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The low lying Nal region in western India, linking the Gulf of Kachchh with the Gulf of Khambhat through the Little Rann and Nal Sarovar is barely 15 m above msl and lacks surface exposures. The evolutionary history of the Nal region using remote sensing data and sub-surface lithological correlation indicated that late Quaternary sedimentation in the Nal region was governed by changes in sea level and by tectonism in the region of Cambay Graben. The geomorphic evidence for changes in sea level was found in the form of inland palaeo-deltas and old mud flats. Abrupt changes in lithological data in the vicinity of Nal region pointed to the role of tectonism. Contrary to the earlier view, a shallow sea linked the Gulf of Kachchh to the Gulf of Khambhat only in a time period around Marine Isotope Stage 5. Our studies also suggest that the Nal region itself may not have witnessed any major uplift (beyond 10 m) during late Quaternary. 相似文献
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Surendra P. Verma Sanjeet K. Verma Kailasa Pandarinath Mar��a Abdelaly Rivera-G��mez 《Pure and Applied Geophysics》2011,168(8-9):1501-1525
Discrimination diagrams to decipher tectonic settings have been in use for nearly 40?years. Although old diagrams have been extensively used, the recent ones based on discriminant functions of ratio variables, with or without log-transformation, proposed during 2004?C2010 for the discrimination of four tectonic settings of island arc, continental rift, ocean-island and mid-ocean ridge, were newly evaluated to show their high success rates of 57.3?C100% and 58.5?C100% for major-element and immobile-element based diagrams, respectively. For the continental arc of the Andes evaluated for its similarity to island arc, these four sets of diagrams showed success rates of 62.1?C83.8%. These four sets of five diagrams per set were therefore used to infer tectonic setting of the Mexican Volcanic Belt (MVB), Los Tuxtlas volcanic field (LTVF), and Central American Volcanic Arc (CAVA). Using this approach, the MVB, especially its western, central and eastern parts, and the LTVF of Southern Mexico show a dominantly continental rift setting and the CAVA shows an arc setting. The west-central part of the MVB is consistent with dual tectonics of arc and rift. These results confirm the application of an unusual mantle upwelling rift-model for the Mexican on-land volcanism, whereas the conventional plate tectonic subduction model seems to be applicable for the CAVA from Guatemala to north-western Costa Rica. 相似文献
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Kailasa Pandarinath Rajasekhariah Shankar Ignacio S. Torres-Alvarado Anish Kumar Warrier 《Arabian Journal of Geosciences》2014,7(7):2851-2860
Magnetic susceptibility and petrographic studies of drilled rock cuttings from two geothermal wells (Az-26 and Az-49) of the important electricity-generating geothermal system, Los Azufres, Mexico, were carried out to determine the relation between the magnetic susceptibility of rocks, the concentration of magnetic minerals and hydrothermal alteration. For this purpose, low-frequency magnetic susceptibility (χ lf) was measured and compared its distribution trends with those of magnetic and Fe–Mg silicate minerals, and with the extent of hydrothermal alteration in rocks of the two geothermal wells. The study indicates a decrease in χ lf values with depth in the two geothermal wells corresponding with: (1) an increase in the reservoir temperature and hydrothermal alteration; and (2) a decrease in the concentrations of Fe–Mg silicates and opaque minerals. The data suggest that ferromagnesian minerals and opaque minerals like ilmenite are the main contributors to the χ lf of rocks. The decrease in χ lf, ilmenite, and Fe–Mg mineral contents with an increase in the hydrothermal alteration degree, pyrite and haematite contents suggests the hydrothermal alteration of ilmenite and Fe–Mg minerals (characteristic of high χ lf values) to pyrite, haematite and other opaque minerals (with low χ lf values). The interaction of hydrothermal fluids with rocks results in the hydrothermal alteration of primary minerals. In a geothermal area, an anomaly of low magnetic susceptibility values of rocks in a homogenous litho unit characterized by high magnetic susceptibility may suggest hydrothermal alteration. Magnetic susceptibility can be a useful parameter, during the initial stages of geothermal exploration, in identifying hydrothermally altered rocks and zones of hydrothermal alteration both at the surface and from drilled wells in geothermal systems. 相似文献
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K. Pandarinath Sushma Prasad R. D. Deshpande S. K. Gupta 《Journal of Earth System Science》1999,108(2):107-116
A 54-m long core was raised from the bed of the Nal Sarovar, a large shallow lake located in the middle of the low-lying region
linking the Gulfs of Kachchh and Khambhat, in western India. A three-layer sequence comprising: Zone-1 (top 3 m), predominantly
silty-clay/clayey; Zone-2 (3–18 m), sandy; and Zone-3 (18–54 m), dominated by sticky silty-clay/clayey-silt with occasional
thin sand layers and basalt fragments was identified. Smectite and illite are the dominant clay minerals with minor amounts
of kaolinite and chlorite. Very high content of smectite (53–97%) in the clays of the lowermost zone (18–54 m) and the geomorphic
features of the surrounding region suggested that the sediments were derived from the basaltic terrain of Saurashtra and/or
via the Gulf of Khambhat. The clay content in the middle zone (3–18 m), dominantly sandy, is very low. Therefore, provenance
for this zone was derived using heavy minerals in the sand fraction. The heavy mineral species in this zone suggested the
mixed metamorphic and igneous terrain of Aravallis as the major source. The grain-size distribution of this zone closely matched
with the sediments underlying the modern Sabarmati riverbed at Ahmedabad, suggesting fluvial depositional environment. Clays
also dominate sediments of the topmost (0–3 m) zone with illite as the dominant (74–81%) specie followed by smectite suggesting
derivation from the mixed metamorphic and igneous terrain of Aravallis. 相似文献
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