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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]

Economically viable limestone deposits are mostly formed by calcite minerals, and these minerals are widely used in manufacturing of cement, mortar, fertilizer and flux for smelting of iron ores, and mapping of such deposits is significant and important in scientific research. This study examines the capability of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) with the wavelength range visible–near-infrared and short-wave infrared spectral bands to map such limestone carbonate deposits and associated lithounits occurred in and around of Chikkanayakanahalli, southern part of the Chitradurga schist belt using minimum noise fraction (MNF) and decorrelation stretching methods. The study results that (1) the RGB image of MNF (R: B1; G: B2; B: B3) of ASTER is capable of discriminating the limestones and associated different rock types, namely banded magnetite quartzites (BMQ), graywackes, Mn- and Fe-rich cherts, metabasalts, granitic gneisses, granitoids and migmatites and (2) the decorrelation stretch image of ASTER bands 8, 3, 1 of the ASTER delineated clearly the limestones and associated rocks of the study area. Study of spectral signatures of field samples of such economic limestones in the wavelength of 350–2500 nm using Fieldspec3 Spectroradiometer showed the spectral absorption near 2.32 μm due to the presence of calcite minerals in the rocks. The results of study are cross-verified in the study area and confirmed through petrological and chemical analyses of the samples. This study bespeaks the potential of ASTER sensor and application of image processing methods to map the economic limestone deposits and associated rocks of the study area. [ABSTRACT FROM AUTHOR]