U N I T E D STATE DEPARTMENT OF THE I N T E R I O R GEOLOGICAL SURVEY

Chemical analyses and rock series classification ~f 102 tonalite samples for the Jurassic magmatic arc,

Alaska-Aleutian Range batholirh, Alaska

Bruce L. Reed, Marvin A. Lanphere, and Alfred T. Miesch

Open-File Report

83-94

This report is preliminary and has not been reviewed for conformity with

U.S. Geological Survey editorial standards and stratigraphic nomenclature

Chemical ana lyses and rock s e r i e s c l a s s i f i c a t i o n of 102 t o n a l i t e samples f o r the J u r a s s i c magmatic a rc ,

I l laska-Aleutian Range b a t h o l i t h , Alaska

Bruce L. Reed, Marvin A. Lanphere, and Alfred T. Miesch

The purpose of t h i s r e p o r t i s t o make a v a i l a b l e major oxide chemi- c a l ana lyses and t h e corresponding CIPW norms of 102 t o n a l i t e samples from t h e J u r a s s i c magmatic a r c i n t h e Alaska-Aleutian Range b a t h o l i t h . Discussion of chemical v a r i a t i o n s and t h e p o l a r i t y of t h e J u r a s s i c a r c i s given i n Reed, Miesch, and Lanphere (1983).

More t h a n 80 percen t of t h e exposed p l u t o n i c rocks i n t h i s p a r t of the J u r a s s i c a r c ( f i g s . 1 and 2 ) comprise a composi t ional ly continuous c a l c - a l k a l i n e s u i t e t h a t ranges from hornb lend i te through hornblende gabbro, hornb lende-b io t i t e d i o r i t e , hornb lende-b io t i t e q u a r t z d i o r i t e , t o n a l i t e , t o r a r e g r a n o d i o r i t e and q u a r t z mozonite. T o n a l i t e and q u a r t z d i o r i t e a r e the dominant rock t y p e s , and t h i s s u i t e of p l u t o n i c rocks i s in formal ly r e f e r r e d t o as t o n a l i t e . I s o l a t e d bodies of high-A1203- type t rondhjemi te on t h e nor thwest s i d e of the b e l t and q u a r t z monzonite and g r a n o d i o r i t e p lu tons p resen t l o c a l l y on t h e s o u t h e a s t margin of t h e b e l t a r e not included i n this s tudy ,

The average and ranges of 64 modal ana lyses made on s t a i n e d s l a b s a r e given i n t a b l e 1. Forty-four of t h e s e samples con ta in less than 1 volume percen t K-feldspar, and on a Q-A-P diagram most of t h e samples f a l l i n t h e q u a r t z d i o r i t e o r t o n a l i t e f i e l d c l o s e t o t h e quar tz-plagio- c l a s e j o i n ( f i g . 3 A ) . Examination of t h i n s e c t i o n s of t h e remaining samples shows them t o c o n t a i n g e n e r a l l y less than 3 volume percen t K- f e l d s p a r . Ferromagnesian minera l s comprise between 15 and 60 percen t of each rock ( f i g . 3B) and c o n s i s t c h i e f l y of green hornblende, brown bio- t i t e , and, r a re ly , pyroxene.

Chemical ana lyses and t h e corresponding CIPW norms f o r t h e 102 samples a r e given i n t a b l e 2 . A s t a t i s t i c a l summary of t h e s e d a t a and a few simple r a t i o s a r e given i n t a b l e 3.

On a t e r n a r y normative f e l d s p a r diagram ( f i g . 4 A ) , a l l 102 samples f a l l i n t h e t o n a l i t e f i e l d . A l l but one are c l a s s i f i e d as c a l c a l k a l i n e on an A-F-M p l o t ( f i g . 4B).

Figures SA, 5B, and 6 show t h a t , f o r t h i s s u i t e of p l u t o n i c r o c k s , use of commonly used x-y rock c l a s s i f i c a t i o n diagrams may r e s u l t i n samples being placed i n d i f f e r e n t rock s e r i e s . The grouping of samples on Si02-versus-Na20+K20 p l o t (fig. SA) i s no t d i s t i n c t , and about half t h e samples l i e i n t h e t h o l e i i t i c f i e l d . The t o n a l i t e samples have a high a l k a l i - l i m e index (2 6 6 , fig. 5 A ) , and t h e i r K20/Na20 r a t i o s a r e low, ranging from 0.08 i n t h e m a f i c rocks t o 0.73 i n t h e more s i l i c i c rocks (table 3 ) . The FeO*/MgO r a t i o s r e l a t i v e t o Si02 have a uni- formly low r a t e of i n c r e a s e ( f i g . 6 ) , range between 1.41 t o 4.75, and

References Cited

Barker, F., 1979, Trondhjemite: definition, environment and hypothesis of origin, p, 1-12, Barker, F., ed., Trondhjemltes, dacites and related rocks, Amsterdam, Elsevier Scientific Publishing Company.

Barker, F., and Arth, J. G., 1976, Generation of trondhjemiric-tonalitic liquids and Archean bimodal trondjhemite-basalt suites: Geology, v. 4, p. 596-600.

Ewart, A , , 1976, Mineralogy and chemistry of modern orogenic lavas-- same statistics and implications: Earth and Planentary Science Let- ters, v. 31, p. 417-432.

Gill J.B., 1981, Orogenic andesites and plate tectonics, v. 16 of Kyllie, P.J., Ed. in Chief, Minerals and Rocks: New York, springe7 Verlaag, 390 p .

Miyashiro, A., 1974, Volcanic rock series in island arcs and active continental margins: American Journal of Science, v. 274, p. 321-355.

OIConnor, J. T., 1965, A classification for quartz-rich igneous rocks based on feldspar ratios: U.S. Geological Survey Professional Paper 525B, p. B79-B84.

Peacock, M. A. , 1931, Classification of igneous rocks: Journal of Geology, v. 39, p. 54-67.

Reed, B. L., Miesch, A. T., and Lanphere, M. A . , 1983, Plutonic rocks of Jurassic age in the Alaska-Aleutian Range batholith: chemical varia- tions and polarity: Geological Society of America Bulletin, in press.

F i g u r e 1.--Map showing Alaska-Aleutian Range b a t h o l i t h and Jurassic magmatic arc (Jurassic p l u t o n i c rocks)

Q (quartz)

4 / C'; \

Granodior i te

Quartz d ior i te

Quar tz monzodiorlte

rnaf ic minerals

plagioclase + alkal i feldspar

F i g u r e 3.--Modal d iag rams of 6 4 plutonic rocks f rom the Jurassic magmatic arc. ( A ) , Q-A-P; (B) Quartzlnafic minerals-total feldspar.

F (total Fe as FeO)

Figure 4A.--Normative p l o t s of An-Ab-Or for Jurassic i ona l i t e samples. Rock c lass i f icat ion af te r 0' Connor (1965) GS

modified 5y Barker (1979).

4B.--A-M-F diagram showing trend of Jurassic tonalitc samples.

Alkaline field

Calc -alkaline

Tholeiitic field

\

Tholeiitic field

N O R M A T I V E PLAGIOCLASE COMPOSITION

Figure 5A.--Plot of Si02 versus K2O+Na20 with least-squares E i t l i n e (dashed) for Jurassic t o n a l i t e samples. Sol id l i n e i s least-squares f i t for CaO. The a lkal i - l ine index (weight percent of S i 0 2 ) , where the K2QtNa20 l i n e intersects the CaO l i n e , for the Jurass ic s u i t e of rocks is about 65, def- ining the rocks as c a l c i c (Peacock, 1931). Alkaline, calc-alkal ine, and . h o l e i i t i c f i e l d s from Barker and Arth (1976). See t ex t for explanation 5f sample numbers and symbols.

5 B . --Plot of normative plagioclase composition versus weight percent A l 2 0 3 . Dashed l i n e separating calc-alkaline and t h o l e i i t i c fields from Irving and Baragar (1971) .

Thole i i t ic f i e l d /

f i e l d

0 0 45 5 0 5 5 60 65 70

SiO, ( w t %)

Figure 6.--Plot of SiO2 versus FeO*/MgO. Dashed line t h a t separates a l k a l i n e and tholeiitic fields from G i l l (1981) , following Miyashi to (1974). See text for explanation of sample numbers and symbols.

Table 1. Averages and ranges of modal analyses (volume percent) of 64 samples collectively referred to as tonalite from the Jurassic magmatic arc in the Alaska-Aleutian Range batholith.

Average Range Standard Deviation

Quartz 15.4 0 - 29.6 Alkali feldspar 2.1 0 - 16.8 Plagioclase 49.1 31 - 69.3 Mafic minerals 33 .O 14 - 57 Unknown .4 0 - 4

Table 2.--Chemical analyses, norms, differentiation indices and location of 102 plutonic rocks collectively referred to as tonalite from the Jurassic magmatic arc in the Alaska-Aleutian Range batholith.

[Rapid chemical analyses of rocks by Lowell Artis, S. D. Botts, Gilson Chloe, P. L. D. Elmore, J. L. Glen, James Kelsey, Herbert Kirschenbaum and Hezekiah Smith. X-ray spectroscopic analyses and partial chemical analyses are indicated by a 7 symbol, and analyses were made by J. W. Barker, E. L. Brandt, E. E. Engleman, G. Manson, H. G. Neiman, F. Newrnan and J. N. Taggar t . ]

(Table 2 begins on page 11 .)

Table 2.--Chemical analyses

Sample No: 1 2 Field No: 65AR-827 70AR-I77

4 5 71AR-34 71AR-35 -- Chemical Adaly ses

61.9 65.1 14.4 13.1 2 .4 2.0 4.6 4.3 3 .0 3.2 6.4 6 .O 2.3 2.1 I .O 1.3 2.6 1,3 .76 .51 .28 .16 .21 .18 -05 .05

CIPW nonuell

Si02 *I2O3 Fe203 FeO MgO CaO Na20 K20

2; p205 Mno C O ~

Diff. Index 38.34 40.70

Latitude and Longitude

Lat IN.) 59.773 60.615 Long (We) 153.645 152.628

Table 2.--Chemical analyses (continued)

Sample No: 10 11 12 Field No: 72AR-47 72AR-46 72AR-48

Chemical asaly ees

$102 59 -0 A1203 16.8 Fe203 2.4 FeO a .8 MgO 6 .0 CaO 7.5 Na20 2.8 K2° 1.7 HtD+ 1 .Z Ti02 .65 P2°5 .12 Mn0 .07 co2 ,02

CIPW norms

-- 5,38 1.64 4,21

28.74 35.05 40.67 32.49 6.68 2.52 5.97 9.81 4.05 3.80 1.79 4.69 1.96 1.46 .61 . f 3 .16 -05

30.39 44.67 Diff. Index 47.43 61.89 43.77

Latitude and longitude

Lat (N.) 60.446 60.478 60.349 Long (W.) 152.790 152.593 152.776

Table 2.--Chemical a n a l y s e e ( c o n t i n u e d )

Sample No: 19 20 21 F i e l d No: 72AR-62 72AR-61 72AR-63

Chemical a n a l y s e s

sioz A1203 p i 0 3

HgO CaO Na20 K20 H2W Ti02

P205 Mno M2

D i f f . i n d e x

L a t i t u d e and l o n g i t u d e

T a b l e 2.--Chemical a n a l y s e s ( c o n t i n u e d )

SampleNo: 28 29 30 F i e l d No: 72AR-100 72AR-99 72AR-107

3 1 32 72AR-113 72AR-114 -- Chemical a n a l y s e s

59.2 57.2 15.2 17.3 2.5 2.2 4.6 4.9 3.9 3 -6 7.7 7.2 2 .8 2.8 1 .2 1.5

.96 I .O -69 .78 . I0 . I 0 .10 .I0 .08 .07

CIPW norms

16 -88 13.34 7.23 9.07

24.16 24.24 25.86 30.90

4 -97 1.89 9.90 9.17 5.53 6.22 3.70 3.26 1.34 1.52

.24 .24 , I 9 .16

48.27 46.64

Sf02 Al2O3 Fe203 FeO M U 0 CaO Na20

K20

2; p205 Etno co2

D i f f . i n d e x 51.51

Lat i tude and l o n g i t u d e

Lac (N.) 59.987 60.015 60.157 Long (W.) 153.248 153.287 153.296

Table 2.--Chemical analyses (continued) I

Sample No: 37 38 39 40 41 42 Field No: 72AR-121 72AR-119 72AR-120 72AR-122 72AR-123 72AR-124

Chemical analysea

S 102 A1203 Fe203 FeO ugo CaO Na20 K20 d2O+ Ti02 ?2O5 Mno '32

CIPW norms

17.84 18.71 10.20 13.30 28.35 27.69 27.24 24.71

.78 1.32 6.83 6.11 3.40 2.91 3.83 3.71 1.14 1.17 .29 .27 .12 .12

56.39 59.70 Diff. index

Latitude and longitude

Lat (N.) 60.197 60.216 60.254 60.284 60.305 60.315 Long (W.) 153.182 153.140 153.180 153.147 153.094 153.044

Table 2.--Chemical analyses (continued)

Sample No: 46 47 18 49 50 Field NO: 72AR-128 72AR-131 72AR-148 72AR-155 72AR-156

Chemical Analyses

Si02 *lz03 Fe203 FeO MU0 CaO Nap0

K20

2: P2°5 Hn0

C02

CIPW Norms

O i f f . index

Latitude and Longitude

Lat (N.) 60.276 60.314 60.595 60.289 60.312 Long(W.) 152.805 152.787 152.701 153.195 153.182

T a b l e 2.--Chemical a n a l y s e s ( c o n t i n u e d )

Sample No: 55 56 57 58 59 F i e l d No: 72AR-164 72AR-162 72AR-163 72AR-165 72AR-166

Chemical a n a l y s e s

S 102 A1203 Fe203 FeO MKO CaO Na20 K20 H20+ Ti02 2;5 cop

D i f f . i n d e x 48.99 51.17 59.21 53.88 49.28

L a t i t u d e and l o n g i t u d e

Lac (N.) 60.423 60.467 60.400 60.360 60.367 Long (W.) 152.916 152.990 153.053 153.077 153.125

Tab le 2.--Chemical a n a l y s e s (continued)

Sample No: 64 F i e l d No: 72AR-227

Chemical a n a l y s e s

s i n 2 57.5 A1203 17.5 Fe203 3.2 FeO 3.8 ago 3 . 2 CaO 8.1 Na20 3 -7 K20 -64 H 2 N .95 TiO? -97 P2°5 .19 no .09 co2 .02

CIPW norme

rl 12 -88 or 3.82 a b 31.65 an 29.57 wo 4.04 en 8.06 fs 2.93 mt 4.69 11 1.86 a!' .45 CC .05

DifE. i n d e x 48.35

L a t i c u d e and Longitude

Lat (N.) 60.187 Long ( W . ) 153.288

Table 2.--Chemical analyses (continued)

Sample No: 73 7 6 7 5 Field No: 78AR-157 78A.R-156 78AR-158

Chemical analy ees

55.9 45.6 17.0 20,8 3.4 h.7 5.4 5.2 5 .4 4.5 7.1 10.6 2.2 3,1 1 .O .27 1.7 2+2 3 0 .9 1 -16 .28 -17 ' .l7 ,02 .02

CIPW norma

Dif f . index Latitude and longitude

Lac (N.) 60.385 60.455 60.472 Long (W.) 153.088 152.834 152,877

Table 2 .-Chemical analyses (continued)

Sample No: 82 8 3 84 Field No: 81AR-4t 81AR-8t 8IAR-lot

85 86 BlAR-LZt 8lhR-14t -- Chemical analyses

61 .O 63.4 16 .O 15.7 1.68 1.84 2.47 3.84 2.45 2.19 5.98 5.75 3.16 2.99 1.28 1.59 .43 .50 .80 .51 .14 .09 .13 .12

<.01 .02

CIPW norms

diOp 59.0 d2O3 16.4 Fe203 2.16 FeO 4.86 MKO 3.47 CaO 7.33 Na2O 2.84

K2O 1.79 H20t .72 Ti02 -70 P2O5 .13 M10 .I3

co2 <.Ol

Diff. index

Latitude and longitude

Lat (N.) 60,634 60,567 60.505 Long ( W . ) 152.482 152,443 152.504

Table 2.--Chemical analyses (continued)

Sample No: 9 1 92 9 3 94 95 96 Fielde NO: 81AR-29t 81AR-317 81AR-337 81AR-387 81AR-39i 81AR-407

Chemical

58.1 16.3 2.07 5.46 3.76 7.13 2.46 1.29 1.81 .56 .08 .14 .02

analyses

59.2 16.2 2.08 4.98 3.30 7.11 2,61 1.60 .89 .63 ,I1 .13 .01

SiOf A1z03 Fa203 FRO ngo CaO No20

K20 HZ@ Ti02 225 GO2

CIPW norms

Dif f . index Laticude and longitude

Lat (N.) 60.491 60.541 60.511 60.394 60.408 60.418 Long (W.) 152.602 152.625 152.886 152.708 152.737 152.772

Table 2.-Chemical analyses (continued)

Sample No: Field No:

100 81~~-175t

Chemical

58.4 17.1 2.93 3.65 2.96 6.47 2.79 1.61 1.97 .62 .I6 .12

C.01

Si02 a203 -g03

w CaO Na20 K20 H20+ Ti02 P205 Hno

co2 1/ S i x samples contain normative C (noa. 33 " .72. -

43 - ,84, 46 - .14, 56 = 1.01, 58 - .56, 68 - .14); 2 samples concain normative £0 (nos. 13 - 4.44, 77 - 4.16); 2 samples contain normative fa (nos. 13 - 3.32, 77 - 1.83); 1 sample contains normative tun (no. 85 - 1.55).

CXPW norpa

index 51.72

Latitude and longitude

Lat (N.) 60.432 60.609 60.641 Long ( W . ) 153.007 152.671 152.595

Table 3.-- Statistical summary of major oxides and CIPW normative minerals

Standard Variable Me an Range Deviation

Chemical variables

S i02 58.29 45.6 - 67.6 3.56 d2°3 16.98 13.1 - 20.8 1.21 Fe203 2.73 1.2 - 4.70 0.63 FeO 4.36 2.0 - 6.38 0.83 Mgo 3.41 1.4 - 5.53 0.80 CaO 7.21 4.4 - 11.50 1.18 Na20 3 .11 2.0 - 4.70 0.49 K2° 1.19 0.27 - 2.20 0.46 H20+ 1 .20 0.36 - 2.70 0.50 Ti02 0 -68 0.21 - 1.00 0.13 P2°5 0.16 0.02 - 0.46 0.08 MnO 0.13 0.04 - 0.21 0.03

C02 0 -05 0.01 - 0.42 0.06 Na20+K20 4.30 3.00 - 6.00 0.61 K20/Na20 0.39 0.08 - 0.73 0.17 Na20/Si02 0.05 0.03 - 0.08 0.009 K20 /Si02 0.02 0.01 - 0.04 0.007 FeO* 6.82 3.81 - 9.43 0 -98 FeO*/MgO 2.06 1.41 - 4.75 0.38 Atomic ~ g / ~ g + ~ e ~ + 0.58 0.36 - 0.69 0 -04 Atomic Mg/MgfsFe 0.47 0.27 - 0.56 0.04

Normative variables

Q 14.98 0 - 30.14 6.08 or 7.14 1.64 - 13.30 2.77 ab 26.78 17.23 - 40.23 4.21 an 29.27 21.14 - 43.72 4.05 wo 2.40 0 - 7.28 1.57 en 8 - 5 2 3.52 - 13.89 1.99 fs 4.89 0 - 9.34 1.62 mt 4.02 1.78 - 7.09 0.91 i 1 1.31 0.41 - 1.96 0.25 aP 0.39 0.05 - 1.11 0.20 c c 0.11 0 - 0.98 0.13

11 DI, Differentiation index = normative Ot.or+ab - 21 CI, Color index normative wo+en-tfs+fo+fa+mt+hm+il - 3/ Normative plagioclase composition = 100(an/278)/(an/278 + abl262) -