Search

The present work reports on the first evidence of a possible hypervelocity impact crater in the Sultanate of Oman. The impact origin of the structure is determined based on field observations, microscopic observations of shatter cones, planar fractures (PFs) and feather features (FFs) in quartz, calcite, and feldspar, and melt-bearing polymict breccias with various types of melts. The structure consists of an elliptical bowl-shaped ridge 750 m long and 550 m wide, oriented roughly north-northeast to south-southwest. The elliptical shape and relief asymmetry indicate an oblique collision. The precursor target lithologies include local late Proterozoic Masirah Bay siliciclastic formations, carbonate and acidic volcanic rocks of the late Precambrian Halfayn Formation, and basement rocks. The crater rim, up to 15–20 m above ground, is composed of quartzite, jasper, agate, monomict siliceous and hematite breccia, and metamorphosed shale (hornfels). An ejecta blanket composed of target rocks covers the floor, outer rim, and the area extending to the immediate northeast and east of the structure. Quaternary aeolian sand covers most of the crater surface, including the 1 to 2 m thick melt-rich polymict breccia found in the crater center. The planar fractures (PFs) and feather features (FFS) in quartz and feldspar suggest a low shock pressure between 5 and 14 GPa. Our observations are consistent with set criterions for impact crater identification, confirming the possible impact origin of the Mahout structure. [ABSTRACT FROM AUTHOR]

Copyright of Sultan Qaboos University Journal for Science is the property of Sultan Qaboos University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study demonstrates the use of ASTER data for the mapping of gypsum deposits and associated geological formations that occurred in the Thumrait region of southern Oman. The measurement of spectra over samples of gypsum in the 1,300–2,500 nm wavelength using a PIMA spectrometer showed the presence of distinct absorptions at 1400–1600, 1750, 1940, 2,100, and 2,400 nm characteristics to OH stretching, H2O combinations, and SO bending overtones and stretching, respectively. Studying the unique spectral absorption characters of gypsum samples, we developed a false color composite (FCC) and an image by decorrelation stretch using the spectral bands 7, 3, and 2 of ASTER. The results FCC showed the regions of gypsum occurrences, and the decorrelated image discriminated the gypsum occurrences from other geological formations of the area. The study of surface mineralogy of the region using the VNIR‐SWIR bands by the spectral angle mapper method showed the presence of sulfate, carbonate, and clay minerals of the geological formations in the study area. We compared the results of ASTER with the results obtained using spectral bands 12, 8, and 4 of Sentinel‐2A processed by the same methods. The study showed that the spectral bands of ASTER can be used for mapping the gypsum and associated geological formations. [ABSTRACT FROM AUTHOR]

Principal Components RGB image (R: PC3, G: PC2 and B: PC1) showing the occurrence of manganese deposits in Ras Al Hadd region, Oman. • This study reviews the capability of ASTER to map mineral resources of the arid region. • It describes spectral absorption characters of minerals. • It discusses suitable ASTER spectral bands and image processing methods to map mineral resources. • It reviews scientific literature published on mapping of the mineral resources of Oman. Advanced Space borne Thermal Emission and Reflection Radiometer (ASTER) has exclusive capability to map minerals and ore deposits, and able to discriminate rock types useful for geological applications. Especially, the improved spectral and spatial resolutions of spectral bands of the sensor are well utilized by the exploration geologists working on arid region where the surface deposits are directly exposed to the sensor without disturbances of the vegetation. Several, fruitful research studies have been carried out to map mineral resources in arid region with inaccessible rugged mountains and deserts area, where it is difficult to do conventional geological mapping. These were demonstrated and documented in the scientific publications using the ASTER spectral bands and image processing methods. This study reviews scientific literatures published on mapping of the economic mineral resources of the Sultanate of Oman using ASTER and simples image processing methods. [ABSTRACT FROM AUTHOR]

In this study, the oxidized and hydrothermally altered zones, including propylitic, argillic and phyllic zones associated with volcanogenic massive sulphide deposits in the Sohar-Shinas region of the Sultanate of Oman are studied based on absorption characters of spectral bands of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). In this work, we have used selected imaging processing methods, including decorrelation stretching, band ratios, linear spectral unmixing (LSU) and Mixture Tuned Matched Filtering (MTMF), as well as petrological and geochemical characteristics of the alteration zones to map and understand the distribution of these alteration zones. Results indicate that 1) the decorrelation of ASTER spectral bands 3, 6, and 8 discriminate extrusive basalts, and the host lithology of altered zones; 2) the application of ASTER band ratios (5/3 + 1/2) (oxidized zone), (4 + 6)/5 (argillic zone) and (5 + 7)/6 (phyllic zone) delineate alteration zones spatially associated with mineralized zones, 3) the utilization of ASTER indices for OH bearing altered minerals (e.g. kaolin and alunite indices) confirmed the presence of alteration minerals in the mineralized zone, 4) alteration end members derived using the spectral angle mapper (SAM) method in combination with linear spectral unmixing (LSU) can be used to map the distribution of the weathering and alteration zones, 5) short wavelength infrared (SWIR) measurements on field samples were used to confirm spectral measurements from ASTER data, and 6) microscopic study and XRD analysis of field samples confirmed the presence of hematite and goethite in the oxidized zone; chlorite, epidote and calcite in the propylitic zone; kaolin and chlorite in the argillic zone; sericite and illite in the phyllic zone, the major minerals responsible to absorptions of ASTER bands 3, 8, 5 and 6 respectively. This study demonstrated the sensor capability of ASTER and the potential use of the image processing methods, and documented the spectral absorptions values of the altered minerals and the field and mineralogical characters of alteration zones of the volcanogenic massive sulphide deposits to map similar deposits elsewhere. [ABSTRACT FROM AUTHOR]

Moho and Moho Transition Zone (MTZ) of the Samail ophiolite of Sultanate of Oman are characteristic to potential occurrences of chromite deposit, hydrothermal mineralization and serpentinization. Mapping of Moho and MTZ, and discriminating them in between the mafic and ultramafic rocks in ophiolite sequence are more significant and important. The present study describes the remote sensing spectral characters of minerals and rocks of the Moho and MTZ and discriminates the Moho of Wadi Al Abyad of Nakhl massif, and Wadi Nidab and Wadi Abda regions of Sumail massif in the visible and near infrared (VNIR), and short wavelength infrared (SWIR) spectral regions using low-cost multispectral satellite data of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Results of this study show that the red–green–blue (RGB) color composite images of ASTER spectral bands 8, 3 and 1, and 8, 7 and 4 are able to delineate the Moho and MTZ of the regions. The RGB images of ASTER band ratios (4/8, 4/1, 3/2 * 4/3 and (1 + 3)/2, (4 + 6)/5, (7 + 9)/8) are capable to discriminate the mantle material (ultramafic harzburgites) and crustal rocks (mafic gabbros). The occurrence of such rock types is demonstrated by detection of their minerals using Spectral Angle Mapper (SAM) image processing method. The presence of Moho and MTZ, and associated lithologies are verified in field at Wadi Al Abyad, Wadi Nidab, Wadi Abda, Wadi Tayin, Wadi Fizh and several locations of Nakhl regions of Samail ophiolites. The laboratory study shows the occurrence of typical minerals namely olivine, orthopyroxene and clinopyroxene in the harzburgite and the minerals such as plagioclase, clinopyroxene, hornblende, orthopyroxene and olivine in the layered gabbro. The spectral properties of the rocks are studied using Portable Infrared Mineral Analyzer (PIMA) spectrometer and the occurrences of minerals are confirmed by X-ray diffraction (XRD) analyses. This study demonstrates the sensor capability of ASTER to map Moho and MTZ, and thus it is recommended to the geoscientists and geophysicists working on Moho and MTZ. The satellite image interpretations of Moho and MTZ, and the associated rocks and minerals are consistent with the field research studies carried out in these regions. Our images have potential to map the chromites mineralized zone and dunites (refractory materials) bearing MTZ. [ABSTRACT FROM AUTHOR]

Abstract: Documentation of chemical weathering and CO2 sequestration in the Samail ophiolite massifs of the Sultanate of Oman represents an important case study for Geological Carbon Capture and Storage System (GCCSS). The present research study demonstrates the capability of remote sensing technique for mapping of weathered zones and potential CO2 sequestration area abundances at different scales within peridotites in the northern mountain region of the Samail ophiolite massifs. The carbonate mineral index (CI) applied with other mineral indices to the TIR wavelength region of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) TIR spectral bands 13 and 14 mapped CO2 sequestered minerals along the structural- and wadi-controlled CO2 flowing regions. Peridotites, the source rocks of CO2 sequestration in the study area, were mapped using an ASTER 8, 3 and 1 band combinations. The decorrelated Landsat TM image discriminated the rock types associated with peridotites of ophiolite sequences and delineated the region of weathered and altered serpentinized peridotites in the zone of CO2 sequestration. CO2 sequestration mapping was carried out using Landsat TM satellite data that span 20years (1986, 1998, 2000, 2003 and 2006) to assess the present status of CO2 sequestration in this region. The image interpretations are verified with existing geological maps and through field and laboratory studies. The spectral measurements of carbonate minerals at 1300 to 2500nm with the spectral resolution of ~7nm using a PIMA SP infrared spectrometer in the field and laboratory show the presence of hydroxyl-bearing minerals and carbonates that have spectral absorption features around 1.4μm, 1.9μm and 2.35μm. The strong absorptions around 2.35μm are mainly due to C O bonds in carbonate minerals such as calcite (CaCO3), dolomite (CaMg(CO3)2), magnesite (MgCO3), aragonite (CaCO3) and siderite (FeCO3), which form 15 to 57%, 12 to 53%, 9 to 38%, 11 to 21% and 3 to 8% respectively in the samples. The absorptions around 1.4μm and 1.9μm are caused by hydration effects of hydroxyl minerals including antigorite and montmorillonite present at 10 to 21% and 37 to 81% respectively in the samples. The alterations of serpentinite are evidenced by the presence of antigorite and lizardite minerals. X-ray powder diffraction analyses further confirms the occurrence of CO2 sequestered major carbonate minerals such as aragonite, calcite and dolomite in the samples. The study demonstrates that the ASTER and Landsat TM satellite multispectral sensors are useful to detect the carbonate minerals, to delineate the peridotites and to discriminate the areal abundance of potential CO2 sequestration. This technique is a useful tool to map and monitor the region of CO2 sequestration in well exposed arid and semi-arid regions and to analyze and understand this aspect of the world geological carbon capture and storage system. [Copyright &y& Elsevier]

Highlights: [•] Spectral sensitivity of carbonate rocks are studied using ASTER satellite data. [•] Satellite image spectra of limestones, listwaenites, marls and carbonatites are studied. [•] Evaluated the study in field and laboratory works. [•] The study proved the remote sensing technique is time and cost-effective. [•] The outcome of the study is useful to geologists and exploration communities. [Copyright &y& Elsevier]

Caves, springs, and large depressions of limestone karst formations are becoming more attractive tourist places and have potential importance on socio-economic development. The present study is a multi-scale point of view on limestone karst, from the space images to microscopic fabric. Here, the karst features consist of limestone formations of Cretaceous (Albian-Cenomanian) age of Tanuf Valley and Tertiary (Late Paleocene-Middle Eocene) age of Sur region of parts of Sultanate of Oman which are mapped in the visible near-infrared and shortwave infrared spectral bands of advanced spaceborne thermal emission and reflection radiometer (ASTER) using decorrelated stretch image processing technique and the occurrences of caves, springs, and depressions of the formations in the field were studied. The decorrelated RGB images of ASTER spectral bands 8, 3, and 1 discriminated well the limestone formations and associated lithology. The limestone formations of Tanuf valley (Natih formations of Hajar unit) are thick-bedded, massive, shallow marine limestone and clayey limestone, which have caves and springs. Large depressions are studied as collapsed structures at the boundary between Abat formations; they consist of gray to white marly or micritic limestone with chert nodules and Seeb Formation of bioclastic limestone, calcarenite, marl, and sandstone of Sur region. Interpretations of limestone formations, their occurrences and distributions of caves, springs and depressions of these regions are verified and confirmed in the field and studied in the laboratory. Occurrences of more springs and depressions in the limestone formations of the study sites are interpreted and located on the Google Earth image. The study proved the capability of ASTER sensor in mapping of limestone formations and recommends the technique to other geographical regions where similar geological questions need to be resolved. [ABSTRACT FROM AUTHOR]

Abstract: Listwaenites are highly altered ultramafic rocks that are potentially associated with economic mineralization and research on these is extremely important worldwide. In the present study, the classification of mineralized listwaenites developed along the serpentinite–amphibolite interface of the Semail Ophiolite, its associated lithology and the zones of alteration and mineralization in the Fanjah Saddle of the Central Oman Mountains region of the Sultanate of Oman are carried out, using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite data. The developed band ratioing, Principal Component Analysis (PCA) and the Spectral Angle Mapper (SAM) supervised classification and image processing techniques applied on the ASTER data set have proved their capability for better interpretation and identification of hydrothermally altered rocks and associated mineralization. The hyperspectral tools (Minimum Noise Fraction (MNF), Pixel Purity Index (PPI) and nD-visualizer) extracted end member spectra and SAM classification clearly show the occurrence of minerals and their spatial distributions. The promising results are verified and confirmed in the field by identification of alteration and mineralization such as listwaenites, silicification, serpentinization and talc alteration and are validated further through laboratory analysis. The confirmation of the occurrence of base metal mineralization along the serpentinite–amphibolite interface in listwaenites suggests that detailed investigation in this and other arid regions which have similar geological conditions may locate mineral deposits. The hyperspectral tools applied on ASTER satellite data show that these can be used as a powerful tool to explore the listwaenites and the potential associated mineralization in other arid geographical regions worldwide. [Copyright &y& Elsevier]

We developed a scientific proposal on spectral absorption in remote sensing and a new image-processing method that is purely based on multispectral satellite image spectra to map ultramafic lamprophyre and carbonatite occurrences. The proposed method provides a simple, yet efficient, tool that will help exploration geologists. In this proposal, in which the spectral absorption is applicable to all satellite images obtained in visible, reflected infrared, and thermal infrared spectral wavelength regions, we found that the carbonatites appear white in colour on a greyscale or RGB thermal infrared image obtained in the thermal infrared wavelength region (3–15 μm) due to molecular emission of thermal energy by such carbonate content, particularly the wavelength recorded by the sensor and that the variation of absorption in spectral bands of an outcrop is due to the differences in percentage of carbonate content or the spectral, spatial, radiometric, or temporal resolution of satellite data or the occurrences of carbonatites to incident energy. The results were confirmed by studying the spectral absorption characteristics of carbonatites in selected world occurrences including parts of Batain Nappe, Oman; Fuerteventura (Canary Islands), Spain; Mount Homa, Kenya; Ol Doinyo Lengai, Tanzania; Mount Weld region, (Laverton), Australia, and Phalaborwa region, South Africa, using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Landsat Thematic Mapper (TM) satellite data. A subsequent study of visible near-infrared (VNIR) and shortwave infrared (SWIR) ASTER spectral bands of Early Cretaceous alkaline ultramafic rocks of Batain Nappe, along the northeastern margin of Oman to map for the occurrences of carbonatite and aillikite (ultramafic lamprophyres) dikes and plugs, showed their detection mainly by the diagnostic CO3absorption (2.31–2.33 μm) in ASTER SWIR band 8. The results of image interpretations were verified and confirmed in the field and were validated through the study of laboratory analyses. A few more carbonatite dike occurrences were interpreted directly over the greyscale image of ASTER bands and true-colour interpretations of a Google Earth image along this margin. The carbonatites and aillikite occurrences of the area are rich in apatite, iron oxide, phlogopite, and REE-rich minerals and warrant new exploration projects. [ABSTRACT FROM PUBLISHER]

This workshop report describes plans for scientific drilling in the Samail ophiolite in Oman in the context of past, current, and future research. Long-standing plans to study formation and evolution of the Samail crust and upper mantle, involving igneous and metamorphic processes at an oceanic spreading center, have been augmented by recent interest in ongoing, low temperature processes. These include alteration and weathering, and the associated sub-surface biosphere supported by chemical potential energy due to disequilibrium between mantle peridotite and water near the surface. This interest is motivated in part by the possibility of geological carbon capture and storage via engineered, accelerated mineral carbonation in Oman. [ABSTRACT FROM AUTHOR]

Abstract: Mafic granulite and spinel lherzolite xenoliths from Cenozoic alkaline basalts near Al-Ashkhara, eastern Oman, have been selected for a systematic mineralogical, geochemical and Sr–Nd–Pb isotopic study. This is the only place in E Arabia where samples of both lower crust and upper mantle can be examined. Lower crustal xenoliths consist of two mineralogically and chemically distinct groups: gabbronorite (subequal abundances of ortho- and clino-pyroxene and plagioclase) and plagioclase pyroxenite (dominant pyroxene and subordinate plagioclase). Temperature estimates for lower crustal xenoliths using the two pyroxene geothermometer (T-Wells) yield 810–865°C. The mineral assemblage (spinel–pyroxene–plagioclase) and Al content in pyroxene indicate that plagioclase-bearing xenoliths equilibrated at 5–8kbar (13 and 30km depth) in the lower crust. εNd and 87Sr/86Sr calculated at 700Ma for Al-Ashkhara lower crustal xenoliths (+6.4 to +6.6; 87Sr/86Sr=0.7028 to 0.7039) are consistent with the interpretation that juvenile, mafic melts were added to the lower crust during Neoproterozoic time and that there was no discernible contribution from pre-Neoproterozoic crust. Upper mantle xenoliths consist of both dry and hydrous (phlogopite-bearing) lherzolites. These peridotites are more Fe-rich than expected for primitive mantle or melt residues and probably formed by pervasive circulation of melts that have refertilized pre-existing mantle peridotites. Mineral equilibration temperatures range from 990 to 1070°C. Isotopic compositions calculated at 700Ma are εNd=+6.8 to +7.8 and 87Sr/86Sr=0.7016 to 0.7025, indicating depleted upper mantle. Pb isotopic compositions indicate that the metasomatism was relatively recent, perhaps related to Paleogene tectonics and basanite igneous activity. Nd model ages for the spinel peridotite xenoliths range between 0.59 and 0.65Ga. The xenolith data suggest that eastern Arabian lower crust is of hotspot origin, in contrast to western Arabian lower crust, which mostly formed at a convergent plate margin. Geochemical and isotopic differences between lower crust and upper mantle indicate that these are unrelated, possibly because delamination replaced the E Arabian mantle root in Neoproterozoic time. [Copyright &y& Elsevier]

Here we report an artiodactyl trackway from Musandam Peninsula, Sultanate of Oman. Epireliefs of the tracks are preserved in poorly consolidated aeolian deposits now making up the ceiling of a coastal cave. As an interesting morphological feature, the trackway documents the trackmaker negotiating a slippery dune slope at an angle. [ABSTRACT FROM PUBLISHER]

One of the major topics of debate in ophiolite geology is the original tectonic setting of ophiolites. New studies show that most ophiolites are formed more frequently in a supra‐subduction zone (SSZ) environment and that only a very small number of ophiolites have formed in an oceanic range (MOR). The Masirah ophiolite is one of the few oceanic ridge ophiolites that have been preserved, and the evidence that was formed in a subduction environment is missing (Moseley and Abbotts 1979, Dilek and Furnes, 2011; Rollinson, 2017). Masirah Island, the Batain and Ras Madrah areas of eastern Oman are almost entirely composed of a well‐developed ophiolite, known as the Masirah ophiolite (Fig. 1), which is, however, completely unrelated to the nearby Semail Ophiolite in the northern Oman Mountains (Fig. 2). The Masirah ophiolite is Jurassic in age and represents oceanic lithosphere derived from the Indian Ocean, but is about 15–20 Myr later than emplacement of mid‐Cretaceous Semail ophiolite in northern Oman. The presence of basaltic to rhyolitic lavas of calc‐alkaline affinity and boninites in the lava sequence of the Semail ophiolite led several researchers to propose a back‐arc basin model for this ophiolite (e.g. Tamura and Arai, 2006; Godard et al., 2008; Rollinson and Adetunji, 2015). The Masirah Ophiolite shows close affinities with MORB peridotites in general. Most of the olivine from the Masirah harzburgites show Fo contents that are similar to those of olivine from MORB. Both pyroxenes in these harzburgites have similar Mg# values, Al2O3 and Cr2O3 contents to those of pyroxenes from MORB peridotites. The observed primitive mantle‐normalized REE patterns showing enrichment in LREEs indicate that the Masirah peridotites have been modified by fluids or melts enriched in LREEs in a MORB environment. Podiform chromitites housed in ophiolites today interpreted as magmatic deposits formed during the reaction of molten rock in environments spike in the middle of the ocean (MOR) or suprasubduccion zone (SSZ) (Arai and Matsukage, 1998; Rollinson and Adetunji, 2015). The Masirah chromitites has a mineral chemistry similar to the mineral chemistry of chromite crystallized from MOR magmas. The Cr# values of chromite in the Masirah chromatite are similar to those of MOR peridotites. These findings suggest that the ultramafic and mafic cumulate rock assemblages overlying the upper mantle peridotites in the Masirah ophiolite represent the products of magma evolution in a MOR initiation stage within the proto Indian Ocean. Coexisting high‐ and low‐Cr# associations of chromitite and dunite have been found in the Semail ophiolite, which illustrates the common situation of ophiolites having both SSZ and MOR geochemical signatures. Cr# varies from 40–60 for shallow chromite bodies, and over the range 70–80 for the deep locations. This diversity of chromitite types suggests two stages of magmatic activity were responsible for the chromitite genesis, in response to a switch of tectonic setting. The first is residual from lower degree, partial melting of peridotite, which produced low‐Cr# chromitites at the Moho transition zone, possibly in a mid‐ocean‐ridge setting. The second chromitite‐forming event involves higher degree partial melting, which produced high‐Cr# discordant chromitite in the upper mantle, possibly in a supra‐subduction zone setting. Assemblages of mono‐ and poly‐phase silicate inclusions (including olivine, orthopyroxene, clinopyroxene, amphibole, phlogopite, serpentine, native Fe, FeO, alloy, sulfide, calcite, laurite, celestine and halite) within chromite have been observed in the low Cr# podiform chromitites from the Semail and Masirah ophiolites. The existence of hydrous silicate inclusions in the chromite calls for a role of hydration during chromite genesis. High‐T bright green hornblende–edenite included in the chromites is evidence of the introduction of water in the magma at the end of the chromite crystallization. Such paragenesis points to the presence of hydrous fluids during the activity of the shear bands. [ABSTRACT FROM AUTHOR]

Masirah Island is almost entirely composed of ophiolite, which is, however, completely unrelated to the nearby Semail Ophiolite of Oman. New studies show that ophiolites form most commonly in a subduction setting and that only few number ophiolites have formed at an ocean ridge. The Masirah ophiolite is one of the few true ocean ridge ophiolites that have been preserved (Moseley and Abbotts 1979; Dilek and Furnes, 2011; Rollinson, 2017) and lacks any indication that it formed in a subduction environment. The Masirah ophiolite is Jurassic in age and comprises two ophiolitic sheets and Mid Cretaceous ophiolitic mélange. The ophiolite is extremely well developed, and as well as the sheeted dykes, there are mantle serpentinites, several varieties of ultramafic to gabbroic cumulates, massive gabbros, pillow lavas, radiolarian chert, limestone and marl (Moseley and Abbotts 1979). The Masirah Ophiolite forms a straight NNESSW trending strip 40 km wide, extending 450 km from Ras Madrakah to the Batain coast. The Batain mélange is composed of several kilometres to a few metres blocks of all the rock types of the ophiolite. The predominant rock within the mélange is altered harzburgite, dunite pods, pyroxenite, with bastite pseudomorphs after orthopyroxene. Several chromitite deposits have been recently discovered in the ophiolite of the Batain mélange at Wadi Musawa, Eastern Oman. This is the first report of podiform chromitite from the Masirah ophiolite. These deposits have been extensively altered and deformed, with the host pyroxenite and dunite. The chromitites occur as separated small concordant, lenticular pods (3–10 m in thickness). The chromitites show mostly disseminated and massive textures. The spinel grains are reddish brown in thin section, and partly to completely altered to black chromite. Most primary silicate minerals are converted to secondary chlorite, serpentinite and pargasite. Olivine and clinopyroxene occurs as inclusions in the spinel grains. The forsterite content of olivine is between 90.0 and 92.0 in harzburgites and dunites. Discriminant geochemical diagrams based on the mineral chemistry of harzburgites indicate a Mid-Ocean-Ridge (MORB) origin. Orthopyroxene and clinopyroxene have moderate CaO, Al2O3 and TiO2 contents, resembling those of moderately depleted abyssal peridotites. Geochemical studies confirm that the Batain chromite is podiform type. Consequently, we propose that the Masirah ophiolite formed in a MORB setting. The chromitite deposits have similar cr# (0.54–0.59), mg# (0.6-0.64), Al2O3 and TiO2 contents to spinels found in MORB and has been interpreted as having formed in amid-ocean ridge setting. It appears that this chromite has been formed through reaction between a mid-ocean-ridge basalt- melt with depleted harzburgite in the uppermost mantle. ReferencesDilek, Y., Furness, H.,(2011): Ophiolite genesis and global tectonics: geochemical and tectonic fingerprinting of ancient oceanic lithosphere. Geological Society of America Bulletin 123, 387-411Rollinson, H. (2017): Masirah - the other Oman ophiolite: A better analogue for mid-ocean ridge processes? Geoscience Frontiers 8, 1253-1262.Moseley, F., Abbotts, I.L., (1979): The ophiolite melange of Masirah, Oman. Journal of the Geological Society of London 136, 713-724. [ABSTRACT FROM AUTHOR]

Abstract: Near the coastal village of As Sifah, NE Oman, eclogite-facies rocks occur in the Saih Hatat window. We investigated a metapelite from this area, which is composed of mm-sized garnet and greenish phengite and minor epidote, blue amphibole, paragonite, albite, quartz, rutile, opaque phases, barite, and carbonate. Garnet exhibits a chemical zonation with Gro17Alm66Pyr6Spe11, Gro22Alm72.5Pyr5Spe0.5, and Gro25Alm65Pyr8Spe2 as inner core, mantle and outermost rim compositions. Inner portions of phengite have Si contents of up to 3.6 per formula unit (pfu), whereas rims are poorer in Si (3.2–3.4 pfu). We constructed a P-T pseudosection in the system Na2O-K2O-CaO-FeO-O2-MnO-MgO-Al2O3-SiO2-TiO2-H2O for the bulk-rock composition of the studied metapelite and contoured it by isopleths of various parameters such as the molar fractions of garnet components. Based on this contouring a P-T path was derived that starts at ultrahigh-pressure conditions. Garnet began to form at 25kbar and 490°C. Subsequently, temperatures increased and pressures decreased to finally reach P-T conditions of 13kbar and 565°C at which low-Si phengite, the outermost rim of garnet, Na-amphibole, epidote, quartz, magnetite, and rutile were in equilibrium. The P-T path is related to events in a subduction channel where the top of subducted oceanic crust, including the studied metasediments, was involved in an upwards-directed mass flow, resulting in the release of about 3wt.% H2O by garnet formation from hydrous minerals such as chlorite and lawsonite. In order to get hints at the interaction of such hydrous fluids, we have analyzed the trace and minor elements in phengite. The contents of B, Rb, Cs, and Tl (20, 397, 6.7 and 1.7ppm, respectively) are nearly constant over the entire Si range of potassic white mica. In contrast, the contents of Ba and Sr increase from 900 and 0.5 to 10500 and 14ppm, respectively, with decreasing Si content in phengite. We hypothesize that this result reflects early leaching of mobile elements during subduction and the later approach of the rock to a barite deposit within a melange ascending in the subduction channel. [Copyright &y& Elsevier]

Abstract: Economically viable chromite deposit occurrences are widespread in the ultramafic rocks of Semail ophiolite massifs of the northern Oman Mountains, particularly in the basal dunite and harzburgite unit of the mantle section. Geological mapping of this region is challenging, primarily due to difficult access, complexity of structures, and lack of resolution and areal integrity of lithological differentiation using conventional mapping techniques. The present research study evaluates the discrimination and occurrence of chromites bearing mineralized zones within ophiolites by analyzing the capabilities of Landsat TM and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite data; using a number of selected methods including decorrelated stretching, different band rationing and Principal Component Analysis image processing techniques exist in the scientific literature. The study results show that the processed VNIR and SWIR spectral wavelength regions are promising in detecting the areas of potential chromite bearing mineralized zones within the ophiolite region, and proved to be successful for mapping of serpentinized harzburgite containing chromites. Exploration geologists, industrialists and mine owners are advised to adopt this technique and avoid the limits in filed data alone for more exploration and exploitation of areas having chromite deposits in arid region elsewhere. [Copyright &y& Elsevier]

Despite significant recent improvements to our understanding of the early evolution of the Order Proboscidea (elephants and their extinct relatives), geographic sampling of the group's Paleogene fossil record remains strongly biased, with the first ~30 million years of proboscidean evolution documented solely in near-coastal deposits of northern Africa. The considerable morphological disparity that is observable among the late Eocene and early Oligocene proboscideans of northern Africa suggests that other, as yet unsampled, parts of Afro-Arabia might have served as important centers for the early diversification of major proboscidean clades. Here we describe the oldest taxonomically diagnostic remains of a fossil proboscidean from the Arabian Peninsula, a partial mandible of Omanitherium dhofarensis (new genus and species), from near the base of the early Oligocene Shizar Member of the Ashawq Formation, in the Dhofar Governorate of the Sultanate of Oman. The molars and premolars of Omanitherium are morphologically intermediate between those of Arcanotherium and Barytherium from northern Africa, but its specialized lower incisors are unlike those of other known Paleogene proboscideans in being greatly enlarged, high-crowned, conical, and tusk-like. Omanitherium is consistently placed close to late Eocene Barytherium in our phylogenetic analyses, and we place the new genus in the Family Barytheriidae. Some features of Omanitherium, such as tusk-like lower second incisors, the possible loss of the lower central incisors, an enlarged anterior mental foramen, and inferred elongate mandibular symphysis and diminutive P(2), suggest a possible phylogenetic link with Deinotheriidae, an extinct family of proboscideans whose origins have long been mysterious.