Paleomagnetic and rock magnetic constraints on the geodynamic evolution of Sakhalin (NW Pacific)

Abstract

Sakhalin is located in a tectonically complex region on the NW Pacific margin.  Ancient subduction and accretion phases have affected Sakhalin, but Neogene to present-day deformation appears to have been accommodated by strike-slip faults, which transect Sakhalin from north to south.  Fundamental questions are addressed in this study regarding the location of plate boundaries, the timing of the transition between tectonic regimes, the structural mechanisms of the transition, and the geodynamic evolution of Sakhalin.  Paleomagnetic declination data from Sakhalin indicate rapid phases of Miocene clockwise vertical-axis crustal rotations. The data contradict published kinematic models that have been proposed to account for deformation in east and southwest Sakhalin.  Analysis of paleomagnetic inclinations suggests that Sakhalin has remained near present-day latitudes throughout the Tertiary.  Magnetic fabrics of Tertiary sedimentary rocks in Sakhalin have lineations that are regionally consistent and correspond to the direction of tectonic transport.  Temporally consistent fabric orientations within regional structural domains are consistent with a plate model that includes the Okhotsk Sea, Eurasian, Amurian, Northern Honshu, Pacific, and North American plates.  Many localities sampled in Sakhalin have been remagnetized.  In most cases the mechanism for remagnetization is uncertain, although rock magnetic properties and microtextural relationships of Miocene mudstones from Okhta River indicate that a synfolding chemical remagnetization is carried by late diagenetic, nodular, pyrrhotite, which formed during a fluid migration event.  Magnetic fabrics, paleomagnetic declinations, and remagnetization observations indicate significant Miocene or post-Miocene tectonic events, which may be associated with opening of the Japan Sea, Kuril Basin, and Tatar Strait Basin.

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