Middle Jurassic oceanic island igneous rocks of the Raohe accretionary complex, northeastern China: Petrogenesis and tectonic implications

作者：Wang Zhi Hui; Ge Wen Chun^*; Yang Hao; Zhang Yan Long; Bi Jun Hui; Tian De Xin; Xu Wen Liang

来源：Journal of Asian Earth Sciences, 2015, 111: 120-137.

DOI：10.1016/j.jseaes.2015.08.005

• Raohe accretionary complex
• Middle Jurassic
• Paleo-Pacific Ocean
• Ocean island basalts
• Major and trace element geochemistry
• Nadanhada Range

Whole-rock major and trace element, and Sr, Nd, and Hf isotopic data, together with zircon U-Pb ages and in situ zircon Hf isotopes, are reported for Middle Jurassic igneous rocks of the Raohe accretionary complex, northeastern China, to investigate their petrogenesis and tectonic implications. The igneous rocks consist of pillow basalt, pyroxenite, gabbro, plagioclasite, and plagiogranite. The zircons from one plagioclasite and one plagiogranite are euhedral-subhedral and display fine-scale oscillatory growth zoning, indicating a magmatic origin. Zircon U-Pb dating gives an emplacement age of 169-167 Ma. The basalts are associated with late Paleozoic to middle Mesozoic sediments typical of ocean plate stratigraphy; i.e., limestone, bedded chert, and siliceous shale. The basalts, which show geochemical features similar to those of oceanic island basalts (OIBs), are enriched in TiO2, light rare earth elements (LREEs) (average: La/Sm-n = 2.12), and Nb (average: Zr/Nb = 12.24), and are characterized by positive Nb anomalies (averages: Nb/Th-pm = 1.46, Nb/La-pm = 1.31). The rocks are depleted in heavy rare earth elements (HREEs) (average: Gd/Yb-n = 2.03) and exhibit high epsilon(Nd)(t) (+8.2 to +8.3) and epsilon(Hf)(t) (+9.0 to +9.1) values. The geochemical features indicate the Jurassic OIB-like basalts were derived by a low degree of partial melting (<5%) of peridotite in the garnet stability field. The intermediate-mafic intrusive rocks show typical OIB affinities and are geochemically similar to the basalts. Most of the intermediate-mafic intrusive rocks are enriched in LREEs and Nb, depleted in HREEs, and show low Zr/Nb ratios and high epsilon(Nd)(t) (+7.2 to +8.2) and epsilon(Hf)(t) (+8.8 to +10.3) values, indicating they were derived from a common source and are the products of fractional crystallization of the OIB-like basalts. All of the igneous rocks are likely fragments of oceanic islands/seamounts. The identification of OIB-like basalts and associated intermediate-mafic intrusive rocks suggests that Jurassic intra-plate magmatism in the Paleo-Pacific Ocean was related to mantle plume activity.

• 出版日期2015-11-1
• 单位吉林大学