.. 

.. 

. 

THIRD SEMIANNUAL PROGRESS REPORT TO THE NATIONAL 

AERONAUTICS AND SP ACE ADMINISTRATION 

Office of Space Science and Aplications 

(NASA-CR-180355) XHEEATIC EA€EEB STUDY OP ~a7-19793 

ALASKAN CFHICLIIES SiEmiannuaf Eroqress 

ftcport (Ccrnell Uciv,) 21 F CSCL 08B 

flnclas 

G3/43 43671 

Project NAS5-28739 

Thematic Mapper Study of Alaskan Ophiolites 

Department of Geological Sciences 

Cornel1 University 

Ithaca, New York 14853-1504 

Principal Investigator: John M. Bird 

Professor of Geology 

February, 1987 
., *. 

.. 1 

Personnel: John M. Bird, Professor of Geolgy 

David J. Harding, Ph.D. Candidate 

Karl R. Wirth, Graduate Student, Ph.D. 

Ann E. Blythe, Graduate Student, Ph.D. 

Teunis Heyn, Graduate Student, Ph.D. 

Summary of Research: August, 1986 to January, 1987 

Introduction 

The major objectives of this project are to use Landsat Thematic Mapper (TM) 

images to produce improved geologic maps of the ophiolites of the Brooks Range, 

and to recognize regional-scale structures that might affect the spatial distribution 

of the ophiolites. From the Thematic Mapper data, we have obtained significant 

new information concerning the distribution of rock types and structures that could 

not easily be acquired with conventional geologic studies. The infomation obtained 

from the TM data, in combination with other geologic data, is being used to further 

our understanding of the tectonic evolution of the Brooks Range. An example of 

our results to date is described in this report. Results of our work in the 

Maiyumerak Mountains area of the western Brooks Range are used to illustrate the 

kind of information being obtained with the Landsat TM data, and the way that the 

information is being integrated with other geologic data. 

The physiographic provinces of northern Alaska are shown in Figure 1. The 

Brooks Range is a fold-thrust belt of Late Jurassic and Early Cretaceous age, 

thought to have formed north of a southward-dipping subduction zone. The thrust 

sheets of the Brooks Range consist of oceanic crust and mantle (termed ophiolite), 

forming the structurally highest sheets, and platform sedimentary rocks. Sediments 

shed from the uplifted Brooks Range were deposited to the north in the Colville 

Basin and to the south in the Yukon-Koyukuk Basin during Cretaceous time. The 

distribution of ophiolite exposures in the western Brooks Range is shown in Figure 

2, a TM Band 7 mosaic of two scenes (path 80, rows 12 and 13). The location of the 

mosaic is shown in Figure 1. The major ophiolite exposures are Asik Mountain, the 

Maiyumerak Mountains, Avan Hills, and Misheguk Mountain. 

The Maiyumerak Mountains are exposures of mafic volcanic rock that were 

mapped as a single basalt unit during reconnaissance mapping by USGS workers; 

1ithoIogic units were not differentiated nor were structures identified. During one 
. ! 

2 

week of reconnaissance mapping in the central Maiyumeraks in 1985, we 

recognized two distinct basalts separated by a north-south trending fault. The - 

eastern basalt weathers reddish-brown and consists of two units, a sheeted dike unit 

(consisting entirely of parallel, planar dikes) that is overlain by a unit of massive 

and pillowed flows. The western basalt weathers grey and consists of flows 

intruded by randomly oriented dikes. The distribution of these rocks is shown in 

Figure 3. The extremely rugged terrain of the Maiyumeraks, and the short time 

available, limited our work to reconnaissance mapping in a small area. The basalts 

could not be differentiated on standard false-color infrared aerial photographs, so 

our reconnaissance work could not be extrapolated to larger areas using the 

photographs. 

Correlations between reflectance. mineralogv. and Peochemistry 

The Thematic Mapper images have made it possible to extrapolate our field 

observations throughout the Maiyumerak Mountains. Figure 4 is a geologic map of 

the Maiyumeraks, interpeted from TM images and constrained by our field 

observations. Where the rocks are not covered by vegetation, four spectrally 

distinct basalts have been recognized using scaled false-color composites and an 

image produced by a principal components transformation. For visual 

identification of units, scaled composite images of Bands 3, 2, and 1 (a 

pseudo-natural color image) and 7,3, and 1 have been most useful (with the bands 

displayed in red, green, and blue, respectively). The scaling of the composites is 

based on statistics for the exposed rocks of interest, rather than for the entire scene, 

in order to enhance subtle reflectance differences. The best principal component 

image for recognition of spectral differences is a combination of components 3,4, 

and 5 (principal components 1 and 2 show reflectance differences that are primarily 

due to slope orientation and vegetation cover, respectively). The Maiyumeraks 

appear to be comprised of two thrust plates of basalt. The lower plate is comprised 

of basalt with relatively low reflectance in Bands 1,2,5, and 7 and high reflectance 

in Band 3, as compared to the basalt of the upper plate. Each thrust plate can be 

divided into two basalts, based on spectral differences, designated basalts A and B in 

the lower plate, and basalts C and D in the upper plate. Basalts A and C correspond 

to the reddish-brown weathering and grey weathering basalts observed in the field. 

The basalts of the lower thrust plate have apparently been exposed in the center of a 

north-trending antiform. Areas of especially high reflectance in Bands 5 and 7 

occur in both thrust plates (outlined by dashed lines in Figure 4). These correspond 

to areas of weak hydrothermal sulfide mineralization. 
I' 

.. 

.. 3 

The cause of the reflectance differences between the basalts of the two thrust 

plates has been studied by examining the mineralogy and chemistry of samples that 

were collected during our field work in 1985. The characteristics of the lower and 

upper basalts are summarized in Figure 5. The TM radiance measurements are 

presented as normalized digital numbers (DN), in which the DN values of the two 

basalts in each of the six reflectance bands have been divided by the DN values in the 

lower basalt (the DN values are averages of several hundred pixels from directly 

illuminated slopes). The reflectance differences between the upper and lower 

basalts are readily apparent in the normalized plot for the upper basalt. The DN 

values differ by less than lo%, corresponding to very small reflectance differences. 

The comparatively high Band 3 reflectance of the lower basalt is produced by 

greater amounts of iron hydroxides in the weathered surfaces on the basalts. X-ray 

diffraction measurements of powders from the weathered surfaces indicate that, 

except for iron hydroxide concentration, there are no significant mineralogic 

differences between the upper and lower basalts. The smaller concentration of iron 

hydroxides within weathered surfaces on the upper basalt accounts for its grey 

weathering color as compared to the reddish-brown weathering color of the lower 

basalt. 

The differing weathered surfaces on the two basalts are apparently due to 

differences in metamorphic mineral assemblages. Both basalts have been 

metamorphosed at greenschist facies conditions, and both contain the iron-bearing 

metamorphic minerals chlorite and epidote. However, primary clinopyroxene is 

preserved in the lower basalt, whereas metamorphic actinolite is present in the 

upper basalt, indicating that the upper basalt was affected by more intense 

metamorphism (eg. slightly higher temperatures, greater fluid activity, and/or 

longer time). The actinolite apparently "binds" iron during weathering, 

suppressing the formation of iron hydroxides. The reflectance differences detected 

by the Thematic Mapper are, therefore, making it possible to map 

metamorphic-facies variations within basalts. 

The metamorphic differences being mapped with the TM data provide 

information that can be used in paleogeographic reconstructions of northern Alaska 

because the metamorphic differences correlate with geochemical differences in the 

basalts that are indicative of tectonic setting. The concentrations of trace elements 

in basalts are diagnostic of origins in different tectonic settings. Figure 6, for 

example, illustrates the discrimination of basalt-types, using hafnium, thorium, and 

tantalum. The Maiyumerak upper-basalt samples are similar to calc-alklaline 

basalts formed in modem island arc or marginal basin settings, whereas the 

lower-basalt samples are similar to modem tholeiitic island arc or marginal basin 
basalts. The Maiyumerak basalts are unlike mid-ocean ridge basalts (MORB), 

which are typical of major ocean basins, as well as ocean island basalts and 

continental flood basalts. The tholeiitic and- calc-alkaline affinities of the 

Maiyumerak basalts are corroborated by the rare-earth-element patterns of the 

samples (Figure 5). 

Similar correlations between reflectance, metamorphic mineral abundances, 

and geochemistry have been identified in basalts of the Angayucham Terrain, along 

the southern margin of the Brooks Range, 300 km west of the Maiyumerak 

Mountains (Figure 5). Previous workers recognized two thrust sheets of basalt in 

the Ambler District of the Angayucham Terrain and, as in the Maiyumeraks, the 

basalts of the upper plate are actinolite-bearing whereas the lower-plate basalts lack 

actinolite. The differences in metamorphic mineral abundances produce reflectance 

differences like those of the Maiyumerak basalts, with the upper basalt having 

relativeIy Iow Band 3 reflectance. The mineralogies correlate with trace element 

and rare earth element variations that suggest that the lower basalt formed in an 

oceanic plateau setting, whereas the upper basalt might have formed in an ocean 

island setting. 

Other ophiolite exposures of the Brooks Range are being examined in a similar 

manner in order to identify previously unrecognized lithologic variations. Gabbros 

and ultramafic rocks are being studied, in addition to basalts. The reflectance 

variations observed in the TM data are making it possible to produce significantly 

improved geologic maps of the ophiolites. 

Recognition of large-scale structures 

Previous mapping in the Brooks Range has emphasized the importance of 

low-angle thrust faults in the structural evolution of the range. High-angle faults 

(ie. strike-slip faults and normal faults) are reportedly less common. The improved 

spatial resolution of the TM data, as compared to Landsat multispectral scanner 

data, and the synoptic coverage, make the TM images especially useful for the 

identification of high-angle faults. High-angle faults are more readily recognized 

than thrust-faults on the TM images because the high-angle structures are 

commonly expressed as abrupt, linear topographic features or contacts between 

rock types. Numerous linear features, interpreted to be faults, have been 

recognized on the TM images during our mapping of the Brooks Range ophiolites. 

For example, the Maiyumeraks are cross-cut by many north-northeast trending, 

high-angle faults (Figure 4). Offsets of lithologic contacts suggest that motion on 
I. 

.. 

.. '. 5 

the faults was down-on-the-west and/or right-lateral. 

The faults in the Maiyumeraks parallel a major topographic lineament that 

separates the basalts of the Maiyumeraks on the west from limestones on the east 

(Figure 2). The lineament is arcuate and extends approximately 100 km, from Asik 

Mountain to Misheguk Mountain (indicated by mows in Figure 2). The lineament 

parallels the eastern margin of the Noatak basin. The Noatak Basin is characterized 

by large-amplitude gravity and aeromagnetic anomalies, suggesting that the basin is 

underlain by ophiolitic rocks. The ophiolites of the Brooks Range form the 

structurally highest thrust-sheets, occurring above the sedimentary rocks. The low 

elevation of the ophiolitic rocks in the basin, as compared to the sedimentary rocks 

to the east of the topographic lineament, suggests that the lineament is the trace of a 

high-angle fault with down-on-the-west displacement. Folding in the sediments 

indicates that there may also have been a component of right-lateral displacement on 

the fault. These displacements coincide with the motions inferred for the smaller 

faults mapped within the Maiyumerak basalts (Figure 4). The Noatak Basin might, 

therefore, be a graben-structure bounded by high-angle faults along the east margin 

of the basin. Less definitive linear structures paralleling the western margin of the 

basin suggest that the basin might also be bounded by faults on the west. 

This previously unrecognized graben structure accounts for the spatial 

distribution of the ophiolites in the western Brooks Range. Figure 7 shows the 

distribution of both exposed and subsurface ophiolites in northern Alaska. It has 

been suggested that the entire Brooks Range was once covered by large ophiolite 

thrust sheets that were subsequently eroded, leaving exposures only at low 

elevations in the Angayucham Terrain and the western Brooks Range. The east-west 

trending line of isolated ophiolite exposures in the western Brooks Range are 

preserved along the axis of a major synclinorium. The large lobe of ophiolitic 

rocks extending south from the synclinorium are preserved in the graben structure 

that was identified on the TM images. The ophiolites have been dropped down with 

respect to the surrounding sedimentary rocks by normal faulting. The age of this 

faulting and its relationship to the tectonic evolution of the Brooks Range is not yet 

understood. 

The results discussed above will be presented in two invited papers at a 

symposium on the tectonic evolution of the Brooks Range. The symposium is a part 

of the Geological Society of America annual Cordilleran Section meeting. Copies 

of the abstracts are included. 
1 

6 

Geochronology of the western Brooks Range oDhiolites 

In order to better constrain events affecting-the ophiolites of the Brooks 

Range, we have dated samples collected during 1985 using the 4oAr/39Ar 

radiometric age-dating technique, The samples are from the Asik Mountain and 

Avan Hills exposures. We have dated both igneous samples, yielding the age of 

formation of the ophiolites, and metamorphic samples, yielding the age of thrusting 

of the ophiolites. The 40Ar/39Ar technique yields the age at which a mineral cooled 

below the temperature at which Ar is retained within the mineral. We have 

analyzed hornblende, biotite, and K-feldspar. Our results are summarized and 

compared to previously published K-Ar dates, in Figure 8. The 4oAr/39Ar 

technique has several advantages as compared to the K-Ar technique; ages can be 

determined more precisely and thermal events that affected the retention of Ar can 

be recognized. Our 4oAr/39Ar ages for the igneous formation of the ophiolite are 

similar to the previous K-Ar ages, but the metamorphic ages, indicating the time of 

thrusting, are approximately 10 million years older than the published ages. 

Thrusting of the o hiolites was the earliest deformational event in the Brooks 

began 10 million years earlier than was previously realized. The data also indicate 

that the ophiolites were thrust soon after their formation, consistent with the 

geochemical data discussed above, which suggest that the ophiolites formed in an arc 

or marginal basin setting. 

Range. The 40 Ar/ 38 Ar data, therefore, indicate that the Brooks Range deformation 

The 40 Ar/ 39 Ar data also provides information about the thermal evolution of 

the ophiolites. This information might help explain the metamorphic facies 

differences that have been recognized from the TM data in the basalts of the 

ophiolites. Because Ar is retained by different minerals at different temperatures 

(the "closure" temperature), a cooling history for the ophiolites can be constructed 

from the 4oAr/39Ar data (Figure 9). The closure temperatures of hornblende, 

bitotite, and K-feldspar are approximately 5OO0C, 35OoC, and 1 50°C, respectively. 

The ophiolites appear to have cooled rapidly soon after thrusting, probably by 

conduction, followed by a long period of slow cooling, probably during uplift of the 

Brooks Range. 

The 40 Ar/ 39 Ar ages are summarized in Figure 10 along with the ages of other 

events affecting northern Alaska. We are using this age data to constrain tectonic 

models for the evolution of the Brooks Range. It is generally thought that the 

Brooks Range formed by southward-directed subduction of a small continental 

block (Arctic Alaska) beneath oceanic lithosphere now preserved as the 

Yukon-Koyukuk Basin (Figure 1). It has been assumed by many workers that 
7 

subduction of the Arctic Alaska block, and construction of the Brooks Range, was 

synchronous with the opening of the ocean basin north of Alaska (the Canada 

Basin). Our 4oAr/39Ar data and other published age data indicate that subduction 

commenced well before opening of the Canada Basin. The data also suggest that 

much, if not all, of the thrusting in the Brooks Range was completed before the 

opening of the Canada Basin. This information requires that tectonic models for the 

evolution of northern Alaska be re-evaluated. Models for the formation and 

accumulation of hydrocarbons in the Colville Basin north of the Brooks Range, (eg. 

at the Prudhoe Bay oil field), must also be reconsidered. We recently received 

Thematic Mapper data for the Colville Basin, as part of the additional allotment of 

scenes provided by NASA. Drainage patterns in the basin appear to record a history 

of recent uplift. Uplift patterns in the basin, determined from the TM images, 

might provide further information on the tectonic evolution of northern Alaska. 
List of Figures 

1. Physiographic provinces of northern Alaska. 

2. Band 7 mosaic of TM scenes for path 80, row 12 and path 80, row 13. The image 

is 185 km across. The location of the image is shown in Figure 1. 

3. Reconnaissance geologic map of the central part of the Maiyumerak Mountains. 

The sheeted dike and flow units of the red-weathering basalt are indicated by the 

center and right-hand patterns. The black-weathering basalt is indicated by the 

left-hand pattern. 

4. Geologic map of the Maiyumerak Mountains, interpreted from TM images and 

constrained by field observations. 

5. Charts comparing the characteristics of the basalts in lower and upper thrust 

sheets in the Maiyumerak Mountains and Angayucham Terrain. 

6. Hf/3-Th-Ta ternary plot showing the compositional fields of modern mafic lavas 

and the compositions of basalts from the western Brooks Range ophiolites. 

7. Distribution of exposed and subsurface ophiolites (in black) in northern Alaska. 

8. 40Ar/39Ar ages for igneous and metamorphic samples from the western Brooks 

Range ophiolites, compared to previous K-Ar ages. 

9. Thermal evolution of the western Brooks Range ophiolites based on 4oAr/39Ar 

data. 

10. Summary of ages for selected events affecting northern Alaska in Jurassic and 

Cretaceous time. 

Abstracts 

Invited papers to be presented at the Geological Society of America Cordilleran 

Section meeting in May, 1987, as part of symposium on Brooks Range tectonics: 

1. Landsat TM studies, Brook Range, Alaska 

2. Basalt Geochemistry, Brooks Range, Alaska 

, 
MAIYUMERAK MOUNTAINS 

0 - 3 km 

N 

1 

Figure 3 
Q) 

rn 

P 

P 

P 

3 

* 

- 

z 

cr) 

E 

Y 

-0 

n 

c, 

D 

a 

cn 

a 

P 

a, 

m 

I 

3 

c 

L 

c, 

zcl 

ms 

.- a Cr 

c, 

S 

0 

0 

.. 

.. 

.. 

I. 

I. 

.. 

I. 

.. 

b. "; 

1 

1 
L , 1 

0.0 

57 

REDDISH BROWN 

~ 

NORMALIZED 

TM DlGlTlAL 

NUMBERS 0.0 

123457 

COLOR DARK GREY 

TECTONIC 

SElTlNG 

(Hf-Th-Ta) 

MAIYUMERAK MAFIC VOLCANIC ROCKS 

ARC OR MARGINAL BASIN ARC OR MARGINAL BASIN 

(THOLEIITIC?) (CALC-ALKALINE?) 

. LOWER BASALT I UPPER BASALT 

1.1 -I I 1.1 -4 - 

ACTINOLITE f EPIDOTE 

f CHLORITE f MAGNETITE 

CHLORITE f EPIDOTE 

f CLINOPYROXENE 

f MAGNETITE 

FE-BEARING 

MINERALS 

AGE I MIDDLE JURASSIC OR OLDER I MIDDLE JURASSIC OR OLDER 

ANGAYUCHAM MAFIC VOLCANIC ROCKS 

(Hltzman et al., 1982; Pallister, 1985) 

NORMALEEC 

TM DlGlTlAL 

NUMBERS 

COLOR 

FE-B EARING 

MINERALS 

fIIIIIII 

RARE EARTH 

ELEMENT 

PAlTERNS 

AGE 

TECTONIC 

SElTlNG 

(Hf-Th-Ta) 

LOWER BASALT 

+::: k; 

TM BAND 0.0 

123457 

BROWN TO BRICK RED 

CHLORITE f EPIDOTE 

f CLINOPYROXENE 

f MAGNETITE #II/lIINIl//IIIII//d 

TRIASSIC 

N-MORB AND E-MORB 

(OCEANIC PLATEAU?) 

UPPER BASALT 

a:::* 

TM BAND 0.0 

123457 

DULL REDDISH BROWN 

CHLORITE f EPIDOTE 

f ACTINOLITE f CLINOPYROXENE 

f MAGNETITE 

JURASSIC 

E-MORB 

(OCEAN ISLAND?) 

\ 

Figure 5 
Hf/3 

Maiyumerak A: N-Type MORB 

B: E-Type MORB and lower basalt X 

upper basalt tholeiitic within-plate 

c: Alkaline within-plate 

D: Destructive platemargin (arc) lavas 

Avan Hills 

(from Wood, 1980) 

calc-alkaline 

Th Ta 

Figure 6 
kern Brooks 

.- 

Alaska 

Range 

Figure 7 
40Ar/ 3gAr Ages 

I Igneous Metamorphic 

*O°F 

- 

hornblende A biotite k-feldspar 

.: .............................................. ......... ~...~ .......... K-Ar ages (previous studies) WMME$&<$d ......................... ., ........................... 

Figure 8 
0 0 

0 0 

(D d 

0 

0 

c\1 

0 
I I 

€ 

u. 

n 

x .- 

U 

a 

Y 

8 

c 

v) 

Y 

.... 

C 

0 

a a 

e 

n 

2 
LANDSAT TM STUDIES, BROOKS RANGE, ALASKA 

HARDING, David J.; WTRTH, Karl R.; BIRD, John M., 

Dept. of Geological Sci., Snee Hall, Cornel1 Univ., Ithaca, NY 14853 

Landsat Thematic Mapper (TM) data of the western Brooks Range are 

being used to map subtle lithologic variations, and large-scale structures, 

that are not readily recognized in the field. Basalt of the Maiyumerak 

Mountains is separable into two spectrally distinct units that are 

interpreted to be thrust sheets; basalt of the upper thrust sheet is 

characterized by high reflectance in TM bands 1, 2, 5 and 7 and low 

reflectance in band 3, as compared to basalt of the lower thrust sheet. The 

reflectance differences are produced by differences in the weathered 

surfaces of the basalts. The surface differences are dependent on the 

basalts' metamorphic mineralogy; both basalts have greenschist-facies 

mineral assemblages, but actinolite is common in the upper thrust sheet 

and rare in the lower sheet. The weathered surfaces on the 

actinolite-bearing, upper basalt contain smaller amounts of hydrous 

iron-oxides. The spectral and mineralogic variations correlate with 

geochemical differences. The geochemical differences indicate that the 

basalts might have formed in different tectonic settings (Wirth et al., this 

volume). 

The thrust sheets in the Maiyumerak Mountains are cut by several 

high-angle, northeast-trending faults. These faults parallel an arcuate 

topographic lineament, recognized on TM images, that bounds the Noatak 

Basin on the east and extends 100 km, from Asik Mountain to Misheguk 

Mountain. The lineament separates ophiolitic rocks on the west from 

alkmhonoas sedimentary rocks on the east. The lineament is interpreted 

to be the trace of a high-angle fault. Offsets of lithologic contacts, and 

folding in the sedimentary rocks, indicate that displacement on the 

inferred fault was down-on-the-west and/or right-lateral. The Noatak 

Basin is characterized by large amplitude gravity and aeromagnetic 

anomalies, suggesting that the basin is underlain by ophiolitic rocks 

(Barnes and Tailleur, 1970). Ophiolitic rocks in the western Brooks 

Range form the structurally highest thrust sheets, occurring above 

allocthonous sedimentary rocks. The low elevation of the ophiolitic rocks 

in the basin, as compared to the surrounding sedimentary rocks, has been 

attributed to a large synformal structure (I. Ellersieck, personal 

communication). Alternatively, the distribution of these ophiolitic rocks 

might be the result of down-on-the-west displacement on high-angle faults 

that bound the east side of the Noatak basin. 
'. . 

BASALT GEOCHEMISTRY, BROOKS RANGE, ALASKA 

WIRTH, Karl R.; HARDING, David J.; BIRD, John M., 

Dept. of Geological Sci., Snee Hall, Cornel1 Univ., Ithaca, NY 14853 

Basaltic flows and dikes at Asik Mountain, Avan Hills, and in the 

Maiyumerak Mountains, western Brooks Range, have diverse 

geochemical characteristics. 

Two basalts, in the western Maiyumerak Mountains, are interpreted to 

be from two different thrust sheets juxtaposed by north-south, high-angle 

faulting (Harding et al., this volume). East of the fault (lower thrust 

sheet), pillowed and massive basalt flows are cross-cut by 

north-south-trending, near vertical and subparallel mafic dikes. The 

flows and dikes have clinopyroxene and plagioclase, with variable 

amounts of secondary chlorite, epidote and calcite. Most basalts east of 

the fault plot in the tholeiite field of some trace element diagrams and have 

flat, or slightly depleted, light rare-earth element (LREE) patterns. West 

of the fault (upper thrust sheet), the basalts are more metamorphosed, 

and are mostly chlorite, actinolite, epidote and calcite. Mafic dikes here 

are less common, and are curved and have variable orientations, in 

contrast to those east of the fault. Basalts from west of the fault plot in the 

calc-alkaline field of some trace element diagrams, and typically have flat 

to LREE-enriched patterns. Both basalts are depleted in Ta relative to Th, 

and have trace element abundances similar to island-arc basalt on trace 

element diagrams, indicating the presence of a subduction- related 

geochemical component (Pearce et al., 1984). 

Mafic flows at Asik Mountain and Avan Hills are structurally overlain 

by Iayered and crystalline mafic and ultramafic rocks and are more 

metamorphosed and deformed than those in the Maiyumerak Mountains. 

Asik Mountain basalts have flat REE patterns, while Avan Hills basalts 

have LREE-enriched patterns. Trace element abundances in the Asik and 

Avan basalts are similar to normal MORB, and enriched MORB or 

tholeiitic within-plate basalt, respectively.