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2000
Holocene sand compositions from the Columbia River Basin: Compositional diversity of sediment from a mixed-provenance region
Carla E. Brock The University of Montana
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Recommended Citation Brock, Carla E., "Holocene sand compositions from the Columbia River Basin: Compositional diversity of sediment from a mixed-provenance region" (2000). Graduate Student Theses, Dissertations, & Professional Papers. 7535. https://scholarworks.umt.edu/etd/7535
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. HOLOCENE SAND COMPOSITIONS FROM THE COLUMBIA RIVER BASIN:
COMPOSITIONAL DIVERSITY OF SEDIMENT FROM A MIXED-PROVENANCE
REGION
by
Carla E. Brock
B.S., Central Washington University, 1998
presented in partial fulfillment of the requirements
for the degree of
Master of Science
The University of Montana
2000
Approved by:
rperson
Dean, Graduate School
6 ^ 3 0 “ Date
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Brock, Carla E., M.S., May 2000 Geology
Holocene Sand Compositions from the Columbia River Basin: Compositional Diversity of Sediment from a Mixed-Provenance Region
Advisor: Marc S. Hendrix
Sand composition is influenced by a number of factors including weathering, transport, and depositional characteristics but ultimately is controlled by the composition of the source rocks. Relationships between sand composition and plate tectonic setting have been described, but actualistic models are needed to provide additional examples of the influences of sampling scale on sand compositions, particularly in basins with mixed provenances and multiple tectonic settings. One of the simplest ways to quantify these relationships is to study the composition of sand derived from known source areas. The Columbia River Basin in the northwest United States contains a diversity of geological provinces which makes it a good area to study the relationship between Holocene sand and known lithology types. Major geological terranes within the basin include granitic plutons exposed through uplift and erosion, continental margin strata, accreted terranes consisting of ancient volcanic arcs and their fore-arc and back-arc basins, flood basalts, volcanic provinces and a young, active, magmatic arc. Eighty-five samples of modem sand were collected from first and second-order drainage systems within the Columbia River Basin. These were mounted in thin section, and each was point-counted to determine the modal composition. These data were compared to modal compositions used in ternary classification models introduced by Dickinson and Suczek (1979) and modified by Dickinson (1983). Results from this study suggest the following: 1) Sand compositions of samples from first and second order systems may reflect tectonic setting, but the exceptions illustrate that care must be taken when trying to interpret tectonic setting based only on sand composition. 2) Sand samples collected in lower order stream systems commonly have compositions that are more closely related to the local source rocks than to the general tectonic setting of the area, showing that sampling scale outweighs tectonic setting as a control on sand composition. 3) Artificial homogenization of low-order sands does not approximate the composition of sands from continental-scale systems because of the lack of stabilization that results from the transport and weathering in a large system. 4) Sand compositions cannot be accurately estimated by modeling the areal coverage of source rocks within the drainage basin.
II
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Page
Abstract...... ii Table of Contents ...... iii List of Tables ...... iv List of Figures ...... v
Introduction ...... 1 Previous Work ...... 6 Geologic Evolution of the Columbia River Basin ...... 8 M ethods ...... 12 Description of Source Provinces ...... 21 Boulder Bathoiith ...... 21 Idaho Bathoiith ...... 24 Kaniksu Bathoiith ...... 30 Challis Volcanics ...... 31 Snake River Plain...... 35 Columbia Basalt Plateau ...... 39 Blue Mountains ...... 43 Kootenay Terrane ...... 47 North Cascades ...... 50 South Cascades ...... 54 Belt Basin...... 59 Discussion ...... 64 Hypothesis lA ...... 66 Hypothesis IB ...... 71 Hypothesis 2 ...... 76 Hypothesis 3 ...... 79 Hypothesis 4 ...... 87 Conclusions ...... 99 References...... 101
ill
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Page Table 1. Sample numbers, site locations and geologic regions ...... 14 Table 2. Raw point-count data ...... 15 Table 3. Grain parameters ...... 17 Table 4. Error Analysis chart ...... 20 Table 5. Samples collected from the Boulder Bathoiith region ...... 24 Table 6. Samples collected from the Idaho Bathoiith region ...... 29 Table 7. Samples collected from the Kaniksu Bathoiith region ...... 31 Table 8. Samples collected from the Challis Volcanics region ...... 33 Table 9. Samples collected from the Snake River Plain ...... 35 Table 10.Samples collected from the Columbia Basalt Plateau ...... 41 Table 11.Samples collected from the Blue Mountains region ...... 47 Table 12.Samples collected from the Kootenay Arc region ...... 50 Table 13.Samples collected from the North Cascades region ...... 54 Table 14.Samples collected from the South Cascades region ...... 59 Table 15.Samples collected from the Belt Basin region ...... 60 Table 16.Average sand compositions by geologic region ...... 63 Table 17.Sampling locations of first-order streams, provenance of basin, and provenance reflected in sand compositions ...... 68 Table 18.Samples grouped by tectonic provenance ...... 80 Table 19.Table showing combination of small-scale drainage basins ...... 91 Table 20.Table of calculated and actual sand compositions ...... 93
IV
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Figure 1. Map of extent of Columbia River Basin ...... 4 Figure 2. Map of Columbia River Basin showing geologic provinces 13 Figure 3. Geologic map of Boulder Bathoiith region ...... 22 Figure 4. QtFL plots of all samples by geologic region ...... 25 Figure 5. QpLvLsm, QmPK, LvLsLm, and LvfLvmLvl plots ...... 26 Figure 6. Generalized geologic map of Idaho ...... 27 Figure 7. Geologic map of Snake River Plain region ...... 36 Figure 8. Plot of Snake River Plain bi-modal sand compositions ...... 38 Figure 9. Extent of Columbia River Basalt Group ...... 40 Figure lO.Geologic map of Blue Mountains region ...... 44 Figure 11.Geologic map of Canyon Mountain Ophiolite Complex ...... 45 Figure 12.Geologic map of the Kootenay Arc region ...... 48 Figure B.Geologic maps of the North Cascades region ...... 51 Figure 14.General geologic map of Washington and Oregon ...... 56 Figure B.Geologic map of the John Day Basin ...... 58 Figure 16.Geologic map and extent of the Belt/Purcell Supergroup ...... 62 Figure 17.Temary plots of single first-order sand samples ...... 67 Figure IS.QtFL plots of average sand compositions representing the three main provenances ...... 72 Figure 19.QtFL plot of randomly selected samples ...... 77 Figure 20.Plots of mean sand compositions from each type of geologic provenance ...... 81 Figure 21.Map showing small-scale drainage basins used in Hypothesis 4 .88 Figure 22.QtFL and LvLsLm plots of actual and calculated sand compositions ...... 94
V
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INTRODUCTION
Numerous studies have described and illustrated the relationship between the
framework grain composition of sand and the tectonic setting from which the sand was
derived (Basu, 1976; Dickinson and Suczek, 1979; Dickinson, 1985; Dickinson et. al.,
1986; Girty et. al., 1988; Girty and Armitage, 1989; Marsaglia and Ingersoll, 1992;
Marsaglia, 1993; Critelli et. al., 1997). Sand composition is controlled by a number of
factors including weathering, transport mechanisms and depositional characteristics but
ultimately is dictated by the source rock composition. Certain tectonic environments
contain similar types of source rocks. Erosion of these source areas can produce sand
with a composition that is characteristic of that setting. In a study designed to test the
predictability of tectonic setting based on sand composition Ingersoll (1990) concluded
that stream size and degree of lithologie integration greatly influences the relationship
between sand composition and tectonic setting, and he identified three categories of
drainage systems based on their size and the diversity of lithologies. First-order systems
are small, localized drainages that contain only one type of source rock. Second-order
systems drain entire mountain ranges and a combination of source rocks. Third-order
drainages are those at the scale of continents and ocean basins that represent a wide
diversity of source rocks. Ingersoll (1990) showed that models relating sand composition
to tectonic setting are only accurate when applied to sands from third-order systems and
1
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that erroneous interpretations may result when attempting to infer tectonic setting from
the composition of sands from lower order systems. Ingersoll et al. (1990) showed that
complex continental settings contain diverse source rocks that result in diverse sand
compositions in first and second order streams and that there is considerable variation in
sand compositions in moderate sized rivers as tributaries enter. Ingersoll et al. (1993)
concluded that only sands that are vigorously homogenized and stabilized by mixing and
weathering are reliable predictors of plate tectonic setting. Based on these conclusions,
Ingersoll et al. (1993) identified the need for actualistic petrologic models relating
Holocene sand composition to known source rocks. Mack (1984) emphasized the need
for a wider range of petrologic data from a variety of source rocks to identify sand
compositions typical of tectonic settings not represented in the models of Dickinson and
Suczek (1979). Mack (1984) cited examples of sandstone composition that erroneously
reflected plate tectonic setting and he stated that it is important to understand the
conditions conducive to the development of sandstones. Girty et al. (1988) found that
petrological data from Holocene sands collected from the Peninsular Ranges of
California generally yield a correct interpretation of tectonic setting but that local source
areas produce sands that reflect erroneous tectonic environments based on their position
on Dickinson’s (1983) provenance models. Girty and Armitage (1989) concluded that
petrologists should be careful about making overly simplistic tectonic interpretations
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based on sand/sandstone QFL provenance diagrams, especially in regions with diverse
geological terranes.
Actualistic models are needed which 1) show sand compositions at a variety of
scales, 2) identify sand compositions from regions not represented on classification
models and 3) provide additional data on the relationship between detrital sand
composition and tectonic setting. These models will provide important information about
composition of detrital sediment derived from known source areas. This information can
be applied to the interpretation of ancient sandstones and can help to provide more
accurate correlations between the composition of sand and the composition of inferred
source rocks.
In this thesis, I use the Columbia River Basin as a natural laboratory to address
these problems by analyzing modem sands derived from a variety of source rocks and
collected at a variety of sampling scales. The Columbia River drains an area of 667,000
km^in the northwest comer of the United States (Figure I). The basin contains an
extensive and well-developed perennial stream system that is easily accessible. The
geology of the basin consists of a large variety of source rocks and can help to illustrate
the composition of sands from a mixed-provenance region. The climate is arid so the
effects of weathering on detrital sand compositions are minimal.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ^ W a ^ i n g t o n I ' V } V \|ie H j % V V . / , 1g y' ... \
Wyoming)
Oregon Maho N evadan.y'^x/^ Utah
Figure 1. Areal extent of the Columbia River Basin
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In this study, I focus specifically on the relationship between sand composition
and plate tectonic setting. Sand collected from first and second order drainage systems
with known provenance is compared to petrologic models established by Dickinson and
Suczek (1979) and modified by Dickinson (1983). 1 artificially homogenize samples
collected from each of the three major provenance categories (continental block,
magmatic arc, and recycled orogen) to test the validity of the petrologic models in this
mixed-provenance region. In addition, I attempt to predict sand compositions by areally
modeling the extent of lithology types within drainage basins.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PREVIOUS WORK
Previous studies of modem sand compositions in the Columbia River Basin are
restricted to a few specific studies and two papers covering general sediment
characteristics and sediment transport characteristics. Whetten et al. (1969) studied and
summarized general sediment characteristics within the basin. They concluded that
sediment is derived from two dominant sources within the basin. Sediment in the upper
reaches of the drainage basin is derived from sedimentary, metamorphic and plutonic
bedrock and sediment in the lower reaches is derived from andesitic volcanic rocks and
associated volcaniclastic sedimentary rocks. They also focused on characteristics of
suspended sediment and bedload and concluded that upstream sediment is mostly fine
grained and carried in suspension and downstream sediment tends to be coarser and
forms the bedload. Their study also summarized the mineral composition of bottom
sediment focusing on the bulk-mineral, dense mineral, and clay mineral compositions.
They found that percentages of unstable materials increase downstream. Generally, they
found that upstream sediments contain more quartz and fewer lithic and feldspar
fragments than downstream sediments and that the percentage of volcanic lithics in
relation to lithics of other compositions increases downstream until virtually all rock
fragments are volcanic in origin. Other comparable studies that examined changes in
modal compositions of modem sand throughout a river basin have been completed on
6
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sands from a southern California drainage system (Critelli et al., 1997), from the
Colorado River (Girty and Armitage, 1989), and from a number of basins in western
China (Graham et al., 1993).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. GEOLOGIC EVOLUTION OF THE COLUMBIA RIVER BASIN
Presently, the Columbia River Basin occupies an active continental margin.
Subduction along the West Coast of the Pacific Northwest is the cause of past and present
volcanism within the region. This plate tectonic motion is generated by the subduction of
the Pacific and Farallon plates under the North American plate. Because of this, the
majority of source rocks within the basin are volcanic and related in some way to
subduction and arc magmatism. Because of the collisional histoiy of the region, there are
numerous accreted terranes as well as a young, active magmatic arc (Dott and Prothero,
1994). A burst of volcanic activity in the Mesozoic led to the emplacement of a number
of large Cretaceous plutons that dot the region. Mesozoic volcanism also accounted for
extensive flows of flood basalts that cover much of the Columbia Basin. Quaternary
volcanic rocks dominate much of the southern and western portions of the basin and can
be attributed to continued subduction along the West Coast (Dott and Prothero, 1994).
During the Proterozoic and Cambrian, the western margin of North America was
a passive stable shelf, subsiding as it rifted from other continents and allowing for the
accumulation of a thick sequence of shelf sediments (Poole et al., 1992). The pre-
Cambrian Belt Supergroup consists of thick packages of sandstone, shale, and limestone
that thicken from east to west and have been dated between 1600 and 1300Ma (Elston
and McKee, 1982; Burchfiel et al., 1992). The tectonic setting of the depositional
8
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environment of the Belt Supergroup is unclear. Hypotheses include a middle Proterozoic
aulacogen (Gabrielse and Yorath, 1989) and an inland basin with no connection to an
open ocean to the west (Hoffman, 1989). Presently, rocks of the Belt Supergroup cover
roughly 20% of the Columbia River Basin along the northeastern margin.
By the Devonian, the western margin was an active subduction zone as shown by
the Antler Orogeny in the west central United States (Speed and Sleep, 1982). West of
the Belt Basin, rocks of the Kootenay Terrane mark the western limit of North American
continental crust based on an initial ^Sr/^Sr ratio of 0.706 (Potter et al., 1992). This
accreted terrane is composed predominantly of Devonian strata of the miogeocline that
have been variably metamorphosed (Poole et al., 1992). Another suspect terrane is found
in central and eastern Oregon and is named the Blue Mountains. Accretion of the Blue
Mountains terrane occurred during the Cretaceous and includes rocks originating in
various tectonic settings (Davis et al., 1978). These settings include ancient volcanic-
arcs, accretionary wedge or forearc basins, and intra-arc and deep forearc basins. The
majority of these rocks have been metamorphosed to blueschist-facies (Miller et al.,
1992). The North Cascades region of the Columbia River Basin also contains
allochthonous terranes accreted during the Cretaceous (Brown, 1987).
During the Mesozoic, subduction continued and by the late Cretaceous all suspect
terranes were in place. These terranes now underlie much of British Columbia,
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Washington and Oregon, and parts of Idaho, Nevada, and California. In the Late
Jurassic, Cordilleran subduction had intensified and become much more rapid (Dott and
Prothero, 1994). The melting of the subducting slab produced an Andean-sized volcanic-
arc that was active from Late Jurassic to Late Cretaceous. The first major phase of
Cordilleran mountain building occurred during this time as the Nevadan Orogeny (Harper
and Wright, 1984). Plutonic basement rocks related to this volcanism and the rapid
spreading and subduction are now exposed as a series of Mesozoic batholiths. Major
batholiths related to rapid spreading include the Idaho Bathoiith and Kaniksu Bathoiith
(Dickinson and Snyder, 1978). Smaller plutonic bodies intruded rocks of the accreted
terranes and are presently exposed in the North Cascades and Kootenay Terrane (Fox et
al., 1977). The peak of mountain building activity occurred in the Late Cretaceous as the
Sevier Orogeny, which represents an eastward shift of arc volcanism into Idaho that has
been attributed to shallowing of the subducting slab (Armstrong, 1974). The
emplacement of numerous small plutons at shallow levels along the Cordillera also has
been attributed to this slab-shallowing (Dickinson and Snyder, 1978). The Boulder
Bathoiith in southwest Montana is one of these plutons. Late Cretaceous to Eocene time
was dominated by the Laramide Orogeny in the central Rockies region in which very
shallow subduction caused a lull in volcanic activity and resulted in folding and thrusting
in the western craton (Engebretson et al., 1985).
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By the end of the Eocene, volcanic activity had resumed as the downgoing plate
apparently reassumed a normal dip (Dickinson and Snyder, 1978). A major arc volcano
complex in central Oregon from late Eocene to early Miocene resulted in thick deposits
of volcanic and volcaniclastic rocks. About this same time, volcanic activity in central
Idaho resulted in the deposition of the Challis Volcanics (Ewing, 1980). In the mid-
Miocene, a third plate, the Farallon plate, began subducting along the western margin,
resulting in the initiation of the San Andreas fault system and Basin and Range extension
in the southwest United States. During this time, huge volumes of flood basalts flowed
out of fissures in present-day southeast Washington and northeast Oregon. Named the
Columbia River Basalts, they cannot be explained by simple plate interactions and may
instead be related to a hot spot (Swanson et al,, 1975). Also credited to a hot spot is the
late Miocene to Pliocene Snake River volcanics (Armstrong et al., 1975). Uplift of the
Rocky Mountains occurred at the end of the Miocene and those rocks long buried by
sediment were re-exposed. Volcanic activity has decreased since the Miocene, probably
due to slower and shallower subduction (Burchfiel et al., 1992). However, volcanism is
still present as evident by the active Cascade magmatic arc that forms the western
boundary of the Columbia River drainage basin.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. METHODS
Eighty-fîve samples of modem sand were collected from first and second order streams
within the Columbia River drainage basin (Figure 2 and Table 1). Special care was taken
to be sure that these samples were fluvial in origin and not transported or deposited by
human activity. Samples were collected from locations above and below the confluence
of two rivers for the purpose of comparing changes in sand compositions between
geologic provinces. Samples were collected from point-bars or longitudinal bars when
available and other samples were collected from the main channel bedload. Each bulk
sample was air-dried and sieved to extract the medium sand-sized fraction (0.25-0.50
mm). If an insufficient quantity of sand of this size was recovered, then the fine-sized
fraction was used (0.124-0.25 mm). The unconsolidated, medium-sized fraction was sent
to Spectrum Petrographies, Inc. in Winston, Oregon and artificially consolidated with
resin and made into a thin-section. Each thin section was stained with sodium
cobaldnitrite for potassium feldspar and alizarin red for calcite.
The thin-sections were point-counted at a step length of 0.064 mm using the
Gazzi-Dickinson point-counting method (Ingersoll, 1984). Five-hundred grains were
counted on each thin-section (Table 2). Modal compositions vary with grain size
primarily due to the breakage of polymineralic rock fragments into their constituent
grains (Ingersoll et al., 1984). Thus, compositional grain-size dependency is eliminated
12
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IT07
ITÔ4 KT05
Figure 2. Gêôlôgicprovuî^s and sampling sites within the CÔÎûmBuTkivcr Basin: 1 = North Cascades, 2 "Kootenay Terrane, 3 "B elt Basin, 4 = Kaniksu Bathoiith, S = Columbia Basalt Plateau, 6 "South Cascades, 7 = Blue Mountains, 8 - Snake River Plain, 9 = Idaho Bathoiith, 10 = Challis Volcanics, 11" Wyoming Fold-Thrust Belt, 12" Boulder Bathoiith
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Samole ID Location Geologic Region WA-01 Swauk Ck. At Swauk Ck. CG North Cascades 14 WA-03 Mad River on Entlat R. Road North Cascades WA-05 Wenatchee R. in Leavenworth, WA North Cascades WA-07 White R. N of Lake Wenatchee North Cascades WA-08 Yakima R. at Umtanum Ck. Columbia Basalt Plateau WA-09 Columbia R. at Vantage, WA North Cascades WA-10 Snake R. iust up from Clearwater R. Columbia Basalt Plateau WA-11 Grande Ronde R. S of Lewiston. ID Columbia Basalt Plateau WA-12 Snake R. down from Ciarkston, WA Columbia Basalt Plateau WA-13-1-6 Columbia R. just above confluence with Snake R. Columbia Basalt Plateau WA-15 Yakima R. just above confluence with Columbia R. Columbia Basalt Plateau WA-17 Spokane R. just above confluence with Columbia R. Kootenay Terrane WA-18 Columbia R. N of Cedonia, WA Kootenay Terrane WA-19-1-5 Columbia R. above Kettle Falls, WA Kootenay Terrane WA-20 Pend-Oreille R. at Usk, WA Kaniksu Bathoiith WA-21 Columbia R. just below John Day Dam Columbia Basalt Plateau WA-22 Columbia R. just below Deschutes R. Columbia Basalt Plateau WA-23-1-3 Columbia R. in Kalama, WA Columbia Basalt Plateau
0R-01 Lewis R. in Ridgefield. WA South Cascades 0R-W2 Willamette R. In Eugene, OR South Cascades OR-03 Deschutes R. near Tumalo St. Pk. South Cascades OR-OS John Day R. at "the swimmin' hole" South Cascades OR-07 John Day R. W of Dayville. OR South Cascades OR-08 John Day R. at C. Holliday St. Pk. South Cascades OR-11 Malheur R. (N.F.) at Chukar Pk. Snake River Plain OR-12 Powder R. just below Phillips Lk. Blue Mountains OR-13 Burnt R. at confluence with Snake R. Blue Mountains OR-14 Snake R. just below Burnt R. Blue Mountains OR-15 OvKyhee R. Snake River Plain
ID4)1 Snake R. near Weiser, ID Snake River Plain ID-02 Boise R. off Hwy 21 Idaho Bathoiith ID-03 Boise R. (N.F.) on Hwy 21 Idaho Bathoiith ID-04 Crooked R. on Hwy 21 Idaho Bathoiith ID-05 Payette R. (S.F.) near Lowman, ID Idaho Bathoiith ID07 Salmon R. below Stanley. ID Idaho Bathoiith ID-08 Salmon R. (E.F.) at confluence with Salmon R. Challis Volcanics ID09 Pashimeroi R. at confluence with Salmon R. Challis Volcanics ID-10 Lochsa R. E of Lowell, ID Idaho Bathoiith ID-11 Clearwater R. between Kamiah and Greer, ID Idaho Bathoiith ID-12 Clearawater R. just before Snake R. Columbia Basalt Plateau ID-13 Priest R. betw een city and lake Kaniksu Bathoiith ID-14 Snake R. - Henry's Fork Snake River Plain ID-15 Snake River above confluence with Henry's Fork Wyoming Fold-Thrust Belt ID-16 Snake R. S of Idaho Falls (Shelly R. Rd) Snake River Plain ID-17 Snake R. at Massacre Rocks St. Pk. Snake River Plain ID-18 Snake R. at 3-Island Crossing St. Pk. Snake River Plain ID-19 Srake R. near Marsing, ID Snake River Plain ID-20 Boise R. near Roswell, ID Idaho Bathoiith ID-21 Snake R. downhver from Boise R. Snake River Plain ID-22 Payette R. near New Plymouth, ID Idaho Bathoiith ID-23 Weister R. near Cambridge, ID Columbia Basalt Plateau ID-24 Little Salmon R. S of Riggins, ID Blue Mountains ID-25 Salmon R. N of Riggins, ID Blue Mountains ID-26 Clearwater R. (S.F.) Idaho Bathoiith
MT-01 Rock Creek Beit Basin MT-02 Clark Fork R. near Gold Creek, MT Boulder Bathoiith MT-03 Little Biackfoot R. W of Avon, MT Boulder Bathoiith MT-04 Clark Fork R. near Galen. MT Boulder Bathokth MT-05 Silver Bow Ck. Near Ramsey, MT Boulder Bathoiith MT-06 Flathead R. (N.F.) at Polebridge. MT Belt Basin MT-07 Flathead R. (M.F) Hwy 2 Belt Basin MT-08 Flathead R. at Kokanee Bend Belt Basin MT-09 Swan R. at FR 966 (S of town) Belt Basin Mr-10 Biackfoot R. on Sunset Hill Dr. Belt Basin MT-11 Clark Fork R. in E. Missoula, MT Belt Basin MT-12 Clark Fork R. at Alt>erton, MT Belt Basin MT-13 Clark Fork R. above corrfluence with Flathead R. Belt Basin MT-14 Clark Fork R. below confluence with Flathead R. Belt Basin MT-15 Flathead R. above confluence with Clark Fork R. Belt Basin
BC-01 Elk R. above confluence with Kootenay r. Belt Basin BC-02 Kootenay R. near Skookumchuck, BC Belt Basin BC-03 Columbia R. near Parson, BC Belt Basin BC-04 Columbia R. in Revelstoke. BC Kootenay Terrane BC-OS Kootenay R. just above confluence with Columbia R. Kootenay Terrane Table 1. Sample number, site location and geologic region
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15
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Further reproduction prohibited without permission. 16 by using the Gazzi-Dickinson method and identifying sand-sized crystals (>0.0625 mm) whether or not they are part of a larger rock fragment. Ingersoll et al. (1984) concluded that this method has advantages over more traditional methods. These advantages include more uniform results for any grain size and the elimination of the need for multiple counts. Using this method, only pure silica is classified as polycrystalline quartz, even the slightest amount of impurity within the grain results in the grain being classified as a lithic fragment. Modal compositions of the samples were recalculated as proportions of 1 ) quartz, including monocrystalline and polycrystalline quartz, 2) monocrystalline feldspars, including both plagioclase and potassium feldspar, and 3) polycrystalline lithic fragments, separated into volcanic lithics, sedimentary lithics and metamorphic lithics (Table 3). Dickinson (1985) identified metamorphic lithics as either metavolcanic fragments or metasedimentary fragments and classified them as Lv and Ls, respectively. For this study, metamorphic rock fragments were classified separately as Lm for two reasons. First, it is often hard to determine the origin of a metamorphic grain. Second, because of the abundance of both volcanic and sedimentary terranes within the study area, metamorphic rock fragments are a unique component in modem sands within the basin. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 17 Counted parameters Recalculated parameters Qp«polycrystalfine quartz (inc. chert) Q=Qp+Qm Qm=monocrystalline quartz F=P+K P=plagioclase feldspar L=Lv+Ls+Lm+xbC03 K=potassium feldspar QFL%Q=100Q/(Q+F+L) Lv=volcanic lithic fragment QFL%F=100F/(Q+F+L) Lvf=feisic volcanic lithic fragment QFL%L=100L/(Q+F+L) Lvm=microlitic volcanic lithic fragment QpLvLsm%Qp=l OOQp/(Qp+Lv+Lsm) Lvl=lathwork vdcanic lithic fragment QpLvLsm%Lv=1 OOLv/(Qp+Lv+Lsm) Lvg=vitric volcanic lithic fragment QpLvLsm%Lsm=l OOLsm/(Qp+Lv+Lsm) Ls-sedimentary lithic fragment QmPK%Qm=l OOQm/(Qm+P+K) xbC03=carbonate lithic fragment QmPK%P=1 OOP/(Qm+P+K) Lm=metamorphic lithic fragment QmPK%K=l OOK/Qm+P+K) bt=biotite LvLsLm%Lv= 1 OOLv/( Lv+Ls+Lm) ms=muscovite LvLsLm%Ls=1 OOLs/(Lv+Ls+Lm) cakcalcite LvLsLm%Lm= 1 OOLm/(Lv+Ls+Lm) heavy=amphiboles/pyroxenes LvfLvmLvl%Lvf= 1 OOLvf/(Lvf+Lvm+Lvl) Lu/nLu=miscellaneous and unidentified LvfLvmLvl%Lvm= 1 OOLvm/(Lvf+Lvm+Lvl) LvfLvmLvl%Lvl=1 OOLvl/(Lvf+Lvm+Lvl) Table 3. Grain parameters (after Ingersoll et al., 1984) Since classification of lithic fragments may vary among petrographers, it is necessary to clarify techniques used in identification for this project. The largest problem is distinguishing between volcanic and sedimentary rock fragments. Dickinson (1970) identified four main types of volcanic rock fragments. Grains containing plagioclase laths in an interstitial matrix are sub-categorized as Lvl and represent basaltic lavas. Fine-grained, microcrystalline grains containing mainly anhedral quartz and feldspars are identified as felsic volcanic lithics and are categorized as Lvf. Vitric volcanic fragments are composed predominantly of volcanic glass and are sub-categorized as Lvg. Microlitic volcanic grains, sub-categorized as Lvm, consist of subhedral to euhedrai Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18 feldspar plates and prisms in a microcrystalline groundmass. These grains are typical of intermediate types of lava. Fragments of microlitic volcanic rocks can be easily mis identified as sedimentary rock fragments. Grains are identified as Lvm if crystals within the grain are lath-like or contain ill-defined boundaries or if the location of minerals within a finer grained matrix is irregular. If rock fragments are fine-grained, lack phenocrysts, have aligned clay minerals or have silt clasts with well-defined boundaries, they are identifed as sedimentary rock fragments. Metamorphic rock fragments are identified by texture and mineral composition. Accessory minerals, such as dense minerals, are tabulated in point-counts but not included in calculated modal compositions. To analyze the data, temaiy diagrams introduced by Dickinson and Suczek (1979) and modified by Dickinson (1983) are used. The sand samples are grouped according to the geologic province from which they were predominantly derived. Since many of the samples may represent a variety of geologic terranes, their compositions are compared to the surrounding geology and categorized with similar samples. The mean of the samples from each geologic province is calculated and plotted on ternary diagrams. The standard deviation (2 sigma) of samples from each province is also calculated and plotted in order to show the range of compositional variability. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19 In order to quantify and minimize error, multiple samples were collected from three of the different sample sites and point-counted. The results of these multiple point- counts are shown in Table 4. To make sure that grain identification remained consistent, throughout the study, some single samples were counted more than once through the point-counting process. The data from these multiple counts can be seen along with the raw data in Table 2. The consistency of the multiple counts of the same sample, and counts of multiple samples from the same location, shows that major grain identification (QFL) was within 5% standard deviation throughout the process and that the compositional results are accurate and reliable. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 to to to ? $ s 3 o g 9 % 9 2 9 2 9 2 2 9 g 53 o o o o o o o D 1 1 2 % 8 S 9 2 S 2 I ÜÎ l i 1 5 C O > c Z 2 o 3 S § 5 i Z 3 f t Ï T o 3 % w w VC (/I > SA £S 22 SS 825 I i ? o — s s ÏÏSÎ m N s5 82 K% £8 2 SS 38 ■i •g W w -V - î; K Û A S f t A ^ — N I/I i&i » c! 8 2 to to % A t 2 2 -M to 6 2 — -M r K 5 ^ u? % % 0» fO o> W ® W o a o o to ft o o o o o o o o c o o ■ I 0 o o o o W ^ o rv O rg ro O to O - O 3 to -» (D ID C i £■ » *■ * O Ô) M N M « o >c O VI O N O to O O FSI -V to I ? 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DESCRIPTION OF SOURCE PROVINCES The Columbia River Basin is divided into eleven geologic provinces for the purpose of this study. Each province contains a distinct type or set of source rocks. The purpose of defining these major provinces within the basin is to compare the sand composition shed from different types of known source rocks. Boulder Batholith The upper Cretaceous Boulder Batholith and related Elkhom Mountain Volcanics are found in southwestern Montana along the eastern most edge of the Columbia River basin (Figure 3). The headwaters of the Clark Fork River drain this geologic province. This granite to granodiorite batholith was emplaced at shallow levels beneath a broad area of Elkhom Mountain volcanics derived from the same magma chamber (Rutland et al., 1989). The overlying volcanic rocks were intruded by the Boulder Batholith and are presently found along its margins and as a small remaining roof pendant (Hamilton and Myers, 1974). The Elkhom Mountain Volcanics contains three informal members (Rutland et al., 1989). The lower member consists predominantly of lava flows, water-laid volcaniclastic rocks and sparse, thin sheets of andesitic ash-flow tuff. The middle member consists of rhyolitic welded tuff and interbedded andesitic and basaltic the lower 21 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 22 114* 00* 113*00* 112* 00* 1 1 1* 00* ■ IMBRICATE THRUST ZONE 3 46* 46* 30" 30" FLINT GREEK RLUTOMS 46* 46* 00*' / 00 ' B A T H O L ^ Low*r T«fiMry «olCAAic ro c M TOBACCO ROOT BATHOLITH OranRle reekt (Gf#l#o#*R$) BATHOLITH Elk Rom M#uoi##a» Votasfilet ' 1 ROCKY I Q%^ ^ MOUNTAIN Rf#ca#NU#m# • ^ FORELAND f«ck« Tkrvti •••«■ P ' boi FmiMi #Mh «KiitnioaBi km 30 ■ ?Î.'50J«A- •••«•I **«*#**1# ■ ■ ■ * IDAHO ' ‘V-.," momOEX MAP Figure 3. Generalized geologic map of the Boulder Batholith region (Rutland et al., 1989) volcaniclastic rocks. The upper member consists predominantly of reworked material of two units, but in northern-most exposures is comprised of basaltic lava flows and flow breccia. The Boulder Batholith is a composite calc-alkaline intrusive body that ranges in composition from potassic ultramafic to granite and syenite. More than 75% of the Boulder Batholith is exposed as the Butte Quartz Monzonite (Rutland et al., 1989). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 23 Four samples of modem sand were collected from the Boulder Batholith region (Table 5). These samples were collected from Silver Bow Creek, Little Blackfoot River and the Clark Fork River (Figure 2). Sands collected from this region are feldspatholithic and have an average composition of Q20 F49 L32. The sand is enriched in feldspars, and plagioclase feldspar is the more abundant feldspar (P/F = 2). Rock fragments comprise about one-third of the samples, are predominantly volcanic in origin and range from felsic to intermediate in composition. Quartz grains make up less than 20% of the sand shed from the Boulder Batholith (QmFLt %Qm=18). The sample taken farthest downstream in this region has a higher percentage of quartz and sedimentary rock fragments that likely reflects the growing dominance of the surrounding pre-Cambrian Belt Rocks. The composition of these sands is similar to those found by Basu (1976) in a study focusing on Holocene sands shed from plutonic source rocks. Samples for his study came from the Boulder Batholith and Idaho Batholith, as well as another plutonic province in Wyoming and had an average composition of Q24 F49 L16 (accessory minerals make up remaining 11%). Using Dickinson’s (1983) compositional diagrams, Holocene sands from the Boulder Batholith fall into the magmatic arc field (Figure 4B). Some overlap occurs into the lithic-poor, continental block-basement uplift field. The polycrystalline components of the sand (Qp5 Lv83 Lsml2) falls entirely within the arc-orogen source field (Figure 5B) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24 BOULDER BATHOLITH SANDS Samole Location QM f LT OT FL OP t v LSM QM P K »L vf WLvm %Lv1 Lv Ls Lm MT-02 Oarfc fork R. 28 4229 304228 6 57 36 40 40 20 54 33 14 61 39 0 MT-03 Lrttle Blackfoot R. 8 32 60 9 32 6 0 1 95 4 20 45 35 55 38 7 96 4 0 WT4)4 CUwlc Fork R. 20SB22 205921 4 93 3 25S3 22 29 66 5 97 3 0 MT-05 Silver Bowv Ck. 18 20 20 §2 18 10 87 3 ?? 53 24 22 76 1 96 2 1 MEAN 18 49 33 204931 5 63 12 27 48 25 40 53 7 87 12 1 STD 8 14 19 9 14 19 4 16 17 9 6 7 1 7 21 5 18 18 1 Table 5. Samples collected from the Boulder Batholith region modeled by Dickinson and Suczek (1979) and modified by Dickinson (1983). Classification of the monocrystalline components (Qm27 P48 K25) on Dickinson’s modified model (1983) shows the dominance of volcanic sources over plutonic sources in these sands (Figure 5C). Idaho Batholith The Idaho Batholith is exposed in central Idaho as two lobes of plutonic rock separated by metamorphic rocks of the Salmon River arch (Figure 6). The batholith was emplaced during the Late Cretaceous and marks the edge of the craton as shown by the Strontium 87/86 ratio and the 0.706 line (Lewis et al., 1987). West of the batholith, a mylonitic zone over a mile wide separates the plutonic rocks from the accreted terranes of the Blue Mountains. Both lobes of the Idaho Batholith consist of granodiorite, granite and two-mica granite (Barton et al, 1988) emplaced between 80 and 65 Ma (Hyndman and Foster, 1989). Lewis et al. (1987) separated the Atlanta Lobe into six major rock Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25 ^ / Recycled Orogen Kootenay TeVane Dissected Arc Wyoming FbJd-Thrust Belt ♦ North Cascade Bèit Basin F “'T " “ %allisVolcafS Transitional Arc Undtssected Arc Recycled Orogen Kaniksu Bathollt Dissected Arc Columbia Bas^rPlateau Idaho BatholitfvT^ fO Snake RiVgr Plain uidef Batholith Undissecftd Arc Transitional A South Cascades L Figure 4. QtFL plots of Holocene sand samples by geologic region Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 26 PtoMftü 2 tfdiifi I f.i i:U' ,1, L'ialcii viufitMld i-'r ivVi rcS'.in. VC^<.3fioC-i Cotumba B ac# Malaau Wyoming F«d-Trrua BluaMouniara Koofanay Twran» $ voicarKS \,4ftom4iAV PfL.V' date BalhoMh nCMcadas Koolanay Tanarva C teik s Lm Lvm SWhGaacaoaa Figure 5. QpLvLsm, QmPK, LvLsLm, and LvfLvmLvl plots of Holocene sand samples by geologic region. Fields shown determined by Dickinson and Suczek (1979) and modified by Dickinson (1983) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 27 117" 114" 111' 49" EXPLANATION Kaniksu Batholith | Snake River Plain volcanic rocks □ Columbia River Basalt Group Chains Volcanics (Eocene) Plutonic rocl@ (Eocene) Plutonic rocks (Mesozoic) Idaho Batholitti and Kaniksu Batholith Voicanic-arc complex (Mesozoic) 0.704-0.706 Sedimentary rocks of Wyoming Fold-Thrust Belt (Mz & Pz) M etasedi mentary rocks of die Belt Supergroup and basement rocks Salmon River Arch Sr 0.704-0.706 line 45" 0 .7 0 4 42® 0 .7 0 6 100 km I______I ± ± Figure 6. Generalized geologic map of Idaho illustrating location of Salmon River Arch, Kaniksu Batholith, Idaho Batholith, Belt Supergroup, Columbia River Basalt Group, Challis Volcanics, and eastern extent of the Blue Mountains (Mesozoic volcanic-arc complex), (Lewis et al., 1987) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28 types. The rock types are tonalité, homblende-biotite granodiorite, muscovite-biotite granite, and leucocratic granite. The Bitterroot Lobe is composed primarily of muscovite-biotite granodiorite and monzogranite with tonalité and quartz diorite along its borders (Toth, 1987). The majority of rocks are felsic, medium-grained, and massive (Hyndman and Foster, 1989). Mafic-rich rocks are found deeper and in border zones of the batholith and large swarms of synplutonic mafic dikes cut the batholith. Younger epizonal plutons of subalkalic syenogranite and quartz syenite are found along the sides of the Bitterroot Lobe along with rhyodacite and rhyolite dikes extending away from the pluton (Toth, 1987). Ten samples of sand were collected from central Idaho and the Idaho Batholith region. The samples came from the Boise River, Crooked River, Payette River, Salmon River, Lochsa River and Clearwater River. The sands are quartzo-feldspathic and have an average composition of Q23 F68 L9 (Table 6). Feldspars dominate the sand composition, and the P/F ratio is 3. Lithic rock fragments account for a very small percentage of the sand composition. These are predominantly volcanic in origin and are mostly felsic in composition. Mafic volcanic fragments are evident in sands from the Clearwater River in western Idaho that is draining part of the Columbia Basalt Plateau. Quartz grains account for about one- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 29 quarter of sands from the Idaho Batholith region, and almost all are monocrystalline grains of plutonic origin. Samples ID-26 and ID-10 show variations in the polycrystalline components and reflect the influence of metamorphic rocks of the Salmon River arch. Sand from the Idaho Batholith region falls within the continental block category on the QFL diagram with overlap into the magmatic arc field (Figure 4B). These sands suggest a basement uplift provenance as described by Dickinson (1983). Dickinson and Suczek (1979) stated that quartzo-feldspathic sands typically come from high relief areas and rapid erosion of uplifted basement rocks. Relative percentages of the polycrystalline components (Qp6 Lv85 Lsm9) of these sands reflect an arc orogen provenance as described by Dickinson and Suczek (1979) (Figure SB). The plot of monocrystalline components (Qm25 P55 K20) shows the dominance of plutonic over volcanic sources (Figure SC). IDAHO BATHOLITH SANDS SamDle Location QM F LT QT F L QP LV LSM QM P K %Lvf «Lvm «LvI Lv Ls Lm ID-02 BofS« R. 22 61 17 23 61 16 6 63 S 27 46 26 42 36 23 95 S 0 ID-03 eoHte R. NF } 7 7 7 7 17 77 7 0 97 3 18 64 16 70 30 0 97 3 0 ID-04 lo o k e d R. 16 79 5 16 79 5 0 77 23 17 65 18 68 6 6 77 9 10-05 PayMtft R. SF 26 67 6 27 67 6 13 86 0 28 S3 19 100 0 0 lD-07 SalmcnR. 18 67 15 16 67 14 4 61 15 21 62 17 100 0 0 84 16 0 1D1Q Loch** R. 2962 9 3062 6 14 79 7 32 46 22 62 35 3 92 5 3 IDtl Qearwstar R. 1973 8 19738 5 95 0 20 52 26 29 3 69 100 0 D ID20 ft. 1874 8 1674 8 5 6213 2056 22 67 17 17 66 0 ID22 Payatte ft. 30 6S 5 30 65 S 8 92 0 31 48 20 54 29 17 100 0 0 ID26 Oearwatar ft. SF 33 S8 9 33 58 9 3 70 27 36 51 13 63 21 17 72 17 11 MEAN 23 68 9 23 66 9 6 a s 9 25 SS 20 61 21 18 91 7 2 STD 6 7 4 6 7 4 5 9 10 7 7 4 22 14 21 10 7 Table 6, Samples collected from the Idaho Batholith region Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30 Kaniksu Batholith The Kaniksu Batholith is located in the panhandle of Idaho and stretches into northeast Washington (Figure 6). It is a small, granitic batholith, emplaced at about the same time as the Idaho Batholith. The Priest River Complex, which is a region of amphibolite-grade metamorphic rocks, surrounds the Kaniksu Batholith. Rocks are mainly pelitic and semi-pelitic schist and gneiss, granodioritic to granitic orthogneiss, and augen gneiss along with amphibolite and quartzite (Rhodes and Hyndman, 1988). Two modem sand samples were taken from the Kaniksu Batholith region. These samples came from the Fend-Oreille River in northeast Washington and the Priest River in the Idaho Panhandle. Sands are quartzo-feldspathic with an average composition of Q32 F61 L7 (Table 7). Plagioclase feldspar grains are twice as abundant as potassium feldspar grains (P/F = 2), and account for half of the monocrystalline components of the sand (QmPK %P=47). The majority of quartz grains are monocrystalline. Lithic grains are mainly volcanic in origin and feldspar rich. Polycrystalline quartz grains in sand from the Pend-Oreille River likely reflect influence from the Kootenay Arc that is found upstream (Figure 2). Metamorphic rock fragments in the sand from the Priest River reflect surrounding metamorphic rocks of the Priest River Complex. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 31 fCAHnCSU BATHOLITH SANDS Samole Location QM f LT QT f L QP LV LSM QM P K %Lvf MLvm »Lvl Lv L$ Lm WA 20 Pand-OroNeR. 33 54 13 36 54 6 38 48 14 38 43 19 66 34 0 78 20 2 JO-13 Pnesi R. 25 67 7 27 67 6 18 58 24 27 51 21 100 0 0 70 1 1 19 MtAN 30 60 10 32 61 7 28 53 19 33 47 20 83 1 7 0 75 IS 10 STO 5 10 4 8 10 2 14 6 7 8 6 2 24 24 0 5 € 11 Table 7. Samples collected from the Kaniksu Batholith region Sand compositions from the Kaniksu Batholith region reflects a basement uplift provenance, according to Dickinson’s revised models (1983) (Figure 4B). The plot of polycrystalline components (Qp28 Lv53 Lsml9) falls partially into the arc orogen source defined by Dickinson and Suczek (1979), but mostly falls outside areas of specified provenance (Figure 5B). The plot showing relative percentages of monocrystalline components (Qm33 P47 K20) reflects a magmatic arc provenance with a high ratio of plutonic to volcanic influence (Figure 5D). Challis Volcanics The Challis Volcanics in east central Idaho are just one part of a belt of widespread Eocene volcanic deposits found across the Pacific Northwest (Figure 6). Volcanism occurred in this region between 51 and 40 Ma (McIntyre et al., 1982). Igneous activity in the province occurred in two episodes, beginning with emplacement of plutons and followed by the eruption of siliceous lava and ash (Orr & Orr, 1996). The older sequence consists of thick deposits of intermediate lava with minor mafic lava and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 32 associated volcaniclastic rocks and ranges in age from 51 to 49 Ma (Hardyman, 1989). The younger sequence is felsic lava and domes that range in age from 45 to 41 Ma (Hardyman, 1989). Challis volcanic rocks are easily distinguishable in hand specimen from rocks of the Idaho Batholith because of their pink color and large crystals. The older sequence of rocks dominates the southern portion of the area. Two sub categories of rocks occur: 1) light-colored dacite with phenocrysts of plagioclase, pyroxene or amphibole and biotitc, and 2) dark, crystal-poor “basalt-like” rocks with phenocrysts of pyroxene or olivine and plagioclase (McIntyre et al., 1982). The younger felsic rocks in the northern Challis area are rhyolitic lava, ash flow tuffs and tephra. The Casto Pluton is one of these younger felsic rock bodies and ranges in composition from pink granite to monzonite. Other distinct pink felsic rocks similar to the pluton make up the rest of the upper sequence of rocks. These rocks are interpreted to be derived from a caldera complex (McIntyre et al., 1982). Between rocks of Challis volcanic activity and those of the Snake River Plain are Cambrian to Permian shallow- to deep-water detritus including bedded limestone and dolomite, and quartzite (Bond, 1978). These are the same rocks found in the Columbia River Basin to the south and east of the Snake River Plain and are part of the Sevier orogenic belt. Rocks of southeast Idaho and western Wyoming consist of thrust-fault- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 33 bounded exposures of Paleozoic miogeoclinal rocks and crystalline basement rocks (Burchfiel et al., 1992). Because of limited access to the Challis Volcanics province, only two modem sand samples were collected from this province. These samples are from the Pashimeroi River and the east fork of the Salmon River. Most of this area is National Forest Land and due to extreme terrain and a lack of roads, it was difficult to access the stream system. Holocene sand samples from the Challis region are feldspatholithic (average composition Q15 F41 L44) (Table 8). The P/F ratio is 2. The majority of quartz grains are monocrystalline. Lithic grains are mostly volcanic and intermediate to felsic in composition. Eleven percent of the lithic grains are sedimentary in origin and reflect the influence of Paleozoic strata in the region. The modal compositions of these sands fall within the transitional magmatic arc field of Dickinson ( 1983) (Figure 4A). Classification of both the polycrystalline components (Qp4 Lv83 Lsml3) and the monocrystalline components (Qm26 P51 K23) THAI i H VfW f A N f l S a m o le 1 o c a t i o AM p 1 T OT F 1 AP I V K M AM P K 4M Vf 4M v m 7FI v( i V 1 < irw rm <^9»lmnr> A P f 1 ? 4 4 4 4 4 4 4 ^ 7 M R 71 44 7A 74 11 11 4 7 F 1 ITW1Q A 1A ^ 7 4 7 1A A7 4 1 q 7 7 1R 71 17 1 7 7 1 FA 1F R I 1F 7 MPAM 14 4 1 1A 4 7 R7 17 7A 11 7 7 7A i n 17 R7 11 ? < T n ? q 7 4 R 7 7 7 Q 7 7 7 R F wvnywR FOI a - t m a i h t RFI T o y F 1 T AT AP IV 1 1M AM P H 4M Vf «M v fn y.1 vl 1 V 1 « 1 7 irw i 41 7Q ?1 47 77 741F lA 1R 7 7 1 1 Table 8. Samples collected from the Challis Volcanic region and Wyoming fold-thrust belt Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 34 reflects volcanic arc orogen sources as defined by Dickinson and Suczek (1979) (Figure 5A and 5C). Sample ID-15 was collected from the Snake River near the eastern boundary of the Columbia River Basin. Source rocks for this sample are part of the Sevier orogenic belt in northwest Wyoming and southeast Idaho and are the same as those found in the Challis region. These are Paleozoic and Mesozoic shailow-water to transitional marine sediments. Lithologies include chert, limestone, dolomite, claystone, shale, siltstone, argillite, sandstone, quartzite and conglomerate (Bond, 1978). This sample has a composition of Q29 F41 L30 (Table 8). It has a P/F ratio of almost 5. Rock fragments are about equal amounts of volcanic and sedimentary grains. Sedimentary rock fragments include limestone and dolomite along with clastic grains. Chert is also common in this sample. Volcanic rock fragments are mostly felsic in composition. Plotting this sample on Dickinson’s revised QFL model (1983) suggests a dissected magmatic arc source (Figure 4A). Plotting polycrystalline (Qp21 Lv42 Lsm37) (Figure 5A) and monociystalline components (Qm34 P56 KIO) (Figure 5D) also reflects an arc orogen source on Dickinson and Suczek’s models (1979). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 35 Snake River Plain The Snake River Plain stretches for more than 500 km across southern Idaho (Figures 6 and 7). The geology of the Snake River Plain is dominated by Cenozoic, bimodal, basalt-rhyolite volcanism. The western Snake River Plain is composed of 15-16 Ma rhyolitic tuffs and ash flows and minor amounts of alkali basalt. Widespread tuffs erupted from numerous volcanic calderas are now covered by younger deposits. A complex package of thick fluvial and lacustrine sediments containing volcanic ash and interbedded basalt flows is also present. The stratigraphy of volcanic rocks in the western half of the Snake River Main is hard to assess because of poor exposure and lateral variations in thickness (Leeman, 1982). The eastern half of the plain contains younger silicic volcanic sequences and basalt flows. Rhyolitic welded tuffs and flows and minor basaltic flows dominate this part of the plain. The basalt of the Snake River Plain is predominantly olivine tholeiite. Rocks are porphyritic and contain plagioclase and olivine phenocrysts with some clinopyroxene SNAKE RIVER PLAIN SANDS Samole Location QM f LT QT F L OP LV LSM QMP K MLvt %Lvl Lv Ls Lm OR-11 R. NF 2 25 74 2 25 74 0 93 7 6 92 2 9 26 65 93 7 0 OR-IS Owyttee R. 6 32 61 8 32 60 1 93 6 19 68 13 13 18 69 94 6 0 ID-01 Snake R. 5 24 71 6 24 70 2 79 19 17 70 13 6 10 84 80 20 0 ID-14 Snake R. HF 14 IB 68 15 18 67 2 94 4 44 33 22 19 60 21 96 4 0 ID-16 Snake R. 9 23 68 13 23 63 7 66 7 27 49 24 64 17 19 92 8 0 10-17 Snake R. 2 8 90 3890 0 93 6 2260 18 10 1276 94 6 0 10-16 Snake R. 23 44 33 27 44 29 12 67 21 34 55 1 51 26 24 76 23 1 10-19 Snake R. 16 34 SO 20 34 4 6 9 64 27 31 51 18 29 46 25 70 30 0 10-21 Snake R. 16 45 39 18 45 36 7 81 12 26 58 16 45 31 23 87 12 1 MEAN 10 26 62 12 26 6 0 4 54 12 25 60 15 27 27 46 87 13 0 STD 7 12 16 8 12 19 4 12 8 1 16 7 21 17 28 9 9 0 Table 9. Samples collected from the Snake River Plain region Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36 national IMHÔ V •t 200 KILOMETERS EXPLANATION Tatiay udjnicntaiy locks QuMiuay built Prc-T«rtiary rocks QuiUmuy ibyolitc and Crataeious Mnatwc rocks Tattay vatcanlc ncte i M Figure 7. Geologic map of southern Idaho showing Snake River Plain (Mabey, 1982) phenocrysts. Rhyolites have high silica contents and phenocrysts typically include quartz, sanidine, sodic plagioclase, and minor ferromagnesian minerals (Leeman, 1982). Nine samples of sand were collected from the Snake River Plain province (Table 9). The majority of these samples come from the Snake River. Other samples are from the Malheur River and the Owyhee River in eastern Oregon. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 37 The majority of modem sand from the Snake River Plain is feldspatholithic. Samples from this region have an average composition of Q12 F29 L59. Abundant rock fragments are predominantly volcanic in origin and reflect a variety of compositions. Mafic grains account for about half of the volcanic fragments, with felsic and microlitic grains of about equal amounts making up the other half. Feldspar grains make up about one-third of the sand and these are predominantly plagioclase. These sands have low quartz contents with QmPK %Qm=25% and QtFL %Qt=12%. On Dickinson’s QtFL model (1983) the composition of these sands fall entirely within the magmatic arc field (Figure 4B) and reflect an undissected arc provenance defined by Dickinson with some overlap into the transitional arc field (average composition Qtl2 F28 L60). The plot of the polycrystalline components (Qp4 Lv84 Lsml2) of these sands lie within the arc orogen field determined by Dickinson and Suczek (1979) (Figure 5B). The monocrystalline components (Qm25 P60 K15) show the dominance of volcanic sources over plutonic sources (Figure 5D). The Lvf-Lvm-Lvl diagram illustrates how the sand composition is influenced by the bimodal nature of volcanic rocks in the Snake River Plain (Figure 8). The variability in the volcanic rock fragments is similar to that found by Critelli et al. (1997) in sands shed from the predominantly basaltic Santa Monica Mountains in California. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38 Lvf Lvm LvI Sample Lvf Lvm LvI ID01 6 10 84 ID17 10 12 78 ID18 51 26 74 OR15 13 18 69 OR11 9 26 65 ID19 29 46 25 ID21 45 31 23 ID14 19 60 21 ID16 64 17 19 Figure 8. Plot showing bi-modal distribution of volcanic rock fragments in sands collected from the Snake River Plain Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 39 Columbia Basalt Plateau The Columbia Basalt Plateau covers an area of 164,000 km^ in Washington, Oregon, and Idaho (Figure 9). Miocene flood basalts erupted from northwest-southeast trending fissures l&ated near the present Washington-Oregon border. The oldest basalt flow is the Imnaha basalt and is dated at 17.5 Ma (Beeson et al., 1989). The youngest basalts are the uppermost members of the Saddle Mountains Basalt, and they are as young as 6 Ma (Beeson et al., 1989). The most voluminous basalt flows, named the Grande Ronde Basalt, occurred between 16.5 and 15.6 Ma. They comprise more than 85% of the Columbia River Basalt Group (Orr&Orr, 1996). Tolan et al. (1989) suggested that there were more than 300 individual large volume flows along with possibly hundreds of smaller volume flows. All major flows of the Columbia River basalt are tholeiitic (Swanson et al., 1989). Fluvial and lacustrine strata are interbedded with the lava flows. As lava poured out of fissures, it encountered and invaded less-dense sediment that had been deposited during lapses in volcanic activity. These invasive flows are especially prominent along the Washington and Oregon Coasts (Beeson et al., 1979). Pillow basalt and palagonite are common at flow boundaries. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40 Washington O^OGAN HIGHZ^^^ Idaho 4 Oregon Figure 9. Coverage of Columbia River Basalt Flows (Orr and Orr, 1994) Twelve samples of modem sand were collected from the Columbia River Basalt Plateau (Table 10). These samples come from the Columbia River, Snake River and major tributaries draining the plateau. The tributaries sampled include the Yakima River in Washington, Grande Ronde River in Oregon, and Weiser River and Clearwater River Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 41 COLUMBIA BASALT PLATEAU SANDS SamDle Location QM f LT QT F L QP LV LSM QM P K MLvf % Lv\ Lv Ls Lm WA-OB Yabm» ft. 24 30 46 29 30 41 12 79 10 45 45 1 11 55 34 89 8 4 WA-09 CblufntMaR. 18 48 34 21 4 8 31 10 56 34 27 49 24 54 36 10 63 33 4 WA-tO Snake R. 18 54 28 19 54 26 5 93 2 25 54 21 31 36 33 98 0 2 WA-II Grande Ronde R. 15 28 56 16 28 56 1 99 1 35 52 13 99 0 WA-12 Snake R. 27 41 32 31 41 28 12 81 7 39 42 18 26 22 52 92 4 MA-t3(ACbk«nlHaR. 21 39 40 26 39 35 13 81 6 35 52 14 21 19 59 93 5 2 WA-1S Yakima R. 6 33 61 8 33 59 2 90 7 16 74 10 16 51 32 92 6 1 MA'21 CdlumbsR. 14 31 56 16 31 54 3 89 8 31 60 9 92 8 0 W A 22 CohanÈna R. 9 25 66 11 25 84 3 91 6 26 60 15 10 10 80 94 5 1 WA-23(A CoAiniOia R. 8 42 50 9 42 49 2 94 4 16 77 7 12 75 13 96 3 1 10-12 O earanttf R. 258016 256016 0 89 11 29 51 20 21 12 67 83 8 3 »0-23 WeuCT IL 10 36 52 10 38 52 0 100 0 20 76 4 0 99 100 0 0 MEAN ... 18.. 3945 183943 5 07 8 29 57 14 20 32 48 91 ? 2 STO 7 11 15 8 11 15 5 12 9 9 12 6 15 2329 109 2 Table 10. Samples collected from the Columbia Basalt Plateau region in Idaho. These sands show high compositional diversity because of the large area drained by these rivers, and they reflect a wide variety of source rocks. Sands are feldspatholithic with a mean composition of Q18 F39 L43. Feldspar grains within the sands are predominantly plagioclase feldspar (P/F ratio = 3). Quartz is relatively rare in sands collected from this region but does make up one-third of the monocrystalline component (QmPK %Qm=29%). Sands are enriched in rock fragments, the majority of which are volcanic in origin and mafic in composition. They are mainly lathwork grains composed of large plagioclase laths in a finer grained matrix containing abundant pyroxene and minor olivine. Microlitic volcanic grains are also abundant and reflect drainage of the Cascade magmatic arc to the west of the Columbia River Plateau. Samples taken from the Yakima River, which drains the eastern side of the Cascade Mountains, contain more microlitic volcanic rock fragments than lathwork fragments. Felsic rock fragments are also present and abundant in Snake River sand, and reflect the range of volcanic compositions from the Snake River Plain province. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 42 Modem sands found in the Columbia River Plateau region are similar to those found in the Snake River Plain region. According to Dickinson’s models (1983), these sands fall into the magmatic arc field (Figure 4B). Columbia River Plateau sands trend more towards the dissected arc field while Snake River Plain sands are more lithic-rich and trend more towards the undissected arc field. These trends in sand composition probably reflect the fact that rocks of the Columbia River Plateau are older and more deeply eroded than those of the Snake River Plain. The high percentage of lithic volcanic fragments over other polycrystalline components (Qp5 Lv87 Lsm8) of the sand reflects the arc orogen source defined by Dickinson and Suczek (1979) (Figure 5A). The plot of monocrystalline components (Qm29 P57 K14) suggests transitional and dissected arc provenances (Figure 5C). The plot of relative proportions of volcanic fragments of felsic, microlitic, and lathwork compositions shows the dominance of mafic grains but reflects a wide range of compositions (Figure 5F). This classification of the volcanic components is similar to that found by Marsaglia (1993) for Hawaiian beach sands which originate from basaltic flows and pyroclastic deposits. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 43 Blue Mountains The Blue Mountains region stretches across northeast Oregon and into southeast Washington and west central Idaho (Figure 10). Rocks within this region represent a diversity of geologic settings. Overall, the region can be classified as a group of exotic terranes accreted to the western edge of the North American continent during the Cretaceous. Four separate terranes have been identified within the region. The northern-most Wallov/a terrane is a volcanic-arc complex consisting of Permian and Triassic intrusive, volcanic, and volcaniclastic rocks, Triassic and Jurassic sedimentary rocks, and Early Cretaceous volcanic rocks (Vallier, 1995). Specific rock types include quartz keratophyre, andésite, spillite, limestone and shale along with flows, tuffs and volcaniclastic sediments. The Baker Terrane lies south of the Wallowa Terrane and has been called the Oceanic Terrane (Vallier et al., 1977) and the Central Melange Terrane (Dickinson and Thayer, 1978). Rocks range in age from Devonian to Late Triassic or Early Jurassic. Rock types include argillite, chert, phyllite, limestone, serpentinite, gabbro, graywacke, and rare blueschist. Volcanic rocks found in this region include mid-ocean ridge type basalts, intraplate basalts and volcanic island-arc basalts. The Canyon Mountain Complex is a Permian ophiolitic block found in this region (Figure 11). Major rock types of the complex include harzburgite, serpentinite, gabbro, plagiogranite and keratophyre Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 44 WASHINGTCm IDAHO CANYON MOUNTAIN U C O M P tE X \ 100 KILOMETERS IDAHO EXPLANATION Cretaceous to Jurassic plutons Wallowa terrane Baker terrane—ShoMtlng Canvon McKintair) Complex and Sparta complex (dark yay areas) bee terrane Olds Ferry terrane Grindstone terrane Contact Thrust fault—Sawteeth on upper plate Figure 10. Generalized geologic map of the Blue Mountains region (Walker, 1995) (Leeman et al., 1982). Bishop (1995) interpreted the Baker Terrane as a subduction complex related to the Olds Ferry volcanic arc. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 45 118* 58' 118'43’ JOHN DAY CANYON FAULT j2 KILOMETERS EXPLANATION ! OS 1 Surficial deposits (Quaternary) La Gabbroic and uhramaflc cumulates 1 Tv 1 Volcanic rocks (Tertiary) Gabbroic and ultramafic metacumulates Adds Creek Formation of the Hanturgite tectonite Aldrich Mountains Group Contact Melange Fault—Dashed where approximate Sill complex Figure 11. Generalized geologic map of the Canyon Mountain Ophiolite Complex (Leeman et al., 1995) The Olds Ferry Terrane is the eastern and southern most terrane within the Blue Mountains. This terrane is poorly exposed and fairly small in extent. Rocks range from middle to upper Jurassic and consist of basalt, andésite, rhyolite and related Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 46 volcaniclastics. Vallier et al. (1977) interpreted these rocks as part of an ancient volcanic arc. The Izee Terrane is characterized by flysch-like turbidites consisting of shale and graywacke with chert, serpentinite and volcanic rock fragments, and crystal fragments of quartz, calcite, plagioclase and spinel. Rocks of this terrane were probably deposited in intra-arc basins and as part of a deep fore-arc basin (Vallier, 1995). These rocks range in age from Late Triassic to Middle Jurassic. Five samples of modem sand were collected from the Blue Mountains region (Table 11). These samples came from the Powder River, Burnt River, Snake River, Little Salmon River and Salmon River. A few other samples reflect the influence of this province on modem sands. Samples OR-07 and OR-08 are grouped with the South Cascade province sands because of their bulk compositions but contain grains of serpentine probably shed from the Canyon Mountain Complex, which is found directly upstream from where the samples were collected. Sample OR-05 contains an abundance of pyroxene grains that also probably originated from ultramafic rocks of the Canyon Mountain Complex. Modem sands collected from the Blue Mountains region are lithofeldspathic and have an average composition of Qtl7 F50 L33. Feldspars are almost entirely plagioclase Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 47 BLUE MOUNTAIN SANDS S«mDle Location QM f LT QT f L QP LV LSM QM P K NLvf %Lvl Lv Ls Lri OR-12 PowOor H 10 31 58 23 31 46 22 33 45 25 71 4 100 0 0 42 56 2 OH-13 Burnt R. 9 51 40 13 51 36 9 60 30 15 63 1 26 33 41 67 25 8 OH-14 Snake R, 14 42 16 42 42 4 73 23 25 58 17 32 21 76 23 1 iO-24 Urtle Salman R. 20 61 20 20 61 20 0 96 4 24 72 4 6 8 64 96 2 1 iO-25 Salmon H. IS 62 22 IS 62 22 1 89 10 20 61 20 51 37 13 90 3 7 MEAN 14 49 37 17 50 3? 7 71 22 22 89 9 43 25 32 74 22 4 STO 4 13 16 4 13 12 9 2S 17 4 10 9 35 2033 2222 4 Table 11. Samples collected from the Blue Mountains Region (P/F = 7) with QmPK %K=9% and QmPK %P=69%. Lithic fragments are predominantly volcanic in origin although sedimentary rock fragments account for significant percentages of the polyciystalline components. Limestone, dolomite, chert and dense minerals are present in these sands to vaiying degrees. Sands collected from this region reflect a magmatic arc provenance when plotted and compared to Dickinsons revised models (1983). The QtFL plot illustrates that sand compositions fall primarily into the transitional magmatic arc field with a small amount of overlap into the dissected arc field (Figure 4A). The polycrystalline components (Qp7 Lv71 Lsm22) suggest an arc orogen source (Figure 5A). Similarly, the monocrystalline components (Qm22 P69 K9) reflect a volcanic arc source (Figure 5C). Kootenay Terrane The Kootenay Arc is located in southeastern British Columbia and northeast Washington as a narrow structural belt that marks the transition from middle- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TROUT " LAKE / KUSKANAX BATHOLIT K-T INTRUSIVE ROCKS JUR. INTRUSIVE ROCKS PENN. > JUR. EUGEOCLINAL ROCKS MILFORD GROUP (MISS.- PENN:} PZ. EUGEOCLINAL STRATA (UNDIFFERENTIATED) sNELSON KOOTENAY LARDEAU GROUP (L. PZ.) LAKE COVADA GROUP AND BRADEEN ASSEMBLAGE (L. PZ.) ORD. AND MINOR SIL. - DEV. TRANSITIONAL STRATA MIOGEOCLINAL STRATA PC - CAMB. ®*C " w a s h : KOOTENA ARC ROBERTS MOUNTAINS ALLOCHTHON Figure 12. Location and extent of the Kootenay Arc (Smith and Gehrels, 1991) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 49 Proterozoic-lower Paleozoic autochthonous continental margin strata to Paleozoic and Mesozoic arc suspect terranes (Smith and Gehrels, 1992). Rocks of the Kootenay Arc are lower Paleozoic eugeoclinal strata. Specific rock types of the Kootenay Arc include phyllite, argillite, slate, limestone, chert, quartzite, rare pillow lavas and tuff, quartzo-feldspathic wacke, quartz arenite, and conglomerate (Smith and Gehrels, 1992). These rocks have been intruded by Cretaceous-Tertiary and Jurassic granitic rocks. Five samples of modem sand were taken from the Kootenay Arc region (Table 12). These samples come from the Columbia River, Kootenay River, and Spokane River. Sands are predominantly quartzo-feldspathic, have an average composition of Qt31 F45 L24, and show wide variability in composition. These sands contain high percentages of quartz relative to other sands collected in the Columbia River Basin, although quartz only comprises one-third of the average, it comprises up to half of individual samples. Plagioclase feldspar dominates over potassium feldspar (P/F = 2.2). Rock fragments are both sedimentary and volcanic in origin, with a slightly higher percentage of volcanic lithics. Because of the high variability in the composition of sands shed from the Kootenay Arc region, plots suggest a diverse range of provenances. The QtFL diagram reflects a magmatic arc provenance and suggests the influences of a continental block Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 50 provenance and a recycled orogen provenance (Figures 4A). A dissected or transitional arc source dominates the provenance models but overlap occurs into the basement uplift field, as well as a small amount of overlap into the recycled orogen provenance. The plot of polycrystalline components (Qpl5 Lv43 Lsm42) also illustrates the dominance of an arc orogen source but also contains overlap into the collision-suture and fold-thrust belt source fields. The sands from the Kootenay Arc region have the same general monocrystalline components (Qm39 P42 K19) as those collected from subduction complexes (Figure 5D). KOriTFNAV TFBBANf tamale ( acatio AM F 1 T OT F 1 OP IV I9M OM 9 K 9M wf 9FI v m 1 V 1 « WA. 1 7 B 10 97 99 in 97 99 0 4 01 71 9A 71 1A 91 97 0 40 91 70 44 41 70 94 70 71 94 AO 99 7 9A A4 O 7A 77 7 74 97 14 7R 97 1R 19 94 7fl 90 47 7fl 99 47 O Afi Ift 14 Rr-04 rrWMn^ia B <9 9Q 7 99 90 9 97 97 97 97 97 9 90 ft 47 R r - n s B 79 71 74 71 A 7 49 n 44 91 90 R 47 100 n n UFAM 7R 49 77 91 49 74 19 49 47 90 47 10 94 47 14 90 9ft 17 < T n 1R 10 79 17 10 71 14 94 94 10 0 17 17 74 77 9A 41 1ft Table 12. Samples collected from the Kootenay Terrane region North Cascades The North Cascades region of the Columbia River Basin stretches from the crest of the Cascade Mountains in northwest Washington, east to the Columbia River, and from Snoqualmie Pass in central Washington, north into British Columbia (Figure 13). It is surrounded on the east-southeast by Miocene flood basalts of the Columbia River Plateau. The geology of this entire region is dominated by the accretion of numerous Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 51 terranes, which consist of predominantly meta-sedimentary rocks accreted mostly prior to Late Cretaceous time (Tabor, 1994) along with younger volcanic and plutonic rocks. Rocks west of the Kootenay Arc belong to the Quesnellia terrane and are included in the North Cascades region. These range in age from Ordovician to Jurassic, and consist of eugeoclinal metagraywacke, argillite, and metavolcaniclastic rocks along with minor marble, greenstone and serpentinite (Rhodes and Hyndman, 1988). Between the HOZAMEEN PASAYTEN FAULT Columbia R. 123" CANADA 122" FAULT > 1 2 0 ' O H anogan R. lia* ...... a u -----Sir...... I ■ ■ . , 4 . . _...... I ■ : Okanogan Highlands S5BÎÊ orthwest thrust system Melamorphic Terrane R O SS LAKE FAULT ZONE Methow- Q Pasayten tielt s o KM W a rtatc h aa STRAIGHT CREEK Unpattemed area# are Tertiary sedimentary FAULT or Igneous rocks, or Quaternary cover. U. Jurassic to A', Cretaceous plutonic rocks mid-U. Cretaceous Shukaan Suite (L. Jurasslc- undifferentiated plutonic rocks; Includes E. Cretaceous metamorpMsml Cretaceous to Eocene U. Jurasslc-U. Cretaceous, undifferentiated Mesozoic and Paleozoic, Mesozoic ■ Paleozoic rocks undifferentiated Figure 13. Geology of the North Cascades region in Washington state (Cowan and Bruhn, 1992), KC=Kettle Complex, OC= Okanogan Complex, RG=Republic Graben Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 52 Columbia River and the Okanogan River in Washington, the Toroden and Republic contain Eocene volcanic and sedimentary rocks. The Okanogan Complex and Kettle Complex, found on either side of the grabens, are small metamorphic-core complexes consisting of high-grade metasedimentary gneiss and schist (Hanson and Goodge, 1988). These complexes are surrounded by Eocene granitic rock and Cretaceous-Tertiary granodiorite. West of the Okanogan River are the north Cascade Mountains. This region is composed of northwest trending belts of metamorphic rocks separated by major faults and intruded by Late Cretaceous and Tertiary granitoid rocks (Misch, 1988). Rocks that compose the eastern side of the north Cascade Mountains include greenschist, blueschist and phyllite. Farther east, metasedimentary rocks dominate. Major rock types include chlorite-kyanite schist, kyanite-sillimanite gneiss and granitic orthogneiss (Misch, 1988). Farther east yet. Upper Jurassic and Cretaceous volcaniclastic strata are strongly folded and variably metamorphosed in the Methow-Pasaytan Belt (Figure 13). 1 collected five samples of modem sand from the Mad River, Entiat River, Wenatchee River and Swauk Creek in the North Cascades region. Sample WA-09 is taken from the Columbia River Plateau but represents drainage of the entire North Cascades area and so is included here. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 53 Modern sand samples are mostly lithofeldspathic (mean Qt23 F53 L24). Plagioclase feldspar is by far the dominant feldspar (P/F =8). Rock fragments are predominantly volcanic in origin, but there are sedimentary and metamorphic fragments to varying degrees within the samples (Qp4 Lv84 Lsml2). Sample WA-03 was collected from the Mad River in Washington, which drains a metamorphic terrane composed of schist and gneiss and some minor exposures of plutonic rocks. This sample has high amounts of both pyroxene and amphibole grains along with some garnet. Sample WA-05 is from the Wenatchee River which directly drains upper-amphibolite facies schist, gneiss, migmatite and plutons of the North Cascade crystalline core (Haugerud et al.,1994). Relatively high percentages of pyroxene (6.4%) and hornblende (3.4%) in the sand were likely derived from these source rocks. Sample WA-07, from the White River, contains significant biotite (5.6%) and pyroxene grains (5.6%). The White River originates in a terrane composed of ultrabasic peridotite and a biotite-homblende quartz diorite pluton (Magloughlin, 1994). The modal composition of sand collected from the North Cascades reflects a combination of magmatic arc and continental block provenances (Figure 4A). Within the magmatic arc field, the compositions reflect both a transitional and dissected arc provenance. The plot of polycrystalline components (Qp4 Lv84 Lsml2) of sands shed from the North Cascades reflects an arc orogen source (Figure 5A). The plot of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54 monocrystalline components (Qm30 P62 K8) reflects a magmatic arc orogen (Figure 5D) and illustrates the dominance of plutonic over volcanic sources. NORTH CASCADE SANDS Sample Location QM F LT QT FL QP LV LSM OM P K Lv Ls Lm WA-OT Swauk Creek 23 39 38 27 39 34 10 73 17 37 52 10 81 12 7 WA-03 Had R. 22 67 11 22 67 n 0 96 4 25 72 3 96 4 0 WA-05 Wenatchee R. 21 65 14 21 65 14 0 96 4 25 71 4 96 4 0 WA-07 White R. 24 46 30 25 46 30 2 95 3 34 65 1 97 1 3 WA-09 Columbia R. 18 48 34 21 48 31 10 56 34 27 49 24 63 33 4 MEAN 22 S3 25 23 53 24 4 84 12 30 62 8 86 11 3 STO 3 12 12 3 12 11 5 1^ 13 6 11 9 15 13 3 Table 13. Samples collected from the North Cascades region South Cascades The South Cascades region of the Columbia River Basin lies in southwest Washington and western and central Oregon and includes the John Day Basin of central Oregon (Figure 14). This region is dominated by recent volcanic activity and can be separated into a younger western half and an older eastern half, often referred to as the High Cascades (Orr and Orr, 1996). The western portion of the South Cascades is dominated by recent volcanic activity of stratovolcanoes Mt. Adams, M t Rainier and Mt. St. Helens. Major rock types surrounding these stratovolcanoes include andésite, dacite, rhyodacite, along with local silicic lava flows and ash flow tuffs. Also found within this region are Oligocene and Miocene shallow plutons such as the Snoqualmie Batholith and older plutons, such as the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 55 Mt. Stuart Batholith. The Snoqualmie Batholith is composed predominantly of homblende-biotite tonalité and granodiorite (Taylor, 1990). In Oregon, Tertiary sedimentary rocks dominate the western Cascades area. Rocks include tuffaceous terrestrial sediments, predominantly sandstone and siltstone, and marine sandstone and carbonaceous siltstone, along with minor basalt sills and flows and tuff-breccias (Walker and MacLeod, 1991). East of these sediments are the volcanic rocks of the High Cascades. Major rock types include basalt, basaltic andésite, and olivine basalt (Walker and MacLeod, 1991). The John Day Basin covers a small portion of central Oregon between the High Cascades and the Blue Mountains (Figure 15). Volcanic rocks of the John Day Formation and the Clamo Formation are interpreted by Robinson et al., 1984 to be renuiants of early Cascade volcanism. The Clamo Formation is composed of lava flows and tuff breccias with subordinate tuffs, ignimbrites, volcanic breccias, intrusive andesitic plugs and tuffaceous sediments (Suayuh and Rogers, 1991). The overlying John Day Formation is composed of calc-alkalic andesitic to dacitic tuffaceous claystone and airfall tuff with numerous interlayered ash-flow sheets and local lava flows of alkalic rhyolite, trachyandesite and alkali-olivine basalt (Robinson et al., 1984). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 56 122' 120* 1 WJUB^ O r e o o 'n ' m É — I 42“ 160km Figure 14. Generalized geologic map of Washington and Oregon showing location and geology of the South Cascades (Duncan and Kulm, 1989): 1 = pre-Tertiary rocks; 2 = Paleocene to Eocene volcanic rocks; 3 = mostly marine Tertiaiy sedimentary rocks; 4 = Eocene and early Oligocene volcanic rocks (including Clamo Formation and John Day Formation); 5 = mostly Oligocene and Miocene volcanic rocks; 6 = Tertiary and Quaternary volcanic rocks of the Cascade Range. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 57 Six samples of modem sand were collected from streams that drain the South Cascades region. These samples were collected from the Lewis River in Washington and from the Deschutes River, Willamette River, and John Day River in Oregon. Sands collected from this region are volcaniclastic (mean Qt2 F22 L76). Plagioclase feldspars are the dominant monocrystalline component (Qm5 P93 K2), with only very small percentages of monocrystalline quartz and potassium feldspar (P/F = 46). Polycrystalline components are dominanted by volcanic rock fragments (Qpl Lv92 Lsm7). The composition of volcanic rock fragments is varied and ranges from mafic to intermediate. Sample OR 01 was collected from the Lewis River which drains the western flanks of Mt. St. Helens, including volcanics from the 1980 eruption. This sand sample is composed almost entirely of zoned plagioclase feldspar and microlitic volcanic rock fragments containing large phenociysts of zoned plagioclase. Similarly, sample WA-23 comes from the Columbia River just as it flows out of the Cascade Mountains, and contains high amounts of plagioclase feldspar and microlitic volcanic rock fragments. The other five samples are dominated by mafic volcanic grains which reflect the basaltic and andesitic influence of the High Cascades and John Day Basin. As previously mentioned, samples OR-07 and OR-08 from the John Day River ccHitain sedimentary rock fragments and grains of serpentine likely derived from rocks in the Blue Mountains Region, but they are dominated by mafic volcanic lithic fragments. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58 Miocene and younger volcanic □ and sedimentary rocks John Day Formation, late Eocene-early Miocene / Clamo Formation, Eocene Mesozoic and Paleozoic rocks Kilometers Figure 15. Generalized geology of the John Day Basin showing the John Day and Clamo Formations within the South Cascades region illustrating the extent of Eocene volcanic activity in central Oregon (Bestland et al., 1996) Plotting South Cascade sands on Dickinson and Suczek (1979) and Dickinson’s revised (1983) models clearly reflects a magmatic arc source (Figure 4B). The QtFL plot Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 59 clearly suggests an undissected arc provenance. The QpLvLsm plot shows the dominance of volcanic lithics over other polycrystalline components and reflects an arc orogen source (Figure SB). The QmPK plot shows the relative abundance of plagioclase feldspar and reflects the great influence of volcanic over plutonic sources in magmatic arc provenances (Figure 5D). SOUTH CASCADE SANDS Sample Location QM F LT QT f L OP LV LSM 3 Deschutes R. 1 25 74 1 25 74 0 99 1 S 95 0 1 30 69 99 1 0 Oft-05 John Day R. 22870 32868 2 90 8 7 90 4 7 17 76 92 6 0 OR‘07 John R. 0 18 81 2 16 6 0 1 72 27 2 98 0 9 27 64 73 27 0 OR-08 JohnDavR. 1 18 81 2 18 80 1 91 8 6 91 3 9 40 51 92 8 0 MEAN 1 22 77 2 22 76 Î 92 7 S 93 2 7 39 54 92 8 0 STD 1 7 8 1 7 8 1 10 10 2 4 2 5 26 27 10 10 0 Table 14. Samples collected from the South Cascades region Belt Basin The Belt Basin region of the Columbia River Basin covers most of western Montana, southeast British Columbia, where it is known as the Purcell Supergroup, and parts of northern Idaho and northeast Washington (Figure 16). The rocks in this region are the oldest of any found in the Columbia River Basin. Rocks of the Belt Supergroup are generally considered to be Middle Proterozoic in age (Winston, 1989) and have ages ranging from 1500 Ma to 900Ma. The Belt Supergroup is sub-divided into four groups that reflect depositional history. The oldest rocks of the Belt Supergroup make up the Lower Belt and consist of evenly laminated and locally graded dark argillite, as well as conglomerate, sandstone, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 60 siliciclastic mudstone and calcareous mudstone. Above the Lower Belt is the Ravalli Group. The Ravalli Group is composed of ripple-marked and mudcracked redbeds, cross bedded and flat-laminated sandstone and green argillite. The Middle Belt Carbonate occurs above the Ravalli Group. Calcareous mudstone and siltstone and interbedded siliciclastic rocks comprise the Middle Belt Carbonate. The overlying Missoula Group BELT BASIN SANDS Sample Location QM F LT QT F L QP LV LSM QM P K Lv Ls Lm MT-01 Rock Oeek 40 37 23 44 37 19 18 29 53 52 30 18 35 65 0 MT-oe Flathead R. NF 27 9 64 33 9 58 9 32 59 76 20 4 35 65 0 MT-07 Flathead R. MF 7 13 80 8 13 79 1 1 98 35 47 18 1 99 0 MT-08 Flathead R. 11 IS 74 131572 2 098 4342 15 0 100 0 MT-09 Swan R. 10 13 76 11 13 76 0 1 98 44 47 9 1 99 0 MT-10 Blackfoot R. IS 7 78 17 7 76 3 40 57 67 25 8 41 59 0 MT-n Clark Fork R, 21 35 44 23 35 42 4 13 83 38 44 19 14 86 0 MT-12 aark Fork R. 26 56 18 26 56 17 5 22 74 31 51 IB 23 77 0 MT-13 Clark Fork R. 20 SO 30 23 50 27 8 13 79 29 SO 22 14 81 4 MT-14 Clark Fork R. 21 51 28 23 51 27 5 20 75 30 49 22 21 75 4 MT-15 Flathead R. 19 21 60 22 21 57 5 2 92 48 51 2 2 97 1 BC-01 Elk R. 4 4 92 9 4 87 5 21 73 53 42 5 23 77 0 BC-02 Kootenay R. S 9 86 5 9 86 0 2 98 35 49 16 2 96 2 BC-03 Columbia R. 25 3046 323038 17 24 59 4644 10 29 1060 MEAN 182557 212554 6 1678 4542 13 17 78 S STO 10 18 25 11 18 26 6 13 17 14 10 7 14 24 16 Table 15. Samples collected from the Belt Basin region consists of redbeds, interbedded green strata, dark carbonaceous strata, coarse sand and intraclast-bearing strata, argillite and local pillow basalts. The Belt Basin region of the Columbia River Basin also contains Paleozoic passive-margin Rocky Mountain sediments. Fourteen samples of sand were collected within the Belt Basin region. Samples were collected from the Clark Fork River, Flathead River, Blackfoot River, Swan River Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 61 and Rock Creek in Montana, and the Elk River, Kootenay River and Columbia River in British Columbia. Holocene sand samples from the Belt Basin are feldspathoiithic and have an average composition of Q21 F25 L54. The majority of quartz grains are monocrystalline. Quartz makes up the majority of the monocrystalline components, and potassium feldspar is rare (Qm45 P42 K13). The mean P/F ratio in these sands is 3. Rock fragments are predominantly sedimentary (Qp6 Lvl6 Lsm78) and include chert, dolomite, limestone, siltstone, and clastic grains. Volcanic rock fragments range in composition from felsic to intermediate; mafic grains were not observed. Ternary diagrams of sand compositions from the Belt Basin reflect a magmatic arc provenance as described by Dickinson and Suczek (1979) and revised by Dickinson (1983). Sands contain high percentages of rock fragments and fall into the undissected and transitional arc fields (Figure 4A). The plot of the polycrystalline components partially suggests a collision suture and fold thrust belt source (Dickinson and Suczek, 1979) but also falls outside defined fields and in a region of mixed orogenic sand composition (Figure 5A). Monocrystalline components (QmPK) plot in the Circum- Pacific Volcanoplutonic suites of Dickinson (1983) and are transitional between magmatic arc sources and continental block sources (Figure 5D). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 62 I t I IK iir Ito* EXPLANATION Minouki e*Mp ««4 «arr«Wi«* PufcM fomwllon* MMM M l CorbgmM vat KltdMMT FormoHen RovoHi Group pad CrooMB ForfMtlan Lowor Bolt, omt corrololWe PurcoM tan M tio m Pro-B ilt eryoMMno re d a YMIowiocW ArmeWom and Lm M Group Tbruottaull Normal touN SiraiivapMe conioel CuNurol boundary *0 40 Figure 16. Geologic map showing extent of pre-Cambrian Belt Supergroup (Winston, 1989) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. AVERAGE SAND COMPOSITIONS BY GEOLOGIC REGION REGION QM F LT QT F L OP LV LSM QM P K Lvf Lvm LvI Lv Ls Lm 3 BLUE MOUNTAINS MEAN 14 49 37 17 50 33 7 71 22 22 69 9 43 25 32 74 22 4 +/- 4 13 16 4 13 12 9 25 17 4 10 9 35 20 33 22 22 4 BOULDER BATHOLITH MEAN 19 48 33 20 48 32 5 83 12 27 48 25 40 53 7 87 12 1 +/- 8 14 19 9 14 19 4 18 17 9 6 7 17 21 5 18 18 1 CHALLIS VOLCANICS MEAN 14 41 45 15 41 44 4 83 13 26 51 23 29 57 13 87 11 2 +/- 3 5 2 4 5 1 1 8 7 7 2 9 7 3 3 8 6 1 COLUMBIA BASALT PLATEAU MEAN 16 39 45 18 39 43 5 87 8 29 57 14 20 32 48 91 7 2 +/• 7 11 15 8 11 15 5 12 9 9 12 6 15 23 29 10 9 2 IDAHO BATHOLITH MEAN 23 68 9 23 68 9 6 85 9 25 5520 63 20 17 91 7 2 +/- 6 7 4 6 7 4 5 9 10 7 7 4 221421 1074 KANIKSU BATHOLITH MEAN 29 61 10 32 61 7 28 53 19 33 47 20 83 17 0 75 15 10 +/- 5 10 4 8 10 2 14 6 7 8 6 2 24 24 0 5 6 11 NORTH CASCADES MEAN 225325 23 53 24 4 84 12 30 62 8 86 11 3 +/- 3 12 12 3 12 11 5 18 13 6 11 9 15 13 3 SOUTH CASCADES MEAN 1 22 76 2 22 76 1 92 7 5 932 7 39 54 92 8 0 +/- 1 7 8 1 7 8 1 10 10 2 4 2 5 28 27 10 10 0 SNAKE RIVER PLAIN MEAN 102862 12 28 60 4 84 12 25 6015 27 2746 87 13 0 + /' 7 12 18 8 12 19 4 12 8 11 16 7 21 17 28 9 9 0 WYOMING FOLD-THRUST BELT 21 41 38 29 41 30 21 42 37 34 56 10 58 27 15 53 47 0 KOOTENAY TERRANE MEAN 2845 27 31 45 24 15 43 42 39 42 19 39 42 19 50 38 12 +/- 161923 17 19 21 14 34 34 19 9 12 17 24 22 36 41 18 BELT BASIN MEAN 18 25 57 21 25 54 6 16 78 45 42 13 17 78 5 +/- 101825 11 18 26 6 13 17 14 10 7 14 24 16 Table 16. Modal sand compositions and error populations for each geologic region CD Q. "O S3 "O 2 Q. CD q : DISCUSSION Ingersoll et al. (1993) identified the need for additional compositional data from sand collected from first and second order streams, in order to develop more complex actualistic petrofacies models. Girty et al. (1988) found that QFL models generally yielded a correct interpretation of tectonic setting but that local source areas produce sands that yield an erroneous interpretation of tectonic setting. Ingersoll (1990) described the need for actualistic petrofacies models for application to ancient petrofacies to better constrain provenance. This data set of Holocene modal sand compositions was collected in reasonably well-established tectonic settings and hence can be used to test four specific hypothesis, described below, illustrating the connection between sand composition and plate tectonic setting. The first hypothesis that I will address is that first and second order sand compositions can be used to accurately infer the tectonic provenance of the basin. First, I will look exclusively at first order samples and then 1 will look at mean samples that represent both first and second order streams. The second hypothesis that I will address is the idea introduced by Ingersoll et al. (1993) that sampling scale outweighs tectonic setting. Ingersoll et al. (1993) emphasized that this is especially true in tectonic settings with diverse source rocks. The diversity of source terranes within the Columbia River Basin is ideal for studying this theory. The third hypothesis is that artificial homogenization of sands will approximate the composition of third order sands and more 64 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 65 accurately reflect provenance on Dickinson’s (1983) revised models. The final hypothesis that I will test with this data set is that sand compositions can be accurately predicted by modeling the areal coverage of source rock types within drainage basins and combining this information from numerous small basins to approximate sand compositions in second order drainage systems. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. HYPOTHESIS #1A The first hypothesis I will test is that sand compositions in first-order drainages can be used to directly infer the tectonic setting of the drainage basin. First-order systems are those that drain only local source rocks, so if this hypothesis is true, only a single tectonic provenance should be reflected in the compositional data. To test this theory, I reviewed sample locations and plotted those samples from first-order drainage systems on a ternary QtFL diagram. Twenty-one modem sand samples from the Columbia River Basin came from first-order drainages and reflect numerous geologic regions within the basin. Figure 17 shows QFL diagrams with compositions of single samples plotted and Table 17 lists the samples and from which geologic region they originated. This table also lists drainage provenance based on major source rock type and known tectonic setting, along with the actual provenance reflected by the samples. Thirteen samples of modem sand from first-order drainages accurately reflect the tectonic origin of the sand. Eight samples suggest a provenance other than that inferred from the bedrock geology. Three samples of sand taken from the South Cascades region accurately reflect an undissected magmatic arc provenance. Four first-order sand samples from the Idaho Batholith plot in the basement uplift field. Samples from the Columbia River Basalt Plateau and Snake River Plain reflect their magmatic arc provenance. Three samples of sand taken from the South Cascades region accurately 66 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0 RECYCLED OROGEN MIXED •MTOt DISSECTED ARC ID10 DISSECTED ARC .IÔOS TRANSITIONAL ARC m at♦mo7 TRANSITIONAL ARC «•IDOaMT^ • H^MTOe ♦Wftll'DM 1004 TMT08 MT03 •♦MT09 ^MT09 UNOISSECTEO A^tMTO? UNDISSECTED A nrat IncreaJjngMalunty. Stability trom yoMmental Block P rovanaw es CiTcuni'Pacific Volcanoplutonic Suites ♦MT05 n e rvin g Ratio o( Plutonic to Sources canic Sources in MagmaticArc Provenances Figure 17. Plots of first order samples and tectonic fields modified by Dickinson (1983), circled points on QmFL diagram indicate change in provenance from QtFL Reprotjucetj with permission of the copyright owner. Further reproctuction prohibitect without permission. 68 Actual Provenance predicted Sample # Geoloalc reaion orovenance bv sand composition MT03 Boulder Batholith Basement Uplift Magmatic Arc MT04 Magmatic Arc* MT05 Maqmatic Arc OR01 South Cascades Magmatic Arc Magmatic Arc 0RW2 Magmatic Arc OR03 Maamatic Arc MTOl Belt Basin Recycled Orogen Magmatic Arc* MT06 Recycled Orogen MT07 Magmatic Arc* MT08 Magmatic Arc MT09 Maqmatic Arc* ID03 Idaho Batholith Basement Uplift Basement Uplift ID04 Basement Uplift ID05 Basement Uplift IDIO Basement Uplift WAIT Columbia R. Basalt Plateau Maqmatic Arc Maamatic Arc ID14 Snake River Plain Magmatic Arc Maamatic Arc WA01 North Cascades Magmatic Arc Magmatic Arc WA03 Basement Uplift WA05 Magmatic Arc WA07 Maamatic Arc Table 17. Sampling locations of first-order streams, provenance of the basin and provenance reflected by the sand composition on QtFL diagram, (“*” represents provenance that is accurately reflected in QmFLt diagram) reflect an undissected magmatic arc provenance. Four first-order sand samples from the Idaho Batholith plot in the basement uplift field. Samples from the Columbia River Basalt Plateau and Snake River Plain reflect their magmatic arc provenance. Six samples reflect a tectonic setting other than that known from the bedrock geology. Sands collected from the Boulder Batholith reflect magmatic arc provenance instead of the continental block-uplifted basement provenance that would be expected. A Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 69 probable explanation for this is the presence of the Elkhom Mountain Volcanics (Hamilton and Myers, 1974). The majority of first-order sands collected from the North Cascades region accurately reflect a magmatic arc provenance. One sample, however, reflects a continental block provenance. Dickinson (1983) stated that similar detritus can be derived from basement uplifts and from eroded plutons in deeply dissected magmatic arcs. Within the North Cascades dissected-arc region, there are a number of small, exposed plutons which likely are shedding sand that is quartzo-feldspathic in composition and nught be suggestive of a continental block provenance. For example, sample WA03 (Mad River, north central Washington) has a composition of Qm22 F53 Lt25, likely reflects input from two small plutons, and suggests a continental block provenance when plotted on Dickinson's (1983) QmFLt diagram (Figure 17B). Five samples of sand were collected from first-order drainages in the Belt Basin region. Of these four, only one reflects the “correct” recycled orogen provenance on the QtFL diagram. However, on the QmFLt diagram, four of the five samples plot within or on the boundary of the recycled orogen provenance field. Clearly, first-order sands collected within the Belt Basin do not generally indicate the current tectonic setting of a recycled orogen provenance, suggesting that recycled detritus from relict tectonic setting of deposition may overshadow current tectonic settings. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 70 The sand compositions plotted on the QmFLt diagrams may reflect different provenances than plots on the QtFL diagrams. Four samples of first-order sands that inaccurately predict provenance on the QtFL diagrams are accurate when plotted on the QmFLt diagram. This discrimination between classification diagrams will be addressed later. In summaiy, the majority of these first order samples reflects the provenance of the drainage basin, but 38% of the samples suggest a tectonic setting other than that known from independent studies of the bedrock geology. This analysis shows that the classification diagrams do not always accurately predict provenance, even when sands are collected on top of the source rocks and there is no mixing of sands from different geologic tenranes. Hence, hypothesis #1A fails; sand compositions in first-order systems cannot always be used to accurately infer the tectonic setting of the drainage basin. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. HYPOTHSIS #1B The second hypothesis is that average ranges of sand composition representing individual tectonic settings and all sampling scales in the Columbia River Basin will more accurately reflect the QtFL petrologic classification models introduced by Dickinson and Suczek (1979) and revised by Dickinson (1983). Dickinson’s revisions (1983) included establishment of nine fields that are characteristic of sand derived from different types of provenances. These are grouped into three major categories: continental block, magmatic arc, and recycled orogen. The continental block category is sub-divided into craton interior, transitional-continental, and basement uplift (Figure 18). The magmatic arc is subdivided into dissected arc, transitional arc, and undissected arc (Figure 18). The recycled orogen field includes subduction complex provenance, collision orogen provenance and foreland uplift provenance. To compare modem sand samples with provenance models, it is necessary to attempt to classify the current tectonic setting of source rocks within the Columbia River Basin. Dickinson and Suczek (1979) described uplifted basement provenance as including uplifted and eroded plutonic belts of arc orogens. The Idaho Batholith and Kaniksu Batholith regions of the Columbia River Basin fit this category. These Mesozoic granitic intrusions are related to volcanic arc activity that occurred along the 71 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. JL KanAsuBalholilti kWioeaiK# Continental Block Notth Cascades Souih Cascades Magmatic Arc K M M t/A lc Belt Basai Recycled Orogen Figure 18. QtFL plots of sand compositions from known tectonic settings for Hypothesis IB Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 73 western continental margin. Sands shed from these two bathoiiths are compositionally very similar. Figure ISA illustrates the average modal compositions of these two regions and the standard deviation of all samples collected within that region. The plots show that sand compositions fall entirely into the uplifted basement-continental block field as described by Dickinson (1983). Given this data, an uplifted basement provenance would be accurately inferred. The Cascade Mountains of Washington and Oregon are split into a northern and southern portion for this study, but together compose a magmatic arc provenance. The North Cascades are composed of older arc rocks with exposure of arc-related plutons and large amounts of volcaniclastic debris. The Southern Cascades are composed of young extrusive rocks with continued volcanic activity. The difference in the source rocks of these two regions is evident in the modem sand samples collected, but samples accurately reflect the magmatic arc provenance (Figure 18B). Sands from the South Cascades plot entirely within the undissected arc provenance presented by Dickinson (1983). Sands from the North Cascades overlap in the transitional arc and dissected arc fields. Given only these data, it would be appropriate to infer a magmatic arc provenance. Dickinson and Suczek (1979) defined recycled orogen provenances as uplifted teiranes of folded and faulted strata from which recycled detritus of sedimentary or metasedimentary origin is prominent. According to these criteria, rocks of the Kootenay Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 74 Arc and the Belt Basin can be classified as recycled orogen. Average compositions of sand collected from these areas plot mostly within the magmatic arc field (Figure 18C). Within standard deviation, sands from the Kootenay Arc reflect a combination of magmatic arc and continental block provenances, and sands from the Belt Basin reflect a combination of magmatic arc and recycled orogen provenance. Given these data alone, a magmatic arc provenance is suggested; a recycled orogen provenance is not evident. Hence, the compositional models presented by Dickinson and Suczek (1979) do not always lead to accurate connection between plate tectonic setting and averaged compositional data for sands collected from known tectonic environments. While sands from the Idaho Batholith accurately reflect an uplifted basement provenance, recycled detritus from the Belt Basin erroneously reflects a magmatic arc provenance. Interpretation may be ambiguous for sand compositions that overlap provenance fields. For the most part, sands from the North Cascades accurately reflect a transitional/dissected arc provenance but overlap into the continental block provenance field may complicate interpretations. In conclusion, while the provenance diagrams established by Dickinson and Suczek (1979) may be helpful in determining tectonic origin of detritus, they are not always accurate. There are enough exceptions given the six groups of sand collected from unambiguous tectonic settings to invalidate the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 75 hypothesis that calculating standard deviation for groups of samples improves the predictability of sand composition from areas of known tectonic setting. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. HYPOTHESIS #2 The second hypothesis that I will address is that sampling scale outweighs tectonic setting in governing detrital sand compositions. Ingersoll et al. (1993) emphasized the need for actualistic petrofacies models based on diverse sampling scales because of the ambiguous provenance interpretations that result from analysis of sands from first and second order drainage basins. They found that in tectonic settings with diverse source rocks, existing petrofacies models were only applicable to third-order sands, and that it is inappropriate to reject the third-order models based on data collected from first and second order samples. The wide diversity of source rocks within the Columbia River Basin make it a good study area for examining this relationship between sampling scale and plate tectonic setting. This hypothesis would be nullified if all individual sand samples reflected the current tectonic setting of the region in which they were collected. To test this, individual samples were randomly selected and plotted on QFL diagrams (Figure 19). They were plotted with symbols reflecting their current tectonic setting. All samples collected within magmatic arc provenances have compositions that reflect their current tectonic setting. Ingersoll et al. (1993) found that sands shed from magmatic arcs accurately reflect their provenance regardless of sampling scale because of the homogeneity of source rocks in these regions. In this respect, sands derived from magmatic arc 76 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 77 Q t T P A f''i ■>iT} ' , -\i ARi F 0 Magmatic Arc provenance L ♦ Conti nental Bl ock provenance + Recycled Orogen provenance Figure 19. Plot of randomly selected individual samples from each major geologic provenance Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 78 provenance in the Columbia River Basin are correlative with the findings of Ingersoll et al. (1993). Samples collected from continental block provenances fall within both the continental block and magmatic arc field (Figure 19). Five samples fall into the basement uplift field, while four reflect a magmatic arc provenance. Only one of nine samples collected from a recycled orogen provenance actually reflects that setting. The majority of sands collected from recycled orogen settings reflect a magmatic arc provenance. Overall, the accuracy of individual samples in reflecting the current tectonic setting is only 54%. In part, the discrepancy between sand composition and tectonic setting exists because of the relative immaturity of these sands. Based on this data, the hypothesis cannot be nullified and it is evident that sampling scale outweighs tectonic setting. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. HYPOTHESIS #3 Hypothesis #2 demonstrated that sampling scale outweighs tectonic setting for Columbia River Basin sand derived from first and second-order streams. Hypothesis #3 provides additional insight into the predictability of tectonic setting from samples collected in first and second-order streams by assessing whether artificial homogenization of these samples will approximate the composition of samples from third-order drainages and hence better predict plate tectonic setting. To test this, I combined all samples collected from each provenance (Table 17) and compared this mean composition to Dickinson’s plots (1983). Continental Block Provenance The recalculated modal compositions of sand shed from the Kaniksu Batholith, Idaho Batholith and Boulder Batholith were combined and plotted on ternary diagrams to compare with continental-block derived sands described by Dickinson and Suczek (1979) (Figure 20). The mean compositions of Holocene sands from uplifted basement provenances in the Columbia River Basin are Qt23 F63 L14 and Qm22 F63 Ltl5 (Figure 20A and 2GB). Within standard deviation, the composition of sands on the (^FL diagram falls in the magmatic arc Held, but there is significant overlap 79 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80 Maqmatic Arc Origin Continental Block Recycled Orogen Sample Location Sample Location Sample Location OR-01 Lewis R. MT-02 Clark Fork R. OR-12 Powder R. 0R-W2 Willamette R. MT-03 Little Blackfoot R. OR-13 Burnt R. OR-03 Deschutes R. MT-04 Clark Fork R. OR-14 Snake R. OR-05 John Day R. MT-05 Silver Bow Ck. ID-24 Little Salmon R. OR-07 John Day R. ID-02 Boise R. ID-25 Salmon R. OR-08 John Day R. ID-03 Boise R. NF WA-09 Columbia R. OR-11 Malheur R. NF ID-04 Crooked R. WA-17 Spokane R. OR-15 Owyhee R. ID-05 Payette R. SF WA-18 Columbia R. ID-01 Snake R. ID-07 Salmon R. WA-19(AVG) Columbia R. ID-14 Snake R. HP ID-10 Lochsa R. BC-04 Columbia R. ID-16 Snake R. ID-11 Clearwater R. BC-05 Kootenay R. ID-17 Snake R. ID-20 Boise R. MT-01 Rock Creek ID-18 Snake R. ID-22 Payette R. MT-06 Flathead R. NF ID-19 Snake R. ID-26 Clearwater R. SF MT-07 Flathead R. MF ID-21 Snake R. WA-20 Pend-Oreille R. MT-08 Flathead R. WA-01 Swauk Creek ID-13 Priest R. MT-09 Swan R. WA-03 MadR. MT-10 Blackfoot R. WA-05 Wenatchee R. MT-11 Clark Fork R. WA-07 White R. MT-12 Clark Fork R. WA-08 Yakima R. MT-13 Clark Fork R. WA-09 Columbia R. MT-14 Clark Fork R. WA-10 Snake R. MT-15 Flathead R. WA-11 Grande Ronde R. BC-01 Elk R. WA-12 Snake R. BC-02 Kootenay R. WA-13(AVG) Columbia R. BC-03 Columbia R. WA-15 Yakima R. WA-21 Columbia R. WA-22 Columbia R. WA-23(AVG) Columbia R. ID-12 Clearwater R. ID-23 Weiser R. Table 18. Sand samples grouped by tectonic provenance into the basement uplift continental block provenance. The composition of sand on the QmFLt diagram falls into the basement uplift continental block with a small amount of overlap into the magmatic arc field. The plot of the polycrystalline components Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 81 Recycled Mixed ' o % Dissected ;CLED OROGEN pYCLED OROGEN Dissected Arc CONTINENTAL BLOCK- Transitional Transitional Arc # füTssected UituisbcCtcd Arc F «C0NT1NENTALBL0CK ^ MAGMATIC ARC Qp Om I Creasing Matunty/Stability !ro \ Continental Block Pro^nartces Subduction Cojfp Source Circuni-Pactlic Volcanoplutonic Suites RECYCLED Mixed Orogenic Sands CONTINENT/L BLOCK MAGMATIC ARC CONTINENTAL BLOCK A k 0/baen Sources rrcreasing Ratio of Plutonic to Volcanic Sources in Maqmatic Arc Provenance MAGMATIC ARC RECYCLED OROGEN Figure 20. Plots of mean sand compositions from each type of geologic provenance Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 82 (QpLvLsm) reflects an arc orogen source as described by Dickinson and Suczek (1979), but their models only identify arc orogen, subduction complex, collision suture, and fold- thrust belt sources (Figure 20C). The plot of monocrystalline components (QmPK) reflects a magmatic arc provenance for these modem sands, but identifies the greater influence of plutonic sources over volcanic sources (Figure 20D). The interpretation of tectonic setting from these sands would be erroneous if classified according to Dickinson and Suczeks (1979) and Dickinsons (1983) models. Sand compositions suggest a combination of continental block and magmatic arc provenances. The two QFL diagrams partially reflect a continental block provenance, and accurately express the uplifted basement sub-field within this provenance. But the overlap into the magmatic arc field, and the clear expression of magmatic arc provenance in the QmPK and QpLvLsm diagrams might lead to inaccurate interpretation of tectonic setting if these petrologic models were strictly applied. Magmatic Arc Provenance Samples collected from the South Cascades, North Cascades, Columbia River Basalt Plateau, and Snake River Plain are classified as being derived from a magmatic arc provenance. The South Cascades is volcanically active, and so can easily be classified as a volcanic arc. The North Cascades is older, with lesser amounts of extrusive volcanics Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83 and more exposure of arc-related volcanic rocks, and can be classified as a transitional to dissected arc. Tectonic classification of the Columbia River Basalt Plateau and Snake River Plain is more difficult. While these areas are dominated by recent volcanic activity, there is no current active magmatism related to an arc orogen. Moreover, the Snake River Plain volcanic field is not attributed to arc magmatism, but to the migration of a hotspot under the continent (Leeman, 1982). However, the overwhelming volcanic signature of these areas led to the inclusion as a magmatic arc provenance. Sands shed from these four geologic regions are plotted on ternary diagrams to compare their compositions with those defined by Dickinson and Suczek (1979) and revised by Dickinson (1983). All four ternary plots clearly express a magmatic arc provenance for these sands (Figure 20). The QFL diagrams reflect overlap in the dissected arc and transitional arc fields as determined by Dickinson (1983) (Figure 20A and 2GB). The plot of polycrystalline components (QpLvLsm) clearly reflects an arc orogen source (Figure 20C), and the plot of monocrystalline components (QmPK) reflects a magmatic arc provenance dominated by volcanic sources (Figure 20D), as described by Dickinson and Suczek (1979). Using classification diagrams introduced by Dickinson and Suczek (1979) and revised by Dickinson (1983), the modal composition of these sands accurately reflects the magmatic arc provenance from which they are derived. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 84 Recycled Orogen Provenance Modem sand samples that reflect current recycled orogen settings were combined and their modal percentages calculated and plotted on ternary diagrams (Figure 20). These samples came from the Belt Basin, Kootenay Arc and Blue Mountains. Accreted sedimentary rocks that have been metamorphosed to varying degrees, along with minor accreted volcanic rocks and orogenic intrusive plutonic rocks, dominate all of these areas. The modem sand samples from these areas have an average composition of Q22 F37 L41. The QFL plots of sand compositions reflect a magmatic arc orogen almost entirely, with a small amount of overlap into continental block provenance (Figure 20A and 20B). There is no overlap into the recycled orogen field. The plot of polycrystalline components reflects a combination of an arc orogen source and a collision suture and fold-thmst belt source, with some overlap into an undefined field explained only as originating from mixed orogenic sources (Figure 20C). The plot of monocrystalline components reflects a magmatic arc provenance that is dominated by plutonic sources (Figure 20D). Tectonic classification of the provenance of these sands would lead to erroneous interpretations using Dickinson and Suczek's (1979) models. Looking at the plots, one would interpret a magmatic arc provenance and not a recycled orogen provenance. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 85 Overall, modem sands collected within in the Columbia River Basin do not accurately reflect the tectonic setting as Dickinson and Suczek (1979) predicted with their models. Cordilleran mountain building, arc magmatism and accretion of suspect terranes have dominated the geologic history of the Columbia River Basin, but the present tectonic settings vary across the region. All modem sand samples from the basin tend to suggest a magmatic arc setting, but the present tectonic settings vary within the basin and include continental block provenances with basement uplift affinities, as well as recycled orogen provenances. Artificial homogenization of all first and second order sands within the basin does little to reduce the discrepancy between observed sand composition and that predicted based on plate tectonic setting, likely because of the important roles that relief, climate, and transport also play important roles in grain attrition (Basu, 1976; Basu, 1985); Dickinson et al., 1986; Critelli et al., 1997; Girty et al., 1988; Girty and Armitage, 1989; Marsaglia, 1993). In first and second order systems the transport distances are shorter and there is less time for compositional stabilization than for sands in third order systems. This will lead to differences in modal compositions between the lower order systems and third order systems and affect interpretations of tectonic provenance from Dickinson and Suczek’s models (1979) which were created based on sands from third order sampling scales. Complex tectonic settings, such as those found in the Columbia River Basin, result in diverse sand compositions at all scales and apparently Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 86 invalidates basin-wide classification of tectonic setting based on Dickinson and Suczeks (1979) models. In conclusion, hypothesis #3 is invalid. Artificial homogenization does not accurately approximate third-order sand compositions and does not lead to correct interpretation of tectonic setting. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. HYPOTHESIS #4 The final hypothesis that I will test is that sand compositions can be estimated by modeling and combining the areal coverage of different lithology types in small drainage basins. To test this, I selected areas that are drained through one substantial drainage, represented a combination of smaller drainage systems, and contained a sample location near the outlet of the drainage (Figure 21). The actual composition of the sand from the drainage was compared to the calculated composition based on the areal coverage of different source rock types. Six combinations of first order drainages were chosen on the basis of the above criteria. Four of these study areas are located in Idaho, one is in Montana, and one is in Oregon (Figure 21). The main lithologies identified and used in this analysis are felsic plutonic, felsic and mafic volcanic, coarse-grained siliciclastic, fine-grained siliciclastic, carbonate and metamorphic rocks. GIS data from the Interior Columbia Basin Ecosystem Management Program (ICBEMP) was used to identify small-scale drainage basins and to estimate lithology types within each basin. Some minéralogie assumptions about the source rocks and the components of the sand shed from them were necessary in order to calculate sand compositions. Two main types of felsic plutonic rocks are found within the study areas. Quartz monzonite is the main rock type of the Boulder Batholith. An average minéralogie composition of quartz- 87 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 88 Figure 21. Map of minor drainage basins used in estimating sand compositions for Hypothesis M4 and actual sample sites used in comparison Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 89 10%, plagioclase feldspar-45%, and potassium feldspar-45% was used to estimate sand composition from the Boulder Batholith. Granodiorite is the main rock type of the Idaho Batholith. An average minéralogie composition of quartz-40%, plagioclase feldspar- 50%, and potassium feldspar-10% was used to estimate sand compositions from the three drainage systems in west-central Idaho. Coarse-grained siliciclastic rocks are assumed to be sandstone and quartzite and sand shed from these areas is assumed to consist entirely of quartz grains. Fine-grained siliciclastic rocks are assumed to shed only silt clasts, which are identified as Ls. Carbonate rocks are assumed to shed only carbonate clasts, identified as Lc, and are grouped with Ls for modal calculations. Metamorphic rocks are assumed to shed only metamorphic fragments, identified as Lm. Sample MT-11 came from the Clark Fork River and represents the combined drainages of the upper Clark Fork River, the Blackfoot River, and Rock Creek. The predominant lithologies in this area are fine-grained siliciclastic rocks and felsic volcanic rocks, along with lesser amounts of plutonic rocks, coarse-grained siliciclastic rocks, carbonate rocks, and metamorphic rocks. The combination of lithologies exposed in the three drainage basins consists of 55% fine-grained siliciclastic rocks, 15% felsic volcanic rocks, 11% felsic plutonic rocks, 10% coarse-grained siliciclastic rocks, 6% carbonate rocks, and 2% metamorphic rocks. Using these percentages of rock types within the drainage basin, the calculated sand composition is Qtl 1 FIG L79 and the calculated lithic Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 90 content is Lv20 Ls78 Lm2 (Tables 19 and 20). The actual composition of sample MT-11 is Qt23 F35 L42 and the lithic content is Lvl4 Ls86 LmO (Figure 22). The calculated composition is much higher in lithic fragments than the actual sand composition representing this drainage. The initial assumptions made about the grains shed from the main lithology types are general and can explain this higher percentage of lithic fragments found in the calculated composition. Siliciclastic rocks may initially shed coarse sands composed entirely of silt clasts, but a very small amount of transport and weathering will result in the breakdown of sand into higher proportions of monocrystalline components. This higher lithic percentage will probably be the case for all calculated compositions throughout the basin and will be addressed further later. Sample ID-22 comes from the Payette River and represents the combined drainages of three forks of the Payette River. This drainage area contains mostly felsic plutonic rocks (71%) of the Idaho Batholith. Other rock types include fine-grained strata (15%), mafic volcanic rocks (11%), and metamorphic rocks (3%). The calculated composition of sands is Qt28 F43 L29 and the calculated lithic content is Lv39 Ls52 LmlO. The actual composition of sample ID-22 is Qt30 F65 L5 and the actual lithic content is Lvl(X) LsO LmO (Table 20). Sample ID-20 was collected from the Boise River and represents the combined drainages of the three forks of the Boise River. The drainage primarily contains felsic Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 91 1 B ?B fTi s e 5 I M H f 1 lU ill I f 1 II III is " " I l l ' l l 11 I m s I S S in i g 2S Î S9 m i s ils Is: ss %5SSÏ g. II ill sS = II II II nil n gg:r r- « p p p p p o o e p p < p p p ss sss II II nil £S gs: s s s p p o p } ss III SSS II is o s is S3 II p p p p p o P s: III gs islli II s s s p p p e p II III g S w* 111! » s is is is ss isss III »* ' p p p p p p I : s s s o o o nsII II n i l II llli o o o p p p I 1 SSS II II II nil II Ô p S 1 S' I p 2 oS: e »O w # 1 o p »3 p I w : «3;: & Q pjg : Ësëls g OOP isopppsis 190 •'{ % « 9 Î w pS = o«evtOM«nj!oo so§ 1 P : I ill e«ew*«weooe sSo e p p P g ^ * S % * P loi 0«raMO<*OAi - :: p I o o s 6eoo^A'O'^ooo s t* 2 3 ; 1 ; £ 1 p is p p I o 8 : 9 z 1 1 g " g o 1 Is O S il p o ; M K g S z s e p o p e 5* y 3 e o o il * s '£ o o e p s s - 3 p p s z I 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 92 plutonic rocks (63%) of the Idaho Batholith, but also contains fine-grained siliciclastic rocks (23%), mafic volcanic rocks (12%), and felsic volcanic and metamorphic rocks (2% each). The calculated composition of sands is Qt24 F37 L39 and Lv36 Ls60 Lm4. The actual composition of sample ID-20 is Q tl8 F74 L8 and Lv87 Lsl3 LmO (Table 20). Sample ID-09 was collected from the Salmon River in east-central Idaho and represents the combined drainages of the upper Salmon River and the Pashimeroi River. Lithology types in this drainage system are felsic volcanic rocks (55%), felsic plutonic rocks (19%), carbonate rocks (11%), and siliciclastic rocks (8% fine-grained, 7% coarse grained). The calculated composition of sands is Qtl 5 FI 1 L74 and Lv74 Ls26 LmO. The actual composition of sample ID-09 is Qtl8 F37 L45 and Lv81 Lsl6 Lm3. Sample ID-16 was collected from the upper Snake River and represents the combined drainages of the Henrys Fork, Teton River, Gros Ventre River, Salt River, Willow River, Greys-Hobock Rivers and Palisades River. Lithology types in this drainage system are felsic volcanic rock (33%), mafic volcanic rock (22%), coarse grained siliciclastic rocks (22%), fine-grained siliciclastic rocks (13%), carbonate rock (8%), and minor amounts of metamorphic rock (2%), and felsic plutonic rock (1%). The calculated composition of sands is Qt21 FI L78 and Lv71 Ls27 Lm2. The actual composition of sample ID-16 is Qtl 3 F24 L63 and Lv92 Ls8 LmO (Table 20). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 93 liMt iftl TalrtilatftH mrwlal Artuai mmdal fit f t t 1 V 1 m O r F 1 t I v ( 1 1 m i n ? ? ?ft% 71% 11% 11% in% 10% 6 1 % S% 1 0 0 % o % 0 % m x ) ?44A 17%, 11% 16% 60% 4% 16% 74% rm 67% 11% 0% moQ 1^^ 11%. 74% 74% 76% 0% 16% 1 7 % 4 1 % 6 1 % 1 6 % 1% miA ? 1 « . 1% 7A% 71% 77% 7% 11% 74% 61% 17% 6% o% w r i t 114A in % . 7 1 % 7 0 % 7 6 % 7% 7 1 % 1 1 % 4 7 % 1 4 % 6 6 % 0 % npn% 70*. n%, 4 ft% 1 7 % 7 % 1% 1% 7 1 % 7 4 % 1 4 % 1% o% mi 6 Vf/Vm 77%. 70%. %*% 1 1 % 7 4 % 6 1 % nn-ni 7%. 1 7 % AA% 1% 7 1 % 7 4 % irwnQ 11%, « % 16% 4 1 % Table 20. Calculated and actual sand compositions from combined drainages in the Columbia River Basin Sample OR 03 comes from the Deschutes River and represents the drainages of the upper Deschutes River, the Little Deschutes River, the Beaver River and the Lower and Upper Crooked River. Lithology types within the basin include mafic volcanic rock (65%), felsic volcanic rock (26%), fine-grained siliciclastic rock (5%), coarse-grained siliciclastic rock (2%), carbonate rock (2%) and metamorphic rock (1%). The calculated composition of sands is Qt2 FD L98 and Lv92 Ls7 Lml. The actual composition of sample OR-03 is Qtl F25 L74 and Lv99 Lsl LmO (Table 20). Figure 22 shows temaiy diagrams of the calculated and actual sand compositions for each of these drainage systems. The greatest amount of difference between the actual and calculated compositions occurs in the percentage of rock fragments (QtFL %L) found in each sample. The calculated compositions always predict a higher percentage of lithics than is found in the actual sand samples. This can be attributed to the assumptions made about sand compositions shed from certain lithology types and the survivability of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 94 Qt •© F L Lv Ls Lm Figure 22. QtFL and LvLsLm plots of actual and calculated sand compositions •ID22 *ID20 Solid symbols are calculated compositions, open and " I DOS circled symbols are actual sample compositions, #1016 boxed symbols reflect revised estimates + M T11 X 0R 03 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 95 the constituents of that sand. For example, the assumption was made that coarse-grained siliciclastic rocks would shed exclusively quartz grains, and that fine-grained siliciclastic rocks would shed exclusively sedimentary rock fragments. Coarse-grained siliciclastic rocks will probably shed sand that is more stable and less susceptible to breakdown through transport. Therefore, it is reasonable to assume that quartz-rich sandstones would shed quartz grains exclusively. On the other hand, fine-grained sedimentary rocks would shed sands dominated by rock fragments but also containing a number of other grain-types, including monocrystalline quartz, feldspars, and other minerals, depending on the amount of weathering and transport and the amount of breakdown of the lithic fragments into their crystal components. Likewise, sand from felsic and mafic volcanic source rocks would contain an abundance of individual plagioclase feldspar grains, as well as volcanic rock fragments. The discrepancy between actual and calculated sand compositions may also be related to data collection methods. The use of the Gazzi-Dickinson point-counting method identities crystals that are larger than silt size (0.0625mm) whether they are part of a larger lithic fragment or not. The identification of minerals within lithic fragments would result in an increase in the percentage of mineral grains in the sand and a decrease in the percentage of lithic grains. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 96 To illustrate how the general assumptions of grain types shed from source rocks influence calculations, I recalculated the compositions of three of the regions dominated by volcanic source rocks (see Table 20). Instead of assuming that all volcanic provenances would shed volcanic rock fragments exclusively, I assumed that both felsic and mafic volcanic rocks shed 35% plagioclase feldspar and 65% volcanic rock fragments. Felsic volcanic rocks, such as rhyolite, often contain phenocrysts of plagioclase in a fine-grained matrix, and mafic volcanic rocks, such as basalt, are composed of laths of plagioclase, so it is a realistic assumption that sands shed from either of these areas would contain plagioclase grains. By changing the types of grains shed from these volcanic provenances, the total lithic content decreased by 19% and the feldspar content increased by 19%. The new calculated composition is Qt22 F20 L58, which is much closer to the actual composition of sample ID-16 (Qtl 3 F24 L63). Changing the assumed compositions of volcanic rocks for sample OR-03 so that it consists of 35% plagioclase feldspar produces a predicted sand composition much closer to the observed composition (Figure 22). The newly calculated composition is (3t2 F32 L66 and the actual composition is Qtl F25 L74. Sample ID-09 reflects a provenance composed primarily of felsic volcanic rocks (55%). Making the same changes as above to the resulting grain types, the newly calculated composition of sands shed from this Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 97 region is Qtl5 F31 L55, which is a much better approximation to the actual composition ofQtl8F37L45. Problems in estimating the compositions of sands shed from certain source rocks arise because of differences in weathering and breakdown of rock fragments into their grain constituents. Volcanic source rocks will shed sands composed mainly of volcanic rock fragments, but these rock fragments are quickly broken down so that sands evolve to contain higher percentages of monomineralic constituents. This same trend toward increased percentages of monocrystalline grains is also likely to exist for metamorphic and fine-grained sedimentary source rocks. Immediately adjacent to the source rocks, sands may consist entirely of lithic fragments reflecting the provenance, but rapid breakdown decreases the amount of rock fragments and increases the amount of mineral grains in the sands. In conclusion, this final hypothesis is not valid. Sand composition can be generally estimated by modeling the areal coverage of lithology types within a drainage basin, although the accuracy when compared with actual sample composition depends on the assumptions made as to the grain types originating from source rocks. It is not realistic to assume that a single grain type results from any one provenance, with the exception of a highly mature quartz-sandstone, because of the rapid breakdown of rock Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 98 fragments into their mineral constituents and the variability of mineral constituents in every rock type. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CONCLUSIONS The data collected from Holocene sand compositions in the Columbia River Basin help to clarify the applicability of models relating sand compositions to tectonic setting. Ingersoll et al. (1984) concluded that the composition of sands shed from a magmadc arc provenance accurately reflect the tectonic setting at all sampling scales. Sand compositions from arc provenances within the Columbia River are consistent with this conclusion, but sands collected from streams draining recycled orogen and continental block provenance settings within the Columbia River Basin do not behave so homogeneously. In fact, none of the sand collected in settings classified as recycled orogen provenance reflect accurately that tectonic provenance. The Columbia River Basin is an excellent example of a mixed-provenance drainage. The wide variety of source rocks within the basin lead to a wide range of compositional variability in sands. Because of the mixing of sands derived from different source regions, petrological models linking sand composition and plate tectonic setting (Dickinson and Suczek, 1979; Dickinson, 1983) are inaccurate in many cases. Although the models may provide helpful information, they cannot be solely relied upon when making inferences about tectonic setting. Four specific conclusions were reached through the analysis of modem sand collected from the Columbia River Basin. 1) Sand compositions from first and second 99 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 order streams cannot always be used to accurately infer the tectonic setting of the drainage basin as described by Dickinson and Suczek’s (1979) models. 2) Sampling scale appears to outweigh tectonic setting; sand samples collected from low order systems have compositions more closely related to the local source rocks than to the general tectonic setting of those rocks. 3) Artificial homogenization of sands in first and second order drainage systems does not accurately approximate compositions in third order systems. This is due to shorter transport distances and a lack of stabilization that comes with weathering and transport. 4) Sand compositions cannot be accurately estimated by modeling areal coverage of source rock types within drainage basins due to complex characteristics of weathering and breakdown of grains that are unique to each drainage system. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 101 References Armstrong, R.L., 1974, Magmatism, erogenic timing, and erogenic diachronism in the Cordillera from Mexico to Canada, Nature, v, 247, p. 348-351. Armstrong, R.L., 1975, Precambrian (1500 m.y. old) rocks of Central Idaho - The Salmon River Arch and its role in Cordilleran sedimentation and tectonics, American Journal of Science, v. 275A, p. 437-467. Armstrong, R.L., Leeman, W.P., and Malde, H.E., 1975, K-Ar dating. Quaternary and Neogene volcanic rocks of the Snake River Plain, Idaho, American Journal of Science, v. 275, p. 225-251. Barton, M.D., Battles, D.A., Debout, G.E., Capo, R.C., Christensen, J.N., Davis, S R., Hanson, R. Brooks, Michelsen, C.J., and Trim, H E., 1988, Mesozoic Contact Metamorphism in the Western United States, in Ernst, W.G., editor, Metamorphism and Crustal Evolution of the Western United States: Rubey Volume VII, p. 110-178. Basu, A., 1976, Petrology of Holocene fluvial sand derived from plutonic source rocks: Implications to paleoclimatic interpretation, Journal of Sedimentary Petrology, v. 46, no. 3, p. 694-709. Basu, A., 1985, Influence of climate and relief on compositions of sands released at source areas, in, Zuffa, G.G., editor. Provenance of Arenites, N.A.T.O. Advanced Study Institute Series, 148, p. 1-14. Basu, A., Young, S.W., Suttner, L.J., James, W.C., and Mack, G.H., 1975, Re-evaluation of the use of undulatory extinction and polycrystallinity in detrital quartz for provenance interpretation. Journal of Sedimentary Petrology, v. 45, no. 4, p. 873- 882. Beeson, M.H., Tolan, T.L., and Anderson, J.L., 1989, The Columbia River Basalt Group in western Oregon; Geologic structures and other factors that controlled flow emplacement patterns, in, Reidel, S P , and Hooper, P R., editors, Volcanism and tectonism in the Columbia River flood-basalt province: Boulder, Colorado, Geological Society of America Special Paper 239, p. 223-246. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 102 Beeson, M.H., Perttu, R., and Perttu, J., 1979, The origin of Miocene basalts of coastal Oregon and Washington, Oregon Geology, v. 41, p. 159-166. Bestland, E.A., Retallack, G.J., Rice, A.E., and Mindszenty, A., 1996, Late Eocene detrital latentes in central Oregon; Mass balance geochemistry, depositional setting and landscape evolution. Geological Society of America Bulletin, v. 108, no. 3, p. 285-302. Bishop, E.M., 1995, High-Pressure, Low-Temperature schistose rocks of the Baker Terrane, Northeastern Oregon, in, Vallier, T.L., and Brooks, H.C., editors. Geology of the Blue Mountains region of Oregon, Idaho, and Washington: Petrology and Tectonic Evolution of Pre-Tertiary Rocks of the Blue Mountains region. United States Geological Survey Professional Paper 1438, p. 211-219. Bond, J.G., 1978, Geologic map of Idaho, 1:500,000 scale, Idaho Department of Lands, Bureau of Mines and Geology, and United States Geological Survey. Brown, E.H., 1987, Structural geology and accretionary history of the Northwest Cascades system, Washington and British Columbia, Geological Society of America Bulletin, v. 99, p. 201-214. Burchfiel, B.C., Cowan, D.S., and Davis, G.A., 1992, Tectonic overview of the Cordilleran orogen in the western United States, in Burchfiel, B.C., Lipman, P.W., and 2Ioback, M L., editors. The Cordilleran Orogen: Conterminous U.S.: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G-3, p. 407-480. Cowan, D.S., and Bruhn, R.L., 1992, Late Jurassic to early Late Cretaceous geology of the U.S. Cordillera, in Burchfiel, B.C., Lipman, P.W., and Zoback, M L., editors. The Cordilleran Orogen: Conterminous U.S.: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G-3, p. 169-203. Critelli, S., Le Pera, E., and Ingersoll, R.V., 1997, The effects of source lithology, transport, deposition and sampling scale on the composition of southern California sand, Sedimentology, v. 44, p. 653-671. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 103 Davis, G.A., Monger, and Burchfiel, B.C., 1978, Mesozoic construction of the Cordilleran “collage,” central British Columbia to central California, in Howell, D.G., and McDougall, K.A., editors, Mesozoic paleogeography of the western United States, Los Angeles, California, Pacific Section Society of Economic Paleontologists and Mineralogists Pacific Coast Paleogeography Symposium 2, p. 1-32. Dickinson, W.R., 1970, Interpreting Detrital Modes of Graywacke and Arkose, Journal of Sedimentary Petrology, v.40, no. 2, p. 695-707. Dickinson, W.R., 1982, Compositions of sandstones in circum-Pacific subduction complexes and forearc basins, American Association of Petroleum Geologists Bulletin, v. 66, p. 121-137. Dickinson, W.R., 1985, Interpreting provenance relations from detrital modes of sandstones, in, Zuffa, G.G., editor. Provenance of Arenites, Hingham, D. Reidel Publishing Company, p. 333-361. Dickinson, W.R., and Snyder, W.S., 1978, Plate Tectonics of the Laramide Orogeny, Geological Society of America Memoir 141, p. 355-366. Dickinson, W.R., and Thayer, T.P., 1978, Paleogeographic and paleotectonic implications of Mesozoic stratigraphy and structure in the John Day inlier of central Oregon, in Howell, D.G., and McDougall, K.A., editors, Mesozoic paleogeography of the western United States, Los Angeles, California, Pacific Section Society of Economic Paleontologists and Mineralogists Pacific Coast Paleogeography Symposium 2, p. 147-162. Dickinson, W.R. and Suczek, C.A., 1979, Plate Tectonics and Sandstone Compositions, Amercan Association of Petroleum Geologists Bulletin, v. 63, p. 2164-2182. Dickinson, W.R., Beard, L.S., Brakenridge, G.R., Erjarec, J.L., Ferguson, R.C., Inman, K.F., Knepp, R.A., Lindberg, F.A., and Ryberg, P.T., 1983, Provenance of North American Phanerozoic Sandstones in relation to Plate Tectonic Setting, Geological Society of America Bulletin, v. 94, p. 222-235. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 104 Dickinson, W.R., Lawton, T.F., and Inman, K.F., 1986, Sandstone detrital modes. Central Utah Foreland region: Stratigraphie record of Cretaceous-Paleogene tectonic evolution. Journal of Sedimentary Petrology, v. 56, no. 2, p. 276-293. Dott, Jr., R.H., and Prothero, D R., 1994, Evolution of the Earth, McGraw-Hill, Inc., 569 P Duncan, R.A., and Kulm, L.D., 1989, Plate tectonic evolution of the Cascades arc- subduction complex, in. Winterer, E.L., Hussong, D M., and Decker, R.W., editors. The Eastern Pacific Ocean and Hawaii; Boulder, Colorado, Geological Society of America, The Geology of North America, Volume N, p. 413-438. Elston, D P. and McKee, E.H., 1982, Age and correlation of the Late Proterozoic Grand Canyon disturbance, northern Arizona, Geological Society of America Bulletin, v. 93, p. 681-699. Engebretson, D C., Cox, A., and Gordon, R.G., 1985, Relative motions between oceanic and continental plates in the Pacific Basin, Geological Society of America Special Paper 206,59 p. Ewing, T.E., 1980, Paleogene tectonic evolution of the Pacific Northwest, Journal of Geology, v. 88, p. 619-638. Fox, K.F. Jr., Rinehard, C D., and Engels, J.C., 1977, Plutonism and orogeny in north- central Washington; Timing and regional context. United States Geological Survey Professional Paper 989, 27 p. Gabrielse, H., and Yorath, C.J., 1989, The Cordilleran Orogen in Canada, Geoscience Canada, v. 16, p. 67-83. Gerlach, D C., Ave Lallemant, H.G., and Leeman, W.P., 1981, An Island Arc Origin for the Canyon Mountain OphioHte Complex, Eastern Oregon, U.S.A., Earth and Planetary Science Letters, v. 53, p. 255-265. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 105 Girty, G.H., Mossman, B.J., and Pincus, S.D., 1988, Petrology of Holocene sand, Peninsular Ranges, California and Baja Norte, Mexico: Implications for Provenance-Discrimination Models, Journal of Sedimentary Petrology, v. 58, no.5, p. 881-887. Girty, G.H., and Armitage, A., 1989, Composition of Holocene Colorado River Sand: An Example of Mixed-Provenance Sand Derived from Multiple Tectonic Elements of the Cordilleran Continental Margin, Journal of Sedimentary Petrology, v. 59, no. 4, p. 597-604. Graham, S.A., Hendrix, M.S., Wang, L.B., and Carroll, A.R., 1993, Collisional successor basins of western China: Impact of tectonic inheritance on sand composition. 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