NW-SE Lineaments Research Articles

Hydrogeochemistry as an aid to geological interpretation: the Glen Roy area, Scotland

The hydrochemistry of first and second order streams, sampled at a density of 1 km 2 , has been used to investigate ways of enhancing information obtained during regional geological mapping. The Glen Roy area of Scotland is a pristine area with large variations in bedrock geology, ranging from Dalradian metasediments (including carbonates), to granite, granodiorite and appinite rocks (coarse-grained lamprophyre) but with relatively minor drift. Alkalinity (HCO 3 ,) is used to determine the extent of water-rock interaction with both silicate and carbonate rocks. The ratio Na/Cl is also used to measure the extent of silicate reaction: dolomitic facies are picked out in areas with carbonate by Mg. Mn, Fe and Y are useful indicators of the weathering of biotite and garnet. A strong and well defined hydrogeochemical anomaly of Ba, Sr and K outline the outcrops of the appinites. Together with HCO 3 , these three elements define an extended NW–SE lineament (Strath Ossian Lineament) which includes possible concealed areas of appinite, the bicarbonate probably reflecting the presence of a carbonate aureole derived from mantle CO 2 . In particular the bedrock characteristics in poorly exposed ground can be inferred and information obtained on the volume of bedrock through which the water has passed.

The shallow structure of Los Humeros and Las Derrumbadas geothermal fields, Mexico

Los Humeros caldera and Las Derrumbadas rhyolitic domes located in the State of Puebla (Mexico) are being extensively studied by Comisión Federal de Electricidad (CFE) to assess the geothermal potential of that area. Both geothermal sites have been locally studied with geological, geochemical and geophysical methods. In order to get a geological picture of the sub-surface of the area comprising both sites, a regional structural survey was conducted together with gravity and magnetics studies. These studies showed a regional weakness zone (the Libres-Oriental depression), where the volcanic activity related to the geothermal manifestations took place. The tectonic events in the area are represented by two systems of structures. The first one (N140°–N170°) gave rise to the folds and overthrusts affecting the sequence of calcareous rocks resting upon the basement. This system is affected by a second system (N40°–70°E). Regionally these tectonic events remodelled the sedimentary sequence giving rise to a series of topographic highs that constitute the core of several ranges, and to depressions that were filled with volcano-sediments during the ensuing volcanic activity. The rhyolitic domes of Las Derrumbadas are emplaced in a regional NW-SE lineament, which reflects clearly on the Bouguer anomaly, and is interpreted as a front of overthrust affecting the marine sedimentary sequence. Estimations of depths to the basement, based on magnetic data, showed that the basement under Los Humeros caldera is shallower than in Las Derrumbadas. The gravity data were interpreted in terms of tabular bodies associated to calcareous rocks, of igneous intrusions, and of depressions filled with volcano-sediments. A joint interpretation of the geological and geophysical data led to a model of the structure of the shallow crust in the area.

Lineament analysis of Cannanore district and their implication on the tectonic evolution of the area

The Cannanore district and the adjoining areas mainly comprise of charnokites, gniesses, high and low-grade schists and various types of igneous intrusives. The lineament fabric of the region indicates that the NNW-SSE, NW-SE, ENE-WSW and NE-SW lineament directions are prominent. It is suggested that the area has undergone at least three distinct phases of tectonic activity. The NW-SE and ENE-WSW lineaments appear to have formed during the phase of NW-SE folding. The NE-SW lineaments may be the result of the cross-folding of the earlier folds. The NNW-SSE lineaments have been related to the Precambrian tectonic activity in South India.

Geological and geomorphological significance of a few mega-lineaments of Northeastern Rajasthan

The Precambrian metamorphites of Northeastern Rajasthan belonging to Pre-Aravalli, Aravalli and Delhi Supergroups exhibit a mature topography where the physiography has faithfully depicted the major structures of area. Few important megalineaments demarcated on the imagery either represent major fault zones or the zones of intense granitic activity. Some of these are oblique to the regional strike of rocks and support drainage running in diagonally opposite direction within the same lineament, indicating thereby upheavels subsequent to the lineament formation. The lineaments fall broadly in two sets which are correlatable to the two major phases of Delhi orogeny. The lineaments of the first set trend NE-SW and are more prominent: than the NW-SE and WNW-ESE running lineaments. The major lineaments such as Sabi-Sota, Mendha and Kakor-Lalsot lineament together with other regional lineaments depict appreciable geomorphological expressions and significant geological evidences.

Geological interpretation of Landsat imageries across Central Nigeria

Investigation of Landsat imageries across Central Nigeria was carried out on a scale of 1:500,000. The multispectral imagery as well as Bands 7 and 4 imageries were combined to provide the basis for meaningful geological interpretation. Results obtained from the analysis include the following: (i) identification of major rock boundaries; (ii) identification of regional structural trends; (iii) identification of different landform patterns; (iv) identification of different landcover and (v) identification of the major drainage patterns. Supplementary remotely sensed data used in conjunction with Landsat imagery to aid geological interpretation include low-altitude aerial photos and topographic maps on a scale of 1:50,000. Recommendations for effective landuse of the areas investigated are provided. Some results from this study have regional geodynamic implications. These include the observation of linear faults on both sides of the Niger and Benue valleys. The NW-SE trending faults bordering the Niger valley suggest a rift origin similar to that of the Benue Trough. Curvelinear structures representing ring intrusions have been identified in areas where they were not known to exist. The geographical extent of the Younger Granite Ring Complex Province around the Jos plateau may be greater than normally envisaged. Three major lineament trends predominate on all the imageries studied. These are NE-SW, NW-SE and N-S. The NE-SW and NW-SE lineaments truncate the N-S trending ones and are therefore younger in age. This tends to suggest that the NE-SW and NW-SE trending lineaments are related to the Kibarian and Pan-African orogenies (younger than 800 Ma). The N-S trending lineaments, on the other hand, are much older and are probably or possibly related to the Liberian orogeny (over 2500 Ma) and Eburnian orogeny (over 1800 Ma). The effects of structures within the basement are evident in the overlying sedimentary cover. L’étude des images Landsat à travers le Nigeria Central a été réalisée à l’échelle du 1/500000. Les images multispectrales et les images provenant des canaux 7 et 4 ont été combinées afin de fournir la base d’une interprétation géologique significative. Les résultats de cette analyse sont les suivants: (i) identification des principales limites lithologiques; (ii) identification des directions structurales régionales; (iii) identification des différents types morphologiques de terrain; (iv) identification des différentes forms de la couverture des terrains et (v) identification du réseau hydrographique majeur. Des données supplémentaires acquise par télédétection ont été combinées avec des images landsat afin de parvenir à obtenir une meilleure interprétation géologique incluant des photographies aériennes et des cartes topographiques à l’échelle du 1/50 000. Des recommandations en vue de l’utilisation effective des terrains étudiés ont été faites. Certains résultats de cette étude one une signification géodynamique régionale. Cela comprend l’observation de failles linéaires sur les deux rives du Niger et la vallée de la Bénoué. Les failles de direction NW-SE qui limitent la vallée du Niger suggèrent que des rifts sont à l’origine de sa formation, similaire à celle de la fosse de la Bénoué. Des structures circulaires représentant des intrusions annulaires ont été identifiées dans des régions où elles étaient considérées comme inexistantes. L’extension géographique de la province des ‘Younger Granite’ et des complexes annulaires autour du Plateau de Jos pourrait étre plus grande qu’on ne l’envisage normalement. Trois directions linéamentaires majeures ont prédominé dans l’observation des images. Ce sont les linéaments NE-SW, NW-SE et NS. Les linéaments NE-SW et NW-SE recoupent la direction NS et sont ainsi plus jeunes. Cela tend à suggérer que les directions linéamentaires NE-SW et NW-SE seraient liées aux orogénies Kibariennes et Panafricaines (moins de 800 Ma) et les linéaments N-S aux l’orogénies Libérienne (plus de 2500 Ma) et Eburnéenne (plus de 1800 Ma). Les effets des structures localisées dans le socle sont évidents dans la couverture sédimentaire qui la recouvre.