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Aksu Gr
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Aksu Gr base reconstruction

Aksu Gr

Period: 
Neoproterozoic

Age Interval: 
late Qingbaikouan, Qb (7)


Province: 
Xinjiang

Type Locality and Naming

NW Tarim Basin. The Aksu Gr was named by Zhang Tairong et al. in 1976, and published by Xinjiang Compiling Group for regional stratigraphic scale. The named section is near Qigebulak between Aksu and Wushi, Xinjiang Weiwuerzhu Zizhiqu (Xinjiang Uygur Autonomous Region).

[Figure: Type section of Aksu Gr]

Synonym: （阿克苏群）


Lithology and Thickness

In the type section, the Aksu Gr is dominated by grey-green, light green sericite-chlorite quartz schist, intercalated with epidote-chlorite quartz schist, thin-bedded quartzite, dolomite, albite-bearing epidote-chlorite-quartz schist. Glaucophane schist occurs as local bands. Aksu Gr has an exposed thickness of 3091 m. [See below – interpreted as subducted oceanic crust.]


Lithology Pattern: 
Lava


Relationships and Distribution

Lower contact

Bottom is not seen.

Upper contact

The top is unconformably overlapped by the Wushinanshan Gr [its lower Yourmeinak Fm or its middle Sugetbulak Fm (Sugaitebulak Fm] of late Nanhuan-Sinian (late Cryogenian-Ediacaran).

Regional extent

Aksu region of NW Tarim Basin – the "Aksu Blueschist Terrane"


GeoJSON

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Fossils


Age 

The glaucophane schist in the group gave a wide range of Rb-Sr whole-rock apparent age dates, such as 1720 Ma, 1907 Ma (Xiong Jibin et al., 1986); 962 ±12 Ma, 944 ±42 Ma (Gao Zhenjia et al., 1993), and the phengite gave a Rb-Sr date of 720 Ma (Xiao Xuchang et al., 1990). Therefore, it was considered as Mesoproterozoic. However, 206Pb/238U dating yielded 820 Ma, and the metamorphosed age in 820-760 Ma are conformed the new age of the Aksu Gr (Zhang Jian et al., 2014). Therefore, assigned as late Qingbaikouan (middle Tonian).

Age Span: 

    Beginning stage: 
Tonian

    Fraction up in beginning stage: 
0.6

    Beginning date (Ma): 
832.00

    Ending stage: 
Tonian

    Fraction up in the ending stage: 
0.8

    Ending date (Ma):  
776.00

Depositional setting

The Aksu Gr includes a rather famous Neoproterozoic blueschist, and is interpreted as exhumed oceanic crust complex at a former subduction zone.


Depositional pattern:  


Additional Information


Compiler:  

Extracts from The Mesoproterozoic Erathem (chapter in Stratigraphic Lexicon of China, draft of 2022) by Gao Linzhi, Ding Xiaozhong, Zhang Chuanheng, Zhang Heng.