' ''0, 

Geochemical Features~ aAd 40At};,Af 

Age of ThpleHtJo and Maiic·Aik4II 

Dikes in AroostooK Go~nf¥, 

Northeastern Mcline @ 

Geochemical Features and 40ArP9

Ar 

Age of Tholeiitic and Mafic-Alkalic 

Dikes in Aroostook County, 

Northeastern Maine 

By DAVID GOTTFRIED, RAYMOND MACDONALD, 

JOHN F. SUTTER, and LOUIS PAVLIDES 

Major 1 minor 1 and trace element 

contents of two tholeiitic suites 

in the Mars Hill and Bridgewater 

quadrangles and a teschenitic 

suite in the Presque Isle quadrangle 

U.S. GEOLOGICAL SURVEY BULLETIN 1612 
DEPARTMENT OF THE INTERIOR 

WilliAM P. ClARK, Secretary 

U.S. GEOLOGICAl SURVEY 

Dallas l. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1984 

For sale by Distribution Branch 

Text Products Section 

U.S. Geological Survey 

604 South Pickett Street 

Alexandria, Virginia 22304 

Library of Congress Cataloging in Publication Data 

Main entry under title: 

Geochemical features and 40Arf39

Ar age of tholeiitic and mafic-alkalic dikes in Aroostook County, northeastern Maine. 

(U.S. Geological Survey bulletin ; 1612) 

Authors: David Gottfried and others. 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1612 

1. Basalt-Maine-Aroostook County. 2. Dikes (Geology)-Maine-Aroostook County. 3. Geochemistry-Maine-Aroostook County. 4. Geological time. I. Gottfried, David. II. Series. 

QE75.B9 no. 1612-B 577.3 s [522'.26'097411] 84-600096 [QE462.B3] 
CONTENTS 

Abstract 1 

Geologic setting 1 

Petrographic features 3 

Geochronologic data 3 

Analytical methods 6 

Analytical results 7 

Major elements and identification of magmatic lineages 7 

Trace elements 7 

Large cations 7 

High valence cations 9 

Rare earth elements 14 

Ferromagnesian elements 15 

Magmatic affinity of the dikes 16 

Tectonomagmatic classification 18' 

References cited 22 

FIGURES 

1. Index map showing general location of zones of metabasaltic dikes of the 

Mars Hill, Bridgewater, and Presque Isle quadrangles in northeastern 

Maine 2 

2. Spectrum diagrams for 40 Ar f39 Ar age of dikes in northeastern Maine 6 

3. Major element variation diagram of dikes in northeastern Maine 10 

4. Plots of Ba, Rb, and Sr contents against P20s in dikes in northeastern 

Maine 13 

5. Nb and Ta contents and Nb:Ta and 100 x Nb:Ti ratios in dikes in 

northeastern Maine 13 

6. Zr and Hf contents and Zr:Hf ratios in dikes in northeastern Maine 14 

7. Th and U contents and Th: U ratios in dikes in northeastern Maine 14 

8. Chondrite-normalized REE abundance patterns in dikes in northeastern 

Maine 15 

9. La, Yb, and Y contents in dikes in northeastern Maine 18 

10. Co, Cr, Ni, Sc, and Zn contents and Ni:Co ratios in dikes in northeastern 

Maine 19 

11. Samples of dike rocks from northeastern Maine plotted on variation 

diagrams for characterization of magma type 20 

12. Samples of dike rocks from northeastern Maine plotted on the 

(Ti:100)-Zr-(Y x 3) discrimination diagram of Pearce and Cann (1973) 21 

13. Samples of dike rocks from northeastern Maine plotted on the (Hf/3)-Th-Ta 

tectonomagmatic discrimination diagram of Wood (1980) 22 

TABLES 

1. Major element chemistry and normative composition of dikes in northeastern 

Maine 4 

2. Geochronologic 40 Arf39 Ar data for dikes in northeastern Maine 8 

3. Trace element abundances in parts per million in dikes in northeastern 

Maine 12 

Contents Ill 

Geochemical Features and 

40 Ar/ 39 Ar Age of Tholeiitic 

And Mafic-Alkalic Dikes 1n 

Aroostook County, 

Northeastern Maine 

By David Gottfried, Raymond Macdonald, John F. 

Sutter, and louis Pavlides 

Abstract 

Major, minor, and trace element contents were determined in 16 samples of metabasaltic dike rocks from northeastern Maine. Chemical and petrographic studies of the 

rocks indicate widespread mobility of various major and 

minor elements and extensive development of secondary 

mineral assemblages. The contents demonstrate that these 

rocks represent at least three magma suites of diverse compositions, as follows. Stable minor and trace elements (such 

as Ti, P, Nb, Ta, Zr, Hf, Th, and Y and rare earth element 

abundances), together with variation trends, indicate that 

metabasaltic dikes in the Mars Hill and Bridgewater 

quadrangles are products of two similar, but not identical, 

continental-type tholeiitic magmas. The metabasaltic dikes 

in the Presque Isle quadrangle are primarily teschenitic 

mafic-alkalic rocks. 

Two samples appear to be geochemically unique. One 

sample, from the Mars Hill dikes, is a depleted-type tholeiite. 

Another sample, from the Presque Isle quadrangle, is a 

biotite albite basalt with alkalic affinities. 

On the basis of the trace element associations of the 

Mars Hill, Bridgewater, and Presque Isle dikes, we conclude 

that the parental magmas were generated within heterogeneous mantle magma sources. Variations in the melting 

process, within a tensional tectonic setting, during a relatively limited timespan produced these rock types. 

We performed 40Ar/39Ar age spectrum analyses on six 

whole rock samples from each of the three geochemically 

identified magma suites. All age spectra are variably discordant, and only three of the six samples record plateau spectra. 

However, the age data are compatible with intrusion of all 

thr.ee magma types in Late Silurian to Middle Devonian times, 

with a subsequent low-grade metamorphic disturbance of 

the chemical and isotopic systems in the Pennsylvanian. 

GEOLOGIC SETTING 

Weakly altered tholeiitic basaltic and alkalic mafic 

dikes and plugs and greenstone dikes intrude folded 

calcareous sedimentary rocks of Ordovician (Caradocian) to Silurian (Wenlockian) age in northeastern 

Maine (Pavlides, 1965 and 1978). Basaltic and greenstone dikes occur in a more or less north-trending belt 

along the east side of the Bridgewater and Mars Hill 

quadrangles. Altered alkalic mafic dikes occur to the 

west of the tholeiitic dikes and are concentrated in one 

small area within the Presque Isle quadrangle (fig. 1; 

also see Pavlides, 1978). 

Dikes in the region generally are not more than 

several meters wide and a few tens of meters to a hundred or so meters long. In many places, a thin contact 

metamorphosed zone has been formed in the impure 

limestones enclosing the dike. The dikes of northern 

Maine intrude a sequence of folded marine metasedimentary rocks such as the Perham and Spragueville Formations (Pavlides, 1978) that contain shelly faunas 

(Boucot and others, 1964) of relatively shallow water 

habitat. Therefore, the dikes were intruded into a continental rather than oceanic plate. All of the country 

rocks, up through Oriskany age of the Lower Devonian 

(Boucot and others, 1964, and Boucot, 1968, table 6-2), 

in the immediate area of the tholeiitic and teschenitic 

rocks were folded and cleaved, presumably during a 

phase of the Acadian orogeny (Pavlides, 1974, p. 70, 

and 1978). The upper age limit for the Acadian orogeny 

in northeastern Maine is fixed by the age of the youngest 

folded rocks below the unconformity that separates 

them from the overlying Mapleton Sandstone of 

Eifelian or Middle Devonian age. The folded Dockendorf Group of rocks of Lower Gedinnian or Early 

Devonian age constitute such pre-Mapleton rocks. 

Because cleavage is absent in the broadly synformal 

Mapleton Sandstone, we consider the cleavage in the 

subjacent folded rocks to have developed in postDockendorf and pre-Mapleton or Lower Gedinnian to 

Eifelian (Middle Devonian) times. The massive dikes 

and plugs cut rocks containing Acadian cleavage and 

are not themselves transected by this cleavage. We, 

therefore, consider them to be of postkinematic age. 

All dikes are weakly metamorphosed. Until this 

report, this metamorphism was assumed to have taken 

place during the waning or cooling stages of the Acadian event (Pavlides, 1978). Geochronologic data 

presented in this report, however, indicate a Pennsylvanian age for this weak metamorphism. We did not 

observe the dikes and plugs to intrude the Mapleton 

Sandstone of Middle Devonian age, although they do 

cut Acadian structures. The Mapleton Sandstone, which 

rests with angular unconformity on the pre-Acadian 

folded rocks that are host to the plugs and dikes 

(Pavlides, 1978), is not obviously metamorphosed. 

However, the sandstone, which occurs in a broad dishshaped syncline, was deformed in post-Acadian time by 

the Maritime disturbance of Pennsylvanian age 

Geologic setting 
EXPLANATION 

1. Bridgewater quadrangle 

2. Mars Hill quadrangle 

3. Presque Isle quadrangle 

A. Zone of basaltic 

dikes and plugs 

B. Zone of teschenitic 

dikes and plugs 

0 50 100 MILES 

0 50 100 KILOMETERS 

Figure 1. General location of zones of metabasaltic dikes ofthe Mars Hill and Bridgewater quadrangles (A, 

continental tholeiitic magmas) and of the Presque Isle quadrangle (B, teschenitic suite) in northeastern Maine. 

2 Geochemical features and 40ArP'Ar age of dikes in Aroostook County, Maine 
(Pavlides, 1974, p. 71), which may be related to the time 

of metamorphism of these dikes. 

The northeastern Maine dikes obviously represent 

a tensional phase of deformation following the compressional regime of the Acadian event. The chemical 

features of the basaltic magmatism that characterize this 

episode of tensional tectonics may be of interest for 

comparisons of similar events elsewhere in the Appalachian-Caledonide orogen. 

PETROGRAPHIC FEATURES 

Mars Hill quadrangle.-The weakly metamorphosed basaltic rocks of the small dikes and plugs of the 

Mars Hill quadrangle are generally massive, finegrained to aphanitic, green to dark-green rocks and may 

contain a gray-white weathered rind up to 0.6 em thick. 

In thin section, textures range from hypidiomorphicgranular to ophitic. Original plagioclase ranges in composition from andesine to labradorite; later saussuritization probably produced the less calcic varieties. The less 

calcic plagioclase commonly has fine-grained scapolite(?) 

alteration. Augitic pyroxene in some places is altered to 

chlorite or actinolite. Ilmenite, an abundant accessory, 

commonly occurs as skeletal crystals; epidote normally 

occurs in veinlets. Fine-grained granules of sphene are 

mostly enclosed in chlorite and may be abundant locally. 

Quartz is a sparse constituent in some rocks. Carbonate 

and rare flakes of brown biotite(?) or stilpnomelane(?) 

are present in a few rocks. 

Bridgewater quadrangle.-The dikes of the 

Bridgewater quadrangle are more altered than those of 

the Mars Hill area and have been referred to as greenstone (Pavlides, 1965, p. 37-38). They are fine-grained 

rocks with allotriomorphic-granular texture in thin section. Chlorite is an abundant alteration product and 

replaces pyroxene and some plagioclase. Large crystals 

of ilmenite and magnetite are common, and locally 

some ilmenite is partly to completely altered to sphene 

or leucoxene. Quartz is a minor constituent, and carbonate occurs in thin veinlets. Well-formed elongate 

crystals of apatite also are present. 

Presque Isle quadrangle.-The meta basaltic dikes 

in the Presque Isle quadrangle consist of analcimebearing basalts and a biotite albite basalt with alkalic affinities (sample 16). The analcime-bearing basaltic rocks 

were originally described as teschenites by Gregory 

(Williams and Gregory, 1900, p. 179-185). They are 

aphanitic to medium-grained mesocratic massive rocks. 

According to Gregory, the principal minerals in these 

teschenites are augite (titanaugite?), andesine, apatite, 

biotite, analcime, and magnetite and lesser amounts of 

alteration products such as chlorite and calcite. We also 

noted thompsonite and nepheline(?) during this study. 

Gregory stated that the analcime in the teschenites 

formed through replacement of nepheline, but he gave 

no petrographic evidence for this reaction. He also 

described andesine as having been altered to analcime 

and chlorite and described analcime as an intergranular 

constituent. Alternatively, the analcime may be a prograde metamorphic product because prehnite-pumpellyite-grade metamorphism is known from rocks to the 

south (Pavlides, 1962, fig. 9, 1965, p. 35, and 1973) and 

to the west and northwest (Richter and Roy, 1976). 

Anita G. Harris (written commun., 1976) reports that 

color alteration index (Epstein, Epstein, and Harris, 

1977) of two widely separated (30 km) conodont collections in the Mars Hill area (Pavlides, 1978) indicates 

temperatures of+ 300°C and 150°-200°C, respectively. 

Such temperatures are compatible with zeolite and low 

greenschist facies metamorphism that may have affected the teschenites of the Presque Isle quadrangle and 

the tholeiitic basalts in the Mars Hill area and may have 

formed the greenstone in the dikes of the Bridgewater 

region. 

A petrographic variant within the Presque Isle 

teschenitic dike area is a biotite albite porphyritic basalt 

represented by sample 16 (table 1). Phenocrysts are 

sodic plagioclase that has been heavily altered to white 

mica and pseudomorphs of chlorite after clinopyroxene. 

The groundmass consists of albite laths, fresh augitic(?) 

pyroxene, chlorite, abundant Fe-Ti oxides, and reddish 

brown biotite that occasionally encloses oxides and 

apatite. Whether the alteration is late deuteric or 

retrograde metamorphic is unclear. No analcime has 

been noted in this rock. 

GEOCHRONOLOGIC DATA 

The isotopic composition of Ar was measured 

with a VG Isotopes, Inc., Model MM-1200B, 1 mass 

spectrometer in the Branch of Isotope Geology, K-Ar 

Laboratory, at the U.S. Geological Survey in Reston, 

Va. Whole rock splits from the basaltic dikes were irradiated in the USGS Central Thimble facility TRIGA 

reactor (GSTR) at the Federal Center in Denver, Colo. 

(Dalrymple and others, 1981). The neutron flux monitor 

used in this study was MMhb-1 hornblende, 519.4 Ma 

(Mega-annum) in age (Alexander and others, 1978), and 

an estimated 1-percent error in the calculated J values 

has been assigned. Corrections for irradiation-produced, interfering isotopes of Ar were made by using 

the values suggested for the Central Thimble facility of 

the GSTR (Dalrymple and others, 1981). Values corrected for 37 Ar were determined by using a decay con-

• Any use of trade names and trademarks in this publication is for 

descriptive purposes only and does not constitute endorsement by the 

U.S. Geological Survey. 

Petrographic features 3 
.a:o. Table 1. Major element chemistry and normative composition of dikes in northeastern Maine 

~ 

,., 

~ 

::r 

I'D 

3 

;:;· 

!. 

;-

~ c 

; 

{II 

Ill 

:I 

a. 

~ ~ Ill 

~ 

s. 

a. 

;: 

~ 

:r 

> 

a 

Q 

{II 

g 

~ 

n 

Q 

c 

:I 

~ 

~ Ill 

;· 

I'D 

Suites 

Sample no. 

Field no. 

SiO, ------------· 

AI,O, ----------- Fe,O, .•••••.•••• 

FeO -------------

MgO ------------- CaO •••••...••••. 

Na,o ------------

K,O -------------

H,O - ----------

H,O + ----------

TiO, -------------

p ,o, ------------ MnO ------------

co, ------------- Total ___ 

SiO, -------------

AI,O, -----------

Fe,O, -----------

FeO ..••••.•.••.. 

MgO ------------

CaO -------------

Na,O ------------

K,O -------------

TiO, -------------

P,O, ------------

MnO ------------

Total .•• 

Q ---------------- c ----------------- Or ---------------

Ab ---------------

An ---------------

Ne ---------------

w 0 --------------

En ---------------

Fs ----------------

Fo ---------------

Fa ---------------

Mt ---------------

II -----------------

Ap --------------- Total •.. 

1 

PA-74-8 

49.7 

14.8 

3.2 

8.9 

5.4 

7.0 

3.4 

1.9 

.51 

2.7 

2.7 

.39 

.19 

.53 

101.32 

51.41 

15.30 

1.24 

10.35 

5.58 

7.24 

3.52 

1.96 

2.80 

.40 

.20 

100.00 

-

-

11.6 

29.8 

20.2 

-

5.5 

8.8 

8.7 

3.6 

3.9 

1.8 

5.3 

.9 

100.1 

Bridgewater 

2 

PA-74-7 

50.9 

13.6 

1.5 

10.4 

4.2 

4.5 

4.1 

.75 

.31 

2.8 

3.0 

.48 

.19 

3.9 

100.63 

54.38 

14.53 

1.60 

11.10 

4.49 

4.80 

4.38 

.80 

3.21 

.51 

.20 

100.00 

4.5 

-

4.7 

37.1 

17.6 

-

1.2 

11.2 

14.1 

-

-

2.3 

6.1 

1.2 

100.0 

3 4 5 

PA-74-9 P-64-8 P-64-27 

53.2 47.1 47.7 

14.4 16.6 17.4 

2.8 1.6 1.7 

10.3 9.5 8.3 

4.9 7.8 6.4 

2.4 7.5 9.5 

4.6 2.5 2.8 

.57 1.7 .58 

.60 .21 .25 

.16 3.2 2.4 

3.3 1.9 1.8 

.59 .24 .24 

.19 .19 .22 

.48 .05 .55 

98.49 100.09 99.84 

55.46 48.7 49.4 

15.00 17.2 18.0 

.83 1.7 1.8 

11.47 9.8 8.6 

5.10 8.1 6.6 

2.50 7.8 9.8 

4.79 2.6 2.9 

.59 1.8 .60 

3.44 2.0 1.9 

.61 .25 .25 

.20 .20 .23 

99.99 100.15 100.08 

7.2 - - 3.4 - -

3.5 10.6 3.5 

40.5 22.0 24.5 

8.4 29.9 34.3 

- - - - 3.0 5.3 

12.7 6.8 11.1 

15.1 4.6 7.8 

- 9.4 3.7 

- 7.0 2.9 

1.2 2.5 2.6 

6.5 3.8 3.6 

1.4 .6 .6 

99.9 100.2 99.9 

Mars Hill 

6 7 8 9 10 

P-64-6 P-64-5 P-64-77 P-63-3 P-64-9 -- -

Major oxide composition' (weight percent) 

47.9 48.9 48.9 49.9 50.6 

15.8 18.0 19.0 16.7 14.9 

3.1 2.0 1.4 1.8 2.9 

8.3 8.8 5.3 8.8 10.2 

7.6 5.3 8.7 6.8 4.4 

6.0 7.8 6.'1 5.5 4.8 

2.7 3.3 3.1 2.8 3.5 

1.1 .95 1.5 .97 .86 

.70 .29 3.6 .52 .49 

4.1 2.3 .44 3.5 3.4 

2.1 1.9 .81 2.1 2.6 

.27 .24 .09 .30 .49 

.23 .20 .13 .19 .23 

- - .06 .II .49 

99.95 100.03 99.93 99.99 99.86 

Adjusted oxides (H,O and C02 free and Fe adjusted2) 

50.4 50.2 51.0 52.1 53.0 

16.6 18.5 19.8 17.4 15.6 

3.3 2.1 1.5 1.9 3.0 

8.7 9.0 5.5 9.2 10.7 

8.0 5.4 9.1 7.1 4.6 

6.3 8.0 7.2 5.7 5.0 

2.8 3.4 3.2 2.9 3.7 

1.2 .98 1.6 1.0 .90 

2.2 2.0 .85 2.2 2.7 

.28 .25 .09 .31 .51 

.24 .21 .14 .20 .24 

100.02 100.04 99.98 100.01 99.95 

Normative mineral composition' (weight percent) 

0.4 - - 4.0 5.9 

- - - 1.9 .7 

7.1 5.8 9.4 5.9 5.3 

23.7 28.8 27.1 24.5 31.3 

29.2 32.3 34.9 26.2 21.5 

- - - - - .1 2.4 .I - - 19.9 9.5 6.9 17.7 11.5 

10.1 8.4 2.3 12.1 13.2 

- 2.8 11.1 - - - 2.7 4.2 - - 4.8 3.0 2.2 2.8 4.4 

4.2 3.8 1.6 4.2 5.1 

.7 .6 .2 .7 1.2 

100.2 100.1 100.0 100.0 100.1 

Presque Isle 

II 12 13 14 15 16 

P-64-26 P-64-7 PA-74-1 PA-74-2 PA-74-3 PA-74-4 - -- -

50.6 51.6 48.6 48.6 48.7 49.5 

16.7 15.0 15.4 15.6 15.7 16.1 

2.3 1.6 4.9 5.0 4.1 3.1 

8.8 10.2 7.1 8.3 8.0 6.6 

6.0 5.0 4.1 3.3 3.1 7.1 

3.0 5.9 7.0 6.2 6.8 5.2 

4.3 4.2 3.3 5.6 5.0 4.0 

.98 .75 1.4 2.0 2.4 1.9 

.51 .17 .93 .62 .81 1.2 

4.0 1.8 2.8 2.9 3.5 2.2 

2.2 2.2 2.2 2.1 2.0 2.1 

.32 .39 .74 .60 .58 .53 

.20 .25 .23 .52 .32 .18 

.12 .52 .01 .01 .44 .01 

100.03 99.58 98.71 101.35 101.45 99.72 

53.0 53.2 50.87 49.34 50.43 51.94 

17.5 15.5 16.II 15.83 16.25 16.89 

2.4 1.7 3.03 3.04 2.17 1.15 

9.2 10.5 10.15 11.16 10.25 7.97 

6.3 5.2 4.29 3.35 3.20 7.45 

3.1 6.1 7.32 6.29 7.04 5.46 

4.5 4.3 3.45 5.68 5.17 4.20 

1.0 .77 1.46 2.03 2.48 1.99 

2.3 2.3 2.30 2.13 2.07 2.20 

.34 .40 .77 .61 .60 .56 

.21 .26 .24 .53 .33 .19 

99.85 100.23 99.99 99.99 99.99 100.00 

2.7 0.4 1.0 

4.2 

5.9 4.5 8.6 12.0 14.6 Il.8 

38.1 36.3 29.2 31.6 30.0 35.5 

13.2 20.7 24.2 11.7 13.8 21.4 

- - - 8.9 7.4 

- 2.9 3.0 6.5 7.2 .9 

15.7 12.9 10.7 2.3 2.6 5.4 

11.5 14.5 12.8 4.3 4.7 3.0 

- - - 4.2 3.7 9.2 

- - - 8.6 7.4 5.7 

3.5 2.4 4.4 4.4 3.1 1.7 

4.4 4.4 4.4 4.0 3.9 4.2 

.8 .9 1.8 1.4 1.4 1.3 

100.0 99.9 100.1 99.9 99.8 100.1 

1

Major elements determined by rapid rock analysis. PA-74-7, PA-74-8, PA-74-9, 2

Fe adjusted as follows: If (Na2b + K20) <4 percent set Fe20, = 1.5 percent. If 

PA-74-1, PA-74-2, PA-74-3, PA-74-4, K. Coates and H. Smith, analysts. P-64-8, (Na20 + K20) >4 percent set Fe20, = 2.0 percent. 

Fe20, -1.5 percent = X or Fe20, - 2.0 percent = X. 

P-64-27, P-64-6, P-64-5, P-64-77, P-64-3, P-64-9, P-64-26, P-64-7, P. Elmore, G. 1.11134 1.11134 

FeO +X= adjusted oxide value. 

Chloe, J. Kelsey, S. Botts, H. Smith, L. Artis, and J. Glenn, analysts. 'Based on adjusted oxides. 
stant of 8.25 x 104 disintegrations per hour for 37Ar. 

Apparent K:Ca ratios were calculated by using the equation given by Fleck and others (1977). Constants used in 

the age calculations were those recommended by Steiger 

and Jager (1977). Concentrations of 39 Ar were calculated by using the measured sensitivity of the mass 

spectrometer and thus have an estimated precision of 

only about 10 percent. Age plateaus have been assigned 

by using the criteria of Fleck and others (1977). The error estimates on the weight-averaged plateau ages are 

simply two times (2 a) the average error assigned to the 

individual ages at the different temperature intervals on 

the plateau, rounded to the next highest million years. 

Error estimates for the apparent ages of individual temperature steps are 1 a (67-percent confidence level) and 

have been assigned by using the equations suggested by 

Dalrymple and others (1981). 

Previous geochronologic studies in this area are 

limited to two conventional K-Ar ages on biotite from a 

small pluton and a dike near Bridgewater and Monticello, Maine (Faul and others, 1963). Their samples 

Me26, from a rhyodacite dike, and Me27, from a small 

garnet porphyry pluton (Pavlides, 1965), yield dates of 

392 ± 8 Ma and 401 ± 8 Ma, respectively, when the decay 

constants currently in use (Steiger and Jager, 1977) are 

applied to their data. Faul and others interpreted these 

dates as times of intrusion and included these in the 

earlier of two Devonian intrusive cycles they identified 

in Maine. 

In the present study, six whole rock samples were 

analyzed by the 40 Ar f3 9 Ar age spectrum method of K-Ar 

dating. The goals of the dating were twofold: (1) to 

estimate the age of original emplacement and crystallization of the dikes and plugs belonging to the three 

general magma types and (2) to estimate the time at 

which the low-grade metamorphic overprint was superimposed on these intrusions. The geochronologic data 

will be discussed according to the three areas of occurrence, which also correspond to the three main magma 

types. These rocks are not especially good candidates 

for absolute age dating because of their altered nature, 

but dating was attempted to see whether the 40 Ar f39 Ar 

age spectrum technique could simultaneously address 

the questions of original crystallization and subsequent 

low-grade metamorphic overprinting. 

Mars Hill quadrangle.-Two basaltic dike 

samples (samples 5 and 6, table 1) were chosen for 

dating. The analytical data are listed in table 2, and the 

age spectra are displayed in figure 2. The age spectrum 

from sample 6 forms an age plateau at 375 ± 8 Ma, and 

this age is interpreted as the time of intrusion. The age 

spectrum of sample 5 does not form an age plateau and 

contains no useful geochronologic information as to age 

of intrusion of this rock. As shown in subsequent age 

spectra of other samples, however, the total-gas age 

(roughly equivalent to a K-Ar age) of about 305 Ma suggests a significant disturbance to the K-Ar isotopic system 

in sample 5. 

Bridgewater quadrangle. -Samples 2 and 3 (table 

1) were chosen for analysis. These analytical data are 

given in table 2 and displayed graphically in figure 2. 

The data from sample 2 define an age plateau of 414 ± 8 

Ma and are interpreted as a close approximation to the 

time of intrusion. An age of 414 ± 8 Ma must be construed with present absolute time scale information to 

represent upper Silurian to lowermost Devonian time. 

On the basis of the Lower Gedinnian to Eifelian age of 

cleavage development outlined on page 1, the plateau 

age of this dike is more likely to be Early Devonian than 

Silurian. However, we believe that this single 40Ar/ 39Ar 

plateau age should not be used to construe anything 

about the absolute time scale because this type of rock is 

not the best material for geochronologic studies employing the 40 Ar f3 9 Ar method. The data for sample 3 do not 

define an age plateau, again indicating a rather severe 

disturbance of the K-Ar isotopic system. The total-gas 

age of this sample (about 299 Ma) is similar to that of 

sample 5 in the Mars Hill area and perhaps reflects the 

same low-grade metamorphic event. 

Presque Isle quadrangle.-Two samples from the 

teschenitic to alkalic basalt suite (samples 15 and 16, 

tables 1 and 2) have been analyzed by the 40 Ar f3 9 Ar 

technique. These samples are among the most highly 

altered Oow-grade metamorphism) of the rocks in the area 

and, on the basis of conodont alteration indexes of nearby country rock samples, have been exposed to postintrusion metamorphic temperatures in the range of about 

150-300°C (Pavlides, 1978). The data from sample 16 

(table 2 and fig. 2) do not define an age plateau, but the 

total-gas age of about 298 Ma is very similar to that of 

other disturbed samples from the area. The data from 

sample 15 (table 2 and fig. 2) define an age plateau of 

293 ± 6 Ma even though the spectrum is quite discordant. This age plateau is not interpreted to represent the 

time of initial intrusion but rather a close approximation to the time of low-grade metamorphism because of 

the high degree of alteration of the sample (sodic plagioclase heavily altered to white mica) and because of the 

temperature to which these rocks could have been exposed. In addition, the total-gas 40 Ar f3 9 Ar ages of the 

four highly disturbed samples (3, 5, 15, and 16) range 

from 298 Ma to 305 Ma, close to the plateau-age of sample 15. 

All the 40Arf39 Ar age spectrum data are compatible with the interpretation that all dike rock types in the 

area originally intruded mid-Ordovician to mid-Silurian 

rocks during late Silurian to mid-Devonian times. The 

superimposed low-grade metamorphic event variably 

disturbed the K-Ar isotopic system in these rocks; this 

disturbance was most likely of Pennsylvanian age. This 

Geochronologic data 5 
400 

350 

300 

450 

<{ 

~ 400 

z 

ui 350 

(!) 

<{ 300 ~ 

z 

w 

a: 250 

<{ 

0.. 

0.. 200 <{ 

150 

Sample 6 (P-64-6) 

tp =375 ±8 Ma 

tr9 -;;376 Ma 

Sample 2 (PA-74-7) 

tp=414±8 Ma 

trg ~390M a 

Sample 15 (PA-74-3) 

tp =293±6 Ma tr ~300 Ma 

Sample 5 (P-64-27) 

tr9 ""305 Ma 

No age plateau 

Sample 3 (PA-74-9) 

trg~299 Ma 

No age plateau 

Sample 16 (PA-74-4) 

tr9 ?: 298 Ma 

No age plateau 

100~~~~~~--~--~--~--~---J--~--_J 

0 50 100 0 50 

ACCUMULATIVE PERCENT OF 39ArK RELEASED 

Figure 2. Spectrum diagrams for 40Arjl'Ar age of dikes in northeastern Maine ( tp, weight-average plateau age; trg, total-gas age). 

may have been the time of folding of the Mapleton 

.Sandstone, a unit of post-Acadian age (Pavlides, 1974, 

p. 71). Other areas of Pennsylvanian disturbance in 

Maine recently have been investigated by the 40Ar/ 39 Ar 

age spectrum method (Dallmeyer, 1982, and Lux, 1982); 

an area of productive future research will be to delineate 

the region affected by this late Paleozoic metamorphic 

event. 

ANALYTICAL METHODS 

Sixteen dikes (samples 1-16) were selected for 

chemical analysis of major (table 1) and trace elements 

(table 3) to cover the petrographic range in our collections. Major elements were determined by using rapidrock methods as outlined in Shapiro (1975). Abundances 

of Ba, Co, Cr, Hf, Rb, REE (rare earth elements), Sc, 

Ta, Th, U, and Zn were determined by instrumental 

neutron activation analysis (L. J. Schwarz, analyst), 

supplemented by epithermal activation analysis for Hf, 

Rb, Ta, and Th in certain samples (P. A. Baedecker, 

analyst). Occurrence of Nb was determined spectrophotometrically (Greenland anQ Campbell, 1974) (J. Kane, 

analyst). C. S. Annell analyzed for Ni and Y by using d-e 

arc emission spectroscopy, and R. G. Johnson determined Sr and Zr abundances by XRF spectrometry. 

6 Geochemical features and 40ArJl 9Ar age of dikes in Aroostook County, Maine 

100 
The estimated precisions (in percent) of trace element determinations (1 a) are as follows: Ba, 5; Co, 2; 

Cr, 5; Hf, 4; Nb, 10; Ni, 15; Rb, 5; Sc, 2; Sr, 5; Ta, 10; 

Th, 10; U, 11; Y, 5; Zn, 5; Zr, 5; La, 7; Ce, 4; Nd, 8; 

Sm, 8; Eu, 4; Gd, 17; Tb, 8; Tm, 18; Yb, 6; and Lu, 6. 

ANALYTICAL RESULTS 

Major Elements and Identification of Magmatic 

Lineages 

The Maine dikes have been metamorphosed up to 

the greenschist facies. Furthermore, the dikes may have 

undergone varying degrees of postcrystallization hydrothermal alteration. Under such circumstances, mobility 

of critical major elements makes identification of 

original magmatic compositions uncertain. Mobility of 

Ca, Mg, Na, K, C02, and H20, as well as changes in the 

original Fe oxidation ratios, is very possible. 

Mobility of the alkali and alkali earth elements is 

demonstrated by plotting these elements against an element stable during low-grade metamorphism. Previous 

investigators (Pearce and Cann, 1973; Floyd and Winchester, 1975; Winchester and Floyd, 1976; Gottfried 

and others, 1977) have shown that P20s and Ti02 

usually remain stable during low-grade metamorphism. 

P 20s is also a particularly useful index of fractionation 

throughout the early and middle stages of fractionation 

of mafic magmas (Anderson and Greenland, 1969). 

However, alkalic suites normally have higher P20s contents than do tholeiitic suites at equivalent stages of differentiation. When rocks of both suites are plotted on 

one P20s variation diagram, P20s contents cannot be 

used to interrelate the differentiation stages of the 

suites. 

Data presented in table 1 confirm petrographic 

evidence of secondary alteration and introduction of 

carbonate into several dikes. On figure 3, the major oxides have been plotted against P 20s. The scatter shown 

by K20, Na20, and CaO clearly reflects variable addition to and removal of these components from the 

dikes. This variation complicates recognition of the 

magmatic affinities of the dikes, but affinity assessment 

can be made by using stable minor and trace element 

data. 

MgO is commonly used in differentiated mafic 

suites as a measure of fractionation (Wright, 1974). 

Although the scatter for MgO for these dikes is much 

less than the scatter for the alkalis, this oxide, or any 

parameter involving it (for example, the Mafic Index), 

still would not make a reliable measure of fractionation 

for the dikes. 

The total Fe content (Fe203 + FeO) is represented 

on figure 3 as FeO. FeO is known to be relatively stable 

during weathering and low-grade metamorphism (Gottfried and others, 1977). 

Si02 shows no scatter and falls within the basalt 

range (<53 percent). Therefore, Si02 appears to have 

been rather stable during metamorphism, and the variations in both FeO and Si02 may be taken to closely approximate magmatic variations. The Si02 contents, in 

particular, indicate that neither the tholeiitic nor the 

teschenitic dikes represent single magmatic lineages. 

Rather, three co magmatic lineages (corresponding to 

the three areas of occurrence) are readily discernible; 

two specimens (samples 8 and 16) represent separate 

geochemical entities and may be inferred to have been 

parts of different magmatic stems. The postulated 

lineages are shown on figure 3. 

The Ti02 data confirm these lineages. Specimen 8 

is assumed to be part of·a low Ti suite. The necessary increase in Ti relative to P required to associate specimen 

8 with the remaining Mars Hill and Bridgewater basaltic 

rocks would imply that P was behaving more compatibly than Ti. Such a behavior is contrary to previous 

results of studies of basaltic sequences (Anderson and 

Greenland, 1969). 

The Ti02-P20s graph (fig. 3) also reveals that the 

Bridgewater and Mars Hill metabasaltic rocks probably 

represent separate, but subparallel, lineages, the 

Bridgewater dikes being slightly more Ti rich. Presque 

Isle sample 16 (table 1) is also slightly more Ti rich than 

the associated teschenites but is notably Fe depleted 

compared to them. The Fe and Ti data agree with the 

Si02 contents and suggest that sample 16 represents a 

rather different chemical type from the teschenites. 

The major element data, therefore, indicate that 

the basaltic dikes in the eastern part of the area (fig. 1) 

can be divided into three types: (1) the Bridgewater 

group, (2) the Mars Hill group (excepting specimen 8, 

table 1), and (3) sample 8, which is geochemically 

unique. The dikes in the Presque Isle quadrangle are apparently represented by two chemically and petrographically distinct types: (1) the teschenites consisting of 

samples 13, 14, and 15 (table 1) and (2) another rock 

type of which sample 16 (table 1) is the only analyzed 

member. 

Trace Elements 

The trace element analyses for northeast Maine 

dike rocks are listed in table 3. Plots of these elements, 

either singly or in ratios, against P 20s are given in 

figures 4-7. 

Large Cations 

Ba, Rb, and Sr.-These elements are particularly 

prone to remobilization during low-temperature 

Analytical results 7 
Table 2. Geochronologic 40Ar/ 39Ar data for dikes in northeastern Maine 

J9ArK 4oAr J9ArK Apparent Apparent Temp. 40Ar/ 39Ar 37 Ar/ 39Ar 36Arj39Ar (percent of (percent of (moles K/Ca age (o() (X 10-2) total) total) X 10·12) (mole/mole) (Ma) 

Sample 61 

450 ------------ 29.73 1.123 1.758 13.9 82.8 4.23 0.44 361 ±4 

550 ------------ 34.38 .494 2.211 3.6 81.1 1.08 .99 404±4 

7 50 ------------ 31.03 1.421 2.045 4.1 80.9 1.23 .34 367±4 

850 ------------ 29.34 1.563 .998 23.4 90.3 7.11 .31 386±4 

1 ()()() ------------ 27.68 2.219 .764 36.9 92.4 11.2 .22 374±4 

FUSE ---------- 30.31 6.948 1.807 18.1 84.3 5.48 .07 377±4 

Total gas age = 376 

Weight-average plateau age = 375 ± 8 

Sample 52 

450 ------------ 30.82 2.241 3.526 15.2 66.7 2.21 0.22 307±4 

7 50 ------------ 27.26 6.019 2.194 12.6 77.9 1.82 .08 316±4 

850 ------------ 23.07 3.970 1.184 43.5 86.2 6.31 .12 297±3 

1 ()()() ------------ 29.47 8.624 3.258 8.3 69.6 1.20 .06 306±4 

FUSE ----------- 27.00 19.24 2.449 20.4 78.7 2.92 .03 316±4 

Total gas age = 305 

No plateau age defined 

Sample 23 

450 ------------ 25.63 0.167 1.188 23.5 86.3 6.19 2.94 328±4 

600 ------------ 30.45 .343 .521 16.9 95.0 4.45 1.43 418±4 

850 ------------ 31.28 .112 .970 22.9 90.8 6.02 4.33 411 ±4 

I 000 ------------ 31.33 .180 .922 24.0 91.3 6.31 2.72 414±4 

FUSE ---------- 35.70 .494 3.256 12.6 73.1 3.32 .99 381 ±4 

Total gas age = 390 

Weight-average plateau age = 414 ± 8 

Sample 34 

350 ------------ 31.71 0.361 6.601 

500 ------------ 20.84 .289 1.144 

650 ------------ 31.05 .332 3.458 

7 50 ------------ 27.60 .464 1.572 

950 ------------ 31.18 1.476 2.354 

FUSE ---------- 43.89 5.400 6.843 

geological processes and are unlikely to be present in the 

dikes in their magmatic concentrations. Plots of Ba, Rb, 

and Sr contents against P20s (fig. 4) show considerable 

scatter and, in the case of Rb and Sr, no systematic increase or decrease with changing P20s values. Ba shows 

a gross trend of increasing concentrations in more differentiated compositions. 

Ascertaining the processes that modified the concentrations of Ba, Rb, and Sr is not possible. Thus, Rb 

may qave been leached from, or added to, the dikes during postemplacement hydration and subsequently during metamorphism. In specimen 8, for example, the 

high Rb (and relatively high K) content is not in accord 

with the low contents of Nb, Ti, total REE, and Zr and 

the high content of MgO in this rock. Both Rb and K 

clearly have been added to the dike by postemplacement 

processes. 

5.9 38.6 0.64 1.36 188 ±4 

43.2 83.9 4.75 1.69 264±4 

12.7 67.2 1.39 1.47 310±4 

14.2 83.3 1.56 1.05 339±4 

9.4 78.0 1.04 .33 357±4 

14.5 54.9 1.59 .09 354±4 

Total gas age = 299 

No plateau age defined 

K:Rb ratio.-Despite the mobile nature of K and 

Rb, the K:Rb ratio in the Mars Hill samples (table 3) 

shows a relatively limited variation of 302 ± 84, a range 

encompassing that of fresh continental tholeiites 

(Wedepohl, 1975). This range implies grossly similar 

geochemical behavior of K and Rb during magmatic 

and postmagmatic processes in the Mars Hill dikes. 

The K: Rb ratio is lower in two Bridgewater 

samples. The lower ratio can be ascribed to the 

preferential addition of Rb during alteration. In contrast, the range of K:Rb ratios (226-667) in the Presque 

Isle dikes indicates some separation of K and Rb during 

postmagmatic processes, possibly related to differing 

groundmass mineralogies and (or) textures of these 

rocks compared to the basaltic dikes in the Bridgewater 

and Mars Hill quadrangles. 

8 Geochemical features and 40Arfl'Ar age of dikes in Aroostook County, Maine 
Table 2. Geochronologic 40Ar/ 39Ar data for dikes in northeastern Maine-Continued 

39ArK •oAr J•ArK Apparent Apparent Temp. 40Arjl 9Ar 37 Arfl9Ar 36Arf3"Ar (percent of (percent of (moles K/Ca age (o() (X 10-2) (mole/mole) (Ma) total) total) X10-12) 

Sample 15 5 

300 ------------ 66.20 1.379 21.76 0.5 3.0 0.29 0.35 32± 12 

400 ------------ 18.39 1.243 3.454 3.1 45.0 1.93 .39 130±2 

550 ------------ 20.57 .346 .221 8.9 96.9 5.50 1.42 293 ±3 

650 ------------ 25.86 .469 .685 4.9 92.3 3.02 1.04 351 ±4 

750 ------------ 25.18 .301 .630 4.3 92.7 2.65 1.63 344±4 

850 ------------ 25.45 .222 1.014 7.9 88.3 4.88 2.21 332±4 

1000 ------------ 23.73 .264 .455 9.7 94.4 6.04 1.86 331 ±4 

1100 ------------ 20.34 .901 .310 32.7 95.8 20.3 .54 292±3 

FUSE ---------- 21.27 2.157 .567 28.0 92.9 17.4 .23 295 ±3 

Total gas age = 300 

Weight-average plateau age = 293 ± 6 

Sample 166 

400 ------------ 20.04 0.826 1.819 

700 ------------ 26.96 1.348 .661 

850 ------------ 24.87 .347 .568 

11 ()() ------------ 19.99 .868 .668 

FUSE ---------- 23.20 4.001 1.347 

1

Sample 6: P-64-6; whole rock diabase dike; Mars Hill 

quadrangle; J =0.009004; sample weight = 0.7717 g. 2

Sample 5: P-64-27; whole rock diabase dike; Mars Hill 

quadrangle; J =0.009004; sample weight =0.7109 g. 3

Sample 2: PA-74-7; whole rock basaltic dike; Bridgewater 

quadrangle; J = 0.009004; sample weight = 0.6900 g. 

High Valence Cations 

Nb and Ta.-On a Nb-P20s plot (fig. 5), at 

similar P20s levels, the Mars Hill dikes are slightly but 

systematically higher in Nb than those from the 

Bridgewater area, a reversal of the relative quantities of 

Ti02 (fig. 3). The lower Nb content results in a lower 

100 x Nb:Ti ratio for the Bridgewater dikes at similar 

P20s contents (fig. 5). The gentle increase in 

100 x Nb:Ti ratio in the Mars Hill specimens contrasts 

with the more common situation in basaltic sequences 

where the ratio remains approximately constant in the 

early and middle stages of differentiation and increases 

significantly only when Fe and Ti oxides become important fractionating phases (Gottfried and others, 1968). 

However, a possible case of gently increasing 

100 x Nb:Ti ratio with increasing differentiation has 

been. recorded by Macdonald and others ( 1981) in a sequence of late Paleozoic Scottish tholeiitic dikes. In 

both the Scottish and Mars Hill suites, Ti may have been 

partitioned into the solid phases more rapidly than Nb. 

The teschenitic rocks (samples 13-15), despite a 

higher alkalinity, do not contaih more Nb than the 

tholeiitic diabases. However, the Nb content of 44 ppm 

for sample 16 is more than twice that of the teschenites 

16.5 73.5 7.94 0.59 225 ±2 

15.3 93.1 7.36 .36 368±3 

20.4 93.3 9.80 1.41 342±3 

25.8 90.4 12.4 .56 272±2 

21.9 84.2 10.5 .12 292±2 

Total gas age = 298 

No plateau age defined 

•sample 3: PA-74-9; whole rock basaltic dike; Bridgewater 

quadrangle; J = 0.009004; sample weight = 0. 7437 g. 5

Sample 15: PA-74-3; whole rock basaaic dike; Presque Isle 

quadrangle; J = 0.009004; sample weight = 0.6778 g. 6

Sample 16: PA-74-4; whole rock basaltic dike; Presque Isle 

quadrangle; J = 0.009004; sample weight = 0. 7496 g. 

at equivalent P20s contents. The high Nb content supports the suggestion, based on major element data, that 

sample 16 represents a different magmatic stem. 

The behavior of Ta closely resembles that of Nb, 

and the Nb:Ta ratio varies (except for sample 8) between 11 and 21, largely within estimated analytical error. The high ratio of 27 in specimen 8 may not be 

significantly different from the ratios in the other 

diabase samples since Ta determinations in the very low 

ppm range are analytically uncertain. 

Zr and Hf-In the Mars Hill (excluding specimen 

8) and Bridgewater dikes, Zr content increases slightly 

less than threefold, reaching a maximum of 321 ppm 

(fig. 6). Concentrations of Hf show a generally similar 

increase. Though scattered, the Zr:Hf ratio shows no indication of decreasing with increasing P 20s content. 

This behavior differs from the behavior of the Great 

Lakes diabase-granophyre suite where the Zr:Hf ratio 

decreased by a factor of two during differentiation from 

the early mafic diabase to granophyric residua (Gottfried and others, 1968). The Zr:Hf ratio of sample 8 

(fig. 6) seems to further distinguish that sample from the 

other Mars Hill dikes. 

The Zr and Hf concentrations in the Presque Isle 

teschenites are uniform at about 255 ppm and 5 ppm 

Analytical results 9 
55 

50 

18 

16 

Iz 

w 14 

u 15 

a: 

w 

a.. 

I-

:I: 10 

(.9 

w 

~ 

5 

10 

5 

10 

5 

FeO 

EXPLANATION 

+ Bridgewater 

e Mars Hill 

6. Presque Isle teschenite 

.&. Presque Isle biotite chlorite 

albite basalt 

~----------- ........ , . •-...... ,-,, ...._......._ e '-, ',A'-,,. 

............ . . ' ~ ',, ........ _. - ' ' .. , - ........ -...__ ---- ) \ + ' ' ..... ____ ...... ----~\ ... ---------- ', 6. _______ ,, 

MgO ', .. ~ __ .. .,.--------

.... ------........ _ _.... -.... _.....,...,. I .............. 

~ ------....--.. ........ ~ ..... _ . . ............... ........... ...._ __ _ ---- CaO 

,------------------,, ,11:::,. /:::,.I 

,,"'' ','-~-------------------

r • _,.,.,.' ,_ .. 

10 Geochemical features and 40Ar/ 39Ar age of dikes in Aroostook County, Maine 
6 

4 

2 

~ 

z 

w 

u 

0: 

w 

a.. 

~ 

I 3.0 

(.9 

w 

~ 

2.5 

2.0 

_,. /,........---.-- ............. ------ <.f_____ --- . • • --- ---... _!.----

(.------------_.-........ -....... __ ....... --

/ " 

,.~,----~ 

/ 

/ 

{~ !:; 

-----------

....... _ -....... 

.................... . '.........: ............... . . . 

\ \ _ _! ____ .... 

"'----------...... 

EXPLANATION 

+ Bridgewater 

e Mars Hill 

.6 Presque Isle teschenite 

-............... ... 

& Presque Isle biotite chlorite 

albit~ basalt 

Figure 3. Major element variation diagram of dikes in northeastern Maine. 

Analytical results 11 
-

N 

~ 

tD 

l"l = 

::r 

tD 

~· Table 3. Trace element abundances in parts per million in dikes in northern Maine 

~ 

;;-

~ c 

; 

Ill 

Dl 

:I 

Q. 

~ ~ Dl 

QQ 

tD 

s. 

Q. 

;.: 

tD 

Ill 

:;-

> 

a 

Ill = Q 

= ~ 

1"'1 

c = 

:I 

~ 

~ Dl s· 

tD 

Suite 

Sample no. 

Field no. 

Rb ---------------

Ba ---------------

Sr ---------------- K:Rb ____________ 

Th ---------------

u ---------------- Zr ----------------

Hf --------------- Nb _______________ 

Ta --------------- Th:U ____________ 

Zr:Hf -----------

Nb:Ta ----------

100 X Nb:Ti ----

Co--------------- Ni ________________ 

Zn ---------------

Cr ---------------

Sc ---------------- Ni:Co ___________ 

La---------------

Ce --------------- Nd _______________ 

Sm _______________ 

Eu --------------- Gd _______________ 

Tb _______________ 

Tm --------------

Yb ---------------

Lu ---------------

La0 - Sm0 ------

y -----------

1 

PA-74-8 

107 

643 

584 

150 

2.3 

217 

4.9 

14 

.79 

-

44 

18 

.09 

37 

44 

151 

71 

37 

1.2 

18 

39 

29 

7.1 

2.23 

5.8 

1.2 

.61 

4.3 

.63 

1.39 

53 

Bridgewater 

2 3 4 

PA-74-7 PA-74-9 P-64-8 

42 13 63 

360 770 305 

379 298 1070 

148 364 222 

3.2 3.0 0.6 

1.1 - .I 

256 321 124 

5.8 6.9 2.8 

14 17 8 

.96 1.07 .50 

2.9 6.0 

44 47 44 

15 16 16 

.08 .09 .07 

29 35 46 

18 23 90 

144 172 142 

30 29 262 

34 38 41 

.6 .7 2.0 

23 23 6 

48 50 20 

33 39 13 

8.3 10.1 3.8 

2.50 2.99 1.40 

6.7 8.8 3.8 

1.6 1.6 1.0 

.56 .70 .46 

5.1 6.7 2.8 

.72 .89 .48 

1.52 1.25 .87 

62 86 44 

Mars Hill 

5 6 7 8 9 

P-64-27 P-64-6 P-64-5 P-64-77 P-64-3 

Large cations 

22 36 32 54 28 

230 292 166 261 496 

346 561 701 516 764 

218 253 247 222 286 

High-valence cations 

1.0 0.9 1.8 0.3 1.4 

.3 .2 .5 .I .2 

112 117 141 69 139 

2.7 3.2 3.7 1.3 3.2 

8 10 9 3 10 

.47 .50 .51 0.11 .48 

3.3 4.5 3.6 3.0 7.0 

41 37 38 53 43 

17 20 18 27 21 

.07 .08 .08 .06 .08 

Ferromagnesian elements 

40 45 42 38 37 

54 74 44 115 50 

120 146 136 92 122 

228 236 227 493 212 

34 41 40 28 39 

1.4 1.6 1.1 3.0 1.4 

Rare earth elements 

8 9 9 2 9 

21 22 26 8 22 

14 17 16 4 17 

3.6 5.1 4.5 1.6 5.0 

1.62 1.84 1.82 ·.68 1.64 

3.5 5.0 5.4 - 4.2 

.82 1.2 1.1 .48 1.1 

.37 .42 .55 .22 .42 

2.5 3.4 3.6 1.2 3.4 

.40 .53 .54 .22 .49 

1.22 .97 1.10 .69 .99 

33 43 44 16 42 

Presque Isle 

10 II 12 13 14 15 16 

P-64-9 P-63-26 P-64-7 PA-74-1 PA-74-2 PA-74-3 PA-74-4 

22 21 22 53 31 58 24 

346 342 250 675 536 452 504 

410 288 401 594 515 573 1159 

323 386 282 226 348 345 667 

2.3 2.2 3.4 8.6 6.8 8.2 3.5 

.5 .5 1.0 2.6 1.8 2.8 1.4 

208 188 231 266 251 257 248 

5.0 4.5 6.1 5.8 4.4 5.4 4.6 

17 13 15 15 18 17 44 

.89 .79 .80 1.35 1.05 1.28 3.29 

4.6 4.4 3.4 3.3 3.8 2.9 2.5 

42 42 38 46 57 48 54 

19 16 19 II 17 13 13 

.II .10 .11 .II .14 .14 .35 

38 40 38 34 29 30 34 

14 66 38 13 II 14 100 

168 134 122 143 148 148 84 

36 171 96 4 5 220 

34 37 31 8 8 9 19 

.4 1.7 1.2 .4 .4 .5 2.9 

18 15 15 49 45 47 29 

44 39 44 99 92 96 55 

30 27 28 45 43 43 27 

8.2 5.8 7.2 8.9 9.1 8.6 5.3 

2.50 2.04 2.48 2.23 2.23 2.20 1.55 

7.4 5.6 8.9 7.6 7.2 7.1 4.2 

1.6 1.3 1.7 1.3 1.3 1.5 .77 

.73 .56 .89 .70 .63 .60 .67 

5.2 3.7 5.4 4.8 4.3 4.6 .31 

.78 .60 .78 .70 ·.59 .64 .31 

1.20 1.42 1.14 3.02 2.71 3.00 3.00 

72 50 74 51 45 55 28 
800 

::1! 600 

0.. 

~ 

z 400 

cU 

III 

200 

0 

100 

80 

::1! 

0.. 

0.. 60 

z 

..0 

cc 40 

20 

0 

~ 1000 0.. 

z 

: 600 

en 

200 0 

---~ 

. -- \ \ ', \. 

\.. \. . . ' ....... ....... ' . ........ __ '-,!_ __ ~~---~ 

• 

0.1 

+ Bridgewater 

• Mars Hill 

• 

EXPLANATION 

t::. Presque Isle teschenite 

6 Presque Isle biotite chlorite 

albite basalt 

0.8 

~igure 4. Plots of Ba, Rb, and Sr contents against P20 5 in dikes 

m northeastern Maine. 

(table 3), respectively, and fall within the range shown 

by the Mars Hill and Bridgewater dikes. These concentrations are unexpected because the Presque Isle dikes 

are more alkalic, but the concentrations are consistent 

with the Nb and Ta data. 

Th and U.-In the Mars Hill dikes, Th and U increase five- or sixfold to a maximum in specimen 12 but 

apparently decrease in sample 10 (table 3). The trend is 

crossed by that of the Bridgewater dikes (fig. 7), which 

also demonstrates a maximum. The variation of Th and 

U thus mimics that of Nb and Ta and of Zr and Hf. 

Whether any phase likely to fractionate from such mafic 

compositions would remove all three elemental pairs 

from the liquids is not clear. If the Mars Hill dikes 

represent a cogenetic sequence, then sample 10 probably 

50 

40 

::1! 

0.. 30 0.. 

~ 

..0 20 

z 

10 

0 

3 

::1! 

0.. 

0.. 2 

z 

cU 

1-

0 

co 30 

1-

..c 

z 20 

10~--~--~~--~--~----~--~----~~~ 

~~ ~ ..c \\ z 0.2 \ ' 

\~-----

~ 0.1 $:!~=~==::::;:=t::f-----==:~. 

0 QL---~--~----~--~--~~--~~~~--~ 

0 0.1 0.2 0.8 

P20 5, IN WEIGHT PERCENT 

EXPLANATION 

+ Bridgewater 

• Mars Hill 

!:::. Presque Isle teschenite 

6 Presque Isle biotite chlorite 

albite basalt 

Figure 5. Nb and Ta contents and Nb:Ta and 100 x Nb:Ti 

ratios in dikes in northeastern Maine. 

has lost the LIL (large ion lithophile) elements, perhaps 

as a volatile phase. More likely, sample 10 represents yet 

another geochemical type within the Mars Hill suite, 

closely comparable to the other members but with slight 

differences in trace element abundances. 

The Th: U ratios of the Mars Hill and Bridgewater 

diabases show rather large variations, ranging from 2.9 

to 7. The variations are consistent with the possibility 

that U has been variably mobilized during low-temperature alteration processes. Previous studies (Gottfried 

and others, 1968) have shown that the Th:U ratio demonstrates little change during fractional crystallization 

of diabasic magmas. 

Analytical results 13 
400 

~ 300 

a.. 

a.. 

z 200 

~' 

N 

100 

0 

~ 8 

a.. 

a.. 

z 4 

....: 

.:r:: 

0 

60 

-

J: 

~ 50 

N 

40 

~ 

~-"~ ~ .. ~ u ... -...... ----~~ _ .. _.,....- e __ ::J l~ A ~~~~~-

~. - --~ _.,....,. L~·--,... 

./ ...... -- .:!..--

0.1 0.2 0.3 0.4 0.5 0.6 

P20 5, IN WEIGHT PERCENT 

EXPLANATION 

+ Bridgewater 6. Presque Isle teschenite 

• Mars Hill .& Presque Isle biotite chlorite 

albite basalt 

0.8 

Figure 6. Zr and Hf contents and Zr:Hf ratios in dikes in northeastern Maine. 

In contrast to the similarities found in Zr, Hf, Nb, 

and Ta between the teschenites and diabases, Th and U 

show significantly higher abundances in the teschenites 

(table 3). The higher abundances agree with the higher 

alkalinity of the teschenites. The abundances of Th and 

U in the teschenites are an example of the decoupling of 

LIL elements from each other; that is, relative enrichment of a suite of rocks in one or more LIL elements 

carries no implication that the suite will be enriched in 

all the remaining LIL elements. 

Rare Earth Elements 

The chondrite-normalized REE patterns of the 

Mars Hill diabase dikes (except sample 8) are rather flat, 

with only a modest enrichment of light rare earth 

elements (LREE) over heavy rare earth elements 

(HREE) and no systematic Eu anomaly (fig. SA). The 

Bridgewater dikes are more LREE enriched (fig. 8B). 

0 ~~~--~.--~~~---~---~------~---~-----1 

7 

3 

/-. ...... , 

/ ' 

/ /• ' ........ , 

/ / / • . " •> / ,. ___ _ 

/ • ./ 16. ------ • ..,....,.,(±) ,' 6.,.. 

I'• ------ + I 6_ ------""' ---- lf....-'"''"' 

1 ~---~------~---~------~---~------~---~---~ 

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 

P205 , IN WEIGHT PERCENT 

EXPLANATION 

+ Bridgewater 

e Mars Hill 

6. Presque Isle teschenite 

.& Presque Isle biotite chlorite 

albite basalt 

Figure 7. Th and U contents and Th:U ratios in dikes in northeastern Maine. 

The patterns are similar to those of continental 

tholeiites, though lower in LREE. Leeman (1977) lists 

La:Sm ratios of 1.4 to 3 for several continental tholeiite 

suites, higher than the 0. 7 to 1.5 in the Mars Hill 

diabases. Although the flatter pattern of these rocks 

may be a real magmatic feature, the Mars Hill rocks 

may have lost some LREE during low-grade metamorphism (Hellman and others, 1979). The similarity of 

the REE patterns in all the Mars Hill diabase samples 

seems to contraindicate LREE loss during metamorphism, and we regard the REE values as magmatic. 

Sample 8 has distinctly lower absolute abundances 

of the REE and a chondrite-normalized pattern that 

shows slightly more LREE depletion relative to HREE. 

These features are consistent with the lower Nb, Ta, Ti, 

Zr, and Hf contents (table 3) of this dike. The variation 

14 Geochemical features and 40Arfl"Ar age of dikes in Aroostook County, Maine 
w 

t9 

<( 

a: 

w 

> <( 

w 

t- 10 

a: 

0 

z 

0 

::c 

u 

.......... 

~ 

u 

0 

a: 

1 

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

A. MARS HILL DIKES 

Figure 8. Chondrite-normalized REE abundance patterns in dikes in northeastern Maine. Numbers are sample numbers. 

patterns of La, Yb, and Y (fig. 9) show small but consistent differences in the abundances of these elements 

between Mars Hill and Bridgewater dikes having the 

same P~o~ content. The La, Yb, and Y differences are 

consistent with the differences noted earlier for Ti02 

and for Nb and provide further support for the existence of two similar but distinct suites. The Presque Isle 

dikes (fig. 8C) are characterized by greater differences 

in the REE- and LREE-enriched patterns compared to 

those of the Mars Hill and Bridgewater dikes. 

Ferromagnesian Elements 

The variation patterns for Co, Cr, Ni, Sc, and Zn 

are shown in figure 10. Ni and Cr show strong depletion 

with higher P20s contents in the Mars Hill diabase 

dikes. These variations are similar to those noted in the 

Great Lakes diabase-granophyre suite (Greenland and 

Lovering, 1966). In the rocks from Mars Hill, the Ni:Co 

ratio decreases from 3 to 0.4 (table 3) with increasing 

fractionation. The teschenite dikes (samples 13-15) of 

the Presque Isle region have low Ni:Co ratios of approximately 0.5. The high ratio (2.9) in the biotite albite 

basalt (sample 16, tab1e 3) confirms its distinction from 

the other Presque Isle dikes. 

The variation in Co is rather limited, ranging from 

29 to 46 ppm for all three suites of rocks (table 3). The 

abundance of Sc in the Mars Hill basaltic dikes is similar 

to that of Co, but the abundances in the teschenite 

samples are distinctly lower ( <IO ppm) than those in the 

tholeiitic basalts (fig. 10). 

Analytical results 15 
w 

(.9 

<( 

a: 

w 

> <( 

w 

~ 

a: 10 0 

z 

0 

::r: 

u ....._ 

~ 

u 

0 

a: 

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

B. BRIDGEWATER DIKES 

Figure 8 (Continued). Chondrite-normalized REE abundance patterns in dikes in northeastern Maine. Numbers are sample 

numbers. 

MAGMATIC AFFINITY OF THE DIKES 

Results of modal and normative mineralogy of the 

altered Maine dikes do not reflect original magmatic 

compositions. A more effective approach to characterize the magmatic affinity is to use stable minor and 

trace element abundances and ratios. As discussed in the 

preceding section, several features of the trace element 

geochemistry suggest that the Bridgewater and Mars 

Hill dikes are of the tholeiitic magma type, whereas the 

Presque Isle rocks have more alkalic affinities. 

Chondrite-normalized patterns accentuate these differences. Specifically, the flat patterns and low REE 

abundances of the diabase dikes of Mars Hill and 

Bridgewater are consistent with tholeiitic affinity, 

whereas the LREE-enriched pattern abundances of the 

Presque Isle teschenitic rocks are more like those of 

alkalic basalt. This magma characterization has been 

further explored by using trace and minor element 

discriminators of magma types proposed by Pearce and 

Cann (1973), Floyd and Winchester (1975), and Winchester and Floyd (1976). Results obtained in this 'Yay 

for the Maine dikes, however, are contradictory. On the 

(Nb:Y)-(Zr:P20s) diagram (fig. 11A) of Winchester and 

Floyd (1976), all the dikes, with the exception of sample 

16, plot in the field of tholeiitic basalts. On the 

Ti02-Zr:P20s diagram (fig. liB) of the same authors, 

all rocks plot in or very close to the alkalic field, except 

specimen 8, which is in the tholeiitic field. This type of 

nonexclusive characterization also is obtained by using 

the TiOrZr, Ti02-(Nb:Y), and P20s-Zr diagrams of 

Floyd and Winchester (1975). 

16 Geochemical features and 40Arf39Ar age of dikes in Aroostook County, Maine 
100 

UJ 

(!) 

<{ 

cc: 

UJ 

> <{ 

UJ 

Icc: 

0 

z 

0 

I 

u 

.......... 

~ 

u 

0 

cc: 

10 

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

C. PRESQUE ISLE DIKES 

Figure 8 (Continued). 

Magmatic affinity of the dikes 17 
~ 50 

a.. 

a.. 

z 30 

~ 

a.. 

a.. 

z 

.o' 

> 

7 

.,..------~, 

,'~ ----- I ' /' " I / tA I 

.,..... ....... , -----~ .. --- 1 ...... ---- -

+ Bridgewater 

• Mars Hill 

EXPLANATION 

~ Presque Isle teschenite 

A. Presque Isle biotite chlorite 

albite basalt 

Figure 9. La, Yb, and Y contents in dikes in northeastern Maine. 

The 100 x Nb:Ti ratio of<.0.1 (fig. 5) for the more 

mafic diabases of Mars Hill is a feature only of tholeiitic 

basalts. Continental tholeiites from diverse geographical localities have shown values of this ratio within the 

range 0.05-0.15 (Gottfried and others, 1968; Gottfried 

and others, 1977; Macdonald and others, 1981). Similar 

ratios also have been found in the Kilauea and Mauna 

Loa tholeiitic suites from Hawaii and in island arc 

tholeiitic suites (Gottfried and others, 1977, and unpublished data). The slightly higher values in the Presque Isle rocks, especially in sample 16, also would be 

consistent with more alkalic chemistry. 

We recognize, therefore, the following magma 

types among the dikes: (1) two rather similar tholeiitic 

suites contained in the Mars Hill and Bridgewater dikes 

(excluding specimen 8) with only minor differences between the suites; (2) the primarily teschenitic maficalkalic suite of the Presque Isle quadrangle; and (3) two 

isolated samples that appear to be geochemically unique 

(sample 8 from the Mars Hill dikes, a depleted-type 

tholeiite, and sample 16 from the Presque Isle quadrangle, a biotite albite basalt with alkalic affinities). 

TECTONOMAGMATIC CLASSIFICATION 

The possible tectonic setting at the time of 

emplacement of the Maine dikes can be assessed by using minor and trace element diagrams as tectonomagmatic discriminators. 

On the (Ti: 100)-Zr-(Y x 3) diagram (fig. 12) of 

Pearce and Cann (1973), the Mars Hill and Bridgewater 

dikes plot within the fields occupied by ocean-floor 

basalts and calc-alkali basalts of island arc series. The 

Presque Isle teschenites fall in the calc-alkalic basalt 

field, and the biotite albite basalt falls in the intraplate 

basalt field. 

Wood (1980) has used a (Hf/3)-Th-Ta diagram to 

classify the tectonic setting of mafic rocks and their differentiates. On this plot (fig. 13), the Bridgewater dikes 

and the Mars Hill depleted tholeiite (sample 8) indicate a 

destructive plate margin environment. The other Mars 

Hill samples fall in the destructive plate margin field 

and theE-type MORB and tholeiitic within-plate basalt 

field. The three Presque Isle teschenitic dike samples 

suggest a destructive plate margin setting, whereas the 

Presque Isle biotite albite basalt suggests an alkaline 

within-plate association. Again, this discriminator fails 

to delineate unequivocally the dike environment. 

The reasons for the inapplicability of these 

diagrams lie in the characteristics of the dike 

chemistries. The Maine rocks have high Y (and HREE) 

abundances relative to the data base used by Pearce and 

Cann (1973) in constructing the (Ti:100)-Zr-(Y x 3) 

diagram. As a result, the dikes are displaced towards the 

Y apex and plot in an "inapplicable" field. The 

analyzed Maine samples appear to have relatively low 

Nb contents, as indicated previously by their low 

100 x Nb:Ti ratios, and by inference of geochemical affinity have low Ta contents. Thus, on the (Hf/3)-Th-Ta 

diagram, the dikes apparently have the characteristics of 

volcanic rocks from destructive plate margins. 

Comparable reasoning may be applied to the 

results obtained in the assessment of magma types. Low 

Nb contents cause the teschenites to be classed as 

tholeiitic on the (Nb:Y)-(Zr:P20s) plot (fig. 11A). 

Among the factors that could result in the nonapplicability of tectonomagmatic discrimination diagrams 

to a particular suite of rocks, four may be particularly 

important: 

( 1) Gottfried and others (1977) pointed out that the 

data base of continental tholeiites used by Pearce 

and Cann (1973) in the construction of their 

18 Geochemical features and 40ArJl'Ar age of dikes in Aroostook County, Maine 
~ 

CL 

CL 

z 

400 

- 200 

.: 

u 

~ 40 

CL 

CL 

z 

c.) 

CJ) 20 

~ 

CL 

200 

CL 150 

z 

c:" 

N 

100 

....-.--...... 

/ /··~­ . 

// . .,- ~ .,-----... (_ ...... 

,, 

I \ 

I&', ' ...... ' ..... \ .... \ ............ '& .... ~ A\ ________ , 

,~- .. -..... __ _ : 6"• I ;; 

I ; 

I ,' I , I , 

I ,' I I I I I ; 

I ,' 

~· ....... ,' 

0.2 0.4 0.6 0.8 

P20 5, IN WEIGHT PERCENT 

.. , I I IAI 

I I I I 

I l I I I \ 

I I I \ ' \ ' \ I \ 

I \ I \ I \ 

I \ I \ ' \ ' ' ' .. ....... 

.... _________ A'r , 

0.2 0.4 0.6 0.8 

P20 5, IN WEIGHT PERCENT 

~ 

CL 

CL 

35 z 

25 

100 

0 

u 

~ 

CL 

CL 

z 

z 

0 

3 u 

z 

0.10 

EXPLANATION 

+ Bridgewater 

• Mars Hill 

6 Presque Isle teschenite 

& Presque Isle biotite· chlorite 

albite· basalt 

Figure 10. Co, Cr, Ni, Sc, and Zn contents and Ni:Co ratios in dikes in northeastern Maine. 

(Ti: 100)-Zr-(Y x 3) diagram was not representative 

of tholeiites from passive continental margins. 

(2) Such tectonomagmatic discrimination diagrams 

may fail to consider the effects of fractionation of 

the relevant elements relative to each other, 

especially in the middle to later stages of differentiation (Graham, 1976). 

(3) Selective contamination of mafic magmas by wall 

rock reactions during ascent through sialic crust 

may result in enrichment of the diagnostic elements. 

(4) The likelihood that the mantle sources of withinplate basaltic magmas are markedly heterogeneous 

as regards the lithophilic elements is being increasingly recognized. Any relation between magma 

chemistry and tectonic setting is therefore complicated. 

Of these petrogenetic factors, the preferred explanation of the nature of the trace element associations 

in the Maine dikes is that the parental magmas were 

generated within heterogeneous mantle sources, both 

Tectonomagmatic classification 19 
2~---------r---------.----------,---------~--------~ 

>-

~1 

z 

• 0~---------L----------~--------~----------~--------~ 0.10 0.20 

A Zr: P20 5 

+ 

+ 

3 

+ 

• 

1-

z 

w 

u .. a: 

w .. 

!::::, !::::, ll.. !::::, 

1- 2 

:I: 

(!) • 

w 

~ 

z 

~ 

0 

i= 

• 

Zr: P20 5 

0~----------------~------------------L-----------------~ 8 0.05 0.10 0.15 

EXPLANATION 

+ Bridgewater .A. Presque Isle biotite 

• Mars Hill 

6 Presque Isle 

teschenite 

chlorite albite basalt 

Figure 11. Samples of dike rocks from northeastern Maine plotted on variation diagrams for characterization of magma 

type (Winchester and Floyd, 1976). A, Plot of Nb:Y against Zr:P20 5• B, Plot of Ti02 against Zr:P20s. 

20 Geochemical features and 40ArJl'Ar age of dikes in Aroostook County, Maine 
EXPLANATION 

FIELDS 

A-8. Low potassium 

tholeiitic basalt 

of tsland arc series 

B. Ocean-floor basalt 

8-C. Calc-alkali basalt 

of island arc series 

D. Intraplate basalt 

SAMPLE LOCALITIES 

+ Bridgewater 

• Mars Hill 

!::. Presque Isle teschenite 

A Presque Isle biotite chlorite 

albite basalt 

Zr 

Ti/100 

c 

A~------------------------------*-------------------------------~ 

Figure 12. Samples of dike rocks from northeastern Maine plotted on the (Ti:100)-Zr-{Y X 3) discrimination diagram of Pearce 

and Cann (1973). 

within the prescribed geographical area and when compared to the source areas of other within-plate suites. 

Variations in the melting process operating within such 

heterogeneous sources may have produced, in one teetonic setting and in a relatively limited time span, a 

range of mafic magmas representing a considerable proportion of the total spectrum of basaltic magmatism. 

Tectonomagmatic classification 21 
EXPLANATION 

FIELDS 

A. N-type MORB 

B. E-type MORB and tholeiitic 

within-plate basalts 

and differentiates 

C. Alkaline within-plate basalts 

and differentiates 

D. Destructive plate margin 

basalts and differentiates 

SAMPLE LOCALITIES 

+ Bridgewater 

• Mars Hill 

6. Presque Isle teschenite 

& Presque Isle biotite chlorite 

albite basalt 

Hf/3 

ThL_~~~L_----~~----~~----~------~------~------~------~------~----~Ta 

Figure 13. Samples of dike rocks from northeastern Maine plotted on the (Hf/3)-Th-Ta tectonomagnmatic discrimination diagram 

of Wood (1980). Dashed lines indicate areas of overlap. 

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___ 1965, Geology of the Bridgewater quadrangle, Maine: 

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Richter, D. A., and Roy, D. C., 1976, Prehnite-pumpellyite 

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References cited 23