Potassic-Ultrapotassic Volcanic Rocks in the Lhasa Block may be Highly Differentiated Rocks:Evidence from Rubidium and Cesium Enrichment
Che Dong
Zheng Mianping
Zhao Yuanyi
Zhang Zhaozhi
Abstract：Post-collisional potassic-ultrapotassic volcanic rocks are widely developed in the Lhasa block,Qiangtang block and Songpan-Ganzi-Kekexili block in the Qinghai-Xizang region.Many previous studies on the potassic-ultrapotassic volcanic rocks in this area show the supernormal enrichment of trace alkali elements such as Rb and Cs in the Lhasa block is much higher than those in other two blocks.In order to quantify this phenomenon and to investigate the causes of enrichment,this paper quantifies the enrichment degree of trace alkali elements in the three blocks,and has attained a preliminary understanding of the causes of enrichment,based on the measured and published data,using statistical methods such as box-plot and systematic mineralogical and geochemical analysis methods,It is concluded that the high degree of magmatic differentiation in the potassic-ultrapotassic volcanic rocks of the Lhasa block is the main cause of the rare alkali elements enrichment of Rb and Cs,and the enrichment zones are mainly located in the central and western part of the Lhasa block,where the volcanic rocks range in age from 25 to 13 Ma.The discrimination range of Zr/Hf and Nb/Ta with high degree of differentiation of potassic-ultrapotassic volcanic rocks in the Lhasa block is also delineated by analogy with the results of highly differentiated granites.
Keywords：Lhasa terranepotassic-ultrapotassic volcanic rocksrare alkaline elements enrichmenthigh differentiationXizangmineralogygeochemistry
Publication Date：2024-03-15
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：18( 850-867 )