Prepared in cooperation with the Commonwealth of Massachusetts, 

Massachusetts Geological Survey 

Bedrock Geologic Map of the Uxbridge Quadrangle, 

Worcester County, Massachusetts, and 

Providence County, Rhode Island 

By Gregory J. Walsh

Pamphlet to accompany

Scientific Investigations Map 3295

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014

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Suggested citation:

Walsh, G.J., 2014, Bedrock geologic map of the Uxbridge quadrangle, Worcester County, Massachusetts, and 

Providence County, Rhode Island: U.S. Geological Survey Scientific Investigations Map 3295, 1 sheet, scale 1:24,000, 

36-p. pamphlet, http://dx.doi.org/10.3133/sim3295.

ISSN 2329-132X
iii

Contents

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

Age of the Rocks / Stratigraphy ...........................................................................................................1

Metasedimentary Rocks of the Blackstone Group ................................................................1

Neoproterozoic Intrusive Rocks .........................................................................................................2

Granitic Gneiss .............................................................................................................................2

Tonalite and Granodiorite Gneiss ..............................................................................................8

Ironstone Quartz Diorite of Emerson (1917) .............................................................................9

Geochemistry................................................................................................................................................10

Results ..................................................................................................................................................10

Structural Geology.......................................................................................................................................20

Ductile Structures ...............................................................................................................................20

Relict Deformation (D1

) ..............................................................................................................20

Second Generation Deformation (D2) .....................................................................................21

Third Generation Deformation (D3 ) .........................................................................................23

Fourth Generation Deformation (D4 ) .......................................................................................24

Comment on the Hope Valley Shear Zone .............................................................................27

Brittle Structures.................................................................................................................................28

Brittle Faults ................................................................................................................................31

Metamorphism .............................................................................................................................................31

Economic Geology.......................................................................................................................................32

Acknowledgments.......................................................................................................................................33

References Cited..........................................................................................................................................33

Figures

 1. Photographs showing the Blackstone Group migmatitic plagioclase porphyroblast 

gneiss adjacent to the Ironstone quartz diorite of Emerson (1917) ......................................2

 2. Photographs showing contact relationships in the granitic gneisses of 

the Uxbridge quadrangle .............................................................................................................4

 3. Photographs of the fine-grained biotite granite gneiss of the Northbridge 

Granite Gneiss ..............................................................................................................................5

 4. Photographs showing the textural differences between the Ponaganset Gneiss 

and the Northbridge Granite Gneiss ..........................................................................................6

 5. Photographs of the tonalite gneiss showing the strongly lineated L-tectonite 

fabric viewed from two different directions ............................................................................8

 6. Photographs of the Ironstone quartz diorite of Emerson (1917), taken in the 

adjoining Blackstone quad rangle ..............................................................................................9

 7. Major and trace element discrimination diagrams for rock samples from 

the Uxbridge quadrangle ...........................................................................................................10

 8. Trace and rare earth element discrimination diagrams for rock samples 

from the Uxbridge quadrangle ..................................................................................................11
iv

 9. Photographs and sketch of relict S

Conversion Factors and Datums

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg)

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).
Introduction

The bedrock geology of the Uxbridge quadrangle consists 

of Neoproterozoic metamorphic and igneous rocks of the 

Avalon zone (Zen and others, 1983). In this area, rocks of 

the Avalon zone lie within the core of the Milford antiform, 

south and east of the terrane-bounding Bloody Bluff fault 

zone (fig. A on map) (Goldsmith, 1991c). Permian pegmatite 

dikes and quartz veins occur throughout the quadrangle. The 

oldest metasedimentary rocks include the Blackstone Group, 

which represents a Neoproterozoic peri-Gondwanan marginal 

shelf sequence. The metasedimentary rocks are intruded by 

Neoproterozoic arc-related plutonic rocks of the Rhode Island 

batholith (Zen and others, 1983; Zartman and Naylor, 1984; 

Bailey and others, 1989; Rast and Skehan, 1990; Skehan and 

Rast, 1990, 1995; Goldsmith, 1991a; Hermes and Zartman, 

1992; Hibbard and others, 2006; Thompson and others, 2012). 

The bedrock is overlain by Pleistocene to Quaternary 

alluvial deposits, stratified glacial deposits, areas of thick till 

in drumlins or drumlinoids, and thin till (Stone and others, 

2008). The northwestern corner of the map area is underlain 

by a considerable amount of exposed bedrock. Elsewhere in 

the quadrangle, however, the bedrock is less well-exposed. 

Previous mapping in the area is limited, and unpublished 

reconnaissance mapping at 1:24,000-scale by H.R. Dixon 

and Richard Goldsmith was the primary source of geologic 

data compiled on the 1:250,000-scale geologic map of 

Massachusetts (Zen and others, 1983) (hereinafter referred to 

as the State map). In addition to the information on the State 

map, much of the work by Goldsmith is contained in several 

important regional papers that followed the publication of 

the State map (Goldsmith, 1991a,b,c; Wones and Goldsmith, 

1991). Early work described the regional geology and 

economic deposits (Jackson, 1840; Emerson and Perry, 1907; 

Emerson, 1917; Dale, 1908, 1923; and Pearre, 1956).

Mapping at 7.5-minute scales in adjacent quadrangles includes work in Grafton (Walsh and others, 2011), 

Milford (Kopera and others, 2007), Oxford (Barosh, 2005), 

Thompson (Dixon, 1974), Chepachet (Quinn, 1967), 

Blackstone (Kopera and Shaw, 2008; McKniff, 1964), 

and Georgiaville (Richmond, 1952).

Age of the Rocks / Stratigraphy

The metamorphic and igneous rocks in the Uxbridge 

quadrangle are largely Neoproterozoic in age. Ages in this 

report conform to the time scale of Gradstein and others 

(2004). The oldest rocks in the quadrangle belong to the 

metasedimentary Blackstone Group. Historically the age of the 

Blackstone Group has been considered Neoproterozoic based 

on crosscutting Neoproterozoic intrusive rocks in the Avalon 

zone (Zen and others, 1983; Zartman and Naylor, 1984; Bailey 

and others, 1989; Goldsmith, 1991a; Hermes and others, 1994; 

Skehan and Rast, 1990, 1995). The Blackstone Group rocks 

are cut by the intrusive rocks of the Rhode Island batholith 

(Goldsmith, 1991a). Based on ages obtained from the adjacent 

Grafton quadrangle (Walsh and others, 2011), the granitic 

gneisses of the Uxbridge quadrangle range in age from about 

612 to 606 Ma (mega-annum).

Metasedimentary Rocks of the Blackstone Group

Large discontinuous screens of biotite schist and quartzite 

of the Blackstone Group (Zb) occur in the southeastern part 

of the Uxbridge quadrangle. Minor amounts of calc-silicate 

rock and tremolite schist are also present. The distribution 

of schist and quartzite is quite variable and the two rock 

types could not be mapped separately. Schist and quartzite 

are present at virtually every outcrop. Locally, quartzite 

outcrops predominate and in these places only small amounts 

of schist are exposed. Large outcrops clearly show that the 

two rocks types are interbedded. Quartzite layers range from 

several centimeters to several meters thick; true thickness is 

locally duplicated where the rocks are isoclinally folded. The 

Blackstone Group locally contains calc-silicate rocks, and 

those locations are indicated as points on the map because 

Bedrock Geologic Map of the Uxbridge Quadrangle, 

Worcester County, Massachusetts, and 

Providence County, Rhode Island 

By Gregory J. Walsh1

1

U.S. Geological Survey, Montpelier, VT 05601.
2 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

their extent and distribution were not mappable into separate 

polygons. New mapping confirms the distribution as depicted 

at State-map scales as either Blackstone Group undivided 

(unit Zb of Zen and others, 1983; Goldsmith, 1991a), 

Blackstone Group undifferentiated (unit Zbu of Hermes and 

others, 1994), or Blackstone Series undifferentiated (unit b of 

Quinn, 1971). Unit Zb in the Uxbridge quadrangle correlates 

with the Blackstone Series quartz-biotite schist (unit bb) of 

Richmond (1952) and McKniff (1964), and with the undivided 

Blackstone Series (unit bs) of Quinn (1967). Mapping partly 

supports the assertion by Goldsmith (1991a, p. E8) that 

“west of Blackstone, the Blackstone Group is difficult to 

divide because outcrops are poor and quartzite and amphibolite are extensively interlayered.” This statement is true 

with the exception that amphibolite was not observed in the 

Blackstone Group within the Uxbridge quadrangle, but was 

seen at one place in the migmatitic gneiss unit (Zbm) adjacent 

to the Ironstone quartz diorite of Emerson (1917) (Ziqd) in the 

neighboring Blackstone quadrangle. 

In the southeastern corner of the map area, the Blackstone 

Group contains migmatitic plagioclase porphyroblast gneiss 

(unit Zbm; fig. 1). The migmatitic gneiss is distributed around 

the Ironstone quartz diorite suggesting that its formation is 

related to the intrusion. McKniff (1964, p. 8) noted the same 

type of rock in the area around the Ironstone type locality, in 

the adjoining Blackstone quadrangle where he described the 

rock as having “been soaked by granitic material.”

Neoproterozoic Intrusive Rocks

Granitic Gneiss

The majority of the quadrangle is underlain by 

Neo proterozoic intrusive rocks which occur in three 

categories: granitic gneiss, tonalitic gneiss, and minor 

amounts of quartz diorite. 

The granitic gniesses include the equigranular Hope 

Valley Alaskite Gneiss, the megacrystic Ponaganset Gneiss, 

and the equigranular to megacrystic Northbridge Granite 

Gneiss. The latter two occur as large sheet-like bodies whose 

geometry was probably produced by a combination of the 

original tabular nature of the intrusions and the subsequent 

penetrative deformation. In this study, we use the nomenclature and ages of Walsh and others (2011) for the granitic 

gneisses. The Hope Valley Alaskite Gneiss is quite limited 

in the Uxbridge quadrangle, occurring mostly as dikes or 

sills. Two small map units of Hope Valley Alaskite Gneiss 

occur within the Northbridge Granite Gneiss along Route 

146. The Hope Valley Alaskite Gneiss yielded a Sensitive 

High Resolution Ion Microprobe (SHRIMP) U-Pb zircon age 

of 606 ± 5 Ma from the adjacent Grafton quadrangle (Walsh 

and others, 2011). The Ponaganset Gneiss is widespread in 

the Uxbridge quadrangle and it maps continuously into the 

Grafton quadrangle, where it yielded a SHRIMP U-Pb zircon 

age of 612 ± 5 Ma (Walsh and others, 2011). Modes of the 

Ponaganset Gneiss are shown in table 1.

Figure 1. Photographs showing the Blackstone Group 

migmatitic plagioclase porphyroblast gneiss (Zbm) adjacent 

to the Ironstone quartz diorite of Emerson (1917) (Ziqd). 

A, Light-colored tonalitic to granitic leucosome in gray gneiss; 

B, Xenolith of quartzite (arrow); C, Dark paleosome, consisting 

largely of biotite schist with minor amounts of amphibolite and 

calc-silicate, invaded by lighter leucosome. Filenames, on this 

and subsequent figures, correspond to georeferenced station 

locations shown in the accompanying GIS database.

A

UX-1199_03.JPG

C

UX-1199_06.JPG

B

UX-1199_04.JPG
Introduction 3

Table 1. Petrographic modes of selected rocks from the Ponaganset Gneiss. 

[—, no data; tr, trace; Cz, clinozoisite; Q, P, and A: normalized quartz (Q), plagioclase (P), and alkali feldspar (A) for the International Union of Geological 

Sciences (IUGS) rock classification]

Total or Sample no. UX-1043 UX-1087 UX-1179 UX-1231 UX-1232 UX-1237 average

Points counted 396 435 388 343 462 371 2,395

Zpg—Megacrystic biotite granite gneiss, in percent

Quartz 36 30 31 28 34 36 33

Plagioclase 34 34 21 36 36 30 32

Alkali feldspar 20 30 30 21 19 26 24

Biotite 9 6 15 12 8 8 10

Muscovite — — tr — tr — tr

Epidote/Cz 1 tr 1 2 2 tr 1

Hornblende 1 tr — 1 1 tr tr

Chlorite — — — — tr tr tr

Opaque tr — — — — — tr

Hematite — — — — — — —

Titanite tr — tr tr — — tr

Apatite — — — — — — tr

Allanite tr — — — — — tr

Garnet — — — — — — —

Zircon — — — — — — —

 Totals 101 100 98 100 100 100 100

Q 41 32 38 33 38 39 33

P 37 36 26 42 40 33 40

A 22 32 36 25 22 28 27

Total or Sample no. UX-1042 UX-1082 UX-1092 average

Points counted 396 391 419 1,206

Zphg - Megacrystic hornblende-biotite granite gneiss, in percent

Quartz 29 35 40 35

Plagioclase 32 35 23 30

Alkali feldspar 35 13 21 23

Biotite 1 13 10 8

Muscovite — tr — tr

Epidote/Cz tr 3 2 2

Hornblende 2 tr 4 2

Chlorite — tr — tr

Opaque — tr — tr

Hematite — — — —

Titanite 1 tr — tr

Apatite 1 — — tr

Allanite — — tr tr

Garnet — — — —

Zircon — — — —

 Totals 101 99 100 100

Q 30 42 48 40

P 33 42 27 34

A 37 16 25 26
4 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

The Northbridge Granite Gneiss is also widespread in the 

Uxbridge quadrangle, and in the Grafton quadrangle it yielded 

a SHRIMP U-Pb zircon age of 607 ± 5 Ma (Walsh and others, 

2011). Field evidence shows that biotite granite gneiss of the 

Northbridge Granite Gneiss (Zncg) intrudes the Ponaganset 

Gneiss (Zpg), and both units are cut by dikes or sills of the 

Hope Valley Alaskite Gneiss (Zhv) (fig. 2). The overlapping 

U-Pb zircon ages and the chemical similarity between the 

C

Zpg

Zncg

UX-1262_3.JPG

A

Zpg

Zncg

UX-1306_1.JPG

B

Zpg

Zncg

UX-1306_2.JPG

D

Zpg Zncg

Zhv

Contacts

Zpg

UX-1488-2.JPG

F

Zt

Zhv

UX-1497-1.JPG

E

Zncgm

Zhv

UX-1489-07.JPG

Figure 2. Photographs showing contact relationships in the granitic gneisses of the Uxbridge quadrangle. A, Ponaganset 

Gneiss (Zpg) with multiple sills of Northbridge Granite Gneiss (Zncg); B, Hand samples of rocks in A; C, Block showing sharp 

contact between Zpg and Zncg; D, Zpg with folded layer of Zncg and thin dike of Hope Valley Alaskite Gneiss (Zhv); E, Two sills 

of alaskite (Zhv) in the Northbridge Granite Gneiss (Zncgm) in an abandoned granite quarry on Quarry Hill; and F, Two thin sills 

of alaskite (Zhv) in the tonalite and granodiorite gneiss (Zt). 
Introduction 5

Northbridge Granite Gneiss and the Hope Valley Alaskite 

Gneiss suggest that they are related to the same plutonic event 

(Walsh and others, 2011). Chemical data presented below 

further support this conclusion. The fine-grained biotite granite 

gneiss of the Northbridge Granite Gneiss (Znfg) has not been 

dated, but xenoliths of Znfg within the coarse-grained biotite 

granite gneiss (Zncg) show that it must be older (fig. 3). Crosscutting relationships of the megacrystic biotite granite gneiss 

(Zncgm) of the Northbridge Granite Gneiss with its adjacent 

units were not directly observed in the field. The texture and 

map distribution of the Zncgm unit suggests that it represents 

a transitional rock between the equigranular coarse-grained 

biotite granite gneiss of the Northbridge Granite Gneiss (Zncg) 

and the distinctly megacrystic biotite granite gneiss of the 

Ponaganset Gneiss (Zpg) (fig. 4). Modes of the Northbridge 

Granite Gneiss are shown in table 2.

A

Zncg

Znfg

Quartz vein

UX-1129_1.JPG

B

Zncg

Znfg

Quartz vein

UX-1129_2.JPG

C

UX-1276_1.JPG

D

UX-1278_4.JPG

Figure 3. Photographs of the fine-grained biotite granite gneiss (Znfg) of the Northbridge Granite Gneiss. The GPS receiver 

in A, B, and C is 10.5 cm long. A and B, Equigranular coarse-grained biotite granite gneiss (Zncg) with xenolith of Znfg, shown 

from two perspectives; C, Downplunge view showing characteristic biotite streaks, pink potassium (K-) feldspar segregations, 

and small (<1 cm) K-feldspar augen (circled); D, Block showing characteristic biotite aggregate lineation (parallel to hammer 

handle) on the foliation surface. 
6 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

Figure 4. Photographs showing the textural 

differences between the Ponaganset Gneiss 

(Zpg) and the Northbridge Granite Gneiss. 

A, Megacrystic biotite granite gneiss of the 

Ponaganset Gneiss (Zpg); B, Inequigranular 

megacrystic biotite granite gneiss of the 

Northbridge Granite Gneiss (Zncgm); 

C, Equigranular biotite granite gneiss of 

the Northbridge Granite Gneiss (Zncg). The 

Zncgm unit in B is a transitional rock between 

the megacrystic (Zpg) and equigranular (Zncg) 

end members. Arrow near top of A shows the 

end of a pen for scale (1 cm diameter). Arrow 

in B shows a quartz vein (gray) with a median 

line of alkali feldspar.

A Zpg

UX-1141_1.JPG

C

Zncg

UX-1105_3.JPG

B

Zncgm

UX-1489_09.JPG
Introduction 7

Table 2. Petrographic modes of selected rocks from the Northbridge Granite Gneiss.

[—, no data; tr, trace; Cz, clinozoisite; incl., including; Mt, magnetite; Q, P, and A: normalized quartz (Q), plagioclase (P), and alkali feldspar (A) for the 

International Union of Geological Sciences (IUGS) rock classification]

Sample no.

Points counted

Quartz

UX-1001

397

42

UX-1025 UX-1105 UX-1121A UX-1291

427 426 492 389

Zncg - Coarse-grained biotite granite gneiss, in percent

27 31 29 34

UX-1587

580

45

Total or 

average

2,711

35

Plagioclase

Alkali feldspar

Biotite

20

33

6

37

33

4

31

27

3

43

21

2

33

29

4

30

18

7

33

26

4

Muscovite — — 6 4 tr tr 2

Epidote/Cz

Hornblende

tr

—

tr

—

tr

—

tr

—

tr

—

tr

—

tr

—

Chlorite tr tr 1 tr tr tr tr

Opaque incl. Mt

Hematite

tr

—

tr

—

tr

—

tr

tr

tr

—

tr

—

tr

tr

Titanite — tr — — tr — tr

Apatite

Allanite

—

—

tr

—

—

—

tr

—

—

tr

tr

—

tr

tr

Garnet — tr — tr — — tr

Zircon — — — — — —

 Totals 101 101 99 99 100 100 100

Q 44 28 34 31 36 48 37

P 21 38 35 46 35 32 35

A 35 34 31 22 30 20 28

Total or Sample no. UX-1001A UX-1157A UX-1425 UX-1528

average

Points counted 420 386 406 423 1,635

Zncgm - Megacrystic biotite granite gneiss, in percent

Quartz 29 32 37 30 32

Plagioclase 39 34 30 44 37

Alkali feldspar 24 24 29 20 24

Biotite 6 9 4 3 5

Muscovite — 1 tr 1 tr

Epidote/Cz tr 1 tr tr tr

Hornblende — — — — —

Chlorite tr tr tr tr

Opaque incl. Mt 2 tr tr 1 1

Hematite — — — tr tr 

Titanite — — tr — tr 

Apatite tr tr — — tr

Allanite — — — tr tr 

Garnet — — — — —

Zircon — — — — —

 Totals 100 101 100 99 99

Q 31 36 38 32 34

P 43 38 31 47 40

A 26 27 30 21 26
8 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

Tonalite and Granodiorite Gneiss

Tonalitic gneiss crops out along the eastern border of 

the quadrangle and in several smaller plutonic bodies in the 

southeastern part of the map area. The rocks are informally 

named the “tonalite to granodiorite gneiss at Uxbridge” for 

the main unit (Zt) exposed in Uxbridge. The type locality is an 

abandoned quarry along Granite Street on the eastern border of 

the map. The rock is characteristically salt and pepper colored 

and may contain a well-developed lineation or L-tectonite fabric 

(fig. 5). The rock intrudes the Blackstone Group rocks and is 

intruded by alaskite dikes. Contacts with the adjacent plutonic 

rocks are not exposed. The rock may be an older, more mafic 

phase of the Ponaganset Gneiss. Modes are shown in table 3.

Emerson (1917) described this rock as a border phase 

of the Milford granite, and suggested that it was part of the 

Ironstone quartz diorite. More detailed work in the southern 

part of the Blackstone quadrangle (McKniff, 1964) showed 

that the quartz diorite was not a border phase of either the 

Milford or Esmond Granites, but predated the granitic plutons. 

The eastern extent of the tonalitic rock, however, has not been 

mapped in the western part of the Blackstone quadrangle 

(McKniff, 1964; Kopera and Shaw, 2008), so its relationship 

to the Milford Granite remains uncertain. 

A

UX-1015_1.JPG

B

UX-1015_2.JPG

Figure 5. Photographs of the tonalite gneiss (Zt) showing 

the strongly lineated L-tectonite fabric viewed from two 

different directions. A, Perpendicular to the lineation; B, 

Parallel to the lineation, looking up plunge. Note the alkali 

feldspar megacrysts circled in B. 

Table 3. Petrographic modes of selected rocks from the tonalite to 

granodiorite gneiss at Uxbridge (Zt).

[—, no data; Cz, clinozoisite; tr, trace; incl., including; Mt, magnetite; Q, P, 

and A: normalized quartz (Q), plagioclase (P), and alkali feldspar (A) for the 

International Union of Geological Sciences (IUGS) rock classification]

Sample no. UX-1569 UX-1016 UX-1148 UX-1398 UX-1004 Total or 

average

Points 

counted

225 631 364 409 391 2,020

Percent

Quartz

Plagioclase

Alkali 

feldspar

Biotite

Muscovite

Epidote/Cz

Hornblende

Chlorite

Opaque 

incl. Mt

Hematite

Titanite

Apatite

Allanite

Garnet

Zircon

 Totals

Q

P

A

19

32

1

22

—

8

15

1

—

—

2

tr

—

—

—

100

37

61

2

35

41

7

12

3

tr

2

—

—

—

tr

tr

—

—

100

42

50

8

33

43

6

8

1

2

6

—

—

—

—

tr

—

—

—

99

40

53

8

26

52

4

14

—

2

1

—

—

—

tr

tr

tr

—

—

99

32

63

5

25

52

4

14

—

2

3

tr

—

—

tr

1

—

—

—

101

31

64

5

29

45

5

13

1

2

4

1

—

—

tr

tr

 tr

—

—

100

37

57

6
Introduction 9

Ironstone Quartz Diorite of Emerson (1917)

The Ironstone quartz diorite (Ziqd) crops out along the 

southeastern border of the quadrangle and extends into the 

adjacent Blackstone quadrangle (McKniff, 1964). The rock is 

equigranular and consists largely of biotite, quartz, plagioclase, 

and hornblende (fig. 6). Plagioclase is partly replaced by epidote. 

It was named by Emerson (1917, p. 168) for a “black, heavy 

rock” exposed near the village of Ironstone, in the adjacent 

Blackstone quadrangle about 1 km east of the quadrangle border 

with Uxbridge. At Ironstone, where the rock is well exposed 

along Elmwood Avenue, just west of Route 146 in the town of 

Uxbridge, a roadcut contains darker enclaves enclosed in lighter 

colored rock having distinct, leucocratic quartz-plagioclase 

Figure 6. Photographs of the Ironstone quartz diorite of 

Emerson (1917) (Ziqd), taken in the adjoining Blackstone quadrangle. A, Equigranular rock exposed north of East Ironstone 

Road; B, Darker, more mafic enclaves within lighter colored, 

more felsic rock along Elmwood Avenue at the type locality. 

B

A

UX-1205_1.JPG UX-1618_5.JPG

aggregates (fig. 6B). The Ironstone intrudes the biotite schist 

and quartzite of the Blackstone Group, and is in turn intruded 

by dikes of biotite granite gneiss. Modes are shown in table 4.

Mapping in the Uxbridge quadrangle shows that the 

Ironstone is not a border phase of the granitic gneiss called 

Milford Granite by Emerson (1917), but instead is an older, 

more mafic pluton, that predates the granitic gneiss now 

mapped as Northbridge. Chemically one sample (UX-1618), 

collected from the type locality 1 km east of the quadrangle 

boundary, is a gabbro (table 5). The sample location is not 

shown on the map but is included in the GIS database. The 

Ironstone quartz diorite is surrounded by migmatitic gneiss 

whose protolith includes the Blackstone Group rocks (fig. 1). 

Table 4. Petrographic modes of selected rocks from the 

Ironstone quartz diorite of Emerson (1917) (Ziqd).

[—, no data; Cz, clinozoisite; tr, trace; Q, P, and A: normalized quartz (Q), 

plagioclase (P), and alkali feldspar (A) for the International Union of 

Geological Sciences (IUGS) rock classification]

Sample no. UX-1202 UX-1207 UX-1617 UX-1618 Total or 

average

Points counted 396 385 407 402 1,590

Percent

Quartz

Plagioclase

Alkali feldspar

Biotite

Muscovite

Epidote/Cz

Hornblende

Chlorite

Magnetite

Opaque

Hematite

Titanite

Apatite

Clinozoisite

Allanite

Garnet

Zircon

 Totals

Q

P

A

18

42

—

8

—

1

30

—

—

—

—

—

tr

—

—

—

—

99

29

71

0

7

32

—

1

—

1

59

—

—

—

—

—

tr

—

—

—

—

100

17

83

0

11

18

—

14

—

1

55

tr

—

tr

—

—

—

—

—

—

—

99

38

63

0

9

13

—

5

—

tr

65

—

—

5

—

—

1

—

—

—

—

98

41

59

0

11

27

—

7

—

1

52

tr

—

1

—

—

tr

—

—

—

—

99

28

72

0
10 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

Geochemistry

Thirty intrusive rock samples were analyzed for major, 

trace, and rare earth elements (REE). Geochemistry data 

are located in table 5 and in the GIS database, and results 

are plotted in figures 7 and 8. Geochemical analyses were 

conducted by SGS Minerals, Toronto, Ontario, Canada. Major 

elements were analyzed by X-ray fluorescence using lithium 

metaborate fused disks (SGS Minerals Method XRF76S). 

Trace elements and REE were analyzed by inductively 

coupled plasma-mass spectrometry using sodium peroxide 

fusion (SGS Minerals Method ICM90A). 

Results

The granitic gneisses are calc-alkaline granites (fig. 7A, B ).

They are mildly peraluminous, with the Ponaganset Gneiss 

plotting along the metaluminous-peraluminous boundary 

(fig. 7C ). The more mafic rocks are tholeiitic tonalites to 

granodiorites (fig. 7A, B ), and they are largely metaluminous 

with one sample plotting in the peraluminous field (fig. 7C ). 

The Rb versus Y+Nb tectonic discrimination diagram (fig. 7D) 

shows the granitic rocks as volcanic-arc to within-plate 

granites, and the more mafic rocks as volcanic-arc granites. 

Chondrite-normalized REE patterns and multi-element “spider 

diagrams” (fig. 8A‒D) are consistent with leucocratic continental rocks showing both crust and mantle sources (Thompson 

and others, 1984). The Ponaganset Gneiss and the intermediate 

to mafic rocks show more primitive signatures, suggesting 

less contamination from continental crust or sediments. Most 

granitic samples have fairly steep abundances of light rare 

earth elements (LREE), with normalized La values ranging 

from about 80 to 300, and relatively flat abundances of heavy 

rare earth elements (HREE) (fig. 8C ). Two samples of the 

Northbridge Granite Gneiss (unit Zncg) show depleted LREE 

(fig. 8C ), possibly related to the fractional crystallization of 

allanite (Thompson and others, 1984). Prominent negative Eu 

Ab Or

An

Granite

Granodiorite

Tonalite

Trondhjemite

Na2O+K2O MgO

FeOT

Calc-Alkaline

Tholeiitic

Zhv

Zpg and Zphg

Zt

Ziqd

Zncgm

Znfg

Zncg

A EXPLANATION B

Al/(Na+K)

0.5 1.0 1.5 0

1

2

3

Al/(Ca+Na+K)

Peralkaline

Metaluminous Peraluminous

C

10 100 1,000

1.0

10

100

1,000

Rb (ppm)

Y+Nb (ppm)

syn-COLG

WPG

VAG

ORG

D

Figure 7. Major and trace element discrimination diagrams for rock samples from the Uxbridge quadrangle. 

A, Na2

0 + K2O – FeOT – MgO (AFM) diagram, modified from Irvine and Baragar (1971). B, Normative An-Ab-Or 

(anorthite-albite-orthoclase) classification diagram modified from O’Connor (1965) and Barker (1979). C, Alumina 

saturation diagram modified from Shand (1951) and Maniar and Piccoli (1989). D, Tectonic discrimination diagram 

modified from Pearce and others (1984). VAG, volcanic arc granites; ORG, ocean ridge granites; WPG, withinplate granite; syn-COLG, syn-collisional granites. See text for discussion. ppm, parts per million.
Geochemistry 11

anomalies are present in all granitic samples from the Northbridge Granite Gneiss and Hope Valley Alaskite Gneiss, but are 

less pronounced in the Ponaganset Gneiss samples (fig. 8A, C ), 

suggesting greater fractional crystallization of plagioclase in the 

more leucocratic rocks. The intermediate to mafic rocks show 

fairly moderate LREE abundances with normalized La values 

ranging from about 80 to 400, and have relatively flat HREE 

(fig. 8A). Eu anomalies are absent to slightly positive in the 

intermediate to mafic samples (fig. 8A). The spider diagrams 

for the granitic Northbridge Granite Gneiss and Hope Valley 

Alaskite Gneiss samples are similar, showing enrichment in 

Rb, Th, and K, with negative Nb, Sr, P, and Ti anomalies that 

are characteristic of continental granites (fig. 8 D). The samples 

of the granitic Ponaganset Gneiss show similar trends to the 

other granitic rocks, but less pronounced anomalies. The intermediate to mafic rocks show even less pronounced anomalies, 

suggesting greater proportion of a mantle source (fig. 8B ). The 

U/Th ratios are quite similar to those reported by Wones and 

Goldsmith (1991) for similar rocks in the Milford antiform, 

with the exception of three samples of the Northbridge Granite 

Gneiss (unit Zncg) that have slightly higher values of Th and 

higher values of U (fig. 8E ).

E

Th, in parts per million

U, in parts per million

Wones and Goldsmith (1991)

0 2 4 6 8

1.0

10

100

From Wones and Goldsmith (1991)

Grafton quadrangle by Walsh and others (2011)

Neoproterozoic batholithic rocks in the Milford

 antiform and the Milford-Dedham zone

0.1

Grafton Gneiss

Rocks of the Milford antiform

D

1.0

10

100

1,000

Ba Rb Th K Nb Ta La Ce Sr Nd P Sm Zr Hf Ti Tb Y Tm Yb

Rock/primitive mantle

Hope Valley Alaskite Gneiss

Northbridge Granite Gneiss

0.1

C

1.0

10

100

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Rock/chondrites

Hope Valley Alaskite Gneiss

Northbridge Granite Gneiss

B

0.1

1.0

10

100

1,000

Rock/primitive mantle

Ponaganset Gneiss

Tonalite and granodiorite gneiss

Ironstone quartz diorite of Emerson (1917)

A

1.0

10

100

Rock/chondrites

Ponaganset Gneiss

Tonalite and granodiorite gneiss

Ironstone quartz diorite of Emerson (1917)

Zhv

Zpg and Zphg

Zt

Ziqd

Zncgm

Znfg

Zncg

EXPLANATION

Figure 8. Trace and rare earth element discrimination diagrams 

for rock samples from the Uxbridge quadrangle. A and C, Rock/

chondrite normalized rare earth element diagram modified from 

Sun and McDonough (1989). B and D, Rock/primitive mantle 

normalized multi-element “spider” diagram modified from 

Thompson and others (1984). E, Th versus U plot; for comparison 

with data from Wones and Goldsmith (1991) and from the Grafton 

quadrangle (Walsh and others, 2011). 
12 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

Table 5. Major, trace, and rare earth element whole-rock geochemistry from the Uxbridge quadrangle.—Continued

[Geochemical analyses were conducted on 30 samples of intrusive rock by SGS Minerals, Toronto, Ontario, Canada. Major elements were analyzed by X-ray 

fluorescence (XRF) using lithium metaborate fused disks (SGS Minerals Method XRF76S). Trace and rare earth elements were analyzed by inductively 

coupled plasma-mass spectrometry (ICP-MS) using sodium peroxide fusion (SGS Minerals Method ICM90A). LOI, loss on ignition; ppm, parts per million]

Sample no. GR-283 UX-1001-A UX-1157-A UX-1291 UX-1425 UX-1434 UX-1001

Map unit Zncgm Zncgm Zncgm Zncgm Zncgm Zncgm Zncg

Major elements (percent)

SiO2

Al O2 3

Fe O2 3

MgO

CaO

74.5

13

2.55

0.38

1.55

75.1

13.2

2.21

0.28

1.3

73.4

13.3

3.73

0.69

2.1

76.4

12.8

2.03

0.25

1.03

75.1

13.3

1.85

0.22

0.98

77.1

12.3

1.81

0.23

0.9

74.1

13

1.78

0.28

1.25

Na2

O

K O2

TiO2

P2 5 O

MnO

3.2

4.53

0.27

0.06

0.05

2.95

5.27

0.23

0.05

0.04

3.26

3.63

0.48

0.12

0.12

3.13

5.09

0.23

0.04

0.04

3.04

5.69

0.19

0.04

0.04

2.9

5.02

0.19

0.03

0.04

3.13

5.06

0.18

0.03

0.03

Cr2 3 O

LOI

< 0.01

0.38

< 0.01

0.12

< 0.01

0.24

< 0.01

0.19

< 0.01

0.25

< 0.01

0.18

< 0.01

0.27

 Totals 100.5 100.7 101.1 101.2 100.7 100.7 99.1

Trace and rare earth elements (ppm)

Ba 924 833 1,060 616 441 344 899

Be < 5 < 5 < 5 < 5 < 5 < 5 < 5

Ca 1.11 0.95 1.56 0.79 0.73 0.69 0.93

Cr 20 10 <10 10 10 20 10

Cu < 5 < 5 < 5 < 5 < 5 < 5 < 5

Fe 1.82 1.54 2.68 1.4 1.24 1.24 1.29

K 3.56 4.16 3 4 4.52 3.96 4.1

Li 20 10 30 <10 20 20 20

Mg

Mn

0.22

400

0.16

330

0.4

890

0.14

270

0.11

270

0.11

270

0.16

270

Ni <5 7 21 <5 19 11 14

P 0.04 0.04 0.07 0.02 0.02 0.03 0.02

Sc 7 9 16 7 < 5 < 5 < 5

Sr 144 125 184 87.3 79.1 75.5 119

Ti 0.16 0.13 0.27 0.13 0.12 0.11 0.11

V 17 14 30 12 8 8 14

Zn 39 32 105 45 30 29 23

Ag

As

<1

< 5

<1

< 5

<1

< 5

<1

< 5

<1

< 5

<1

< 5

<1

< 5

Bi < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1
Geochemistry 13

Table 5. Major, trace, and rare earth element whole-rock geochemistry from the Uxbridge quadrangle.—Continued

[Geochemical analyses were conducted on 30 samples of intrusive rock by SGS Minerals, Toronto, Ontario, Canada. Major elements were analyzed by X-ray 

fluorescence (XRF) using lithium metaborate fused disks (SGS Minerals Method XRF76S). Trace and rare earth elements were analyzed by inductively 

coupled plasma-mass spectrometry (ICP-MS) using sodium peroxide fusion (SGS Minerals Method ICM90A). LOI, loss on ignition; ppm, parts per million]

Sample no.

Map unit

GR-283

Zncgm

UX-1001-A

Zncgm

UX-1157-A

Zncgm

UX-1291

Zncgm

UX-1425

Zncgm

UX-1434

Zncgm

UX-1001

Zncg

Trace and rare earth elements (ppm)—Continued

Cd

Ce

Co

Cs

Dy

Er

Eu

Ga

Gd

Ge

Hf

Ho

In

La

Lu

Mo

Nb

Nd

Pb

Pr

Rb

Sb

Sm

Sn

Ta

Tb

Th

Tl

Tm

U

W

Y

Yb

Zr

< 0.2

99.6

2.6

1

5.68

3.12

1.09

16

6.15

1

6

1.13

< 0.2

52.6

0.46

<2

13

40

16

10.7

115

< 0.1

7.6

4

0.9

0.96

12.5

<0.5

0.46

2.45

<1

31.3

3.2

238

< 0.2

92.2

1.8

2.8

3.16

1.62

0.97

14

3.95

1

3

0.59

< 0.2

48.8

0.25

<2

10

35.4

14

9.83

130

< 0.1

5.8

1

0.8

0.63

12.3

0.6

0.23

3.68

<1

17

1.7

140

< 0.2

115

4.4

2.3

7.25

3.51

1.72

17

7.85

2

5

1.23

< 0.2

60.3

0.46

<2

16

50.2

17

12.4

118

< 0.1

9.3

1

1.1

1.14

13

<0.5

0.5

2.5

<1

35.2

3.4

227

< 0.2

135

1.6

1.1

9.07

4.4

1.25

16

10.1

2

4

1.54

< 0.2

91.4

0.59

<2

14

71.9

12

18.7

133

< 0.1

13.1

2

1

1.52

13

0.6

0.61

2.66

<1

46.4

4.3

168

< 0.2

73.6

1.4

1.3

4.74

2.83

0.6

15

3.72

1

4

0.9

< 0.2

21.1

0.59

<2

12

20.1

16

5.12

155

< 0.1

4.2

1

1.2

0.72

12.4

0.6

0.48

1.55

<1

27.8

3.1

134

< 0.2

52.3

1.4

1.2

4.3

2.47

0.63

14

4.22

1

4

0.83

< 0.2

29.4

0.52

<2

13

25.5

16

6.55

141

< 0.1

4.6

2

1.1

0.63

13.9

0.6

0.45

2.5

<1

26.9

3.1

140

< 0.2

67

2

2.4

3.51

1.99

0.7

14

3.8

2

3

0.62

< 0.2

38.4

0.36

<2

13

27

23

7.04

167

< 0.1

4.6

2

1.3

0.58

15.8

0.7

0.31

3.75

<1

19.7

2.3

118
14 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

Table 5. Major, trace, and rare earth element whole-rock geochemistry from the Uxbridge quadrangle.—Continued

[Geochemical analyses were conducted on 30 samples of intrusive rock by SGS Minerals, Toronto, Ontario, Canada. Major elements were analyzed by X-ray 

fluorescence (XRF) using lithium metaborate fused disks (SGS Minerals Method XRF76S). Trace and rare earth elements were analyzed by inductively 

coupled plasma-mass spectrometry (ICP-MS) using sodium peroxide fusion (SGS Minerals Method ICM90A). LOI, loss on ignition; ppm, parts per million]

Sample no. UX-1025 UX-1025 UX-1105 UX-1116 UX-1121-A UX-1004 UX-1016 UX-1112

Map unit Zncg Zncg Zncg Zncg Zncg Zt Zt Zt

Major elements (percent)

SiO2

Al O2 3

Fe O2 3

MgO

CaO

77.1

12.4

1.08

0.04

0.49

77.3

12.7

1.14

0.05

0.74

76.6

12.7

1.46

0.12

0.91

77.4

12.6

1.18

0.13

0.63

76.7

13.1

0.79

0.06

0.23

66.1

14.4

6.91

1.09

4.28

76.6

11.8

4.48

0.3

1.91

64.6

14

8.6

1.35

5.81

Na2

O

K O2

TiO2

P2 5 O

MnO

3.73

4.53

0.04

< 0.01

0.03

3.67

4.88

0.05

< 0.01

0.02

3.37

4.95

0.12

0.02

0.03

3.66

4.68

0.14

0.02

0.06

3.88

4.97

0.09

0.01

0.01

3.63

1.86

0.75

0.23

0.17

3.13

1.65

0.38

0.07

0.1

2.85

1.16

1.21

0.4

0.21

Cr2 3 O

LOI

< 0.01

0.27

< 0.01

0.24

< 0.01

0.68

< 0.01

0.36

< 0.01

0.34

< 0.01

0.28

< 0.01

0.44

< 0.01

0.44

 Totals 99.7 100.8 101 100.9 100.2 99.7 100.9 100.6

Trace and rare earth elements (ppm)

Ba 45.7 34.1 164 1,120 337 545 1,040 268

Be 6 7 < 5 < 5 < 5 < 5 < 5 < 5

Ca 0.46 0.55 0.74 0.49 0.2 2.98 1.4 4.14

Cr 10 10 <10 10 <10 10 20 10

Cu 7 < 5 < 5 < 5 21 < 5 9 31

Fe 0.73 0.74 1.01 0.82 0.52 4.83 3.14 5.77

K 3.74 3.78 3.79 3.68 3.83 1.53 1.33 0.96

Li 30 30 20 20 <10 20 30 30

Mg

Mn

0.02

230

0.02

150

0.08

230

0.06

450

0.03

100

0.6

1,260

0.18

730

0.78

1,570

Ni 13 8 6 7 17 15 13 21

P < 0.01 < 0.01 < 0.01 0.02 < 0.01 0.09 0.04 0.18

Sc < 5 < 5 < 5 6 8 30 21 37

Sr 22.8 16.2 40.7 88.9 43 322 289 370

Ti 0.03 0.02 0.07 0.08 0.05 0.42 0.21 0.65

V < 5 < 5 7 < 5 < 5 37 13 57

Zn 30 25 28 43 18 108 73 113

Ag

As

<1

< 5

<1

< 5

<1

< 5

<1

< 5

<1

< 5

<1

< 5

<1

< 5

<1

< 5

Bi < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 0.2
Geochemistry 15

Table 5. Major, trace, and rare earth element whole-rock geochemistry from the Uxbridge quadrangle.—Continued

[Geochemical analyses were conducted on 30 samples of intrusive rock by SGS Minerals, Toronto, Ontario, Canada. Major elements were analyzed by X-ray 

fluorescence (XRF) using lithium metaborate fused disks (SGS Minerals Method XRF76S). Trace and rare earth elements were analyzed by inductively 

coupled plasma-mass spectrometry (ICP-MS) using sodium peroxide fusion (SGS Minerals Method ICM90A). LOI, loss on ignition; ppm, parts per million]

Sample no.

Map unit

UX-1025

Zncg

UX-1025

Zncg

UX-1105

Zncg

UX-1116

Zncg

UX-1121-A

Zncg

UX-1004

Zt

UX-1016

Zt

UX-1112

Zt

Trace and rare earth elements (ppm)—Continued

Cd

Ce

Co

Cs

Dy

Er

Eu

Ga

Gd

Ge

Hf

Ho

In

La

Lu

Mo

Nb

Nd

Pb

Pr

Rb

Sb

Sm

Sn

Ta

Tb

Th

Tl

Tm

U

W

Y

Yb

Zr

< 0.2

16.8

< 0.5

4.6

7.01

4.62

0.1

16

4.05

2

2

1.5

< 0.2

4.2

0.75

<2

22

6.7

19

1.41

213

< 0.1

2.8

4

2.3

0.95

16.5

0.9

0.69

5.97

<1

42.8

5

61.1

< 0.2

22.6

< 0.5

5.9

15.6

8.7

0.18

21

10.8

2

4

2.98

< 0.2

10.9

1.26

<2

26

17.9

20

3.68

276

0.1

7.5

5

3.4

2.26

19.8

1.2

1.37

6.46

<1

96

8.8

81.9

0.2

46

0.9

2.3

10.9

6

0.45

16

8.32

1

3

2.03

< 0.2

22.1

0.7

<2

38

24.4

19

5.48

190

0.1

6.7

1

1.8

1.55

28.5

0.8

0.84

7.75

<1

54.3

5.4

94.7

< 0.2

84.6

< 0.5

1.6

4.66

2.4

1.79

15

5.62

1

3

0.85

< 0.2

39.2

0.35

<2

15

37

17

9.04

114

< 0.1

7

<1

0.9

0.78

9.8

<0.5

0.34

1.37

<1

25.2

2.1

87.4

< 0.2

50.6

< 0.5

2.6

7.43

3.59

1.09

17

7.76

2

3

1.33

< 0.2

25.9

0.47

<2

25

30.9

21

6.97

137

0.1

7.6

1

1.3

1.23

10

0.5

0.47

3

1

40.1

3.2

74.9

< 0.2

81.3

6.6

2.1

6.61

3.33

2.88

18

7.4

2

8

1.17

< 0.2

40.8

0.48

<2

19

41.5

8

9.44

51.1

< 0.1

8.1

<1

0.8

1.08

5.7

<0.5

0.48

1.27

<1

32.7

3.3

414

< 0.2

34.6

2.3

2.8

4.05

2.09

1.8

14

4.7

1

8

0.74

< 0.2

19.7

0.32

<2

14

21

12

4.42

46.7

< 0.1

4.9

<1

0.5

0.67

3.4

<0.5

0.32

1.01

<1

18.6

2.2

381

< 0.2

47.3

8.2

4.2

5.03

2.68

2.84

19

5.66

1

14

0.88

< 0.2

22.3

0.39

<2

16

26.3

8

5.83

47.1

< 0.1

5.2

<1

0.7

0.78

3.3

<0.5

0.37

1

<1

25

2.5

774
16 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

Table 5. Major, trace, and rare earth element whole-rock geochemistry from the Uxbridge quadrangle.—Continued

[Geochemical analyses were conducted on 30 samples of intrusive rock by SGS Minerals, Toronto, Ontario, Canada. Major elements were analyzed by X-ray 

fluorescence (XRF) using lithium metaborate fused disks (SGS Minerals Method XRF76S). Trace and rare earth elements were analyzed by inductively coupled 

plasma-mass spectrometry (ICP-MS) using sodium peroxide fusion (SGS Minerals Method ICM90A). LOI, loss on ignition; ppm, parts per million]

Sample no. UX-1134 UX-1148 UX-1398 UX-1042 UX-1043 UX-1082 UX-1087 UX-1092

Map unit Zt Zt Zt Zphg Zpg Zphg Zpg Zphg

Major elements (percent)

SiO2

Al O2 3

Fe O2 3

MgO

CaO

66.4

13.6

7.92

1.2

5.47

76.4

11.9

3.93

0.26

2.61

69.9

13.9

5.38

0.74

3.46

73.9

13.6

2.23

0.35

1.49

73.1

13.1

3.55

0.6

2.27

74.8

12.4

2.33

0.28

1.36

69.8

14.4

4.16

0.99

2.57

72

13.7

3.95

0.69

2.53

Na2

O

K O2

TiO2

P2 5 O

MnO

2.85

0.89

1.11

0.36

0.19

3.25

1.72

0.33

0.07

0.1

3.71

2.26

0.54

0.16

0.13

4.19

4.35

0.27

0.06

0.04

3.2

3.81

0.43

0.11

0.07

3.27

4.36

0.25

0.05

0.05

3.1

4.48

0.57

0.15

0.08

3.28

3.92

0.48

0.13

0.08

Cr2 3 O

LOI

< 0.01

0.43

< 0.01

0.39

< 0.01

0.28

< 0.01

0.3

< 0.01

0.2

< 0.01

0.18

< 0.01

0.38

< 0.01

0.25

 Totals 100.4 101 100.5 100.8 100.4 99.3 100.7 101

Trace and rare earth elements (ppm)

Ba 242 1,100 711 930 769 655 583 871

Be <5 <5 <5 <5 <5 6 <5 <5

Ca 3.81 1.85 2.42 1.09 1.56 0.97 1.85 1.78

Cr 20 <10 <10 10 20 20 <10 10

Cu <5 <5 <5 6 <5 9 <5 <5

Fe 5.51 2.68 3.78 1.51 2.45 1.69 2.92 2.66

K 0.75 1.36 1.79 3.46 2.96 3.49 3.51 3.06

Li 20 20 20 10 20 30 40 20

Mg

Mn

0.67

1,420

0.15

740

0.42

940

0.2

320

0.33

510

0.16

420

0.57

650

0.38

560

Ni 10 11 24 6 6 21 19 9

P 0.17 0.03 0.08 0.02 0.04 0.02 0.08 0.04

Sc 36 12 23 7 12 12 17 15

Sr 375 277 267 201 160 105 176 173

Ti 0.6 0.18 0.31 0.15 0.24 0.14 0.32 0.27

V 50 10 26 17 31 15 56 36

Zn 108 61 87 45 56 52 60 60

Ag

As

<1

<5

<1

<5

<1

<5

<1

<5

<1

<5

<1

<5

<1

<5

<1

<5

Bi < 0.1 < 0.1 < 0.1 0.6 < 0.1 < 0.1 < 0.1 < 0.1
Geochemistry 17

Sample no.

Map unit

UX-1134

Zt

UX-1148

Zt

UX-1398

Zt

UX-1042

Zphg

UX-1043

Zpg

UX-1082

Zphg

UX-1087

Zpg

UX-1092

Zphg

Trace and rare earth elements (ppm)—Continued

Cd

Ce

Co

Cs

Dy

Er

Eu

Ga

Gd

Ge

Hf

Ho

In

La

Lu

Mo

Nb

Nd

Pb

Pr

Rb

Sb

Sm

Sn

Ta

Tb

Th

Tl

Tm

U

W

Y

Yb

Zr

< 0.2

40.8

8

2.3

4.57

2.34

2.97

18

5.17

1

13

0.81

< 0.2

19.5

0.37

<2

16

23.9

7

5.16

29.2

< 0.1

5.3

<1

0.7

0.74

2.4

< 0.5

0.31

0.68

<1

23

2.3

756

< 0.2

86.5

2

1.4

3.73

1.85

2.98

15

4.55

1

7

0.67

< 0.2

44.1

0.34

<2

11

37.6

8

9.04

59

< 0.1

5.9

<1

<0.5

0.67

5.6

< 0.5

0.26

1.16

<1

19.5

2

381

< 0.2

85.7

4.9

1.5

7.91

4

2.7

18

8.37

1

8

1.36

< 0.2

41.7

0.58

<2

19

45.2

10

9.92

63.1

< 0.1

9.1

2

1

1.26

6.4

< 0.5

0.6

2.05

<1

38

3.7

358

< 0.2

85

2.8

2.2

6.48

3.98

0.97

16

5.71

1

5

1.3

< 0.2

35.7

0.6

<2

14

29.9

27

7.88

130

< 0.1

6

3

1.5

1.04

14.3

0.6

0.58

2.35

<1

39

4.1

187

< 0.2

189

4.3

2.2

7.42

3.52

1.4

17

8.07

1

7

1.25

< 0.2

100

0.52

<2

14

65

11

17.7

111

< 0.1

10.2

2

0.9

1.2

17.3

< 0.5

0.49

2.47

<1

37.4

3.8

252

< 0.2

97.5

1.8

1.4

7.56

3.97

1.27

16

7.9

1

5

1.47

< 0.2

51.5

0.61

<2

15

44.4

13

11.1

118

< 0.1

8.4

2

1

1.19

10.7

< 0.5

0.6

1.53

<1

41.8

4.1

211

< 0.2

85.8

7

5.1

7.28

4.12

1.25

18

7.42

2

4

1.36

< 0.2

44.7

0.59

<2

19

40

16

9.81

161

< 0.1

8.1

3

1.6

1.18

12.3

0.7

0.62

3.61

<1

40.5

4.1

157

< 0.2

85.6

4.8

1.6

7.22

3.52

1.54

16

7.5

1

4

1.33

< 0.2

42.7

0.51

<2

16

42.5

13

9.98

101

< 0.1

8.9

1

0.8

1.24

7.3

< 0.5

0.53

1.76

<1

38.9

3.3

185

Table 5. Major, trace, and rare earth element whole-rock geochemistry from the Uxbridge quadrangle.—Continued

[Geochemical analyses were conducted on 30 samples of intrusive rock by SGS Minerals, Toronto, Ontario, Canada. Major elements were analyzed by X-ray 

fluorescence (XRF) using lithium metaborate fused disks (SGS Minerals Method XRF76S). Trace and rare earth elements were analyzed by inductively coupled 

plasma-mass spectrometry (ICP-MS) using sodium peroxide fusion (SGS Minerals Method ICM90A). LOI, loss on ignition; ppm, parts per million]
18 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

Table 5. Major, trace, and rare earth element whole-rock geochemistry from the Uxbridge quadrangle.—Continued

[Geochemical analyses were conducted on 30 samples of intrusive rock by SGS Minerals, Toronto, Ontario, Canada. Major elements were analyzed by X-ray 

fluorescence (XRF) using lithium metaborate fused disks (SGS Minerals Method XRF76S). Trace and rare earth elements were analyzed by inductively coupled 

plasma-mass spectrometry (ICP-MS) using sodium peroxide fusion (SGS Minerals Method ICM90A). LOI, loss on ignition; ppm, parts per million]

Sample no. UX-1179 UX-1237 UX-1122 UX-1274 UX-1276 UX-1591 UX-1618

Map unit Zpg Zpg Zhv Znfg Znfg Znfg Ziqd

Major elements (percent)

SiO2

Al O2 3

Fe O2 3

MgO

CaO

68.6

14.8

3.82

1.02

1.94

75.5

12.4

3.11

0.19

1.81

77

12.7

1.06

0.08

0.48

78.1

11.8

1.65

0.19

0.47

77.3

12.8

1.41

0.09

0.5

76.5

12.7

1.83

0.17

1.09

46.5

12.9

18.2

5.44

9.4

Na2

O

K O2

TiO2

P2 5 O

MnO

3.07

5.38

0.54

0.15

0.07

3.15

3.61

0.23

0.05

0.07

3.68

4.92

0.13

0.02

0.05

2.85

5.2

0.11

0.01

0.03

3.93

4.76

0.07

0.01

0.05

3.29

4.61

0.15

0.03

0.04

1.91

0.75

3.03

0.58

0.29

Cr2 3 O

LOI

< 0.01

0.46

< 0.01

0.3

< 0.01

0.3

< 0.01

0.34

< 0.01

0.2

< 0.01

0.18

< 0.01

0.36

 Totals 99.9 100.4 100.4 100.8 101.1 100.6 99.4

Trace and rare earth elements (ppm)

Ba 796 2,100 670 430 108 353 148

Be <5 <5 <5 <5 <5 <5 <5

Ca 1.4 1.39 0.39 0.36 0.41 0.79 6.7

Cr 10 10 20 <10 10 10 10

Cu 9 <5 <5 <5 <5 9 45

Fe 2.7 2.13 0.74 1.19 0.94 1.31 12.4

K 4.23 2.78 3.91 4.03 3.77 3.66 0.7

Li 30 10 10 20 20 <10 20

Mg

Mn

0.56

580

0.13

510

0.04

400

0.1

190

0.04

320

0.09

310

3.2

2,260

Ni 16 8 7 19 18 10 16

P 0.05 0.01 0.02 <0.01 <0.01 0.02 0.26

Sc 13 11 6 <5 <5 6 47

Sr 178 198 55.3 43.9 35.4 71.1 308

Ti 0.31 0.13 0.07 0.07 0.04 0.09 1.89

V 49 8 <5 <5 <5 7 450

Zn 63 50 40 33 32 26 164

Ag

As

<1

<5

<1

<5

<1

<5

<1

<5

<1

<5

<1

<5

<1

<5

Bi < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1
Geochemistry 19

Table 5. Major, trace, and rare earth element whole-rock geochemistry from the Uxbridge quadrangle.—Continued

[Geochemical analyses were conducted on 30 samples of intrusive rock by SGS Minerals, Toronto, Ontario, Canada. Major elements were analyzed by X-ray 

fluorescence (XRF) using lithium metaborate fused disks (SGS Minerals Method XRF76S). Trace and rare earth elements were analyzed by inductively coupled 

plasma-mass spectrometry (ICP-MS) using sodium peroxide fusion (SGS Minerals Method ICM90A). LOI, loss on ignition; ppm, parts per million]

Sample no.

Map unit

UX-1179

Zpg

UX-1237

Zpg

UX-1122

Zhv

UX-1274

Znfg

UX-1276

Znfg

UX-1591

Znfg

UX-1618

Ziqd

Trace and rare earth elements (ppm)—Continued

Cd

Ce

Co

Cs

Dy

Er

Eu

Ga

Gd

Ge

Hf

Ho

In

La

Lu

Mo

Nb

Nd

Pb

Pr

Rb

Sb

Sm

Sn

Ta

Tb

Th

Tl

Tm

U

W

Y

Yb

Zr

< 0.2

62.9

6.7

4.1

6.74

3.59

1.15

16

6.14

1

4

1.18

< 0.2

22.6

0.44

<2

18

25.8

29

6.06

156

< 0.1

6

2

1.3

0.95

8.9

0.7

0.49

1.91

<1

34.1

3.5

174

< 0.2

113

1.6

1.3

4.26

2.07

2.04

16

5.11

1

6

0.8

< 0.2

57.5

0.34

<2

11

45.9

12

11.4

68.7

< 0.1

7.4

<1

0.5

0.71

7.4

<0.5

0.32

1.05

<1

21.5

2.1

258

< 0.2

75

< 0.5

1.7

4.75

2.41

1.97

16

6.2

1

3

0.87

< 0.2

36.3

0.35

<2

14

39.2

18

8.93

117

< 0.1

7.8

<1

0.8

0.83

11.7

<0.5

0.32

1.7

<1

25

2.2

97.7

< 0.2

58.2

0.6

1.1

4.43

2.91

0.35

14

2.87

1

4

0.91

< 0.2

16.7

0.51

<2

14

15.7

16

3.88

115

< 0.1

2.9

1

0.8

0.56

9.2

0.5

0.45

1.13

<1

29.5

3.1

133

< 0.2

36.7

< 0.5

1.4

10.1

6.4

0.36

18

7.46

2

5

2

< 0.2

16.1

1.13

<2

24

21.2

21

4.81

204

< 0.1

6.3

3

2.7

1.42

16

1

1.01

3.8

<1

68

7.4

126

< 0.2

57.8

1

3.3

5.01

3.33

0.6

16

4.28

2

4

1

< 0.2

27.1

0.57

<2

15

24.5

18

6.12

163

0.3

4.7

2

1.5

0.7

12.3

0.8

0.54

2.42

<1

29.7

3.8

129

0.3

42.4

54.6

1.4

8.02

4.65

2.04

21

8.19

2

3

1.65

< 0.2

17.7

0.62

<2

39

30.2

<5

6.26

20.5

0.2

7.9

3

1.8

1.33

1.9

<0.5

0.59

0.37

<1

40.3

3.7

101
20 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

Structural Geology

Ductile Structures

The rocks of the Uxbridge quadrangle occur in the core 

of the Milford antiform. At least four generations of ductile 

deformation and associated structures are recognized, and 

they are designated by their relative ages as D1 to D4. In the 

following discussion, we present the ductile structures in order 

of their relative ages, from oldest to youngest.

Relict Deformation (D1)

The oldest foliation is a relict layer-parallel schistosity 

(S1) observed in rocks of the Blackstone Group. The relict 

S1 foliation is found parallel to bedding in tight to isoclinal 

F2 folds (fig. 9). The relict foliation is characterized by a 

lepidoblastic texture of aligned mica, quartz, and amphibole. 

Definitive F1

 folds associated with this oldest foliation 

were not observed in this quadrangle. This relict foliation is 

reported to be a deformational and metamorphic fabric that 

predates the intrusion of the plutonic rocks in the Avalon zone, 

indicating that it is Neoproterozoic (Bailey and others, 1989; 

Goldsmith, 1991c). In the Uxbridge quadrangle, this relict 

S1 foliation predates the migmatitic rocks around the small 

plutons of the Ironstone quartz diorite (fig. 9C ), showing that 

the foliation is, in places, related to a Neoproterozoic metamorphic and deformational event. The plutonic rocks locally 

contain a deformed foliation that predates the dominant S2

foliation in the rocks. This rare, older foliation appears along 

and parallel to the contacts between rocks of the Ponaganset 

Gneiss and Northbridge Granite Gneiss, and parallel to rare 

compositional banding in these rocks. It represents either an 

igneous flow foliation or relict metamorphic foliation.

A

UX-1162_4.JPG

Figure 9. Photographs and sketch of relict S1 foliation and F2 folds in rocks of the Blackstone Group. A, Folded amphibole-bearing 

calc-silicate layers define deformed compositional layering (S0 ) that is parallel to the relict S1

 foliation in the biotite schist in unit Zb. 

The composite S1 / S0

 foliation is deformed into an F2 fold with the dominant foliation (S2 ) marking the axial surface. Steeply dipping 

upright cleavage (S3 ) deforms the older foliations. B, Sketch of A. C, Rootless isoclinal F2

 fold in the plane of the dominant foliation S2 , 

showing deformed relict S1

 foliation in the migmatitic gneiss (Zbm). Light-colored granitic dikes cut the dominant foliation. GPS 

receiver is 10.5 cm long. D, Isoclinal F2

 fold of relict S1 / S0 in the plane of the dominant foliation S2 , showing deformed relict S1 foliation

in the Blackstone Group (Zb).

C

F2 fold

of relict S1

Zbm

UX-1199_09.JPG

D

F2 fold

of relict

S1/S0

S2

Zb

Quartz-rich schist

Quartzite

UX-1538_7.JPG

B S1/S0

S2

S3

S3

Lichen

Lichen

Lichen

Calc-silicate

Schist

Zb
Structural Geology 21

Second Generation Deformation (D2)

The second generation foliation (S2 ) is the dominant 

planar fabric in the Uxbridge quadrangle. The S2 foliation is a 

schistosity in the Blackstone Group rocks and a gneissosity to 

nonpenetrative foliation in the plutonic rocks. The S2 foliation 

is axial planar to tight to isoclinal folds of relict S1 foliation in 

the metasedimentary Blackstone Group rocks (fig. 9D), and 

is axial planar to rare folds of igneous flow foliation in the 

intrusive rocks. Generally, the S2 foliation in the plutonic rocks 

is more penetrative to the north and less penetrative to the 

south. This observation supports Goldsmith’s (1991c) claim 

that the intensity of the foliation increases as the Bloody Bluff 

fault (fig. A on map) is approached. In areas where S2 is a lesspenetrative planar fabric, the foliation is weakly developed 

and locally anastomoses through the rock. In these places, 

the plutonic rocks generally possess an L-tectonite fabric 

(fig. 5) having a pronounced northeast-trending L2

 lineation 

(fig. 10A ). Locally the S2

 fabric is mylonitic, and in these 

places thin mylonite zones range from several centimeters 

(fig. 11) to several meters thick. S2 is deformed into a north- to 

northwest- or west-striking and gently east- to northeastdipping orientation across the quadrangle, and the poles to the 

foliation define a great circle corresponding to deformation 

across the Milford antiform (fig. 10A). Second-generation 

mineral lineations (L2 ) form “aggregate lineations” and 

“grain lineations” (Piazolo and Passchier, 2002; Passchier and 

Trouw, 2005). The mineral lineations consist of quartz rods, 

and aligned biotite, hornblende, and recrystallized garnet, and 

deformed and recrystallized feldspar tails around microcline 

augen consistent with formation during upper greenschist- to 

lower amphibolite-facies metamorphic conditions. The L2

mineral lineations show a very consistent northeast trend, 

subparallel to the F2 fold axes or intersection lineations, 

suggesting high strain during D2 deformation (fig. 10A). 

N

A

 Pi pole

 24°, 39°

 114°, 61°

Poles to S2 (n=519)

L2 mineral lineations (n=334)

F2 fold axes or intersection lineations (n=45)

N

Poles to S3 (n=42, 2%)

L3 mineral lineations (n=16)

F3 fold axes or intersection lineations (n=12)

B

Figure 10. Summary diagrams of D2 and D3 ductile structures. A, Lower hemisphere equal-area projection 

(stereonet) of dominant foliation (S2 ) showing the poles to S2 , best-fit great circle to poles, the Pi pole to 

a best-fit great circle, L 2

 mineral lineations, and F2 fold axes. B, Stereonet of poles to S3 including F3 axial 

surfaces, F3

 fold axes and intersection lineations, and L3 mineral lineations. The number of points and the 

contour interval (where plotted) are shown in parentheses at the bottom of each diagram. Diagrams were 

plotted using the Structural Data Integrated System Analyzer (DAISY) software by Salvini (2010).
22 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

A

Zncg

UX-1105_1.JPG

B Zpg

UX-1089_1.JPG

C

Zpg

UX-1232_1.JPG

D

Zpg

UX-1231_2.JPG

Figure 11. Photographs showing variation in the S2 foliation in granitic rocks. A, Weakly developed nonpenetrative S2 foliation 

is defined by darker bands of aligned biotite and recrystallized quartz and feldspar in the Northbridge Granite Gneiss (Zncg). 

B, Moderately well-developed S2

 foliation with a thin mylonite zone (under pencil) in the Ponaganset Gneiss (Zpg). C, Welldeveloped S2

 foliation with thin anastomosing mylonite zones in the Ponaganset Gneiss. GPS receiver is 10.5 cm long. 

D, Penetrative mylonitic S2

 foliation in the Ponaganset Gneiss. 
Structural Geology 23

Third Generation Deformation (D3 )

The third generation of ductile deformation produced the 

Milford antiform and open to tight folds (F3 ) of the dominant 

foliation (S2 ) (figs. 9A, 10). The F3 folds are associated with a 

crenulation cleavage in the fine-grained rocks of the Blackstone 

Group (figs. 9A, 10). In the coarser grained rocks, such as 

the granitoids and quartzites, the cleavage is very weakly 

developed or not recognized, and the D3 fabric is expressed 

as thin mylonite zones, shear bands, or kink bands (fig. 12). 

In the granitic rocks of the Milford antiform, outcrop-scale 

F3 folds or S3 cleavage were rarely observed. Across the 

quadrangle, the folding of the dominant S2 foliation defines 

the northeast-plunging Milford antiform as a major map-scale 

D3

 structure. The trend of F3 fold axes and L3 intersection 

lineations plunge to the north-northeast (fig. 10B ). The strike 

and dip of S3 is somewhat variable, but the general strike is 

northeast with a steep dip, although some axial surfaces and 

shear bands strike northwest with a northeast dip (fig. 10B ). 

The northwest direction is at a high angle to the northeast 

trend of the Milford antiform, but matches the trend of the 

Oxford anticline (Goldsmith, 1991c; Barosh, 2005) (fig. A on 

map). The northwest trend was also observed in the Grafton 

quadrangle to the north, but to a lesser extent (Walsh and 

others, 2011). 

Figure 12. Photographs showing S3 mylonite zones and 

shear bands. A, Thin northeast-striking, steeply dipping 

mylonite zone (between arrowheads) in the Northbridge 

Granite Gneiss (Zncg) at the Exit 2 northbound offramp on 

Route 146. B, Close-up of A. GPS receiver is 10.5 cm long. 

C, Sinistral shear band with localized vein quartz in the 

Pon aganset Gneiss (Zpg).

C

UX-1090_5.JPG

Zpg

Vein

A

Zncg

UX-1117_1.JPG

B

Zncg

UX-1117_2.JPG
24 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

L3

 mineral lineations occur as aggregate lineations 

defined by aligned and recrystallized biotite, quartz, and 

feldspar in the plane of thin subvertical D3 mylonite zones 

and shear bands. In the Grafton quadrangle to the north, 

aligned hornblende locally defines an L3 mineral lineation, but 

in the Uxbridge quadrangle this was not observed. Instead, 

hornblende occurs both as aligned grains parallel to L2 and as 

randomly oriented post-D2 fascicular overgrowths in the plane 

of S2 (fig. 13). 

Map- and outcrop-scale S3 mylonite zones are most 

abundant in the southeastern part of the quadrangle, and in 

this area three mylonitic faults are shown on the map. Asymmetric quartz ribbons, s-c fabrics, and oblique foliation or 

c-type shear bands (Passchier and Trouw, 2005, p. 128) from 

a sample (station 1121) in the vicinity of Exit 22 on Route 146 

show sinistral, west-side-up displacement. The mapped fault 

east of Exit 2 was drawn based on the apparent truncation 

of a small belt of alaskite (Zhv) seen along the southbound 

onramp of Route 146. It should be noted that only a single 

sample was collected for kinematics from the Exit 2 area, and 

outcrops in the area contain multiple thin S3 mylonite zones 

whose kinematics have not been studied in detail. A second 

S3 mylonitic fault is mapped near the junction of Chestnut 

and Aldrich Streets based on the presence of steeply dipping 

northeast-striking mylonitic fabric exposed at two places 

(stations 1077 and 1078) on Acorn Drive (street name not on 

base map). A third fault is mapped near Aldrich Pond where 

S3 mylonitic fabric with foliation-parallel quartz veins deforms 

the older S2 foliation into a map-scale dextral shear band. A 

sample (station 1574) collected just south of the gas pipeline 

north of Aldrich Pond yielded no conclusive kinematic 

indicators, and the offset along this fault is interpreted from 

the mapped deflection of the S2 foliation west of the fault.

2

The location of Route 146 is not precisely depicted on the topographic 

base map. The latest revision to the base map occurred in 1979, and the 

highway is shown as a single line. Currently the highway is divided into 

northbound and southbound lanes. The line on the map generally shows the 

location of the two northbound lanes, and the two southbound lanes are not 

shown. Modifications to the interchanges also are not shown.

Zb

hb

UX-1162_7.JPG

Figure 13. Photograph showing syntectonic and posttectonic hornblende. On the left, hornblende (hb) is aligned 

parallel to L 2

 (parallel to the red arrow and pencil), and to the 

right hornblende occurs as larger, post-D2 , randomly oriented 

fascicular overgrowths in the plane of S2 . Rock is a titaniteepidote-plagioclase-quartz-hornblende-biotite schist xenolith 

of the Blackstone Group (Zb) within the Northbridge Granite 

Gneiss (Zncgm). Section of pencil shown is about 10 cm long. 

Fourth Generation Deformation (D4 )

A fourth period of deformation produced open, late folds 

that deform the S3 foliation. This deformation was observed 

at only one place, north of Whitinsville (station 1435). 

In addition to the late folds, numerous quartz veins and 

pegmatite dikes postdate the D3 fabric, and their orientations 

are summarized in figure 14. The veins and dikes represent 

a continuum of extensional deformation from D3 to D4 , as 

veins and dikes also occur in the plane of D3 ductile shear 

bands (figs. 12C and 15A). Late, tabular, crosscutting quartz 

veins and pegmatite dikes are shown on the map by strike and 

dip symbols. In many places, the veins and dikes are zoned 

and show gradations from quartz veins to muscovite granite 

pegmatite and more rarely biotite granite pegmatite along 

the margins or along the median line (figs. 4 and 15C, D). 

Veins show a preferred northwest strike and steep northeast 

dip (fig. 14A) corresponding to a principal trend of 301o ± 7o 

(fig. 14B ), and a subordinate trend to the northeast. The 

pegmatite dikes show random orientations (fig. 14C ). 
Structural Geology 25

N

Quartz veins (n = 69, 2%)

A

N

(n=10)

D

N

Pegmatite dikes (n=14, 2%)

C

N

(n=45)

301°± 7°

B

Figure 14. Summary diagrams showing the orientation of quartz veins and pegmatite dikes. A, Stereonet of 

contoured poles to strike and dip of veins. B, Normalized azimuth-frequency (rose) diagram of steeply dipping (dips 

> 60o) veins. The principal trend (301o ± 7o) is shown with one standard deviation error. C, Stereonet of poles to strike 

and dip of dikes. D, Rose diagram of steeply dipping (dips > 60o) dikes. For all diagrams, the number of points and the 

contour interval (where plotted) are shown in parentheses at the bottom of each diagram. Diagrams were plotted 

using the Structural Data Integrated System Analyzer (DAISY) software by Salvini (2010).
26 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

B

Vein Zpg

UX-1054_4.JPG

A

Vein

Pegmatite

Zphg

UX-1090_7.JPG

D

Zncgm

UX-1281_3.JPG

C

Zpg

UX-1104_2.JPG

Figure 15. Photographs of quartz veins and 

pegmatite dikes. A, Quartz vein in a shear band 

showing marginal granitic pegmatite within the 

Ponaganset Gneiss (Zphg). B, Multiple quartz 

veins at Reservoir No. 5 in Sutton. C, Tabular, 

approximately 30-cm-thick vein with a pegmatitic 

margin exposed at the Douglas Elementary School. 

D, Zoned granitic pegmatite dike in the Northbridge 

Granite Gneiss (Zncgm). The center of the dike 

contains coarse biotite and pale-green-weathering 

plagioclase. GPS receiver in C and D is 10.5 cm long.
Structural Geology 27

Comment on the Hope Valley Shear Zone

An Alleghanian fault called the Hope Valley shear zone 

(HVsz) has been interpreted to pass through the Uxbridge 

quadrangle and represent a regionally significant terrane 

boundary between the Hope Valley terrane to the west and 

the Esmond-Dedham terrane to the east (O’Hara and Gromet, 

1985). The northern part of the shear zone is supposed to be 

at the contact between the Hope Valley Alaskite Gneiss and 

the Ponaganset Gneiss in the Grafton quadrangle (O’Hara and 

Gromet, 1985; Gromet and O’Hara, 1985; Hermes and others, 

1994). Mylonitic foliation found in the Ponaganset Gneiss on 

Route 146 in the town of Sutton in the Grafton quadrangle 

(Walsh and others, 2011) was attributed to southward thrusting 

at a high angle to the overall right-lateral offset along the 

Hope Valley shear zone (O’Hara and Gromet, 1985; Gromet 

and O’Hara, 1985). Wayne and others (1992) obtained 

conventional U-Pb ages of 285 ± 25 and 270 ± 92 Ma from 

metamorphic zircons in a mylonite at this location, indicating 

Alleghanian deformation and metamorphism of the Neoproterozoic plutonic rocks. Gromet and O’Hara (1985) noted 

correctly that the mylonites and foliation at the roadcut in the 

Grafton quadrangle strike at a right angle to the inferred trend 

of the HVsz, but Wayne and others (1992) incorrectly stated 

that the mylonites had a north-south strike and dipped gently 

to the west parallel to the HVsz.

Mapping in the Grafton and Uxbridge quadrangles does 

not support the existence of the Hope Valley shear zone for the 

following reasons:

• Numerous thin (<10-cm-thick) mylonite zones are 

visible at the Route 146 roadcut in the Grafton quadrangle (and at many other roadcuts), but no single zone 

appears to be more significant than the other. Each thin 

mylonite zone represents internal deformation parallel 

to the dominant foliation within the Ponaganset Gneiss. 

• The Hope Valley Alaskite Gneiss intrudes both 

the Ponaganset Gneiss and the Northbridge Granite Gneiss, and there is no distinct mylonitic fabric 

between the Hope Valley Alaskite Gneiss and the 

Ponaganset Gneiss. 

• In the Grafton quadrangle, there is no fabric in the rock 

that strikes north-south and dips subvertically, parallel 

to the proposed HVsz. The dominant foliation and the 

thin mylonite zones near the proposed location of the 

HVsz strike east-west and dip gently north. Thus, the 

dominant foliation is virtually at a right angle to the 

proposed location of the shear zone (recognized by 

Gromet and O’Hara, 1985). In the Uxbridge quadrangle, the north-south-striking, steeply dipping shear 

zones and thin mylonites are related to D3 deformation and represent internal deformation within the 

Ponaganset Gneiss and Northbridge Granite Gneiss, 

but these shear zones do not continue north into the 

Grafton quadrangle. 

• O’Hara and Gromet (1985) and Gromet and O’Hara 

(1985) stated that considerable differences existed 

between the rocks of the Hope Valley and EsmondDedham terranes on either side of the HVsz. This may 

be true in Rhode Island at the type locality, but in 

contrast, geochemical and geochronologic data (this 

study and Walsh and others, 2011) for the Hope Valley 

Alaskite Gneiss and Northbridge Granite Gneiss are 

quite similar and demonstrate that these rocks, located 

on either side of the proposed HVsz, cannot be separated into two terranes on a geochemical or age basis. 

Chemical data from the Grafton and Uxbridge quadrangles support work by Wones and Goldsmith (1991), 

suggesting that the Hope Valley and Northbridge 

(formerly Scituate) are similar. 
28 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

Brittle Structures

The planar brittle structures in this study are also called 

fractures. Fractures with slickensides or visible displacement 

are brittle faults. Fractures without visible displacement are 

separated based on whether or not they are related to an older 

fabric in the metamorphic and igneous rocks, as follows: 

• Parting fractures occur where the rocks break, or part, 

along a pre-existing fabric. Parting fractures are related 

to older sedimentary, igneous, or metamorphic fabrics 

due to structural inheritance and occur along dikes, 

veins, axial surfaces of folds, shear bands, cleavage, 

and foliation. 

• Fractures that cross the metamorphic or igneous fabric 

of the rocks include brittle faults, joints, and joint sets. 

The orientation of measured joints includes those with 

trace lengths greater than 20 cm (Barton and others, 1993). 

Joints were measured subjectively using methods described 

in Spencer and Kozak (1976) and Walsh and Clark (2000), 

and the database includes only the most conspicuous joints 

observed in a given outcrop. Fracture data (fig. 16) are 

plotted on azimuth-frequency or rose diagrams and stereonets 

(lower hemisphere equal-area projections) using Structural 

Data Integrated System Analyzer (DAISY) software 

(Salvini, 2010). The software generates rose diagrams using 

a Gaussian curve-fitting routine for determining peaks in 

directional data (Salvini and others, 1999) that was first 

described by Wise and others (1985). The rose diagrams 

include strike data for steeply dipping fractures (dips ≥ 60°, 

after Mabee and others, 1994). 

Fracture data are summarized in figure 16 and the 

original data are located in the GIS database. In general, the 

most conspicuous fractures occur in three categories (fig. 17): 

(1) parting fractures parallel to the dominant foliation (called 

“foliation-parallel fractures” by Manda and others, 2008), 

(2) steeply dipping fractures that cross the foliation at a high 

angle, and (3) steeply dipping fractures that are orthogonal 

to the foliation. In the northwestern part of the quadrangle 

where there is extensive outcrop, pronounced topographic 

features (lineaments) are controlled by these three fracture 

types. Gently dipping sheeting fractures are not widespread in 

this quadrangle because most of the gently dipping fractures 

are parting fractures that occur parallel to the dominant S2

foliation (fig. 16A). Steeply dipping joints are dominated by 

either abutting or throughgoing fractures that cross entire 

outcrops with trace lengths on the order of meters (fig. 17). 

Throughgoing joints tend to cross the foliation at a high angle, 

and these joints are called “crossing” fractures (Barton and 

others, 1993). These steeply dipping crossing fractures show 

preferred northeast trends (19o – 34o, fig. 16). The northeast 

trend of steeply dipping crossing fractures is similar to the 

trend of some planar pegmatite dikes, the trend of the dominant mineral lineation, and the trend of the Milford antiform, 

suggesting that brittle failure was inherited and occurred not 

only along igneous planar features but also along ductile 

linear features in the rock. The steeply dipping, generally 

northwest-southeast to east-west trend represents joints that 

are orthogonal to the dominant foliation (fig. 17). 

The spacing of fractures, although not quantified in 

this study, rarely exceeds a few meters. Spacing of steeply 

dipping, crossing and orthogonal joints in igneous rocks 

locally exceeds several meters. The spacing and abundance of 

foliation-parallel fractures, or parting fractures, is related to 

rock type: finer grained rocks exhibit more parting fractures 

and smaller spacing. Joint data, separated by generalized 

rock type (fig. 16D ‒ G), show that the metasedimentary and 

igneous rocks have overall similar joint trends, with northeasttrending joints showing more prominence in the igneous rocks 

than in the metasedimentary rocks. Parting by rock type is 

shown in table 6. Generally, the Northbridge Granite Gneiss 

exhibits less parting than the Ponaganset Gneiss, while the 

Blackstone Group metasedimentary rocks exhibit the most 

parting, although overall the degree of parting is quite similar.

Table 6. Summary of foliation-parallel parting fractures by 

formation and rock type. 

Formation 

or rock type

Number of 

measurements 

that exhibit 

parting fractures 

along the 

foliation

Total number 

of foliation 

measurements

Parting 

fractures as 

a percentage 

of total 

foliation 

measurements

Formation

Hope Valley 

Alaskite 

Gneiss 

Tonalite and 

granodiorite 

gneiss

Blackstone 

Group

Ponaganset 

Gneiss 

Northbridge 

Granite 

Gneiss

5

10

53

136

100

6

15

92

244

204

83

67

58

56

49

Rock type

Metasedimentary 

rocks

Igneous rocks

53

251

92

469

58

54
Structural Geology 29

N

n=1190 (1%, max=9%)

All fractures

S2 foliation

A All fractures (dip >59°)

280°±6°

n=705

87°±6°

32°±6°

19°±5°

N

B Parting fractures 

N

n=350

C

N

n=118 (2%, max=16%)

All joints in

metasedimentary rocks

D

n=101 

285°±8° 86°±6°

Joints in metasedimentary

rocks (dip >59°) 

N

E

N

n=704 (1%, max=7%)

All joints in

igneous rocks

F

n=549 

21°±6°

34°±6°

84°±9°

295°±7°

278°±6°

Joints in igneous

rocks (dip >59°)

N

G

Figure 16. Stereonets and rose 

diagrams of fractures. A, Contoured 

poles to all fractures. B, Rose diagram 

of steeply dipping fractures. C, Poles to 

parting fractures. Note that the dataset 

is dominated by parting fractures 

parallel to the dominant S2

 foliation. 

D, Contoured poles to joints in the 

Blackstone Group. E, Rose diagram of 

steeply dipping data in D. F, Contoured 

poles to joints in the igneous rocks. 

G, Rose diagram of steeply dipping data 

in F. “N” indicates north, and “n” shows 

the number of points in the dataset. 

Poles are contoured at 1 or 2 percent 

intervals, and the maximum value 

is indicated in parentheses. Rose 

diagrams include a subset of the data 

shown in the corresponding stereonet 

for dips > 59o. Principal peaks on the 

rose diagrams are shown with one 

standard deviation error.
30 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

Figure 17. Photograph showing three main categories of fractures. Parting fractures (1) occur along the 

dominant foliation and create the overhanging block in this photograph. The main cliff face (2) is a northeaststriking throughgoing joint. Joints that are orthogonal to the foliation (3) are both throughgoing and abutting 

in this example. Outcrop is Ponaganset Gneiss. Hammer for scale (arrow). 

1

1

1 1

3 1 1

1 3 2 2

3 3

2

2

1

3

3

3

EXPLANATION

Major fracture categories

1 Parting along dominant foliation

2 Northeast-striking, steeply 

 dipping joint

3 Joints orthogonal to foliation
Metamorphism 31

Brittle Faults

Five outcrop-scale brittle faults were identifed by 

slickensides or Riedel shears, and they are shown on the 

map with strike and dip symbols and their associated bearing 

and plunge of linear slickenlines. The faults show normal 

(1), reverse (2), and left-lateral (3) strike-slip motion. The 

orientations are variable and the small number of faults 

prevents a comprehensive analysis. Assuming, however, that 

the faults are coeval, a calculation of the mean P and T axes 

(Angelier, 1979) (fig. 18) shows a calculated average stress 

field that is consistent with Late Triassic to Early Jurassic 

northwest-southeast extension associated with rifting of the 

New England crust during the initial opening of the Atlantic 

basin (Kaye, 1983; de Boer and Clifford, 1988; Manning and 

de Boer, 1989; Goldsmith, 1991c). The limited brittle fault 

data in Uxbridge agree with findings in the Grafton quadrangle 

to the north (Walsh and others, 2011).

N

n=5

EXPLANATION

 Slickenlines

σ3

σ3

σ2

σ2

σ1

σ1

Calculated principal stress axes

Figure 18. Stereonet showing results of brittle fault 

inversion analysis. Projection shows fault planes, 

slickenlines, and calculated stress tensors including 

the mean P and T axes for five brittle faults (n = number 

of faults). Shortening (P) axis = σ1, and extension (T) 

axis = σ3. Inversion analysis was calculated using the 

Structural Data Integrated System Analyzer (DAISY) 

software by Salvini (2010).

Metamorphism

The Avalon zone makes up the lower-plate rocks on the 

south side of the Bloody Bluff fault. These rocks experienced a 

different metamorphic history than the Nashoba zone rocks of 

the upper plate to the north and west (Wintsch and Aleinikoff, 

1987; Goldsmith, 1991c). In the area of the Milford antiform, 

the upper-plate rocks in the Nashoba zone experienced upper 

amphibolite-facies metamorphic conditions, whereas the rocks 

in the lower-plate Avalon zone experienced upper greenschist- to lower amphibolite-facies metamorphic conditions. 

The timing of peak metamorphism in the Nashoba zone is 

considered to be early Paleozoic (Goldsmith, 1991c; Wintsch 

and others, 1991, 1992, 1993, 2007; Hepburn and others, 

1995; Stroud and others, 2009). In contrast to the Nashoba 

zone, early metamorphism in the Avalon zone is considered to 

be Neoproterozoic (Goldsmith, 1991c; Hepburn and Bailey, 

1998; Attenoukon and others, 2005; Attenoukon, 2008), and 

peak metamorphism is considered to be late Paleozoic, related 

to Alleghanian orogenesis (Wintsch and Sutter, 1986; Wintsch 

and Aleinikoff, 1987; Zartman and others, 1988; Gromet, 

1989; Getty and Gromet, 1992a,b; Wintsch and others, 1991, 

1992, 1993, 1998, 2007; Gromet and others, 1998; Walsh and 

others, 2007; Attenoukon, 2008).

The timing of Neoproterozoic metamorphism in relation to the earliest episode of deformation (D1 ) is not well 

constrained. Goldsmith (1991c) reported that the metamorphism predated the Neoproterozoic plutonic events, and that 

metamorphism may have been related to subduction. Hepburn 

and Bailey (1998) attributed the early thermal event to contact 

metamorphism. In this map area, migmatization adjacent 

to the Ironstone quartz diorite of Emerson (1917) provides 

solid evidence for Neoproterozoic contact metamorphism, 

and shows that it postdates a relict metamorphic fabric in the 

Blackstone Group rocks. In the Grafton quadrangle to the 

north (Walsh and others, 2011) the early D1 fabric is locally 

observed as aligned tremolite in the Westboro Formation. 

Attenoukon (2008) reported a 40Ar/ 39Ar amphibole cooling 

age of 588 Ma from a gabbro in the Holliston quadrangle in 

the northeastern part of the Milford antiform, providing firm 

evidence for a Neoproterozoic thermal event. 

The dominant metamorphic event produced the 

penetrative gneissic fabric (S2 ) in the rocks of the Milford 

antiform. The timing of D2 deformation in the Milford 

antiform is constrained by the age of syn-D2 mylonites dated 

in the Grafton quadrangle and by syntectonic development 

of L 2 hornblende lineations and lower amphibolite-facies 

mineral assemblages in S2 . Wayne and others (1992) report 

conventional U-Pb metamorphic zircon ages of 285±25 and 

270±92 Ma from mylonitic rocks exposed in the Grafton 

quadrangle on Route 146 in the Ponaganset Gneiss; these 

mylonites developed during D2. 40Ar/ 39Ar amphibole and 
32 Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island

biotite cooling ages in the Milford antiform range from 

268 to 250 Ma, and K-feldspar cooling ages range from 

254 to 227 Ma (Attenoukon and others, 2005; Attenoukon, 

2008). Within the Avalon zone, Attenoukon (2008) documented an Alleghanian metamorphic gradient that increases 

to the west and is truncated by the Bloody Bluff fault. The 

rocks in the Uxbridge quadrangle are within the area affected 

by peak Alleghanian ampibolite-facies metamorphism. Thus, 

peak Alleghanian metamorphism probably occurred during the

late Carboniferous to early Permian, followed by continuous 

cooling associated with uplift. Randomly oriented hornblende 

porphyroblasts in the plane of S2

 (fig. 13), found here and in 

the Grafton quadrangle, indicate that Alleghanian hornblende 

crystal growth continued after D2. D3 fabrics include formation of the Milford antiform and associated shear bands and 

thin mylonite zones developed during the waning stage of 

Alleghanian deformation and metamorphism. The late D4

intrusion of tabular pegmatites and quartz veins marks the 

final extensional stage of deformation during upper greenschist- to lower amphibolite-facies metamorphism.

Economic Geology

The locations of 16 abandoned granite quarries and 

1 abandoned silver mine were confirmed during mapping in 

the Uxbridge quadrangle, and are shown on the map and in 

the GIS database. Dale (1923) provides a detailed description 

of the Blanchard quarries on Quarry Hill in Uxbridge, and 

this area represents the largest granite quarrying operation 

in this quadrangle. The Blanchard quarries opened in 1864 

(Dale, 1923) and were known for producing some of the 

finest granites in Worcester County (Crane, 1907). The rock is 

locally referred to as the “Blanchard granite” (Rowcroft and 

Doherty, 2007). The map and GIS database show one quarry 

symbol on Quarry Hill, but the area in fact contains a number 

of closely spaced water-filled quarries that are shown as small 

ponds on the map (see also fig. 2E ). The abandoned Scadden 

Silver Mine is located on the property of the Blissful Meadows 

Golf Club on Chockalog Road in Uxbridge. Jackson (1840, 

p. 74) reported the presence of galena, sphalerite, and pyrite in 

a quartz-feldspar vein, but greatly overestimated the amount 

of silver in the ore at 7.110 pounds per ton. Nearby outcrops 

consist of Blackstone Group quartzite. The failed mine was 

briefly operational around 1837 according to a sign posted 

at the golf course (fig. 19) and the course’s Web site,3

 which 

cites an article from a former local newspaper, the Uxbridge 

Compendium, dated May 28, 1886. The location of the silver 

mine is inaccurately shown on the U.S. Geological Survey 

(USGS) Mineral Resources Data System,4 about 2.8 km to 

the east-northeast of the actual site, probably because it was 

derived from a 1:500,000-scale map (Pearre, 1956). The site is 

shown as a lead-zinc occurrence by Pearre (1956).

3

http://www.blissfulmeadows.com/

4

http://tin.er.usgs.gov/mrds/

Mine

A

UX-1531_3.JPG

Figure 19. Photographs of the abandoned Scadden Silver Mine. A, Outcrop of quartzite to the left shows a pronounced L2

intersection lineation (parallel to arrow) plunging to the northeast. Mine tailings (center) are located next to the gated mine 

shaft (right). B, Sign posted on the gate.

B

UX-1531_1.JPG
References Cited 33

Acknowledgments

This report was improved by the thoughtful, constructive 

comments of Daniel P. Murray of the University of Rhode 

Island and Arthur J. Merschat of the USGS. 

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Manuscript approved on March 27, 2014

Prepared by the USGS Science Publishing Network

 Publishing Service Centers

 Edited by James R. Estabrook, Reston

Cartography and graphics by Linda M. Masonic, Reston

 Layout by Caryl J. Wipperfurth, Raleigh

 Web support by Angela E. Hall, Reston

For more information concerning this report, contact

Gregory J. Walsh

U.S. Geological Survey

P.O. Box 628

Montpelier, VT 05601 
Walsh—Bedrock Geologic Map of the Uxbridge Quadrangle, Worcester County, Massachusetts, and Providence County, Rhode Island—Scientific Investigations Map 3295

ISSN 2329-132X (online)

http://dx.doi.org/10.3133/sim3295