TY - JOUR
T1 - Paleomagnetism of the Mid-Tertiary Ayacara Formation, southern Chile
T2 - Counterclockwise rotation in a dextral shear zone
AU - Rojas, C.
AU - Beck, M. E.
AU - Burmester, R. F.
AU - Cembrano, J.
AU - Hervé, F.
N1 - Funding Information:
Acknowledgments--This research was funded by NSF grants EAR 8718896 and INT 9020524, National Geographic Society grant 3738-88, and FONDECYT projects 0568/89, 920914 and 1931096. We wish to thank Chris Suczee who made helpful suggestions to the Ayacara Formation facies analysis. R. Drake and E Munizaga are acknowledged for the 40Ar/39Ar radiometfic age determinations. J.N. KeUogg and an anonymous reviewer provided helpful comments. We thank C. Maureira, who typed the final manuscript. Drafting of fig. 1 was done by Judith Oliva C.
PY - 1994/1
Y1 - 1994/1
N2 - Relative motions of the southern Chilean forearc are assessed through a paleomagnetic study of teh Eocene-Miocene Ayacara Formation. This marine volcaniclastic unit was studied at three localities, all immediately west of the Liquiñe-Ofqui fault zone (LOFZ), a 1000-km-long, NS-trending intracontinental shear zone with probable Cenozoic right-lateral displacement. A paleomagnetic pole (74.8S; 44.0E; A-95, 8.5°) was calculated by combining 11 site-mean VGP from the Ayacara Fm. with three sites from the nearby Oligocene Cocotue Beach basalts (previously published). When compared with a 20-40 Ma North American cratonic pole rotated into the South American reference framework this pole implies counterclockwise rotation of 14.6±11.8. We speculate that this counterclockwise rotation results from processes that tend to impel a detached sliver of continental crust northward along the continental margin, against a buttress. In our model, northward displacement of the trailing edge of the sliver is accomplished by segmenting the sliver into lens-shaped blocks which rotate counterclockwise as they move northward. The geometry of the LOFZ clearly supports this model, which may have application to other buttressed strike-slip fault zones.
AB - Relative motions of the southern Chilean forearc are assessed through a paleomagnetic study of teh Eocene-Miocene Ayacara Formation. This marine volcaniclastic unit was studied at three localities, all immediately west of the Liquiñe-Ofqui fault zone (LOFZ), a 1000-km-long, NS-trending intracontinental shear zone with probable Cenozoic right-lateral displacement. A paleomagnetic pole (74.8S; 44.0E; A-95, 8.5°) was calculated by combining 11 site-mean VGP from the Ayacara Fm. with three sites from the nearby Oligocene Cocotue Beach basalts (previously published). When compared with a 20-40 Ma North American cratonic pole rotated into the South American reference framework this pole implies counterclockwise rotation of 14.6±11.8. We speculate that this counterclockwise rotation results from processes that tend to impel a detached sliver of continental crust northward along the continental margin, against a buttress. In our model, northward displacement of the trailing edge of the sliver is accomplished by segmenting the sliver into lens-shaped blocks which rotate counterclockwise as they move northward. The geometry of the LOFZ clearly supports this model, which may have application to other buttressed strike-slip fault zones.
UR - http://www.scopus.com/inward/record.url?scp=0028325586&partnerID=8YFLogxK
U2 - 10.1016/0895-9811(94)90033-7
DO - 10.1016/0895-9811(94)90033-7
M3 - Article
AN - SCOPUS:0028325586
SN - 0895-9811
VL - 7
SP - 45
EP - 56
JO - Journal of South American Earth Sciences
JF - Journal of South American Earth Sciences
IS - 1
ER -
