Open AccessPalaeomagnetic study of a subaerial volcanic ridge (São Jorge Island, Azores) for the past 1.3 Myr: evidence for the Cobb Mountain Subchron, volcano flank instability and tectonomagmatic implications
Author(s) -
Silva P. F.,
Henry B.,
Marques F. O.,
Hildenbrand A.,
Madureira P.,
Mériaux C. A.,
Kratinová Z.
Publication year - 2012
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2011.05320.x
Subject(s) - geology , lava , volcano , flank , subaerial , paleontology , paleomagnetism , archipelago , ridge , geomagnetic pole , earth's magnetic field , oceanography , physics , quantum mechanics , sociology , anthropology , magnetic field
SUMMARY We present a palaeomagnetic study on 38 lava flows and 20 dykes encompassing the past 1.3 Myr on S. Jorge Island (Azores Archipelago—North Atlantic Ocean). The sections sampled in the southeastern and central/western parts of the island record reversed and normal polarities, respectively. They indicate a mean palaeomagnetic pole (81.3°N, 160.7°E, K = 33 and A 95 = 3.4°) with a latitude shallower than that expected from Geocentric Axial Dipole assumption, suggesting an effect of non‐dipolar components of the Earth magnetic field. Virtual Geomagnetic Poles of eight flows and two dykes closely follow the contemporaneous records of the Cobb Mountain Subchron (ODP/DSDP programs) and constrain the age transition from reversed to normal polarity at ca. 1.207 ± 0.017 Ma. Volcano flank instabilities, probably related to dyke emplacement along an NNW–SSE direction, led to southwestward tilting of the lava pile towards the sea. Two spatially and temporally distinct dyke systems have been recognized on the island. The eastern is dominated by NNW–SSE trending dykes emplaced before the end of the Matuyama Chron, whereas in the central/western parts the eruptive fissures oriented WNW–ESE controlled the westward growth of the S. Jorge Island during the Brunhes Chron. Both directions are consistent with the present‐day regional stress conditions deduced from plate kinematics and tectonomorphology and suggest the emplacement of dykes along pre‐existing fractures. The distinct timing and location of each dyke system likely results from a slight shift of the magmatic source.