Geoquímica fluvial e balanço de denudação em Tinguaítos de Poços de Caldas, Minas Gerais

The Ariranha Stream basin, Pocos de Caldas Volcanic Caldera, Brazil, is formed by tinguaite alkaline rocks (intrusive phonolites). There are not studies on relief evolution in regions with this type of rock, so the present work aimed to evaluate the denudate balance in this hydrographic basin. For this purpose, the following parameters were collected and evaluated during one hydrological year: flow rate (m 3 /s), precipitation (mm), pH, electrical conductivity (μS/cm), dissolved oxygen (mg/L), total dissolved and suspended solids (mg/L). Flow rate and temperature averages were 0.12 m 3 /s and 20.80oC, respectively. The pH values were close to neutrality (6.4); the electrical conductivity varied from 30 to 78 μS/cm; and the dissolved oxygen concentrations from 5.4 to 7.9 mg/L. The total of 15.5 t/km 2 /year of dissolved material were transported by surface waters, and the atmospheric input was of 6.0 t/km 2 /year, obtaining an annual removed material by the tinguaite alkaline rocks chemical alteration of 9.5 t/km 2 /year with weathering rate of 3.6 m/Myr. Regarding the suspended material, approximately 9.9 t/km 2 /year were transported by drainage, with an atmospheric input of 1.2 t/km 2 /year. It indicates annual flow of 8.7 t/km 2 of removed material associated with the basin soils denudation, or approximately 200 thousand years to change 1 soil meter in the current climatic conditions.