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Paleomagnetic evidence for post‐Late Miocene intra‐arc rotation of South Kyushu, Japan
Author(s) -
Kodama Kazuto,
Nakayama Kenichi
Publication year - 1993
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/92tc01712
Subject(s) - geology , paleomagnetism , seismology , paleontology , arc (geometry) , late miocene , geometry , mathematics , structural basin
Paleomagnetism of sedimentary rocks of the late Miocene Uchiumigawa Group exposed in southeast Kyushu yielded 17 tilt‐corrected paleomagnetic directions with significant westward declinations. Fourteen of these were of reversed polarity, and three at the intervening horizons were of antipodal normal polarity. The overall formation mean direction is D = 322.0°, I = 48.6° with α 95 = 6.0°. This is statistically indistinguishable from the mean direction of D = 331.2°, I = 41.3° with α 95 = 9.9° for the middle Miocene deposits in Tanegashima Island of the northern Ryukyu arc. The common mean direction is D = 333.2°, I = 45.1° with α 95 = 4.9°. This indicates that both south Kyushu and the northernmost Ryukyu arc have experienced 27° ± 6° of counterclockwise rotation with respect to the Eurasian continent after the latest Miocene, or during the last 6 m.y. This counterclockwise rotation cannot be fully explained by either a conventional model which links an arc rotation with the formation of back‐arc oceanic crust, or the collision of the Kyushu‐Palau ridge with southwest Japan arc. We propose that this intra‐arc rotation took place during the period of extension of the continental crust behind the north Ryukyu arc. This study demonstrates that arc rotation may generally occur when the back‐arc spreading is of a much less advanced phase.