This article presents the first palaeomagnetic results from 13 independent cooling units in the C... more This article presents the first palaeomagnetic results from 13 independent cooling units in the Chiapanecan Volcanic Arc (ChVA). Six sites were directly dated by Ar–Ar or K–Ar methods: their dates range from 2.14 to 0.23 Ma. We isolated the characteristic palaeodirections for all 13 lavas. Eleven non-transitional directions yield a mean direction with inclination, I = 30.7°, declination, D = 4.1°, and precision parameters k = 63 and α95 = 5.8°. The corresponding mean palaeopole position is Plat = 83.3°, Plong = 203.8°, K = 227, A95 = 5.1°. The mean inclination is in good agreement with the expected value for the last 5 million years, as derived from the synthetic North American polar wander path [Besse and Courtillot 2002, Apparent and true polar wander and the geometry of the magnetic field in the last 200 million years: Journal of Geophysical Research, v. 107, no. B11, p. 2300], but a measured rotation of the palaeodeclination of about 8° with respect to the expected direction suggests the possibility of a clockwise rotation of the studied ChVA units. We have estimated the characteristics of palaeosecular variation through study of the scatter of virtual geomagnetic poles, obtaining a palaeosecular variation parameter Sb = 14.5° with upper limit SU = 19.6° and lower limit SL = 11.7°, in reasonable agreement with the fit of model G [McFadden et al., 1988, Dipole/quadrupole family modeling of paleosecular variation: Journal of Geophysical Research, v. 93, no. B10, p. 11583–11588; 1991, Reversals of the Earth's magnetic field and temporal variations of the dynamo families: Journal of Geophysical Research, v. 96, no. B3, p. 3923–3933] to the Johnson et al. [2008, Recent investigations of the 0–5 Ma geomagnetic field recorded by lava flows: Geochemistry, Geophysics, Geosystems, v. 9, no. 4, ID Q04032, doi:10.1029/2007GC001696] databases for the last 5 million years. In those cases in which age determinations are available, the polarity obtained for the studied flows is consistent with their stratigraphic positions, except for the Huitepec site, which probably reflects the transitional geomagnetic regime prior to the Matuyama–Brunhes geomagnetic reversal.
Since 2010 a team of the “Laboratorio de Geofísica y Geotectónica” started the construction of a ... more Since 2010 a team of the “Laboratorio de Geofísica y Geotectónica” started the construction of a magnetic observatory as part of the Aiguá Geophysical Observatory (34° 20’ S; 54° 42’ W) located in the south-east side of the Uruguayan territory. The aim of this project is to study the phenomena related to the Space Weather and its influence over the entire region covered by the South Atlantic Anomaly (SAA). Due to its proximity to the centre of the Anomaly and the scarce research done in the Rio de la Plata area, the new magnetic observatory will provide a closer look to the SAA related phenomena. Currently the equipment consists on a GEM 90S Overhauser magnetometer for the absolute measurement of the total field and a GSM-90F5D suspended dIdD as variometer for the continuous record the (X,Y,Z) field components. Both sensors were supplied by GEM Systems Inc. This is the first magnetic observatory located in Uruguayan territory. The preliminary data was analyzed and used for the calcu...
The Facultad de Ciencias with support from Comision Sectorial de Investigacion Cientifica (CSIC),... more The Facultad de Ciencias with support from Comision Sectorial de Investigacion Cientifica (CSIC), PEDECIBA Geociencias, and the Ministerio de Educacion y Cultura (MEC) is installing the first Geophysical (Geomagnetic) Observatory. Uruguay is located in the South Atlantic Magnetic Anomaly, a region that has recorded the lowest values of magnetic field worldwide. This observatory will minimize an important gap in the global network of magnetic observatories allowing better monitoring of the South Atlantic Magnetic Anomaly. The implications and the vulnerability to harmful radiation and susceptibility to geomagnetic storms, with consequences at the level of TV and radio waves disruptions, and the generation of induced currents in power lines and mineral and oil pipelines are still poorly unknown. Therefore, the installation of a Geomagnetic Station will be useful in various areas such as navigation, engineering, aeronomy (the physics of the upper atmosphere), geophysical prospecting, d...
The Dom Feliciano Belt was developed during West Gondwana amalgamation as a result of collision b... more The Dom Feliciano Belt was developed during West Gondwana amalgamation as a result of collision between the Rio de la Plata and Kalahari cratons. In that context, an association of mafic-ultramafic rocks embedded in mylonites is developed. Based on lithotectonic association it is defined here as La Tuna Ophiolitic Complex. Preliminary petrographic and chemical analysis (mineral assemblages and whole rock
The Playa Hermosa Formation (Fm.) (Playa Verde Basin) is a volcano-sedimentary unit that crops ou... more The Playa Hermosa Formation (Fm.) (Playa Verde Basin) is a volcano-sedimentary unit that crops out in the extreme south of the Dom Feliciano Belt in Uruguay. This formation has traditionally been interpreted as non-glacial in origin, but recently it has been suggested that the lower part at least may be glacially influenced. The stratigraphic position of the Playa Hermosa Fm. and its correlation with other Neoproterozoic units of Uruguay, Argentina and southern Brazil remains in dispute. An age ofc.580 Ma is indicated by a hornblende39Ar/40Ar age on magmatism regarded as coeval with syn-sedimentary volcanism. Preliminary palaeomagnetic data suggest a primary remanence and a mean geomagnetic pole consistent with the proposed apparent polar wander path for the Río de La Plata craton. In combination, these data suggest mid-Ediacaran glacial sedimentation in low to intermediate latitudes on the Río de la Plata craton. However, this conclusion needs to be reinforced by more thorough stud...
Two occurrences of iron formations from the Precambrian of Uruguay were mineralogically and petro... more Two occurrences of iron formations from the Precambrian of Uruguay were mineralogically and petrographically investigated. One of these deposits, located to the north of Minas City is associated with a low metamorphic grade Ediacaran succession (Minas Formation - Arroyo del Soldado Group) where glacial influence has been suggested. Fine grained quartz, Fe-rich amphibole (grunerite), magnetite porphyroblasts and hematite laths characterize these BIFs. Although an earlier increase of ferrous iron in solution in deeper water through the glacial episode is a probable factor, the identification of volcaniclastic acid rocks in the sequence indicates that Fe-fluids of volcanic origin played also an important role. A Rapitan type for this deposit is indicated by geological features and age constrains. The other analyzed deposit is associated with a highly deformed low- to medium- grade metamorphic supracrustal succession (Zanja del Tigre Formation) occurring as tectonic slices in a pre- Neo...
Pecoits et al . (2010) question the stratigraphic and glacigenic origins of a tiny section of the... more Pecoits et al . (2010) question the stratigraphic and glacigenic origins of a tiny section of the Zanja del Tigre Formation that constitutes the least well-constrained of all confirmed and suspected glacial deposits in the Rio de La Plata craton (Pazos et al . 2008, 2010). Pecoits et al . assert that in the ‘latest compilations of the geology of Uruguay' the Zanja del Tigre Formation is part of the Carape Group and not …
The Dom Feliciano Belt was developed during West Gondwana amalgamation as a result of collision b... more The Dom Feliciano Belt was developed during West Gondwana amalgamation as a result of collision between the Rio de la Plata and Kalahari cratons. In that context, an association of mafic-ultramafic rocks embedded in mylonites is developed. Based on lithotectonic association it is defined here as La Tuna Ophiolitic Complex. Preliminary petrographic and chemical analysis (mineral assemblages and whole rock
The Facultad de Ciencias with support from Comision Sectorial de Investigacion Cientifica (CSIC),... more The Facultad de Ciencias with support from Comision Sectorial de Investigacion Cientifica (CSIC), PEDECIBA Geociencias, and the Ministerio de Educacion y Cultura (MEC) is installing the first Geophysical (Geomagnetic) Observatory. Uruguay is located in the South Atlantic Magnetic Anomaly, a region that has recorded the lowest values of magnetic field worldwide. This observatory will minimize an important gap in the global network of magnetic observatories allowing better monitoring of the South Atlantic Magnetic Anomaly. The implications and the vulnerability to harmful radiation and susceptibility to geomagnetic storms, with consequences at the level of TV and radio waves disruptions, and the generation of induced currents in power lines and mineral and oil pipelines are still poorly unknown. Therefore, the installation of a Geomagnetic Station will be useful in various areas such as navigation, engineering, aeronomy (the physics of the upper atmosphere), geophysical prospecting, d...
This article presents the first palaeomagnetic results from 13 independent cooling units in the C... more This article presents the first palaeomagnetic results from 13 independent cooling units in the Chiapanecan Volcanic Arc (ChVA). Six sites were directly dated by Ar–Ar or K–Ar methods: their dates range from 2.14 to 0.23 Ma. We isolated the characteristic palaeodirections for all 13 lavas. Eleven non-transitional directions yield a mean direction with inclination, I = 30.7°, declination, D = 4.1°, and precision parameters k = 63 and α95 = 5.8°. The corresponding mean palaeopole position is Plat = 83.3°, Plong = 203.8°, K = 227, A95 = 5.1°. The mean inclination is in good agreement with the expected value for the last 5 million years, as derived from the synthetic North American polar wander path [Besse and Courtillot 2002, Apparent and true polar wander and the geometry of the magnetic field in the last 200 million years: Journal of Geophysical Research, v. 107, no. B11, p. 2300], but a measured rotation of the palaeodeclination of about 8° with respect to the expected direction suggests the possibility of a clockwise rotation of the studied ChVA units. We have estimated the characteristics of palaeosecular variation through study of the scatter of virtual geomagnetic poles, obtaining a palaeosecular variation parameter Sb = 14.5° with upper limit SU = 19.6° and lower limit SL = 11.7°, in reasonable agreement with the fit of model G [McFadden et al., 1988, Dipole/quadrupole family modeling of paleosecular variation: Journal of Geophysical Research, v. 93, no. B10, p. 11583–11588; 1991, Reversals of the Earth's magnetic field and temporal variations of the dynamo families: Journal of Geophysical Research, v. 96, no. B3, p. 3923–3933] to the Johnson et al. [2008, Recent investigations of the 0–5 Ma geomagnetic field recorded by lava flows: Geochemistry, Geophysics, Geosystems, v. 9, no. 4, ID Q04032, doi:10.1029/2007GC001696] databases for the last 5 million years. In those cases in which age determinations are available, the polarity obtained for the studied flows is consistent with their stratigraphic positions, except for the Huitepec site, which probably reflects the transitional geomagnetic regime prior to the Matuyama–Brunhes geomagnetic reversal.
Since 2010 a team of the “Laboratorio de Geofísica y Geotectónica” started the construction of a ... more Since 2010 a team of the “Laboratorio de Geofísica y Geotectónica” started the construction of a magnetic observatory as part of the Aiguá Geophysical Observatory (34° 20’ S; 54° 42’ W) located in the south-east side of the Uruguayan territory. The aim of this project is to study the phenomena related to the Space Weather and its influence over the entire region covered by the South Atlantic Anomaly (SAA). Due to its proximity to the centre of the Anomaly and the scarce research done in the Rio de la Plata area, the new magnetic observatory will provide a closer look to the SAA related phenomena. Currently the equipment consists on a GEM 90S Overhauser magnetometer for the absolute measurement of the total field and a GSM-90F5D suspended dIdD as variometer for the continuous record the (X,Y,Z) field components. Both sensors were supplied by GEM Systems Inc. This is the first magnetic observatory located in Uruguayan territory. The preliminary data was analyzed and used for the calcu...
The Facultad de Ciencias with support from Comision Sectorial de Investigacion Cientifica (CSIC),... more The Facultad de Ciencias with support from Comision Sectorial de Investigacion Cientifica (CSIC), PEDECIBA Geociencias, and the Ministerio de Educacion y Cultura (MEC) is installing the first Geophysical (Geomagnetic) Observatory. Uruguay is located in the South Atlantic Magnetic Anomaly, a region that has recorded the lowest values of magnetic field worldwide. This observatory will minimize an important gap in the global network of magnetic observatories allowing better monitoring of the South Atlantic Magnetic Anomaly. The implications and the vulnerability to harmful radiation and susceptibility to geomagnetic storms, with consequences at the level of TV and radio waves disruptions, and the generation of induced currents in power lines and mineral and oil pipelines are still poorly unknown. Therefore, the installation of a Geomagnetic Station will be useful in various areas such as navigation, engineering, aeronomy (the physics of the upper atmosphere), geophysical prospecting, d...
The Dom Feliciano Belt was developed during West Gondwana amalgamation as a result of collision b... more The Dom Feliciano Belt was developed during West Gondwana amalgamation as a result of collision between the Rio de la Plata and Kalahari cratons. In that context, an association of mafic-ultramafic rocks embedded in mylonites is developed. Based on lithotectonic association it is defined here as La Tuna Ophiolitic Complex. Preliminary petrographic and chemical analysis (mineral assemblages and whole rock
The Playa Hermosa Formation (Fm.) (Playa Verde Basin) is a volcano-sedimentary unit that crops ou... more The Playa Hermosa Formation (Fm.) (Playa Verde Basin) is a volcano-sedimentary unit that crops out in the extreme south of the Dom Feliciano Belt in Uruguay. This formation has traditionally been interpreted as non-glacial in origin, but recently it has been suggested that the lower part at least may be glacially influenced. The stratigraphic position of the Playa Hermosa Fm. and its correlation with other Neoproterozoic units of Uruguay, Argentina and southern Brazil remains in dispute. An age ofc.580 Ma is indicated by a hornblende39Ar/40Ar age on magmatism regarded as coeval with syn-sedimentary volcanism. Preliminary palaeomagnetic data suggest a primary remanence and a mean geomagnetic pole consistent with the proposed apparent polar wander path for the Río de La Plata craton. In combination, these data suggest mid-Ediacaran glacial sedimentation in low to intermediate latitudes on the Río de la Plata craton. However, this conclusion needs to be reinforced by more thorough stud...
Two occurrences of iron formations from the Precambrian of Uruguay were mineralogically and petro... more Two occurrences of iron formations from the Precambrian of Uruguay were mineralogically and petrographically investigated. One of these deposits, located to the north of Minas City is associated with a low metamorphic grade Ediacaran succession (Minas Formation - Arroyo del Soldado Group) where glacial influence has been suggested. Fine grained quartz, Fe-rich amphibole (grunerite), magnetite porphyroblasts and hematite laths characterize these BIFs. Although an earlier increase of ferrous iron in solution in deeper water through the glacial episode is a probable factor, the identification of volcaniclastic acid rocks in the sequence indicates that Fe-fluids of volcanic origin played also an important role. A Rapitan type for this deposit is indicated by geological features and age constrains. The other analyzed deposit is associated with a highly deformed low- to medium- grade metamorphic supracrustal succession (Zanja del Tigre Formation) occurring as tectonic slices in a pre- Neo...
Pecoits et al . (2010) question the stratigraphic and glacigenic origins of a tiny section of the... more Pecoits et al . (2010) question the stratigraphic and glacigenic origins of a tiny section of the Zanja del Tigre Formation that constitutes the least well-constrained of all confirmed and suspected glacial deposits in the Rio de La Plata craton (Pazos et al . 2008, 2010). Pecoits et al . assert that in the ‘latest compilations of the geology of Uruguay' the Zanja del Tigre Formation is part of the Carape Group and not …
The Dom Feliciano Belt was developed during West Gondwana amalgamation as a result of collision b... more The Dom Feliciano Belt was developed during West Gondwana amalgamation as a result of collision between the Rio de la Plata and Kalahari cratons. In that context, an association of mafic-ultramafic rocks embedded in mylonites is developed. Based on lithotectonic association it is defined here as La Tuna Ophiolitic Complex. Preliminary petrographic and chemical analysis (mineral assemblages and whole rock
The Facultad de Ciencias with support from Comision Sectorial de Investigacion Cientifica (CSIC),... more The Facultad de Ciencias with support from Comision Sectorial de Investigacion Cientifica (CSIC), PEDECIBA Geociencias, and the Ministerio de Educacion y Cultura (MEC) is installing the first Geophysical (Geomagnetic) Observatory. Uruguay is located in the South Atlantic Magnetic Anomaly, a region that has recorded the lowest values of magnetic field worldwide. This observatory will minimize an important gap in the global network of magnetic observatories allowing better monitoring of the South Atlantic Magnetic Anomaly. The implications and the vulnerability to harmful radiation and susceptibility to geomagnetic storms, with consequences at the level of TV and radio waves disruptions, and the generation of induced currents in power lines and mineral and oil pipelines are still poorly unknown. Therefore, the installation of a Geomagnetic Station will be useful in various areas such as navigation, engineering, aeronomy (the physics of the upper atmosphere), geophysical prospecting, d...
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