Geochemistry and Geological Significance of the Mid-Jurassic Volcanic Rocks in Dunhuang Basin

ZHANG Zhicheng, GUO Zhaojie

(Department of Geology, Peking University,Beijing,100871)

HAN Zuozhen

(Department of Geology, Shandong Mining College,Taian,271019)


Abstract:
There are 3-4 layers of volcanic rocks in Mid Jurassic sections at Tuoge, Duobagou and Lucaogou in Dunhuang basin between Xinjiang and Gansu, China.The volcanic rocks are composed of alkaline basalt within plate. The characteristics of trace element and Rare Earth Element(REE) of the Volcanic rocks indicate that it is similar to the alkaline basalt of the typical continental rift. According to the regional and basin analysis, the volcanic rocks were controlled by the same normal fault. From the lower to upper,the contents of the SiO2 increase; and athe total REE increase from 0.00036093 to 0.00053349. This evolution is associated with crystallization differentiation. The total REE, La/Yb, (Ce/Yb)cn and Sm/Nd are increased regularly from Tuoge To Lucaogou. The increase indicates that the thickness of the crust becomes thinner from Tuoge to Lucaogou.

Key words:
volcanic rocks; geochemistry; Dunhuang basin; Mid-Jurassic

(R.D.1997-01-27 P.D.1998-01-20 Vol.34 No.1 pp.72-79)



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