ASTER spectral sensitivity of carbonate rocks – Study in Sultanate of Oman

Remote sensing satellite data plays a vital role and capable in detecting minerals and discriminating rock types for explorations of mineral resources and geological studies. Study of spectral absorption characters of remotely sensed data are under consideration by the exploration and mining companies, and demonstrating the spectral absorption characters of carbonates on the cost-effective multispectral image (rather than the hyperspectral, Lidar image) for easy understanding of all geologists and exploration communities of carbonates is very much important. The present work is an integrated study and an outcome of recently published works on the economic important carbonate rocks, includes limestone, marl, listwaenites and carbonatites occurred in parts of the Sultanate of Oman. It demonstrates the spectral sensitivity of such rocks for simple interpretation over satellite data and describes and distinguishes them based on the absorptions of carbonate minerals in the spectral bands of advanced spaceborne thermal emission and reflection radiometer (ASTER) for mapping and exploration studies. The study results that the ASTER spectral band 8 discriminates the carbonate rocks due to the presence of predominantly occurred carbonate minerals; the ASTER band 5 distinguishes the limestones and marls (more hydroxyl clay minerals) from listwaenite (hydrothermally altered rock) due to the presence of altered minerals and the ASTER band 4 detects carbonatites (ultramafic intrusive alkaline rocks) which contain relatively more silicates. The study on the intensity of the total absorptions against the reflections of these rocks shows that the limestones and marls have low intensity in absorptions (and high reflection values) due to the presence of carbonate minerals (calcite and dolomite) occurred in different proportions. The listwaenites and carbonatites have high intensity of absorptions (low reflection values) due to the occurrence of Mn-oxide in listwaenites and carbonates in carbonatites apart the influence of major carbonate minerals that occurred predominantly in these rocks. The study of ASTER thermal infrared (TIR) spectral bands distinguished the marls have low emissivity of energy due to the presence of hydroxyl bearing alumina-silicate minerals from the other rocks such as limestones, listwaenites and carbonatites which have high emissivity due to the absence of hydroxyl bearing alumina-silicate minerals and the presence of carbonate minerals and carbonates.     

Titanium estimates of the central peaks of lunar craters: Implications for sub-surface lithology of moon

Central peaks of 24 lunar craters, having mafic rocks, were studied to estimate their average titanium content and infer the nature of the subsurface lithologies. Titanium contents were derived from Clementine UV–Vis data (415, 750 nm) following the approach of Lucey et al. [Lucey, P.G., Blewett, D.T. and Jolliff, B.L., Lunar iron and titanium abundance algorithms based on final processing of Clementine ultraviolet–visible images, J. Geophys. Res.106 (E8), 20297–20,305, 2000]. _TiO2${\mathrm{TiO}}_2$ content exceeding 1 wt% suggests presence of mantle derived mafic sub-surface rock types (plutonic/volcanic) within the central peaks. Even though, the algorithm used for deriving titanium content is susceptible to variation in topography and sun angle, especially at higher latitudes, careful selection and analyses of data for regions within the central peaks revealed compositional heterogeneities. The results indicate a preponderance of mafic lithologies with low _TiO2${\mathrm{TiO}}_2$ content (<1 wt%) in the central peaks of lunar craters populating the equatorial region. Average titanium content of central peaks can serve as a useful tracer for distinguishing mantle derived mafic subsurface lithologies from those formed during global magma ocean episode.     

月面克里普岩成分特征及REE等资源开发利用前景

克里普岩(KREEP)最早发现于Apollo-12样品，后来在所有返月样品中都发现3克里普岩碎片，尤其以Apolio-12和Apolio-14着陆点样品中最多，因其富含元素K1REE和P而被称之为KREEP．克里普岩在月面上的分布极为重要，不但因其对月壳形成期间及形成以后的月球的演化具有重要的意义，而且由于克里普岩中富含REE等重要资源性元素，被认为可能是除钛铁矿外最重要的月球矿产资源储存库．本文在综合已有探测资料和研究成果的基础上，通过克里普岩的化学成分与矿物组成特征，Th在风暴洋区丰度的异常特征，以及克里普岩中Th与REE相关关系的分析，探讨了KREEP岩石在月面上的分布区域，进而对月球REE资源的开发利用前景进行了初步评估．