- 责任者：Gao Xiaofeng (Research Center for Orogenic Geology ; Xi’an Center of Geological Survey ; China Geological Survey ; Xi’an 710054 ; China) ; Xiao Peixi
- 刊名：Earth Science
- 出版年：2013
- 卷期：38(6)
- 关键词：火山岩 ; volcanic rocks ; 新疆 ; Xinjiang
- 页码：p.1169-1182
- 图表：9 illus., 3 tables, 57 refs.
- 分类号：0801
- issnNo：ISSN1000-2383
- isbnNo：CN42-1233/P
This paper presents petrological and geochemical features and zircon U-Pb age of a suite of bimodal volcanic rocks in the Bulunkuole Group from the Taishuihai Massif, NW China. The zircon U-Pb dating results yield a mean ^238U/^206 Pb age of 521.3±3. 3 Ma, representing the extrusion time of the dacites in the Middle Cambrian, which indicates that the previously defined Paleoproterozoic Butunkuole Group also includes early Paleozoic volcanic rocks. The basalts and dacites belong to low-K affinities. The basalts show enrichment in Rb, Ba, K and LREE, and depletion in Nb-Ta and Th, suggesting that they were derived from a previously metasomatized depleted mantle. The dacites also show more enrichment in LILE and Th, and larger depletion in Nb-Ta, Sr and Ti in comparison with the basalts. Different REE patterns and trace element features between the two rock types, and the absence of differentiation trend from the basalts to dacites, argue against the origin for the dacites as the differentiates of the basalts. Combining the dacites geochemical features and the experimental data suggest that they are melts of lower crustal mafic protoliths heated by contemporaneous underplating basaltic magmas at relatively low pressure conditions. The occurrence of the bimodal volcanic rocks reflects that the region experienced an extensional tectonic-magmatic event during early Paleozoic. The new data suggests that the previously defined ＂Paleoproterozoic Bulunkuole Group＂ includes at least three components： （1） the Paleoproterozoic khondalite series; （2） the Indo-Sinian high pressure metamorphic complexes and （3） the early Paleozoic volcano-sedimentary associations.