Cenozoic volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, China: Petrochemical eviden

• 出 处: Chinese Journal of Geochemistry
• 发表日期: 2007年03期
• 关键词: volcanic China Qiangtang northern Tibet mantle melting crust Cenozoic rock magma

Neogene volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, are represented by a typical intermediate-basic and intermediate alkaline rock association, with latite-trachyte as the main rock type. The results of chemical analysis are: SiO2=52%–62%, Al2O3>15%, Na2O/K2O>1 and MgO<3.30%. In addition, the volcanic rocks are LREE-enriched with LREE/HREE=10–13, (La/Yb)N=15–19, and show a weak negative Eu anomaly with δEu=0.71–0.89. The close relationship between Mg# and SiO2 and the co-variation of the magmatophile elements and ultra-magmatophile elements such as La/Sm-La and Cr-Tb indicate that this association of volcanic rocks is the product of comagmatic fractional crystallization. The rock association type and lower Sm/Yb values (Sm/Yb=3.23–3.97) imply that this association of volcanic rocks should have originated from partial melting of spinel lherzolite in the lithospheric mantle. On the other hand, the weak negative Eu anomaly and relative depletion in Nb, Ta and Ti reflect the features of terrigenous magma. So the Neogene Belog Co alkaline volcanic rocks should be the result of partial melting of the special crust-mantle transition zone on the Qinghai-Tibet Plateau.

Neogene volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, are represented by a typical intermediate-basic and intermediate alkaline rock association, with latite-trachyte as the main rock type. The results of chemical analysis are: SiO2 = 52% 62% Al2O3> 15%, Na2O / K2O> 1 and MgO <3.30% In addition, the volcanic rocks are LREE-enriched with LREE / HREE = 10-13, (La / Yb) show a weak negative Eu anomaly with δ Eu = 0.71-0.89. The close relationship between Mg # and SiO2 and the co-variation of the magmatophile elements and ultra-magmatophile elements such as La / Sm-La and Cr-Tb indicate that this association of volcanic rocks is the product of comagmatic fractional crystallization. The rock association type and lower Sm / Yb values ​​(Sm / Yb = 3.23-3.97) imply that this association of volcanic rocks should have originated from partial melting of spinel lherzolite in the lithospheric mantle On the other hand, the weak negative Eu anomaly and relative depletion in Nb, Ta an dT reflect the features of terrigenous magma. So the Neogene Belog Co alkaline volcanic rocks should be the result of partial melting of the special crust-mantle transition zone on the Qinghai-Tibet Plateau.