А.N.Didenko,А.I.Tikhomirova,А.V.Kudymov

Kosygin Institute of Tectonics and Geophysics,Far East Branch,Russian Academy of Sciences,Khabarovsk,Russia

PALEOMAGNETISM AND GEODYNAMICS OF THE MESOZOIC ZHURAVLEVKAAMUR AND KISELEVKA-MANOMA COMPLEXES IN THE NORTHERN SIKHOTE-ALIN

А.N.Didenko,А.I.Tikhomirova,А.V.Kudymov

Kosygin Institute of Tectonics and Geophysics,Far East Branch,Russian Academy of Sciences,Khabarovsk,Russia

Thepaperconsidersthe formationhistoryofgeological structures flanking the northwestern Pacific Ocean.The original paleomagnetic data are given on Cretaceous rocks of the Utitsa and Kiselevka formations of the Northern Sikhote-Alin.

Deposits of the marginal pull-apart basin filled with turbidites constituting the Zhuravlevka-Amur Complex［1］, an 80 km wide belt extending for 800 km in a northeastern direction,occur in much of the Sikhote-Alin territory.The complexismadeupofCretaceous,mainly LowerCretaceous, sandstone,siltstone and mudstone as thick as 15 000 m［2］. More ancient siliceous-argillaceous rocks are restricted to the axial part of the complex.We have studied the littoral sediments that complete the section of the complex on the Amur left bank between the bays Sitoga and Medvezhiy, where most of the Utitsa Formation occur,whose description corresponds to the Explanatory Note to the Geological Map of scale 1∶200 000（sheet М-54-I）［3］and our own field observations.

The characteristic component of the natural remanent magnetization（NRM）of volcanic rocks of the Utitsa Formation of the Zhuravlevka-Amur Complex has been separated as a result of paleomagnetic studies.The paleolatitude at which rocks formed and the coordinates of the paleomagnetic pole（plat=81.6°,plong=208.2°,dp= 10.8,dm=12.5°）of the Utitsa Formation were defined according to the direction of the characteristic component. A comparison between present-day latitude（51.4°N）and paleolatitude（53.7±10.8°N）values does not suggest any major horizontal displacements of the Utitsa Formation rocks relative to the Late Cretaceous margin of the Eurasian continent and indicates that deposits completing the section of the Zhuravlevka-Amur Complex are autochthonous.

Earlier we［4］studied volcano-sedimentary rocks of the Kiselevka Formation of the Kiselevka-Manoma Complex defined by many researchers［5-6］as a fragment of the mid-Cretaceous accretionary wedge.The characteristic component of NRM for the volcano-sedimentary rocks of the Kiselevka Formation was isolated in the course of paleomagnetic studies.It has a fold test positive response and an age close to that of the rocks.The paleolatitude at which rocks of the Kiselevka Formation formed and the paleomagnetic pole coordinates（plat=18.6°,plong=222.4°, dp=5.2,dm=9.1°）were defined based on the direction of the characteristic component.The distance betweenpresent-day latitudinal（51.4°N）and paleolatitudinal（18±5°N）positions of the studied volcano-sedimentary rocks is over 3500 km,which is indicative of large-scale horizontal movement of sedimentary rocks of the Kiselevka Formation.

The following model of the Cretaceous history of the region is suggested based on the new paleomagnetic data on Cretaceous volcano-sedimentary rocks of the Utitsa and Kiselevka Formations of the Northern Sikhote-Alin as well as geological and geochemical data on their genesis（Fig. 1）.Some 135-105 Ma ago,rocks of the Kiselevka block moved on the Izanagi plate northwestward at 15-20 cm/a, thus travelling more than 5000 km as far as the eastern margin of Eurasia（the Korean Peninsula area）.About 105-95 Ma ago,they moved northward as part of the accretionary complex along the transform margin of Eurasia at 4-5 cm/a.Rocks of the Utitsa Formation formed further north.By the end of the Cretaceous,the Kiselevka block has reached its present position,not far from the place where the Utitsa Formation originated.

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錫霍特－阿林北部地區(qū)中生代Zhuravlevka-Amur和Kiselevka-Manoma雜巖的古地磁學(xué)和地球動力學(xué)

А.N.Didenko,А.I.Tikhomirova,А.V.Kudymov

俄羅斯科學(xué)院遠(yuǎn)東分院大地構(gòu)造和地球物理研究所，俄羅斯哈巴羅夫斯克

1671-1947（2015）03-0281-02

P318.4；P541

A

2014－06－20.編輯：張哲．

Thisstudy isperformedundertheProgram ofBasicResearchoftheFEBRAS“The FarEastofRussia”（projectnos.12-I-0-ОНЗ-07,12-II-СО-08-026, and 14-III-В-08-215）.

Fig.1 Cretaceous geodynamic reconstruction of the eastern margin of Asia