地质科学2026，Vol.61Issue(4)：1111-1134,24.DOI:10.12017/dzkx.2026.075
秦祁结合部晚奥陶—早志留世埃达克质片麻状花岗闪长岩体年代学、地球化学及其构造意义
Chronology,geochemistry and tectonic implications of the Late Ordovician-Early Silurian adakitic gneissose granodiorite in the Qinling-Qilian junction
摘要
Abstract
The Longshan area is located at the junction of Qinling and Qilian,and the Qijiawan adakitic gneissose granodiorite is located at the eastern end of the North Qilian orogenic belt in the Longshan area,intruding into the Longshan rock group.Zircon and monazite U-Pb geochronological studies conducted on this pluton yielded weighted mean ages of 445.3±2.3 Ma and 435.9±2.2 Ma,respectively.Zircon U-Pb dating of the mafic enclaves within it provided a weighted mean age of 445.0±3.8 Ma.These results indicate that the Qijiawan rock mass formed during the Late Ordovician and that this phase of magmatic activity persisted over an extended period(445～436 Ma).The gneissose granodiorite exhibits high SiO2(64.97％～69.70％),Al2O3(15.66％～17.00％),and Na2O(4.40％～5.99％)contents,with K2O/Na2O ratios of 0.22～0.35,and A/CNK values of 0.88～1.06,classifying it as metaluminous to weakly peraluminous and calc-alkaline.The pluton is characterized by low Y(3.95×10-6～9.21×10-6),low Yb(0.37×10-6～0.97×10-6),high Sr(604×10-6～762×10-6),high Sr/Y ratios(73～181),and δEu values of 0.69～1.38.Analyses of major and trace elements,along with U-Pb isotopes,reveal that the pluton exhibits characteristic features of adakitic rocks.It originated from the partial melting of a subducted oceanic slab,followed by interaction with mantle materials to a certain extent.Based on the regional geological context,we propose that the Qijiawan gneissose granodiorite formed in a back-arc basin setting induced by northward subduction of the eastern North Qilian oceanic crust.This magmatic event persisted over an extended duration,spanning from the Late Ordovician to the Early Silurian.关键词
北祁连造山带/晚奥陶—早志留世/片麻状花岗闪长岩/埃达克岩/弧后盆地Key words
North Qilian orogenic belt/Late Ordovician-Early Silurian/Gneissose granodiorite/Adakite/Back-arc basin分类
天文与地球科学引用本文复制引用
支浩天,罗金海,畅莹磊,陈卓..秦祁结合部晚奥陶—早志留世埃达克质片麻状花岗闪长岩体年代学、地球化学及其构造意义[J].地质科学,2026,61(4):1111-1134,24.基金项目
国家自然科学基金项目(编号:42072231)资助 （编号:42072231）
