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Winter 1977 Petrology and Major Element Geochemistry of Albite Granite near Sparta, Oregon Robert Brayton Almy III Western Washington University
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Recommended Citation Almy, Robert Brayton III, "Petrology and Major Element Geochemistry of Albite Granite near Sparta, Oregon" (1977). WWU Graduate School Collection. 792. https://cedar.wwu.edu/wwuet/792
This Masters Thesis is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Graduate School Collection by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. PETROLOGY AND MAJOR ELEMENT GEOCHEMISTRY OFJ\LBITE GRANITE NEAR SPARTA, OREGON
A Thesis '
Presented to
The Faculty of
Western Washington State College
In Partial Fulfillment
Of the Requirements for the Degree
Master of Science
by
Robert B. Almy III
March, 1977
345c 112 MASTER'S THESIS
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Date:
I PETROLOGY AND MAJOR ELEMENT GEOCHEMISTRY OF ALBITE GRANITE NEAR SPARTA, OREGON
by
Robert B. Altny III
Accepted in Partial Completion of the Requirements for the Degree
Master of Science
Dean of Graduate School
ADVISORY COMMITTEE
Chairperson ABSTRACT
Albite granite near Sparta, Oregon occurs in an igneous complex con taining serpentinite, gabbro, diorite, tonalite and granite with overlying keratophyric and spilitic volcanic rocks. This igneous suite is overlain by Triassic limestones of reef origin. In all the igneous rocks primary hypidiomorphic and porphyritic textures predominate but a metamorphic overprint of the prehnite-pumpellyite facies is widespread. Whole rock chemical analyses show that albite granite has relatively high Si02
(69-81%) and Na20 (4-7%) and low K2O (0.1-1%). Rare plagioclase potassium' feldspar granite contains up to 3.6% K2O.
Although local isochemical alteration is demonstrable and local metasomatic replacement is probable, the albite granite body as a whole did not apparently form by metasomatic replacement of associated diorite as postulated by Gilluly (1933). Igneous contacts and variable chemical and mineralogical composition show that the Sparta granite is comprised of several bodies intruded separately but more or less contemporaneously.
These intrusions were probably emplaced at shallow levels as indicated by oscillatory zoning and porphyritic textures. Albite granite and quartz keratophyre are assumed to be comagmatic on the basis of identical major element chemistry and mutually gradational textures.
The gabbro and related mafic and ultramafic rocks in northeastern
Oregon may be fragments of oceanic crust. However, the albite granite and apparently cogenetic keratophyre are best interpreted to represent island arc magmatism developed on that oceanic crust. TABLE OF CONTENTS
ABSTRACT
LIST OF FIGURES
LIST OF PLATES
LIST OF TABLES
INTRODUCTION ‘ ^
ACCESS
GENERAL GEOLOGY ^ Paleozoic Rocks 7 Mesozoic Plutonic Rocks 7 Mesozoic Sedimentary Rocks -jO Jurassic-Cretaceous Plutonic Rocks -12 Tertiary Unconformity and Post-Cretaceous Rocks 12
PURPOSE 13
FIELD RELATIONS AND PETROGRAPHY OF UNITS STUDIED Gabbro 13 Diorite and Tonalite 15 Granite 21 Clover Creek Greenstone 31 Dikes 35
WHOLE ROCK CHEMICAL ANALYSES Method 40 Discussion 40
METASOMATISM Gilluly's Theory 49 Evidence of the Present Study 51 Field Evidence 5I Textural Alteration 52 Chemical Evidence 53 Discussion 54 Summary of Alteration Data 61 CONCLUSIONS
ACKNOWLEDGEMENTS
BIBLIOGRAPHY
APPENDIX I
APPENDIX II LIST OF FIGURES
Figure Page
1 Location of the study area. 2
2 Previous study areas. 3
3 Typical vegetation cover on the northern portion of Sparta uplands, Wallowa Mountains in the background. 4
4 Typical exposure along Goose Creek near Sucker Creek. 4
5 Shallow gorge of the Powder River, 25 kilometers west of Richland, Oregon on State Route 89. 5
6 Flat undissected uplands near Sparta, Oregon in the middle background, view is toward the west. 5
7 Generalized stratographic section of pre-Tertiary geology near Sparta, Oregon. 6
8 Regional occurrence of major orogenic events in the northwestern United States, from Rogers et al (1974), p. 1922. 9
9 Sketch map of the regional geology of northwestern Oregon. 11
10 Layering in gabbro, Ih kilometers south of the Macey Mine along State Route 86. 14
11 Rhodonized gabbro, 2 kilometers south of the Macey Mine along State Route 86. 14
12 Photomicrograph of aligned plagioclase grains, layered gabbro, crossed Nicols. 16
13 Photomicrograph of hornblende crystal with pyroxene cores, hornblende gabbro, crossed Nicols. 16
14 Weakly foliated quartz hornblende diorite, 40 meters west of J. N. Bishop Spring, scale is 15 cm. 17
15 Irregular grain size in diorite, middle Goose Creek, scale is 6 inches. 17
16 Pegmatitic biotite quartz plagioclase pod, 100 meters east of J. N. Bishop Spring, scale is 15 cm. 18
17 Photomicrograph of oscillitory zoning in plagioclase (red) and interstitial orthoclase (yellow), tonalite stained chip, reflected light. 19 fl3.ure Page
18 Photomicrograph of chlorite replacing hornblende, quartz hornblende diorite, plane polarized light. 18
19 Photomicrograph of porphyritic albite granite, crossed Nicols. 23
20 Photomicrograph of granophyric texture, albite granite, crossed Nicols. 23
21 Photomicrograph of porphyritic albite granite, quartz intergrowths in margins of albite pheno- cryst, embayed quartz phenocryst, crossed Nicols. 24
22 Photomicrograph of zoned plagioclase (An«^20- An5) with orthoclase overgrowth, oligoclase albite granite, crossed Nicols. 24
23 Photomicrograph of mortar texture in albite granite, crossed Nicols. 25
24 Photomicrograph of sheared quartz hornblende diorite with sutured quartz grains, same field as Fig. 25, crossed Nicols. 25
25 Photomicrograph of sheared quartz hornblende diorite with sutured quartz grains, same field as Fig. 24, plane polarized light. 26
26 Photomicrograph of stain twinning in plagioclase, crossed Nicols. 26
27 Photomicrograph of sheared "augen" of quartz and a quartz albite glomerblast, crossed Nicols. 28
28 Photomicrograph of extremely fine-grained quartz albite intergrowths, albite granite, crossed Nicols. 28
29 Photomicrograph of fine-grained quartz albite intergrowths, albite granite, crossed Nicols. 29
30 Photomicrograph of medium-grained quartz albite intergrowths (granophyric textures), albite granite, crossed Nicols. 29
31 Photomicrograph of medium-grained granophyric texture with interstitial orthoclase (yellow), orthoclase albite granite, stained chip, reflected light. 30 Fiqu Page
32 Photomicrograph of poikill tic quartz, albite granite, plane polarized light. 32
33 Photomicrograph of zoned amygdule filled with chlorite (core), albite and quartz (rim), spilite, plane polarized light. 32
34 Photomicrograph of clear albite rimming a weakly zoned albite phenocryst, cal cite filled amygdule, spilite, crossed Nicols. 34
35 Photomicrograph of a stained, embayed quartz phenocryst, quartz keratophyre, crossed Nicols. 34
36 Photomicrograph of twinned albite and quartz phenocrysts, quartz keratophyre, crossed Nicols. 36
37 Photomicrograph of quartz in veinlets and fine grained rims on albite phenocrysts, quartz keratophyre, same field as Fig. 38, crossed Nicols. 36
38 Photomicrograph of quartz in veinlets and fine grained rims on albite phenocrysts, quartz keratophyre, same field as Fig. 37, plane polarized light. 37
39 Small silicic dike, west side of Goose Creek near Sucker Creek, scale is 15 cm. 37
40 Diorite porphyry dike crosscutting silicic dike, west side of Goose Creek near Sucker Creek, hammer handle is 1 m. 38
41 Photomicrograph of zoned hornblende phenocrysts, diorite porphyry, plane polarized light. 39
42 Frequency histogram, weight % SiO-, Sparta igneous rocks. ^ 42
43 Weight % Si02 vs. weight % K^O (log scale) plot of Sparta igneous rocks. ^ 43
44 Weight % KpO vs. weight % CaO plot of Sparta igneous rocks. 44
45 Weight % Si Op vs. FeoVMgO plot of Sparta igneous rocks. 45
46 AFM ternary diagram showing distribution of Sparta igneous rocks. 46 Weight % Na^O vs. FeoVwgO plot of Sparta igneous rocKS.
Ca-Na-K atomic ratio ternary diagram showing distribution of Sparta Igneous rocks.
Weight % K^O vs. Weight % CaO plot of altered albite granites.
Weight % SiO^ vs. FeoVwgO plot of altered albite granites.
AFM ternary diagram showing distribution of altered albite grantes.
Weight % Na^O vs. FeO^/MgO plot of altered ablite granites.
Ca-Na-K atomic ratio ternary diagram showing distribution of altered albite granite.
Qz-An-^Alkali Feldspar ternary diagram showing normative plots of Sparta plutonic rocks, based on I.U.G.S. classification.
Ab-An-Or ternary diagram showing normative plots of Sparta silicic volcanic rocks, based on classification of O'Connor (1965). TABLES Page 1 Whole rock major element analyses of Sparta igneous
rocks - GABBRO 66
2 Whole rock major element analyses of Sparta igneous
rocks - BASIC DIKES 68
3 Whole rock major element analyses of Sparta igneous
rocks - SPILITE 70
4 Whole rock major element analyses of Sparta igneous rocks - DIORITE/TONALITE 72
5 Whole rock major element analyses of Sparta igneous
rocks - ALBITE GRANITE 74
6 Whole rock major element analyses of Sparta igneous
rocks - GRANITE 78
7 Whole rock major element analyses of Sparta igneous
rocks - QUARTZ KERATOPHYRE 80
8 Whole rock major element analyses of Sparta igneous
rocks - SHEARED ALBITE GRANITE/QUARTZ KERATOPHYRE 82 PLATES
1 Geologic map of the Sparta 15' Quadrangle, Oregon,
scale 1:62,500, by Harold J. Prostka
2 Sample location map, Sparta 15' quadrangle, Oregon,
and a portion of Sawtooth Ridge 1%' Quadrangle,
Oregon, scale 1:62,500 INTRODUCTION
The study area is near Sparta, Oregon, in the southern foothills of the Wallowa Mountains in the northeastern part of the state. It extends from Clover Creek in the Sawtooth Ridge quadrangle east to Eagle Creek in the Sparta quadrangle and from Glasgow Butte north to the Lily White
Environmental Field Station in the Sparta quadrangle (Figs. 1, 2). Rock exposure is good along Goose Creek from Red Gulch to Sawmill Creek (Figs.
3, 4), in side canyons along Eagle Creek, and in the shallow gorge cut by the Powder River along Route 86 west of Richland, Oregon (Fig. 5). Very poor exposure is found on the flat undissected uplands south of Sparta
Butte (Fig. 6). Approximately one-thousand meters of vertical relief occurs between the Powder River and Sparta Butte, the highest point in the area studied.
ACCESS
Access to the Sparta area is by State Highway 86 east from Baker,
Oregon, to numerous U. S. Forest Service logging roads to all parts of
Federally owned lands which comprise half the area studied. Ranch roads, with permission of landowners, provide access to the remaining privately owned areas. Secondary roads are generally open from May through October but are impassable during the rest of the year due to snow.
GENERAL GEOLOGY
A very generalized geologic section of rocks in the Sparta area may be divided into two sequences separated by a profound Tertiary unconfor mity (Fig. 7). Rocks older than the unconformity range from Permian to
Cretaceous in age and include meta-sediments, gabbro, diorite, albite
1 FIGURE 3 Typical vegetation cover on the northern portion of Sparta uplands, Wallowa Mountains in the background.
FIGURE 4 Typical exposure along Goose Creek near Sucker Creek. FIGURE 5 Shallow gorge of the Powder River, 25 kilometers v/est of Richland, Oregon on State Route 89.
FIGURE 6 Flat undissected uplands near Sparta, Oregon in the middle background, view is toward the west. Sparta, Oregon
Explanation
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X X i ^ 2 X iij Section based on geology by Prostka( 1962), Almy 7 granite, siliceous and basaltic volcanic rocks, volcaniclastic and arkosic sedimentary rocks, and limestones. Miocene to recent units overlying the unconformity include flows of the Columbia River basalts, lacustrine deposits, and Quaternary gravel deposits (Prostka, 1963). Paleozoic Rocks The oldest rock unit, occurring 5 km southwest of Glasgow Butte, is an intensely deformed meta-sediment and greenstone unit known as the Elkhorn Ridge Argillite (Washburn, 1903; Gilluly, 1937) and interpreted to be a flysch sequence (ie. eugeosynclinal greywackes) by Brooks (1976, 1976 personal communication). Mesozoic Plutonic Rocks The Elkhorn Ridge Argillite is intruded by, or is in tectonic con tact with, an igneous complex containing peridotite, pyroxenite, layered gabbro, serpentinite, diorite and albite granite (Prostka, 1962). Numerous diabasic and silicic dikes intrude the gabbro, diorite and albite granite. Small bodies of major crystalline units (e.g. diorite and albite granite) are commonly present as more or less altered masses, probably xenoliths, within adjacent units (gabbro, diorite and albite granite) of the complex. This complex has been assigned an early Mesozoic age by Gilluly (1933) and Triassic (?) by Prostka (1962) on the basis of albite granite clasts contained in overlying fossil-bearing marine sedimentary units of late Triassic age (Bostwick and Koch, 1962). Hornblende diorite and albite granite are believed to intrude gabbro at least locally (Prostka, 1962; Brooks, 1976 personal communication). Mafic and ultramafic rocks of the Sparta complex form part of a belt of rocks of similar lithology which include Triassic ophiolites in the 8 Klamath Mountains of northern California and southwestern Oregon (Hamilton, 1969; Bailey and Blake, 1974), the Canyon Mountain Complex (Thayer and Himmelberg, 1968) eighty miles west of Sparta, and smaller bodies of serpentine, gabbro, diorite and albite granite through the adjacent Baker quadrangle (Gilluly, 1937). The Sparta complex is included in a zone of Mesozoic (probably Jurassic) orogeny by Burchfiel and Davis (1972). Rogers al_ (1974) and Thayer and Brown (1973) postulate the existence of a marginal, or back-arc basin in this region during the Triassic with subsequent closing and accretion of an arc-type rock assemblage to the craton during the Permo-Triassic Sonoma orogeny (Fig. 8) (Rogers et 1974). This terrain may represent an extension of the Intermontane Belt of the Canadian Cordillera described by Monger et ^ (1972) which they interpret to be oceanic crust developed during late Paleozoic to early Mesozoic time. They assign later arc development in the Intermontane Belt to the upper Triassic. The albite granite body at Sparta, Oregon, was described by Gilluly (1933) and interpreted to have a metasomatic replacement origin. He interpreted it to be the result of late or post magmatic albitization and partial silicification of a pre-existing hornblende quartz diorite. The fluids responsible for this alteration were thought to have been derived by filter pressing from lower portions of the partially solidi fied diorite magma and guided upward through brecciated zones in the overlying solid diorite. Evidence cited by Gilluly for this hypothesis includes microscopic textures believed indicative of alteration and gradational field relations between the two rock types. An alternative hypothesis considered by Gilluly (1933, 1935), which Q Fij^ure 8. Location of cratonic margin of the western United States at various limes (in part modified from Burchfid and !>avis, 1972). Maps constructed as de scribed in caption for Figure 1. Studied suites for the different lime periods .ire labeled according to their environment of formation: o, (Kcanic ridge, island, or bchind-the-arc basin; i, island arc; m, continental mar gin; c, craton. A. Pre-Antler time. The margin is the western limit of Prcc.imbrian continental rt»cks. Oceanic assemblages cast of the margin are allochthons thrust from the ensimatic eugcosyncline to the west. B. Post-Antler, pre-Sonoma time. Essentially no con struction of craton during Antler orogeny and similar volcanic pattern to that of pre-Antler time. Oce.inic and island-arc rocks east of the margin are allochthons from the eugeosynclinc. C. Triassic time. Cratonic and continental margin assemblages arc interior of a margin drawn somewhat westward from the pre-Sonoma margin, island-arc assemblages at (iarson City, Keno, and the central Ore gon iniier arc shown as occurring on a crust (hachiired) that is transitional between oceanic and contineni.il because true oceanic, ensimatic assemblages are absent from the area. The position of the western margin of the transitional crust is uncertain. FIGURE 8 From Rogers et ^ (1974) 10 he thought unlikely, is that the albite granite was co-magmatic with keratophyre and spilite. Mesozoic Sedimentary Rocks A section of upper Triassic volcanic and volcanic-rich clastic rocks of more than 3000 meters thick has been described in the northern part of the Sparta quadrangle (Plate 1) (Prostka, 1963). The lower portion of this sequence consists of spilite, keratophyre, quartz keratophyre and related volcaniclastic sediments and occurs extensively throughout northeastern Oregon and western Idaho. In the Sparta quad rangle, this unit is named the Clover Creek Greenstone (Gilluly, 1935; Prostka, 1963) and east of Eagle Creek it is named the Lower Sedimentary Series or Gold Creek Greenstone (Smith and Allen, 1941; Prostka, 1963). Other similar rocks are named Seven Devils Volcanics in the Snake River Canyon and western Idaho region (Brooks and Vallier, 1967; Morganti, 1972; Vallier, 1974). Although the unit as a whole is of substantial lateral extent (Fig. 9), individual beds or members generally show marked local facies changes. Distinctive marker beds are lacking and individual units are difficult or impossible to correlate from outcrop to outcrop. Low grade static metamorphism of prehnite-pumpellyite to lower greenschist facies is pervasive. Prehnite, chlorite or epidote are ubiquitous in volcanic units, although phenocrysts, flow structures and zoning of individual minerals are preserved to greater or lesser extent. The upper portion of the upper Triassic rocks of the Wallowa Mountains region is a sequence of reef-type limestone, clastic lime stone ane euxinic fine-grained shale between 300 and 600 meters thick 12 named the Martin Bridge Formation (Smith, 1919; Laudon, 1956; Prostka, 1963). It is at least locally conformable with the underlying Clover Creek Greenstone and Lower Sedimentary Series. This formation, which occurs throughout the Wallowa Mountains, is well exposed in Eagle Creek and near Kinney Point in the Snake River Canyon (Prostka, 1963). It is thought to represent island reefs, clastic wedges near these reefs and lagoon or other calm shallow marine basins (Prostka, 1963). Jurassic-Cretaceous Plutonic Rocks Quartz diorite and granodiorite batholiths and rare basic dikes and sills occur 10 km north-northeast and immediately south of the study area. The petrology and structure of these intrusive bodies have been described by Goodspeed (1929), Krauskopf (1943), Taubeneck (1957, 1964, 1967), and Prostka (1963). They display igneous textures, well developed contact aureoles, and are thought to have been emplaced as intrusive magmas (Taubeneck, 1964; Prostka, 1963). These felsic batholiths of Jurassic-Cretaceous age have been interpreted as magma from zones of partial melting under island arcs (Brooks, 1976). Tertiary Unconformity and Post-Cretaceous Rocks Early Tertiary time in much of the northwest United States is marked by a profound unconformity overlain by Columbia River and Snake River Plain basalts, related lacustrine rocks with local Quaternary gravels. Pre-Tertiary rocks in the study area are exposed below this unconformity in areas where the basalt cover has been eroded. In some areas weathering of pre-Tertiary rocks is especially deep which may be due to development of the present weathering horizon locally coincident with the Tertiary weathering zone. 13 PURPOSE The purpose of the present study is to examine the major igneous rock types of the Sparta, Oregon area petrographically and geochemically and determine their mutual relationships. Three major questions will be dealt with. (1) Is the albite granite body, as a K-poor leucocratic body, a primary igneous body, or is its present lithology and extent the result of extensive metasomatism? (2) Are the various igneous rock types in the area comagmatic, do they represent separate unrelated intrusive and volcanic events, or did they form within the same tectonic environ ment, but not necessarily from a single source? (3) What was the tectonic environment of formation of the Sparta Igneous Complex? FIELD RELATIONS AND PETROGRAPHY OF UNITS STUDIED Gabbro Gabbro exhibits locally continuous layering which dips northeast from 15 to 40 degrees. Plagioclase-rich layers 2-10 cm thick alternate with more pyroxene-rich layers of similar thickness (Fig. 10). The layering (igneous lamination in the terminology of Wager and Brown, 1967) is presumably cumulus in origin. Alteration is widespread within the gabbroic mass. Entire outcrops up to ten square meters in area are altered to rhodingite (Fig. 11). Veinlets of quartz and albite occur in less altered rocks. Prostka (1963) describes the rhodingite alteration in detail and concludes that this hydrothermal alteration may be related to "formation of metasomatic albite granite" (p. 125). Thin section study shows this gabbro to be primarily gabbronorite. It was hypidiomorphic granular texture. The principle minerals present FIGURE 10 Layering in gabbro, 2% kilometers south of the Macev Mine along State Route 86. 15 are euhedral to subhedral plagioclase (Angg_gQ), subhedral augite and orthopyroxene (generally hypersthene). Plagioclase exhibits alignment of grains in layered rock (Fig. 12). Orthopyroxene is mostly replaced by chlorite or serpentine. This replacement of orthopyroxene in other wise fresh gabbro is not apparently related to development of rhodingite. Hornblende gabbro is common; well developed igneous textures indicate that it represents a late stage magmatic alteration of gabbronorite. All stages of replacement of clinopyroxene by green or brown hornblende may be setn in thin section, from hornblende rims on augite to poikilitdc hornblende crystals with relict pyroxenes cores (Fig. 13). Orthopyroxene in hornblende gabbro is completely replaced by chlorite. Plagioclase is relatively fresh with minor epidote occurring as "saussurite" alteration. Diorite and Tonalite Intermediate igneous rocks near Sparta grade irregularly from horn blende diorite to trondhjemite (to albite granite). A decrease in percentage of mafic minerals, an increase in percentage of quartz, and a decrease in the anorthite content of plagioclase are the most obvious mineralogical changes attendant with this gradation. With minor exceptions, diorite near the main gabbro mass is more mafic becoming more felsic near albite granite. Outcrops near the gabbro contact are commonly weakly foliated (Fig. 14). Small (2-20 cm) irregularly shaped, sharply bounded zones of fine grained diorite are widespread in the usually medium to coarse grained diorite (Fig. 15). Pegmatitic zones also occur; those 100 meters east of J. N. Bishop Spring are especially well exposed (Fig. 16). Gabbro xenoliths up to 3 meters in length occur in the diorite near the gabbro. 16 I______X.O FIGURE 12 Photomicrograph of aligned plagioclase grains, layered gabbro, crossed Nicols. J.-0 ______I FIGURE 13 Photomicrograph of hornblende crystal with pyroxene cores, hornblende gabbro, crossed Nicols. 17 FIGURE 14 Weakly foliated quartz hornblende diorite, 40 meters west of J. N. Bishop Spring, scale is 15 cm. 18 FIGURE 18 Photomicrograph of chlorite replacing hornblende, quartz hornblende diorite, plane polarized light. 19 # i* FIGURE 17 Photomicrograph of oscillitory zoning in plagioclase (red) and interstitial orthoclase (yellow), tonalite stained chip, reflected light. 20 Tonalite is commonly associated with quartz diorite as a more quartz-rich member of these intermediate rocks. Their mutual contacts are gradational. Both quartz diorite and tonalite occur also as small bodies with indistinct contacts within granite. These relations are especially well exposed in Goose Creek 1/2 mile south of Sucker Creek. Upon close examination, indistinct,apparently gradational, contacts can be seen to be obscured by local low-grade alteration. Where diorite is heavily altered, mottled albite and intragranular epidote replace more calcic plagioclase. Interstitial secondary mafic minerals (chlorite and epidote) replace hornblende and biotite, and ultimately comprise the same proportion of altered rock that hornblende and biotite did in unaltered rock. This altered rock is lighter weathering than fresh diorite and causes apparent gradation in outcrop, however, contacts with albite granite and greenstone dikes are actually sharp and presumably igneous. Microscopically diorite and tonalite of the Sparta area exhibit hypidiomorphic granular texture. Generally plagioclase is euhedral with either simple or oscillatory zoning (Fig. 17). Cores of plagioclase are slightly saussuritized to completely replaced by epidote. Cores are A>^4o_]5 fresh; outer zones are andesine, oligoclase or rarely albite. Euhedral to subhedral hornblende is partially altered to actinolite or chlorite in roughly half the specimens examined (Fig. 18). Locally this replacement is complete. Biotite is widespread but only locally abundant. It is always at least partially altered to chlorite. Quartz is anhedral and occurs interstitially except in tonalite where it is rarely subhedral. Orthocliase occurs as a minor interstitial mineral (Fig. 17), as do accessory sphene, apatite, and opaque minerals. 21 Diorite and tonalite often show effects of mild shearing. Strained elongate quartz with sutured grain boundaries and fractures filled with prehnite, unstrained quartz or epidote are widespread but never abundant. Granite Granite of the Sparta Igenous Complex is highly variable in mineralogical composition and texture. It ranges in composition from an albite orthoclase granite to albite alaskite. Textures range from coarse grained hypidiomorphic to fine grained allotriomorphic granular* granophyric, to mylonitic or porphyritic. Locally, albite granite is more or less sheared with metamorphic alteration products or iron oxide straining due to weathering concentrated along attendant fractures. Granitic dikes and small irregular intrusions of various diorite to granitic compositions are well exposed in roadcuts along Goose Creek from the Daddy Mine to Forshey Creek. Both dikes and small granitic intrusive bodies have sharp contacts with, and occasionally chilled margins against, surrounding rock. Granitic dikes both crosscut and are crosscut by more mafic diabase dikes- (Fig. 40, 41). Field relations and petrology of dikes are discussed more fully below. Albite granite is found within the serpentinite and pyroxenite masses near Glasgow Butte (Plate B). Although poor exposure does not permit examination of contacts, these small granitic bodies are assumed to be intrusive into the more mafic units on the basis of intrusive relations which can be observed in the Baker, Oregon 30' quadrangle immediately to the west (Brooks, 1976 personal conmunication) . Principal minerals of the granitic rocks in the Sparta area are albite, quartz, epidote, chlorite, and orthoclase. Minor amounts of 22 amphibole, biotite, zircon, apatite, sphene and opaque minerals are also present. Plagioclase in the granitic rocks is predominantly dusty or cloudy appearing albite. In over half of the specimens examined it exhibits normal or oscillatory zoning with the cores being more heavily saussuritized than the rims. Cores of these zoned plagiocalse crystals are albite, oligoclase or rarely andesine (?). Locally clear, unaltered albite occurs as rims on dusty oligoclase or albite, or as clear unaltered grains in allotriomorphic granular granite and cataclastically deformed rocks. Microscopically, granite of the Sparta area shows considerable variation in texture. Fresh, unsheared granite occurs with the following textures: (1) porphyritic with euhedral to subhedral phenocrysts of quartz and albite (Fig. 19), (2) granophyric with quartz albite inter growths predominating (Fig. 20), and (3) hypidiomorphic to allotriomorphic granular with euhedral to subhedral albite and anhedral quartz. Various combinations of these textures are common (Fig. 21). Orthoclase occurs as overgrowths on euhedral albite (Fig. 22) or interstitially. Subordinate mafic minerals, chlorite and epidote probably replacing hornblende, are anhedral and generally interstitial. Accessory apatite, sphene, pyrite and other opaque minerals are euhedral to subhedral and are generally inter stitial. Pyrite and sphene rarely occur as subhedral phenocrysts. Deformation textures are common, and all of the previously described textures in the granite may be found more or less cataclastically deformed (Figs. 23, 24, 25, 26). Other albite quartz rocks are fine grained mylonites or pseudo-porphyritic cataclastic rocks containing irregular glomeroblasts or augen of quartz and albite (Fig. 27). 23 FIGURE 19 Photomicrograph of porphyritic albite granite, crossed Nicols. ^ ,C> FIGURE 20 Photomicrograph of granophyric texture, albite granite, crossed Nicols. 24 I______Jj ,Q /w/» Photomicrograph of porphyritic albite granite, quartz intergrowths in margins of albite pheno- cryst, embayed quartz phenocryst, crossed Nicols. FIGURE 22 Photomicrograph of zoned plagioclase (An^20- An5) with orthoclase overgrowth, oligoclase albite granite, crossed Nicols. I. 25 FIGURE 23 Photomicrograph of mortar texture in albite granite, crossed Nicols. FIGURE 24 Photomicrograph of sheared quartz hornblende diorite with sutured quartz grains, same field as Fig. 25, crossed Nicols. 26 FIGURE 25 Photomicrograph of sheared quartz hornblende diorite with sutured quartz grains, same field as Fig. 24, plane polarized light. L /O FIGURE 26 Photomicrograph of stain twinning in plagioclase, crossed Nicols. 27 Although several sheared granitic rocks examined contain a relatively small amount of mafic minerals, so do several of the undeformed albite granite samples. Thus, in contrast to conclusions of Gilluly (1933) and Prostka (1963), the present study finds no evidence for an inverse correlation between cataclastic deformation and amount of mafic minerals in albite granite. Albite intergrowths with quartz are widespread in granite. These intergrowths range in size from extremely fine grained radiating inter growths to well developed medium grained symplectites (Figs. 28, 29, 30). Medium grained symplectite most commonly consists of a twinned albite core with optically continuous vermicular quartz intergrown with the outer portion of the albite. Other rare symplectites appear to consist of a quartz core with radiating vermicular albite intergrowths invading its outer portions. Albite intergrown with quartz is generally twinned; rarely faint "chessboard" twinning is exhibited. Gilluly's (1933) description of "n^rmekites" in the Sparta albite granite concerns granophyric and symplectite textures, not true myrmekite as succinctly defined by Phillips (1974), since orthoclase feldspar, essential to this narrow definition, was not mentioned in Gilluly's textural description of these albite granites.. No niyrmekitic textures, in sensu strictu, were found in any of the rocks studied. Symplectite was found in orthoclase albite granite, but spatial relations between the intergrowths and interstitial orthoclase are not those demanded by Phillips' (1974) definition (Fig. 31). Quartz in albite granite occurs in several other forms besides inter growths with albite. Where porphyritic, it is euhedral to subhedral and somewhat embayed. In hypidiomorphic granular rocks it is subhedral. 28 FIGURE 27 Photomicrograph of sheared "augen" of quartz and a quartz albite glomerblast, crossed Nicols. / / 1 OJ FIGURE 28 Photomicrograph of extremely fine-grained quartz albite intergrowths, albite granite, crossed Nicols. 29 j______0--^S mm FIGURE 29 Photomicrograph of fine-grained quartz albite intergrowths, albite granite, crossed Nicols. FIGURE 30 Photomicrograph of medium-grained quartz albite intergrowths (granophyric textures), albite granite, crossed Nicols. 30 FIGURE 31 Photomicrograph of medium-grained granophyric texture with interstitial orthoclase (yellow), orthoclase albite granite, stained chip, reflected 1ight. 31 Strained and sutured intragrain boundaries of quartz are widespread in slightly sheared and otherwise fresh appearing granite. Rarely quartz is poikilitic (Fig. 32), enclosing twinned laths of albite, and often having concave grain boundaries against the albite. The origin of this texture is uncertain; two possibilities are (1) metasomatic addition of silica and (2) recrystallization of interstitial quartz to achieve optical continuity. Mafic minerals in granite are anhedral . Epidote and chlorite, as alteration products of rare hornblende and biotite, predominate. Clover Creek Greenstone The Clover Creek Greenstone consists of a sequence of spilite and quartz keratophyre flows, related pyroclastic deposits and volcanic sandstones with minor intercalated argillite, conglomerate, chert and limestone (Fig. 3). This unit as mapped by Prostka (1962) in the Sparta area, is exposed on the southern limb of a northwest-southeast trending syncline (Plate 1). Gilluly (1937) and Prostka (1963) have estimated its thickness to be approximately 1,300 meters. Since the present study neither proposes major changes nor adds new descriptions of this unit, only selected important points are emphasized below. The upper and lower contacts of the Clover Creek Greenstone are poorly exposed. An absence of contact metamorphic effects from albite granite and clasts of albite granite occurring in conglomerate beds of the Clover Creek are strong evidence in favor of an at least locally depositional contact between these two units. However, dikes of diorite porphyry and small bodies of porphyritic albite granite intrude Clover Creek Greenstone at several locations in the field area. These bodies 32 /.O nt m FIGURE 32 Photomicrograph of poikill tic quartz, albite granite, plane polarized light. I/-o futffl FIGURE 33 Photomicrograph of zoned amygdule filled with chlorite (core), albite and quartz (rim), spilite, plane polarized light. 33 and dikes seems to be most common near the contact with the albite granite. The upper contact of the Clover Creek Greenstone with limestone of the Martin Bridge Formation is described by Prostka (1962) as being conformable. The various lithologies within the Clover Creek Greenstone are usually discontinuous. The unit is apparently devoid of prominent con tinuous marker beds. Volcanic flows and breccias, especially, tend to be lensoid, attaining substantial thicknesses then pinching out rapidly. Amygdules are common in spilite. This distribution is irregular, occurring both at the margins of flows and in irregular zones within central portions. Amygdule fillings are variable; cal cite, chlorite, epidote, quartz or actinolite are common (Fig. 33). Prostka (1963) reports albite, celadonite, biotite, prehnite and pumpellyite as well. Spilite is usually more or less porphyritic. Phenocrysts range in size from 2 mm to 2 cm and consist of albite, clinopyroxene (augite where preserved) and pyrite. Groundmass minerals include albite, epidote, chlorite, augite, actinolite, prehnite, pumpellyite, sphene, pyrite and other opaques. Albite phenocrysts are euhedral , twinned and contain up to 90% saussurite alteration. Saussurite is evenly distributed throughout albite phenocrysts and often imparts a green color to them in hand speci mens. Clear, untwinned albite rims mantle albite phenocrysts in several specimens (Fig. 34). Microscopically quartz keratophyre of the Clover Creek Greenstone is porphyritic and hoiocrystalline. Phenocrysts are twinned albite, embayed quartz (Fig. 35) and rarely pyrite. Groundmass minerals include quartz, albite, epidote, chlorite, cal cite, actinolite, pyrite, and other opaque minerals. 34 FIGURE 34 Photomicrograph of clear albite rimming a weakly zoned albite phenocryst, cal cite filled arnygdule, spilite, crossed Nicols. FIGURE 35 Photomicrograph of a stained, embayed quartz phenocryst, quartz keratophyre, crossed Nicols. 35 Albite phenocrysts are euhedral and saussuritized, but unzoned. Quartz phenocrysts are commonly embayed, some sections exhibit dipyramidal forms (Fig. 36). Extremely fine grained granular quartz and albite occur in some specimens as a rim around albite phenocrysts (Fig. 37). Vesicles and amygdules are not found in quartz keratophyre. Fracturing and shearing is rare. Where it occurs, quartz or prehnite filled fractures cut phenocrysts and groundmass rock exhibiting sharp contacts (Fig. 37, 38). Di kes Numerous dikes of varying mineralogy intrude gabbro, diorite, granite and Clover Creek Greenstone. Although widespread, they are not usually well exposed. They trend N 70 W and are nearly vertical. Dikes occur singly or in small swarms and nowhere resemble sheeted dikes reported from classic ophielites. They range in width from 6 cm to 6 m and in composition from albite granite to gabbro porphyry. Generally they are metamorphosed hornblende diorite porphyry. Although mafic dikes both crosscut and are crosscut by more silicic dikes, the former case is more common (Figs. 39, 40). Microscopically, dikes consist of fine grained hornblende diorite porphyry (Fig. 41) containing pyrite, other opaque minerals and rare quartz in the groundmass. The more mafic varieties contain augite pheno crysts instead of hornblende, while silicic types consist of porphyritic or granophyric albite and quartz with less than 5 per cent chlorite and epidote. Alteration is nearly universal. Plagioclase is altered to albite, epidote, and cal cite; hornblende to chlorite, actinolite, and epidote; and groundmass minerals to a mat of chlorite, epidote, albite. 36 ^.O ATT FIGURE 36 Photomicrograph of twinned albite and quartz phenocrysts, quartz keratophyre, crossed Nicols. FIGURE 37 Photomicrograph of quartz in veinlets and fine grained rims on albite phenocrysts, quartz keratophyre, same field as Fig. 38, crossed Nicols. Jl.,0 y'^yy\ FIGURE 38 Photomicrograph of quartz in veinlets and fine grained rims on albite phenocrysts, quartz keratophyre, same field as Fig. 37, crossed Nicols. FIGURE 39 Small silicic dike, west side of Goose Creek near Sucker Creek, scale is 15 cm. 38 FIGURE 40 Diorite porphyry dike crosscutting silicic dike, west side of Goose Creek near Sucker Creek, hammer handle is 1 m. FIGURE 41 Photomicrograph of zoned hornblende pheno- crysts, diorite porphyry, plane polarized 1ight. 40 cal cite and opaque minerals. Altered mafic dikes weather rapidly, and iTre difficult to correlate from outcrop to outcrop. WHOLE ROCK CHEMICAL ANALYSES Method Whole rock analyses for nine major elements (Si, A1, Ti, Fe, Mg, Mn, Ca, Na, K) were obtained using x-ray fluorescence utilizing an EDAX-EXAM model 707 energy dispersive spectrophotometer. Raw intensity data were referenced to a set of 15 international standards and converted to per cent oxide using the method of Lucas-Tooth (1964). Two sigma uncertainty in per cent of each oxide present is considered to be approxi mately as follows: Si02, 2%; AI2O3, 5%; Ti02, MnO, 4%; CaO, 2%; Na20> 10%; K2O, 5%. Additional experimental details are explained in Appendix II. Two major elements, Na20 and MgO, were also determined using atomic absorption techniques because of the relatively large uncertainty of the x-ray fluorescence data (±10%). A Perkins-Elmer model 306 atomic absorp tion unit was employed. Two sigma uncertainty in per cent of each oxide is considered approximately 6% for both Na20 and MgO. Additional experi mental conditions are explained in Appendix II. The major element composition for 60 samples are listed in Table 1. Each of the major igneous rock types of the Sparta area are represented. Discussion The two most obvious features of whole rock chemical data from Sparta igenous rocks are (1) a bimodal distribution of weight per cent Si02 in both volcanic and plutonic rocks (Fig. 42) and (2) low K for most rocks, even the most silicic (Fig. 43). 41 Martin and Piwinskii (1972) have identified a bimodal distribution of differentiation index (DI = normative Ne + Lc + Ks + Ab + Or + Qz) of igneous rocks formed in a tensional tectonic environment (versus a normal distribution for rocks formed in a compressional environment). Thus, using their criteria, and assuming no sampling bias, rocks of the Sparta Igneous Complex are more likely to have formed a tensional rather than compressional environment. Coleman and Peterman (1975) outline several rock categories, including oceanic plagiogranite, on a plot of weight per cent K2O (log scale) versus weight per cent Si02. Sparta albite granite and kerato- phyre occur within the field of oceanic trondhjemite when plotted on this diagram (Fig. 43). Gabbros in the Sparta complex appear to exhibit a tholeiitic trend (Figs. 44, 45, 46). Spilites have roughtly similar trends, but are relatively enriched in alkalies, particularly Na20 (Figs. 47, 48). This enrichment in Na is consistent with spilites worldwide (Reinhardt, 1969; Lehmann, 1974; Bamba, 1974; Piirainen and Rouhuhkask, 1974; Sukheswala, 1974). Rocks of the Sparta Igneous Complex appear to exhibit a rather dispersed calc-alkaline trend with respect to Figs. 45, 46. Typical calc-alkaline trends are represented by the fields of Tonga Arc Volcanics and the Snoqualmie Batholith. However, when the alkalies Na and K are treated as independent variables (rather than total alkalies), trends closer to abyssal or trondhjemitic rocks are evident (Figs. 44, 48). The reason for this discrepancy could be relative enrichment of Na with differentiation while K remains low. In summary, six points may be drawn from the whole rock chemical 42 Number of Samples FIGURE 42 Freque ncy histogram, weight SiO., Sparta volcanic rocks (green) and Sparta intrusive rocks (red). 43 Si02 A GAEURO A SPRITE □ DIORITE/TOIIALITC O ALBITE GRANITE O ORTKOCLASE ALBITE GRANITE • QUARTZ KERATOPHYRE FIGURE 43 weight S10, vs. weight % K,0 (log scale) plot of Sparta igneous rocks; diagram and fields^ after Coleman and Peterman (1975"). 44 3 GABBRO SPILITE DIORITE/TONALITE ALBITE GRANITE ORTHOCLASE ALBITE GRANITE 2 QUARTZ KERATOPHYRE KgO 1 ^ A 0 ____ i_^k_____ 1 2 4 6 8 10 12 14 16 CaO FIGURE 44 Weight S K^O vs. weight % CaO plot for Sparta igneous rocks; data for fields from Wager and Brown (1967), Erickson (1969), Ewart et al (1973), Bailey and Blake (1974). 45 Si02 FeOVMgO FIGURE 45 Weight ^ SiO^ vs. FeOVMgO plot of Sparta igneous rocks; data for fields from Wager and Brown (1967), Erickson (1969), Ewart ^ iL (1973). 46 FIGURE 46 AFM ternary diagram of Sparta igneous rocks; data for trends and fields from Wager and Brown (1967), Erickson (1969), Bailey and Blake (1974). 100 Lucas-Tooth (1964). These calculations were celebrated to the following international standards: 6SP, G1, JBl, JGl, GH, GA, ZGI-BM, NIM-G, BR, BCR, NIM-N, ZGI-G, W1, and AGV (Flanagen, 1973). Atomic Absorption 0.3 g excess rock powder from the chip pressing step above was fused with 0.6 g lithium metamorate at 1000° C for 20 minutes. The molten bead was dissolved in 10% HCl then diluted to the linear working range of the equipment employed; <0.5 ppm for Mg, <1 ppm for Na. Lithium (10 ppm) and lanthanum (1 ppm) spikes were added to both standards and unknowns in order to minimize interelement interference. Solutions were analyzed employing a Perkins-Elmer model 306 atomic absorption unit with commercial source lamps. Lamp voltage, wave length of light employed, and absorbance range are as follows: Element Lamp Voltage Wave Length Absorbance Reading Na 12 295 nm 0-.280 Mg 20 mA 285 nm 0-.220 Various dilutions of a multi-element standard solution simulating major element concentrations of silicate rocks was employed to generate a curve of absorbance versus concentration for each element. Least squares regression was used to fit data points obtained to a straight line. Multi-sample analysis from selected rock specimens indicates an experimental two sigma confidence range of 5-8% of oxide present for both MgO and NaO. 99 APPENDIX II WHOLE ROCK ANALYSIS X-Ray Fluorescence ' Sample Preparation Rocks were crushed and weathered fragments were discarded. Samples were split to approximately 100 gram fractions. These fractions were ground to -200 mesh. Approximately ten grams of sample powder were pressed into a 1" diameter by 3/8" thick pellet at a pressure of 22 tons. Analysis This chip was analysed in a vacuum using an EDAX-EXAM model 707, energy dispersive spectrophotometer. A gold target tube was employed at 10 Kev and 256 /jamps. Samples were counted for 200 seconds. Energy levels and window widths for each of the elements determined were as fol1ows: lement Energy Level Window Width Na 1.040 Kev + 0.40 Kev (1.000 Kev-1.080 Kev) A1 1.260 Kev + 0.40 Kev (1.220 Kev-1.300 Kev) Si 1.740 Kev ± 0.40 Kev (1.700 Kev-1.780 Kev) K 3.300 Kev + 0.40 Kev (3.260 Kev-3.340 Kev) Ca 3.680 Kev + 0.40 Kev (3.640 Kev-3.720 Kev) Ti 4.599 Kev ± 0.40 Kev (4.460 Kev-4.540 Kev) Fe 6.400 Kev + 0.40 Kev (6.360 Kev-6.440 Kev) Mn 5.900 Kev + 0.40 Kev (5.840 Kev-5.940 Kev) Raw intensity data was corrected for machine drift with a drift coefficient obtained from an established standard counted alternately with unknown samples. Oxide % was calculated from corrected intensity data using an influence-coefficient calculation based on the method of 98 filled fractures are common. S1075-122 Pseudo-porphyritic cataclastically deformed albite granite. Chlorite and epidote filled fractures are common. Glomero- blasts and augen of quartz are common. SI075-128 Quartz albite t^ylonite. Chlorite and epidote filled fractures are common. S1075-186 Medium-grained moderately sheared granophyric albite granite. 97 S976 -78 Porphyritic quartz keratophyre. Phenocyrsts of quartz albite and brown chlorite. Plagioclase is 15% altered to saussurite. S976-79 Porphyritic quartz keratophyre. Phenocyrsts of quartz, albite and epidote. Plagioclase is slightly altered to saussurite. S976-81A Porphyritic quartz keratophyre. Phenocyrsts of quartz albite and blue chlorite. Plagioclase is 40% altered to saussurite. Sheared Albite Gram'te/Keratophyre SI075-129 Quartz albite mylonite. SI 075-135 Pseudo-porphyritic cataclastically deformed albite granite. Prehnite filled fractures common. S1075-186 Moderately sheared medium-grained granphyric albite granite Chlorite and epidote in fractures. S1075-43 Pseudo-porphyritic cataclastically deformed albite granite. Prehnite filled fractures common. S1075-44 Pseudo-porphyritic cataclastically deformed albite granite, chlorite and epidote filled fractures common. SI 075-67 Moderately sheared medium-grained albite granite. Well developed mortar texture. Sheared Albite Granite/Quartz Keratophyre SI075-91 Pseudo-porphyritic cataclastically deformed albite granite. chlorite and epidote filled fractures are common. S1075-115 Fine-grained heavily sheared albite granite. Chlorite and epidote filled fractures are common. S1075-116 Fine-grained moderately sheared albite granite. Prehnite 96 clase is 70% altered to epidote and mottled albite. Horn blende is replaced by chlorite and epidote. Granite SI 075-130 Medium-grained allotriomorphic granular albite orthoclase granite. Even, pervasive mild alteration of plagioclase. S1075-180 Medium-grained hypidiomorphic granular orthoclase albite granite. Zoned plagioclase is mantled by oligoclase. Saussuritization is 40% in cores of plagioclase. S1075-103 Coarse-grained slightly sheared allotriomorphic granular orthoclase albite granite. Zoned plagioclase is 80% saussuritized in cores. S976-84 Medium-grained slightly sheared granophyric orthoclase albite granite. S976-85 Medium-grained hypidiomorphic granular hornblende granite. Oscillatory zoning in plagioclase is selectively replaced by saussurite. 107 5-48 Medium-grained slightly sheared porphyritic hornblende oligoclase albite granite. Hornblende and minor biotite are partially replaced (20%) by chlorite. Oscillatory zoning in plagioclase is selectively replaced by saussurite. Quartz Keratophyre S976-2 Porphyritic quartz keratophyre. Weakly zoned plagioclase is 30% altered to saussurite in cores. S976-62 Slightly sheared porphyritic quartz keratophyre. Weakly zoned plagioclase 80% altered to saussurite in cores. S976 -68 Porphyritic quartz keratophyre. Plagioclase is 40% altered to saussurite. 95 is strained and has sutured grain boundaries. S976-108 Fine-grained hypidiomorphic granular hornblende diorite. Plagioclase is slightly altered (<.5%) to saussurite. Albite Granite S1075-22 Medium-grained granophyric albite granite. SI 07.5-25 Medium-grained allotriomorphic granular albite granite. 20% saussuritization of albite. SI 075-41 Medium-grained granophyric albite granite. S976-66 Fine-grained porphyritic albite granite. S976-71 Fine-grained porphyritic albite granite. 20% saussuriti zation of plagioclase. S976-89 Medium-grained granophyric albite granite. S976-133 Fine-grained porphyritic albite granite. Slight (<.5%) saussuritization of albite. S976-137 Fine-grained porphyritic albite granite. Slight saussuri tization of weakly zoned albite. S976-138 Medium-grained allotriomorphic granular albite granite. Weakly zoned albite phenocrysts with 15% alteration to saussurite in cores. S976-139 Medium-grained allotriomorphic granular albite granite. Weakly zoned albite phenocrysts with saussuritized cores locally altered to epidote. S976-100 Medium-grained granophyric albite granite. S976-86 Medium-grained moderately sheared allotriomorphic granular granite. Plagioclase is 15% altered saussurite. Hornblende is replaced by chlorite and epidote. S976-87 Medium-grained allotriomorphic granular granite. Plagio- 94 S976-50 Porphyritic amygduloidal spilite. Zoned plagioclase phenocrysts 30% altered to saussurite in cores. Chlorite pseudomorphs pyroxene phenocrysts completely. S976-64 Porphyritic spilite. Zoned plagioclase phenocrysts 95% altered to saussurite in cores. Chlorite pseudomorphs pyroxene phenocrysts completely. S976-65 Porphyritic amygduloidal spilite. Plagioclase phenocrysts 40% altered to saussurite. S976-128 Porphyritic spilite. Augite phenocrysts are 40% altered to chlorite. Tonalites and Diorites SI 075-126 Fine-grained slightly porphyritic hornblende tonalite. Weakly zoned plagioclase is 80% altered to saussurite in cores. S1075-131 Fine-grained porphyritic quartz hornblende diorite. Weakly zoned plagioclase is 70% altered to saussurite. S976-99 Medium-grained hypidiomorphic granular hornblende diorite. Weakly zoned plagioclase is 70% altered to saussurite in cores. S976-96 Fine-grained slightly porphyritic hornblende tonalite. Weakly zoned plagioclase is 85% altered to saussurite in cores. S375-13 Medium-grained hypidiomorphic granular quartz hornblende diorite. Plagioclase is 30% altered to saussurite, biotite is 90% replaced by chlorite. S375-15 Medium-grained allotriomorphic hornblende quartz biotite diorite. Plagioclase is 15% altered to saussurite, quartz 93 Pi kes S1075-77 Fine-grained holocrystalline hornblende diorite porphery. Zoned plagioclase is saussuritized in the cores. S1075-86 Very fine-grained hypidiomorphic granular quartz hornblende diorite. Slight replacement (< 5%) of plagioclase by saussurite, slight replacement (<5%) of hornblende by chlorite. S1075-105 Fine-grained slightly porphyritic hypidiomorphic granular quartz hornblende diorite. Weakly zoned plagioclase is 40% replaced by saussurite in cores. S1075-109 Fine-grained slightly porphyritic hypidiomorphic granular hornblende diorite. Weakly zoned plagioclase is 30% replaced by saussurite in cores. S976-142 Fine-grained hypidiomorphic granular hornblende quartz diorite. Hornblende is 95% altered to chlorite and opaques, plagioclase is 25% altered to saussurite. S976-143 Fine-grained allotriomorphic granular hornblende quartz diorite. Hornblende is altered (95%) to chlorite and opaques, plagioclase is heavily (90%) saussuritized. Spilite S976-45 Porphyritic spilite, plagioclase phenocrysts 40% altered to saussurite. S976-47 Porphyritic atnygduloidal spil ite. Plagioclase phenocrysts 80% altered to saussurite. S976-44 Porphyritic spilite. Plagioclase phenocrysts 30% altered to saussurite. Pyroxene phenocrysts 50% altered to chlorite. 92 APPENDIX I BRIEF PETROGRAPHIC DESCRIPTIONS OF SPECIMENS ANALYSED Gabbros SI075-71 Medium-grained allotriomorphic granular hornblende gabbro. Hornblende is 40% altered to chlorite, plagioclase is 20% altered to Saussurite. S1075-156 Medium-grained hypidiomorphic granular hypersthene augite gabbronorite. Hypersthene is 60% altered to chlorite or serpentine, plagioclase is slightly altered to saussurite. S1075-157 Medium-grained hypidiomorphic granular hypersthene augite gabbronorite. Hypersthene is 70% altered to serpentine or chlorite, plagioclase is slightly altered to saussurite. S1075-159 Medium-grained hypidiomorphic granular hypersthene augite gabbronorite containing 13% opaques (pyrite and chalcopyrite). Hypersthene is 50% altered to chlorite or serpentine, augite is 10% altered to hornblende and chlorite, plagioclase is <5% altered to saussurite. S1075-201 Fine-grained hypidiomorphic granular augite gabbro containing 8% opaques (pyrite and chalcopyrite). Augite is slightly altered to chlorite, plagioclase is slightly altered to saussurite. S1075-20 Medium-grained allotriomorphic granular hornblende gabbro. Hornblende is 25% altered to chlorite, plagioclase is 15% altered to saussurite. 91 eastern Oregon and western Idaho interpreted as a pre-Cretaceous island-arc system: G.S.A. Abst. with Programs, v. 5, no. 1, pp. 115-116. Thayer, T. P., and Himmelberg, G. R., 1968. Rock succession in the alpine-type mafic complex at Canyon Mountain, Oregon: address before XXIII Internat. Geol. Cong., v. 1, pp. 175-186. Vallier, T. L., 1974. A preliminary report on the geology of part of the Snake River Canyon, Oregon and Idaho: Oregon Dept. Geol. and Min. Indus. Publ . GMS-6. Wager, L. R., and Brown, G. M., 1967. Layered Igneous Rocks, San Francisco, W. H. Freeman & Co., 588 p. Wagner, N. S., 1955. Summary of Wallowa Mountains geology: Ore Bin, V. 17, no. 5, pp. 31-35. Washburn, C., 1903. Notes on the marine sediments of eastern Oregon: Jour. Geol. v. 11, pp. 224-225. White, D. E., 1974. Diverse origins of hydrothermal ore fluids: Econ. Geol., v. 69, no. 6, pp. 954-973. Wilson, R. A. M., and Ingham, F. T., 1959. The geology of the Xeros- Troodos area: Geol. Sur. Dept, of Cyprus, Memoir #1, 84 p. 90 Ross, C. P., 1938. Geology of the Wallowa Mountains, Oregon: Oregon Dept. Mines and Geol. Bull. 3, pp. 1-74. Smith, R. E., 1968. Redistribution of major elements in the alteration of some basic lavas during burial metamorphism: Jour. Petrol., V. 9, part 2, pp. 191-219. Smith, W. D. P., 1919. The salient features of the geology of Oregon: Jour. Geol., v. 27, no. 2, pp. 79-120. Smith, W. D. P., and Allen, J. E., 1941. Geology and physiography of the northern Wallowa Mountains, Oregon: Oregon Dept. Geol. and Min. Indus. Bull. 12, pp. 1-65. Spooner, E. T. C., Beckinsale, R. D., Fyfe, W. S., and Smewing, J. D., 1974. 0^^ enriched ophiolitic metabasic rocks from E. Liguria (Italy), Pindos (Greece), and Troodos (Cyprus): Contrib. Min. Petrol., V. 47, pp. 41-62. Sukheswala, R. N., 1974. Gradation of tholeiitic Deccan basalt into spilite, Bombay, India: jj^Amstutz, G. C., ed., Spilites and Spilitic Rocks, I.U.G.S., series A, no. 4, pp. 229-252. Taubeneck, W. H., 1957. Geology of the Elkhorn Mountains, northeastern Oregon: Bald Mountain batholith: Geol. Soc. Am. Bull., v. 68, no. 2, pp. 181-238. , 1964. Cornucopia stock, Wallowa Mountains, north eastern Oregon - field relations: Geol. Soc. Am. Bull., v. 75, no. 11, pp. 1093-1115. , 1967. Petrology of Cornucopia tonalite unit. Cornu copia stock, Wallowa Mountains, northeastern Oregon: Geol. Soc. Am. Spec. Paper 91, 56 p. Thayer, T. P., and Brown, C. E., 1973. Blue Mountain region of north- 89 of the Canadian Cordillera: a plate tectonic model: Am. Jour. Sci., V. 272, pp. 577-602. Morganti, J. M., 1972. Geology and ore deposits of the Seven Devils volcanics. Seven Devils mining district. Hells Canyon, Idaho: unpublished M. S. thesis, Washington State Univ., 152 p. Phelps, D. W., 1977. Origin of albite granites near Sparta, northeastern Oregon: G.S.A. Abst. with Programs, v. 9, no. 4, p. 481. Phillips, I. R., 1974. Myremekite - one hundred years later: Lithos, V. 7, pp. 181-194. Piirainen, T., and Rouhunkoski, P., 1974. General features of the spilitic rocks in Finland: in Amstutz, G. C., ed., Spilites and Spilitic rocks, I.U.G.S., series A, no. 4» pp. 191-206. Prostka, H. J., 1962. Geology of the Sparta quadrangle, Oregon: Oregon Dept. Geol. and Min. Indus., Geol. Map Series 1, scale 1:62,500. Prostka, H. J., 1963. Geology of the Sparta quadrangle, Oregon: unpublished Ph.D. dissertation, Johns Hopkins Univ., 245 p* O'Connor, J. T., 1965. A classification for quartz-rich igneous rocks based on feldspar ratios: in Geol. Sur. Res., 1965, U.S.G.S. Prof. Paper 525-B, pp. B79-B84. Reinhardt, B. M., 1969. On the genesis and emplacement of ophiolites in the Oman Mountains geosyncline: Schweiz. Min. Petrog. Mitt., V. 49, pp. 1-30. Rogers J. J. W., Burchfiel, B. C., Abbot, E. W., Anapohl , J. K., Ewing, A. H., Koehnken, P. J., Novitsky, J. M., and Talukdar, S. C., 1974. Paleozoic and lower mesozoic volcanism and continental growth in the western United States: Geol. Soc. Am. Bull., v. 85, no. 12, pp. 1913-1924. 88 , 1975. Generation of potassium-poor magmas in the northern Sierra Nevada and the Svecofennian of Finland: U.S.G.S. Jour. Res., V. 3, no. 6, pp. 631-645. I.U.G.S. Subcommission on the systematics of igneous rocks, 1973. Plutonic rocks: Geotimes, v. 18, no. 10, pp. 26-30. Krausfopf, K. B., 1943. The Wallowa batholith, Oregon: Am. Jour. Sci., V. 241, pp. 607-628. Laudon, T. S., 1956. The stratigraphy of the upper Triassic Martin Bridge Formation and "lower sedimentary series" of the northern Wallowa Mountains, Oregon: unpublished M. S. thesis, Univ. of Wisconsin, 100 p. Lehmann, E., 1974. Environmental effects in magmatic spilite: in. Amstutz, G. C., ed., Spilites and Spilitic Rocks, I.U.G.S., series A., no. 4, pp. 23-38. Lidiak, E. G., 1964. Petrology of the andesitic spilitic and kerato- phyric lavas, north-central Puerto Rico: Geol. Soc. Am. Bull., V. 76, no. 1, pp. 57-88. Lindgren, W., 1901. The gold belt of the Blue Mountains of Oregon: U.S.G.S. 22nd Annual Rept., part 2, pp. 585-586. Lucas-Tooth, J., and Pyne, C., 1964. The accurate determination of major constituents by x-ray fluorescent analysis in the presence of large interelement effects: Adv. X-ray Analysis, v. 7, p. 523. Martin, R. F., and Piwinskii, A. J., 1972. Magmatism and tectonic settings: Jour. Geophys. Res., v. 77, no. 26, pp. 4966-4975. Miyashiro, A., 1973. Metamorphism and Metamorphic Belts, New York, John Wiley & Sons, 492 p. Monger, J. W. H., Souther, J. G., and Gabrielse, H., 1972. Evolution 87 genesis: in Amstutz, G. C., ed., Spilities and Spilitic Rocks, I.U.G.S., series A, no. 4, pp. 373-386. Dickinson, W. R., 1964. Metasomatic quartz keratophyre in central Oregon: Am. Jour. Sci., v. 260, no. 4, pp. 249-266. Erickson, E. H., Jr., 1969. Petrology of the composite Snoqualmie Batholith, central Cascade Mountains, Washington: Geol. Soc. Am. Bull., V. 80, no. 11, pp. 2213-2236. Ewart, A., Bryan, W. G., and Gill, J. B., 1973. Mineralogy and geo chemistry of the younger volcanic islands of Tonga, southwest Pacific: Jour. Petrol., v. 14, pp. 429-465. Flanagan, F. J., 1973. 1972 values for international geochemical reference samples: Geochim. et Cosmochim. Acta., v. 37, pp. 1189- 1200. Gary, M., McAfee, R., Jr., and Wolf, C. L., eds., 1972. Glossary of Geology: Am. Geol. Inst., Washington, D. C., 805 p. Gilluly, J., 1933. Replacement origin of the albite granite near Sparta, Oregon: U.S.G.S. Prof. Paper 175-C, pp. 65-81. , 1935. Keratophyres of eastern Oregon and the spilite pro blem: Am. Jour. Sci., v. 29, no. 171, pp. 225-252 and pp. 336-352. , 1937. Geology and mineral resources of the Baker quadrangle, Oregon: U.S.G.S. Bull. 879, 119 pp. Goodspeed, G. E., 1929. The mode of origin of a reaction porphyry dike of Cornucopia, Oregon: Jour. Geol., v. 37, pp. 158-170. Hamilton, W., 1969. Mesozoic California and the underflow of Pacific mantle: Geol. Soc. Am. Bull., v. 80, no. 12, pp. 2409-2430. Hietanen, A., 1947. Archean geology of the Turku District in southwestern Finland: Geol. Soc. Am. Bull., v. 58, no. 11, pp. 1019-1084. 86 BIBLIOGRAPHY Ave Lallemant, H. G., and Phelps, D. W., 1977. The Mesozoic orogenic events in the southeastern part of the Blue Mountain region, Oregon: G.S.A. Abst. with Programs, v. 9, no. 4, p. 383. Bailey, E. H., and Blake, M. C., Jr., 1974. Major chemical character istics of Mesozoic Coast Range ophiolite in California: Jour. Research, U.S.G.S., v. 2, no. 6, pp. 637-656. Bamba, T., 1974. A series of magmatism related to the formation of spilite: iji Amstutz, G. C., ed., Spilites and Spilitic Rocks, I.U.G.S., series A, no. 4, pp. 83-112. Battey, M. H., 1974. Spilites as weakly metamorphosed tholeiites: iji Amstutz, G. C., ed., Spilites and Spilitic Rocks, I.U.G.S., series A, no. 4, pp. 365-372. Bostwick, D. A., and Koch, G. S., Jr., 1972. Permian and Triassic rocks of northeastern Oregon: Geol. Soc. Am. Bull., v. 75, no. 3, pp. 419-422. Brooks, H. C., 1976. Pre-Cenozoic tectonic framework, eastern Oregon and western Idaho: G.S.A. Abst. with Programs, v. 8, no. 3, p. 357. Brooks, H. C., and Vallier, T. L., 1967. Progress report on the geology of part of the Snake River Canyon, Oregon and Idaho: Ore Bin, V. 29, pp. 233-266. Burchfiel, B. C., and Davis, C. A., 1972. Structural framework and evolution of the southern part of the Cordilleran orogen, western United States: Am. Jour. Sci., v. 272, pp. 97-118. Coleman, R. G., and Peterman, Z. E., 1975. Oceanic plagiogranite: Jour. Geophys. Res., v. 80, no. 8, pp. 1099-1108. Coombs, D. S., 1974. On the mineral facies of spilitic rocks and their 85 ACKNOWLEDGEMENTS The writer wishes to thank Dr. E. H. Brown, chairman of the advisory committee, for his invaluable suggestions and aid given during the course of this research. Thanks are also extended to Dr. R. S. Babcock and Dr. D. R. Pevear for serving on the advisory committee and for their critical reading of the manuscript. Thanks are conveyed to H. C. Brooks of the Oregon Department of Geology and Mineral Industries for discussions and suggestions regarding regional geology. Dr. G. E. Young and others connected with Eastern Oregon State College allowed the use of their excellent facility, the Lily White Environmental Field Station. This use is deeply appreciated. Finally, thanks are due to my wife, Joan Almy, who drafted the figures, and to Patty Combs who typed the manuscript. Their patience and attention to detail helped insure the completion of this research. 84 TABLE 8. Continued SHEARED ALBITE GRANITE/QUARTZ KERATOPHYRE Sample Number: SI 075-116 S107 5-122 S1075-128 SI 075-186 Major Elements: Wt% Si02 79.19 78.61 74.89 77.96 AI2O3 11.09 9.75 11.73 11.04 Ti02 0.21 0.28 0.18 0.19 Fe as Fe203 0.81 2.25 2.48 1.58 MgO 0.03 0.18 0.60 0.71 MnO 0.01 0.01 0.03 0.02 CaO 1.79 2.06 0.65 1.05 Na20 5.07 4.23 7.12 6.69 K2O 0.12 0.12 0.12 0.12 Total 98.3 97.5 97.79 99.35 83 TABLE 8. Continued SHEARED ALBITE GRANITE/QUARTZ KERATOPHYRE Sample Number: SI 075-44 S1075-67 SI 075-91 S1075-115 Major Elements: Wt% Si02 80.31 76.53 78.54 79.63 AI2O3 7.37 12.16 10.60 10.50 Ti02 0.27 0.14 0.38 0.11 Fe as Fe203 3.51 1.55 1.26 1.15 MgO 0.39 0.31 0.27 0.10 MnO 0.06 0.01 0.01 0.02 CaO 1.03 2.57 0.96 0.85 Na20 3.55 6.61 5.37 7.42 bz 0 C\J 0.05 0.21 0.85 0.11 Total 96.5 100.1 98.2 99.9 82 TABLE 8. Whole Rock Major Element Analyses of Sparta Igneous Rocks SHEARED ALBITE GRANITE/QUARTZ KERATOPHYRE Sample Number: S1075-129 S1075-135 S1075-186 S1075-43 Major Elements: Wt% Si02 76.08 75.88 77.96 82.22 AI2O3 11.55 10.71 11.04 7.37 Ti02 0.18 0.29 0.19 0.34 Fe as F6202 2.02 2.81 1.58 2.37 MgO 0.65 1.35 0.71 1.90 MnO 0.01 0.0 0.02 0.06 CaO 1.71 4.42 1.05 0.0 Na20 6.19 4.58 6.69 4.50 0 CM 0.11 0.18 0.12 0.17 Total 98.5 100.2 99.3 99.4 81 TABLE 7. Continued QUARTZ KERATOPHYRE Sample Number: S976 -78 S976-79 S976-81A Major Elements: WU Si02 73.93 73.87 69.79 AI2O3 12.26 12.17 13.90 Ti02 0.28 0.27 0.42 Fe as Fe203 2.41 2.47 3.21 MgO 1.04 0.22 1.93 MnO 0.02 0.01 0.07 CaO 0.16 0.0 0.07 Na20 6.57 6.42 5.42 0 CM 0.06 0.50 0.22 Total 96.7 95.9 95.0 Modes: Groundmass 65.4 64.3 Quartz 12.3 9.6 A1 bi te 19.5 19.9 Plagioclase (An75) - - Chlorite 2.6 . 1.8 Epidote - 4.1 Opaques 0.1 0.3 Total 100.0 100.0 80 TABLE 7. Whole Rock Major Element Analyses of Sparta Igneous Rocks QUARTZ KERATOPHYRE Sample Number: S976-2 S976-62 S976-68 Major Elements: WU Si02 72.59 67.97 75.78 AI2O3 11.82 13.55 13.12 Ti02 0.32 0.54 0.18 Fe as Fe203 2.82 5.31 0.82 MgO 1.68 3.06 2.26 MnO 0.10 0.07 0.0 CaO 0.31 0.21 0.30 Na20 7.62 6.43 5.12 K2O 0.39 0.42 0.49 Total 97.6 97.6 98.1 Modes: Groundmass 67.2 48.3 Quartz 11.5 20.1 Albite 12.1 28.9 Plagioclase (An75) 9.5 - Chlori te - 2.7 Epidtoe - - Opaques - - Total 100.0 100.0 79 TABLE 6. Continued GRANITE Sample Number: S976 -84 Major Elements: Wt% Si02 75.22 AI2O3 11.33 Ti02 0.27 Fe as 2.36 MgO 0.93 MnO 0.03 CaO 2.36 Na20 5.07 0 CM 1.16 Total 96.7 Modes : Quartz 35.4 Albite 34.4 Plagioclase 19.9 Orthoclase - K-Spar 13.7 Chlorite 1.8 Epidote 5.6 Hornblende - Biotite - Opaques 0.1 Apatite - Total 100.0 78 TABLE 6. Whole Rock Major Element Analyses of Sparta Igneous Rocks GRANITE Sample Number: SI 075-48 S107 5-130 S1075-180 S1075-1I Major Elements: Wt% Si02 71.71 76.32 76.54 72.82 AI2O3 13.43 12.48 11.09 11.04 Ti02 0.29 0.07 0.24 0.40 Fe as ^^2^2 2.90 1.03 2.35 4.56 MgO 0.65 0.21 0.10 0.86 MnO 0.04 0.0 0.02 0.10 CaO 2.38 0.38 1.32 1.51 Na20 4.29 5.23 3.86 4.88 K2O 1.05 3.89 1.66 1.61 Total 96.7 99.6 97.2 97.8 Modes : Quartz 38.8 37 .1 43.7 34.9 Albite 42.8 17.5 15.9 41.0 Plagioclase 0.0 - 17.1 10.1 Orthoclase 11.7 - - - K-Spar - 41.1 15.6 4.4 Chlorite 0.3 3.7 7.4 5.6 Epidote 0.6 0.6 0.3 2.0 Hornblende 2.0 - - 1.4 Biotite 1.4 - - - Opaques 2.4 - - 0.6 Apatite - tr 7 tr Total 100.0 100.0 100.0 100.0 77 TABLE 5. Continued ALBITE GRANITE Sample Number: S976-85 S976 -86 S976-87 Major Elements: Wt% Si02 68.18 69.35 39.34 AI2O3 12.02 12.95 14.78 TiO^ 0.50 0.40 0.49 Fe as 4.41 4.38 3.65 MgO 0.81 1.68 1.93 MnO 0.06 0.07 0.04 CaO 3.20 5.15 2.67 Na20 5.91 4.37 3.52 0 1.17 0.22 1.12 r o Total 96.3 98.6 97.5 Modes : Quartz 34.1 43.8 Albite 33.3 33.7 Plagioclase 20.0 - Orthoclase 0.7 - K-Spar - - Chlorite 1.8 6.9 Epidote 1.1 15.6 Hornblende 7.0 - Biotite 0.1 - Opaques 1.8 - Apatite tr - Total 100.0 100.0 76 TABLE 5. Continued ALBITE GRANITE Sample Number: S976-1 38 S976-139 S976-86 Major Elements: Wt% Si02 72.79 72.85 69.35 AI2O3 14.14 13.13 12.95 Ti02 0.38 0.34 0.40 Fe as Fe202 2.89 2.45 4.38 MgO 1.31 1.03 1.68 MnO 0.02 0.02 0.07 CaO 0.21 1.54 5.15 Na20 5.02 5.27 4.37 K2O 0.06 0.62 0.22 Total 96.8 97.2 98.56 Modes : Quartz 34.6 32.1 43.8 Albite (An5) 53.3 51.1 33.7 Plagioclase (An 10) - 7.1 - Chlorite 8.6 4.1 6.9 Epidote 3.1 5.4 15.6 Prehnite - - - Opaques 0.4 0.2 - Sphene - - - Apatite - - - Total 100.0 100.0 100.0 75 TABLE 5- Continued ALBITE GRANITE Sample Number: S976-71 S976-89 S976-133 S976-137 Major Elements: Wt% Si02 83.18 77.59 74.16 72.32 AI2O3 8.13 11.30 13.64 13.11 Ti02 0.21 0.14 0.30 0.32 Fe as 1.23 1.18 1.33 2.55 MgO 1.63 1.01 0.72 1.03 MnO 0.0 0.0 0.01 0.0 CaO 0.0 0.57 0.68 1.96 Na20 4.52 5.51 5.82 5.14 K2O 0.14 0.21 0.46 0.60 Total 98.9 97.5 97.1 97.0 Modes : Quartz 40.4 42.2 32.7 35.9 Albite 56.5 55.2 63.2 58.1 Plagioclase (An >10) - Chlorite 1.8 1.0 2.9 4.1 Epidote 1.1 1.3 1.0 1.8 Prehnite - Opaques 0.2 - 0.2 - - Sphene - 0.3 - Apatite - Total 100.0 100.0 100.0 100.0 74 TABLE 5. Whole Rock Major Element Analyses of Sparta Igneous Rocks ALBITE GRANITE Sample Number: S1075-22 S1075-25 SI 075-41 S1075-66 Major Elements: Wt% Si02 78.73 69.07 73.88 79.35 AI2O3 10.50 13.34 11.36 11.74 1 — 0 0.18 0.58 0.32 0.13 ro Fe 4s FejOj 1.64 4.43 3.37 1.13 MgO 0.30 0.69 0.68 0.45 MnO 0.03 0.21 0.06 0.0 CaO 1.78 3.67 1.33 0.01 N320 6.61 5.63 7.75 4.96 0 CM 0.16 0.41 0.20 0.32 Total 99.9 98.0 98.9 98.0 Modes : Quartz 44.8 34.6 36.5 36.6 Albite 48.4 46.9 54.2 59.2 Plagioclase (An 10) - - - - Chlorite 2.5 10.5 4.8 2.6 Epidote 4.2 7.5 3.8 0.3 Prehnite 0.1 0.1 - - Opaques - 0.1 0.4 1.3 Sphene - 0.2 0.3 - Apatite - tr - - Total 100.0 100.0 100.0 100.0 73 TABLE 4. Continued DIORITE/TONALITE Sample Number: S375-13 S375-15 S976-108 Major Elements: Wt% Si02 56.68 67.86 50.31 AI2O3 16.11 12.28 16.28 Ti02 0.69 0.57 1.54 Fe as Fe202 9.35 4.95 14.33 MgO 6.09 1.73 3.65 0.21 MnO 0.18 0.80 CaO 7.53 4.44 7.72 Na20 2.96 3.52 3.70 1.10 K2O 1.33 0.55 Total 100.9 96.5 98.29 72 TABLE 4. Whole Rock Major Element Analyses of Sparta Igneous Rocks DIORITE/TONALITE Sample Number: SI 075-99 S1075-126 S1075-131 Major Elements: Wt% Si02 55.80 63.11 56.04 AI2O3 16.69 14.41 14.96 Ti02 0.91 1.11 0.87 Fe as Fe203 8.80 7.41 8.40 . MgO 3.65 2.91 4.59 MnO 0.13 0.08 0.06 CaO 7.33 4.60 6.40 Na20 4.37 5.15 5.82 0 CM 1.33 0.35 0.53 Total 99.4 99.0 99.2 Modes : Quartz 4.8 5.3 5.9 Plagioclase 52.5 66.2 (An20) 64.4 (An20) Hornblende 39.6 11.8 26.1 Opaques 1.3 4.4 2.2 Chlori te 0.3 0.2 0.2 Epidote 0.4 0.3 0.6 Prehnite 1.0 - 0.6 Apatite - tr - Sphene - 0.1 - Total 100.0 100.0 100.0 71 TABLE 3. Continued SPILITE Sample Number: S976-64 S976-65 S976 -128 Major Elements: Wt% Si02 50.40 52.45 48.55 AI2O3 16.30 14.62 14.09 Ti02 1.01 1.16 0.67 Fe as Fe202 11.26 11.70 10.87 MgO 6.40 4.71 10.72 MnO 0.22 0.15 0.17 CaO 6.86 8.91 12.34 Na20 4.56 5.75 1.54 K2O 0.74 0.06 10.72 Total 97.8 99.51 99.0 TABLE 3. Whole Rock Major Element Analyses of Sparta Igneous Rocks SPRITE Sample Number: S976 -45 S976-44 S976-47 976-50 Major Elements: Wt% Si02 54.23 62.63 49.24 52.98 AI2O3 15.68 14.31 16.29 14.48 Ti02 0.93 0.73 1.43 0.83 Fe as Fe203 8.36 6.38 13.13 9.75 MgO 0.79 2.41 7.29 6.31 MnO 0.12 0.11 0.18 0.18 CaO 9.46 1.36 7.17 6.81 Na20 7.12 5.80 3.56 5.45 K5O 0.0 2.59 0.88 0.02 Total 97.0 96.3 99.2 96.8 69 TABLE 2. Continued BASIC DIKES Sample Number: S976 -143 S1075-109 S1075-T Major Elements: Wt% Si02 54.79 52.54 56.49 AI2O3 15.10 16.09 14.54 0 C\J 0.80 1.24 1.37 Fe as 11.24 11.05 9.60 MgO 10.24 5.22 4.41 MnO 0.11 0.17 0.14 CaO 1.27 8.68 6.73 N320 1.98 2.92 5.05 K2O 0.52 1.11 0.50 Total 97.0 99.0 98.8 Modes : Plagioclase 44.7 (An5) 51.2 62.9 Hornblende - 46.4 27.2 Opaque 1.3 1.6 2.3 Quartz 13.0 0.8 2.9 Chlorite 35.8 - - Epidote 5.2 - - Albite • - - 3.9 Prehnite - - 0.8 Apatite tr tr tr Total 100.0 100.0 100.0 68 TABLE 2. Whole Rock Major Element Analyses of Sparta Igneous Rocks BASIC DIKES Sample Number: S1075-77 SI 075-86 S976-142 Major Elements: Wt% Si02 48.93 51.22 57.19 AI2O3 15.00 14.65 14.02 Ti02 0.76 0.75 0.68 Fe as 11.33 10.49 7.90 MgO 7.28 9.81 9.79 MnO 0.17 0.16 0.09 CaO 12.00 6.74 2.32 Na20 3.12 4.78 4.24 K2O 1.92 1.13 0.19 Total 100.5 99.7 96.4 Modes : Plagioclase 27.8 30.0 43.6 ( Hornblende 8.7 56.8 - Opaque 1.2 1.0 0.8 Quartz - - 14.2 Groundmass 62.3 - - Chlorite - 10.8 34.9 Epidote - 0.8 6.5 Actinolite - 0.6 - Apatite tr tr - Total 100.0 100.0 100.0 67 TABLE 1. Continued GABBRO Sample Number: S1075-159 S1075-201 S375 -20 Major Elements: Wt% Si02 43.80 45.95 48.88 AI2O3 13.34 15.16 17.96 Ti02 1.54 1.48 2.34 Fe as Fe203 15.44 15.54 12.64 MgO 10.88 4.69 5.54 MnO 0.16 0.25 0.20 CaO 13.54 11.04 10.34 Na20 0.53 1.44 2.17 0 0.17 0.19 0.19 ro Total 99.4 95.7 100.3 Modes: Plagioclase 36.5 52.2 Hornblende - - Augite 14.8 37.3 Opx 25.9 1.2 Chlorite 9.6 0.8 Epidote - 0.3 Opaque 13.2 8.2 Prehnite - - Total 100.0 100.0 66 TABLE 1. Whole Rock Major Element Analyses of Sparta Igneous Rocks GABBRO Sample Number*: S1075-71 S1075-156 SI 075-1! Major Elements: Wt% Si02 47.17 48.86 46.61 AI2O3 17.42 18.62 14.13 Ti02 0.75 0.36 0.26 Fe as 6.76 9.01 10.62 MgO 9.72 8.29 12.00 MnO 0.20 0.13 0.16 CaO 9.31 14.33 12.77 Na20 3.86 0.69 0.51 K2O 0.19 0.02 0.15 Total 98.2 100.3 97.2 Modes : Plagioclase 66.7 49.1 60.6 Hornblende 19.8 1.0 - Augite - 22.4 21.3 Opx - 20.9 17.4 Chlorite 10.6 2.0 0.1 Epidote 0.9 4.0 0.3 Opaque 2.0 0.6 0.2 Prehnite - - 0.1 Total 100.0 100.0 100.0 *A11 sample numbers are preceded by department prefix "56-". 65 Or FIGURE 55 Ab-An-Or (ATbite-Anorthite-Orthoclase) ternary diagram showing normative plots of Sparta silicic volcanic rocks, based on the classifi cation of O'Connor (1965). 64 FIGURE 54 Q-A-P (Quartz-Total Alkali Feldspar-Plagioclase) ternary diagram showing normative plots of Sparta felsic Plutonic rocks based on I.U.G.S. 0973) classification; a=alkali granite, b=granite, c=tonalite, d=diorite. 63 island arc was developed. Quartz keratophyre and albite granite thus represent volcanic flows and underlying plutonic magma sources, respectively, that were developed in this arc environment. 62 Crosscutting relationships of silicic and mafic dikes indicate that intrusions of silicic and mafic dikes were contemporary. These dikes also occur locally in, and are chimically similar to, volcanics of the Clover Creek Greenstone. They are assumed to be the feeders of spilite and quartz keratophyre flows of that unit. Albite granite and quartz keratophyre have identical major element chemistry, are closely associ ated in the field, have mutually gradational textures, and are thus pro bably comagmatic. The Clover Creek Greenstone has been interpreted as a fossil island arc on the basis of abundant volcanic flows, pyroclastic materials, a capping of reef limestones and occurrence in a belt of similar island arc derived rocks in eastern Oregon and western Idaho (Brooks and Vallier, 1967; Thayer and Brown, 1973; Vallier, 1974; Brooks, 1976). Granite near Sparta, therefore, can be interpreted to be of island arc origin as well. Gabbro and ultramafic rocks associated with the albite granite at Sparta have been interpreted to be tectonically dismembered ophiolite (Brooks, 1976; Ave Lallemont and Phelps, 1977), possibly representing oceanic crust upon which the arc was developed. Although low pressure differentiation of gabbro during generation of oceanic crust may produce oceanic plagiogranite as suggested by Coleman and Peterman (1975), silicic rocks thus formed would probably account for less than 10% of the volume of an ophiolite (Wilson and Ingham, 1959; Reinhardt, 1969; Coleman and Peterman, 1975). The volume of albite granite compared to that of gabbro in the Sparta complex is far too great to be the result of fractionation of the gabbro. It thus seems that the albite granite and quartz keratophyre developed independently of the gabbro. Possibly the gabbro represents oceanic crustal material upon which a youthful 61 of mobile species (e.g. Na, K, Si) cannot be discounted. Predominance of igneous textures, apparent absence of widespread metasomatic altera tion, and absence of a suitable source for large amounts of silica necessary to produce a granite body of this size (Plate 1) indicate that the Sparta albite granite is a primary igneous body. Summary of Alteration Data These results show that cataclastically deformed zones do not appear to have experienced more replacement of Si and Na than undeformed rock, thus, these zones do not appear to have acted as channels for altering fluids as suggested by Gilluly (1933). Likewise, the development of metamorphic minerals appears to be an isochemical process. Thus, field relations and textural and chemical evidence indicate that the Sparta albite granite is a primary igneous body. These conclusions disagree with Gilluly's (1933) hypothesis of a replacement origin for this albite granite body. CONCLUSIONS The chemical and textural data of this research indicate that the Sparta albite granite body is of igneous origin. Phelps (1977) has independently reached a similar conclusion based on field and petro graphic study and microprobe analysis of mineral grains in albite granite. The relatively high Si and Na and generally low K are probably primary. Poorly preserved igneous contacts and variable chemical and mineralogical composition show that Sparta granite probably consists of several bodies that were intruded separately. These intrusions were probably emplaced at shallow levels as indicated by oscillatory zoning and porphyritic textures generally found in unaltered granite. 60 connate water (White, 1974), and (3) magmatic water. Two types of water-rock interaction are possible: (1) reaction between fluid and molten or partially molten rock, and (2) reation between fluid and rock at subsolidus temperatures, but at least those which would result in prehnite-pumpellyite facies assemblages. Spilite and quartz keratophyre of the Sparta Igneous Complex show low temperature mineralogy. As mentioned above, spilite is enriched in sodium relative to typical tholeiitic basalt. Many geologists who have studied spilites (e.g. Smith, 1968; Battey, 1974; and Coombs, 1974) con clude that the Na-enrichment and low temperature mineralogy are probably due to reaction with sea vater during "burial" (Smith, 1968) or "ocean- floor" (Miyashiro, 1973) metamorphism. On the basis of intercalated fossiliferous marine sediments, spilites in the Clover Creek Greenstone can be inferred to be marine, thus sea water-rock interaction is expected. The depth to which this water was the predominant fluid is difficult to determine, however, penetration to depths of 4-5 km deep at oceanic ridges has been postulated on the basis of isotopic data (Spooner 1974). Underlying albite granite does not exhibit con sistent enrichment of Na or Si, although K content is generally low, but irregular. Because of the mobility of this last element in a wide variety of aqueous fluids, no significant conclusions can be drawn about this fluid from K distribution. Unsheared, altered granite preserves igneous textures and is chemically similar to unaltered granite occurring in the same outcrop. It is postulated that isochemical, subsolidus reaction with a fluid phase is responsible for local alteration within the granite. Although where studied this alteration appears to be isochemical, local migration 59 FIGURE 53 Ca-Na-K atomic ratio ternary diagram plot of altered albite granite, field from Fig. 48. 58 FIGURE 52 Weight " Na^O vs. FeoVwgO plot of altered albite granTts, field from Fig. 47. 57 FIGURE 51 AFM ternary diagram plot of altered albite granites, field from Fig. 46. 56 SiO. FIGURE 50 Weight SiO^ vs. FeoVMgO plot of altered albite granites, fifeld from Fig. 45. 55 16 FIGURE 49 Weight S K^O vs. weight « CaO plot of altered albite granites, field from Fig. 44. 54 In order to test the correlation between development of cataclastic textures and chemical composition, twelve cataclastically deformed albite granite samples were analyzed and results were plotted on variation diagrams (Figs. 49, 50, 51, 52, 53). For comparison, the field of unsheared albite granite and quartz keratophyre were plotted on each of these diagrams. There is a consistent chemical similarity between the sheared granite and undeformed granitic rocks. Thus it is evident that cataclastically deformed granites have undergone no more metasomatic addition of Si and Na than fresh albite granite. In order to test the correlation between mineral alteration and chemical composition, three samples (S976-85, -86, -87) were collected from an outcrop exhibiting a continuous gradation from fresh (S976-85) to altered (S976-86, -87) hornblende granite. This alteration, where complete (S976-87), consists of replacement of hornblende by chlorite and epidote, and alteration of oligoclase cores of zoned plagioclase to epidote and mottled albite. All three of these rocks are chemically similar (Table 6); the more altered samples show no enrichment of either Si or Na. Thus, at least locally, granite has undergone isochemical, static metamorphism. Neither percentage of mafic minerals nor percentage of quartz appear to depend on amount of cataclastic deformation or degree of development of low temperature mineralogy as postulated by Gilluly (1933). Discussion The presence of hydrous replacement minerals implies the local presence of an aqueous fluid. Three types of aqueous fluids could have altered the Sparta igneous rocks: (1) entrapped sea water, (2) evolved 53 (1964) study area from rhyolite to quartz keratophyre, primary igneous textures are blurred and ultimately obliterated. There is no evidence that quartz keratophyre near Sparta is formed by replacement processes which destroy primary textures. Chemical Evidence Gilluly (1933) hypothesized that zones of brecciated rock provided a channel through which flowed a "pegmatitic juice" responsible for wide spread alteration. It is reasonable to assume that these brecciated rocks, in contact with Si and Na rich fluid, should have experienced substantial metasomatism. Fourteen samples of altered albite granite were analyzed in order to test (1) if there is a correlation between development of cataclastic texture and chemical composition and (2) if there is a correlation between mineral alteration and chemical composi tion. Textural and mineralogical criteria were used to distinguish altered granite from fresh granite, and to establish relative degrees of altera tion. The purpose of this was to allow a comparison of the chemical composition of fresh and altered rock. Textural criteria included those relating to deformation; strain twinning, mortar texture, development of foliation, and those relating to replacement; pseudomorphic replacement, corroded grain boundaries, poikilitic quartz with concave grain boundaries against albite. Mineralogical criteria used were: alteration of horn blende and biotite to chlorite and epidote, saussuritization of plagio- clase, overgrowths of clear albite on cloudy appearing ablite, veinlets of low temperature alteration minerals and presence or total absence of twinning in feldspar. 52 in Goose Creek 1/2 mile south of Sucker Creek. These contacts are sharp, not blurred or diffuse as would be expected if metasomatic alteration had occurred. Textural Evidence Textures indicative of both igneous processes and replacement pro cesses occur in gabbro (ie. rhodingite), diorite, tonalite, and granite. Igneous textures predominate although mineralogical modification by low grade metamorphism is widespread. Igneous textures include hypidiomor- phic granular, porphyritic, and oscillatory zoning (Figs. 19, 21, 22). Replacement textures are embayment of crystal margins, alteration of hornblende and biotite to chlorite and epidote, and development of epidote and albite pseudomorphs after plagioclase (Fig. 18, 32). Development of low temperature mineralogy is variable and localized. Typical metamorphic assemblages occurring in these altered rocks are albite + epidote + chlorite, or prehnite + calcite + chlorite. These phase assemblages indicate prehnite-pumpellyite facies metamorphism. Near Sucker Creek fresh hornblende granite grades to an albite epidote chlorite rock with relict igneous texture and similar chemical composi tion (discussed below). This transition occurs within 4 meters. The cause of this local variation in degree of alteration is not clear, but replacement of hornblende by chlorite indicates the presence of an aqueous phase. Well preserved albite granite and quartz keratophyre of the Sparta area contrast strongly with quartz keratophyre studied by Dickinson (1962) in central Oregon, which he postulated to have formed by metaso matism of a fresh rhyolite flow. As alteration progresses in Dickinson's 51 Of primary mafic minerals, and the "notably blue color of the quartz". The third line of evidence developed by Gilluly is chemical. Four whole rock analyses are presented which show a transition from diorite to "pseudophyritic" albite granite. These analyses define nearly straight lines when plotted on a variation diagram of Si02 versus other major element oxides. Since points on these curves plot close to a straight line between end members (a) quartz diorite and (b) an idealized pegmatitic end stage fluid, Gilluly believes they are supportive of the replacement hypothesis. For further amplification, the reader is referred to Gilluly (1933, p. 74-76). Gilluly (1933, p. 74) cautions against using any of the above evidence alone. "No one of the features just enumerated can be considered conclusive in itself of the correctness of the hypothesis advanced. Nevertheless, their cumulative force is great, and when taken ... 'in total' ... they have led to the formulation of the replacement hypothesis." Evidence of the Present Study Intergranular chemical mobility on the scale of centimeters is apparent in thin section (Fig. 32), but predominance of igneous textures in Sparta igneous rocks show that these replacement textures may not indicate widespread metasomatism. In order to test Gilluly's (1933) hypothesis regarding formation of the albite granite, three types of evidence were examined: (1) field relations of various bodies within the albite granite; (2) textural evidence exhibited by altered and unaltered granite; and (3) whole rock major element chemical evidence. Field Evidence Apparent primary contacts between granite and tonalite are preserved 50 reacting with quartz diorite contained predominantly Si02 with AI2O2J Na20 and minor K2O (p. 75). Four possible sources for the albitizing solutions are discussed by Gilluly: 1. "... from nearby portions of the solid diorite" by metasomatism. 2. "... from the intruded greenstones" (ie. Clover Creek Greenstone), 3. "... as rest magmas from local source", 4. "... as hydrothermal solutions of deep-seated origin". Gilluly presents three main types of evidence for his conclusions: (1) gradational field relations from diorite to albite granite, (2) microscopic replacement features, and (3) transitional chemical composi tions from diorite to albite granite. Field relations he observed in Maiden Gulch and in lower Goose Creek consist of a gradational transition "from dark gray, almost quartz-free diorite to light gray highly quartzose albite granite." The gradation consists of an increasing percentage of quartz, replacement of hornblende by biotite and/or bastingsite, and a general decrease in percentage of major minerals. Microscopic evidence suggestive of replacement is divided by Gilluly (1933) into two types, "textural features" and "mineralogic features". Textural features include: (1) a direct correlation between cataclastic textures and per cent of quartz and albite, (2) partial pseudomorphing of plagioclase by more albite rich feldspar, (3) lobate, penetrative quartz against albite in granite, and (4) "myrmekite" (actually grano- phyric quartz-albite) in albite granite presumes to indicate the presence of albitic solutions. Mineralogic features cited as suggestive of replacement are "chessboard albite", "remarkable poverty of the anorthite molecule in the albite granite", the local irregular develop ment of hastingsite in hornblende, widespread presence of epidote instead 49 analyses. 1. Rocks of the Sparta Igneous Complex are generally low in potassium ( 1%). 2. The various rock types of the complex are probably not comag- matic, although, 3. Albite granite and quartz keratophyre are chemically identical, thus are possibly comagmatic. 4. In terms of potassium based trends, the complex as a whole is not calc-alkaline. 5. Gabbros exhibit a tholeiitic trend. 6 . Spilites are possibly tholeiitic, but are sodium-rich compared to typical rocks of this suite. METASOMATISM Gilluly's Theory Gilluly (1933) interpeted the albite granite near Sparta, Oregon to be a replacement body resulting from "albitization and partial silici- fication of an earlier quartz diorite" (p. 65). Although discussing other hypotheses, he favored the concept that the fluids were "derived ... through filter pressing from lower portions of the same mass. The solutions were guided, at least in part, and probably entirely, by brecciated zones in the quartz diorite" (p. 65) and granite. This interpretation coincides closely with accepted definitions of metasoma tism (e.g. Gary e^afl^, eds., 1972), although Gilluly (1933) did not use that term in his descriptions. Citing petrographic data and a variation diagram of Si02 versus other major element oxides, Gilluly deduced that the aqueous fluid 48 FIGURE 48 Ca-Na-K atomic ratio ternary diagram of igneous rocks; date for fields from Erickson (1969), Bailey and Blake (1974), Heitanen (1975). 47 A GABBRO A SPRITE □ UIORITE/TONALITE O ALBITE GRANITE O ORTHOCLASE ALBITE GRANITE • QUARTZ KERATOPHYRE FIGURE 47 Weight % Na^O vs. FeoVMgO plot of igneous rocks; data for fields from Wager and Brown (1967), Erickson (1969), Ewart et al (1973). I