?

?

?

?

?

?

?

?

?

?

?

A

A'

SOmb

Sap

Sabg

Sam

SOmb

SOmba

DSd

Ong

SOmba

Sag

Pcm(?)

Otb

Ons

Sag

Sab

Sab

Ssbh

Ssb

Ons

Ons

Ong

Sap

Ons

Ssbh

Ong

Ong

Ong

Ssd

Ons

Ons

Jrd

DSp

Ong

DSp

0

75

7070

85

75

5960

80

31

25

10

84

15

82

80

7085

8570

64

70

75

85

68

7075

78

75

85

30

6050

65

7080

8544

82

7050

82

75

80

40

35

71

68

62

4048

72

38

32

45

34

45

7035

62

1540

4733

15

45

25

65

65

32

25

68

55

50

19

25

25

20

4536

38

45

3030

52

25

17

5665

75

75

70

42

64

70

75

70

SOmb

Sam

Sabg

Sap

Sap

SOmb

CLINTON - NEWBURY FAULT ZONE

DRAFT IN REVIEW

Zone of sheared rocks (? denotes uncertainty as to degree of shearing in Sap)

Location approximate

Lithologic Contacts

Bedrock Exposure

Individual Outcrop Areas of abundant outcrops or shallow bedrock

(within 10 ft (3 m) of surface)

Faults

Contact, location generally approximate

32

32

32

32

47

50

Structural Symbols

Strike and dip of dominant foliation / vertical foliation (includes mylonitic foliation). Compositional layering generally parallels foliation in stratified rocks

Planar Features

Linear Features

Strike and dip of axial plane of minor fold

Strike and dip of cleavage

Trend and plunge of mineral lineation

Antiformal axis, location inferred

Synformal axis, location inferred

EXPLANATION OF MAP SYMBOLS

Only faults traceable at map-scale and on surface are shown

Strike and dip of bedding

Strike and dip of overturned bedding

32

Approximate strike and dip of heavily deformedfoliation / vertical deformed foliation

Mine or bedrock quarry

A'500 ft

-500

-1000

-1500

-2000

sea level

CLIN

TON

- NEW

BURY

FAU

LT

ZONE

MER

RIM

AC

K B

ELT

NA

SHO

BA

TER

RA

NE

Sha

wsh

een

Riv

er

Mar

ricm

ac R

iver

Law

renc

eA

ndov

er

Spi

cket

t Riv

er

Spickett River

Met

huen

Law

renc

e

New

Ham

pshi

reM

assa

chus

etts

A200 m

-200

-400

-600

sea level

SOmb

SOmbSOmba

SOmba

Pcm(?)

SamSap

Sab

Ons

EXPLANATION OF LITHOLOGIC UNITS

MERRIMACK BELT

Metasedimentary Rocks

Coal Mine Brook Formation (?)

Dark blue-gray, prominently foliated, highly contorted, very fine-grained, graphite-bearing carbonaceous phyllite. Existence uncertain as exposure has been covered or destroyed.

Merrimack Group (Silurian or Ordovician following Lyons and others, 1997)

Berwick Formation

Light-gray to purplish-gray beds from cms. to 1 meter thick of calcareous metasiltstone, biotite-feldspar-quartz granofels, impure quartzite and metasiltstone interbedded with lesser amounts of thin-bedded dark-gray micaceous phyllite, schist and impure quartzite.

Berwick Fm., Actinolitic granofels

Light-gray to light-greenish-gray, massive, actinolite-bearing calcareous granofels and quartzite; commonly more calcareous than SOmb.

Igneous Rocks

Dracut Diorite

Medium- to coarse-grained, generally massive, black to light-gray, greenish to brown weathering, sulfide-bearing, hornblende-pyroxene-plagioclase diorite and gabbro. More foliated tonalitic varieties exist near the contact with the Berwick Fm. Sulfides are scattered throughout the mapped area and locally concentrated at Nickel Mine Hill. Locally intensely sheared and altered.

Pegmatite

Areas north of the Merrimack River where coarse-grained, white to light-gray muscovite-quartz-alkali-feldspar pegmatite is common.

NASHOBA TERRANE

Metasedimentary and Metavolcanic Rocks

Tadmuck Brook Schist

South of the Clinton-Newbury Fault. Well foliated, rusty weathering, dark-gray to silvery-gray mica schist, phyllite and phyllonite (?). Locally contains amphibolite interlayers.

Nashoba Formation

Nashoba Fm., Biotite gneiss

Gray to dark-gray, medium-grained paragneiss. Biotite-quartz-feldspar gneiss predominates with lesser amounts of interlayered biotite-rich schist, amphibolite, calc-silicate granofels, gray sillimanite-bearing mica schist and quartzo-feldspathic granofels or gneiss. Interlayering takes place on all scales from a few cm. to tens of meters. Included within the mapped Nashoba Fm. are small bodies, lenses and sheets of pegmatite and granite. Migmatitic granite veins and lenses are locally abundant.

Nashoba Fm., Schist

Fine- to medium-grained, well foliated, commonly rusty-brown weathering, gray to silvery-gray quartz-mica schist that may contain biotite, garnet and/or sillimanite.

Igneous Rocks

Diabase

Fine-grained, massive, dark-gray to black diabase composed chiefly of plagioclase and pyroxene and their alteration products.

Andover Granite

Andover Granite, pegmatite facies

Medium to extreamly coarse-grained, massive, white to light-gray pegmatite and monzogranite. Composed mainly of microcline, plagioclase, quartz and muscovite. Biotite occurs locally and garnet is a common accessory. Broad areas underlain entirely by pegmatite.

Andover Granite, binary granite facies

Medium-grained, massive to weakly foliated, white to light-gray monzogranite composed mainly of plagioclase, quartz, muscovite and biotite with accessory garnet. Pegmatites too small to map separately are locally prominent.

Andover Granite, fine-grained granite-gneiss facies

Fine- to medium-grained, generally prominently foliated, light-gray to white monzogranite-gneiss.

Andover Granite, biotite granite-gneiss facies

Chiefly coarse-grained, weakly foliated, light-gray monzogranite-gneiss composed mainly of microcline, plagioclase, quartz, biotite and muscovite with accessory garnet. Cross-cut locally by pegmatite and diabase dikes.

Andover Granite, muscovite granite-gneiss facies

Chiefly coarse-grained, faintly to prominently foliated, white monzogranite-gneiss composed chiefly of microcline, plagioclase, quartz and muscovite. Biotite and garnet are accessory. Cross-cut locally by pegmatite and diabase dikes.

Sharpners Pond Tonalite

Sharpners Pond Tonalite, hornblende diorite facies

Medium- to coarse-grained, massive, medium-gray to black hornblende diorite and tonalite composed mainly of plagioclase and hornblende with variable by small amounts of quartz. Biotite only locally composes as much as 10% of the rock. Principal accessories include magnetite, sphene and apatite.

Sharpners Pond Tonalite, biotite-hornblende tonalite facies

Medium-grained, massive to weakly foliated, medium to dark-gray biotite tonalite composed mainly of plagioclase, hornblende, quartz and biotite.

DSd

DSp

Jrd

Ong

Ons

Otb

Pcm

Sab

Sabg

Sag

Sam

Sap

SOmb

SOmba

Ssbh

Ssd

Folded pegmatite veins in the actinolite facies of the Berwick Formation (Smba)

Strongly foliated Andover muscovite-granite gneiss immediatelysouth of the Clinton-Newbury Fault Zone

Jurassic diabase (Jrd) cross-cutting Andover muscovite-granite gneiss

Fine- to medium-grained binary Andover granite (Sab)

Sill of pegmatitic Andover granite (Sap) intruding biotite-hornblende tonalite facies of Sharpners Pond tonalite.

OFFICE OF THE MASSACHUSETTS STATE GEOLOGISTUNIVERSITY OF MASSACHUSETTS

1:25,000 scale topographic base scanned from U.S. Geological Survey, 1966 (photorevised 1979)Polyconic projection. 1927 North American DatumDigitally reprojected to 1983 North American Datum, 1:24,000 scale10,000 foot grid ticks based on Massachusetts state plane coordinate system, mainland zone

Bedrock geology by R.O. Castle (1951-1952, 1992).Updated and revised by J.C. Hepburn and J.P. Kopera (2004). Digitized by J.P. Kopera (2005).

Prepared in cooperation with the COMMONWEALTH OF MASSACHUSETTS

STATE GEOLOGISTBEDROCK GEOLOGIC MAP

LAWRENCE QUADRANGLE, MASSACHUSETTSv. 1.0

Stratigraphic correlation chart accompanies map

This manuscript is submitted for publication with the understanding that the United States Government is authorized to reproduce and distribute reprints for government use.

This research was supported by U.S. Geological Survey, National Cooperative Geologic Mapping Program, under assistance Award No. 04HQAG0028. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.

Citation:Castle, R.O, Hepburn, J.C., and Kopera, J.P., Bedrock geologic map of the Lawrence quadrangle, Massachusetts, v 1.0, Massachusetts Geologic Survey (4th), (in review, April 2005)

Note: This manuscript is currently undergoing peer review, and is not a final version.

Affiliations:

1United States Geological Survey Menlo Park, CA2Department of Geology and Geophysics Boston College Chestnut Hill, MA, 02467

3Corresponding Author: Office of the Massachusetts State Geologist Department of Geosciences University of Massachusetts, Amherst, MA 01003 jkopera@geo.umass.edu

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15 / 1 2

QUADRANGLE LOCATION

BEDROCK GEOLOGIC MAP OF THE LAWRENCE QUADRANGLE, MASSACHUSETTSBy

Robert O. Castle1, J. Christopher Hepburn2, and Joseph P. Kopera3

2005 (in review)