Petrogenesis of Potassic Volcanic Rocks in the Middle-South Parts of the Yishu Deep Fault Zone: Constraints from Elemental Geochemistry and Sr-Nd-Hf Isotopes
详细信息
- 责任者：Qiu Jiansheng (School of Earth Sciences and Engineering ; Nanjing University ; Nanjing 210093 ; China) ; Liu Liang
- 刊名：Acta Geologica Sinica
- 出版年：2013
- 卷期：87(9)
- 关键词：火山岩 ; volcanic rocks ; 沂沭断裂带 ; Yishu Fault Zone
- 页码：p.1193-1210
- 图表：13 illus., 4 tables, 66 refs.
- 分类号：0801
- issnNo：ISSN0001-5717
- isbnNo：CN11-1951/P
摘要
Summary" name="EnDivSummary">In this paper,we report the petrological,major and trace element geochemistry and Sr-Nd-Hf isotope data for the potassic volcanic rocks around the Junan-Dadian region in the middle-south parts of the Yishu deep fault zone,with aims to constrain the enrichment mechanism of the mantle source and to elucidate the petrogenesis.Potassic volcanic rocks outcropped around Junan are a set of latitic volcanic-subvolcanic rock association,and those in Dadian consist mainly of trachyte.They have consistent zircon LA-ICP-MS U-Pb ages of about 118Ma.Chemically,they show higher K<sub>2sub>O+Na<sub>2sub>O contents with Rittmann’s indices ranging from 4.10to 5.07,and enriched in potassium（K<sub>2sub>O=4.21%<sup>5sup>.77%）.On the SiO<sub>2sub>-K<sub>2sub>O and K<sub>2sub>O-Na<sub>2sub>O plots,these volcanic rocks all fall into the field of shoshonite series.Both the latitic and trachytic volcanic rocks are enriched in LILE（e.g.,Cs,Rb,Th,U,Pb）and LREE,and depleted in HFSE（e.g.,Nb,Ta,Ti,P）,but the trachytes show distinct negative anomalies of Ba and Eu in the primitive mantlenormalized trace element spidergrams,and have lower LREE/HREE ratios.The volcanic rocks have homogeneous and enriched Sr-Nd isotopic compositions with I<sub>Srsub> ratios of 0.7086 0.7091andε<sub>Ndsub>（t） values of-16.9<sup>-sup>18.2,and show distinct negative zirconε<sub>Hfsub>（t）values（specially-22.3<sup>-sup>24.3for the latitic volcanic rocks,and-19.7<sup>-sup>23.6for the trachytes）.Based on a synthesis of the elemental and isotopic geochemistry,we suggest that the mantle source of the potassic volcanic rocks might have underwent multiple enrichment events induced by source contamination of continental crustal materials both from deep subduction of the Yangtze Craton and lithospheric delamination of the North China Craton.During Early Cretaceous,the continued extension of Tanlu Fault induced the upwelling of asthenospheric mantle and led decompression partial melting of these multiple modified enriched mantle.The generated magmas subsequently suffered further differentiation,thus finally resulted in the formation of these potassic volcanic rocks.