| Geochronology of the Dahongshan Group |
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| 摘 要： |
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| 关 键 词： | 地球年代学 大红山组 地层学 钕同位素 原生代 同位素地质年代学 |
Geochronology of the Dahongshan Group |
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| Authors: | Hu Aiqing Zhu Bingquan Mao Cunxiao Zhu Naijuan Huang Rongsheng |
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| Institution: | (1) Institute of Geochemistry, Academia Sinica, China |
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| Abstract: | The Dahongshan Group is divided into five formations from the bottom to the top: the Laochanghe Formation; the Manganghe Formation;
the Hongshan Formation, the Feiweihe Formation and the Potou Formation. As can be seen from the U-Pb concordia plot for zircon
fractions collected from the metamorphic sodic lava of the Hongshan Formation, the upper intersect age with the concordia
is 1665.55
-10.86
+13.56
Ma. Sm-Nd dating of four whole-rock samples and one hornblende from the Manganghe and Hongshan formations yielded an isochron
age of 1657 ± 82 Ma. This result is in good agreement with the zircon U-Pb age and thus can represent the formation age of
the Dahongshan Group. The initial143Nd/144Nd ratio is estimated at 0.510646. with ENd (T) = + 3.1 ± 1.8. In addition the Dahongshan Group rocks are characterized by
low REE contents, with δEu>1. All this goes to show that the original rocks of the Dahongshan Group were derived from a depleted
mantle. The calculated Sm-Nd model ages range from ∼ 1900 to ∼ 2000 Ma. representing the time of crust/ mantle differentiation
in the area studied.
From the above results, in conjunction with the time-scale scheme for China, the Dahongshan Group should be assigned to the
Middle Proterozoic. |
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| Keywords: | |
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