@article{DupasMusolffJawitzetal.2017, author = {Dupas, R. and Musolff, A. and Jawitz, J. W. and Rao, P. S. C. and J{\"a}ger, Christoph G. and Fleckenstein, J. H. and Rode, M. and Borchardt, D.}, title = {Carbon and nutrient export regimes from headwater catchments to downstream reaches}, series = {Biogeosciences}, volume = {14}, journal = {Biogeosciences}, number = {18}, pages = {4391 -- 4407}, year = {2017}, abstract = {Excessive amounts of nutrients and dissolved organic matter in freshwater bodies affect aquatic ecosystems. In this study, the spatial and temporal variability in nitrate (NO3-), dissolved organic carbon (DOC) and soluble reactive phosphorus (SRP) was analyzed in the Selke (Germany) river continuum from three headwaters draining 1-3 km2 catchments to two downstream reaches representing spatially integrated signals from 184-456 km2 catchments. Three headwater catchments were selected as archetypes of the main landscape units (land use  ×  lithology) present in the Selke catchment. Export regimes in headwater catchments were interpreted in terms of NO3-, DOC and SRP land-to-stream transfer processes. Headwater signals were subtracted from downstream signals, with the differences interpreted in terms of in-stream processes and contributions from point sources. The seasonal dynamics for NO3- were opposite those of DOC and SRP in all three headwater catchments, and spatial differences also showed NO3- contrasting with DOC and SRP. These dynamics were interpreted as the result of the interplay of hydrological and biogeochemical processes, for which riparian zones were hypothesized to play a determining role. In the two downstream reaches, NO3- was transported almost conservatively, whereas DOC was consumed and produced in the upper and lower river sections, respectively. The natural export regime of SRP in the three headwater catchments mimicked a point-source signal (high SRP during summer low flow), which may lead to overestimation of domestic contributions in the downstream reaches. Monitoring the river continuum from headwaters to downstream reaches proved effective to jointly investigate land-to-stream and in-stream transport, and transformation processes.}, language = {en} } @article{RosiereSantosSilveiraBragaetal.2021, author = {Rosi{\`e}re, C. A. and Santos, J. O. S. and Silveira Braga, F. and Hensler, Ana-Sophie and Rolim, V. K. and Bekker, A.}, title = {Multiple Hydrothermal Iron-Formation Upgrading Events in Southeastern S{\~a}o Francisco Craton}, series = {The Journal of Geology}, volume = {129}, journal = {The Journal of Geology}, number = {3}, publisher = {The University of Chicago Press}, address = {Chicago}, doi = {10.1086/715242}, pages = {283 -- 296}, year = {2021}, abstract = {Large-scale, hypogene iron mineralization systems developed recurrently in the S{\~a}o Francisco craton in association with two orogenies. During the ca. 2.1-2.0 Ga Trans-Amazonian orogeny, low-temperature and low-to-moderate-salinity metamorphic fluids resulted in carbonatization-related iron enrichment of the early Paleoproterozoic Cau{\^e} Iron Formation (IF) of the Minas Supergroup (MSG) as well as short-distance iron mobilization. Monazite from the iron-oxide veins yielded a SHRIMP 232Th/208Pb date corresponding to fluid circulation coeval with the migmatization of the Archean tonalite-trondhjemite-granodiorite crust. During the Ediacaran to Cambrian Brasiliano orogeny, when the S{\~a}o Francisco craton was consolidated in its present configuration, hydrothermal fluids repeatedly mineralized the Cau{\^e} IF and the younger IFs of the lower Espinha{\c{c}}o Supergroup. Far-field hydrothermal alteration associated with distinct Fe mineralization episodes widely affected Meso- to Neoproterozoic sequences as well as Archean to Paleoproterozoic terranes of the cratonic core. Circulation of hydrothermal fluids during the Brasiliano orogeny caused desilicification, iron mobilization, and widespread alteration of the rocks. The alteration events are dated with monazite and xenotime intergrown with hematite, anatase, and recrystallized rims of detrital zircons from interlayered quartzites and of igneous zircons from pegmatites, granites, acidic volcanic rocks, and orthogneisses, yielding U-Pb dates between 542 and 493 Ma. U-Pb dates point to five Cambrian hydrothermal events from the waning stages to the aftermath of the Brasiliano orogeny. These hydrothermal fluid circulation events correspond to the emplacement ages of four granite suites and pegmatites that lasted from the final stages of the collision to the collapse of the Ara{\c{c}}ua{\´i}-West Congo orogen. Episodic circulation of fluids continued for approximately 2 billion years after IF deposition on the eastern S{\~a}o Francisco craton with the formation of high-grade iron ore deposits and resetting of the IF trace-element inventory.}, language = {en} }