Magmatic Processes associated with crustal accretion in the West Philippine Basin: Constraints from mineral and whole rock geochemistry

Abstract:

Long Yuan^1,2, Quanshu Yan^1,2*

1, Key Laboratory of Marine Geology and Metallogeny, First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China

2, College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China

E-mail: yanquanshu@163.com;

During earlier period of late Cenozoic, the West Philippine Basin (WPB) in the Philippine Sea Plate experienced overlapping effects from back-arc spreading and mantle plume processes. In this study, we obtained in situ trace element and major element compositions of minerals in basalts collected from the Benham rise and the Central Basin Fault (CBF) in the WPB, and K-Ar ages of these host rocks. Based on the bulk rock compositions of the basalts and the calculated primary melt composition, we inferred that the source lithology of the Benham Rise basaltic rocks could be garnet pyroxenite, and yet that of the CBF could be spinel-lherzolite. The calculated mantle potential temperature beneath the Benham Rise is 1439°C–1473°C, which is significantly higher than that beneath the CBF (1345°C–1381°C), suggesting there existed thermal anomaly during basaltic magmatism. The temperature and pressure of the clinopyroxenes from the CBF and the average temperature and pressure of the plagioclases from the Benham Rise and the CBF are calculated. We suggest that the Benham Rise basaltic rocks may be related to a mantle plume (e.g., the Oki-Daito mantle plume), and the CBF was once located in a back-arc spreading center behind an active subduction zone. The extinction of the Oki-Daito mantle plume activity might be at about 20.9 Ma, and cessation of the back-arc spreading of WPB was at about 29.1 Ma or younger. (This study was supported by National Science Foundation of China nos. 41776070, U1606401, 41322036 and Taishan Scholarship from Shandong Province).

Key words: mantle plume; magmatic processe; primary melt composition; source lithology

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