A case of paleohorizontal restoration of plutonic bodies using paleomagnetic data: The Sierra de Valle Fértil magmatic complex, western Argentina

RAPALINI, A., PINOTTI, L. DERAMO, F., OTAMENDI, J.E.,. VEGAS, N., SINGER, S., A., TUBIA, J., Y VUJOVICH, G.,

Congreso; Geosur 2010 International Geological Congress on the Southern Hemisphere; 2010

Reliable paleohorizontal control is essential in any tectonic or paleogeographic application of paleomagnetic studies. As such, the use of paleomagnetic data from plutonic bodies, for which paleohorizontal control is frequently lacking, is severely restricted. However, if magnetization age can be determined or constrained and the expected paleomagnetic direction is already known, paleomagnetic information can be very useful in reconstructing the original position of plutonic bodies, providing important information for the understanding of emplacement processes. Recently Castro et al. (2008) proposed that the magmatic structures related to the mechanical interaction between mafic magmas and granitoids in the Early Ordovician Sierra del Valle Fértil magmatic complex are the result of top-to-down intrusions of a mafic magma into a granodiorite-tonalite mass. These sinking structures would be the result of a reverselly stratified magma chamber with gabbros and diorites at the top and granodiorite-tonalite at the bottom. This interpretation would not be valid if the plutons have been subsequently tilted so that sub-vertical to high inclination pipe- like structures were originally subhorizontal, reflecting a different layering process.  A paleomagnetic study was carried out on fifty-one oriented cores from the Sierra de Valle Fértil magmatic complex in order to evaluate to which extent these plutonic rocks have been subsequently tilted, and in such way to provide independent information to improve the petrological model of Castro et al. (2008).