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Precambrian basement rocks of Wadi-Khuda-Shut area, South Eastern Desert of Egypt: Geology and remote sensing analysis
The Egyptian Journal of Remote Sensing and Space Sciences xxx (xxxx) xxx
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Precambrian basement rocks of Wadi-Khuda-Shut area, South Eastern Desert of Egypt: Geology and remote sensing analysis Mahmoud M. Shokry a,⇑, Mohamed F. Sadek b, Aly F. Osman c, Baher A. El Kalioubi c a
Egyptian Mineral Resources Authority (EMRA), Cairo, Egypt National Authority for Remote Sensing and Space Sciences (NARSS), Cairo, Egypt c Faculty of Science, Geology Department, Ain Shams University, Cairo, Egypt b
a r t i c l e
i n f o
Article history: Received 8 August 2019 Revised 1 December 2019 Accepted 22 December 2019 Available online xxxx Keywords: Precambrian Khuda-Shut Egypt Basement rocks Landsat-8 ASTER
a b s t r a c t Wadi Khuda-Wadi Shut area in the South Eastern Desert (SED) of Egypt is mainly made up of gneisses, ophiolitic serpentinites and intermediate schistose metavolcanics. These metamorphic rock units are intruded by syn-late-tectonic diorite, granodiorite, ultramafic-mafic, and monzogranite intrusions. The gneisses comprise biotite hornblende gneiss, hornblende gneiss and migmatites. They are of granodiorite and diorite composition. The ophiolitic serpentinite with talc carbonate rocks were thrusted over the metavolcanics with NW-SE thrust contact. The late tectonic ultramafic-mafic rock units are represented in the study area by Dahanib pluton, which is consisted of layered peridotite-dunite associated with olivine gabrro, normal gabbro and gabbro-norite as well as rare hornblende gabbro. These varieties are related to the layered intrusions rather than Alaskan-types, and formed by magmatic differentiation. The granodiorite and monzogranite represent the youngest basement rock units in the study area. The principal components and band ratios of ASTER and Landsat-8 data were successfully used for the first time in lithological discrimination and geological mapping of the study area. This study concluded that, the interpreted data of ASTER and Landsat-8 combined with field study and petrographic investigation clearly discriminated the exposed rock units. Accordingly, a detailed geological map emphasizing the lithological units in Khuda-Shut area has been presented. Ó 2019 National Authority for Remote Sensing and Space Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-ncnd/4.0/).
1. Introduction The Arabian-Nubian Shield (ANS) as a part of the Pan-African orogenic belt was initiated as an intra-oceanic island arc that underwent obduction-accretion processes through the Neoproterozoic (e.g. Stern et al., 1991). The late Neoproterozoic basement rock units in the South Eastern Desert of Egypt is dominated by gneiss domes, ophiolitic-related assemblages, island-arc metavolcanics and their derivative volcaniclastics. These rock units were episodically intruded by suites of syn-late to post-tectonic ultrabasic-basic and granitoid intrusions and intruded by post tectonic dykes and intraplate granites. The remote sensing data are very effective in geological mapping and detecting the mineralized alteration zones (Sadek, 2005, Sadek et al., 2008; Gad and Kusky, 2007; Yazdi et al., Peer review under responsibility of National Authority for Remote Sensing and Space Sciences. ⇑ Corresponding author. E-mail address: [email protected] (M.M. Shokry).
2011; Hassan et al., 2014; Hassan and Ramadan, 2015; Gabr et al., 2015; Sadek et al., 2015; Ali-Bik et al., 2017, 2018; Hassan and Sadek, 2017; Asran and Hassan, 2019). Wadi Khuda-Wadi Shut area lies in the southern sector of the Eastern Desert along the Red Sea coast. It covers an area of about 800 km2 between Latitudes 23° 330 –23° 500 N and longitudes 35° 050 –35° 260 E (Fig. 1). The area is mainly built up of Precambrian metamorphic and intrusive assemblages. Economically, the exposed monzogranites and gneissic granodiorite show blocky appearance, and suitable to be quarried to use as ornamental and decoration rock slabs. The Wadi Khuda-Wadi Shut area was subjected to few studies focused on the geology and tectonic setting of Wadi Khuda gneisses. None of the previous studies used the remote sensing data to discriminate the lithological units for detailed geological mapping of the area, except Asran and Hassan (2019), regarding the small outcrop of leucogranite along Wadi Khuda. The main objective of this study is to discriminate the lithological units and detailed geological mapping of the basement rocks at Wadi Khuda-Wadi Shut area based on the integrated data of previous
https://doi.org/10.1016/j.ejrs.2019.12.005 1110-9823/Ó 2019 National Authority for Remote Sensing and Space Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: M. M. Shokry, M. F. Sadek, A. F. Osman et al., , The Egyptian Journal of Remote Sensing and Space Sciences, https://doi.org/ 10.1016/j.ejrs.2019.12.005
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Fig. 1. Location and detailed geological map of Wadi Khuda-Wadi Shut area modified after Baranis Quadrangle Geological Map published by EGSMA (1992).
geological mapping, field study, petrographic investigation and the analyzed data of Landsat-8 and ASTER.
analyzed. Both band ratio and principal component image processing techniques using Erdas-Imagine 2015, ENVI V.5.3 and ARCGIS 10.5 Software have been applied on ASTER and landsat-8 spectral bands to discriminate the lithological units.
2. Data and methods 2.2. Field study 2.1. Remote sensing The processed remote sensing data of satellite images have been used in this study to enhance the discrimination of the lithological units. Landsat-8 scene (Path 173/Row 43) and ASTER Level 1B data, acquired on October 2016 and July 2003 respectively were
Field study has been carried out to verify the interpreted data of satellite images and to check the geological setting and to classify the exposed rock units in the study area. Rock samples representing these rock units have been collected for the petrographic investigation.
Please cite this article as: M. M. Shokry, M. F. Sadek, A. F. Osman et al., , The Egyptian Journal of Remote Sensing and Space Sciences, https://doi.org/ 10.1016/j.ejrs.2019.12.005
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3. Geological setting and petrography The Wad Khuda-Wadi Shut area consists mainly of gneissesmigmatites, ophiolitic serpentinite with talc carbonate rocks and schistose metavolcanics. These rock varieties are intruded by syn to late tectonic diorite, granodiorite, ultramafic-mafic and monzogranite intrusions and dissected by post orogenic veins, dykes and quartz plug (Fig. 1). 3.1. Gneisses and migmatites These rocks were described in some localities in the SED of Egypt, e.g. Wadi Hafafit (Greiling et al., 1994; Fowler and El Kalioubi, 2002); Wadi Bitan (Abdel Khalek et al., 1999). Gneisses
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with the associated migmatites are the oldest rock units encountered in Wadi Khuda area, they are related to Bitan and Khuda gneisses group (Egyptian Geological Survey and Mining Authority, EGSMA, 1992) and para-gneisses of sedimentary origin, intercalated with amphibolite lenses of igneous origin (Asran et al., 2000; Asran and Hassan, 2019). These gneisses are exposed as strongly foliated, banded, migmatized and folded outcrops, they are intruded by diorite, granodiorite and Umm Itly monzogranite. These gneisses comprise three varieties; biotite hornblende gneiss, hornblende gneiss and migmatites, they are characterized by alternation of dark biotite and hornblende rich melanosome bands with bright feldspars and quartz rich leucosome bands (Fig. 2a). The average thickness of melanosome bands is up to 100 cm thick while the leucosome
Fig. 2. (a) Alternating of dark biotite and hornblende rich melanosome bands with bright feldspars and quartz rich leucosome bands in Wadi Khuda gneisses. (b) Folding in gneisses, Wadi Khuda. (c) Photomicrograph showing hornblende rich bands (Hb) alternating with felsic bands rich with quartz (Q) and plagioclase (Pl) showing gneissic texture, C.N., X = 63. (d) Serpentinite rocks (Sp) overthrusting the schistose metavolcanics (Mv), southwestern sector of the mapped area. (e) Photomicrograph showing mesh texture in serpentinite rock, C.N, X = 63. (f) Schistosity in schistose metavolcanics, the western sector of the mapped area.
Please cite this article as: M. M. Shokry, M. F. Sadek, A. F. Osman et al., , The Egyptian Journal of Remote Sensing and Space Sciences, https://doi.org/ 10.1016/j.ejrs.2019.12.005
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Fig. 3. (a) and (b): Granodiorite (Gd) intruding gneisses (Gn) and diorite (Dr), Wadi Khuda. (c) Gneissose texture of Plagioclase (Pl), hornblende (Hb) and quartz (Qz) in granodiorite, Gabal Hindiyah, C.N., X = 63. (d) Gabal Dahanib ultramafic-mafic intrusion (Um + Mf) intruding the surrounding diorite (Dr), Wadi Shut. (e) Olivine (Ol), labradorite (Pl) and pyroxene (Px) crystals in olivine gabbro, Gabal Dahanib. (f) Myrmekitic intergrowth texture in monzogranite, Gabal Umm Itly, C.N., X = 63.
bands range from 0.5 to about 30 cm. Wadi Khuda biotite hornblende gneisses are medium-grained and granodiorie-diorite in composition, in places they are intercalated with hornblende-rich gneissic bands which are conformable with the general NW-SE foliation trend with average dip angle 45° towards NE. At the northern flank of Wadi Khuda, the gneissic rocks are thrown into doubly plunging anticlinal and synclinal folds with common ptygmatic folds (Fig. 2b). Microscopically, biotite hornblende gneisses consist essentially of alternating mafic and felsic bands. Biotite, hornblende, and mus-
covite with rare felsic minerals are the main constituents of the mafic bands, while the felsic bands is are composed essentially of sodic plagioclase and quartz with rare biotite and hornblende. Sericite, epidote and chlorite are present as secondary minerals. The mafic and felsic bands show sub-parallel orientation giving the characteristic gneissic texture (Fig. 2c). The hornblende gneisses consist essentially of hornblende, plagioclase, quartz and little biotite. Epidote, and iron oxides are accessories. The intercalated migmatites are mainly composed of coarser granied melanosome and leucosome bands. Biotite and
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Fig. 4. Reflectance spectra of the rock types using Landsat-8 data.
hornblende with few feldspars and quartz are the main constituents of melanosomes while leucosomes consist mainly of feldspars and quartz with little biotite and hornblende.
3.2. Ophiolitic serpentinite-talc carbonates rocks The highly sheared serpentinite-talc carbonate rocks are cropping out at the extreme southwestern sector of the mapped area representing the eastern extension of the ophiolitic serpentinite mass forming Gabal Abu Dahr (Gahlan et al., 2015). These serpentinite rocks represent a part of the tectonic ophiolitic mélange, which consists of tectonic lenses of serpentinite, talc carbonate rocks, highly deformed schistose metavolcanics and talc magnesite tremolite actinolite schist. The serpentinite-talc carbonate associations are thrusted onto the surrounding schistose metavolcanics with NW-SE thrust contact and low thrust angle of about 35° SW (Fig. 2d). These serpentinite rocks are intruded by gabbroic rocks and dissected by magnesite and quartz veins. Petrographically, serpentinite rocks are very fine to mediumgrained, and consist entirely of antigorite, chrysotile and magnetite with common mesh texture which is marked by replacing the relics of olivine crystals along Y-cracks by serpentine minerals and magnetite (Fig. 2e). Talc carbonate rocks consist mainly of fibrous talc replaced by magnesite and iron oxides.
3.3. Schistose metavolcanics These metavolcanic rocks are cropping out at the western sector of the mapped area forming strongly schistose and deformed belt. They show NW-SE schistose fabric with low dip angle of 35° SW (Fig. 2f). These metavolcanic rocks were overthrusted by the ophiolitic serpentinite-talc carbonate slices and sheets, and intruded by syn tectonic granodiorite and diorite bodies. Microscopically, metavolcanic rocks are fine-grained, aphanitic and mostly andesitic in composition. They consist of chlorite, actinolite, tremolite, altered plagioclase, epidote and quartz. They show distinct schistose texture marked by the parallel orientation of epidotized plagioclase, quartz and the mafic minerals.
3.4. Syn – tectonic diorites These rocks are widely outcropping in the area forming Gabal Umm Akra at the southern flank of Wadi Khuda, Gabal Shinshif, the northern sector of Gabal Umm Qubur and along Wadi Abu Hoqban in the northwestern part of the mapped area (Fig. 1). These dioritic rocks intrude gneisses (Fig. 3a) while they are intruded by granodiorite of Gabal Hindiyah (Fig. 3b). They enclose abundance of gneiss xenoliths up to 10 cm in lengths. Microscopically, diorites consist mainly of variable proportions of plagioclase, hornblende, biotite associated with minor quartz and iron oxides as accessory minerals. Equigranular, hypidiomorphic and poikilitic textures are common. Secondary constituents are chlorite, epidote, sericite and carbonates. 3.5. Syntectonic granodiorites Granodiorites represent the widely exposed granitoid rock types in the study area (Fig. 1); they are cropping out along Wadi Shut, Gabal Hindiyah and south of Gabal Umm Itly. These rocks are jointed and exhibit exfoliated weathering. The granodiorites intrude gneisses and diorite where irregular dark xenoliths and enclaves of gneisses and diorites are enclosed within the granodiorites. Granodiorites are locally gneissose with nice and beautiful appearance and can be quarried to use in several industrial purposes. Microscopically, the granodiorites are medium to coarsegrained. Equigranular, hypidiomorphic with development of myrmekitic, and perthitic intergrowhs. They consist mainly of plagioclase, quartz, few K-feldspars, muscovite and biotite as essential minerals, while iron oxides are found as accessory minerals. gneissose texture is observed (Fig. 3c). Secondary minerals are epidote, sericite, and chlorite. 3.6. Late-tectonic ultramafic-mafic intrusions The ultramafic-mafic intrusions exposed in the study area and environs have been described by many authors, e.g. Gabal Dahanib late Precambrian layered mafic-ultramafic intrusion (Dixon, 1981;
Please cite this article as: M. M. Shokry, M. F. Sadek, A. F. Osman et al., , The Egyptian Journal of Remote Sensing and Space Sciences, https://doi.org/ 10.1016/j.ejrs.2019.12.005
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Fig. 5. Spectral characteristics behaviors using ASTER spectral bands (a) VNIR-SWIR and (b) TIR.
Azer et al., 2017); El-Motaghairat (Kallalat) and Um Ginud ultrabasic-basic intrusion (Elnazer, 2013; Abdel Halim et al., 2016); Gabal Um Bissilla gabbroic intrusion (Sadek et al., 1989); El Genina Gharbia and gabbro Akarem Alaskan-type mafic–ultramafic intrusion (Helmy et al., 2014, 2015); Abu Hamamid intrusion (Farahat and Helmy, 2006; Helmy et al., 2015; Khedr and Shoji Arai, 2016), Gabal Mikbi and Gabal Zeiatit Alaskan-type (Abdallah et al., 2018; Mogahed, 2019). The Wadi Shut ultramafic-mafic rocks constitute the highest mountainous outcrops, namely; Gabal Dahanib and Gabal Umm Qubur intrusions (Fig. 1). The Gabal Dahanib maficultramafic intrusion was described by Dixon (1981) as a layered mafic-ultramafic sill, composed of peridotite, pyroxenite and olivine gabbro with rare anorthosite, all have a bulk komatiite composition. This intrusion was described as cumulus assemblages pertaining to chrome dunite, chrome wehrlite, chrome harzbur-
gite, plagioclase lherzolite and gabbro (Abdel Meguid and El Metwally, 1998). The Dahanib intrusion mainly consists of a suite of ultramafic rocks including dunite, peridotite, lherzolite, wehrlite and pyroxenite at the bottom overlying by a suite of mafic rocks comprising olivine gabbro, normal gabbro and gabbro-norite with rare anorthosite. Peridotite and dunite rocks are massive, dark and medium to coarse-grained, cropping out as layers on the top of the cumulate and intercalated with other gabbroic types. These rocks intrude the surrounding diorite and granodiorite (Fig. 3d). Petrographically, peridotite and dunite consist mainly of variable proportions of partially serpentinized olivine and pyroxene with minor hornblende as essential constituents and significant amount of opaque minerals (mainly magnetite). Secondary minerals are iddingsite, iron oxides, carbonate and chlorite with common mesh textures.
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Fig. 6. Landsat-8 grey scale principal component (PC) images: (a): (PC2), (b): (PC3), (c): (PC4), (d): (PC5).
Olivine gabbros consist essentially of labradorite, ortho-and clinopyroxene as well as substantial olivine content and Fe-Ti oxides (Fig. 3e). Ophitic, subophitic, poikilitic textures are common in addition to mesh and corona textures. The accessory minerals are mainly magnetite. Secondary minerals are iddingsite, chlorite, sericite, epidote and saussurite. Normal gabbros are composed mainly of labradorite, clinopyroxene (mainly augite) and olivine with iron oxides as accessory minerals. The secondary minerals include epidote, saussurite, chlorite and iddingsite. Ophitic, sub-ophitic and corona textures are common. Gabbro-norite rock type is composed essentially of labradorite, bytownite, ortho-pyroxene (hypersthene and enstatite) with few augite crystals. Iron oxides minerals are found as accessories. 3.7. Late tectonic monzogranites These rocks are cropping out near the southern side of Wadi Khuda entrance forming the moderate relief of Gabal Umm Itly. They intrude gneisses, diorite and granodiorites. Irregular xenoliths of variable sizes and enclaves from these rocks are hosted within monzogranites. Monzogranites show blocky weathering with narrow space joints, they can be quarried to use as ornamental stones. Microscopically, monzogranites are medium to coarse-grained and consist essentially of K-feldspars (mainly microcline), plagio-
clase, quartz, biotite, muscovite, and hornblende. Garnet, sphene and iron oxides occur as accessory minerals, while epidote, sericite and chlorite are found as secondary minerals. Perthitic intergrowth and myrmekitic textures are common (Fig. 3f).
4. Results and discussions 4.1. Lithological discrimination and geological mapping 4.1.1. Remote sensing analysis In this study, the enhanced images of ASTER and Landsat-8 have been analyzed to discriminate the different lithological units for the study area as well as the detailed geological mapping based on the spectral characterizations of the exposed lithological units. Fig. 4 revealed that, most of lithological units show moderate absorption features around bands 2 and 3 of Landsat-8 image, while they display well emphasized absorption features around bands 5, 7 and 11 (0.845, 0.885, 2.1–2.3 and 11.5–12.5 lm) respectively. The ASTER spectral profiles of the exposed rock units have absorption features around 2.14–2.185 and 2.185–2.225 lm bands 5 and 6 respectively (VNIR and SWIR), while they show strong absorption around VNIR-SWIR-TIR ASTER spectral bands 2, 8 and 10 (0.52–0.60, 2.295–2.365 and 8.125–8.475 lm) respectively (Fig. 5). The examined average spectral profiles representing the
Please cite this article as: M. M. Shokry, M. F. Sadek, A. F. Osman et al., , The Egyptian Journal of Remote Sensing and Space Sciences, https://doi.org/ 10.1016/j.ejrs.2019.12.005
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Fig. 7. Landsat-8-PC images on RGB: (a): PC2, PC4, PC5; (b): PC2, PC3, PC5.
different lithological units on Landsat-8 and ASTER spectral bands are successfully used to define the best band ratios for discrimination the lithological units in the study area. 4.1.1.1. Principal component analysis (PCA). The PCA is used to minimize redundant information of the multispectral and hyperspectral satellite data (Curran,1985). The derivative first principal component band contains the maximum variance related to the original multispectral or hyperspectral bands. In PCA eigenvector statistics the spectral information of any rock unit is loaded within each PC image. The loading informations indicate the spectral characteristics of the desired mineral/rock using some quantitative interpretation of eigenvector statistics (Crosta and Moore, 1989). In the present study, PCA has been utilized on both ASTER and Landsat-8 data to enhance the lithological discrimination. As shown in Fig. 6, the encountered rock units in the study area have been enphasized on the Landsat-8 grey scale principal component images. Accordingly, Wadi Shut gabbroic rocks have been discriminated with light grey tone and Umm Itly monzogranites
with black tone on PC2 image (Fig. 6a). On the other hand Umm Itly monzogranites are emphasized with light white colour on images PC3 and PC5 images (Fig. 6b and d), the diorite and granodiorite along the southern side of Wadi Khuda display light grey tone on PC3 and PC4 images (Fig. 6b and c). Wadi Shut late tectonic ultramafic-mafic rocks show black tone on PC4 and PC5 images (Fig. 6c and d). In addition, the ophiolitic serpentinite rocks are discriminated with light grey tone in PC5 image (Fig. 6d). On the Landsat-8 image (PC2, PC4, PC5) on RGB (Fig. 7a), Wadi Shut gabbroic rocks are clearly discriminated with dark red colour, Umm Itly monzogranites are emphasized with a characteristic cyan colour, serpentinite-talc carbonate rocks show blue colour and Dahanib ultramafic rock associations display dark magenta colour. On the other hand, Landsat-8 image (PC2, PC3, PC5) discriminates the granodiorites with dark green colour (Fig. 7b). As shown in figure (8a) the ASTER-PC grey scale image PC2 emphasizes the serpentinite-talc carbonate rocks with black colour while the gabbroic rocks are discriminated with dark grey tone. The monzogranites are emphasized with white colour on PC4
Please cite this article as: M. M. Shokry, M. F. Sadek, A. F. Osman et al., , The Egyptian Journal of Remote Sensing and Space Sciences, https://doi.org/ 10.1016/j.ejrs.2019.12.005
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Fig. 8. ASTER grey scale-PC images: (a) PC2, (b) PC4 (c) PC5 (d) PC6.
image (Fig. 8a and b). Wadi Shut ultramafic rocks are differentiated with dark grey colour, Umm Itly monzogranites exhibit black colour on PC5 image (Fig. 8c). In addition, the PC6 image emphasizes the Dahanib gabbroic rocks with dark grey colour (Fig. 8d). On the other hand, ASTER-PC image PC7, PC5, PC6 on RGB image (Fig. 9a), Wadi Shut Late tectonic ultramafic rocks are emphasized with red colour, the surrounding gabbroic rocks are emphasized with yellowish green colour, the serpentinite-talc carbonate rocks display dark magenta colour and the granodiorites show yellow colour. On the other hand, the PC4, PC2, PC5 image on RGB (Fig. 9b) discriminates the gabbroic rocks with dark magenta colour, the ophiolitic serpentinites with red colour, while granodiorites are emphasized with dark green colour. 4.1.1.2. Landsat-8 band ratio images. Band rationing is one of the most common spectral image enhancement techniques which can be used to minimize the topography effect on the multispectral image (Sabins, 1999). The different band ratios has been used to display the output in a colour composite image to detect variation in colours for the exposed rocks and facilitate their discriminations. In the present study, band rationing technique is used in detailed lithologic mapping, where several band ratio images of Landsat-8 were applied. The hydroxyl content index (band ratio image b6/b7) of Sultan et al. (1987) discriminates the ophiolitic
serpentinites and Wadi Shut late tectonic ultramafic rocks with white tone (Fig. 10a). Band ratio image (b6/b2) emphasizes the granitic rocks with white colour (Fig. 10b), while band ratio image (b6/b4) discriminates serpentinite talc-carbonate rocks with black colour and monzogranites with light grey tone (Fig. 10c). In addition, Band ratio image (b6/b5) clearly emphasizes the serpentinites and gabbroic rocks with black colour (Fig. 10d). As shown in figures (11a and b), Landsat-8 grey scale band ratio images (b7/b6) and (b7/b5) successfully discriminate the ophiolitic serpentinites, Wadi Shut ultramafic and gabbroic rocks with dark grey to black tone, while the granitoids and gneisses are emphasized with white tone. The grey scale band ratio image (b5/b3) emphasizes monzogranite with light grey tone (Fig. 11c). Most of the ultramafic-mafic and metavolcanic rocks are discriminated with dark grey to black tone. On the other hand, gneisses and granitoid rocks display white tone on the band ratio image (4/7) (Fig. 11d). In addition, the band ratio image (b2/b3xb4/b3) emphasizes the monzogranites with dark grey tone (Fig. 11e), while these rocks display white tone on the band ratio image (b6/b5*b4/b5) (Fig. 11f). Various images were derived from the grey scale band ratio images of Landsat-8 to enhance the lithological discrimination in the study area (Figs. 12 and 13). Accordingly, the band ratio image (b6/b2, b6/b7, b6/b4xb4/b5) on RGB (Fig. 12a) successfully discriminated both ophiolitic serpentinite-talc carbonate rocks and
Please cite this article as: M. M. Shokry, M. F. Sadek, A. F. Osman et al., , The Egyptian Journal of Remote Sensing and Space Sciences, https://doi.org/ 10.1016/j.ejrs.2019.12.005
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Fig. 9. ASTER-PC images on RGB: (a) PC7, PC5, PC6 (b) PC4, PC2, PC5.
Wadi Shut late tectonic ultramafic rocks with bright red colour. On this image, the gabbroic rocks are clearly differentiated with dark red colour and granodiorites display dark cyan colour and monzogranite is well discriminated with whitish pink colour. On the other hand, the band ratio image (b4/b2, b6/b7, b6/b5) on RGB (Fig. 12b) emphasizes the serpentinite rocks, Wadi Shut ultramafic rocks and the metavolcanics with light orange, red and blue colours respectively, while gneisses and Umm Itly monzogranites display rose colour. The Landsat-8 band ratio image (b4/b7, b5/b3, b7/b6) successfully discriminated Wadi Shut ultramafic rocks with a characteristic reddish magenta colour and the serpentinite rocks display a ruby orange colour, monzogranites show light green colour (Fig. 13a). The band ratio image (b7/b5, b5/b3, b7/b6) differentiated the serpentinite rocks with green colour and Wadi Shut ultramafic rocks with blue colour, while monzogranites show light green colour and granodiorites display bright magenta colour (Fig. 13b). 4.1.1.3. ASTER spectral indices. ASTER band rationing (spectral indices) method has been used by many authors for mineralogi-
cal mapping purposes (Yamaguchi and Naito, 2003; Ninomiya et al., 2006; Rowan and Mars, 2003; Hassan and Ramadan, 2015; Hassan and Sadek, 2017 and others). Accordingly, various ASTER spectral indices images have been used to emphasize the lithological units in the study area based on their mineralogic composition. Ferric oxides index image (b3/b4) discriminates Gabal Dahanib and Gabal Umm Qubur mafic and ultramafic rocks with white colour, while ASTER band ratio image (b4/b1) distinguishes Gabal Umm Itly monzogranite with white colour (Fig. 14a and b). ASTER band ratio image (b4/b5) emphasizes the alteration zones with white colour, while ASTER kaolinite index (b7/b5) discriminates the schistose metavolcanics and granodiorite with white colour (Fig. 15a and b). The ASTER band ratio image (b4/ b7, b3/b4, b5/b7) on RGB (Fig. 16) emphasizes the schistose metavolcanics with magenta colour and Umm Itly monzogranite are clearly discriminated with red colour, the granodiorites show very dark green colour. On the other hand, Wadi Shut Late tectonic ultramafic and gabbroic rocks display yellowish orange and green colours respectively.
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Fig. 10. Landsat-8 grey scale band ratio: (a) Band ratio image (b6/b7), (b) Band ratio image (b6/b2), (c) Band ratio image (b6/b4), (d) Band ratio image (b6/b5).
4.2. Detailed geological mapping The remote sensing data analysis with field and petrographic investigations in addition to the previous geological mapping have been integrated and detailed geological map is produced for the study area (Fig. 1). Comparing the produced detailed geological map with the published Baranis quadrangle geological map published by EGSMA (1992), the modifications in the present geological map are summarized as the following: 1) Accurate mapping of Wadi Shut late tectonic ultramaficmafic rock assoctions forming Gabals Dahanib and Umm Qubur and mapping the small scattered ultramafic outcrops within Umm Qubur gabbroic mass. 2) Modification the contacts between Umm Itly monzogranites and the surrounding granodiorites as well as the granodiorites and diorites forming Gabals Hindiyah and Shinshif.
3) Wadi Khuda gneisses are mapped intruded by granodiorites from the north while these gneisses were mapped in EGSMA map intruded by gabbroic rocks. 4) Modification the contacts between the schistose metavolcanics and the overthrusted serpentinites exposed in the southwestern part of the mapped area. 5. Conclusions Wadi Khuda-Wadi Shut area in the SED of Egypt is predominantly made up of Precambrian basement rocks comprising gneisses, serpentinites-talc carbonate association and schistose metavolcanics as metamorphic assemblages; they were intruded by syn tectonic diorite, granodiorite, and late tectonic intrusions of ultramafic-mafic association and monzogranite. The whole sequence is dissected by post tectonic dykes, veins and quartz plug.
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Fig. 11. Landsat-8 grey scale band ratio images: (a): (b7/b6), (b): (b7/b5), (c): (b5/b3), (d): (b4/b7), (e): (b2/b3xb4/b3) and (f): (b6/b5xb4/b5).
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Fig. 12. Landsat-8 band ratio images on RGB: (a) (b6/b2, b6/b7, b6/b5xb4/b5) and (b) (b4/b2, b6/b7, b6/b5).
Wadi Khuda gneisses with the associated hornblende-rich gneisses are of diorite-granodiorite in composition. The ophiolitic serpentinite and talc carbonate rocks are tectonically overthrusted onto the schistose meta-andesites with NW-SE thrust contact. Wadi Shut ultramafic-mafic intrusions form the two mountainous masses of Gabals Dahanib and Umm Qubur. Gabal Dahanib in the western side of the Wadi is a layered type similar to other
intrusions in the SED (e.g. Abu Fas intrusion, Sadek and El Ramly, 1996) rather than Alaskan-type intrusion as interpreted by many authors for nearby mafic-ultramafic intrusions. Both ultramafic and mafic varieties seem to have evolved from a parent magma through a process of fractional crystallization. Umm Itly monzogranites and Hindiyah gneissic granodiorites show nice appearance and they can be quarried for using as ornamental and decoration stones and various industrial purposes.
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Fig. 13. Landsat-8 band ratio images on RGB: (a) (b4/b7, b5/b3, b7/b6), (b) (b7/b5, b5/b3, b7/b6).
The proposed principal components and band ratios of ASTER and Landsat-8 data which were used for the first time in the study area improved the lithological discrimination and enhanced their boundaries in the produced geological map compared with the previous published geological maps, particularly
Baranis Quadrangle geological map published by EGSMA (1992). The undertaken procedures in the present study are very effective in lithological discrimination and detailed geological mapping and could be applied in similar areas covered by basement rocks.
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Fig. 14. ASTER grey scale band ratio images: (a) (b3/b4), (b) (b4/b1).
Fig. 15. ASTER grey scale band ratio mages: (a) (b4/b5), (b) (b7/b5).
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Fig. 16. ASTER band ratio image (b4/b7, b3/b4, b5/b7) on RGB.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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Precambrian basement rocks of Wadi-Khuda-Shut area, South Eastern Desert of Egypt: Geology and remote sensing analysis Mahmoud M. Shokry a,⇑, Mohamed F. Sadek b, Aly F. Osman c, Baher A. El Kalioubi c a
Egyptian Mineral Resources Authority (EMRA), Cairo, Egypt National Authority for Remote Sensing and Space Sciences (NARSS), Cairo, Egypt c Faculty of Science, Geology Department, Ain Shams University, Cairo, Egypt b
a r t i c l e
i n f o
Article history: Received 8 August 2019 Revised 1 December 2019 Accepted 22 December 2019 Available online xxxx Keywords: Precambrian Khuda-Shut Egypt Basement rocks Landsat-8 ASTER
a b s t r a c t Wadi Khuda-Wadi Shut area in the South Eastern Desert (SED) of Egypt is mainly made up of gneisses, ophiolitic serpentinites and intermediate schistose metavolcanics. These metamorphic rock units are intruded by syn-late-tectonic diorite, granodiorite, ultramafic-mafic, and monzogranite intrusions. The gneisses comprise biotite hornblende gneiss, hornblende gneiss and migmatites. They are of granodiorite and diorite composition. The ophiolitic serpentinite with talc carbonate rocks were thrusted over the metavolcanics with NW-SE thrust contact. The late tectonic ultramafic-mafic rock units are represented in the study area by Dahanib pluton, which is consisted of layered peridotite-dunite associated with olivine gabrro, normal gabbro and gabbro-norite as well as rare hornblende gabbro. These varieties are related to the layered intrusions rather than Alaskan-types, and formed by magmatic differentiation. The granodiorite and monzogranite represent the youngest basement rock units in the study area. The principal components and band ratios of ASTER and Landsat-8 data were successfully used for the first time in lithological discrimination and geological mapping of the study area. This study concluded that, the interpreted data of ASTER and Landsat-8 combined with field study and petrographic investigation clearly discriminated the exposed rock units. Accordingly, a detailed geological map emphasizing the lithological units in Khuda-Shut area has been presented. Ó 2019 National Authority for Remote Sensing and Space Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-ncnd/4.0/).
1. Introduction The Arabian-Nubian Shield (ANS) as a part of the Pan-African orogenic belt was initiated as an intra-oceanic island arc that underwent obduction-accretion processes through the Neoproterozoic (e.g. Stern et al., 1991). The late Neoproterozoic basement rock units in the South Eastern Desert of Egypt is dominated by gneiss domes, ophiolitic-related assemblages, island-arc metavolcanics and their derivative volcaniclastics. These rock units were episodically intruded by suites of syn-late to post-tectonic ultrabasic-basic and granitoid intrusions and intruded by post tectonic dykes and intraplate granites. The remote sensing data are very effective in geological mapping and detecting the mineralized alteration zones (Sadek, 2005, Sadek et al., 2008; Gad and Kusky, 2007; Yazdi et al., Peer review under responsibility of National Authority for Remote Sensing and Space Sciences. ⇑ Corresponding author. E-mail address: [email protected] (M.M. Shokry).
2011; Hassan et al., 2014; Hassan and Ramadan, 2015; Gabr et al., 2015; Sadek et al., 2015; Ali-Bik et al., 2017, 2018; Hassan and Sadek, 2017; Asran and Hassan, 2019). Wadi Khuda-Wadi Shut area lies in the southern sector of the Eastern Desert along the Red Sea coast. It covers an area of about 800 km2 between Latitudes 23° 330 –23° 500 N and longitudes 35° 050 –35° 260 E (Fig. 1). The area is mainly built up of Precambrian metamorphic and intrusive assemblages. Economically, the exposed monzogranites and gneissic granodiorite show blocky appearance, and suitable to be quarried to use as ornamental and decoration rock slabs. The Wadi Khuda-Wadi Shut area was subjected to few studies focused on the geology and tectonic setting of Wadi Khuda gneisses. None of the previous studies used the remote sensing data to discriminate the lithological units for detailed geological mapping of the area, except Asran and Hassan (2019), regarding the small outcrop of leucogranite along Wadi Khuda. The main objective of this study is to discriminate the lithological units and detailed geological mapping of the basement rocks at Wadi Khuda-Wadi Shut area based on the integrated data of previous
https://doi.org/10.1016/j.ejrs.2019.12.005 1110-9823/Ó 2019 National Authority for Remote Sensing and Space Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: M. M. Shokry, M. F. Sadek, A. F. Osman et al., , The Egyptian Journal of Remote Sensing and Space Sciences, https://doi.org/ 10.1016/j.ejrs.2019.12.005
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Fig. 1. Location and detailed geological map of Wadi Khuda-Wadi Shut area modified after Baranis Quadrangle Geological Map published by EGSMA (1992).
geological mapping, field study, petrographic investigation and the analyzed data of Landsat-8 and ASTER.
analyzed. Both band ratio and principal component image processing techniques using Erdas-Imagine 2015, ENVI V.5.3 and ARCGIS 10.5 Software have been applied on ASTER and landsat-8 spectral bands to discriminate the lithological units.
2. Data and methods 2.2. Field study 2.1. Remote sensing The processed remote sensing data of satellite images have been used in this study to enhance the discrimination of the lithological units. Landsat-8 scene (Path 173/Row 43) and ASTER Level 1B data, acquired on October 2016 and July 2003 respectively were
Field study has been carried out to verify the interpreted data of satellite images and to check the geological setting and to classify the exposed rock units in the study area. Rock samples representing these rock units have been collected for the petrographic investigation.
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3. Geological setting and petrography The Wad Khuda-Wadi Shut area consists mainly of gneissesmigmatites, ophiolitic serpentinite with talc carbonate rocks and schistose metavolcanics. These rock varieties are intruded by syn to late tectonic diorite, granodiorite, ultramafic-mafic and monzogranite intrusions and dissected by post orogenic veins, dykes and quartz plug (Fig. 1). 3.1. Gneisses and migmatites These rocks were described in some localities in the SED of Egypt, e.g. Wadi Hafafit (Greiling et al., 1994; Fowler and El Kalioubi, 2002); Wadi Bitan (Abdel Khalek et al., 1999). Gneisses
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with the associated migmatites are the oldest rock units encountered in Wadi Khuda area, they are related to Bitan and Khuda gneisses group (Egyptian Geological Survey and Mining Authority, EGSMA, 1992) and para-gneisses of sedimentary origin, intercalated with amphibolite lenses of igneous origin (Asran et al., 2000; Asran and Hassan, 2019). These gneisses are exposed as strongly foliated, banded, migmatized and folded outcrops, they are intruded by diorite, granodiorite and Umm Itly monzogranite. These gneisses comprise three varieties; biotite hornblende gneiss, hornblende gneiss and migmatites, they are characterized by alternation of dark biotite and hornblende rich melanosome bands with bright feldspars and quartz rich leucosome bands (Fig. 2a). The average thickness of melanosome bands is up to 100 cm thick while the leucosome
Fig. 2. (a) Alternating of dark biotite and hornblende rich melanosome bands with bright feldspars and quartz rich leucosome bands in Wadi Khuda gneisses. (b) Folding in gneisses, Wadi Khuda. (c) Photomicrograph showing hornblende rich bands (Hb) alternating with felsic bands rich with quartz (Q) and plagioclase (Pl) showing gneissic texture, C.N., X = 63. (d) Serpentinite rocks (Sp) overthrusting the schistose metavolcanics (Mv), southwestern sector of the mapped area. (e) Photomicrograph showing mesh texture in serpentinite rock, C.N, X = 63. (f) Schistosity in schistose metavolcanics, the western sector of the mapped area.
Please cite this article as: M. M. Shokry, M. F. Sadek, A. F. Osman et al., , The Egyptian Journal of Remote Sensing and Space Sciences, https://doi.org/ 10.1016/j.ejrs.2019.12.005
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Fig. 3. (a) and (b): Granodiorite (Gd) intruding gneisses (Gn) and diorite (Dr), Wadi Khuda. (c) Gneissose texture of Plagioclase (Pl), hornblende (Hb) and quartz (Qz) in granodiorite, Gabal Hindiyah, C.N., X = 63. (d) Gabal Dahanib ultramafic-mafic intrusion (Um + Mf) intruding the surrounding diorite (Dr), Wadi Shut. (e) Olivine (Ol), labradorite (Pl) and pyroxene (Px) crystals in olivine gabbro, Gabal Dahanib. (f) Myrmekitic intergrowth texture in monzogranite, Gabal Umm Itly, C.N., X = 63.
bands range from 0.5 to about 30 cm. Wadi Khuda biotite hornblende gneisses are medium-grained and granodiorie-diorite in composition, in places they are intercalated with hornblende-rich gneissic bands which are conformable with the general NW-SE foliation trend with average dip angle 45° towards NE. At the northern flank of Wadi Khuda, the gneissic rocks are thrown into doubly plunging anticlinal and synclinal folds with common ptygmatic folds (Fig. 2b). Microscopically, biotite hornblende gneisses consist essentially of alternating mafic and felsic bands. Biotite, hornblende, and mus-
covite with rare felsic minerals are the main constituents of the mafic bands, while the felsic bands is are composed essentially of sodic plagioclase and quartz with rare biotite and hornblende. Sericite, epidote and chlorite are present as secondary minerals. The mafic and felsic bands show sub-parallel orientation giving the characteristic gneissic texture (Fig. 2c). The hornblende gneisses consist essentially of hornblende, plagioclase, quartz and little biotite. Epidote, and iron oxides are accessories. The intercalated migmatites are mainly composed of coarser granied melanosome and leucosome bands. Biotite and
Please cite this article as: M. M. Shokry, M. F. Sadek, A. F. Osman et al., , The Egyptian Journal of Remote Sensing and Space Sciences, https://doi.org/ 10.1016/j.ejrs.2019.12.005
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Fig. 4. Reflectance spectra of the rock types using Landsat-8 data.
hornblende with few feldspars and quartz are the main constituents of melanosomes while leucosomes consist mainly of feldspars and quartz with little biotite and hornblende.
3.2. Ophiolitic serpentinite-talc carbonates rocks The highly sheared serpentinite-talc carbonate rocks are cropping out at the extreme southwestern sector of the mapped area representing the eastern extension of the ophiolitic serpentinite mass forming Gabal Abu Dahr (Gahlan et al., 2015). These serpentinite rocks represent a part of the tectonic ophiolitic mélange, which consists of tectonic lenses of serpentinite, talc carbonate rocks, highly deformed schistose metavolcanics and talc magnesite tremolite actinolite schist. The serpentinite-talc carbonate associations are thrusted onto the surrounding schistose metavolcanics with NW-SE thrust contact and low thrust angle of about 35° SW (Fig. 2d). These serpentinite rocks are intruded by gabbroic rocks and dissected by magnesite and quartz veins. Petrographically, serpentinite rocks are very fine to mediumgrained, and consist entirely of antigorite, chrysotile and magnetite with common mesh texture which is marked by replacing the relics of olivine crystals along Y-cracks by serpentine minerals and magnetite (Fig. 2e). Talc carbonate rocks consist mainly of fibrous talc replaced by magnesite and iron oxides.
3.3. Schistose metavolcanics These metavolcanic rocks are cropping out at the western sector of the mapped area forming strongly schistose and deformed belt. They show NW-SE schistose fabric with low dip angle of 35° SW (Fig. 2f). These metavolcanic rocks were overthrusted by the ophiolitic serpentinite-talc carbonate slices and sheets, and intruded by syn tectonic granodiorite and diorite bodies. Microscopically, metavolcanic rocks are fine-grained, aphanitic and mostly andesitic in composition. They consist of chlorite, actinolite, tremolite, altered plagioclase, epidote and quartz. They show distinct schistose texture marked by the parallel orientation of epidotized plagioclase, quartz and the mafic minerals.
3.4. Syn – tectonic diorites These rocks are widely outcropping in the area forming Gabal Umm Akra at the southern flank of Wadi Khuda, Gabal Shinshif, the northern sector of Gabal Umm Qubur and along Wadi Abu Hoqban in the northwestern part of the mapped area (Fig. 1). These dioritic rocks intrude gneisses (Fig. 3a) while they are intruded by granodiorite of Gabal Hindiyah (Fig. 3b). They enclose abundance of gneiss xenoliths up to 10 cm in lengths. Microscopically, diorites consist mainly of variable proportions of plagioclase, hornblende, biotite associated with minor quartz and iron oxides as accessory minerals. Equigranular, hypidiomorphic and poikilitic textures are common. Secondary constituents are chlorite, epidote, sericite and carbonates. 3.5. Syntectonic granodiorites Granodiorites represent the widely exposed granitoid rock types in the study area (Fig. 1); they are cropping out along Wadi Shut, Gabal Hindiyah and south of Gabal Umm Itly. These rocks are jointed and exhibit exfoliated weathering. The granodiorites intrude gneisses and diorite where irregular dark xenoliths and enclaves of gneisses and diorites are enclosed within the granodiorites. Granodiorites are locally gneissose with nice and beautiful appearance and can be quarried to use in several industrial purposes. Microscopically, the granodiorites are medium to coarsegrained. Equigranular, hypidiomorphic with development of myrmekitic, and perthitic intergrowhs. They consist mainly of plagioclase, quartz, few K-feldspars, muscovite and biotite as essential minerals, while iron oxides are found as accessory minerals. gneissose texture is observed (Fig. 3c). Secondary minerals are epidote, sericite, and chlorite. 3.6. Late-tectonic ultramafic-mafic intrusions The ultramafic-mafic intrusions exposed in the study area and environs have been described by many authors, e.g. Gabal Dahanib late Precambrian layered mafic-ultramafic intrusion (Dixon, 1981;
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Fig. 5. Spectral characteristics behaviors using ASTER spectral bands (a) VNIR-SWIR and (b) TIR.
Azer et al., 2017); El-Motaghairat (Kallalat) and Um Ginud ultrabasic-basic intrusion (Elnazer, 2013; Abdel Halim et al., 2016); Gabal Um Bissilla gabbroic intrusion (Sadek et al., 1989); El Genina Gharbia and gabbro Akarem Alaskan-type mafic–ultramafic intrusion (Helmy et al., 2014, 2015); Abu Hamamid intrusion (Farahat and Helmy, 2006; Helmy et al., 2015; Khedr and Shoji Arai, 2016), Gabal Mikbi and Gabal Zeiatit Alaskan-type (Abdallah et al., 2018; Mogahed, 2019). The Wadi Shut ultramafic-mafic rocks constitute the highest mountainous outcrops, namely; Gabal Dahanib and Gabal Umm Qubur intrusions (Fig. 1). The Gabal Dahanib maficultramafic intrusion was described by Dixon (1981) as a layered mafic-ultramafic sill, composed of peridotite, pyroxenite and olivine gabbro with rare anorthosite, all have a bulk komatiite composition. This intrusion was described as cumulus assemblages pertaining to chrome dunite, chrome wehrlite, chrome harzbur-
gite, plagioclase lherzolite and gabbro (Abdel Meguid and El Metwally, 1998). The Dahanib intrusion mainly consists of a suite of ultramafic rocks including dunite, peridotite, lherzolite, wehrlite and pyroxenite at the bottom overlying by a suite of mafic rocks comprising olivine gabbro, normal gabbro and gabbro-norite with rare anorthosite. Peridotite and dunite rocks are massive, dark and medium to coarse-grained, cropping out as layers on the top of the cumulate and intercalated with other gabbroic types. These rocks intrude the surrounding diorite and granodiorite (Fig. 3d). Petrographically, peridotite and dunite consist mainly of variable proportions of partially serpentinized olivine and pyroxene with minor hornblende as essential constituents and significant amount of opaque minerals (mainly magnetite). Secondary minerals are iddingsite, iron oxides, carbonate and chlorite with common mesh textures.
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Fig. 6. Landsat-8 grey scale principal component (PC) images: (a): (PC2), (b): (PC3), (c): (PC4), (d): (PC5).
Olivine gabbros consist essentially of labradorite, ortho-and clinopyroxene as well as substantial olivine content and Fe-Ti oxides (Fig. 3e). Ophitic, subophitic, poikilitic textures are common in addition to mesh and corona textures. The accessory minerals are mainly magnetite. Secondary minerals are iddingsite, chlorite, sericite, epidote and saussurite. Normal gabbros are composed mainly of labradorite, clinopyroxene (mainly augite) and olivine with iron oxides as accessory minerals. The secondary minerals include epidote, saussurite, chlorite and iddingsite. Ophitic, sub-ophitic and corona textures are common. Gabbro-norite rock type is composed essentially of labradorite, bytownite, ortho-pyroxene (hypersthene and enstatite) with few augite crystals. Iron oxides minerals are found as accessories. 3.7. Late tectonic monzogranites These rocks are cropping out near the southern side of Wadi Khuda entrance forming the moderate relief of Gabal Umm Itly. They intrude gneisses, diorite and granodiorites. Irregular xenoliths of variable sizes and enclaves from these rocks are hosted within monzogranites. Monzogranites show blocky weathering with narrow space joints, they can be quarried to use as ornamental stones. Microscopically, monzogranites are medium to coarse-grained and consist essentially of K-feldspars (mainly microcline), plagio-
clase, quartz, biotite, muscovite, and hornblende. Garnet, sphene and iron oxides occur as accessory minerals, while epidote, sericite and chlorite are found as secondary minerals. Perthitic intergrowth and myrmekitic textures are common (Fig. 3f).
4. Results and discussions 4.1. Lithological discrimination and geological mapping 4.1.1. Remote sensing analysis In this study, the enhanced images of ASTER and Landsat-8 have been analyzed to discriminate the different lithological units for the study area as well as the detailed geological mapping based on the spectral characterizations of the exposed lithological units. Fig. 4 revealed that, most of lithological units show moderate absorption features around bands 2 and 3 of Landsat-8 image, while they display well emphasized absorption features around bands 5, 7 and 11 (0.845, 0.885, 2.1–2.3 and 11.5–12.5 lm) respectively. The ASTER spectral profiles of the exposed rock units have absorption features around 2.14–2.185 and 2.185–2.225 lm bands 5 and 6 respectively (VNIR and SWIR), while they show strong absorption around VNIR-SWIR-TIR ASTER spectral bands 2, 8 and 10 (0.52–0.60, 2.295–2.365 and 8.125–8.475 lm) respectively (Fig. 5). The examined average spectral profiles representing the
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Fig. 7. Landsat-8-PC images on RGB: (a): PC2, PC4, PC5; (b): PC2, PC3, PC5.
different lithological units on Landsat-8 and ASTER spectral bands are successfully used to define the best band ratios for discrimination the lithological units in the study area. 4.1.1.1. Principal component analysis (PCA). The PCA is used to minimize redundant information of the multispectral and hyperspectral satellite data (Curran,1985). The derivative first principal component band contains the maximum variance related to the original multispectral or hyperspectral bands. In PCA eigenvector statistics the spectral information of any rock unit is loaded within each PC image. The loading informations indicate the spectral characteristics of the desired mineral/rock using some quantitative interpretation of eigenvector statistics (Crosta and Moore, 1989). In the present study, PCA has been utilized on both ASTER and Landsat-8 data to enhance the lithological discrimination. As shown in Fig. 6, the encountered rock units in the study area have been enphasized on the Landsat-8 grey scale principal component images. Accordingly, Wadi Shut gabbroic rocks have been discriminated with light grey tone and Umm Itly monzogranites
with black tone on PC2 image (Fig. 6a). On the other hand Umm Itly monzogranites are emphasized with light white colour on images PC3 and PC5 images (Fig. 6b and d), the diorite and granodiorite along the southern side of Wadi Khuda display light grey tone on PC3 and PC4 images (Fig. 6b and c). Wadi Shut late tectonic ultramafic-mafic rocks show black tone on PC4 and PC5 images (Fig. 6c and d). In addition, the ophiolitic serpentinite rocks are discriminated with light grey tone in PC5 image (Fig. 6d). On the Landsat-8 image (PC2, PC4, PC5) on RGB (Fig. 7a), Wadi Shut gabbroic rocks are clearly discriminated with dark red colour, Umm Itly monzogranites are emphasized with a characteristic cyan colour, serpentinite-talc carbonate rocks show blue colour and Dahanib ultramafic rock associations display dark magenta colour. On the other hand, Landsat-8 image (PC2, PC3, PC5) discriminates the granodiorites with dark green colour (Fig. 7b). As shown in figure (8a) the ASTER-PC grey scale image PC2 emphasizes the serpentinite-talc carbonate rocks with black colour while the gabbroic rocks are discriminated with dark grey tone. The monzogranites are emphasized with white colour on PC4
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Fig. 8. ASTER grey scale-PC images: (a) PC2, (b) PC4 (c) PC5 (d) PC6.
image (Fig. 8a and b). Wadi Shut ultramafic rocks are differentiated with dark grey colour, Umm Itly monzogranites exhibit black colour on PC5 image (Fig. 8c). In addition, the PC6 image emphasizes the Dahanib gabbroic rocks with dark grey colour (Fig. 8d). On the other hand, ASTER-PC image PC7, PC5, PC6 on RGB image (Fig. 9a), Wadi Shut Late tectonic ultramafic rocks are emphasized with red colour, the surrounding gabbroic rocks are emphasized with yellowish green colour, the serpentinite-talc carbonate rocks display dark magenta colour and the granodiorites show yellow colour. On the other hand, the PC4, PC2, PC5 image on RGB (Fig. 9b) discriminates the gabbroic rocks with dark magenta colour, the ophiolitic serpentinites with red colour, while granodiorites are emphasized with dark green colour. 4.1.1.2. Landsat-8 band ratio images. Band rationing is one of the most common spectral image enhancement techniques which can be used to minimize the topography effect on the multispectral image (Sabins, 1999). The different band ratios has been used to display the output in a colour composite image to detect variation in colours for the exposed rocks and facilitate their discriminations. In the present study, band rationing technique is used in detailed lithologic mapping, where several band ratio images of Landsat-8 were applied. The hydroxyl content index (band ratio image b6/b7) of Sultan et al. (1987) discriminates the ophiolitic
serpentinites and Wadi Shut late tectonic ultramafic rocks with white tone (Fig. 10a). Band ratio image (b6/b2) emphasizes the granitic rocks with white colour (Fig. 10b), while band ratio image (b6/b4) discriminates serpentinite talc-carbonate rocks with black colour and monzogranites with light grey tone (Fig. 10c). In addition, Band ratio image (b6/b5) clearly emphasizes the serpentinites and gabbroic rocks with black colour (Fig. 10d). As shown in figures (11a and b), Landsat-8 grey scale band ratio images (b7/b6) and (b7/b5) successfully discriminate the ophiolitic serpentinites, Wadi Shut ultramafic and gabbroic rocks with dark grey to black tone, while the granitoids and gneisses are emphasized with white tone. The grey scale band ratio image (b5/b3) emphasizes monzogranite with light grey tone (Fig. 11c). Most of the ultramafic-mafic and metavolcanic rocks are discriminated with dark grey to black tone. On the other hand, gneisses and granitoid rocks display white tone on the band ratio image (4/7) (Fig. 11d). In addition, the band ratio image (b2/b3xb4/b3) emphasizes the monzogranites with dark grey tone (Fig. 11e), while these rocks display white tone on the band ratio image (b6/b5*b4/b5) (Fig. 11f). Various images were derived from the grey scale band ratio images of Landsat-8 to enhance the lithological discrimination in the study area (Figs. 12 and 13). Accordingly, the band ratio image (b6/b2, b6/b7, b6/b4xb4/b5) on RGB (Fig. 12a) successfully discriminated both ophiolitic serpentinite-talc carbonate rocks and
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Fig. 9. ASTER-PC images on RGB: (a) PC7, PC5, PC6 (b) PC4, PC2, PC5.
Wadi Shut late tectonic ultramafic rocks with bright red colour. On this image, the gabbroic rocks are clearly differentiated with dark red colour and granodiorites display dark cyan colour and monzogranite is well discriminated with whitish pink colour. On the other hand, the band ratio image (b4/b2, b6/b7, b6/b5) on RGB (Fig. 12b) emphasizes the serpentinite rocks, Wadi Shut ultramafic rocks and the metavolcanics with light orange, red and blue colours respectively, while gneisses and Umm Itly monzogranites display rose colour. The Landsat-8 band ratio image (b4/b7, b5/b3, b7/b6) successfully discriminated Wadi Shut ultramafic rocks with a characteristic reddish magenta colour and the serpentinite rocks display a ruby orange colour, monzogranites show light green colour (Fig. 13a). The band ratio image (b7/b5, b5/b3, b7/b6) differentiated the serpentinite rocks with green colour and Wadi Shut ultramafic rocks with blue colour, while monzogranites show light green colour and granodiorites display bright magenta colour (Fig. 13b). 4.1.1.3. ASTER spectral indices. ASTER band rationing (spectral indices) method has been used by many authors for mineralogi-
cal mapping purposes (Yamaguchi and Naito, 2003; Ninomiya et al., 2006; Rowan and Mars, 2003; Hassan and Ramadan, 2015; Hassan and Sadek, 2017 and others). Accordingly, various ASTER spectral indices images have been used to emphasize the lithological units in the study area based on their mineralogic composition. Ferric oxides index image (b3/b4) discriminates Gabal Dahanib and Gabal Umm Qubur mafic and ultramafic rocks with white colour, while ASTER band ratio image (b4/b1) distinguishes Gabal Umm Itly monzogranite with white colour (Fig. 14a and b). ASTER band ratio image (b4/b5) emphasizes the alteration zones with white colour, while ASTER kaolinite index (b7/b5) discriminates the schistose metavolcanics and granodiorite with white colour (Fig. 15a and b). The ASTER band ratio image (b4/ b7, b3/b4, b5/b7) on RGB (Fig. 16) emphasizes the schistose metavolcanics with magenta colour and Umm Itly monzogranite are clearly discriminated with red colour, the granodiorites show very dark green colour. On the other hand, Wadi Shut Late tectonic ultramafic and gabbroic rocks display yellowish orange and green colours respectively.
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Fig. 10. Landsat-8 grey scale band ratio: (a) Band ratio image (b6/b7), (b) Band ratio image (b6/b2), (c) Band ratio image (b6/b4), (d) Band ratio image (b6/b5).
4.2. Detailed geological mapping The remote sensing data analysis with field and petrographic investigations in addition to the previous geological mapping have been integrated and detailed geological map is produced for the study area (Fig. 1). Comparing the produced detailed geological map with the published Baranis quadrangle geological map published by EGSMA (1992), the modifications in the present geological map are summarized as the following: 1) Accurate mapping of Wadi Shut late tectonic ultramaficmafic rock assoctions forming Gabals Dahanib and Umm Qubur and mapping the small scattered ultramafic outcrops within Umm Qubur gabbroic mass. 2) Modification the contacts between Umm Itly monzogranites and the surrounding granodiorites as well as the granodiorites and diorites forming Gabals Hindiyah and Shinshif.
3) Wadi Khuda gneisses are mapped intruded by granodiorites from the north while these gneisses were mapped in EGSMA map intruded by gabbroic rocks. 4) Modification the contacts between the schistose metavolcanics and the overthrusted serpentinites exposed in the southwestern part of the mapped area. 5. Conclusions Wadi Khuda-Wadi Shut area in the SED of Egypt is predominantly made up of Precambrian basement rocks comprising gneisses, serpentinites-talc carbonate association and schistose metavolcanics as metamorphic assemblages; they were intruded by syn tectonic diorite, granodiorite, and late tectonic intrusions of ultramafic-mafic association and monzogranite. The whole sequence is dissected by post tectonic dykes, veins and quartz plug.
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Fig. 11. Landsat-8 grey scale band ratio images: (a): (b7/b6), (b): (b7/b5), (c): (b5/b3), (d): (b4/b7), (e): (b2/b3xb4/b3) and (f): (b6/b5xb4/b5).
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Fig. 12. Landsat-8 band ratio images on RGB: (a) (b6/b2, b6/b7, b6/b5xb4/b5) and (b) (b4/b2, b6/b7, b6/b5).
Wadi Khuda gneisses with the associated hornblende-rich gneisses are of diorite-granodiorite in composition. The ophiolitic serpentinite and talc carbonate rocks are tectonically overthrusted onto the schistose meta-andesites with NW-SE thrust contact. Wadi Shut ultramafic-mafic intrusions form the two mountainous masses of Gabals Dahanib and Umm Qubur. Gabal Dahanib in the western side of the Wadi is a layered type similar to other
intrusions in the SED (e.g. Abu Fas intrusion, Sadek and El Ramly, 1996) rather than Alaskan-type intrusion as interpreted by many authors for nearby mafic-ultramafic intrusions. Both ultramafic and mafic varieties seem to have evolved from a parent magma through a process of fractional crystallization. Umm Itly monzogranites and Hindiyah gneissic granodiorites show nice appearance and they can be quarried for using as ornamental and decoration stones and various industrial purposes.
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Fig. 13. Landsat-8 band ratio images on RGB: (a) (b4/b7, b5/b3, b7/b6), (b) (b7/b5, b5/b3, b7/b6).
The proposed principal components and band ratios of ASTER and Landsat-8 data which were used for the first time in the study area improved the lithological discrimination and enhanced their boundaries in the produced geological map compared with the previous published geological maps, particularly
Baranis Quadrangle geological map published by EGSMA (1992). The undertaken procedures in the present study are very effective in lithological discrimination and detailed geological mapping and could be applied in similar areas covered by basement rocks.
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Fig. 14. ASTER grey scale band ratio images: (a) (b3/b4), (b) (b4/b1).
Fig. 15. ASTER grey scale band ratio mages: (a) (b4/b5), (b) (b7/b5).
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Fig. 16. ASTER band ratio image (b4/b7, b3/b4, b5/b7) on RGB.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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Please cite this article as: M. M. Shokry, M. F. Sadek, A. F. Osman et al., , The Egyptian Journal of Remote Sensing and Space Sciences, https://doi.org/ 10.1016/j.ejrs.2019.12.005