Petrogenesis of Mesozoic High-Mg Diorites in Western Shandong: Evidence from Chronology and Petro-geochemistry

查看全文 作　　者：Yang [1,2]Chenghai;Xu [3]Wenliang;Yang [3]Debin;Liu [2]Changchun;Liu [4]Xiaoming;Hu [4]Zhaochu 机构地区：[1]College of Earth Sciences, Jilin University, Changchun 130061, China;[2]Bureau of Geology and Mineral Resources of Shandong Province, Jinan 250013, China;[3]College of Earth Sciences, J ilin University, Changchun 130061, China;[4]Key Laboratory of Continental Dynamics, Northwestern University, Xi'an 710069, China 出　　处：《Journal of China University of Geosciences》索引2005年第16卷第4期,共12页 基　　金：ThispaperissupportedbytheNationalNaturalScienceFoundationofChina(Nos.40472033,40133020)andtheKeyLaboratoryofContinentalDynamics,NorthwesternUniversity. 摘　　要：The high-Mg diorites, widely occurring in western Shandong, have important implications in the study of the relationship between the Mesozoic magmatism and the nature of the lithosphere and its thinning period in the eastern North China craton (NCC). The Tietonggou and Jinling intrusions are typically representatives. LA-ICP-MS zircon U-Pb dating, major and trace element and Sr-Nd isotopic compositions of the Mesozoic intrusive rocks from western Shandong, eastern China, were analyzed. The weighted mean 206Pb/ 238U ages from LA-ICP-MS zircon U-Pb dating results for early norite-diorite, late pyroxene-diorite from the Tietonggou intrusion and biotite-diorite from the Jinling intrusion are (131.4±4.9) Ma(n=15), (134.5±2.3) Ma(n=13), and (132.8±4.2) Ma(n=12), respectively, implying that they were formed in the Early Cretaceous. The weighted mean 207Pb/ 206Pb ages for round zircons from late pyroxene-diorite in the Tietonggou intrusion is (2 513±54) Ma(n=8), suggesting that the basement of the North China craton should exist in the research area. The high-Mg diorites are characterized by enrichment in MgO, Na2O, and light rare earth elements (LREE), and they are poor in heavy rare earth elements (HREE) and high field strength elements (HFSE), being similar to adakite. The existence of the mantle peridotite xenoliths with a high-Mg feature for these intrusive rocks implies that their primary magma should be derived from the upper mantle. However, Sr-Nd isotopic compositions (I sr: 0.704 75-0.707 15; ε Nd(130 Ma) values: -3.95 to -13.30), depletion in HFSE, and the occurrence of Archean inherited zircons suggest that crustal materials could be involved in the derivation of the primary magma. The compositional difference between the diorites from the Tietonggou and Jinling intrusions could be attributed to those of magma sources and degrees of partial melting. The Early Cretaceous high-Mg diorites are considered to have been formed by the mixed melting of the delaminated lithosphere (lithospheric mantle + crust) and asthenosphere, based on their geochemistry, the mantle-derived xenoliths, and the Early Mesozoic lithospheric evolutionary history of the eastern North China craton. 关 键 词：中生代 岩石成因论 山东 闪长岩 镁 年代学 地球化学