 11

Description: College Hill Granite Gneiss at Stratton Mountain

Field number: 87Rat–2 

Method: TIMS

Age: 1,244±8 Ma

Sample location coordinates (WGS 84 datum): 43°07′37′′N., 72°52′15′′W. 

Sample location description: Exposure in woods near Pearl Buck Drive, 400 m west of the boundary between Bennington 

and Windsor Counties in the southwestern corner of the Jamaica quadrangle. 

87Rat-2 

College Hill (TIMS)

Figure 11. Conventional concordia plot of TIMS U-Pb data for zircon from College Hill Granite Gneiss at Stratton 

Mountain, Vermont. Circles represent data from cores; black-filled diamond represents material removed by 

abrasion. Best-fit regression (dashed line) is calculated through four analyses of cores (white-filled circles), yielding 

an upper intercept age of 1,240±9 Ma. The weighted average of 207Pb/206Pb ages from these four fractions is 

1,244±8 Ma (preferred age). Black dots probably represent mixtures of cores and rims. Black diamond suggests 

presence of metamorphic overgrowths. Abbreviations are as follows: m, meters; Ma, millions of years (megaannum); MSWD, mean square of the weighted deviates; TIMS, thermal ionization mass spectrometry; WGS 84, 

World Geodetic System datum of 1984.
34

Sample number: 12

Description: Granitic gneiss, which crosscuts older and deformed intrusive rocks (suite ranging in age from 1.3 to 1.4 Ga) 

and paragneiss

Field number: VT/Lo 1–89

Method: TIMS

Age: 1,221±4 Ma

Sample location coordinates (WGS 84 datum): 43°11′19′′N., 72°52′15′′W. 

Sample location description: Western side of Winhall Hollow Road between Peru and Landgrove, north of French Hollow 

Road.

Figure 12. Conventional concordia plot of TIMS U-Pb data for zircon from granitic gneiss. Circles represent data 

from cores; black-filled diamond represents material removed by abrasion. Best-fit regression (dashed line), forced 

through a regionally reasonable lower intercept age of 425±25 Ma, is calculated through two analyses of cores 

(white-filled circles), yielding an upper intercept age of 1,221±4 Ma. Black dots represent slightly younger ages, 

probably the result of mixtures of cores and rims. Black diamond suggests presence of metamorphic overgrowths.

Abbreviations are as follows: m, meters; Ma, millions of years (mega-annum); MSWD, mean square of the 

weighted deviates; TIMS, thermal ionization mass spectrometry; WGS 84, World Geodetic System datum of 1984.
35

Sample number: 13

Description: Megacrystic augen gneiss at Brandon Gap

Field number: MC6000

Method: SHRIMP

Age: 1,149±8 Ma

Sample location coordinates (WGS 84 datum): 43°50′24′′N., 72°58′03′′W. 

Sample location description: Roadcut located on the northern side of Vermont Route 73, about 15 m west of the Long 

Trail, at the summit of Brandon Gap.

MC6000

Megacrystic augen gneiss

concordia age =

1149 ± 8 Ma

Figure 13. Conventional concordia plot of SHRIMP U-Pb data for zircon from megacrystic augen gneiss at 

Brandon Gap, Vermont. Concordia age is calculated for data from oscillatory-zoned cores, represented by whitefilled error ellipses (n=15). Two slightly older analyses (horizontally ruled ellipses; approx. 1.16, 1.19 Ga) excluded 

from age calculation suggest minor inheritance. Gray error ellipse represents reversely discordant data from 

metamorphic rim (dark, unzoned in CL; approx. 1.00 Ga). Abbreviations are as follows: approx., approximately; CL, 

cathodoluminescence; Ga, billions of years (giga-annum); m, meters; Ma, millions of years (mega-annum); 

SHRIMP, sensitive high resolution ion microprobe; WGS 84, World Geodetic System datum of 1984.
36

Sample number: 16

Description: Migmatite gneiss in Pine Hill slice

Field number: R2008

Method: SHRIMP

Age: 1,037±6 Ma

Sample location coordinates (WGS 84 datum): 43°23′40′′N., 73°05′00′′W. 

Sample location description: At the Pike Industries quarry property. The outcrop is located on a forested east-facing slope, 

just west of the runaway truck ramp, about 200 m west of U.S. Route 7.

concordia age =

1037 ± 6 Ma

Figure 14. Conventional concordia plot of SHRIMP U-Pb data for zircon from migmatite gneiss in the Pine Hill 

slice, Vermont. Concordia age is calculated for data from oscillatory-zoned cores, represented by white-filled error

ellipses (n=17). Two slightly discordant analyses (dashed outlines of error ellipses) excluded from age calculation, 

suggest minor lead loss. Abbreviations are as follows: m, meters; Ma, millions of years (mega-annum); SHRIMP, 

sensitive high resolution ion microprobe; WGS 84, World Geodetic System datum of 1984.
37

Sample number: 22

Description: Newfane tonalite, which intrudes the Cram Hill Formation near South Newfane

Field number: VT/Br 2–89

Method: SHRIMP

Age: 502±4 Ma

Sample location coordinates (WGS 84 datum): 42°56′00′′N., 72°42′24′′W. 

Sample location description: Roadcut on Auger Hole Road about 350 m south of road junction in South Newfane, Newfane 

quadrangle. 

Figure 15. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon from Newfane tonalite near South 

Newfane, Vermont. White-filled error ellipses represent data from oscillatory-zoned cores used in the weighted 

average calculation of 206Pb/

238U ages (see inset) for determining the time of emplacement of the igneous protolith. 

Horizontally ruled ellipses represent older ages (approx. 520–550, 650 Ma; 1,520-Ma analysis not shown) in cores 

from inherited zircon. Abbreviations are as follows: approx., approximately; m, meters; Ma, millions of years (megaannum); MSWD, mean square of the weighted deviates; SHRIMP, sensitive high resolution ion microprobe; WGS 

84, World Geodetic System datum of 1984.
38

Sample number: 23

Description: Trondhjemite in the Barnard Gneiss proper (of Richardson, 1924) north of Proctorsville

Field number: L–18

Method: SHRIMP

Age: 496±8 Ma

Sample location coordinates (WGS 84 datum): 43°25′24′′N., 72°38′12′′W. 

Sample location description: Outcrop in the woods about 200 m south of a powerline cut, about 5 km north of 

Proctorsville, in the Ludlow quadrangle.

Figure 16. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon from trondhjemite in the Barnard 

Gneiss proper (of Richardson, 1924) north of Proctorsville, Vermont. White-filled error ellipses represent data from 

oscillatory-zoned cores used in the weighted average calculation of 206Pb/

238U ages (see inset) for determining the 

time of emplacement of the igneous protolith. Horizontally ruled ellipse represents older age (approx. 530 Ma; 

1,260-Ma analysis not shown) in core from inherited zircon. Abbreviations are as follows: approx., approximately; 

km, kilometers; m, meters; Ma, millions of years (mega-annum); MSWD, mean square of the weighted deviates; 

SHRIMP, sensitive high resolution ion microprobe; WGS 84, World Geodetic System datum of 1984.
39

Sample number: 24

Description: Tonalite gneiss in the North River Igneous Suite near Bartonsville

Field number: SR3053

Method: TIMS

Age: 486±3 Ma

Sample location coordinates (WGS 84 datum): 43°14′17′′N., 72°32′34′′W. 

Sample location description: Outcrop in the woods near the top of a hill, about 1.5 km north-northwest of Bartonsville and 

about 100 m west of Whitney Road, in the Saxtons River quadrangle.

Figure 17. Conventional concordia plot of TIMS U-Pb data for zircon from tonalite gneiss in the North River 

Igneous Suite near Bartonsville, Vermont. Because data are nearly concordant with no spread, a best-fit regression 

was not calculated. Age, determined by calculating the weighted average of 207Pb/206Pb ages (n=6), is the time of 

igneous emplacement. Horizontally ruled ellipses represent older age (approx. 504 Ma) in cores from inherited 

zircon. Abbreviations are as follows: approx., approximately; Fm., Formation; km, kilometers; m, meters; Ma, 

millions of years (mega-annum); MSWD, mean square of the weighted deviates; SHRIMP, sensitive high resolution

ion microprobe; WGS 84, World Geodetic System datum of 1984.
40

Sample number: 25

Description: Felsic volcanic layer interlayered with mafic volcanic rocks in the Cram Hill Formation at Springfield

Field number: SP450

Method: SHRIMP

Age: 483±3 Ma

Sample location coordinates (WGS 84 datum): 43°21′58′′N., 72°28′47′′W. 

Sample location description: Sample collected from an outcrop about 2.8 km north-northeast of North Springfield 

Reservoir, about 1.2 km west of Weathersfield Center Road, in the Springfield quadrangle.

concordia age =

483 ± 3 Ma

Figure 18. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon from felsic volcanic layer within 

mafic volcanic rocks in the Cram Hill Formation at Springfield, Vermont. Concordia age, calculated for data from 

oscillatory-zoned cores represented by white-filled error ellipses (n=20), is the time of volcanic crystallization.

Abbreviations are as follows: Fm., Formation; km, kilometers; Ma, millions of years (mega-annum); SHRIMP, 

sensitive high resolution ion microprobe; WGS 84, World Geodetic System datum of 1984.
41

Sample number: 38

Description: Granite in the Braintree Intrusive Complex

Field number: MC3432

Method: SHRIMP

Age: 421±7 Ma

Sample location coordinates (WGS 84 datum): 43°59′56′′N., 72°41′59′′W. 

Sample location description: Abandoned quarry on a trail on the western side of Ferry Hill, about 600 m north of Mud 

Pond, in the Randolph quadrangle. 

concordia age =

421 ± 7 Ma

Figure 19. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon from granite in the Braintree 

Intrusive Complex, Vermont. Concordia age, calculated for data from oscillatory-zoned cores represented by whitefilled error ellipses (n=14), is the time of igneous emplacement. Two slightly discordant analyses (dashed outlines 

of error ellipses) excluded from age calculation suggest minor lead loss. Abbreviations are as follows: m, meters; 

Ma, millions of years (mega-annum); SHRIMP, sensitive high resolution ion microprobe; WGS 84, World Geodetic 

System datum of 1984.
42

Sample number: 39

Description: Trondhjemite of the Newport Intrusive Complex

Field number: VT–Nq–1–97

Method: SHRIMP

Age: 425±3 Ma

Sample location coordinates (WGS 84 datum): 44°59′19′′N., 72°14′43′′W. 

Sample location description: Outcrop on the southwestern side of Lake Road, west of Maxfield Point and south of 

Maxfield Point Road in Newport.

VT-Nq-1-97

trondhjemite

Figure 20. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon from trondhjemite of the Newport 

Intrusive Complex, Vermont. White-filled error ellipses represent data from oscillatory-zoned cores used in the 

weighted average calculation of 206Pb/

238U ages (see inset) for determining the time of igneous emplacement. 

Discordant analyses (dashed outlines of error ellipses) caused by lead loss due to both somewhat high uranium 

concentrations (636–1,718 ppm; table 3) and cracked, deformed grains. Pale-gray error ellipse represents an older 

206Pb/238U age that is due to a very high uranium concentration (2,852 ppm; table 3), which caused matrix effects 

(Williams and Hergt, 2000) that resulted in an inaccurate analysis. Abbreviations are as follows: Ma, millions of 

years (mega-annum); ppm, parts per million; MSWD, mean square of the weighted deviates; SHRIMP, sensitive 

high resolution ion microprobe; WGS 84, World Geodetic System datum of 1984.
43

Sample number: 46

Description: Granite in the Chester dome

Field number: VT–CSTR–2 

Method: SHRIMP

Age: 392±6 Ma

Sample location coordinates (WGS 84 datum): 43°19′53′′N., 72°35′06′′W. 

Sample location description: Small abandoned quarry east of Dean Brook Road, about 300 m north of Vermont Route 10, 

in the Chester quadrangle. 

Figure 21. Conventional concordia plot of SHRIMP U-Pb data for zircon from granite in the Chester dome, 

Vermont. White-filled error ellipses represent data from oscillatory-zoned cores used in the weighted average 

calculation of 206Pb/

238U ages (see inset) for determining the time of igneous emplacement. Horizontally ruled 

ellipses represent older ages (approx. 1.17, 1.29, 1.37 Ga) in cores from inherited zircon. Abbreviations are as 

follows: approx., approximately; Ga, billions of years (giga-annum); m, meters; Ma, millions of years (megaannum); MSWD, mean square of the weighted deviates; SHRIMP, sensitive high resolution ion microprobe; WGS 

84, World Geodetic System datum of 1984.
44

Sample number: 47

Description: Barre Granite at Rock of Ages quarry

Field number: Barre#2

Method: SHRIMP

Age: 368±4 Ma

Sample location coordinates (WGS 84 datum): 44°09′17′′N., 72°28′50′′W. 

Sample location description: Rock of Ages quarry, main pit at the 11th-level deep, Barre. 

Figure 22. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon from Barre Granite, Rock of Ages 

quarry, Barre, Vermont. White-filled error ellipses represent data from oscillatory-zoned cores used in the weighted 

average calculation of 206Pb/

238U ages (see inset) for determining the time of igneous emplacement. Pale-gray error 

ellipse represents an older 206Pb/238U age that is due to a very high uranium concentration (18,759 ppm; table 3), 

which caused matrix effects (Williams and Hergt, 2000) that resulted in an inaccurate analysis. Abbreviations are 

as follows: Ma, millions of years (mega-annum); MSWD, mean square of the weighted deviates; ppm, parts per 

million; SHRIMP, sensitive high resolution ion microprobe; WGS 84, World Geodetic System datum of 1984.
45

Sample number: 48

Description: Black Mountain pluton

Field number: VT/Br 1–89

Method: SHRIMP

Age: 364±4 Ma

Sample location coordinates (WGS 84 datum): 42°55′31′′N., 72°36′33′′W. 

Sample location description: Abandoned quarry on the western slope of Black Mountain, due east from West Dummerston 

across the West River.

concordia age =

363 ± 2 Ma

Figure 23. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon and monazite from the Black 

Mountain pluton, Vermont. In plot to left (zircon data), white-filled error ellipses represent data from low-uranium 

oscillatory-zoned cores; pale-gray error ellipses represent older 206Pb/238U ages that are due to a very high uranium

concentration (10,177–30,266 ppm; table 3), which caused matrix effects (Williams and Hergt, 2000) that resulted

in inaccurate analyses. Age was determined by (1) calculating the weighted average of the low-uranium 206Pb/238U 

ages, (2) calculating the weighted average of the high-uranium 207Pb/206Pb ages, (3) calculating a combined 

weighted average of the ages from (1) and (2) (see inset). This age was interpreted as the time of igneous 

emplacement. In plot to right (monazite data), the concordia age was calculated for data from sector-zoned cores, 

represented by white-filled error ellipses (n=23). The age agrees with the zircon SHRIMP U-Pb age. Gray-filled 

ellipses (n=5) represent data from unzoned rims, suggesting a slightly younger, post-crystallization thermal event. 

Slightly older ages of about 375 Ma, represented by two horizontally ruled error ellipses, may be due to inheritance.

Abbreviations are as follows: approx., approximately; Ma, millions of years (mega-annum); MSWD, mean square of 

the weighted deviates; ppm, parts per million; SHRIMP, sensitive high resolution ion microprobe; WGS 84, World 

Geodetic System datum of 1984.
46

Sample number: 49

Description: Granite dike south of Plymouth

Field number: VT/Pl 2–91

Method: SHRIMP

Age: 365±5 Ma

Sample location coordinates (WGS 84 datum): 43°30′14′′N., 72°43′23′′W. 

Sample location description: The sampled outcrop is located in the western part of a sand pit about 170 m east of Vermont 

Route 100, and about 150 m north-northeast of the junction of Frog City Road and Route 100.

Figure 24. Tera-Wasserburg concordia plot of SHRIMP U-Pb data for zircon from a granite dike near Plymouth, 

Vermont. White-filled error ellipses represent data from oscillatory-zoned cores used in the weighted average 

calculation of 206Pb/

238U ages (see inset) for determining the time of igneous emplacement. Abbreviations are as 

follows: m, meters; Ma, millions of years (mega-annum); MSWD, mean square of the weighted deviates; ppm, parts 

per million; SHRIMP, sensitive high resolution ion microprobe; WGS 84, World Geodetic System datum of 1984.