Structural controls on bedrock weathering in crystalline basement terranes and its implications on groundwater resources

Abstract

Crystalline basement rock aquifers underlie more than 20% of the earth’s surface. However, owing to an inadequate understanding of geological structures, it is challenging to locate the groundwater resources in crystalline hard rock terranes. In these terranes, faults, fractures, and shear zones play an important role in bedrock weathering and ultimately groundwater storage. This study integrates important geological structures with 2D high-resolution subsurface resistivity images in understanding the factors that influenced bedrock weathering and groundwater. The results reveal the variability of weathered zone depth in different structural zones (Zone-I to Zone-IV). This is due to the presence of foliations, fractures, and faults. A thicker weathered zone develops when a fracture/fault overprints a pre-existing planar pervasive structure like foliations (Zone-II) as compared to zones only with faults/fractures (Zone-III). Further, the transmissivity of boreholes also shows relatively higher in Zone-II than Zone-III, which implies a good pact between different structural features and possible groundwater storage. The study also demonstrates the role of paleostress and different tectonic structures influencing the depth of the “Critical Zone”. While the geology may vary for different structural terranes, the approach presented in this paper can be readily adopted in mapping bedrock weathering and groundwater resources in crystalline basement terranes globally.

Transgressive rocky coasts in the geological record: Preserved or eroded? Insights from Miocene granitic rocky shorelines and modern examples.

“…The effect of chemical and physical weathering on producing rounded granite boulders is well documented by several authors (Ollier, 1971;Durgin, 1977;Vasile and Vespremeanu-Stroe, 2016;Twidale and Vidal-Romaní, 2020). These weathering products tend to concentrate forming rather flat profiles in homogeneous and non-faulted terrains or they can be distributed forming highly asymmetric and irregular profiles in heterogeneous and structurally complex basements (Pradhan et al, 2022). The presence of faults and fractures in granitic and crystalline basements has a direct influence on the development of deep weathering profiles, as documented in the granitic and low-grade metamorphic terrains of the Aravalli-Delhi Mobile belt in NW India (Pradhan et al, 2022) and the sub-Cretaceous inclined peneplain of the South Swedish Dome, in Sweden (Lidmar-Bergström et al, 2017).…”

“…These weathering products tend to concentrate forming rather flat profiles in homogeneous and non-faulted terrains or they can be distributed forming highly asymmetric and irregular profiles in heterogeneous and structurally complex basements (Pradhan et al, 2022). The presence of faults and fractures in granitic and crystalline basements has a direct influence on the development of deep weathering profiles, as documented in the granitic and low-grade metamorphic terrains of the Aravalli-Delhi Mobile belt in NW India (Pradhan et al, 2022) and the sub-Cretaceous inclined peneplain of the South Swedish Dome, in Sweden (Lidmar-Bergström et al, 2017). The weathering profiles there are highly irregular and show deeply incised weathered basement zones, 10's up to 100 meters deep, which developed preferentially through fractures and faults.…”

Assessing regional variation in yield from weathered basement aquifers in West Africa and modelling their future groundwater development and sustainability

“…These lithologies and the associated weathered basement aquifers are expected to have different hydrogeological properties. In particular, Archean and Phanerozoic rocks, which are related to the development of major cratons and typically comprise massive granite and orthogneiss, tend to have low primary intergranular porosity and conductivity, but they can be associated with relatively productive weathered basement aquifers having a well-developed and relatively highly transmissive fracture zone (Lachassagne et al 2021;Pradhan et al 2022). In contrast, Proterozoic metamorphic rocks, related to collisional and extensional tectonic events of the older cratons that are heavily sheared and schistose, are likely to have a higher intergranular porosity, but the productivity of the associated weathered basement aquifers depends on the dip of the foliation, with more favourable conditions when it is near vertical (Lachassagne et al 2021).…”

Elements of Metamorphic Rocks (Marble and Quartzite) of Bukit Cinta Gunung Gajah, Klaten

“…Metamorphic rocks control groundwater, in that lithological aspects control groundwater distribution (Coyte & Vengosh, 2020;Pradhan et al, 2022). Metamorphic rocks do not have pores but have cavities or fractures to be filled with water so that they can store water.…”