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Jian-Bo Zhou, Jilin University (China)
Xing-Zhou Zhang, Jilin University (China)
Simon Wilde, Curtin University of Technology (Australia)
Zhi-Hong Ma, Jilin University (China)
Wei Jin, Jilin University (China)
Yong-Jiang Liu, Jilin University (China)
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The Heilongjiang blueschist complex, located in the Eastern margin of the Central Asian Orogenic Belt (CAOB), was a collision belt between both massifs of the Jiamusi and Songliao. Field and petrographic investigations indicate that the Heilongjiang complex is composed predominately of granitic gneiss, marble, mafic-ultramafic rocks, blueschist, greenschist, quartzite, muscovite-albite schist and two-mica schist that were tectonically interleaved, indicating they represent a subduction complex. Although the Heilongjiang blueschist belt is one of the largest High-pressure metamorphism belt in China, its nature and tectonic setting of this belt is still disputed.
In this study, we carried out zircon U-Pb dating in combination with Ar-Ar isotope analysis, which ware demonstrated to be suited for refining the tectonic evolution history of these rocks, for blueschist-facies metamorphic rocks at Heilongjiang province, NE China. The results not only provide unambiguous evidence for the blueschist complex in this belt, but also presence the subduction timing between the Songliao and Jiamusi massifs.
Most zircons from Heilongjiang blueschist complex are colorless, transparent and euhedral in shape. CL imaging reveals that most grains have prominent oscillatory zoning, indicating they are of magmatic origin. The ages of blueschist ware dated at ca. 200 Ma to ca. 260 Ma, indicates that the protolith ages for the blueschist rocks. Total 500 detrital grains of Heilongjiang complex show the four major age populations.
(1) 200-310 Ma with peak age at 260 Ma, indicates that the protolith ages of the Heilongjiang complex was Permian to Triassic.
(2) 350-420 with peak age at 380 Ma, correspond to ages in the Jiamusi Massif.
(3) 440-570 Ma with peak age at 500 Ma, correspond to ages in the Jiamusi Massif, including the Mashan complex, probably formed part of an exotic block from Gondwana, affected by late Pan-African orogenesis.
And (4) 690-950 Ma with peak age at 720 Ma, correlates to ages in the South China block, as well as the South China block-derived protolith of the Dabie UHP rocks.
Those results together with the ages of 180-210 Ma of biotite and phengite from the blueschist and mica schist by Ar-Ar method in the Heilongjiang blueschist complex, indicted that the collision between the Jiamusi Massif and the Songliao Massif might be at Triassic, unrelated to the Central Asian Orogenic Belt. We also suggest that the Heilongjiang blueschist belt might be Eastern extending of the Dabie-Sulu orogenic blet.
This study was funded by grants from the Natural Science Foundation of China (40672148 and 40739905).
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