Geophysical investigation of the Colônia structure,Brazil

The origin of the nearly circular Colônia structure, located at the southwestern edge of the city of São Paulo, Brazil, has been the subject of a long‐standing debate, ever since the 1960s when the structure was first investigated by geophysical methods. The structure still raises interest for geological research, as its sedimentary infill holds important paleoclimatic information about the evolution of the tropical rainforest, as well as the interplay between the South American summer monsoon, the Intertropical Convergence Zone, and the southern Westerly wind belt—for possibly as long as several million years. In addition, the search for evidence to conclusively establish the origin of this structure continues, and the answer most likely lies in the lower portions of the basin's sedimentary infill, which also holds a significant potential for underground water resources. Here, we present the results from recent seismic (reflection and HVSR), gravimetric, and geoelectrical surveys. They have provided a reliable image of the sedimentary infill, and the maximum depth to basement within the structure has been constrained consistently by the different methods to approximately ?400 m. The geophysical data have also allowed to map the lateral contact between the crystalline basement rocks and the sedimentary infill, which indicates a diameter of approximately 2.8 km for the sedimentary basin, with 3.6 km being the diameter of the outermost limit of the structure. A total of six seismic stratigraphic boundaries were identified within the sedimentary infill, providing a framework for the planning of a deep drilling campaign and subsequent sampling program aimed at geological and paleoclimatology studies.     

Hypotheses concerning a regmagenic network controlling metallogenic and other geologic events in the South American Austral Cone

The statistical processing of megafractures and lineaments of the Argentinean, Chilean and Uruguayan territories, and the determination of the structurogenetic orientations of more than fifty phylohydrothermal mineral deposits has led to the development of a hypothesis of the existence of two planetary fracture network systems in the South American Austral Cone.An orthogonal netting, referred to as the »Gondwana Region Network«, with a N60W-N30E trend and a 25 km basic equidistance, belonging to a major net system of 200 km on a side, is located approximately north of 39 south latitude. Another orthogonal netting, referred to as the »Patagonian Region Network«, is located south of the Gondwana Region Network. The Patagonian Region Network has a N35W-N55E, trend with an equidistance of 35 km, and is located in a major net of 140 km on a side.A statistical review of 371 ore deposits in the Gondwana Region, primarily those of copper, gold, lead and zinc, lead to the inference that the Large Ore Deposits (such as Chuquicamata, Salvador, Potrerillos, Agua de Dionosio, Famatina, Pachon-Pelambre, Disputada and Teniente) are situated near networks of 100 and 200 km on a side. Also, the 83 Outstanding Ore Deposits are clearly controlled by the key equidistance of 25 km and the Minor Ore Deposits are not dependent on the regmagenic network and are therefore randomly distributed.Fifty-four mineral deposits have been processed in the Patagonian Region to date, with four Outstanding Ore Deposits distributed with a portion of the Minor Ore Deposits in a net system of between 70 and 140 km on a side. However, the Minor Ore Deposits are more closely associated with a key alternation of 35 km.Sixty percent of the pre-Mesozoic granitiod bodies are also controlled by supraregional fracture networks which will be discussed in this paper.

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Zusammenfassung Die statistische Auswertung von Gro\brüchen und Lineamenten in Argentinien, Chile und Uruguay und die Bestimmung der strukturgenetischen Orientierung von mehr als 50 hydrothermalen Minerallagerstätten hat zur Entwicklung einer Hypothese über die Existenz zweier gro\räumiger Bruchsysteme im südlichen Südamerika geführt.Ein rechtwinkliges Netz mit einem Gitterabstand von 25 km und N60W-N30E Streichen befindet sich innerhalb eines Gro\systemes von ca. 200 km Seitenlänge, nördlich von ungefähr 39 südlicher Länge. Es wird hier als »Gondwana Region Network« bezeichnet.Ein anderes, südlich des ersteren gelegenes, wird »Patagonien Region Network« genannt. Es ist ebenso rechtwinklig, streicht aber N35W-N55E, mit Gitterabständen von 35 km innerhalb eines Gro\netzes von ca. 140 km Gittergrö\e.Die statistische Betrachtung von 371 Erzlagerstätten, besonders Kupfer, Gold, Blei und Zink, der Gondwana Region zeigt deren Beziehung zu den Netzsystemen: Die gro\en Erzlagerstätten, z.B. Chuquicamata, Salvador, Potrerillos, Agua de Dionisio, Famatina, Pachon-Pelambre, Disputada und Teniente, befinden sich in den gro\en Bruchsystemen mit 100 und 200 km Seitenlänge; das Auftreten von 85 anderen bekannten Erzlagerstätten wird eindeutig von den Netzwerken mit 25 km Seitenlänge kontrolliert; kleinere Lagerstätten sind zufällig, unabhängig von den regmagenetischen Bruchsystemen verteilt.Im Gebiet Patagoniens mit bisher erst 54 ausgewerteten Erzlagerstätten, sind die vier grö\ten Lagerstätten in den 70 und 140 km-Systemen verteilt, zusammen mit einigen kleineren Lagerstätten. Allerdings sind diese kleineren Lagerstätten auch häufig an ein 35 km Raster gebunden.Entsprechend werden 60 % der vormesozoischen Granitoidkörper von den überregionalen Bruchsystemen kontrolliert. Auch ein Zusammenhang von Erdölvorkommen und Uranerzlagerstätten mit den Bruchsystemen kann beobachtet werden.

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Resumen El procesamiento estadístico de las megafracturas y lineamientos de los territorios de La Argentina, Chile y Uruguay y la determinación de las orientaciones estructurogenéticas de más de medio centenar de yacimientos minerales filohidrotermales, ha permitido proponer una hipótesis sobre la existencia de dos mallas de fracturamiento planetario en el Cono Sur Sudamericano.Una malla ortogonal, de rumbo N60W-N30E, con equidistancia básica de 25 km, dentro de una red principal de 200 km de lado, ubicada aproximadamente al norte de los 39 de Latitud Sur que denominamos Malla de la Región Gondwánica. La otra, al sur de la anterior. que la designamos como Malla de la Región Patagónica, también ortogonal pero con rumbos N35W-N55E, con equidistancia básica de 35 km, en una red principal de 140 km de lado.El examen estadístico de 371 yacimientos de la Región Gondwánica, principalmente de cobre, oro, plomo y cinc, permite concluir que, en sus relaciones con las mallas propuestas, los Grandes Yacimientos (Chuquicamata, Salvador, Potrerillos, Agua de Dionisio, Famatina, Pachón, Pelambre, Disputada y Teniente) se encuentran muy próximos a las mallas de 100 y 200 km; que los 83 Yacimientos Destacados están claramente controlados por la equidistancia básica de 25 km y que los Yacimientos Menores se distribuyen independientemente de la red regmagénica.En la Región Patagónica, con solo 54 depósitos procesados, los cuatro Yacimientos Destacados se distribuyen practicamente en las mallas de 70 y 140 km junto a parte de los Yacimientos Menores, aunque estos se ajustan más frecuentemente a la alternancia básica de 35 km.De igual manera el 60% de los cuerpos granitoides pre Mesozoicos aparecen controlados por las mallas de fracturamiento supraregional propuestas. También se observa una asimilación a ellas de yacimientos petrolíferos y uraníferos.

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, - , 50 . 25 N 60W-N 30E 200 39 . » «., , » «. , N 35W-N 55E 35 140 . 371 , , , , : , .: Chuquicamata, Salvadoe, Potrerillos, Agua de Dionisio, Famatina, Pachon-Pelambre, Disputada Teniente, , 100 200 ; 83 , 25 . . 54 4 , , 70 140 . 35 . 60 % . .

     

Effect of chloride concentration on the decomposition of aqueous sodium nitrate by sunlight

Summary Rates and yields of nitrite formation in solutions, upon irradiation of aqueous sodium nitrate with ultraviolet light, are found to be consistently and considerably enhanced by their chloride content. The process is investigated under conditions met both, in the laboratory and under sunlight illumination, and the effects of altitude and temperature on the reaction studied in the field, are evaluated.