Recycling of subducted oceanic crust: Geochemical evidence from Late Cretaceous-Paleocene intraplate alkaline basalts in the Kyrgyz Tianshan orogenic belt

Objective Different from the plate margin magmatism, the genetic mechanism of magmatism developed within the plate remains controversial due to its significant chemical heterogeneity. This study investigates the Late Cretaceous−Paleocene intraplate alkaline basalts in the Uchkuduk area of the Kyrgyz Tianshan orogenic belt to clarify the genetic mechanism and mantle source characteristics.

Methods We conducted the in−situ major and trace elements of olivines and whole−rock Mg−Li isotope analyses.

Results The Fo contents of olivine phenocrysts in Uchkuduk basalts is 70.3~88.6 mol%. These olivines are characterized by higher Ni and Fe/Mn ratios, lower Ca and Mn compared with MORB olivine phenocrysts. The primary magmas are rich in MgO and poor in CaO contents, and show moderate enrichment of TFeO and TiO₂. Therefore, it is believed that pyroxenite components were involved in the source region. In the mantle source discrimination diagrams, the low 10000*Zn/Fe (7.36~16.2) and high Mn/Zn (9.20~16.7) and 100*Mn/Fe (1.17~2.08) of Uchkuduk olivine phenocrysts suggest that the mantle source of Uchkuduk basalts is from a mixed source of peridotite and pyroxenite. The δ⁷Li values (+1.0‰~+5.7‰) of the Uchkuduk basalts is similar to the mantle, but their δ²⁶Mg values (δ²⁶Mg=−1.80‰~−0.33‰) are lighter than those of the mantle. These results indicate that the mantle source region may be metasomatized by carbonated melts derived from recycled oceanic crust, which is likely inherited from the stagnant Paleo−Asian Ocean subducted slab.

Conclusions This study shows that the stagnant Paleo−Asian oceanic slab contributes to the upper mantle heterogeneity beneath the Kyrgyz Tianshan orogenic belt.