Mapping of ferric (Fe3+) and ferrous (Fe2+) iron oxides distribution using band ratio techniques with ASTER data and geochemistry of Kanjamalai and Godumalai, Tamil Nadu, south India

The iron ores found in Tamil Nadu State, South India, are major varieties that have been confined with banded magnetite quartzite. The occurrence, distribution, and grade of these deposits significantly vary according to their geological structure and geomorphologic control. In this article, presents a novel approach, based on spectral remote sensing and digital processing of ASTER data, to identify and characterize the iron ores of Kanjamalai and Godumalai areas located in Tamil Nadu, India. By analyzing the ASTER images, the abundance of iron oxides including ferric (Fe3+) and ferrous (Fe2+) components was determined. The band ratioing technique, a multiband analysis was used to generate the abundance of iron oxide content in various parts of the study area using different band combinations such as band 2/band 1 (for Fe3+) and band 5/band 3 + band 1/band 2 (for Fe2+). The geochemical analysis is an important part of this work to arrive with the outcome of band ratio techniques to decipher the relationship of the band ratio to the chemical composition of the ore samples. Accordingly, the correlation between the results of the geochemical analysis of the samples collected from the random locations was determined by Pearson's coefficient of correlation (ρ) and compared with the corresponding locations in the abundance image. In addition to ρ, various factors such as mean (μ), variance (σ2) and corresponding standard deviations (σ) were also analyzed for a comparative analysis. This comparative analysis indicated that most of the samples have considerably high iron oxide content in the locations. Thus, this study shows the possibility of detecting iron oxide content and its spatial distribution by using ASTER satellite images analysis. Hence, from the mapping results, it is evident that the band ratio technique of ASTER images can be used to map and characterize with limited fieldwork and geochemistr

Early Mesozoic stratigraphy, sedimentology and structure of the

The Gharian area is used as a case study to examine the sedimentary succession, structural evolution and timing of sedimentary and structural events during basin development in the Early Mesozoic. These sediments (Kurrush, Al Aziza and Abu Shaybah Formations) are examined in order to provide palaeonvironmental and palaeogeographic reconstructions for the study area. The formations are described using facies analysis. The Kurrush is probably deposited in delta plain environment. A complete section (140 m) has been logged and seven facies from the Al Aziza Formation represent a shallow shelf platform area (inner ramp: an intertidal-subtidal carbonate flat to shelf lagoonal environment), which was deposited during the opening of the Early Triassic Neo-Tethys Ocean. Eleven localities from the Abu Shaybah Formation have been investigated with a cumulative thickness of 125 m. Ten facies from the Abu Shaybah Formation represent deposition in a shallow marine environment as part of low gradient continental margin, succeeded by sand deposition in braided and meandering fluvial systems. Regional tectonic activity, regional relative sea-level fluctuations and climatic conditions led to control of the sedimentary megasequences (266 m coarsening upward and fining upward megasequence). A magnetostratigraphic analysis was undertaken in the above units as their depositional age is poorly constrained and currently based on limited fossil evidence. Most of these samples convey a weak but stable remanent magnetization. The Al Aziza Formation yielded a primary remanence that has suffered a substantial post-acquisition clockwise rotation (~50˚). Restoration of the rotation about a simple vertical axis would place the pole on the APW path at an appropriate point in time. The palaeomagnetic data from the studied formations yield a distinct series of polarity zones that provide clear local and regional correlation and are readily tied to a recently compiled global magnetostratigraphic time scale. The Al Aziza Formation at Gharian is latest Ladinian in age, whilst the Abu Shaybah Formation is earliest Carnian in age. The Abu Shaybah Formation at Gharian suggests that the stratigraphic equivalence with the Aziza Formation at Azizyah and Kaf Bates (Jafarah Plain). The study established that the Gharian area is the expression of major normal faults (NNE-SSW, WNW to ESE, NW to NNW and NE-SE) in a system of half-grabens which formed as part of the African extensional margin on the southern Tethyan margin in Latest Early Cretaceous.Libyan Governmen

Composition and age of Cenozoic volcanism in Libya

Libya has five major Cenozoic volcanic provinces (Garian, Jabal Al Haruj al Aswad, Jabal Al Hasawinah, Jabal as Sawda and Jabal Nuqay) that have a surface area of approximately 66,000 km2. These volcanic provinces are dominated by alkali to mildly alkali basalts. The provinces are aligned NNW-SSE, typically occurring where NE-SW trending structural features intersect the main regional uplift structures. Small volumes of phonolites are associated with the basaltic volcanism at Garian and Jabal Al Hasawinah. Despite their size and relative accessibility the Cenozoic volcanic provinces of Libya have been rarely studied. In the first part of this thesis I report a new study of the petrology, geochemistry (major and trace elements, REE, Sr-Nd isotopes) and geochronology (40Ar/39Ar) of basalts and phonolites from the Garian volcanic province in north Libya. These analyses indicate that the plateau and late basalts are not distinct basalt types produced from melting of different mantle regions at different times as proposed by earlier studies. They are the product of fractional crystallisation of a common parent. There is little indication of crustal contamination. Trace element and REE data support an origin in 2 to 12 % melts of heterogeneous sub-lithosphere mantle. Trace elements and Nd and Sr isotopic composition of the Garian basalts overlap values measured in metasomatised peridotite xenoliths in the GVP. They are compositionally similar to Cenozoic volcanism of northern Libya (e.g. Jabal Al Haruj) and southern Italy (e.g. Etna and Pantelleria; European asthenosphere mantle reservoir), and they lack the influence of enriched mantle present in other North African Cenozoic basalt provinces. Compositional variation in the Garian province phonolitic magmas is dominated by extensive fractional crystallisation (50-83%) of plagioclase and alkali feldspars combined with an unusual style of assimilation (2-45%) of old upper crust typical of Pan-African shield. The new high precision age determinations of the phonolites suggest that they were produced over a very short period at ~8.1 Ma. This contrasts strongly with previous age determinations that were 40-50 Ma. In the second half of the thesis I report new Ar/Ar chronology measurements for extrusive and intrusive rocks all the major Cenozoic volcanic fields in Libya. The major pulse of basaltic volcanism in Garian in the north (from 6 to 2 Ma) overlaps in time in Jabal Al Haruj province in southern Libya. Jabal Al Hasawinah and Jabal as Sawda basalts were erupted significantly earlier (23-10 Ma). Dykes and plugs at all provinces imply basaltic volcanism started in Miocene, followed by periods of erosion. There is no systematic trend of time in Cenozoic basaltic volcanism of Libya. It appears to be related to reactivation of ancient structures during the passive rifting that has been produced in response to interaction of African and European plates since the late Mesozoic