The Kings-Kaweah ophiolite melange in east-central California is thought to be an obducted oceanic fracture zone and provides the rare opportunity to examine in detail the complex nature of this type of terrain. It is anticipated that the distribution and abundance of components in the melange can be used to determine the relative importance of geologic processes responsible for the formation of fracture zone crust. Laboratory reflectance spectra of field samples indicate that the melange components have distinct, diagnostic absorptions at visible to near-infrared wavelengths. The spatial and spectral resolution of AVIRIS is ideally suited for addressing important scientific questions concerning the Kings-Kaweah ophiolite melange and fracture zones in general

Mustard, John F.

Pieters, Carle M.

English

NASA Technical Reports Server

N89-22166 
APPLICATION OF IMAGING SPECTROMETER DATA TO THE KINGS-KAWEAH 
OPIIIOLITE MELANGE 
JOHN F. MUSTARD and CARLE M.  PIETERS, Department of Geological Sciences, Box 
1846, Brown University, Providence, RI 02912 
Abstract 
'The Kings-Kaweah ophiolite melange in east-central California is thought to be an ob- 
ducted oceanic fracture zone and provides the rare opportunity to examine in detail thc com- 
plex nature of this type of terrain. It is anticipated that the distribution and abundance of 
components in the melange can be used to determine the relative importance of geologic 
processes responsible for the formation of fracture zone crust. Laboratory reflectance spectra 
of field samples indicate that the melange components have distinct, diagnostic absorptions at 
visible to near-infrared wavelengths. The spatial and spectral resolution of AVIRIS is ideally 
suited for addressing important scientific questions concerning the Kings-Kaweah ophiolite 
melange and fracture zones in general. 
Introduction 
The development of imaging spectrometers as accurate and reliable tools for the examina- 
tion of geologic terrain (Goetz et al, 1986) has opened up a whole new range of scientific 
problems that can be addressed. The application of imaging spectrometer data is advanced 
even further by the development of powerful analytical tools which can reduce the enormous 
volume of data obtained by such instruments to basic information about the wrface (i.e 
Kruse, 1988; Mustard and Pieters, 1987; Adams et al, 1986). However, not all  geologic 
problems are amenable to this type of analysis and careful merging of scientific goals, the 
specific geology and nature of the terrain, and capabilitites of the instrument are necessary in  
order to exploit the unique perspectives provided by imaging spectrometer data. 
The Kings-Kaweah ophiolite melange poses scientific questions which are best addressed 
with imaging spectrometer data. The overall composition and nature of deformation in this 
ophiolitic terrain led Saleeby (1978, 1979) to conclude that i t  is an obducted oceanic fracture 
zone. There are few well documented fracture zone assemblages exposed sub-aerially and the 
Kings-Kaweah ophiolite melange is particularly interesting because of the range of fracture 
zone processes exposed. It provides a rare opportunity to examine the net result or the deror- 
malion of oceanic crust to form fracture zone crust. Fundamental questions remain regarding 
the development of the melange matrix and the relative importance of various processes 
thought to be active in fracture zones. We propose to map the distribution and abundance of 
important mineral components in the matrix of the melange with imaging spectrometer data 
and relate regional geochemical variations to the tectonic development of fracture /one crust. 
Background 
Fracture zones, which are common and well recognized features in oceanic crust, are 
typically hundreds to thousands of kilometers long and 5-50 kilometers in width. 'I'hc crust 
within the boundaries of a fracture zone is commonly refered to as fracture zone crust. In 
regions where oceanic crust is being formed at a rapid rate (i.e the East Pacific Rise) fracture 
zone crust comprises about 10-15% of the ocean floor while in areas of extremely slow 
spreading (i.e. Southwest Indian Ridge) fracture zone crust may reach 50% of the ocean floor 
(Abott, 1987). Although some basic characteristics of fracture zone crust have been deduced 
from geophysical investigations and examination of material dredged from fracture zones (Fox 
and Gallo, 1984; Forsythe and Wilson, 1984) the exact nature of the processes responsible For 
its forination as well as the details of the interactions between active processes in fracture 
zones are still not well understood, 
122 
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n i 
'Rtogenonlranslorm %age transform 
ccmer' (RN corner) corner' (RT coroer) 
-Fraclure Zone' 
/ / / / / / / # / / # / # / / # /  / / / / I  / 
\ 
'Aseismr ExIemon' 'Aseismc Exlensdon' Tranrlorm Fault' (TFJ - -Spreading Center' 
A A' 
Sealloor 
LU 
A' 
-1 
u B' 
'Axs 01 spreaaog' 
= 'RlCge creSr 
Sealioor 
Lithosphorr Lithosphere 
Figure 1. General terminology and spatial relationships of components as- 
sociated with fracture zones (from Kastens, 1987).  
f 
In general a fracture zone consists of two primary segments (Fig. 1 ) ;  the transform 
domain which occurs in the region between offset spreading centers and the non-transform or 
aseismic extension which can extend for many hundreds of kilometers beyond the ridge-trans- 
form intersections. Deformation processes within these domains are variable, complex, and 
polyphase. The  active processes can be summarized as consisting of strike-slip and dip-slip 
faulting, hydrothermal alteration and metamorphism, ridge crest magmatism, diapiric intru- 
sion of serpentinized ultramafics, and sedimentation. These processes are active with variahle 
intensity throughout both segments of a fracture zone, but generally have localized 7ones of 
maximum intensity (i .e.  the principal region of strike-slip deformation occurs in the trans- 
form domain while ridge crest magmatism is localized at the ridge-transform intersection 
(Karson and Dewey, 1978) .  The principal driving forces are spreading at the ridge crests and 
the offset thermal decay histories of the oceanic segments on either side of the fracture zone. 
Serpentinization and protrusion of ultramafic mantle material is thought to he a corninon, 
and perhaps dominant process in fracture zones (MacDonald and Fyfe, 1985). The serpen- 
tinization of mantle rocks is facilitated by the highly fractured crust in fracture Tones, 
availability of abundant water, and the discontinuity of thermal profiles across the fracture 
zone which can drive vigorous hydrothermal cells. Under these conditions serpentinite hodies 
are very mobile. Diapiric emplacement of serpentine is facilitated by the density contrast he- 
tween the serpentine bodies and the surrounding country rock as well as the weak shear 
strength of serpentine. A consequence of these processes is that abundant fine-grained 
sheared serpentined is created which is then available to form the matrix. Tn addition, verti- 
cal mixing of ophiolitic components is enhanced by diapiric activity (Saleeby, 1984). 
The  net result of these processes is that the standard three layer straiigraphy of oceanic 
crust is disrupted and blocks and fragments of typical ophiolite crust are distributed i n  a fine- 
grained mobile matrix creating fracture zone crust. Although the matrix is predoniinantly ser- 
123 
pentine, contributions from the mafic components and the effects of the mechanical a n d  
geochemical processes operating in fracture zones can alter the overal bulk chemistry. ‘l’here- 
fore, the distribution and abundance of mineral components within the melange matrix con- 
tains important information for understanding these complex geologic zones. Most of the pre- 
vious work on sub-aerially exposed fracture zones have focused on the structural relationqhips 
between components and chemical analysis of the protoliths (Saleeby, 1977; Karson a n d  
Dewey, 1978).  Analysis of regional geochemical variations in the matrix has not been 
pursued becaused of the diffuculty in obtaining unbiased samples for analysis (due to [he ex- 
treme, small-scale heterogeneity of the matrix components). However a tool such as AVlRlS  
is ideally suited for examining the nature of regional geochemical variations in this type of  ter- 
rain. The  pixel size (20 m) averages the small scale heterogeneity and allows large scale 
processes to be recognized. Also, characteristic minerals in the melange have diagnostic fea- 
tures throughout the AVIRIS wavelength range. 
General Geology and Spectroscopic Character 
The Kings-Kaweah ophiolite melange is located in the eastern foothills of the Sierra 
Nevada near Fresno, California (Fig. 1 ) .  In constrast to the classical interpretation that 
ophiolite-melange associations are indicative of a convergent margin emplacement ( i .  e .  
Coleman, 1971), the primary tectonic mixing and melange development for the Kings- 
Figure 2 .  Location map for the Kings-Kaweah ophiolite melange showing the 
distribution of tectonic slabs and blocks. Also shown is the melange unit map 
of the Kaweah serpentinite melange (from Saleeby, 1979).  
124 
Kaweah ophiolite melange occured on the ocean floor in a fracture zone environment 
(Saleeby, 1977). This interpretation is based on the observations that no continental or arc 
rocks and sediments are found in the melange, no  minerals typical of subduction eniplace- 
ment are found, continental margin rocks are deposited unconformably over the melange, and 
the range and nature of the polyphase deformation is most consistent with. an oceanic fracture 
zone. The  Kings-Kaweah ophiolite belt was emplaced against the truncated margin of North 
America in Triassic to Middle Jurassic time and was contact metamorphosed to the 
hornbiende-hornieis facies during the iiitrusiori of the Sierra Nevada piutoiis beiween 12 5 aiid 
102 my ago (Saleeby, 1977).  
The  Kings-Kaweah ophiolite melange is composed of two primary segments (Fig. 1 ) :  the 
Kings River ophiolite in the northern part of the belt and the Kaweah serpentinite melange in 
the southern part of the belt. The  Kings River ophiolite contains large slabs of hasalt, 
peridotite, and gabbro seperated by thin zones of serpentine melange. In contrast the Kaweah 
serpentinite melange contains no  tectonic slabs and the serpentine matrix is very well 
developed (Saleeby, 1978; 1979). We have chosen to focus on the Kaweah serpentinite 
melange because the fracture zone assemblage is more highly developed and therefore the 
cilmplex interactions between the processes responsible for :he overall charactcr of fracture 
zone crust should be better represented. 
The  Kaweah serpentinite melange consists of coherent to semi-coherent blocks dis- 
tributed in a pervasively deformed matrix. The blocks range in size from millimeter sized par- 
ticles to fragments tens to hundreds of meters in length. The  blocks consist of harzhurgite, 
peridotite, serpentinized ultramafics, gabbro, basalt, silica-carbonate rocks, and chert. 'I'hey 
commonly show a tectonic fabric which parallels the schistosity of the matrix and the general 
southeast-northwest trend of the belt (Saleeby, 1979).  Bidirectional reflectance spectra of a 
few representative handsamples collected from the field are shown in Fig. 3a. All spectra 
were measured from naturally weathered surfaces. Fez' and Fe3' absorptions dominate in the 
visible and near-infrared portions of the spectra while overtones and combination overtones 
of fundamental OH- absorptions are primarily responsible for the narrow features i n  the in- 
frared portions of the spectra. 
The  matrix primarily consists of schistose serpentine, ophicalcite, and silica-carbonate 
rocks, although talc and tremolite are locally abundant. Variations in matrix composition 
reflect shifts in the bulk chemistry (i .e.  the presence of talc over serpentine represents a 
siliceous shift in the bulk chemistry) (Saleeby, 1979).  This variation is of fundamental itn- 
portance for addressing questions relaled to the character and developement of fracture zone 
crust. Some examples of reflectance spectra from exposed matrix surfaces are shown i n  Fig. 
3b. Like Ihe spectra shown for the block lithologies, the visible to near-infrared portion or the 
spectra are dominated by Fez' and Fe3' absorptions while the infrared portions of the speclra 
are dominated by absorptions related to OH-. 
I t  will be nccewry  lo 
remove the spectral signatures of the grasses using an appropriate mixing model (Mllslard and  
Pieters, 1987; Adams et al, 1986) while the soils may provide clues as to the nalure of 
geochemical variation within the subsurface. We have collected an extensive series or grass 
and soil samples and some examples of reflectance spectra from these are shown i n  Fig. 3c. 
Field spectra of rocks, soils, and grasses have also been acquired with PIDAS ( G o c ' l ~ ,  1987) 
to characterize the actual ground reflectance of these surface types as well as potential calihra- 
tion targets. A PIDAS spectrum of typical grass cover is shown in Fig 3d. This typc of  d a t a  is 
an essenlial link between laboratory and remotely acquired reflectance data. 
Much of the field area has a variable cover of soils and grass. 
125 
Figure 3. RELAB reflectance spectra of some components in the Kaweah serpentinite melangc. A )  
Some typical block lithology spectra where (a) is a serpentinized peridotite, (b) is a gabbro, and ( c )  i s  
a pillow basalt. R )  Examples of matrix lithology spectra where (a) is predominantly talc bearing, (11) 
has both talc and tremolite, (c) is from a serpentine rich region, and (d) is an ophicalcite. C )  Ex- 
amples of grass and soil spectra where (a) is dry, brown grass, (b) is partially decayed grass, ( c )  i s  a 
talc rich soil, and (d) is a soil containing Fe-oxide. D) Field spectrum of a grassy area.  The spectra of 
the components grass, decayed grass, soil, and shade are all contribute to this average spectrum 
126 
Imaging Spectrometer Analysis 
Imaging spectrometer data were acquired over the field site on  September 14,  1987 with  
AVIRIS. Although the principal science target was not covered by the AVIRIS overflight, 
some secondary targets were imaged as well as a calibration target. Examination of these data 
indicate that the spatial resolution of the instrument is very good for addressing the scientific 
goals outlined above. However, the complexity of the field site and nature of the extraneous 
ground cover (grasses) requires that the instrument p e r f o r m  at optimum p r e c i s i o n  a n d  ac- 
curacy. Due to the low signal to noise during this flight, and other problems outlined hy 
others in this volume, i t  is not possible to address our scientific goals with these data. 
daniental scientific questions concerning the formation and development of oceanic fracture 
zones and the general behavior of oceanic crust during intense disruption. An imaging 
spectrometer such as AVIRIS permitts the mapping of the distribution and abundance of diag- 
nostic minerals in the highly deformed and complex matrix, and this information, which is 
not readily obtained by other methods and techniques, allows one to begin to unravel the 
complexity of such terrain. We look forward to analyzing high quality AVIRIS data over !he 
principal science target in the near future. 
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Application of imaging spectrometer data to the Kings-Kaweah ophiolite melange

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