Differentiation of Neotethyan ophiolitic mélange and an approach revealing its surficial chromite deposits using ASTER image and

spectral measurements (Sivas/TURKEY)

Kaan Şevki Kavak*a, Yavuz Töreb, Haluk Temiza, Osman Parlakc, Hande Çığlab, Mustafa Yakanb

a Cumhuriyet University, Dept. of Geology, 58140 Sivas/TURKEY b Cumhuriyet University, Inst. of Applied and Natural Sciences, 58140 Sivas/TURKEY

c Cukurova University, Dept. Of Geology, 01330 Balcalı, Adana/TURKEY

ABSTRACT

This work is aimed at differentiation of ophiolitic mélange rocks which were outcropped 60 km far from Sivas city

center using image processing and spectral measurement methods. These rocks are known as oceanic crust remnants

which were made up of different rocks. Turkey hosts several paleo-oceans and their realms in Alpine-Himalayan

orogenic belt. The Neotethyan ophiolites in Turkey are characterized by supra subduction zone (SSZ-type) ophiolites.

Ophiolitic rocks are generally coloured with greenish tones and human eye could not separate these tone differences. But

satellite images such as ASTER can realize these separation utilizing spectral enhancement methods such as

classification and decorrelation stretching. Chromite is a valuable mineral and is formed in only ophiolitic rocks. Dunites

and harzburgites named as also ultramafic tectonits of ophiolitic serie mainly contain these deposits in study area. In this

study, an approach was also realized to find target regions of chromite deposits with the aid of spectral methods. Spectral

measurements were realized to determine boundaries between different mélange rocks using spectroradiometer.

Reflectance curves collected from field and laboratory analysis were evaluated together and compared with ASTER

image of the study area respectively. A detailed differentiation generally was accompanied with petrographic and

geochemical analyses.

Keywords: ASTER, differentiation, chromite, enhancement, ophiolitic mélange, remote sensing, spectra,

spectroradiometer.

*kaank@cumhuriyet.edu.tr; phone +90 346 2191010-1303; fax 90 346 2191171

1. INTRODUCTION

This work is aimed at differentiation of Upper Cretaceous Divriği ophiolitic mélange rocks. Study area is located on the

margin between Kırşehir Massif and Anatolide-Tauride Block (Okay and Tüysüz, 1999, Figure 1) and approximately 70

km away from Sivas city center (Figure 2). In this study, an approach was realized to find target regions of valuable

chromite deposits in ophiolitic mélange rocks with the aid of ASTER image of the region. Both in the study area and

laboratory, spectral measurements were also realized to determine boundaries between different mélange rocks using

Earth Resources and Environmental Remote Sensing/GIS Applications, edited by Ulrich Michel, Daniel L. Civco,Proc. of SPIE Vol. 7831, 78310D · © 2010 SPIE · CCC code: 0277-786X/10/$18 · doi: 10.1117/12.864549

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spectroradiometer. Spectral reflectance curves collected from field and laboratory analysis were evaluated together and

compared with ASTER image of the study area respectively.

Figure 1. Tectonic map of northeastern Mediterranean region showing the major sutures and continental blocks (Okay and Tüysüz,

1999).

Figure 2 : Study area

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2. MATERIAL AND METHOD

As is well known, the ASTER system consists of three different subsystems, namely the visible near infrared (VNIR),

short-wave infrared (SWIR) and thermal infrared (TIR). VNIR subsystems (0.52–0.86 mm) have four band wavelengths

with a spatial resolution of 15m. SWIR bands have 30m spatial resolution and consist of five spectral bands. Their

wavelengths cover 2.145– 2.430 mm. TIR data coverage of the ASTER multispectral system mainly comprises six

different bands (8.125–11.65 mm) and has a 90m resolution. ASTER data provides information complementary to

lithological mapping (Rowan and Mars, 2003). SWIR band wavelengths provide valuable lithological information for

Al-O-H in clays, micas and sulphate minerals, CO3 in carbonates, Mg-O-H in amphiboles, and H-O-H in evaporites and

clays. Er Mapper professional software has been used extensively in image processing efforts. On the other hand,

spectral measurements were also realized to determine absorbtion features of the different ophiolitic rocks using

spectroradiometers. This FieldSpec ® FR spectroradiometer has 350-2500 nm spectral range. These elecromagnetic

wawelength values allow the chance of separation between rock units which were outcropped in the region.

3. GEOLOGICAL FRAMEWORK

Study area is located on the southeastern margin of the Sivas Basin and is also very important understanding

paleotectonic evolution of the region (Figure 1). It is possible to summarize stratigraphic features of the region from

bottom to top: The basement of the studya area is composed of Upper Triassic-Lower Cretaceous crystallized Yilanlidag

limestones. Upper Cretaceous Divrigi ophiolitic mélange and Upper Cretaceous-Paleocene reefal Tecer limestones

which were contained chromite deposits overlain tectonically these basement rocks. Eocene Bozbel formation

sedimentary rocks transgressively cover all rocks at the bottom levels. These rocks are also overlained by continental-

shallow marine Oligocene gypsum rocks. Lower Miocene Deliktas formations are represented with red conglomerates

and gray sandstones and shales. Upper Miocene-Lower Pliocene Soğukpınar, Plio-Quaternary Parmaklıtepe formations

and Quaternary rocks were composed youngest rocks of the region.

3.1. Ophiolitic mélange rocks

Ophiolitic suite shows an association with serpantinite, gabro, volcanic rocks and chert (Figure 3). These rocks are also

known oceanic crust materials. These kinds of rocks have magmatic origin. Firstly, they were described in Western Alps

and Appenines. Oceanic crust is represented by opiholitic sequence and these rocks are produced on the divergent plate

margins. Chromite deposits are abundantly found also in these rock units.

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Figure 3: Oceanic crust ant its components

Chromite is a natural component of the earth crust and used also in metallurgy, chemical and refractory industries as

among the basic elements. Stainless steel, chromium, is also known as the main material. Besides this, chromium

chemicals, due to anti-rust properties are widely used in industry, aircraft and ships. Chrome mining in Turkey, starting

from today is developed as export-oriented.

4. IMAGE PROCESSING PROCEDURES ASTER image of the region shows that NE-SW oriented ophiolitic rocks including surficial chromite bodies represented

with dark colour tones in the study area (Figure 4). Vegetation lack in the region allows researchers to evaluate

diffrerentiation between outcropping rock units with utilized visual and image processing efforts.

Figure 4: ASTER 631 (RGB) band combination image of the study area

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To be able to analyze spectral responses of surface cover types using SWIR ASTER data it is necessary to apply log

residual algorithm, which reduces noises from topography, instrument and sun illumination (Rowan and Mars, 2003).

The resultant data is assumed to be more representatives of the soils or lithologies of the exposed areas (Figure 5)

Figure 5: Log residual application using ASTER 4.5 and 8 to red, green and blue bands respectively. In this image, dunit, pyroxenite, limestone, gabro and chromites were differentiated.

On the other hand, minimum noise fraction (MNF) method used routinely for hyperspectral images has provided better discrimination between rock units

Figure 6: Minimum Noise Fraction method og ASTER SWIR bands

5. SPECTRAL MEASUREMENTS As is well known, absorbtion values of earth materials have distinctive features. Spectral curves determine these distinctive points in

reflectance-wavelength graphics. Ophiolitic rocks and chromite have approximately 1.4 and 1,75 micrometers in electromagnetic

spectrum. Chromite spectral curve measured from field sample is shown in Figure 7 graphically.

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Figure 7: Chromite spectra measured from outcropped field samples.

6. CONCLUSION

Spectral enhancement methods increase visual human capacity particularly in scarcely vegetation cover regions. Multispectral ASTER

images provide better discrimination according to geologic mapping efforts in field. These interdisciplinary works completes classical

field efforts. Furthermore, spectra measurements gathered from field using spectroradiometer give also satisfactory results for surface

and subsurface exploration studies. This work proves economically the needs of interdisciplinary performance in earth sciences.

REFERENCES

1. Green, A.A and Craig, M.D., "Analysis of aircraft spectrometer data with logarithmic residuals." JPL Publ. 85-41, 111-119, (1985) 2. Okay, A.İ. and Tüysüz, O., “Tethyan Sutures of northern Turkey. In: Durand, B., Jolivet, L., Hovarth, F., and Séranne, M. (Eds), The Mediterranean Basins: Tertiary Extension within the Alpine Orogen”. Geological Soc. London Spec. Publ., 156, 475-515, (1999) 3. Rowan, L.C., and Mars, J.C., “Lithologic mapping in the Mountain Pass, California area using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data” Remote Sensing of Environment, 84, 3, 350-366 (2003)

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