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| Titel |
A detailed paleomagnetic investigation of Cretaceous igneous rocks: New contributions from Colombia and Paraguay |
| VerfasserIn |
Lisa Kapper, Manuel Calvo-Rathert, Ruben Cejudo Ruiz, Leda Sanchez Bettucci, Alicia Irurzun, Ángel Carrancho, Avto Gogichaishvili, Juan Morales, Ana Sinito, Victoria Mejia, Alvaro Nivia Guevara |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250130381
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| Publikation (Nr.) |
 EGU/EGU2016-10630.pdf |
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| Zusammenfassung |
| We present rock magnetic results, paleodirections and –intensities from Cretaceous samples
from two locations from South America. On the one hand we report paleomagnetic results
from the Western Cordillera of Colombia from 15 sites north of Cali. These volcanic rock
samples were related to age determinations from close localities of 92.5 ± 1.1 Ma on
average, occuring during the Cretaceous Normal Superchron (CNS). On the other hand we
show results from an alkaline dike swarm in the Asunción Rift, Eastern Paraguay. Previous
investigations suggest that these dikes extruded in a rather short period of 126-127 Ma,
during normal and reversed polarity field configuration, right before the onset of the
CNS.
Rock magnetic measurements of both sites show that the main magnetic component is a
low-coercivity mineral, e.g., (titanium)magnetite, with a large range of grain sizes from
multi- to single domain, or mixtures of several grain sizes in a sample. For the Colombian site
we obtained an average Virtual Geomagnetic Pole (VGP), whose latitude compares well with
those for South and North America of Besse and Courtillot (2002) with a similar age. For the
determination of the Virtual Dipole Moments (VDMs) the Thellier-Coe method did
not give successful results, probably due to minerals in the range of multidomain
grain size. Therefore, we applied the multispecimen protocol on ten specimens.
Six successful determinations produced an average VDM of 2.3 x 10−22 Am2.
This value is rather low, but in good agreement with other data from the same time
period. Directional investigation of the Eastern Paraguayan dike swarm show highly
clustered promising results with six out of 22 sites having an α95 ≤ 10.0˚ . Most of
these sites show a reversed polarity; however, one intermediate polarity site has a
very reliable direction as well. This and the occurrence of normal polarity sites
suggest that the dikes may have not appeared at the same time but rather during the
transition from normal to reversed polarity right before the CNS at around 126-127 Ma.
Specimens from nine sites are promising for paleointensity determination due to their
linear vector diagrams showing one component, the occurrence of magnetite as
magnetic carrier, and their magnetic stability. Future work will be focused on a
more concise investigation of the directions. This includes the measurement of
specimens from a second field campaign located close to the first one. Furthermore,
paleointensity determinations are planned, after choosing the most successful specimens. |
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