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Nb-depleted, continental rift-related Akaz metavolcanic rocks (West Kunlun): implication for the rifting of the Tarim Craton from Gondwana

By
Chao Yuan
Chao Yuan
1
Guangzhou Institute of Geochemistry, Chinese Academy of Sciences
,
Guangzhou 510640, China
2
Department of Earth Sciences, The University of Hong Kong
,
Pokfulam Road, Hong Kong, China
minsun@hkucc.hku.hk
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Min Sun
Min Sun
2
Department of Earth Sciences, The University of Hong Kong
,
Pokfulam Road, Hong Kong, China
minsun@hkucc.hku.hk
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Jingsui Yang
Jingsui Yang
3
Institute of Geology, Chinese Academy of Geological Sciences
,
26 Baiwanzhuang Road, Beijing 100073
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Hui Zhou
Hui Zhou
4
Department of Geology, Peking University
,
Beijing 100871, China
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Mei-Fu Zhou
Mei-Fu Zhou
2
Department of Earth Sciences, The University of Hong Kong
,
Pokfulam Road, Hong Kong, China
minsun@hkucc.hku.hk
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Published:
January 01, 2004

Abstract

The Akaz metavolcanic rocks of the West Kunlun Mountains possess low to intermediate SiO2 (42.3–64.7 wt%) and MgO (2.69–7.54 wt%) and high TiO2 (0.94–3.05 wt%) and Fe2O3T (7.64–18.47 wt%), indicating a basaltic to andesitic protolith. These rocks have high contents of Zr (89.6–470 ppm), Nb (10.0–40.3 ppm), Y (19.7–52.7 ppm), Th (0.86–15.96 ppm) and total REE (67.7–407 ppm), and are characterized by relatively high Ti/Y (183–649), Th/Yb (0.5–3.9), and low Hf/Ta (3.0–8.6) ratios. They are LREE-enriched (La/Yb = 5.4–20) and most have small negative Nb anomalies (Nb/Nb* = 0.20–1.16). These characteristics are transitional between within-plate and subduction-related basalts. The relatively high Gd/Yb ratios (1.4–2.9) distinguish these rocks from island-arc tholeiites and the high Zr/Y (3–12), Ta/Yb (0.3–0.7) and low Zr/Nb (<12) ratios strongly support a continental affinity. The protoliths for the Akaz metavolcanic rocks are interpreted to be continental rift basalts formed during rifting of the Tarim Craton from Gondwana. Stratigraphic and palaeontological data indicate that the rifting occurred in Sinian to Cambrian times, roughly contemporaneously with rifting in the East Kunlun and North Qilian orogenic belts farther to the east.

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Geological Society, London, Special Publications

Aspects of the Tectonic Evolution of China

J. Malpas
J. Malpas
The University of Hong Kong, Hong Kong
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C. J. N. Fletcher
C. J. N. Fletcher
The University of Hong Kong, Hong Kong
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J. R. Ali
J. R. Ali
The University of Hong Kong, Hong Kong
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J. C. Aitchison
J. C. Aitchison
The University of Hong Kong, Hong Kong
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Geological Society of London
Volume
226
ISBN electronic:
9781862394742
Publication date:
January 01, 2004

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