Petrology of the Welded Tuff of 

Devine Canyon, Southeastern Oregon 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 797 

Petrology of the Welded Tuff of 

Devine Canyon, Southeastern Oregon 

By ROBERT C. GREENE 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 797 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1973 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress catalog-card No. 73-600097 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402- Price 65 cents domestic postpaid or 45 cents GPO Bookstore 

Stock Number 2401-00331 
CONTENTS 

Page 

Abstract ---------------------------------------------------------------------------------------- 1 

Introduction -------------------------------------------------------------------------------- 1 

Topographic and geologic setting ------------------------------------ 1 

Acknowledgments -------------------------------------------------------------- 1 

General features -------------------------------------------------------------------------- 3 

Age---------------------------------------------------------------------------------------- 3 

Vitric tuff ------------------------------------------------------------------------------ 3 

Devitrified tuff -------------------------------------------------------------------- 7 

Lateral and vertical variations ------------------------------------------------ 8 

Measured sections -------------------------------------------------------------- 8 

Devitrification ---------------------------------------------------------------------- 9 

Density ---------------------------------------------------------------------------------- 9 

Phenocrysts -------------------------------------------------------------------------- 9 

Lateral and vertical variatio~Continued Page 

Pumice ---------------------------------------------------------------------------------- 11 

Source ------------·----------------------------------------------------------------------------- 11 

Petrology -------------------------------------------------------------------------------------- 12 

Mineralogy -------------------------------------------------------------------------- 12 

Alkali feldspar ------------------------------------------------------------ 12 

Quartz ---------------------------------------------------------------------------- 12 

Clinopyroxene -------------------------------------------------------------- 18 

Bulk composition ---------------------------------------------------------------- 18 

Analyses ------------------------------------------------------------------------ 18 

Norms---------------------------------------------------------------------------- 19 

Groundmass composition --------------------------·------------------------ 21 

Interpretation of magmatic history ---------------------------------------- 23 

References cited -------------------------------------------------------------------------- 25 

ILLUSTRATIONS 

Page 

FIGURE 1. Map showing outcrop area, with minimal downdip projection, of welded tuff of Devine Canyon ------------------------------ 2 

2. Map showing location and extent of major welded tuff sheets of southeastern Oregon ------------------------------------------------ 4 

3. Isopach map of welded tuff of Devine Canyon ----------·----------------------------------------------------------------------------------------------------------- 5 

4. Photograph of Juntura section--------------------------------------·----------------------------------------------------------------------------------------------------------- 6 

5. Photograph of Drinkwater Pass section ---------------------------------------------------------------------------------------------------------·---------------------- 7 

6. Photomicrograph of nonwelded vitric tuff, section 153, specimen 1 ---------------------------------------------------------------------------------- 7 

7. Photomicrograph of slightly welded vitric tuff, section 154, specimen 4 ------------------------------------------------------·----------------- 7 

8. Photomicrograph of moderately dense vitric tuff, section 154, specimen 1 ------------------------------------------------··------------·--·----- 8 

9. Photomicrograph of dense vitric tuff, specimen 144 ..... ·------------------------------------------------------------------------------------·---------------------- 8 

10. Photograph of basal part of Poison Creek section ------·----------------------------------------------------------------------------------------------------------- 9 

11. Photograph of Silvies Canyon section--------------------------·-------------------------------------------------------------------------------------·----------------·----- 10 

12. Photograph of Poison Creek section, reference section for welded tuff of Devine Canyon --------------------·---------------------- 10 

13. Photograph of Lower Silvies River section------------------------------------------------------------------------------------------------------------------------------ 11 

14. Photomicrograph of devitrified tuff from section 160, specimen 3 --------------------------------------------------------------·---------------------- 11 

15. Photomicrograph of devitrified tuff from section 163, specimen 3 --------------------------------------------------------------.. ·-------------------- 11 

16. Photomicrograph of devitrified tuff from section 9, specimen 1 ---------------------------------------------------------------------------------------- 12 

17. Photomicrograph of tuff from section 158, specimen 3 ------------------------------------------------------------------------------------------------------ 12 

18. Measured sections of welded tuff of Devine Canyon, northwestern part ------------------------------------------------------------------------ 13 

19. 'Measured sections of welded tuff of Devine Canyon, north-central part ------------------------------------------------------------------------ 14 

20. Measured sections of welded tuff of Devine Canyon, eastern part -------------------------------------------------------------------------------·-- 15 

21. Measured sections of welded tuff of Devine Canyon, southern part -------------------------------------------------------------------------------- 16 

22. Map showing alkali feldspar phenocrysts in basal few feet of tuff sheet------------------------------------------------------------------------ 17 

23. Cross sections illustrating variations in alkali feldspar phe:O()cryst content ------------------------------------------------------------------ 18 

24. Histogram showing relative volumes of tuff with various phenocryst contents -------------------------------------------------------------- 19 

25. Partial triangular diagram showing normative feldspar components of analyzed samples in the system Ab-Or-An 22 

26. Partial triangular diagram showing normative compositions of analyzed samples in the system Q-Or-Ab -------------- 22 

27. Partial triangular diagram showing normative compositions of whole rock, phenocrysts, and groundmass 

for samples of table 9 in the system Q-Or-Ab ---------------------------------------------------------------------------------------------------------------- 23 

III 
IV CONTENTS 

TABLES 

Page 

TABLE 1. Major welded tuff units in southeastern Oregon--------·----------------------------------------------------------------------------------------------------------- 3 

2. Potassium-argon dates on the welded tuff of Devine Canyon ---------------------------------------------------------------------------------------------- 6 

3. Analyses of alkali feldspar phenocrysts from the welded tuff of Devine Canyon ------------------------------------------------------------ 18 

4. Optical properties of pyroxene from welded tuff of Devine Canyon ----------------------------------------------------------------------------------·- 18 

5. X-ray diffraction data for pyroxene from sample 148-3 -------------------------------------------------------------------------------------------------------- 19 

6. Rapid rock analyses of vitric and devitrified welded tuff of Devine Canyon -------------- ·----------------------------------------------------- 20 

7. Semiquantitative six-step spectrographic analyses of some samples of the welded tuff of Devine Canyon ------------------ 20 

8. Norms of analyzed samples of vitric and devitrified tuff------------------------------------------------------------------------------------------------------ 21 

9. Average composition of analyzed devitrified tuffs and calculated partial groundmass compositions of selected 

devitri:fied tuffs ---------------------------------------··-···-····--------····-------------------------------------------------------------------------------------------------------- 24 
PETROLOGY OF THE WELDED TUFF OF DEVINE CANYON, 

SOUTHEASTERN OREGON 

By ROBERT c. GREENE 

ABSTRACT 

The welded tuff of Devine Canyon, the most widespread ashflow tuff in southeastern Oregon, is centered around the Harney 

Basin lowland south of Burns; it originally covered about 7,200 

square miles and had a volume of over 47 cubic miles. Its age is 

early Pliocene, about 9 million years. Thickness ranges from a 

few feet to over 100 feet. Most sections under 35 feet thick are 

entirely vitric; thicker sections are devitrified but have a vitric 

base. 

The distribution of the tuff suggests that the source area lies 

buried beneath Quaternary sediments in the northwest part of 

the Harney Basin lowland. Downwarping of this lowland may 

be related to the expulsion of magma from beneath to form the 

Devine Canyon and other welded tuff sheets. 

Phenocrysts are mostly alkali feldspar (Or42Ab5s) and quartz 

with minor iron-rich pyroxene. Alkali feldspar phenocryst content ranges from 1 to 29 percent and increases markedly upwards in most sections. 

Analyses of 14 samples :show that the devitrified tuff is uniform in composition. Unlike the welded tuffs of southern 

Nevada, samples that are rich in phenocrysts are similar in 

composition to samples that are not; this fact· indicates that 

phenocrysts crystallized in the magma chamber without significant crystal settling. A water pressure of between 800 and 1,800 

bars during phenocryst crystallization is indicated by comparison with the experimental data of Tuttle and Bowen. Resorption of phenocrysts at all levels in the magma indicates 

reduction in water pressure prior to ash-flow eruption, probably 

by venting of water vapor plus minor air-fall tuff. Eruption 

onto a very flat plain produced an exceptionally widespread 

but relatively thin tuff sheet. 

INTRODUCTION 

The study of ash-flow tuffs has gained considerable 

impetus in recent years, particularly through the work 

of Smith (1960a, b) and Ross and Smith (1961). Smith 

has described with clarity and precision the characteristics of welding and crystallization zones, and the 

nomenclature he established has been widely accepted. 

Work at the Atomic Energy Commission Nevada Test 

Site in southern Nevada has resulted in the mapping 

and description of many heretofore unknown ash-flow 

tuffs (Hinrichs and Orkild, 1961; Lipman and Christiansen, 1964; Lipman and others, 1966; Byers and 

others, 1968). Many of these tuffs show striking compositional zonation, commonly from phenocryst-poor 

rhyolite at the base to phenocryst-rich quartz latite at 

the top. 

The welded tuff of Devine Canyon in southeastern 

Oregon (fig. 1), is a very widespread but thin unit. Like 

those of southern Nevada, it is zoned from a phenocrystpoor base to a phenocryst-rich upper part. However, the 

bulk composition is uniform, and phenocrysts appear to 

have crystallized in place in the preeruption magma 

chamber without settling appreciably. Eruption of the 

magma produced a tuff zoned as to phenocryst content, 

but not recording significant magmatic differentiation. 

TOPOGRAPHIC AND GEOLOGIC SETTING 

The area underlain by the welded tuff of Devine 

Canyon is part of the "High Lava Pl~ins" section of 

Oregon (Baldwin, 1959; Walker, 1969, p. 77). It is a 

region of high plateaus, locally broken into tilted fault 

blocks and cut in places by deep canyons. Rocks are 

mainly flat-lying to gently tilted Miocene, Pliocene, 

and Quaternary volcanic and continental sedimentary 

rocks, with local occurrences of pre-Tertiary rocks. In 

the central part of the region is a basin floored mostly 

with Quaternary lake sediments, herein referred to as 

the Harney Basin Lowland (fig. 1). 

Numerous ash-flow tuffs have been recognized in 

southeastern Oregon (fig. 2; Walker, 1970). All are of 

late Miocene or Pliocene age (table 1). The welded 

tuffs of Devine Canyon, Double 0 Ranch, and the 

Trout Creek Mountains are the most voluminous and 

complex; the others are much smaller. Welded tuffs of 

Devine Canyon, Prater Creek, and Double 0 Ranch 

form an important threefold sequence on the north side 

of the Harney Basin lowland (north of Burns). All 

three are well exposed in Devine Canyon, Poison Creek, 

and Silvies River canyon (Greene, 1972; Greene and 

others, 1972). 

ACKNOWLEDGMENTS 

The writer gratefully acknowledges the contribution 

of mapping by George W. Walker, both in the Adel and 

the south-central part of the Burns 1 o by 2° quad1 
2 PETROLOGY OF THE WELDED TUFF OF DEVINE CANYON, SOUTHEASTERN OREGON 

1200 

r-----------------------------------------~1~19~----------------------------------------~11~ 

X X 

X 

X 

)( 

X 

X 

X 

CANYON 

X X 

X 

X 

ADEL QUADRANGLE 

X X 

X 

QUADRANGLE 

.:·:.:::/Probable 

source area 

Harney Basin 

Lowland 

X 

X 

FIGURE !.-Outcrop area, with minimal downdip projection, of welded tuff of Devine Canyon. 

rangles. R. C. Erd supplied powder and single-crystal I sium-argon dates were determined by J. C. Engels, 

X-ray data for the pyroxene from sample 148-3. Potas- M. A. Lanphere, and J. C. Von Essen. 
GENERAL FEATURES 3 

TABLE 1.-Major welded tuff units in southeastern Oregon 

Name and (or) location1 

Age 

(m.y) Age reference Map reference 

Pliocene 

West side Hampton Butte ............ 3.6 Walker (1970, p. 102) -------------------------- Walker and others (1967). 

Rattlesnake Formation -------·---------· 6.4 

Double 0 Ranch------------------------------ 6.8 

Evernden and others (1964) -----------·-··· Greene and others (1972) --------------------

Brown and Thayer (1966). 

Walker (1963), Walker and Repenning 

(1965), Walker and others (1967), Greene 

and others (1972), reconnaissance by 

G. W. Walker (1968-70) and 

D. A. Swanson (1968). 

Prater Creek ------------------------------------ Greene and others (1972) ................... . Greene and others (1972). 

Wagontire ------···············---------------···· G. W. Walker (oral commun., 1969) .. Walker and others (1967), Greene and 

others (1972). 

Devine Canyon .............................. 9.2 This paper ............................................. . Walker and Repenning.(1965), Brown and 

Thayer (1966), Greene and others (1972), 

reconnaissance by G. W. Walker (1968-70). 

Buchanan ··--·-···········-······---·········--·- Greene and others (1972) ................... . Greene and others (1972). 

Walker and others (1967). 

Kittleman and others (1967). 

South Fork Crooked River ......... . G. W. Walker (oral commun., 1969) __ Wildcat Creek Welded Ash-flow .. Tuff of Kittleman and others 

(1965). 

Kittleman and others (1965) ............. . 

Miocene 

Trout Creek ................................... . Dinner Creek Welded Tuff ......... . G. W. Walker (oral commun., 1969) .. Walker and Repenning (1965). 

Kittlemanandothers (1967, Haddock (1967), 

reconnaissance by G. W. Walker (1969-70). 

Kittleman and others (1965) ............. . 

Leslie Gulch Ash-flow Member of 

Sucker Creek Formation of 

Kittleman and others (1965). 

Kittleman and others (1965) ............. . Kittleman and others (1967). 

1Welded tuffs are arranged in approximate stratigraphic order. Relative position within groups is uncertain. 

GENERAL FEATURES 

The welded tuff of Devine Canyon consists of soda 

and alkali rhyolites, as defined by Rittmann ( 1952, p. 

81). The tuff sheet contains porous vitric, dense vitric, 

dense devitrified, and vapor phase zones, much as 

described by Smith ( 1960b) and Ross and Smith 

(1961). Most of the tuff is strongly welded. Lithophysae are absent. Groundmass consists of shards and 

pumice, both of which are variously flattened and 

stretched, so that the rocks have a wide range of 

densities. Phenocrysts are alkali feldspar and quartz, 

with trace amounts of pyroxene (ferrohedenbergite), 

ilmenite, and magnetite. Rock fragments are sparse and 

are mostly andesite. 

This tuff forms a simple cooling unit (Ross and 

Smith, 1961). It seems to be composed of a single ash 

flow, although local obscure partings suggest the possibility of more than one flow. 

The original extent and volume of the tuff were calculated from an isopach map (fig. 3), which was prepared on the basis of outcrop pattern (fig. 1) and 

thickness data. The zero isopach shows the inferred 

original extent of the tuff. The tuff must have covered 

an area of about 7,200 square miles (18,600 sq km) and 

had a total volume of about 4 7 cubic miles ( 195 cu km). 

This places it in order 6 or 7 of Smith (1960a), which 

suggests that it originated in a subsidence structure. 

AGE 

Potassium-argon dates on the tuff range from 8.5 to 

9. 7 m.y. (table 2); all five dates were made on alkali 

feldspar phenocrysts from fresh vitric tuff. The determinations on samples from Diamond and Catlow Valley, however, were done in different laboratories while 

dating techniques were still being developed. The 

. average of the other three is 9.2 m.y., and the total 

deviation only 0.6 m.y. 

VITRIC TUFF 

Vitric tuff occurs in the basal and, rarely, the upper 

parts of the tuff sheet and is the dominant type near 

the outer margin. It varies considerably in density. 

Much is moderately dense (2.0-2.2) and medium to 

light gray (N5-N7), or medium to light greenish to 

olive gray (5GY 6-8/1, 5¥ 6-8/1), more rarely light 

brownish gray (5YR 6/1). Alternating lenticular color 

bands of darker and lighter values of the same hue are 

common. The weathered surface uf this type of tuff is 

slightly darker or browner than a fresh surface, but the 

tuff remains coherent even after moderate weathering. 

Fracture is planar to conchoidal (fig. 4). 

Denser (2.2-2~35) vitric tuff is generally greenish 

gray ( 5GY 5-6/1) and in places is streaked with light 

olive or light brownish gray (5Y-5YR 6/1). Its texture 

is commonly perlitic. This tuff has hackly fracture and 

weathers to small bits. 

Vitric tuff of low density (1.1-2.0) is light to very 

light gray (N7-8) and is visibly porous. The least dense 

rock crumbles when touched, breaking down to individual shards and pumice lumps. This incoherent rock 

was found only at the Drinkwater Pass section (fig. 5). 
4 PETROLOGY OF THE WELDED TUFF OF DEVINE CANYON, SOUTHEASTERN OREGON 

121° 120° 119° 118° 45° -------------------,--------------------,-------------------~-------------------~~-- 117° 

\~···--· ··----- ....._ ____ ~~tlesnake · ··---......._ _...,....... ... ........____ 

.............. _ ···.-John Day ) 

..........___o, ·--- .---'' ·--.... ---··· 

• Baker 

• Prineville 

;--.....-------..._ 

// ,--~, 

/ J 1 Double 0 '-....::: 

l I \ Ranch(?) ) '\ South Fork I _______ ; ......-·-~ 

/Crooked River 1 

( ,- ~ ~ I ~"-...,L_!?ouble 0 Ranch \ 

""' ; \./ -- I 

·1 Dinner 

}Creek 

·~\ '-....../ '- /'') I 

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West side · '--- ., .-----,1 

Hampton Butte( ~ \, ___ 1 ()/ \~~(."":~---:\ \ ) 

.___/ , \'·Prater Creek-( /A. 8 h \ .. \) ,,~ .,_ . :' 1 ~ uc a nan "'.-f :-...~~Bu~~~-···;:--.::.:.:=:..:..·:.:.=~.) : -~Wildcat ----:--..~ I .ycreek 

........ :--... __ ) \ / 

(

/ "",, .\). , Devine Canyon 

,wagontir~J ------ ""- /,/ -- ,_y 

/ 

I 

'-, 

' '-

r----- ./; " 

I ----- "' \ 

\ 

' " \ 

\ 

Double 0 Ranch 

"---....... _ 

-------, 

I 

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"-....._/ 

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/-~ 

~--- \ 

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\__,--

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Vale I 

( 

30 

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~ ( ( ( Creek 1 

• Lakeview / ""' \ \ \ \ I 

42°---------_l _____ /QREGO~~~~-\L _ \_ ____ L __ j ___ ---j NEVADA McDermitt 

FIGURE 2.-Location and extent of major welded tuff sheets of southeastern Oregon (see table 1 for relative ages and references). 

Glass shards in a matrix of glass "dust" characterize 

the groundmass of the vitric tuffs (fig. 6). The shards 

are generally colorless and the matrix is either uniform 

pale brown(fig. 9)or irregular pale to dark brown (figs. 

7, 8). Degree of flattening and stretching of the shards 

is proportional to the density of the tuff. Shards are 

severely flattened near phenocrysts, where they "flow" 

in smooth parallel streaks around the crystal (figs. 

7-9). Minute voids between shards account for much 

of the porosity; in places, visible pores are sparse in 

rocks of relatively low density (fig. 7, specimen 153-4, 

density=l.833). The progressive compaction and flattening of the shards in the vitric tuffs is illustrated in a 

sequence of photomicrographs (figs. 6-9). 

Pumice occurs in a variety of forms. In tuffs of low 

density it occurs as highly porous ragged to lenticular 

) 
0 

GENERAL FEATURES 

118° ----------------------------------~ 

/ 

I 

I 

I 

I 

/ / 

// 

/ 

~ 

/ 

163 Little 

------------- -----

---

Lost Creek X 

S_ilver Ca(lyon 

6 MosquitoiF iat 1 "- I ~ 7 Mosquito Flat 2 

'\ \ \ 9 Devine Canyon 

X I I J~ x 158 1 1 ,r, 

wamp Creek /

1

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"' /I 1 ' / / ',, /// // / / 

Poison I 1 I 1{1 x

59 _Cree k \ 1

1

\ ,,, , 1 '6 \ ,,, \Lower\ ,\,',' ..... o· , ~Si vies' ... .-..... _,. \ ' '-....', '..?o ___ _ 

\: iver ~~~-~::~~~::u:~ '......, '-..... ...... _____ _._.....- t1 f 

'-..... I ~ .................... \ \ 

........... ' \ -.. '..?o ' 

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149 Jack Mou ntai n x 

-------------------'-------

x 148 Diamond 

153 X 

Dn nkwater X 154 

Pass D Ju ntura ~I 

0 R EG 

x 5 Black 

Butte 

\ 

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F IGURE 3.-Isopach map of welded tuff of Devine Canyon, showing locations of measured sections. Lines dashed where uncertain. 

fragments (fig. 10). In dense tuffs, it appear as palebrown to colorless glass in lenses or "knots" of small to 

nil porosity. 

Phenocrysts of alkali feldspar and quartz vary in 

amount from rare to very abundant. Nearly every thin 

section studied contains a few quartz and feldspar 
6 PETROLOGY OF THE WELDED TUFF OF DEVINE CANYON, SOUTHEASTERN OREGON 

TABLE 2.-Potassium-argon dates on the welded tuff of Devine Canyon 

Age (m.y) Sample No. Location Section. township, range Analyst and year (reference) 

8.5±0.3 ...................... GWW-176-62 Diamond Sec. 34, T. 29 S., R. 33 E. Kistler, Whitehead, and Schlocker 

(1963), in Greene and others (1972). 

8.9 .............................. KA122S Drinkwater Pass Sec. 34, T. 20 S., R. 36 E. Evernden (1964), in Evernden 

and others (1964). 

9.21±0.50 .................. RCG-248-66 Devine Canyon Sec. 16, T. 21 S., R. 31 E. Von Essen (1967), in Greene 

and others (1972). 

9.45± .21 .................. GWW-16-65 Swamp Creek Sec. 1, T. 22 S., R. 23 E. Engles and Lanphere (1966), in 

Greene and others (1972). 

9.7±0.3 ...................... GWW-140-61 Catlow Valley Sec. 26, T. 34 S., R. 29 E. Kistler and Walthal (1963), in Walker 

and Repenning (1965). 

FIGURE 4.---..Juntura section. Tuffaceous sediments at base of exposure, followed by 1 foot of bedded pumice. Welded tuff, 23 feet 

thick, all moderately dense vitric, somewhat brecciated at base. Platy horizontal joints dominant, suggestion of spheroidal 

weathering forms. 

phenocrysts that are euhedral (figs. 8, 15, 16), but the 

vast majority of phenocrysts show some rounding or 

embayment (figs. 7, 9, 14, 16, 17). Resorption effects 

show no apparent relation to position in the section, or 

to abundance of phenocrysts. A few percent of the 

phenocrysts in each thin section are broken fragments 

(figs. 9, 15, 16). Alkali feldspar is generally recognized 

by cleavage and twinning, but some is distinguished 

from quartz only with difficulty. 

Phenocrysts of ferro-magnesian minerals consist of 

very rare pyroxene and opaque minerals. Pyroxene 

crystals (fig. 8) are pleochroic in green and yellow 

green. Where unaltered, magnetite and ilmenite crystals are opaque and steel gray in reflected light; where 
GENERAL FEATURES 7 

FIGURE 5.-Drinkwater Pass section, 341f2 feet thick. Tuff is all of low density, densest in middle (fig. 20, sec. 153). Horizontal 

joints produce slabs in middle and upper parts; lower part of very low density disintegrates to small lumps, producing notch 

at base. 

FIGURE 6.-Photomicrograph of tuff from section 153, specimen 

1. Nonwelded vitric, crystal-poor basal part of section, round 

pores resemble vesicles. One phenocryst of feldspar (F) in 

right center. Plain light. 

altered, they are partly decomposed to other Fe-Ti 

oxides that appear brownish and translucent. 

DEVITRIFIED TUFF 

Devitrified tuff constitutes the central and most 

FIGURE 7.- P hotomicrograph of tuff from section 154, specimen 

4. Slightly welded vitric tuff, shards somewhat flattened, bend 

around phenocrysts. Euhedral alkali feldspar phenocryst (F) 

in center notably embayed; alkali feldspar phenocryst at 

bottom somewhat rounded. Ragged end of pumice lump in 

upper right corner. Plain light. 

voluminous part of the tuff sheet. Most of it is nonporous and has a density greater than 2.3. Where low 

in phenocrysts, the tuff is commonly uniform medium 
8 PETROLOGY OF THE WELDED TUFF OF DEVINE CANYON, SOUTHEASTERN OREGON 

FIGURE B.-Photomicrograph of tuff from section 154, specimen 

1. Moderately dense vitric tuff, shards substantially flattened 

and stretched. Pyroxene crystal (P) left center, dark margin 

is relief effect, margin is unaltered; ilmenite inclusions (I) 

top center and bottom of phenocryst. Alkali feldspar crystal 

(F) above pyroxene. Euhedral quartz crystal (Q) upper 

right has typical rhombic outline formed by pyramid faces, 

showing crystallization as ,8-quartz. Plain light. 

lmm 

FIGURE 9.-Photomicrograph of tuff from specimen 144. Dense, 

compact vitric tuff with flattened and stretched shards (colorless) and uniform, pale-brown glass matrix. Alkali feldspar 

phenocrysts (F) (white) rounded and fractured. Rock fragment (R) in bottom center is andesite; plagioclase phenocrysts visible against dark groundmass. Pyroxene crystal (P) 

in upper right. Plain light. 

gray (N-5) to light brownish gray (5 YR 6/1), tough 

and coherent, and weathers only to large blocks (figs. 

11, 12). Where richer in phenocrysts the rock is commonly streaked and mottled medium to light gray 

(N5-N7) with pinkish, yellowish, and greenish gray 

(5 YR 8/1, 5Y 8/1, 5GY 6/1). Such tuffs tend to disintegrate to hackly bits upon moderate weathering (fig. 

13). Devitrified tuff with density less than 2.3 is visibly 

porous, commonly light to very light gray (N7-8) or 

yellowish gray ( 5Y 8/1), and quite coherent; it characistically weathers into large blocks. 

The groundmass is a fine aggregate of light minerals 

with interstitial dark material. Where finest grained, it 

is dark brown and nearly opaque (fig. 15); where somewhat coarser, it is mottled light and dark browns. Shard 

structure is clearly evident in some samples (fig. 14) 

and faint (fig. 15) to obliterated (figs. 16, 17) in others, 

consisting only of faint parallel streaks around the 

corners of phenocrysts (fig. 16). Where shards are 

clearly defined, devitrification products are alined in 

parallel or spherulitic texture. 

Devitrification has affected pumice and phenocrysts 

in varying degree. Voids lined with a few crystals mark 

the position of completely collapsed pumice. Relatively 

coarse, light-colored aggregates also suggest relict 

pumice fragments. Feldspar and quartz phenocrysts are 

much like those in the vitric tuff. Pyroxene, magnetite, 

and ilmenite tend to be more decomposed and rimmed 

with dark-brown material. Rock fragments, recognizable as andesite in vitric tuff, are mostly dark and 

indeterminate in samples of devitrified tuff. 

LATERAL AND VERTICAL VARIATIONS 

MEASURED SECTIONS 

The welded tuff of Devine Canyon varies both laterally and vertically in density, phenocryst content, 

pumice content, and degree of devitrification. Data 

from 28 measured sections, and from additional localities near the margins of the tuff sheet, provide the basis 

for the major conclusions concerning these variations. 

The locations of the sections are shown in figures 3 and 

22, and the data for the sections, including thickness, 

devitrification, modes, and reciprocal density, are summarized in figures 18-21. 

At most of the measured sections, actual contacts 

with underlying units were not observed because these 

units are soft sediments and do not form good outcrops. 

However, the presence of vitric welded tuff, locally of 

lower density, in the lower parts of most sections suggests proximity to the base of the unit. Sections in 

which vitric bases are not exposed are mostly the 

thickest ones, located in the area north of Burns. These 

may indeed be somewhat thicker than shown in the diagrams and may show changes such as decrease in phenocrysts at their true bases; however, the discrepancy 

would not significantly affect the volume computations. 

The tops of most sections occur either at rims, where 

there are no overlying formations, or at covered intervals, above which is basalt or younger welded tuff. In 

some sections decreasing density or increasing pumice 

content at the top suggests proximity to the top of the 

ash flow. Little pumiceous or ashy sediment rich in 
LATERAL AND VERTICAL VARIATIONS 9 

F IGURE 10.-Basal part of Poison Creek section, No. 158 (figs. 12, 19). Length of hammer 11 inches, head 1 inch wide. Abundant 

pumice lumps 2-3 inches long, longest lump about 20 inches. Abundant phenocrysts of alkali feldspar and quartz distributed 

throughout both pumice and groundmass. 

alkali feldspar crystals appears in sediments younger 

than the welded tuff of Devine Canyon. Probably no 

more than a few feet of poorly welded ash-flow tuff has 

been excluded at the tops of measured sections. 

DEVITRIFICATION 

At most sections devitrified tuff overlies a relatively 

thin basal zone of vitric tuff with sharp contact, commonly represented by a notched or cavernous zone in 

the outcrop (fig. 11). Locally, however, as at the Poison 

Creek section (fig. 12; sec. 158, fig. 19), there is a transition zone of partly devitrified tuff. At a few sections 

(for example, sees. 110 and 164, fig. 18) vitric zones 

overlie a devitrified part. 

All sections less than 25 feet thick, and some up to 

35 feet thick, consist entirely of vitric tuff (figs. 18-21). 

A few sections between 25 and 35 feet thick are partly 

devitrified; this fact suggests that the ash-flow material 

that accumulated at these places was either hotter or 

richer in volatiles than that of the sections which 

remained entirely vitric (Smith, 1960a). 

DENSITY 

Density values have been determined for specimens 

from measured sections, and the reciprocal density (a 

measure of the degree of inflation, or percent pore space 

in the tuff) is plotted in figures 18-21 to the left of the 

bar representing the groundmass. The typical pattern 

of density variation is from low density at the base of a 

section, to higher density in the middle, to decreased 

density at the top. Some sections, however, have a fairly 

uniform high density throughout or have decreased 

density at the top or base (not both), with various 

minor fluctuations. All sections probably have at least 

a narrow zone of tuff of low density at both top and 

base that would show in the measured sections if 

exposure were perfect. 

Low density near the base implies cooling and welding beyond the point of possible further compaction 

before the deposition of much overlying tuff. This cooling and welding in turn suggests either multiple flow 

emplacement or very rapid cooling near the base. Tuff 

near the top is less dense because there was less overburden to compact it and because it was inflated by 

escaping volatiles. 

PHENOCRYSTS 

The variation in alkali feldspar and quartz phenocryst content is the outstanding feature of the welded 
10 PETROLOGY OF THE WELDED TUFF OF DEVINE CANYON, SOUTHEASTERN OREGON 

FIGURE 11.-Silvies Canyon section (fig. 19, sec. 160). A typical 

section, 82 feet thick, showing a composite of features. Small 

colwnns in vitric basal part (17 feet), discontinuous parting 

or notch separates devitrified main part with larger colwnns 

formed by more widely spaced joints. Gl's cavity zone near 

top. This section phenocryst-poor from base to top. 

tuff of Devine Canyon. Alkali feldspar phenocryst content ranges from about 1 to over 29 percent, generally 

increasing stratigraphically upward (figs. 18-23). 

Quartz phenocryst content ranges from 0 to 7 percent 

and follows much the same pattern as the alkali feldspar variations. The basal few feet of the welded tuff 

contains less than 10 percent alkali feldspar phenocrysts throughout most of its extent, but it contains 

much higher percentages in the central area, where the 

FIGURE 12.-Poison Creek section, reference section for welded 

tuff of Devine Canyon (fig. 19, sec. 158). Section, 104 feet 

thick, features even colwnnar joints from base to top. Transition zone vitric-devitrified tuff not marked by visible change. 

Crystal and pumice rich at base; both decrease upwards. 

Weathers to large blocks shown on slope below. 

tuff is thickest (fig. 22). Percentages are intermediate 

in the northwest and northeast. In most sections phenocryst content increases upward from the base, but in 

some it varies little from base to top (fig. 18, sec. 162; 

fig. 19, sec. 160; fig. 23, sees. A, B), and in a few it 

decreases upwards (fig. 19, sees. 9, 158, 159; fig. 23, sec. 

C), probably because of limited overturn of magma 

during ascent. 

Information from the measured sections and other 

localities has provided the basis for estimating the 

volume of the welded tuff with various proportions of 

alkali feldspar phenocrysts. The volume has been sepa-
SOURCE 11 

1 lmm 1 

FIGURE 14.-Photomicrograph of tuff from section 160, specimen 3. Devitrified tuff with well-developed flattened shards. 

Pyroxene crystal (P) right center with ilmenite crystals (I) 

at margin, light phenocrysts are alkali feldspar (F), stretched 

pumice lumps in top portion. Plain light. 

FIGURE 13.- Lower Silvies River section (fig. 19, sec. 159). Section is 85 feet thick. Very widely spaced jointing and abundant gas cavities a re features here, tuff is rich in phenocrysts. ... -

Base is a flood plain. Silvies River has carried away debris. lmm 

rately calculated for 0-5,6-10, 11-15, 16-20, 21-25 and 

over 25 percent phenocrysts (fig. 24) . The results reveal 

that, unlike more highly differentiated tuffs, such as 

those in southern Nevada (Lipman and others, 1966; 

Lipman and Christiansen, 1964; and others), a relatively high proportion of the welded tuff of Devine Canyon is rich in phenocrysts. This is believed to be owing 

to relatively rapid growth of phenocrysts and eruption 

of the magma, as discussed later. 

PUMICE 

Pumice content varies irregularly. In the more 

densely welded devitrified tuffs, pumice has commonly 

collapsed and has been reduced to mere streaks in the 

groundmass. Pumice contents are highest in the lower 

parts of sections in the central thickest and most 

crystal-rich part of the tuff. Two sections in the northern 

and several in the south-central part of the tuff sheet 

FIGURE 15.-Photomicrograph of tuff from section 163, specimen 3. Devitrified shards and pumice show only as faint, 

scattered residuals in groundmass. Phenocrysts are alkali 

feldspar (F); the larger ones euhedral, the smaller ones 

brokfin fragments. Plain light. 

have high pumice contents. In general, pumice content 

decreases towards the margins of the sheet, suggesting 

that it was winnowed out of the advancing ash flow 

before the ash reached its maximum extent (Fisher, 

1966). 

SOURCE 

Regional evidence does not point directly to a source 

area for the welded tuff of Devine Canyon, nor does it 

provide much indication of the shape or depth of the 

magma chamber. The isopach map (fig. 3) shows that 

the thickest part of the tuff is in the west-central part 

of the sheet, near Burns, which is at the northwest 
12 PETROLOGY OF THE WELDED TUFF OF DEVINE CANYON, SOUTHEASTERN OREGON 

1 lmm 1 

FIGURE 16.-Photomicrograph of tuff from section 9, specimen 

1. Abundant phenocrysts, mostly alkali feldspar (F), some 

quartz (Q); some euhedral, some rounded and embayed, some 

fragments. Very fine dark devitrified groundmass partially 

recrystallized (lighter parts). A few light streaky areas are 

pumice residuals. Plain light. 

lmm 

FIGURE 17.-Photomicrograph of tuff from section 158, specimen 3. Quartz phenocrysts (Q), left and right center, alkali 

feldspar (F) top and bottom. Devitrified groundmass has 

recrystallized to quartz and alkali feldspar with feathery 

texture, obliterating all vestiges of shard structure. Plain light. 

corner of the Harney Basin lowland (fig. 1). Regional 

mapping (Piper and others, 1939; Greene and others, 

1972; Greene, 1972) has shown the Harney Basin Lowland to be a down warped and downfaulted area. In particular, the sequence of Pliocene welded tuffs and sediments, including the Devine Canyon, Prater Creek, and 

Double 0 Ranch (table 1), dips southerly on the north 

side of the Harney Basin lowland and is covered by 

Quaternary sediments at the margin of the lowland. 

Thus, the source area is probably buried and cannot be 

exactly located. However, because the tuff is thickest 

and richest in crystals north of Burns, the most likely 

source area is considered to lie in the lowland immediately to the south, as indicated in figures 1 and 3. 

Downwarping of the Harney Basin Lowland may be 

in part related to the expulsion of large volum~s of 

magma from beneath. The welded tuffs of Devine 

Canyon, Prater Creek, and Double 0 Ranch probably 

amount to over 100 cubic miles in total volume and all 

may have come from beneath the lowland. The fact that 

the lowland is such a large down warped area (about 

1,000 sq mi) and no smaller collapse features have been 

identified, suggests that the magma bodies that erupted 

to form these tuffs were most likely of broad, discoidal 

shape rather than thick cylinders. 

PETROLOGY 

MINERALOGY 

The microscopic appearance of vitric and devitrified 

groundmass in specimens of this tuff has already been 

described. X-ray patterns show groundmass minerals 

in devitrified tuff to be alkali feldspar, cristobalite, 

quartz, and, more rarely, tridymite. Alkali feldspar is 

ubiquitous and may be accompanied by one, two, or all 

three of the silica minerals. In the finest grained, irresolvable groundmass, cristobalite is found (fig. 15); 

where any bladed, spherulitic, or axiolitic textures 

appear, quartz is present (fig. 17). Tridymite appears 

as spongy masses lining small cavities. 

Alkali feldspar.-Alkali feldspar phenocrysts are 

present in all of the tuff and are its most distinctive 

feature. Amounts range from less than 1 (fig. 6) to 29 

percent (fig. 16). In each thin section there are a few 

euhedral grains showing (100), (010), (001), (110), 

(101), a majority of grains with some faces and some 

rounded and embayed surfaces, and some broken fragments (fig. 6-9, 14-17). Carlsbad twins are rare, but 

almost all grains show faint grid twinning near extinction. Refractive indices, determined on several grains 

from sample GWW-140-61 (Catlow Valley, near 

southern limit of tuff sheet), using the spindle stage, 

are al.523-4, (31.528-9, y1.529-30. The 2V's on grains 

from the same sample ranged from 34 ° to 37° (-). 

Chemical analyses of two samples (table 3) show that 

both have a composition close to Or12Ab57Ano.G· Feldspar of this composition and high-temperature origin 

is generally termed sanidine. The monoclinic-triclinic 

field boundary is placed at Or37Ab63 ; the more potassic 

monoclinic feldspars are called sanidine and the more 

sodic triclinic feldspars, anorthoclase (Smith and 

MacKenzie, 1958, p. 874). 

Quartz.-Quartz phenocrysts, like alkali feldspar, 

are ubiquitous. They range in amount from less than 1 

to 7 percent. As seen in thin section, they are euhedral, 

rounded and embayed, or angular fragments. Euhedral 

crystals commonly show prism faces doubly terminated 
I . 

. ' 

. 

. 

164. Swamp 

Creek 

PETROLOGY 

157. Flat Creek 

80 

60 

Vitric 

groundmass 40 

ground 

Devitrified 

-

mass 

20 

0 .6 0.5 0.4 

13 

EXPLANATION 

Alkali feldspar 

D 

Quartz 

Pumice 

10 20 30 

RECIPROCAL DENSITY, CUMULATIVE VOLUME 

IN CUBIC CENT!- OF CRYSTALS OR 

11 0. Foundation Creek METERS PER GRAM PUMICE, IN PERCENT 

163. Little Emigrant Creek 

11 . Sawtooth Creek 

162. Skull Creek 

FIGURE 18.-Measured sections of welded tuff of Devine Canyon, northwestern part. Central bar of each diagram shows thickness 

of section and devitrification of groundmass. Line to left indicates reciprocal density; patterns to right, cumulative volume 

percent of crystals or pumice. 
GALLEY 16--.......... ·-······· GOV. PTRG. OFF.-MBT-10 Prof Paper 979 AC's-3-27-73-2-Pacific Typo 12443 ....... . 

14 PETROLOGY OF THE WELDED TUFF OF DEVINE CANYON, SOUTHEASTERN OREGON 

2. Hall Creek 

160. Silvies Canyon 

6. Mosquito FIat 1 

7. Mosquito Flat 2 

1. Lost Creek 

~ •

.. :.:-:·:-:-:·> :· .. "'··· 

-:-:-:-:-:-:-:-:-. ::.·: 

I I < .. ·· 

3. House Creek 

9. Devine Canyon 

EXPLANATION 

FEET 

100 

80 

60 Alkali feldspar 

158. Poison Creek Ill 

159. Lower Silvies 

River 

Vitric 

ground mass 40 

Ill 

Devitrified 20 

ground mass 

0.7 0.6 0 .5 0.4 

RECIPROCAL DENSITY. 

IN CUBIC CENTIMETERS 

PER GRAM 

Quartz 

Pumice 

10 20 30 

CUMULATIVE VOLUME 

OF CRYSTALS OR 

PUMICE, IN PERCENT 

FIGURE 19.-Measured sections of welded tuff of Devine Canyon, north-central part. Central bar of each diagram shows thickness 

of section and devitrification of groundmass. Line to left indicates reciprocal density; patterns to right, cumulative volume 

percent of crystals or pumice. 
4. Crane 

PETROLOGY 

153. Drinkwater Pass 

154. Juntura 

EXPLANATION 

FEET 

80 

60 

5. Black Butte Alkali feldspar 

143. Coyote Creek 

Vitric 

ground mass 40 

Quartz 

- 20 

Devitrified 

ground mass Pumice 

0 .9 0.8 0.7 0.6 0.5 0.4 10 20 30 

CUMULATIVE VOLUME 

OF CRYSTALS OR 

PUMICE, IN PERCENT 

RECIPROCAL DENSITY, 

IN CUBIC CENTIMETERS 

PER GRAM 

142. Spurlock Ranch 

II 

141. Crowley 

15 

FIGURE 20.-Measured sections of welded tuff of Devine Canyon, eastern part. Central bar of each diagram shows thickness of section and devitrification of groundmass. Line to left indicates reciprocal density; patterns to right, cumulative volume percent 

of crystals or pumice. 
16 PETROLOGY OF THE WELDED TUFF OF DEVINE CANYON, SOUTHEASTERN OREGON 

EXPLANATION 

Ill 

Vitric 

ground mass 

-

FEET 

60 

40 

Devitrified 20 

ground mass 

L__j_ 

0 .7 0.6 0.5 0.4 

RECIPROCAL DENSITY, 

IN CUBIC CENTIMETERS 

PER GRAM 

Alkali feldspar 

Quartz 

Pumice 

10 20 30 

CUMULATIVE VOLUME 

OF CRYSTALS OR 

PUMICE, IN PERCENT 

149. Jack Mountain 

151. Keg Springs 

Val ley 

L_~~~~~~~~~------

150. Frenchglen 

147. Windy Point 

146. Malheur Cave 

140. Folyfarm 

148. Diamond 

FIGURE 21.-Measured sections of welded tuff of Devine Canyon, southern part. Central bar of each diagram shows thickness of 

section and devitrification of groundm.ass. Line to left indicates reciprocal density; patterns to right, cumulative volume percent of crystals or pumice. 
440 

PETROLOGY 17 

119° 118° r-----------~------------~~------------------------~ 

EXPLANATION 

Percentage of alkali feldspar 

phenocrysts 

D 

0-5 

D 

6-10 

11-15 

-

16-20 

a 

21-28 

A A' 

Cross section shown in 

tig).Jre 23 

x159 

Location and number of measured section 

X 

Other sample localities 

-----------

I 

I 

I 

I 

I 

I 

---

FIGURE 22.-Alkali feldspar phenocrysts in basal few feet of tuff sheet. 
18 PETROLOGY OF THE WELDED TUFF OF DEVINE CANYON, SOUTHEASTERN OREGON 

163 110 projected 157 

A 

FEET 

EXPLANATION 

157 

I 

Lo cation and number of measu red section 1:0: j ___ __j__ 10 _ _ ___j_ 20 __ _ 30 MILES 

I I I 162 160 3 

8 

164 159 158 9 153 154 

149 projected 147 146 projected 141 

151 149 

FIGURE 23.-Cross section illustrating variations in alkali feldspar phenocryst content. (See fig. 22.) 

TABLE 3.-Analyses of alkali feldspar phenocrysts from the 

welded tuff of Devine Canyon 

[Partial chemical analyses for SiO,, AJ,Q,, Fe,O,, CaO, Na,O, and K,O, by Lois M. Jones and Lois B. Schlocker. Quantitative spectrographic analyses for Sr and Ba by R. E. Mays. Quantitative spectrographic analyses for Li, 

Cs, and Rb by Harry Bastron] 

WT 6 Windy Point 

SiO, .................................... 67.5 

Al,O, .................................. 18.4 

Fe,O,' ................................ .47 

CaO .................................... .11 

Na,O .................................. 6.2 

K,O .................................... 7.0 

Sr........................................ .0026 

Ba ...................................... .016 

Li ........................................ .0002 

Rb ...................................... .004 

Normative values: 

An.................................. .55 

Ab .................................. 57.1 

Or .................................. 42.4 

1

Total iron expressed as Fe-.!03. Cs not detected. 

140-61 Catlow Valley 

67.5 

18.5 

.36 

.13 

6.2 

6.8 

.0040 

.022 

.0003 

.004 

.67 

57.8 

41.7 

by pyramid faces at the ends, suggesting crystallization 

as beta-quartz (fig. 8, pyramid faces only). 

Clinopyroxene.-Sparse clinopyroxene phenocrysts 

are visible in about two-thirds of the thin sections studied and are probably sparsely distributed throughout 

the tuff. The tiny crystals can rarely be seen in hand 

specimen. In thin section, the clinopyroxene is pleochroic from dark to pale green where fresh, or pale green 

to colorless where altered. Some crystals are rimmed 

with a dark to opaque margin, probably owing to oxidation during eruption. Characteristic pyroxene cleavage 

is visible, and faces of the forms (100), (101), (101) 

(fig. 8), ( 010), and ( 110). Refractive indices and optic 

angles (table 4) indicate compositions of Wo21E14FSa9 

and Wo38Fs62 for two samples (Hess, 1949). X-ray 

single crystal and powder data for one sample (table 5) 

indicate a composition of Wo42EnsFSso (Brown, 1960). 

The high refractive indices are responsible for the 

higher Fs content indicated by the optical data. However, all determinations fall in the ferrohedenbergite 

field according to Poldervaart and Hess' nomenclature 

(1949). 

BULK COMPOSITION 

ANALYSES 

Analyses of 14 samples of the welded tuff of Devine 

Canyon (table 6) indicate that in terms of composition 

TABLE 4.-0ptical properties of pyroxene from welded tuff 

of Devine Canyon 

Sample 148-3 163-1 162-2 

a 1.726-32 1.731-5 

f3 .............. 1.743-7 1.740--5 1.744--8 

y 1.762-5 1.761 

2V ............ 53°-54° 61°-62° 
PETROLOGY 19 

13 

Total volume, 4 7 cub ic miles. 

12 Equivalent to a cube 3.6 

mi les on edge. 

Area covered, 7,200 square 

miles. 

Average thickness, 35 feet. 

(/) 

UJ 

--' 

~ 

u 

a:J 

::J 

u 

~ 

w 6 

~ 

::J 

--' 

0 

> 

4 

0 5 10 15 20 25 30 

PERCENTAGE OF ALKALI FELDSPAR PHENOCRYSTS 

FIGURE 24.-Histogram showing relative volumes of tuff 

with various phenocryst contents. 

the vitric and devitrified tuffs each from a rather 

homogeneous group. Vitric tuff has less NazO, less Si02, 

more K20, and more H20 + than devitrified tuff, probably as a result of selective leaching of Na from the 

vitric tuff by ground water (Lipman, 1965). Na is 

replaced by K. Water remains in the structure, its 

added weight causing a decrease in the weight percent 

of the most abundant component, Si02. Slight increase 

of AlzOa in the vitric tuffs, as suggested by Lipman, is 

not borne out by these data; iron is generally less 

oxidized. 

Inasmuch as there is no nonhydrated glass, the devitrified tuffs best represent magmatic compositions (Lipman and others, 1969). Since the Na20 contents of 

these tuffs range from 3. 7 to 4.3 percent (table 6), they 

are unlikely to have lost Na during crystallization as 

did the comendite tuffs, with initial Na contents over 

5 percent, that Noble (1970b) described. Compositions 

TABLE 5.-X-ray diffraction data for pyroxene from sample 148--3 

[Analyses by R. C. Erd. Chart X3417, ilmenite peaks abstracted; Cu/Ni, 

Si internal standard; '-A, 0

, 1,4" /minute] 

Calculated Measured Calculated Measured 

d (A) d (A) d (A) d (A) 

hkl hkl hlcl I hkl hkl hlcl 

110 6.531 6.524 88 112 2.216 

200 4.735 4.735 36 222 2.202 

020 4.509 4.507 10 022 2.199 

Iu 4.404 330 2.177 2.176 26 

111 3.672 331 2.149 2.147 22 

021 3.360 3.358 4 421 2.123 2.120 16 220 3.266 3.265 58 420 2.096 

221 3.007 3.008 66 041 2.058 2.058 4 

310 2.980 2.979 100 240 2.036 

311 2.909 2.905 14 402 2.017 2.017 8 

130 2.865 202 2.010 

l31 2.583 2.584 14 132 1.973 

221 2.534 2.534 28 241 1.968 

202 2.523 511 1.910 002 2.518 

l12 

331 1.876 

2.512 510 1.854 1.854 6 

131 2.408 422 1.841 400 2.368 2.367 4 222 1.836 311 2.319 1.772 22 040 2.255 2.254 1 1.637 36 

312 2.222 1.633 36 

1.579 10 

1.566 18 

1.536 8 

1.503 10 

1.468 3 

1.418 6 

A. Precession data: a (A)=9.830 

C z/c b =9.014 /3=105°34' c =5.250 B. X-ray powder data: (least squares refinement) a (A) =9.834±0.002 

b =9.018±0.001 =105°37'±2' c =5.320±0.004 Vol. (A') =446.7±0.3 c. b: c = 1.090: 1:0.5800 a sin /3=9.470A 

C. X-ray fluorescence shows (pyroxene+ilmenite) 

Major Fe>>Ca MinorTi>Mn D. d-spacings of associated ilmenite (chart X3417) indicate near end mem- ber ilmenite (Berry and Thompson, 1962, p. 175; Deer, Howie, and Zussman, 1962, p. 31). E. Crystal chosen had forms [100], [010], [110] F. Compare with data for augite from Kahanui, New Zealand (Clark and others, 1969, p. 34, table 2); also note large cell volume. G. Diagram of Brown (in Deer and others, 1962, p. 111) gives Wo.2 Ens Fsoo from powder data, and W043 Ento Fsn from precession value for b. 

of the devitrified tuff form a closely knit group that fall 

partly in the soda rhyolite field and partly in the alkali 

rhyolit~ field on Rittman's diagrams (1952). 

Semiquantitative spectrographic analyses (table 7) 

reveal only minor fluctuations in trace elements from 

sample to sample, except that some samples relatively 

rich in calcium are also high in strontium and barium. 

NORMS 

Computer-calculated CIPW norms of the 14 analyzed samples (table 8) show that quartz, orthoclase, 

and albite are the major normative components. Proportions of orthoclase and albite vary between vitric 

and devitrified samples, as do the K20 and Na.O contents, although further complications, such as Al20a 

content, affect these normative components in some 

samples. 

In eight samples there is insufficient Al20a to use up 

all the Na20 in albite, and the excess Na20 appears as 
20 PETROLOGY OF THE WELDED TUFF OF DEVINE CANYON, SOUTHEASTERN OREGON 

TABLE 6.-Rapid rock analyses of vitric and devitrified welded tuff of Devine Canyon 

[Samples 147- 1, 160- 1, 154- 1, 147- 3, 151-2, and 160- 4 analyzed by P. Elmore, G. Chloe. J. Kelsey, S. Botts, H. Smith, L. Artis, and J. Glenn by method described by Shapiro ( 1967). Other samples analyzed by P. Elmore, H . Smith, G. Chloe, J. Kelsey, and J. Glenn by method described by Shapiro and Brannock ( 1962), 

supplemented by atomic absorption] 

Sample ................... 147-1 160- 1 154- 1 Section ....... --------·---···-··· Windy Point Silvies Canyon Juntura Vitric Vitric Vitric 

SiO, ........................ 73.2 73.8 73.8 

Al,O, ---------------------- 10.6 11.4 11.0 

Fe,O, ...................... 2.6 1.0 2.2 

FeO -------·-··············· .62 .86 .78 

MgO ·······-······-------- .37 .10 .10 

CaO ........................ .44 .24 .30 

Na,O ------·-·············· 3.4 3.4 3.0 

K,O ········-·········--···· 5.1 5.0 5.6 

H,O+ --·······---········ 2.7 2.5 2.6 

H,O- -------------------- .76 .17 .25 

TiO, ........................ .18 .19 .18 

P.o •........................ .02 .02 .02 

MnO ··············-------- .04 .03 .04 co •.......................... <.05 <.05 <.05 

Sample 151- 2 149-3 149- 5 Section Keg Spr ings Jack Mountain Jack Mountain Valley Devitrified Devitrified Devitrified 

SiO, ........................ 74.2 75.4 75.3 

Al,O, -------------··-······ 11.0 11.0 12.0 

Fe,O, ...................... 3.2 .60 .76 

FeO ·······-················ .02 .60 .76 

MgO -·······-----·-·····-- .31 .10 .10 

CaO ........................ .83 .25 .31 

Na,O ····-·········-······· 4.3 4.0 3.7 

K,O ············-------·-··· 4.3 4.5 4.9 

H,O+ ···-··········--·--- .75 .75 .53 

H,O- ··················-- .55 .55 .27 

TiO, ........................ .20 .21 .24 

P,O •........................ .06 .08 .06 

MnO ·············--------- .05 .05 .04 co ........................... <.05 <.05 <.05 

acmite. This has no relationship to the mode, as the 

small amount of clinopyroxene present is nonsodic. 

Plots of the normative feldspar components on the 

lower central part of the An-Or-Ab triangular diagram 

(fig. 25) reflect the secondary K20-Na20 variations 

discussed above. The vitric tuffs have more than 50 

percent orthoclase, and the devitrified ones have more 

than 50 percent albite. The reason that a few samples 

contain normative anorthite is that their Al20 3 (not 

147- 3 4-7 4-12 4- 16 Windy Point Crane Crane (4-ane Devitrified Devitrified Devitrified Devitrified 

75.2 74.1 75.0 75.1 

10.8 10.9 11.0 11.4 

2.8 2.8 3.2 2.5 

.46 .36 .76 .36 

.29 .35 .13 .20 

.25 .69 .30 .42 

4.2 4.0 4.0 4.1 

4.4 4.6 4.5 4.6 .91 .83 .54 .70 

.49 .83 .54 .70 

.18 .14 .18 .14 

.03 .09 .10 .04 

.04 .06 .07 .06 

<.05 <.05 <.05 <.05 

160- 4 9-1 9-3 9-6 Silvies Canyon Devine Canyon Devine Canyon Devine Canyon Devitrified Devitrified Devitrified Devitrified 

75.3 75.2 73.6 74.1 

11.4 11.6 11.2 12.0 

3.0 1.6 2.1 2.2 .00 1.6 .56 .76 

.18 .13 .83 .24 

.43 .25 .77 .34 

4.3 3.7 3.8 4.0 

4.2 4.4 4.5 4.6 

.57 .57 .87 .67 

.40 .53 .53 .63 

.19 .21 .26 .28 

.04 .03 .06 .06 

.04 .08 .07 .07 

<.05 <.05 <.08 <.05 

CaO) content is higher than the others. The normative 

composition of the feldspar from sample GWW-140-61 

(table 3) falls among the group of normative feldspar 

components from devitrified tuffs; this fact suggests 

that phenocryst feldspar and groundmass feldspar are 

similar in composition. 

The ratios of normative quartz-orthoclase-albite for 

the devitrified tuffs plot in a loose cluster on the Q-OrAb triangle (fig. 26). The fact that Q+Or+Ab totals 

TABLE 7.- Semiquantitative six-step spectrographic analyses of some samples of the welded tuff of Devine Canyon 

[In ppm. N = nol detected. Looked for but not detected: Ag, As, Au, Bi, Cd, Co, Ni, Pd, Pt, Sb. Sc, Sn . Tc, U, W, Zn, Ge, Hf, In, Li, Re, Ta, Th, Tl, Pr, Sm, En, Gd, Tb, Dy, Ho, Er, Tm, Lu. Samples 147- 1, 160 1, 154- 1, 147-3, 151-2, and 160- 4 analyzed by R. E. Mays. Other samples analyzed by Chris Heropoulos] 

Sample 147-1 160- 1 154-1 147-3 4-7 4- 12 4-16 Section · : : :::Windy Point Silvies Canyon Juntura Windy Point Crane Crane Crane Vitric Vitric Vitric Devitrified Devitrified Devitrified Devitrified 

B ················-····--····· 50 50 50 50 50 30 50 

Ba ·········-····-····-···--- 30 70 30 30 150 50 100 

Be ···················-···-·- 7 7 7 7 7 7 7 

Cr. ·····················-···- N N N N 1.5 1 1 

Cu ··········-··············- 15 10 15 15 10 7 7 

La ·········-·········-·-···- 100 70 100 50 150 100 100 

Mo .......................... N N N N N N N 

Nb -·····-···········-······· 100 100 100 100 50 70 70 

Ni ········-·--····-··-··-·-· 20 20 20 20 N N N 

Pb ··········-·····-·--·--·-· 50 50 50 50 30 30 50 

Sn ............................ N N N N N 7 7 

Sr ............................ 10 7 N N 30 10 15 

v ··········--·······-········ N N N N 10 7 10 

y ···················-···-··-· 200 150 150 150 150 150 100 

Zr ............................ 1,500 1,500 1,500 1,500 1,000 1,000 1,000 

Ce ............................ N N N N 150 150 150 

Ga -············ ··-·-····· ··- 30 30 30 30 50 30 30 

Yb ··· ··-·····-····--··-··· ·- 20 20 20 20 15 15 15 

Nd ···············-·····-··-· N N N N 100 70 100 
PETROLOGY 21 

TABLE 7.-Semiquantitative six-step spectrographic analyses of some samples of the welded tuff of Devine Canyon-Continued 

Sample ........................... 151-2 Section ........................... Keg Springs 

B ···························· Ba ·········-··············· Be ......................... . Cr ........................... . Cu ......................... . La ......................... . Mo ......................... . Nb ......................... . Ni ........................... . Ph ......................... . Sn ......................... . Sr ........................... . v ........................... . y ........................... . Zr ........................... . Ce ......................... . Ga ......................... . Yb ......................... . Nd ......................... . 

Valley 

Devitrified 

50 

70 

7 

N 

20 

50 

N 

100 

20 

50 

N 

20 

N 

150 

1,500 

N 

30 

20 

N 

149-3 Jack Mountain Devitrified 

50 

70 

5 

1.5 

7 

100 

5 

50 

N 

20 

N 

15 

7 

150 

1,000 

200 

30 

15 

100 

149-5 Jack Mountain Devitrified 

20 

200 

3 

1 

5 

150 

5 

30 

N 

20 

N 

15 

7 

70 

700 

200 

30 

10 

100 

160-4 Silvies Canyon 

Devitrified 

50 

70 

7 

N 

15 

70 

N 

100 

20 

50 

N 

20 

N 

150 

1,500 

N 

30 

15 

N 

9-1 

Devine Canyon 

Devitrified 

30 

200 

5 

3 

7 

150 

N 

30 

N 

30 

N 

15 

N 

100 

700 

200 

30 

10 

150 

9-3 

Devine Canyon 

Devitrified 

30 

300 

2 

3 

7 

100 

N 

30 

N 

10 

N 

70 

10 

70 

500 

200 

20 

7 

100 

9-6 Devine Canyon 

Devitrified 

20 

200 

3 

3 

7 

200 

N 

50 

N 

20 

N 

30 

7 

100 

700 

300 

30 

10 

150 

TABLE B.-Norms of analyzed samples of vitric and devitrifiedwelded tuff of Devine Canyon 

Sample ........................... 147-1 Section ........................... Windy Point 

Q ........................... . c ........................... . Or ........................... . Ab ......................... . An ......................... . Ac ......................... . Wo ......................... . En ......................... . Fs ........................... . Mt ......................... . Hm ....................... . II ........................... . Tn ......................... . 

Ap ·························· Q+Ab+Or ......... . 

Vitric 

33.5 

30.1 

26.1 

2.3 

.87 

.92 

1.6 

.69 

.34 

.47 

89.7 

Sample ........................... 151-2 Section ............... ............. Keg Springs 

Q ···························· c ........................... . Or ........................... . Ab ......................... . An ......................... . Ac ......................... . Wo ......................... . En ......................... . Fs ......................... . Mt ......................... . Hm ....................... . II ........................... . Tn ......................... . 

Ap ·························· Q+Ab+Or ......... . 

Valley 

Devitrified 

32.4 

25.5 

32.7 

3.3 

1.4 

.77 

2.1 

.15 

.30 

.14 

90.6 

160-1 Silvies Canyon 

Vitric 

34.5 

.007 

29.9 

29.1 

1.1 

.25 

.50 

1.47 

.37 

.05 

93.5 

149-3 Jack Mountain Devitrified 

35.3 

26.7 

31.7 

2.05 

.30 

.25 

1.5 

.3 

.40 

.19 

93.7 

154-1 

Juntura 

Vitric 

34.5 

33.1 

25.4 

.01 

.56 

.23 

1.83 

.94 

.53 

.05 

93.0 

149-5 Jack Mountain Devitrified 

34.4 

.19 

29.0 

31.3 

1.1 

.25 

1.9 

.4 

.46 

.14 

94.7 

90 percent or more in each case shows that these points 

approximate the magma composition. 

GROUNDMASS COMPOSmON 

Major-element groundmass compositions have been 

calculated for several of the analyzed devitrified tuffs 

(table 9). These calculations show that the composition of the groundmass is similar to that of the bulk 

rock in rocks with few phenocrysts but significantly 

different in rocks with many. In phenocryst-rich rocks 

the groundmass contains more Si02 and less Al20 3 , 

147-3 Windy Point Devitrified 

34.3 

26.0 

31.0 

3.9 

.39 

.72 

1.1 

.68 

.34 

.07 

91.3 

160-4 Silvies Canyon 

Devitrified 

32.9 

24.8 

35.2 

2.5 

.57 

.45 

2.1 

.09 

.36 

.10 

92.9 

4-7 

Crane Devitrified 

33.0 

27.3 

30.6 

3.0 

1.2 

.88 

1.0 

1.1 

.27 

.21 

90.9 

9-1 

Devine Canyon 

Devitrified 

35.6 

.37 

26.0 

31.3 

1.0 

.32 

1.4 

2.3 

.40 

.07 

92.9 

4-12 

Crane Devitrified 

34.7 

26.6 

31.5 

2.0 

.35 

.32 

2.2 

1.0 

.34 

.23 

92.8 

9-3 

Devine Canyon 

Devitrified 

32.5 

26.8 

32.4 

.2 

1.35 

2.09 

1.3 

1.2 

.50 

.14 

91.7 

4-16 

Crane Devitrified 

33.4 

27.2 

33.1 

1.5 

.76 

.50 

1.0 

1.3 

.27 

.10 

93.7 

9-6 Devine Canyon 

Devitrified 

32.3 

27.2 

33.9 

1.2 

.04 

.60 

1.9 

.9 

.53 

.14 

93.4 

Na20, and K20 than the rock as a whole. This indicates 

a loss of feldspar components and a corresponding 

increase in silica in the groundmass (that is, the feldspar-silica mineral ratio is higher in phenocrysts than 

in the groundmass1 ). 

The groundmass compositions of the phenocrystrich rocks also differ significantly from the average 

bulk-rock composition (table 9), but the bulk-rock 

compositions of these same rocks do not differ signifi1This ratio is between 2 and 20 for phenocrysts from most samples. Feld- spar-silica ratio of average whole-rock normative composition is 1.74. 
22 PETROLOGY OF THE WELDED TUFF OF DEVINE CANYON, SOUTHEASTERN OREGON 

60 35 55 40 50 

Ab 

~~~--------~~ 

50 40 55 35 60 

Or 

~ 

14 7 ~-1 ----"-1-54~ -1 -------"-----------------''---0 

X 

EXPLANATION 

0 0 

Sample with vitric groundmass Sample with devitrified groundmass Feldspar sample 

FIGURE 25.-Normative feldspar components of analyzed samples plotted on part of the feldspar triangle. 

Includes normative components of one analyzed sample of alkali feldspar phenocrysts. 

40. 

I 

25 

35 

\ 

\ I 

I 

I 

30 

30 

Q 

t 

I 

\ 

35 

I 

40 45 

~ 

Or 

EXPLANATION X 0 

Sample with vitric groundmass Sample with devitrified groundmass 

FIGURE 26.-Normative compositions of analyzed samples in the system Q-Or-Ab. Curved lines represent isobaric minima in this system, after Tuttle and Bowen (1958, p. 75), at various water pressures, given in bars. Position of thermal minima indicated by dash or ternary intersection. 

cantly from the average. These relationships are illustrated by normative compositions in the system 

Q-Or-Ab (fig. 27). Phenocryst compositions fall in the 

bottom part of the diagram and groundmass compositions in the top part. The whole-rock compositions of 

the samples plot in the center on tielines (not drawn) 

connecting phenocrysts and groundmass, and cluster 

closely about the position of the average of the wholerock samples. 

The rocks rich in phenocrysts must be the products of 

crystallization of the magma now represented by their 

own groundmasses and could not have formed by crystal settling. If crystal settling had occurred, the wholerock compositions would vary more. Those rocks that 

had lost phenocrysts would plot on the opposite side of 

the average (or "original") composition from the 
INTERPRETATION OF MAGMATIC HISTORY 23 

Q 

t 

50 

EXPLANATION 

40 

0 

Average whole rock 

6. 

Whole rock 

Phenocrysts 

0 

Groundmass 

~Or 

30 

FIGURE 27.-Nonnative compositions of whole rock, phenocrysts, and groundmass for samples of table 9 in the 

system Q-Or-Ab. 

phenocryst composition, and those that had gained 

phenocrysts would plot on the side toward the phenocrysts.2 

INTERPRETATION OF MAGMATIC HISTORY 

The welded tuff of Devine Canyon grades upward 

from a phenocryst-poor base to a phenocryst-rich upper 

part, but the bulk composition does not vary significantly with the phenocryst content. In this way it 

differs from the tuffs of southern Nevada (Lipman and 

others, 1966; Hinrichs and Orkild, 1961; O'Connor, 

1963; Noble and others, 1964), most of which grade 

upward from a crystal-poor rhyolitic base to a crystalrich quartz latitic cap rock. In the southern Nevada 

tuffs, the magma chamber was apparently zoned in the 

reverse sense-rhyolitic at the top, quartz latitic at 

greater depth. 

The Q-Ab-Or diagram for the welded tuff of Devine 

Canyon (fig. 26) seems at first glance to exhibit a trend 

2Demonstration of crystallization in place in the magma column has been 

dependent on the greater feldspar-silica ratio in the phenocrysts than in the 

groundmass. If the ratio were the same in each, all points on figure 27 would 

cluster in the center, and whether or not settling had taken place would be 

indeterminate from considerations in the Q-Or-Ab system. 

in some of the samples, in particular, from samples 9-6 

to 9-1. However, although 9-1 is at the base of the 

Devine Canyon section, it is very rich in phenocrysts 

and is probably a relatively late eruptive product rather 

than a sample from the top of magma column (Lipman 

and others, 1966, p. F42). The others in this "trend" 

are also in confused order. Most of the variations in the 

position of points on this diagram are due to variations 

in content of Al2 0 3 or CaO or in the oxidation state of 

iron. The method by which norms are calculated causes 

these factors to affect the Or-Ab ratio and the Q 

content. 

It is apparent from the foregoing that the preeruption magma column was zoned as to phenocryst content 

but uniform in bulk composition. The lower levels of the 

column were simply in a more advanced state of crystallization. 

Kennedy (1955) points out that water diffuses in a 

magma chamber so that its chemical potential (for 

practical purposes, its partial pressure) is uniform 

throughout. This means that water will be concentrated near the top and edges of the chamber owing to 

lower temperature, and gradually decrease downward 

owing to increase in both temperature and confining 

pressure. It follows that magma will be saturated with 

water only at the top and edges, and elsewhere will be 

undersaturated. 

Thus, in the Devine Canyon magma, although the 

increase in temperature with depth would have tended 

to inhibit crystallization, the accompanying decrease in 

water content apparently offset this and allowed crystallization to proceed rapidly at depth. Subsequent 

events leading to eruption followed before enough time 

had elapsed for significant crystal settling. 

The possibility of determining the water pressure 

obtained just prior to eruption of an ash-flow tuff by 

use of .-the experimental data of Tuttle and Bowen 

(1958) has been considered by Lipman (1966) and 

Noble (1968). Lipman plots the normative Q-Ab-Or 

proportions of samples of several compositionally zoned 

welded tuffs from southern Nevada on the triangular 

diagram of these components and superposes the isobaric lines and thermal minima of Tuttle and Bowen 

(1958). The plots (Lipman, 1966, figs. 1-5; Lipman 

and others, 1966, fig. 26) show a differentiated series 

following a fractional crystallization path toward a 

thermal minimum at pressures ranging from 500 to 

1,200 bars for several different ash-flow tuffs. He concludes that the positions of the points representing the 

most silica-rich rocks in these series represent the probable preemption water pressure. 

An important problem, however, is whether or not 

the ash-flow magmas considered are saturated with 
TABLE 9.-Average composition of analyzed devitrified tuffs and calculated partial groundmass compositions of selected devitrified tuffs 

Average in percent, 11 devitrified tuffs: 

Si02 AhOa F~Oa FeO MgO CaO Na20 K20 H20+ H20- Ti02 P205 

74.8 11.2 2.5 .57 .26 .44 4.0 4.5 .70 .45 .20 .06 

Sample 147-3 151-2 160-4 4--16 149-3 149-5 

Difference Difference Difference Difference Difference Difference 

Ground- from Ground- from Ground- from Ground- from Ground- from Ground- from Ground- mass• whole rock mass whole rock mass whole rock mass whole rock mass whole rock mass whole rock mass 

Si02 ...................................................... 75.3 +0.1 74.5 +0.3 75.0 -0.3 75.7 +0.6 76.4 +1.0 75.6 +0.3 76.6 

Al20a ...................................................... 10.6 -.2 10.7 -.3 11.1 -.3 10.4 -1.0 10.0 -1.0 10.7 -1.2 9.0 

Fe20a2 •••••••••••••••••••••••••••••••••••••••••••••••••••• 3.4 +.2 3.4 +.2 3.4 +.4 3.5 +.6 3.3 +.6 3.8 +1.3 5.4 

MgO ...................................................... .30 +.01 .33 +.02 .20 +.02 .25 +.04 .12 +.02 .16 +.04 .2 

CaO ...................................................... .26 +.01 .89 +.06 .48 +.05 .5 +.08 .29 +.04 .44 +.13 .35 

Na20 .................................................... 4.1 -.1 4.3 0 4.3 0 3.8 -.3 3.7 -.3 3.1 -.6 2.7 

K20 ........................................................ 4.3 -.1 4.2 -.1 4.1 -.1 4.3 -.3 4.2 -.3 4.6 -.3 3.4 

Weight percent alkali 

9-1 

Difference 

from 

whole rock 

+1.4 

-2.6 

+2.0 

+.07 

+.1 

-1.0 

-1.0 

feldspar phenocrysts .................. 2.5 6.1 9.3 16.9 16.3 28.3 33.5 

Weight percent 

quartz phenocrysts .................... 0 1.1 3.6 1Composition of feldspar from sample WT-6, table 4, utilized in calculation of groundmass compositions. 2 Total iron expressed as F4!20a. 

3.2 3.1 8.0 6.4 

to.:) 

.;:... 

~ 

ttj 

~ 0 

~ 

0 

0 

~ 

0 

~ 

~ 

::c: 

ttj 

~ ~ 

t:1 

ttj 

t:1 

~ ~ 

~ 

0 

~ 

t:1 

ttj 

<: 

~ 

z 

ttj 

0 

> z 

~ 

0 

~z 

00. 

0 

~ ::c: 

ttj 

> 00. 

~ ~ 

z 

0 

~ 

ttj 

0 

0 

z 
REFERENCES CITED 25 

water. Lipman (1966, p. 824) suggests that Tuttle and 

Bowen's data ( 1958) might still be applicable to undersaturated magmas, with the partial pressure of water 

substituted for total pressure. Water content must then 

be estimated by other means, and total pressure and 

depth to the magma chamber can be estimated from a 

graph such as that which Kennedy (1955, fig. 1) used 

to show the equilibrium distribution of water in a melt 

of albite composition. 

The near uniformity of composition of the welded 

tuff of Devine Canyon precludes establishing a differentiation trend by the plotting of points on the Q-Ab-Or 

diagram (fig. 26, discussion above). However, the 

cluster of points between about 800 and 1,800 bars 

suggests crystallization in the magma chamber under 

a partial water pressure in this range. If the uppermost 

part of the magma were water saturated, the median 

value of 1,300 bars would indicate a water content of 

about 5 percent, a temperature of about 720°C, and a 

depth to the top of the magma of about 3 miles during 

crystallization of the phenocrysts. Assuming a uniform 

partial pressure of water, at greater depths the magma 

would contain less water, and would be undersaturated 

(Kennedy, 1955, fig. 1). 

The prevalence of resorbed phenocrysts at all levels 

in the welded tuff of Devine Canyon indicates that the 

entire magma column was affected by a drop in pressure at some late stage prior to eruption. This pressure 

drop caused the less dense, liquid, phase to be favored, 

causing resorption of phenocrysts in a magma undersaturated with water (Noble, 1970a; D. C. Noble, written commun., 1971). Reduction in pressure was probably caused by the ascent of the magma which may 

have been accompanied by eruption of minor amounts 

of air-fall tuff. Such tuff is present beneath the ash-flow 

tuff at the Juntara and Drinkwater Pass sections (154 

and 153), and may be covered elsewhere. 

When eruption finally occurred, the ash must have 

flowed onto a very flat plain, judging from the tuff's 

great areal extent and roughly uniform thickness. 

Moore's observations ( 1967) on deposits of the base 

surge from recent volcanic eruptions show that topography has a strong influence on deposition. The base 

surge that he observed at Taal Volcano constituted a 

cold ash flow which must be in many ways analogous 

to the hotter ash flow or flows which formed the welded 

tuff of Devine Canyon. 

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Baldwin, E. M., 1959, Geology of Oregon: Eugene, Univ. of 

Oregon, Cooperative Book Store, 136 p. 

Berry, L. G., and Thompson, R. M., 1962, X-ray powder data 

for ore minerals-the Peacock Atlas: Geol. Soc. America 

Mem. 85, 281 p. 

Brown, C. E., and Thayer, T. P., 1966, Geologic map of the 

Canyon City quadrangle, northeastern Oregon: U.S. Geol. 

Survey Misc. Geol. lnv. Map 1-447, scale 1:250,000. 

Brown, G. M., 1960, The effect of ion substitution on the unit 

cell dimensions of the common clinopyroxenes: Am. Mineralogist, v. 45, nos. 1-2, p. 15-38. 

Byers, F. M., Jr. Orkild, P. P., Carr, W. J., and Quinlivan, 

W. D., 1968, Timber Mountains Tuff, southern Nevada, 

and its relation to cauldron subsidence: Geol. Soc. America 

Mem. 110, p. 87-97. 

Clark, J. R., Appleman, D. E., and Papike, J. J., 1969, Crystal 

chemical characterization of clinopyroxenes based on eight 

new structure refinements, in Pyroxenes and amphibolesCrystal chemistry and phase petrology: Mineralog. Soc. 

America Spec. Paper 2, p. 31-50. 

Deer, W. A., Howie, R. A., and Zussman, J., 1962, Rock-forming 

minerals, v. 2, Chain silicates: London, Longmans, Green 

and Co., 379 p. 

Evernden, J. F., Savage, D. E., Curtis, G. H., and James, G. T., 

1964, Potassium-argon dates and the Cenozoic mammalian 

chronology of North America: Am. Jour. Sci., v. 262, p. 

145-198. 

Fisher, R. V., 1966, Mechanism of deposition from pyroclastic 

flows: Am. Jour. Sci., v. 264, no. 5, p. 350-363. 

Greene, R. C., 1972, Generalized geologic map of the Burns and 

West Myrtle Butte 15-minute quadrangles, Oregon: U.S. 

Geol. Survey Misc. Geol. Inv. Map I-680. 

Greene, R. C., Walker, G. W., and Corcoran, R. E., 1972, Geologic map of the Burns (AMS) quadrangle, Oregon: U.S. 

Geol. Survey Misc. Geol. lnv. Map I-680. 

Haddock, G. H., 1967, The Dinner Creek welded ash-flow tuff 

of the Malheur Gorge area, Malheur County, Oregon: 

Eugene, Univ. of Oregon, Ph. D. thesis, 111 p. 

Hess, H. H., 1949, Chemical composition and optical properties 

of common clinopyroxenes, pt. I: Am. Mineralogist, v. 34, 

nos. 9-10, p. 621-666. 

Hinrichs, E. N., and Orkild, P. P., 1961, Eight members of the 

Oak Spring formation, Nevada Test Site and vicinity, Nye 

and Lincoln Counties, Nevada, in Geological Survey research, 1961: U.S. Geol. Survey Prof. Paper 424-D, p. 

D96-D103. 

Kennedy, G. C., 1955, Some aspects of the role of water in rock 

melts, in Poldervaart, Arie, ed., Crust of the earth-a symposium: Geol. Soc. America Spec. Paper 62, p. 489-503. 

Kittleman, L. R., Green, A. R., Haddock, G. H., Hagood, A. R., 

Johnson, A. M., McMurray, J. M. Russell, R. G., and 

Weeden, D. A., 1967, Geologic mapof the Owyhee region, 

Malheur County, Oregon: Oregon Univ. Mus. Nat. History 

Bull. 8, scale 1: 125,000. 

Kittleman, L. R., Green, A. R., Hagood, A. R., Johnson, A.M., 

McMurray, J. M., Russell, R. G., and Weeden, D. A., 1965, 

Cenozoic stratigraphy of the Owyhee region, southeastern 

Oregon: Oregon Univ. Mus. Nat. History Bull. 1, 45 p. 

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D1-D23. 

--1966, Water pressures during differentiation and crystallization of some ash-flow magmas from southern Nevada: 

Am. Jour. Sci., v. 264, no. 10, p. 810-826. 

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A compositionally zoned ash-flow sheet in southern 

Nevada: U.S. Geol. Survey Prof. Paper 524-F, p. F1-F47. 
26 PETROLOGY OF THE WELDED TUFF OF DEVINE CANYON, SOUTHEASTERN OREGON 

Lipman, P. W., Christiansen, R. L., and Van Alstine, R. E., 

1969, Retention of alkalis by calc-alkalic rhyolites during 

crystallization and hydration: Am. Mineralogist, v. 54, 

p. 286-291. 

Moore, J. G., 1967, Base surge in recent volcanic eruptions: 

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magmas: Am. Jour. Sci., v. 266, p. 860-864. 

---1970a, Significance of phenocryst resorption for the 

intratelluric crystallization and eruptive history of silicic 

pyroclastic rocks [abs.]: Geol. Soc. America, Abs. with 

Programs,v.2,no.2,p.125. 

---1970b, Loss of sodium from crystallized comendite 

welded tuffs of the Miocene Grouse Canyon Member of the 

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81, p. 2677-2688. 

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872-889. 

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no. 6, p. 795-841. 

---1960b, Zones and zonal variations in welded ash flows: 

U.S. Geol. Survey Prof. Paper 354-F, p. 149-159. 

Swanson, D. A., 1969, Reconnaissance geologic map of the east 

half of the Bend quadrangle, Crook, Wheeler, Jefferson, 

Wasco, and Deschutes Counties, Oregon: U.S. Geol. Survey Misc. Geol. Inv. Map 1-568, scale 1:250,000. 

Tuttle, 0. F., and Bowen, N. L., 1958, Origin of granite in the 

light of experimental studies in the system NaA1SiaOsKA1SiaOs-SiO:rH20: Geol. Soc. America Mem. 74, 153 p. 

Walker, G. W., 1963, Reconnaissance geologic map of the eastern half of the Klamath Falls (AMS) quadrangle, Lake 

and Klamath Counties, Oregon: U.S. Geol. Survey Mineral 

lnv. Field Studies Map MF -260, scale 1:250,000. 

---1969, Geology of the High Lava Plains province, in Mineral and water resources of Oregon: Oregon Dept. Geology 

and Mineral Industries Bull. 64, p. 77-79. 

---1970, Cenozoic ash-flow tuffs of Oregon: The Ore Bin, v. 

32, no. 6, p. 97-115. 

Walker, G. W., Peterson, N. V., and Greene, R. C., 1967 Reconnaissance geologic map of the east half of the Crescent 

quadrangle, Lake, Deschutes, and Crook Counties, Oregon: 

U.S. Geol. Survey Misc. Geol. lnv. Map 1-493, scale 

1:250,000. 

Walker, G. W., and Repenning, C. A., 1965, Reconnaissance 

geologic map of the Adel quadrangle, Lake, Harney, and 

Malheur Counties, Oregon: U.S. Geol. Survey Misc. Geol. 

Inv. Map 1-446, scale 1:250,000. 

-tt u.s. GOVERNMENT PRINTING OFFICE: 1973-515-657/44